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The role of the nucleus reticularis tegmenti pontis in locomotion: A lesion study in the rat
Brain Research Bulletin, Vol. 12, pp. 511-520, 1984. % Ankho International
0361-9230/84 $3.00 -t .oO
Inc. Printed in the U.S.A.
The Role of the Nucleus Reticularis Tegmenti Pontis in Locomotion: A Lesion Study in the Rat STEFAN
Departnwnr
M. BRUDZYk%W
of Physiology,
AND GORDON
J, MOGE~~~N~
University of Western Ontario, London, Ontario, Canada N6A 5621 Received 21 December
f983
BRUDZYfiSKI, S. M. AND G. J. MOGENSQN. The role qf’the nucierts rrticularis tegmenri pontis in locomation: A lesion study in rhe wt. BRAIN RES BULL 12(s) 513-520, 1984.-Bilateral anodal and cathodal electrolytic lesions of the nucleus r&icuIaris tegmenti pontis (NRTP) increased forward locomotion in rats. The correlation between the magnitude of locomotion and percent of NRTP damage demonstrated that the more complete the NRTP destruction the greater the increase of locomotion. The lesioned rats exhibited at the same time low level rearing and running wheel activity as well as some lack of motor coordinatjon during body balance tests. Taking into consideration the neural connections of the NRTP we suggest that disruption of NRTP-cerebeilar pathways, rather than connection with forebrain structures is associated with the lesion-induced increase of forward locomotion.
Nucleus reticularis tegmenti pontis Rats Galloping
Electrolytic
lesions
Forward locomotion
Body balance
trolyticafly under Nembutal anesthesia tpentobarbital sodium 5 mgf100 g of body weight, IP) in a Kopf stereotaxic instrument. The coordinates for NRTP were +0.2 mm anterior to -0.2 mm posterior to interaural line, 1.0 mm lateral to the midline and 8.5 to 9.0 mm below the surface of the dura with incisor bar -2.4 mm below the ear bars. The electrode was a No. 00 steel insect pin coated with insulating resin with 0.5 mm of the tip bared. In 24 rats, a direct anodaf current of 1 mA was passed for 5 to 15 sec. A rectal electrode was used to complete the circuit, The effectiveness of the anodal lesioning is shown in the Fig. 1. Six rats received cathodaf lesions with a current of 1 mA for 10 to 15 set duration. A group of Eve rats served as sham-operated controls. The electrode was lowered 1 mm above the NRTP in these animals and was withdrawn after 10 set without passage of current. The animals were given a 24 hr recovery period after surgery, Locomotor activity was recorded in a running wheel (G. N. Wahmann MFG. Co., Baltimore, MD) and in large open-fiefd area (247.5~55 cm). Its surface was divided into I8 equal squares (27.5x27.5 cm), comparable in size to that of the rat’s body. The number of lines crossed and number of rearings were recorded on a laboratory counter (Clay-Adams Inc., NY). A line was regarded as being crossed by the rat when more than half of the rat’s head passed over the line. The reliability of recording was checked using independent measurements by two persons. AI1 the locomotor activity tests were carried out during five min-periods in the marning and repeated once a day for five successive days before
THE neural substrates of locomotor activity have received increasing attention in recent years 122,461. A number of forebrain and brainstem structures have been implicated 122, 33,34,481 but the neural circuits and integrative mechanisms for the initiatian and control of locomotion are poorly un-
derstood. However, since locomotion is a fundamental component of a number of adaptive behaviors, such as food procurement or escape from predators, it seems likeiy that there are multiple forebrain influences on brainstem systems associated with locomotion, Dramatic effects on locomotor activity have been reported following lesions of the nucleus reticufaris tegmenti pontis (NRTP) in rats [IO, 11, 121. A rapidly accelerating forward locomotion and galloping appeared after electrolytic lesions of NRTP. The present study was undertaken to investigate this phenomenon in more detail. The objective was to set the stage for elucidating the functional relationship of brainstem structures, such as NRTP and mesencephalic locomotor region [22], to forebrain systems that might under certain circumstances be the initiators of locomotion. METHOD
Thirty-eight adult male albino rats weighing 20.5-390 g at the time of surgery were used. The animals were housed in indiv~du~ cages with food and water ad lib in a tempe~ture-fight-~ontrolfed room with a 1212 hr fighti dark cycle. The NRTP and/or surrounding reticular formation of the ventral pontine tegmentum were damaged elec~-~
‘Visitor from Department of Animal Physiology, Institute of Physiology and Cytology, University of Lodz, Lodz, Poland. ‘Requests for reprints should be addressed to G. J. Mogenson.
513
BRirDZYrjSKI
AND MOGENSON
The effects of lesions were assessed statistically with repeated measures analysis of variance 1551.This was followed by t-test comparisons of the first test day after surgery with the last test day before surgery. After completion of the tests the animals were sacrificed by an overdose of urethane, their brains perfused with 50 ml of 09% NaCl followed by 50-100 ml of buffered formaiin and fixed in formalin. Frozen 80 p brain sections were stained with thionin for histological lesion location and assessment of percentage of NRTP damage. RESULTS
The animals were divided into four groups according to lesion placement. The first group (Fig. 2A, NRTP group, n= 12) included rats with lesions which destroyed at least 50% of NRTP. The second group (Fig. 2B, ventral group, n=4) comprised rats with lesions ventral to NRTP, mainly in pontine gray and medial lemniscus. In two of these rats there was damage of ventrolateral part of NRTP. In the third group (Fig. 2C, dorsal group, n=4) lesions were dorsal to the NRTP in the reticular formation. Two of these lesions slightly damaged the border of medial raphe and the dorsal aspect of NRTP. In the fourth group (Fig. 2D, lateral group, n=4) lesions were in ventrolateral part of the reticular formation at the level of NRTP. Histological examination of lesions revealed that they were between stereotaxic frontal planes 1.O mm anterior to 2.0 mm posterior from interaural plane with maximal destruction between frontal plane 0.3 mm anterior to 1.5 mm posterior from zero plane. A representative photomicrograph of an NRTP lesions is shown in Fig. 1A.
FIG. 1. A-Photomicrograph of anodal lesion placid bilaterally in NRTP (1 mA. 10 sec. 0.5 mm bared tin of steel electrode). The animal was sacrificed 46 days after surgery. Thionin staining. The bar represents 1.0 mm. Abbreviations: PAG-central gray; CIcoIficuius inferior; CS-colliculus superior; LM-medial lemniscus; MR-medial raphe nucleus; PF-pyramidal fibres; PCS-superior cerebeflular peduncte; ~NL~ventrocaud~ nucleus of lateral lemniscus. B-Effectiveness of anodal Iesioning characterized by the volume of damaged tissue in relation to the duration of 1 mA current passage. Vertical bars represent s.e.m. surgery and 10 times after surgery. The tests were repeated during five successive days after surgery and then every second day up to the 15th postoperative day. The animals, however, were still observed up to the 30th day after surgery. Body balance of rats was assessed by placing them on the top of perpendicularly fixed board (2 cm width, 18 cm high, and 88 cm long). The time that the rat was able to balance on the 2 cm edge of the board untif it fell orjumped down to the table surface was measured. If the rat remained on the board, the time measurement was terminated at 5 min.
The effects of NRTP lesions on locomotor activity are shown in Fig. 3. It is clear that when tested after surgery the two groups with NRTP lesions displayed a considerable increase in locomotor activity compared to the sham group and the groups with lesions dorsal, ventral and lateral to NRTP. An analysis of variance for the six groups for the 15 postoperative days indicated highly significant differences, F(5,29)=7.71, p~O.001. Subsequent statistical tests showed that the two groups with anodal and cathodal lesions of NRTP did not differ from one another postoperatively @O. 10). Further statistical tests were carried out to assess the four-fold increase in activity of the NRTP-lesioned animals. Activity the first test day after surgery was significantly greater than for the last presurgery test day (anodal NRTP NRTP group, t( 11)=3.12, p
R~TICULOTEGMENTAL
LESIONS
515
AND LOCOMOTION C-- NRTP-I:
b-l=6
o-
NRTP -a
II=12
.-
SHAM
n=S
I-
DORSAL
n-4
v-
VENTRAL
n=4
.-
LATLRAL
#I=4
TIME tdavs)
FIG. 3. Locomotor activity in open field area before and after electrolytic lesions (arrow) placed in pontine tegmentum of rats. The animals with anodal lesions are divided into groups according to lesion location as in Fig. 2. There is also a sham-operated group (SHAM). Locomotion after NRTP destruction is shown separately for anodal (NRTP-a) and for cathodal (NRTP-c) lesions. Locomotor activity is expressed as number of lines crossed. Statistical comparison using analysis of variance showed that forward locomotion was significantly greater for the NRTP-a and NRTP-c groups. s.e.m. values included in Table 2.
u FIG. 2. Location of anodal lesions in four groups of rats: A-NRTP lesion group, 12 rats. The outer border of the 12 lesions is presented since it is not possible to show 12 individual lesions. B-ventral lesion group, 4 rats; C-dorsal lesion group, 4 rats: D-lateral lesion group. 4 rats; See text for histological description. Abbreviations: RF-reticular formation: others as in Pig. I.
body-balance disturbances and general lack of motor coordination during body-balance tests when they were placed on the top of a perpendicularly fixed board. Usually, they fell to the table surface within a short time, unlike the control rats. The time spent on the top of the board was significantly shorter in lesioned rats then for control animals (all measurements for NRTP group: r(88)=5.13, p
c
c A
i
o NRTP
n=lZ
.
SHAM
n-5
.
DORSAL
n=J
.
VENTRAL
n=4
.
LATERAl
n-4
B
1 TIME fdavs)
FIG. 4. Running wheel activity (A) and rearing (B) before and after anodai lesion (arrow) placed in pontine tegmentum of rats divided into groups according to lesion location as in Fig. 2 including shamoperated controls (SHAM). s.e.m. values included in Table 2.
BRilDZYhSKI
516 TABLE THE SET OF BEHAVIORAL
PATTERNS
AND MOGENSON
I
AFTER EFFECTIVE NRTP LESIONS (A-ANODAL, DAYS POSTOPERATIVE PERIOD
Total Number of Occurrence
C-C’ATHODAL)
Number of Rats Affected
Percent C
Behavioral Pattern
DURING 30
(60- 100%)
A fn- 12)
C (tl==b)
A. General Locomotion Increased forward locomotion (IO@%or more than control level)
61
32
6
Increased forward locomotion (less than 100%but more than 50%)
22
3
3
Locomotion associated with circling
14
0
0
B. Leaping and Galloping
7
4
5.8%
6.6%
2
Slow symmetric gallop-like locomotion or sequences of leaps
11
6
9.1%
10.0%
2
Slow asymmetric gallop-like locomotion or sequences of leaps
12
6
IO.@%
10.0%
2
4
0
3.3%
0
0
Single rabbit-like leaps or hopping movements
Fast gallop
C. Other Responses Elevated rear part of the body with arched back
8
4
6.6%
6.6%
I
Elevated tail
9
5
7.5%
8.3%
2
Body-balance disturbances during locomotion
5
1
4. I%
1.6%
1
Disturbances of locomotion itself
3
0
2.5%
0
0
Relation Between Lesion Location and Locomotion Since there was some variation in the size and locus of the lesions we calculated locomotor activity in relation to extent of damage to the NRTP. As shown in Fig. 6, locomotion was directly related to the percentage of NRTP damage. There was a significant increase in locomotion when 50% of the NRTP was destroyed and locomotion was increased 14-fold in animals with 90-100% of NRTP damaged. Unilateral damage of NRTP had no effect on locomotion (n=3). The change in locomotion was also related to the locus of NRTPdamage. We compared results of lesions placed anteriorly to the NRTP with lesions placed in the centre of NRTP and in its caudal extension, considering also the dorsal, ventral and lateral lesions illustrated in Fig. 2. Comparing the locomotion levels from five sessions before and five after surgery, we plotted the responses relevant to these lesion locations in a three-dimensional diagram in Fig. 7. One may observe that the lesions of the NRTP itself, and especially its caudal aspect, are associated with the increase in forward locomotion. However, all other ne~h~u~ng areas ventral, dorsal, lateral, and anterior to NRTP were ineffective in producing locomotion, even when some of these lesions damaged some part of NRTP.
OP.
OP.
A DORSAL
LESIONS
FIG. 5. Equilibrium and body coordination tests on the perpendicularly fixed board in non operated fn=55), sham operated fn=20) and lesioned rats. NRTP (n=35), and vent& with dorsal (n=30) groups of rats correspond to lesion location from Fig. 2. Vertical bars represent s.e.m.
RETI~ULOTEGMENTAL
LESIONS AND LOCOMOTION
517
TABLE MEAN VALUES
-c S.E.M. OF LOCOMOTION,
RUNNING
2
WHEEL ACTIVITY AND REARING AFTER NRTP LESIONS
1
3
SECOND DAY BEFORE AND
Days After Surgery
Days Before Lesion Group of Animals
FOR EVERY
5
1
3
5
9
13
79.2224.4 88.7-+ 19.3 9.62 4.2 15.72 10.4 25.01 7.2 16.02 10.2
863226.7 80.0% 16.2 17.0% 6.3 5.75 5.1 7.2% 2.3 6.0-c 2.6
86.5k40.7 68.7t19.0 11.6% 3.5 16.72 9.5 28.52 17.3 14.72 10.7
94.82 19.2 54.0114.2 21.2r 5.6 21.2k20.9 26.01: 15.6 35.0t 13.2
3.5 7.9 0.3 3.5 1.8
2.72 2.5rt 0 7.72 16.21
7.8 8.1
3.62 8.0+ 0.32 3.72 11.22
3.4 4.9 0.3 3.7 9.6
1.9 2.1 2.0 1.1 0.4
lO.Ot 4.21 2.52 5.01 2.5~
2.5 1.5 2.5 4.0 0.8
9.lr 6.42 3.52 5.5t 10.21
1.8 2.8 4.1 2.6 1.3
Locomotion NRTP-c NRTP-a Sham Dorsal Ventral Lateral
4.5.6i 8.1 22.1t 7.0 31.6t11.4 38.3% 14.4 23.7-t 7.0 34.0-c 12.2
24.72 6.0 12.62 3.6 26.4% 7.5 0.3% 0.2 14.7rlr10.1 5.2t 1.9
N RTP-a Sham Dorsal Ventral Lateral
10.01r: 0.6 3.72 2.3 5.01-2.6
5.72 16.7ir 6.02 6.02 13.72
NRTP-a Sham Dorsal Ventral Lateral
9.7* 14.22 5.02 8.2? 5.72
6.1& IO.22 0 4.8% 2.5rt
27.32 11.12 20.42 1.5t 13.7t 2.22
6.3 3.2 6.4 1.2 10.6 1.6
74.2~ 48.9? 13.01 0.21 18.22 5.52
3.4 5.3 3.8 1.5 5.5
5.6t 9.0% 0.3t 7.82 6.2t
3.2 7.7 0.3 4.2 3.7
2.4* 9.2% 0 1.02 4.2~
1.9 2.6
8.22 6.42 I.22 6.0t 1.0+
2.6 2.7 1.4 4.1 0.7
9.02 3.0t 0.3-c 5.7+ 2.5?
19.6 16.7 6.4 0.2 8.0 5.5
Running Wheel 2.1 5.4 0.6 4.2
5.7% I.72 0 6.0~ 5.2-t
3.5 0.8 6.1 5.2
6.0% 18.8t 0.32 6.32 7.7t
9.22 3.4% 1.72 3.7% 3.7+
1.6 1.4 1.2 1.5 3.4
6.8+ 5.42 I.72 2.0% 1.02
1.5 1.6
Rearing 2.1 3.2 2.3 3.4 2.0
3.1 1.9
2.3 f.2 0.3 2.2 1.8
140
,g
12a
E
P
100
e > G (a
40
!
60
ro 9 8
40
20
0
1
V’
2
3
4
s
TIME (days) FIG. 6. Open field locomotion of 23 rats with effective NRTP lesions (arrow) arranged according to the percentage of NRTP damage: 90106% damage (8 rats), 60-80% damage (8 rats), less than 50% damage (7 rats), SHAM-sham operated controls (5 rats); C-control values before surgery. Locomotor activity expressed in number of lines crossed.
FIG. 7. Three dimensional distribution of effects of the lesions on open field locomotion in rats. Blank columns represent mean values from 5 tests before and dotted ones from 5 tests after lesion. Locomotor activity is expressed in number of lines crossed (numbers inside columns). The rostra1 (a), central (b), and caudal (c) location of the lesions is shown in the parasagittal brainstem drawing in the insert. a-Lesions placed rostrally to NRTP comprising also anterior aspect of NRTP; 3 rats. b-Lesions placed in the centre of NRTP destroying 90-100% of this nucleus; 7 rats. The difference is significant, r(121=3.09, p
518
BRuDZYfiSKI DISCUSSION
Electrolytic lesions of NRTP induced foward locomotion which gradually increased over the first 5 days, and lasted for at least seven days after surgery. Since both the anodal and cathodal electrolytic lesions had similar effects on locomotion it appears that the increase in locomotion is not the rest& of irritative effects from deposition of ferric ions, as has been suggested for other experiments [ 1.5,41,54] but depends on the destruction of the NRTP. The damaged area common to the rats that exhibited increased forward locomotion was limited to the NRTP. The correlation between the magnitude of locomotion and percent of NRTP damage shows that the more complete NRTP destruction the greater the increase of locomotion. There is evidence that damage adjacent to NRTP is not responsible for the increase in locomotion level. Lesions of the lateral and dorso-lateral reticular formation in the present study did not induce forward locomotion. Localized electrolytic lesions of tectospinal tract also did not elicit an increase of locomotor activity [%I. An increase of locomotor activity was reported after median raphe lesions in some studies [Zl, 24, 25, 291 while similar electrolytic lesions did not influence locomotor activity in the others 123,431. Also serotonergic neurons located in the medial raphe nucleus and even within NRTP and adjacent reticular formation [ 14,201, projecting to the septal nuclei [27], do not seem to be responsible for the lesion-induced locomotion. Indeed, damage of these neurons by a selective serotonergic neuro~oxin has been reported to decrease activity or have no effect 123, 25, 431. It appears, therefore, that the NRTP itself is the critical structure responsible for the initial increase in locomotion. although serotoninergic mechanisms may be associated with the period of recovery. When NRTP-lesioned rats had partially regained the capacity to inhibit locomotor activity it was lost when serotoninergic blockers were administered [ll]. The results of the present study indicate that NRTP lesions release locomotor mechanisms from an inhibitory influence, as suggested by other investigators [ 10. 11, 12, SO]. It is unlikely, however, that the NRTP itself represents a direct source of this inhibitory influence. Furthermore, the NRTP does not appear to be the brainstem region, associated in the cat, with motor inhibition during paradoxical sleep [35, 36, 371. This inhibitory locomotor region is dorsomedial and caudal to NRTP. The effects on locomotion of lesions of NRTP may instead be related to disruption of its interaction with more distant structures such as cerebellum [I. 3, 4, 6, 7, 8, 9, 17. 19, 31, 321, senso~motor cortex 151, superior colliculus [ 16,261, vestibular nuclei [28,53], and adjacent reticular formation [38,52]. Several of these structures are associated with neural systems involved in body coordination, equilibrium maintenance, and eye- and head-movements. Some of our behavioral observations after lesioning, suggest interference with such systems. Low levels of rearing and running wheel activity in the presence of relatively normal Iocomotion may be the result of a deficit in utilizing information about body position in space. Furthermore, running wheel activity and locomotion may involve different neural mechanisms related to the differential contributions of teleceptive, oculomotor, vestibular and kinesthetic systems to these behaviors. Body-balance disturbances and tail elevation (Table 1C) as well as the six-fold decrease in the time spent by rats on a perpendicular board may be due to some lack of
AND MOGENSON
motor coordination and equilib~um maintenance. Behavioral patterns such as single rabbit-like leaps and gallopingfike sequences of movement observed by us. as well as the festinating character of movement and difficulty in stopping in front of an obstacle as reported previously [ 10, 11, 121, appear to be similar to some of the elements of dysmetria and asynergia observed after cerebellectomy. These observations suggest that the lesion-induced increase of locomotion results, at least partially, from interference with NRTP-cerebellar circuits. The location of NRTP lesions and the analysis of the associated changes in locomotion further support this conclusion for the following reasons. First, destruction of rostra1 and dorsal parts of the NRTP which, have no cerebellopetal connections 161,did not influence locomotion. Second, lesions placed in the caudai extension of the NRTP did induce an increase in locomotion. probably due to partial destruction of the cerebellofugat contralateral pathway. which reaches NRTP via the brachium conjunctivum and descends caudally at the same level as NRTP [ 191. Third, unilateral lesions of the NRTP were ineffective in three rats tested, possibly because the NRTP has strong ipsi- and contralateral connections with cerebellum [ 171. It is also known that reticular formation and cerebellum have reciprocal relations 1441 and that reticula-spinal neurons, being under tonic influence of the cerebellum, change their firing pattern during locomotion in the absence of the cerebellum [39,40]. NRTP lesions disrupt not only its connections with the cerebellum but with cerebral cortex as well [S] and this interference in the cerebra-cerebellar circuit might also be responsible for the changes in locomotion and especially for the galloping movements. Sprague and Chambers [45] disrupted this circuit by neocortical lesions in cerebellectomized cats and observed gallop-like behavior with the NRTP intact. After NRTP damage, galloping develops over a period of 20 to 40 [I I] and, in some cases, up to 55 days 1121. In our experiments we did not observe the galloping response during the first IS days after NRTP lesions. A tendency to gallop-like behavior began to occur after this time and was observed in eight of the 12 rats at the end of observation period (30 days). Although. 6 of a large number of NRTP-lesioned rats displayed exaggerated locomotion as soon as they recovered from anesthesia [ 127. in most animals in earlier studies as well as in the present study increased locomotion did not occur for two or three weeks. and followed a period of hypokinesia. This suggests that the behavioral pattern may be, in part at least, the result of neural degeneration to distant structures [42]. For example. transections of the brachium conjunctivum resulted after 2 weeks in marked loss of acetylcholinesterase activity in the red nucleus and ventral thalamic nuclei 1301. The connections of NRTP with both cortex and cerebellum may modulate locomotion but the cerebella-cerebellar loop may be the more important one. There is some electrophysiological evidence, supporting this statement, which indicates that NRTP neurons are driven mainly by cerebellar input while cortical input provides only modulatory influences (for review see [2]). Furthermore, the finding of impulse reverberation between NRTP and nucleus interpositus of the cerebellum along an excitatory loop [Sl] support the physiological importance of this connection. Also from the anatomical point of view the cerebella-NRTP-cerebellar loop seems to be stronger than others between cerebellum and pontine gray. inferior olive, and lateral reticular nucleus [Z]. Thus disruption of NRTP-cerebellar rather than the connec-
RETI~ULOTE~MENTAL
LESIONS
AND LOCOMOTION
tions with cerebral cortex and other structures is more likely associated with the lesion-induced increase of locomotion. Finally, pontine tegmental lesions can result in metabolic disturbances which, in turn, might be responsible for some of the behavioral effects observed. The increase of locomotion, in the present study however. seemed to be unrelated to metabolic changes. NRTP-lesioned rats exhibited high level of locomotion regardless of whether their body weight was maintained or was decreasing with time (2 rats among 18). Although, it has been suggested that the cerebellum contributes to movement initiation [18] there is also evidence that basai forebrain structures may be associated with response initiation (e.g., [34, 47, 481). It appears that basal forebrain areas are involved in initiation of locomotion connected with biologically important adaptive behaviors [47] while ponto-cerebellar areas contribute to the regulation of motor performance. Teitelbaum and coworkers [49.50] have postulated several separate movement subsystems, such as
head scanning, forward locomotion, head-orienting, mouthing, and postural support, which are related to ponto- and reticula-cerebellar areas. These areas may contribute to the integration of movement subsystems [ 131 and if one subsystem is disrupted by a lesion there may be a compensatory increase in the activity of another system, for example, in locomotion [49]. It is also possible that damage to one or more of the subsystems will influence proprioceptive information to reflexively-induced locomotion [49]. Clearly, further investigation is needed to understand the increased locomotion after NRTP lesions.
ACKNOWLEDGEMENTS
The authors thank Becky Woodside for assistance in preparing the illustrations. The research was supported by a grant from the National Science and Engineering Research Council of Canada.
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Achenbach, K. E. and D. C. Goodman. Cerebellar projections to ports, medulla and spinal cord in the albino rat. Bruin ~~~~f~~, Evol 1: 43-57, 1968. 2. Allen, G. J. and N. Tsukahara. Cerebrocerebellar communication system. Physiol Rev 54: 957-1006, 1974. 3. Bishop, G. A., R. A. Mccrea and S. T. Kitai. Afferent projections to the nucleus interpositus anterior (NIa) and lateral nucleus (LN) of the cat cerebellum. Anat RW 184: 360, t976. 4. Bloedel. J. R. and J. Courville. Cerebeflar efferent systems. In: Hi~fl~b(~~)~ of Ph~ls;f~l~j~y, SW. I, The ‘~~~r~~~~~.~ Sy.str,m. vol 2, edited by V. B. Brooks. Bethesda, MD: American Physiological Society, 1981, pp. 735-829. S. Brodal, A. and P. Brodal. The organization of the nucleus reticularis tegmenti pontis in the cat in the light of experimental studies of its cerebral cortical afferents. Exp Brnin RVS 13: 90110, 1971. 6. Brodal, A. and J. Jansen. The ponto-cerebellar projection in the rabbit and cat. .t Camp Ncxlmt/ 84: 31-118, 1946. 7. Brodal, A., A. M. Lacerda, J. Destombes and P. Angaut. The pattern in the projection of the intracerebellar nuclei onto the nucleus reticularis tegmenti pontis in the cat. An experimental anatomical study. &rp Brain Rrs 16: 140-160. 1972. 8. Brodal, A. and G. Szikla. The termination of the brachium conjunctivum descends in the nucleus reticularis tegmenti pontis. An experimental anatomical study in the cat. Brrrirr Res 39: 337-351, 1972. 9. Chart-Palay, V. C’erebellar dentate nucleus. Orgnnizrrtion. C‘ytology und Trutzsmirtc,rs. New York: Springer Verlag, 1977, pp. I7921 I. IO. Cheng, J.-T., T. SchaJlert, M. De Ryck and P. Teitelbaum. Galloping induced by pontine tegmentum damage in rats: A form of “Parkinsonian festination“ not blocked by haloperidol. Prtx Nud Acrid Sci USA 78: 3279-3283, 1981. II Chesire, R. M.. J.-T. Cheng and P. Teitelbaum. Reinstatement of festinating forward locomotion by antiserotonergic drugs in rats partially recovered from damage in the region of the nucleus reticularis tegmenti pontis. Exp Neurnl 77: 286294, 1982. 12. Chesire, R. M., J.-T. Cheng and P. Teitelbaum. The inhibition of movement by morphine or haloperidol depends on an intact nucleus reticularis tegmenti pontis. P~~~~s~[~IBchft~~ 30: 809-818, 1983. 13. Corvaja. N., J. Grofova, 0. Pompeiano and F. Walberg. The lateral reticular nucleus in the cat. II. Effects of lateral lesions on posture and reflex movements. Neurnscienc~c~ 2: 929-943. 1977.
14. Dahlstrom. A. and K. Fuxe. Evidence for the existence of monoamine-containing neurons in the central nervous system. I. Demonstration of monoamines in the cell bodies of brain stem neurons. Acru Physid Scnnd 62: Suppl 232, I-55, 1964. 15. Dubuc, P. U. and R. W. Reynolds. Hypothalamic metallic depositions and the production of experimental obesity. Physiol Behav lo: 677-68 I, 1973. 16. Edwards, S. B., C. L. Ginsburgh, C. K. Henkel and B. E. Stein. Sources of subcortical projections to the superior colliculus in the cat. J Crtmp Nrrcruf 184: 309-330, 1979. 17. Eller, T. and V. Chan-Palay. Afferents to the cerebellar lateral nucleus. Evidence from retrograde transport of horseradish peroxidase of pressure injections through micropipettes. ./ Comp Neural 166: 285-302, 1976. 18. Evarts. E. V. and W. T. Thach. Motor mechanisms of the CNS: Cerebrocerebellar interactions. Annu Rrv Ph.v.siol 31: 45 l-498, t 969. 19. Faull. R. L. M. The cerebellofugal projections in the brachium conjunctivum of the rat. II. The ipsilateral and contralateral descending pathways. J Camp Ncurol 178: 519-535, 1978. 20. Felten, D. L., A. M. Laties and M. B. Carpenter. Monoaminecontaining cell bodies in the squirrel monkey brain. Am J Anut 139: 153-166, 1974. 21. Geyer, M. A., A. Puerto, D. B. Menkens, D. S. Segal and A. J. Mandell. Behavioral studies following lesions of the mesolimbic and mesostriatal serotonergic pathways. Bruin Rcs 106: 257270, 1976. 22 Grillner, S. Control of locomotion in bipeds, tetrapods, and fish. In: Handbook elf‘ Physiology. SW. I, N~,urophysio/oXy, vol 2, edited by V. B. Brooks. Bethesda, MD: American Physiological Society, 1981, pp. 1179-1236. 77 Heym, J. and W. E. Gladfelter. Locomotor activity and ingestive behavior after damage to ascending serotonergic systems. Physiol B&x 29: 459-467, 1982. 24. Jacobs, B. L.. W. D. Wise and K. M. Taylor. Differential behavioral and neurochemical effects following lesions of the dorsal or median raphe nuclei in rats. Bruin Res 79: 353-361, 1974. 25. Karen, E. A. and H. C. Fibiger. An analysis of neuronal elements within the median nucleus of the raphe that mediate lesion-induced increase in locomotor activity. Brrrin Rcls 26& 21 l-223, 1983. 26. Kawamura, K., A. Brodal and G. Hoddevik. The projection of the superior colliculus onto the reticular formation of the brain stem. An experimental anatomical study in the cat. Exp Bruin Rc~s 19: I-19. 1974. ..a
t
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27. Krayniak, P. F., R. C. Meibach and A. Siegel. Origin of brain stem and temporal cortical afferent fibers to the septal region in the squirrel monkey. Exp Neural 72: 113-121, 1981. 28. Ladpli, R. and A. Brodal. Experimental studies of commissural and reticular formation projections from the vestibular nuclei in the cat. Bruin Res 8: 65-96, 1969. 29. Lorens, S. A., J. P. Sorensen and L. M. Yunger. Behavioral and neurochemical effects of lesions in the raphe system of the rat. J Comp Physiol Psychoi 77: 48-52, 1971. 30. Marshall, K. C., B. A. Flumerfelt and D. G. Gwyn. Acetylcholinesterase activity and acetylcholine effects in the cerebella-rubro-thalamic pathway of the cat. Brain Res 190: 493-504, 1980. 31. Martin, F. G. Projections of the cerebellum to pre-cerebellar relay nuclei in the opossum. Anar Ret 175: 384, 1973. 32. Martin, G. F., I. S. King and R. Dom. The projections of the deep cerebellar nuclei of the opossum, Didelphis marsupialis virginiana. J ~irnforsch IS: 545-573, 1974. 33. Mogenson, G. J. Limbic-motor integration-with emphasis on initiation of exploratory and goal-directed locomotion. In: Modulation ofSensorimotor Activity During Altered Behnviorul St&es, edited by R. Bandler. New York: Alan R. Liss Inc., 1983, in press. 34. Mogenson, G. J., L. W. Swanson and M. Wu. Neural projections from nucleus accumbens to globus pallidus, substantia innominata, and lateral preoptic-lateral hypothalamic area: An anatomical and electrophysiological investigation in the rat. .I Neurosci 3: 189-202, 1983. 35. Mori, S., M. L. Shik and A. S. Yagodnitsyn. Role of pontine tegmentum for locomotor control in mesencephalic cat. .! Neurophysial40: 284-295, 1977. 36. Mori, S., H. Nishimura, C. Kurakami, T. Y~amura and M. Aoki. Controlled locomotion in the mesencephalic cat: Distribution of facilitatory and inhibitory regions within pontine tegmentum. I Neurophysiol41: 1580-1591, 1978. 37. Morrison, A. R., G. L. Mann and J. C. Hendricks. The relationship of excessive exploratory behavior in wakefulness to paiadoxical sleep without atonia. Sleep 4: 247-257, 1981. 38. Nauta. W. J. H. and H. G. J. M. Kuvners. Some ascending pathways in the brain stem reticular fixation. In: Reti~~~l*~ Formution of the Brain, Henry Ford Hospital Symposium, edited by H. H. Jasper and L. D. Proctor. Boston: Little, Brown and Co., 1958, pp. 3-30. 39. Orlovskii, G. N. Work of the reticula-spinal neurones during locomotion. Biophysics 15: 761-771, 1970. 40. Orlovskii, G. N. Influence of the cerebellum on the reticulospinal neurones during locomotion. Bj~~physi~.~ 15: 929-936, 1970. 41. Reynolds, R. W. An irritative hypothesis concerning the hypothalamic regulation of food intake. Psycho/ Rev 72: 105-116, 1965.
BRDDZYfiSKI
AND MOGENSON
42. Schoenfeld, T. A. and L. W. Hamilton. Secondary brain changes following lesions: A new paradigm for lesion experimentation. Phsy&f Behuv 18: 9Sl-%7, 1977. 43. Shahid Salles. M. S.. J. Hevm and W. E. Gladfelter. Effects of damage to median raphe nucleus on ingestive behavior and wheel running activity. Brain Res Bull 4: 643-649, 1979. 44. Sprague, J. M. and W. W. Chambers. Control of posture by reticular formation and cerebellum in the intact, anesthetized and unanesthetized and in the decerebrated cat. Am J fhy,siof 176: 52-64, 1954. 45. Sprague, J. M. and W. W. Chambers. An analysis of cerebellar function in the cat, as revealed by its partial and complete destruction, and its interaction with the cerebral cortex. Arc,h IIN/ Bid 97: 68-88, 1959. 46. Stein, P. S. G. Motor systems, with special reference to the control of locomotion. Annrr Rrr Neurosci I: 61-81, 1978. 47. Swanson, L. W. and G. J. Mogenson. Neural mechanisms for the functional coupling of autonomic. endocrine and somatomotor responses in adaptive behavior. Bruin Rtv Rev 3: l-34, 1981. 48. Swanson, L. W., G. J. Mogenson, C. R. Gerben and P. Robinson. Evidence for a projection from the lateral preoptic area and substantia innominata to the “mesencephalic locomotor region” in the rat. Brain Res 295: 161-178, 1984. 49. Teitelbaum, P., T. Schallert and I. Q. Whishaw. Sources of spontaneity in motivated behavior. In: Hu&ho& ~~~B~h~l~;~~r~~~ Neurobiology, vol 6, edited by E. Satinoff and P. Teiteibaum. New York: Plenum Publishing Corporation, 1983, pp. 23-65. 50. Teitelbaum, P., H. Szechtman, D. W. Sirkin and I. Golani. Dimensions of movement, movement subsystems and local reflexes in the dopaminergic systems underlying exploratory locomotion. In: Beh~~,j(~r~~~ ~[~~e~~~and the An&is of Drug Action. Proceedings of the 27th OHOLO Conference, Zichron Y6 acov, Israel, edited by M. Y. Spiegelstein and A. Levy. Amsterdam: Elsevier Scientific Publishing Company. 1982, pp. 357-385. 51. Tsukahara, N., T. Bando, S. T. Kitai and T. Kiyohara. Cerebella-pontine reverberating circuit. Bruin Res 33: 233-237. 1971. 52. Valverde, F. Reticular formation of the albino rat’s brain stem. Cytoarchitecture and corticofugal connections. .I C’omp Nctrrctf 119: 25-53, 1962. 53. Walberg, F. and A. Brodal. Spino-pontine fibersin the cat. An experimental study. J C’omp Neural 99: 251-288. 1953. 54. Whishaw, I. Q. and T. E. Robinson. Comparison of anodal and cathodal lesions and metal deposition in eliciting postoperative locomotion in the rat. Ph,ysiof Behuv 13: 539-551, 1974. 55. Winer, 8. J. S~~t~sr~~~ll ~rin~,ipies in Exp~,rirn[,~~[ilDrsi~n. New York: McGraw-Hill, 1962. 56. Winterkorn, J. M. S. and T. H. Meikle, Jr. Lesions of the tectospinal tract of the cat do not produce compulsive circling. Bruin Rcs 190: 597-600. 1980.
0361-9230/84 $3.00 -t .oO
Inc. Printed in the U.S.A.
The Role of the Nucleus Reticularis Tegmenti Pontis in Locomotion: A Lesion Study in the Rat STEFAN
Departnwnr
M. BRUDZYk%W
of Physiology,
AND GORDON
J, MOGE~~~N~
University of Western Ontario, London, Ontario, Canada N6A 5621 Received 21 December
f983
BRUDZYfiSKI, S. M. AND G. J. MOGENSQN. The role qf’the nucierts rrticularis tegmenri pontis in locomation: A lesion study in rhe wt. BRAIN RES BULL 12(s) 513-520, 1984.-Bilateral anodal and cathodal electrolytic lesions of the nucleus r&icuIaris tegmenti pontis (NRTP) increased forward locomotion in rats. The correlation between the magnitude of locomotion and percent of NRTP damage demonstrated that the more complete the NRTP destruction the greater the increase of locomotion. The lesioned rats exhibited at the same time low level rearing and running wheel activity as well as some lack of motor coordinatjon during body balance tests. Taking into consideration the neural connections of the NRTP we suggest that disruption of NRTP-cerebeilar pathways, rather than connection with forebrain structures is associated with the lesion-induced increase of forward locomotion.
Nucleus reticularis tegmenti pontis Rats Galloping
Electrolytic
lesions
Forward locomotion
Body balance
trolyticafly under Nembutal anesthesia tpentobarbital sodium 5 mgf100 g of body weight, IP) in a Kopf stereotaxic instrument. The coordinates for NRTP were +0.2 mm anterior to -0.2 mm posterior to interaural line, 1.0 mm lateral to the midline and 8.5 to 9.0 mm below the surface of the dura with incisor bar -2.4 mm below the ear bars. The electrode was a No. 00 steel insect pin coated with insulating resin with 0.5 mm of the tip bared. In 24 rats, a direct anodaf current of 1 mA was passed for 5 to 15 sec. A rectal electrode was used to complete the circuit, The effectiveness of the anodal lesioning is shown in the Fig. 1. Six rats received cathodaf lesions with a current of 1 mA for 10 to 15 set duration. A group of Eve rats served as sham-operated controls. The electrode was lowered 1 mm above the NRTP in these animals and was withdrawn after 10 set without passage of current. The animals were given a 24 hr recovery period after surgery, Locomotor activity was recorded in a running wheel (G. N. Wahmann MFG. Co., Baltimore, MD) and in large open-fiefd area (247.5~55 cm). Its surface was divided into I8 equal squares (27.5x27.5 cm), comparable in size to that of the rat’s body. The number of lines crossed and number of rearings were recorded on a laboratory counter (Clay-Adams Inc., NY). A line was regarded as being crossed by the rat when more than half of the rat’s head passed over the line. The reliability of recording was checked using independent measurements by two persons. AI1 the locomotor activity tests were carried out during five min-periods in the marning and repeated once a day for five successive days before
THE neural substrates of locomotor activity have received increasing attention in recent years 122,461. A number of forebrain and brainstem structures have been implicated 122, 33,34,481 but the neural circuits and integrative mechanisms for the initiatian and control of locomotion are poorly un-
derstood. However, since locomotion is a fundamental component of a number of adaptive behaviors, such as food procurement or escape from predators, it seems likeiy that there are multiple forebrain influences on brainstem systems associated with locomotion, Dramatic effects on locomotor activity have been reported following lesions of the nucleus reticufaris tegmenti pontis (NRTP) in rats [IO, 11, 121. A rapidly accelerating forward locomotion and galloping appeared after electrolytic lesions of NRTP. The present study was undertaken to investigate this phenomenon in more detail. The objective was to set the stage for elucidating the functional relationship of brainstem structures, such as NRTP and mesencephalic locomotor region [22], to forebrain systems that might under certain circumstances be the initiators of locomotion. METHOD
Thirty-eight adult male albino rats weighing 20.5-390 g at the time of surgery were used. The animals were housed in indiv~du~ cages with food and water ad lib in a tempe~ture-fight-~ontrolfed room with a 1212 hr fighti dark cycle. The NRTP and/or surrounding reticular formation of the ventral pontine tegmentum were damaged elec~-~
‘Visitor from Department of Animal Physiology, Institute of Physiology and Cytology, University of Lodz, Lodz, Poland. ‘Requests for reprints should be addressed to G. J. Mogenson.
513
BRirDZYrjSKI
AND MOGENSON
The effects of lesions were assessed statistically with repeated measures analysis of variance 1551.This was followed by t-test comparisons of the first test day after surgery with the last test day before surgery. After completion of the tests the animals were sacrificed by an overdose of urethane, their brains perfused with 50 ml of 09% NaCl followed by 50-100 ml of buffered formaiin and fixed in formalin. Frozen 80 p brain sections were stained with thionin for histological lesion location and assessment of percentage of NRTP damage. RESULTS
The animals were divided into four groups according to lesion placement. The first group (Fig. 2A, NRTP group, n= 12) included rats with lesions which destroyed at least 50% of NRTP. The second group (Fig. 2B, ventral group, n=4) comprised rats with lesions ventral to NRTP, mainly in pontine gray and medial lemniscus. In two of these rats there was damage of ventrolateral part of NRTP. In the third group (Fig. 2C, dorsal group, n=4) lesions were dorsal to the NRTP in the reticular formation. Two of these lesions slightly damaged the border of medial raphe and the dorsal aspect of NRTP. In the fourth group (Fig. 2D, lateral group, n=4) lesions were in ventrolateral part of the reticular formation at the level of NRTP. Histological examination of lesions revealed that they were between stereotaxic frontal planes 1.O mm anterior to 2.0 mm posterior from interaural plane with maximal destruction between frontal plane 0.3 mm anterior to 1.5 mm posterior from zero plane. A representative photomicrograph of an NRTP lesions is shown in Fig. 1A.
FIG. 1. A-Photomicrograph of anodal lesion placid bilaterally in NRTP (1 mA. 10 sec. 0.5 mm bared tin of steel electrode). The animal was sacrificed 46 days after surgery. Thionin staining. The bar represents 1.0 mm. Abbreviations: PAG-central gray; CIcoIficuius inferior; CS-colliculus superior; LM-medial lemniscus; MR-medial raphe nucleus; PF-pyramidal fibres; PCS-superior cerebeflular peduncte; ~NL~ventrocaud~ nucleus of lateral lemniscus. B-Effectiveness of anodal Iesioning characterized by the volume of damaged tissue in relation to the duration of 1 mA current passage. Vertical bars represent s.e.m. surgery and 10 times after surgery. The tests were repeated during five successive days after surgery and then every second day up to the 15th postoperative day. The animals, however, were still observed up to the 30th day after surgery. Body balance of rats was assessed by placing them on the top of perpendicularly fixed board (2 cm width, 18 cm high, and 88 cm long). The time that the rat was able to balance on the 2 cm edge of the board untif it fell orjumped down to the table surface was measured. If the rat remained on the board, the time measurement was terminated at 5 min.
The effects of NRTP lesions on locomotor activity are shown in Fig. 3. It is clear that when tested after surgery the two groups with NRTP lesions displayed a considerable increase in locomotor activity compared to the sham group and the groups with lesions dorsal, ventral and lateral to NRTP. An analysis of variance for the six groups for the 15 postoperative days indicated highly significant differences, F(5,29)=7.71, p~O.001. Subsequent statistical tests showed that the two groups with anodal and cathodal lesions of NRTP did not differ from one another postoperatively @
R~TICULOTEGMENTAL
LESIONS
515
AND LOCOMOTION C-- NRTP-I:
b-l=6
o-
NRTP -a
II=12
.-
SHAM
n=S
I-
DORSAL
n-4
v-
VENTRAL
n=4
.-
LATLRAL
#I=4
TIME tdavs)
FIG. 3. Locomotor activity in open field area before and after electrolytic lesions (arrow) placed in pontine tegmentum of rats. The animals with anodal lesions are divided into groups according to lesion location as in Fig. 2. There is also a sham-operated group (SHAM). Locomotion after NRTP destruction is shown separately for anodal (NRTP-a) and for cathodal (NRTP-c) lesions. Locomotor activity is expressed as number of lines crossed. Statistical comparison using analysis of variance showed that forward locomotion was significantly greater for the NRTP-a and NRTP-c groups. s.e.m. values included in Table 2.
u FIG. 2. Location of anodal lesions in four groups of rats: A-NRTP lesion group, 12 rats. The outer border of the 12 lesions is presented since it is not possible to show 12 individual lesions. B-ventral lesion group, 4 rats; C-dorsal lesion group, 4 rats: D-lateral lesion group. 4 rats; See text for histological description. Abbreviations: RF-reticular formation: others as in Pig. I.
body-balance disturbances and general lack of motor coordination during body-balance tests when they were placed on the top of a perpendicularly fixed board. Usually, they fell to the table surface within a short time, unlike the control rats. The time spent on the top of the board was significantly shorter in lesioned rats then for control animals (all measurements for NRTP group: r(88)=5.13, p
c
c A
i
o NRTP
n=lZ
.
SHAM
n-5
.
DORSAL
n=J
.
VENTRAL
n=4
.
LATERAl
n-4
B
1 TIME fdavs)
FIG. 4. Running wheel activity (A) and rearing (B) before and after anodai lesion (arrow) placed in pontine tegmentum of rats divided into groups according to lesion location as in Fig. 2 including shamoperated controls (SHAM). s.e.m. values included in Table 2.
BRilDZYhSKI
516 TABLE THE SET OF BEHAVIORAL
PATTERNS
AND MOGENSON
I
AFTER EFFECTIVE NRTP LESIONS (A-ANODAL, DAYS POSTOPERATIVE PERIOD
Total Number of Occurrence
C-C’ATHODAL)
Number of Rats Affected
Percent C
Behavioral Pattern
DURING 30
(60- 100%)
A fn- 12)
C (tl==b)
A. General Locomotion Increased forward locomotion (IO@%or more than control level)
61
32
6
Increased forward locomotion (less than 100%but more than 50%)
22
3
3
Locomotion associated with circling
14
0
0
B. Leaping and Galloping
7
4
5.8%
6.6%
2
Slow symmetric gallop-like locomotion or sequences of leaps
11
6
9.1%
10.0%
2
Slow asymmetric gallop-like locomotion or sequences of leaps
12
6
IO.@%
10.0%
2
4
0
3.3%
0
0
Single rabbit-like leaps or hopping movements
Fast gallop
C. Other Responses Elevated rear part of the body with arched back
8
4
6.6%
6.6%
I
Elevated tail
9
5
7.5%
8.3%
2
Body-balance disturbances during locomotion
5
1
4. I%
1.6%
1
Disturbances of locomotion itself
3
0
2.5%
0
0
Relation Between Lesion Location and Locomotion Since there was some variation in the size and locus of the lesions we calculated locomotor activity in relation to extent of damage to the NRTP. As shown in Fig. 6, locomotion was directly related to the percentage of NRTP damage. There was a significant increase in locomotion when 50% of the NRTP was destroyed and locomotion was increased 14-fold in animals with 90-100% of NRTP damaged. Unilateral damage of NRTP had no effect on locomotion (n=3). The change in locomotion was also related to the locus of NRTPdamage. We compared results of lesions placed anteriorly to the NRTP with lesions placed in the centre of NRTP and in its caudal extension, considering also the dorsal, ventral and lateral lesions illustrated in Fig. 2. Comparing the locomotion levels from five sessions before and five after surgery, we plotted the responses relevant to these lesion locations in a three-dimensional diagram in Fig. 7. One may observe that the lesions of the NRTP itself, and especially its caudal aspect, are associated with the increase in forward locomotion. However, all other ne~h~u~ng areas ventral, dorsal, lateral, and anterior to NRTP were ineffective in producing locomotion, even when some of these lesions damaged some part of NRTP.
OP.
OP.
A DORSAL
LESIONS
FIG. 5. Equilibrium and body coordination tests on the perpendicularly fixed board in non operated fn=55), sham operated fn=20) and lesioned rats. NRTP (n=35), and vent& with dorsal (n=30) groups of rats correspond to lesion location from Fig. 2. Vertical bars represent s.e.m.
RETI~ULOTEGMENTAL
LESIONS AND LOCOMOTION
517
TABLE MEAN VALUES
-c S.E.M. OF LOCOMOTION,
RUNNING
2
WHEEL ACTIVITY AND REARING AFTER NRTP LESIONS
1
3
SECOND DAY BEFORE AND
Days After Surgery
Days Before Lesion Group of Animals
FOR EVERY
5
1
3
5
9
13
79.2224.4 88.7-+ 19.3 9.62 4.2 15.72 10.4 25.01 7.2 16.02 10.2
863226.7 80.0% 16.2 17.0% 6.3 5.75 5.1 7.2% 2.3 6.0-c 2.6
86.5k40.7 68.7t19.0 11.6% 3.5 16.72 9.5 28.52 17.3 14.72 10.7
94.82 19.2 54.0114.2 21.2r 5.6 21.2k20.9 26.01: 15.6 35.0t 13.2
3.5 7.9 0.3 3.5 1.8
2.72 2.5rt 0 7.72 16.21
7.8 8.1
3.62 8.0+ 0.32 3.72 11.22
3.4 4.9 0.3 3.7 9.6
1.9 2.1 2.0 1.1 0.4
lO.Ot 4.21 2.52 5.01 2.5~
2.5 1.5 2.5 4.0 0.8
9.lr 6.42 3.52 5.5t 10.21
1.8 2.8 4.1 2.6 1.3
Locomotion NRTP-c NRTP-a Sham Dorsal Ventral Lateral
4.5.6i 8.1 22.1t 7.0 31.6t11.4 38.3% 14.4 23.7-t 7.0 34.0-c 12.2
24.72 6.0 12.62 3.6 26.4% 7.5 0.3% 0.2 14.7rlr10.1 5.2t 1.9
N RTP-a Sham Dorsal Ventral Lateral
10.01r: 0.6 3.72 2.3 5.01-2.6
5.72 16.7ir 6.02 6.02 13.72
NRTP-a Sham Dorsal Ventral Lateral
9.7* 14.22 5.02 8.2? 5.72
6.1& IO.22 0 4.8% 2.5rt
27.32 11.12 20.42 1.5t 13.7t 2.22
6.3 3.2 6.4 1.2 10.6 1.6
74.2~ 48.9? 13.01 0.21 18.22 5.52
3.4 5.3 3.8 1.5 5.5
5.6t 9.0% 0.3t 7.82 6.2t
3.2 7.7 0.3 4.2 3.7
2.4* 9.2% 0 1.02 4.2~
1.9 2.6
8.22 6.42 I.22 6.0t 1.0+
2.6 2.7 1.4 4.1 0.7
9.02 3.0t 0.3-c 5.7+ 2.5?
19.6 16.7 6.4 0.2 8.0 5.5
Running Wheel 2.1 5.4 0.6 4.2
5.7% I.72 0 6.0~ 5.2-t
3.5 0.8 6.1 5.2
6.0% 18.8t 0.32 6.32 7.7t
9.22 3.4% 1.72 3.7% 3.7+
1.6 1.4 1.2 1.5 3.4
6.8+ 5.42 I.72 2.0% 1.02
1.5 1.6
Rearing 2.1 3.2 2.3 3.4 2.0
3.1 1.9
2.3 f.2 0.3 2.2 1.8
140
,g
12a
E
P
100
e > G (a
40
!
60
ro 9 8
40
20
0
1
V’
2
3
4
s
TIME (days) FIG. 6. Open field locomotion of 23 rats with effective NRTP lesions (arrow) arranged according to the percentage of NRTP damage: 90106% damage (8 rats), 60-80% damage (8 rats), less than 50% damage (7 rats), SHAM-sham operated controls (5 rats); C-control values before surgery. Locomotor activity expressed in number of lines crossed.
FIG. 7. Three dimensional distribution of effects of the lesions on open field locomotion in rats. Blank columns represent mean values from 5 tests before and dotted ones from 5 tests after lesion. Locomotor activity is expressed in number of lines crossed (numbers inside columns). The rostra1 (a), central (b), and caudal (c) location of the lesions is shown in the parasagittal brainstem drawing in the insert. a-Lesions placed rostrally to NRTP comprising also anterior aspect of NRTP; 3 rats. b-Lesions placed in the centre of NRTP destroying 90-100% of this nucleus; 7 rats. The difference is significant, r(121=3.09, p
518
BRuDZYfiSKI DISCUSSION
Electrolytic lesions of NRTP induced foward locomotion which gradually increased over the first 5 days, and lasted for at least seven days after surgery. Since both the anodal and cathodal electrolytic lesions had similar effects on locomotion it appears that the increase in locomotion is not the rest& of irritative effects from deposition of ferric ions, as has been suggested for other experiments [ 1.5,41,54] but depends on the destruction of the NRTP. The damaged area common to the rats that exhibited increased forward locomotion was limited to the NRTP. The correlation between the magnitude of locomotion and percent of NRTP damage shows that the more complete NRTP destruction the greater the increase of locomotion. There is evidence that damage adjacent to NRTP is not responsible for the increase in locomotion level. Lesions of the lateral and dorso-lateral reticular formation in the present study did not induce forward locomotion. Localized electrolytic lesions of tectospinal tract also did not elicit an increase of locomotor activity [%I. An increase of locomotor activity was reported after median raphe lesions in some studies [Zl, 24, 25, 291 while similar electrolytic lesions did not influence locomotor activity in the others 123,431. Also serotonergic neurons located in the medial raphe nucleus and even within NRTP and adjacent reticular formation [ 14,201, projecting to the septal nuclei [27], do not seem to be responsible for the lesion-induced locomotion. Indeed, damage of these neurons by a selective serotonergic neuro~oxin has been reported to decrease activity or have no effect 123, 25, 431. It appears, therefore, that the NRTP itself is the critical structure responsible for the initial increase in locomotion. although serotoninergic mechanisms may be associated with the period of recovery. When NRTP-lesioned rats had partially regained the capacity to inhibit locomotor activity it was lost when serotoninergic blockers were administered [ll]. The results of the present study indicate that NRTP lesions release locomotor mechanisms from an inhibitory influence, as suggested by other investigators [ 10. 11, 12, SO]. It is unlikely, however, that the NRTP itself represents a direct source of this inhibitory influence. Furthermore, the NRTP does not appear to be the brainstem region, associated in the cat, with motor inhibition during paradoxical sleep [35, 36, 371. This inhibitory locomotor region is dorsomedial and caudal to NRTP. The effects on locomotion of lesions of NRTP may instead be related to disruption of its interaction with more distant structures such as cerebellum [I. 3, 4, 6, 7, 8, 9, 17. 19, 31, 321, senso~motor cortex 151, superior colliculus [ 16,261, vestibular nuclei [28,53], and adjacent reticular formation [38,52]. Several of these structures are associated with neural systems involved in body coordination, equilibrium maintenance, and eye- and head-movements. Some of our behavioral observations after lesioning, suggest interference with such systems. Low levels of rearing and running wheel activity in the presence of relatively normal Iocomotion may be the result of a deficit in utilizing information about body position in space. Furthermore, running wheel activity and locomotion may involve different neural mechanisms related to the differential contributions of teleceptive, oculomotor, vestibular and kinesthetic systems to these behaviors. Body-balance disturbances and tail elevation (Table 1C) as well as the six-fold decrease in the time spent by rats on a perpendicular board may be due to some lack of
AND MOGENSON
motor coordination and equilib~um maintenance. Behavioral patterns such as single rabbit-like leaps and gallopingfike sequences of movement observed by us. as well as the festinating character of movement and difficulty in stopping in front of an obstacle as reported previously [ 10, 11, 121, appear to be similar to some of the elements of dysmetria and asynergia observed after cerebellectomy. These observations suggest that the lesion-induced increase of locomotion results, at least partially, from interference with NRTP-cerebellar circuits. The location of NRTP lesions and the analysis of the associated changes in locomotion further support this conclusion for the following reasons. First, destruction of rostra1 and dorsal parts of the NRTP which, have no cerebellopetal connections 161,did not influence locomotion. Second, lesions placed in the caudai extension of the NRTP did induce an increase in locomotion. probably due to partial destruction of the cerebellofugat contralateral pathway. which reaches NRTP via the brachium conjunctivum and descends caudally at the same level as NRTP [ 191. Third, unilateral lesions of the NRTP were ineffective in three rats tested, possibly because the NRTP has strong ipsi- and contralateral connections with cerebellum [ 171. It is also known that reticular formation and cerebellum have reciprocal relations 1441 and that reticula-spinal neurons, being under tonic influence of the cerebellum, change their firing pattern during locomotion in the absence of the cerebellum [39,40]. NRTP lesions disrupt not only its connections with the cerebellum but with cerebral cortex as well [S] and this interference in the cerebra-cerebellar circuit might also be responsible for the changes in locomotion and especially for the galloping movements. Sprague and Chambers [45] disrupted this circuit by neocortical lesions in cerebellectomized cats and observed gallop-like behavior with the NRTP intact. After NRTP damage, galloping develops over a period of 20 to 40 [I I] and, in some cases, up to 55 days 1121. In our experiments we did not observe the galloping response during the first IS days after NRTP lesions. A tendency to gallop-like behavior began to occur after this time and was observed in eight of the 12 rats at the end of observation period (30 days). Although. 6 of a large number of NRTP-lesioned rats displayed exaggerated locomotion as soon as they recovered from anesthesia [ 127. in most animals in earlier studies as well as in the present study increased locomotion did not occur for two or three weeks. and followed a period of hypokinesia. This suggests that the behavioral pattern may be, in part at least, the result of neural degeneration to distant structures [42]. For example. transections of the brachium conjunctivum resulted after 2 weeks in marked loss of acetylcholinesterase activity in the red nucleus and ventral thalamic nuclei 1301. The connections of NRTP with both cortex and cerebellum may modulate locomotion but the cerebella-cerebellar loop may be the more important one. There is some electrophysiological evidence, supporting this statement, which indicates that NRTP neurons are driven mainly by cerebellar input while cortical input provides only modulatory influences (for review see [2]). Furthermore, the finding of impulse reverberation between NRTP and nucleus interpositus of the cerebellum along an excitatory loop [Sl] support the physiological importance of this connection. Also from the anatomical point of view the cerebella-NRTP-cerebellar loop seems to be stronger than others between cerebellum and pontine gray. inferior olive, and lateral reticular nucleus [Z]. Thus disruption of NRTP-cerebellar rather than the connec-
RETI~ULOTE~MENTAL
LESIONS
AND LOCOMOTION
tions with cerebral cortex and other structures is more likely associated with the lesion-induced increase of locomotion. Finally, pontine tegmental lesions can result in metabolic disturbances which, in turn, might be responsible for some of the behavioral effects observed. The increase of locomotion, in the present study however. seemed to be unrelated to metabolic changes. NRTP-lesioned rats exhibited high level of locomotion regardless of whether their body weight was maintained or was decreasing with time (2 rats among 18). Although, it has been suggested that the cerebellum contributes to movement initiation [18] there is also evidence that basai forebrain structures may be associated with response initiation (e.g., [34, 47, 481). It appears that basal forebrain areas are involved in initiation of locomotion connected with biologically important adaptive behaviors [47] while ponto-cerebellar areas contribute to the regulation of motor performance. Teitelbaum and coworkers [49.50] have postulated several separate movement subsystems, such as
head scanning, forward locomotion, head-orienting, mouthing, and postural support, which are related to ponto- and reticula-cerebellar areas. These areas may contribute to the integration of movement subsystems [ 131 and if one subsystem is disrupted by a lesion there may be a compensatory increase in the activity of another system, for example, in locomotion [49]. It is also possible that damage to one or more of the subsystems will influence proprioceptive information to reflexively-induced locomotion [49]. Clearly, further investigation is needed to understand the increased locomotion after NRTP lesions.
ACKNOWLEDGEMENTS
The authors thank Becky Woodside for assistance in preparing the illustrations. The research was supported by a grant from the National Science and Engineering Research Council of Canada.
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