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Responses of single units in the inferior olive nucleus to stimulation of the splanchnic afferents in the cat
Journal o f the A u t o n o m i c ~}ervous System, 2 (1980) 15-22 © Elsevier/North.Holland Biomedical Press
15
R E S P O N S E S O F S I N G L E UNITS IN T H E I N F E R I O R OLIVE NUCLEUS TO STIMULATION OF THE SPLANCHNIC AFFERENTS IN "rilE CAT
J. PERRIN and J. CROUSILLAT Departement de Neurophysiologie Vdgetatwe. INP. 01, C.N.R.S.. 3 ! ('hem in Joseph A iguier. 132 74 Marseille Cedex 2. and Departement de Bio~;lectrwit~. Umcer,~ite de Provence, Place Victor :tugo, 1333 t Marseilic Cedex 3 t l":enc~)
(Received October 23rd, 1979) (Accepted December 13th, 1979) Keywords:
inferior olive -- splanchnic mechanoreceptor,, .... c'.imbmg fibers -cat
ABSTRAC'I
The activity of olivary neurons of the caudal parts of the medial accessory olive (MAO) and dorsal accessory olive (DAO) was recorded with extracellular microelectrodes in anesthetized cats. The responses were obtained by electrical stimulation of the contralateral splanchnic nerve and mechnical stimulations of gastro-intestinal and peritoneal receptors. The stimulated mechanoreceptors were slowly adapting muscular receptors of the stomach (connected with C fibers) and slowly .,dapting peritoneal m o v e m e n t receptors (connected with A 7 5 or B fibers). Splanchno-visceral, splanchno-somatic and splanchno-cortical converge~ces were observed, as in the cerebellum (lobule V mid VI). So, the inferior olive :nust be considered as an integrating structure not only for central ~md somatic messages, but also for visceral ones.
INTRODUCTION Many anatomical and eteetrophysiological stu :lies have been perfoxmec' to identify spino-olivary, cortico-olivary and olivo-cerebellar pathways a:l(i cortical and otivary projecting zones of the somatic afferents. This work is well presented in general reviews [1,5,6,23] and in individual papers [2--4,9--11,12,16]. It has been shown al~(~ th~.;: the stimulation of vi.~cerat receptors and nerves modifies the cerebc!l:u" I'terkinje cells discharged via mossy and climbing fiber pathways [7,8,13,17--21,27,29,30,32]. So far, however, visceral projections to the inferior olive, which is considered to be the principal or the only source of climbing fi )ers, have not been studied.
16 In order" to complete studies of the cerebellum previously performed [ 27], we recorded how olivary neuron activity was modified by stimulation of visceral afferents (splanchnic nerves and mechanoreceptors). The unitary responses of these olivary neurons were recorded in different inferior olive nuclei, the medial accessory olive (MAO) and the dorsal accessory olive IDAO) by extracellular microelectrodes. M E T H 0 DS
Experiments were performed on 12 adult cats (weighing 2--3.5 kg). Ten cats were anesthetized with chloralose (100 mg/kg i.v.)and the remaining two with soGium pentobarbital (15 mg/kg i.v.). Each animal was fixed in at sWreotaxic apparatus, curarized (Flaxedil)and artificially ventilated. The rectal temperature was maintained between 37 and 38°C by means of a heating blanket. The right inferior olive was reached through a ventral approach: the base of the skull was exposed by reflecting the pharynx forward and an opening was made to expose the ventral surface of the medulla. The rxtracellular microelectrodes (KCI 3 M, 1 M ~ ) used were implanted sterotaxically. The recording sites in the olive nuclei were determined from Berman's atlas and in some cases confirmed by Pontamine marking techniques [ 15]. Pairs of stimulating electrodes were placed under ipsilateral and contralateral splanchnic nerves at tl-.c abdominal or thoracic level. Trains of 3--4 pulses (0.5 msec: ~r-1.; 0.5 at 50 V) at a frequency of 300 Hz were the most efficient stimuli. The conduction velocity of the left (contralateral) splanchmc fibers was determined by methods previously described [:).7]. In most experiments the vagus nerves were also stimulated at the inferior cervical level with a pair of stimulatit~g electrodes (0.5 msec:J-t; 0.5 at 50 V). Tissues of the limbs and thorax were stimulated by means of hypodermic needles. Bipolar electrodes (5--10 V) were used to stimulate the cerebellar cortex (vermis of lobule V and VI) and cerebral cortex (.,;ornate-sensor', area S1 and SII). Mechanical stimulations of peritoneum and gastro-intestina! tract receptors were performed using previously described techniques [28]. I~.ESt' t,'rs Most of the olivm'y neurons activatecl I)y the splanchnic nerw ~,stimulation showed little or no spontaneous activity under experimental conditions i m p e n d . When spontaneous activity was recorded, it was irregular and infrequent (frequency <3 ltz). Thirty-nine neurons of the right inferior olive were activated by contralateral splanchnic ne~-~e stimzflation; 15 of them were also activated by mechanical stimulation of receptors located in the gastro-intestinal tract or in the mesentery. All these neurons were located in the caudal parts of the medial accessory olive (MAO) and the do~sal accessory oliw, (DAO} (stereotaxlc plans 1 1--1,t.5) {Fig. 1 ).
17
Fig. 1. Localization of the recording site of the microelectrode. Trans,ter.c,e section made through th : brain stem (frontal plane 1 1.2 f r o m Berman's atlas). T h e arrow indicates the position of the tip of the microelectrode (×6.5).
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Fig. 2. Lal.encies of olivary neurons' responses. The histograms show distribution of !atenc: responses induced by stimulation of: cgntralaterai splanchnic nerve (A); ip.~ilateral cerebral cortex: (SI area) (B); ipsilateral cerebral cortex: (SII area) {C); and contralateral eerebel;ax cortex: (vermis of Iobule V; a n t i d r o m i c stimulation) (D).
18
Response latencies The latencies of responses evoked by stimulating contralateral splanchnic nerve (thoracic electrodes) were determined for all the neurons. They ranged between 9 and 56 msec (mean value: 27 msec + 10; Fig. 2A). For most of these neuzons, the latencies of the responses to the electrical stimulations of the ipsilateral cerebral cortex were also determined. For somato-sensory area SI they ranged between G and 31 msec (mean value: 14 msec +- 6; Fig. 2B); for somato-sen~ory area SII they ranged between 8 and 27 msec (mean value: 15 msec +-5; Fig. 2C). The latencies of the responses to SI stimulations were in mast cases (70%) shorter than those of the responses to SII stimulations. The latencies of the responses to antidromic stimulations of contralateral cerebellar cortex areas (vermis of Iobule V) were between 2.5 and 6.5 msec (mean value: 4 msec -+.1; Fig. 2D). Some responses to orthodromic cerebellar stimulations were observed, they ranged from 10 to 15 msec.
Splanchnic l iber types The type of peripheral fibers activating olivary neurons was determined from their conduction velocity values: 26 exhibited velocities ranging bet~veen 3 and 15 m/sec (A ~ 5 or B fibers) and 3 others 2 m/sec (C fibers). T w o A~ fibers were identified from their stimulation thresholds (conduction velocities could not be determined for this fiber type).
Mechanorecep tots As previously indicated, 15 among the 39 olivary neurons activated by electrical stimulation also responded to mechanical stimulation of the gastro-intestinai tract or peritoneum. The corresponding visceral mechanoreceptors belong to two types respectively: slowly adapting muscular receptors and peritoneal " m o v e m e n t " receptors. The activity of two olivary neurons was modified (Fig. 3,) by stimulating muscular mecaanoreceptors of the stomach (slowly adapting receptors inncrvated by C fibers). These receptors were activated by displacement and dis~;nsion of the stomach (distension was produced by inflating a small ball,,on intxoduced into the stomach through tile mouth). These mechanical stimulations produced an increase in neuron activity, which persisted during the : timulation. The basal activity was rapidly re-established after deflation. T ~e activity of 13 neurons was modified (Fig. 3:) by stimulating peritom,al mechanoreceptors sensitive to movement (slowly adapting receptors inne,wated by A 3' 5 or B fibers). These receptors were mainly located in the mesentery and ti~e perirenal peritoneum. They were activated by displacement of whole organs (kidney, stomach) or by local stimulation of the peritoneum. These local punctate stimulations induced short and reproducible responses (Fig. 32). It was not possible to accurately d e t e r m i ~ latencies of
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Fig. 3. Responses of olivary neurons to stimulations of splanchnic mechanoreceptors. 1: muscular mechanoreceptors of the stomach. The response was produced by: A, displacement of stomach; B, gastric distension activated with a small balloon. 2: movement mechanoreceptors of the peritoneum. Response produced by: A, displacement of mesentery; B, p u n ct a~ stimulation.
these mechanically-induced responses under experimental conditions prevailing. Con vergences
Numerous con~ergences were observed (Fig. 4) in this work. Actually, all the cells studied were activated by both contralateral and homolateral splanchnic nerve s~imulations and some (40% of the tested neurons) by vagus
A
B
Fig. 4. Examples of convergen~es ubserved in the same olivary neuron. Responses produced respectively to electrical stimulation of: A, contralateral splanchnic nerve; B, contralateral vagus nerve; C, ispsilateral cerebral cortex: SI area; and D, contralat, ral forelimb, tissue afferents.
20 nerve stimulations. Impulses arising from one or several limbs and from the thorax of the animal also converged on these neurons, as did those coming from coriieal SI (30 neurons) and SII (24 neurons) areas. DISCUSSION
The present work has revealed the effects of electrical stimulations of splanchnic nerve and mechanical stimulations of the gastro-intestinal and peritoneal receptors on the activity of olivary neurons. These olivary neurons were located in the caudal parts of the medial accessory olive (MAO) and dorsal accessory olive (DAO). These results axe consistent with those reported previously [5,6,9,16,24]. Indeed, the authors referred to demonstrated by histochemical or electrophysiological techniques that the climbing fibers originating from these olivary nuclei project to the vermis of the cerebellar antelior and posterior lobes. Our previous work [27], in addition to confirming the studies of others [20,29,32] presented evidence for an important amount of splanchnic afferents input to this cerebellar area (vermis of lobules V and VI). The latencies of the olivary responses to electrical stimulations of the contralateral splanchnic ner:e agree with our previous results obtained in the cerebellum. The conduction velocities of olivo-cerebellar axons have been established by other authors [5,14]. According to their data, the mean value (27 msec) of the latencies that we obtained for olivary responses did correspond to those found (33 msec) for climbing fiber-induced responses recorded in the cerebellum after ipsilateral splanchnic nerve stimulations. The mean latencies of olivary responses to electrical stimulations of cerebral cortex areas (S[: J4 msec and SII: 15 msec) were slightly longer than those ( 8 - 9 msec) obtained by Armstrong [4,5] after stimulation of sensory motor cortex (pericrucial area). But they are not very different from those (12.8 msec mean) mentioned by Allen and Tsukahara [1] and obtained by Sedgwick and Williams [31] and by Crill [ 12]. These differences in the latencies reported by various authors might be due to the locations and sizes of the stimulated areas of the cerebral cortex as well as the recording sites; these varied considerably in the several experi~aents. The range and mean (4 msec) values of latencies found for the olivary r e s p o n d s evoked by cerebt, ii,-u" antidromic stimulation corresponded to the results reported by Armnt rong [2,5] and Crill [12]. Our e;,periments demonstrate that the splanchnic fibers projecting on the inferior olive are most A ' I 5 or B fiber:;. There are few C or A/J fibers which induce an olivary response to electrical stimulat, ion. This generalizalion holds for the diff,,rent types of identified mechalmreceptors: most of them were movement-sensing peritoneal mechanoreceptors connected with A 7 5 or B fibers). This is ill agreement with our previous ro~ults concerning the cerebellar projections [27]. It is the first report whicl~ shows that the activity of olivary neurons can be modified not only by visceral nerve stimulations but also by different mechanical stirnulati(ms oi" splanchnic receptors.
21 The p r e ~ n t work present~ evidence for many convergences on the otiv~y neurons. We have demonstrated that, besides somatic and cerebral impulses, visceral impulses (splanchnic and vagus) could also activate one single olivary neuron. The splanchno-somatic, splanchno-visceral and splanchno-cortical interactions observed at the cerebellar level were also obs,~rved at the olivary level. The great number of viscero-somatic convergences in the cerebellum as well as in the inferior olive could be due to the fact that in these two structures the visceral projection zones partially everlap the limb projection zones [24]. The inferior olive may be considered to be a structure integrating not only information coming from the. superior centers, from somesthetic sources, but also from visceral organs. Our experiments sh,.;,.,, thai splanchnic afferents, like somesthetic afferents feed into the spino-olivary pathway and project, on the cerebellar cortex through climbing fibers via il,fcrior olive. ACKNOWLEDGEMENTS
The authors thank Doctor N. Mei, sous-directeur de I'lnstitut de Neurophysiologm et de Psychophysiologie for his helpful advice in the course of the work, Andr4 Boyer for technical assistance, and Franqoise Farnarier for correcting the English. REFERENCES
1 Allen, G.I. and Tsukahara, N., Cerebro-cerebellar communication :~y.~Wm.% Phy.~iol. Rev., 54 (1974) 957--1006. 2 Armstrong, D.M. and Harvey, R.J., Responses in the inferior oliw, to slinmlation ~f the cerebt~llar and cerebral ccrtice~ in the cat, J. Physiol. (Lond.), 187 (1966) 553--574. 3 Armstrong, D.M., Eccles, J.C., Harvey, R.J. and Matthews, PB.C., .Responses in the dorsal accessory olive of the cat to stimulatio, of hindlimb afferents, J. Physiol. (Lond.), 19-] (1968) 125--145. 4 Armstrong, D.M. and Harvey, R.J., Responses of a spino-olivo-cerebellar pathway in the cat, J. Physiol. (Lond.), 194 (1968) 1.17--168. 5 Armstrong, D.M., Functional significance of connections of the inferior olive, Physiol. Rev., 5-1 ( 197,t } 358--.t 17. 6 Armstrong, D.M., Harvey, R.J. and Schiid, R.F., Topographical locahsatLon m the, olivo-ceretel]ar projection' an electrophysiological .~tudy in the cat, J. comp. Neurol . 15,t ( 197,] } 2 8 7 - - 3 0 2 7 Bratus, N.V., Elektri-cheskie reakshii razlichnykh .~loev kory mozzhechka I)rJ raz(h-az henii visceral 'nykh nervov, I,'izml. Zh. Leningr., .18 (1962) 304--30~ 8 Bratus, N.V., Electricheskie reakshii kory mozzhechka pri razdrazhcnii vi.~c~'ral 'nykh nervov l:,osle desherebrashii, Byull. eksp. Biol. Med., 10 (1962) 3 - 8 . 9 Brodal, A.. Walberg, F. and Blaekstad, Th., Termination of spinal af&..,'cnt~ to nlfel'l~,r olive in cat, J. Neurophysiol., 13 (1950) 431---t54. 10 Brodal, A. and Walberg, F., The olivocerebellar projection in the eat studied with the m e t h o d of retrograde axonal transport o f horseradish peroxidase. IV. The proiection to the anterior lobe, J. comp. Neurol., 172 (1977) 85--108. 11 Carrea, R., Ruarte, A. and Volkind, R., Single unit activity at the inferi~,~ ~,ii~,., ,~ the cat, J. uerv. ment. Dis., 1-17 (1968) 70--8.1.
22 12 Criil, W., Unitary multiple-spiked responses in cat inferior olive nucleus, J. Neurophysiol., 33 (1970) 199--209. 13 Dell, D. and Olson, R., Projections thalamiques, corticales et c~r~belleuses des affdrences visc~rales vagales, C.R.Soc. Biol. (Paris), 145 (1951) 1084--1088. 14 Eccies, J.C., Llinas, R. and Sasaki, K., The excitatory synaptic action of climbing fibres on the Purkinje cells of the cerebellum, J. Physioi. (Lend.), 182 (1966) 268--296. 15 Godfraind, J.M., Localisation de i'extr~mit~ de~ micro~lectrodes de verre dans le syst6me nerveux central par electrophor~se de p o n t a m i n e , J. Physiol. (Paris), 61 (1969) .136. 16 Groenewegen, H.J. and Voogd, J., The parasagittal zonal organisation within the olivocerebellar projection. I. Climbing fibre distribution in the vermis o f cat cerebellum, J. comp. Neurol., 17,1 ( 1 9 7 7 ) 4 1 7 - - 4 8 8 . 17 Hennemann, H.E. and Rubia, F.J., Vagal representation in the cerebellum of the cat, PfliJgers Arci] ges. Physiol., 375(2) (1978) 119--123. l,q Langhof, H., |lbppener, V. and Rubia, F.J., Climbing fiber responses to splanchnic nerve stimulation, Brain Res., 53 (1973) 232--236. 19 l,evchuk, O.V., Grigor'yan, R.A. and Bratus, N.V., Responses of Purkinje cells and other neurons of the m o n k e y cerebellar cortex to vagus nerve stimulation, Proc. Acad. Sci. U.S.S.R., 238(1/6) (1978) 72--73. 20 Newman, P.P., The representation of some visceral afferents in the anterior lobe of cerebellum, J. Physiol. (Lond.), 182 (1966) 1 9 5 - 2 0 8 . 21 N e w m ' m , P.P. and Paul, D.H., The effects of stimulating cutaneous and splanchnic afferer ts on cerebellar unit discharges, J. Physiol. (Lond.), 187 (1966) 575--582. 22 Newman, P.P. and Paul, D.H., The projection o f splanchnic afferents on the cerebellum of tile cat, J. Physiol. (Lond.), 202 (1969) 223--237. 23 Oscarsson, O., Functional organization of spinccerebellar paths. In A. Iggo (Ed.), I l a n d b o o k of Sensory Physiology, Vol. II, S o m a l o s e n s o r y system, Springer, Berlin, Heidelberg, Ncw York, 1973, pp. 339--380. 2 . 1 0 s c a r s s o n , O., Sjt~lund, B., The ventr~ll spino-olivocerebellar system in the cat. I. Identification of five paths and their termimition in the cerebellar anterior lobe, Exp. Brain Res., 2~4 (1977) 469-.186. 25 Oscarsson, O. and Sji~hm(!, B., The ventral spino-olivocerebellar system in the cat. lI. Termination zones in the cerebellar posterior lobe, Exp. Brain Res., 28 (1977) .187--503. 26 Oscarsson, O. and SjShmd, B., Tile ventral spino-olivocercbellar system in the cat. III. Functional characteristics of the five paths, Exp. Brain Res., 28 (1977) 505--520. 27 Perrin, J. et ('rousillat, d , Effects de la stimulation des m~canor~cepteurs splanchniques sur I'aetivit6 des cellules cerebelleuses de Purkinje, Exp. Brain Res., 37 (1979) 405--.116. 28 lianit,,'i, F., Mei, N. et Crousillat, J., Les :: ffdrcnccs splanchniqiles provenant des me('antu'deeptcars gash'o-intt'stinaux el pcri oneaux. Exp. Brain R c s , 16 (1973) 275 -290. _,) Ruhia. F 3., The proiecthm of viscw'al afferen~s to the ccrebellar cortox of tile eat, Pflii~(,rs Arch. gcs. Physiol., 320 (1970) 97--1 IL~. 30 Ruhia, F.,I. and Pl:elps, J.B., Responses of th,' eercbellar cortex to cutaneous and
visceral ,qfl'erenls, Pfl(igers Arch. ges. Physiol., 31.t (1970) 68--95. 31 Sedgwick, E. and Williams, T.,t. Responses ('f sin~,h, unit~ in the inferior olive to s;.in~uhfl;on t~[" flu, limb nerv('s, p,.. "ipheral skin receptoks, cerebellum, caudatc nucleus
;nld n l t ) l o f cortex, ,I. Physiol. ',1. n ,3 .~ 189 (19{17) 261--279. 32 Widdn, L., Cerebeltar rep,','~,,~(z: ":, of high threshold afferents it] the splanchnic llt, rve wtth ot)servatiol,s on ',~. cereL, ellar projection of birth '.hrt, shold somatic afferent :'ib,-es, :\eta physiol, scand., 117 Suppl., 32 (1955) 1 - 6 9 .
15
R E S P O N S E S O F S I N G L E UNITS IN T H E I N F E R I O R OLIVE NUCLEUS TO STIMULATION OF THE SPLANCHNIC AFFERENTS IN "rilE CAT
J. PERRIN and J. CROUSILLAT Departement de Neurophysiologie Vdgetatwe. INP. 01, C.N.R.S.. 3 ! ('hem in Joseph A iguier. 132 74 Marseille Cedex 2. and Departement de Bio~;lectrwit~. Umcer,~ite de Provence, Place Victor :tugo, 1333 t Marseilic Cedex 3 t l":enc~)
(Received October 23rd, 1979) (Accepted December 13th, 1979) Keywords:
inferior olive -- splanchnic mechanoreceptor,, .... c'.imbmg fibers -cat
ABSTRAC'I
The activity of olivary neurons of the caudal parts of the medial accessory olive (MAO) and dorsal accessory olive (DAO) was recorded with extracellular microelectrodes in anesthetized cats. The responses were obtained by electrical stimulation of the contralateral splanchnic nerve and mechnical stimulations of gastro-intestinal and peritoneal receptors. The stimulated mechanoreceptors were slowly adapting muscular receptors of the stomach (connected with C fibers) and slowly .,dapting peritoneal m o v e m e n t receptors (connected with A 7 5 or B fibers). Splanchno-visceral, splanchno-somatic and splanchno-cortical converge~ces were observed, as in the cerebellum (lobule V mid VI). So, the inferior olive :nust be considered as an integrating structure not only for central ~md somatic messages, but also for visceral ones.
INTRODUCTION Many anatomical and eteetrophysiological stu :lies have been perfoxmec' to identify spino-olivary, cortico-olivary and olivo-cerebellar pathways a:l(i cortical and otivary projecting zones of the somatic afferents. This work is well presented in general reviews [1,5,6,23] and in individual papers [2--4,9--11,12,16]. It has been shown al~(~ th~.;: the stimulation of vi.~cerat receptors and nerves modifies the cerebc!l:u" I'terkinje cells discharged via mossy and climbing fiber pathways [7,8,13,17--21,27,29,30,32]. So far, however, visceral projections to the inferior olive, which is considered to be the principal or the only source of climbing fi )ers, have not been studied.
16 In order" to complete studies of the cerebellum previously performed [ 27], we recorded how olivary neuron activity was modified by stimulation of visceral afferents (splanchnic nerves and mechanoreceptors). The unitary responses of these olivary neurons were recorded in different inferior olive nuclei, the medial accessory olive (MAO) and the dorsal accessory olive IDAO) by extracellular microelectrodes. M E T H 0 DS
Experiments were performed on 12 adult cats (weighing 2--3.5 kg). Ten cats were anesthetized with chloralose (100 mg/kg i.v.)and the remaining two with soGium pentobarbital (15 mg/kg i.v.). Each animal was fixed in at sWreotaxic apparatus, curarized (Flaxedil)and artificially ventilated. The rectal temperature was maintained between 37 and 38°C by means of a heating blanket. The right inferior olive was reached through a ventral approach: the base of the skull was exposed by reflecting the pharynx forward and an opening was made to expose the ventral surface of the medulla. The rxtracellular microelectrodes (KCI 3 M, 1 M ~ ) used were implanted sterotaxically. The recording sites in the olive nuclei were determined from Berman's atlas and in some cases confirmed by Pontamine marking techniques [ 15]. Pairs of stimulating electrodes were placed under ipsilateral and contralateral splanchnic nerves at tl-.c abdominal or thoracic level. Trains of 3--4 pulses (0.5 msec: ~r-1.; 0.5 at 50 V) at a frequency of 300 Hz were the most efficient stimuli. The conduction velocity of the left (contralateral) splanchmc fibers was determined by methods previously described [:).7]. In most experiments the vagus nerves were also stimulated at the inferior cervical level with a pair of stimulatit~g electrodes (0.5 msec:J-t; 0.5 at 50 V). Tissues of the limbs and thorax were stimulated by means of hypodermic needles. Bipolar electrodes (5--10 V) were used to stimulate the cerebellar cortex (vermis of lobule V and VI) and cerebral cortex (.,;ornate-sensor', area S1 and SII). Mechanical stimulations of peritoneum and gastro-intestina! tract receptors were performed using previously described techniques [28]. I~.ESt' t,'rs Most of the olivm'y neurons activatecl I)y the splanchnic nerw ~,stimulation showed little or no spontaneous activity under experimental conditions i m p e n d . When spontaneous activity was recorded, it was irregular and infrequent (frequency <3 ltz). Thirty-nine neurons of the right inferior olive were activated by contralateral splanchnic ne~-~e stimzflation; 15 of them were also activated by mechanical stimulation of receptors located in the gastro-intestinal tract or in the mesentery. All these neurons were located in the caudal parts of the medial accessory olive (MAO) and the do~sal accessory oliw, (DAO} (stereotaxlc plans 1 1--1,t.5) {Fig. 1 ).
17
Fig. 1. Localization of the recording site of the microelectrode. Trans,ter.c,e section made through th : brain stem (frontal plane 1 1.2 f r o m Berman's atlas). T h e arrow indicates the position of the tip of the microelectrode (×6.5).
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Fig. 2. Lal.encies of olivary neurons' responses. The histograms show distribution of !atenc: responses induced by stimulation of: cgntralaterai splanchnic nerve (A); ip.~ilateral cerebral cortex: (SI area) (B); ipsilateral cerebral cortex: (SII area) {C); and contralateral eerebel;ax cortex: (vermis of Iobule V; a n t i d r o m i c stimulation) (D).
18
Response latencies The latencies of responses evoked by stimulating contralateral splanchnic nerve (thoracic electrodes) were determined for all the neurons. They ranged between 9 and 56 msec (mean value: 27 msec + 10; Fig. 2A). For most of these neuzons, the latencies of the responses to the electrical stimulations of the ipsilateral cerebral cortex were also determined. For somato-sensory area SI they ranged between G and 31 msec (mean value: 14 msec +- 6; Fig. 2B); for somato-sen~ory area SII they ranged between 8 and 27 msec (mean value: 15 msec +-5; Fig. 2C). The latencies of the responses to SI stimulations were in mast cases (70%) shorter than those of the responses to SII stimulations. The latencies of the responses to antidromic stimulations of contralateral cerebellar cortex areas (vermis of Iobule V) were between 2.5 and 6.5 msec (mean value: 4 msec -+.1; Fig. 2D). Some responses to orthodromic cerebellar stimulations were observed, they ranged from 10 to 15 msec.
Splanchnic l iber types The type of peripheral fibers activating olivary neurons was determined from their conduction velocity values: 26 exhibited velocities ranging bet~veen 3 and 15 m/sec (A ~ 5 or B fibers) and 3 others 2 m/sec (C fibers). T w o A~ fibers were identified from their stimulation thresholds (conduction velocities could not be determined for this fiber type).
Mechanorecep tots As previously indicated, 15 among the 39 olivary neurons activated by electrical stimulation also responded to mechanical stimulation of the gastro-intestinai tract or peritoneum. The corresponding visceral mechanoreceptors belong to two types respectively: slowly adapting muscular receptors and peritoneal " m o v e m e n t " receptors. The activity of two olivary neurons was modified (Fig. 3,) by stimulating muscular mecaanoreceptors of the stomach (slowly adapting receptors inncrvated by C fibers). These receptors were activated by displacement and dis~;nsion of the stomach (distension was produced by inflating a small ball,,on intxoduced into the stomach through tile mouth). These mechanical stimulations produced an increase in neuron activity, which persisted during the : timulation. The basal activity was rapidly re-established after deflation. T ~e activity of 13 neurons was modified (Fig. 3:) by stimulating peritom,al mechanoreceptors sensitive to movement (slowly adapting receptors inne,wated by A 3' 5 or B fibers). These receptors were mainly located in the mesentery and ti~e perirenal peritoneum. They were activated by displacement of whole organs (kidney, stomach) or by local stimulation of the peritoneum. These local punctate stimulations induced short and reproducible responses (Fig. 32). It was not possible to accurately d e t e r m i ~ latencies of
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Fig. 3. Responses of olivary neurons to stimulations of splanchnic mechanoreceptors. 1: muscular mechanoreceptors of the stomach. The response was produced by: A, displacement of stomach; B, gastric distension activated with a small balloon. 2: movement mechanoreceptors of the peritoneum. Response produced by: A, displacement of mesentery; B, p u n ct a~ stimulation.
these mechanically-induced responses under experimental conditions prevailing. Con vergences
Numerous con~ergences were observed (Fig. 4) in this work. Actually, all the cells studied were activated by both contralateral and homolateral splanchnic nerve s~imulations and some (40% of the tested neurons) by vagus
A
B
Fig. 4. Examples of convergen~es ubserved in the same olivary neuron. Responses produced respectively to electrical stimulation of: A, contralateral splanchnic nerve; B, contralateral vagus nerve; C, ispsilateral cerebral cortex: SI area; and D, contralat, ral forelimb, tissue afferents.
20 nerve stimulations. Impulses arising from one or several limbs and from the thorax of the animal also converged on these neurons, as did those coming from coriieal SI (30 neurons) and SII (24 neurons) areas. DISCUSSION
The present work has revealed the effects of electrical stimulations of splanchnic nerve and mechanical stimulations of the gastro-intestinal and peritoneal receptors on the activity of olivary neurons. These olivary neurons were located in the caudal parts of the medial accessory olive (MAO) and dorsal accessory olive (DAO). These results axe consistent with those reported previously [5,6,9,16,24]. Indeed, the authors referred to demonstrated by histochemical or electrophysiological techniques that the climbing fibers originating from these olivary nuclei project to the vermis of the cerebellar antelior and posterior lobes. Our previous work [27], in addition to confirming the studies of others [20,29,32] presented evidence for an important amount of splanchnic afferents input to this cerebellar area (vermis of lobules V and VI). The latencies of the olivary responses to electrical stimulations of the contralateral splanchnic ner:e agree with our previous results obtained in the cerebellum. The conduction velocities of olivo-cerebellar axons have been established by other authors [5,14]. According to their data, the mean value (27 msec) of the latencies that we obtained for olivary responses did correspond to those found (33 msec) for climbing fiber-induced responses recorded in the cerebellum after ipsilateral splanchnic nerve stimulations. The mean latencies of olivary responses to electrical stimulations of cerebral cortex areas (S[: J4 msec and SII: 15 msec) were slightly longer than those ( 8 - 9 msec) obtained by Armstrong [4,5] after stimulation of sensory motor cortex (pericrucial area). But they are not very different from those (12.8 msec mean) mentioned by Allen and Tsukahara [1] and obtained by Sedgwick and Williams [31] and by Crill [ 12]. These differences in the latencies reported by various authors might be due to the locations and sizes of the stimulated areas of the cerebral cortex as well as the recording sites; these varied considerably in the several experi~aents. The range and mean (4 msec) values of latencies found for the olivary r e s p o n d s evoked by cerebt, ii,-u" antidromic stimulation corresponded to the results reported by Armnt rong [2,5] and Crill [12]. Our e;,periments demonstrate that the splanchnic fibers projecting on the inferior olive are most A ' I 5 or B fiber:;. There are few C or A/J fibers which induce an olivary response to electrical stimulat, ion. This generalizalion holds for the diff,,rent types of identified mechalmreceptors: most of them were movement-sensing peritoneal mechanoreceptors connected with A 7 5 or B fibers). This is ill agreement with our previous ro~ults concerning the cerebellar projections [27]. It is the first report whicl~ shows that the activity of olivary neurons can be modified not only by visceral nerve stimulations but also by different mechanical stirnulati(ms oi" splanchnic receptors.
21 The p r e ~ n t work present~ evidence for many convergences on the otiv~y neurons. We have demonstrated that, besides somatic and cerebral impulses, visceral impulses (splanchnic and vagus) could also activate one single olivary neuron. The splanchno-somatic, splanchno-visceral and splanchno-cortical interactions observed at the cerebellar level were also obs,~rved at the olivary level. The great number of viscero-somatic convergences in the cerebellum as well as in the inferior olive could be due to the fact that in these two structures the visceral projection zones partially everlap the limb projection zones [24]. The inferior olive may be considered to be a structure integrating not only information coming from the. superior centers, from somesthetic sources, but also from visceral organs. Our experiments sh,.;,.,, thai splanchnic afferents, like somesthetic afferents feed into the spino-olivary pathway and project, on the cerebellar cortex through climbing fibers via il,fcrior olive. ACKNOWLEDGEMENTS
The authors thank Doctor N. Mei, sous-directeur de I'lnstitut de Neurophysiologm et de Psychophysiologie for his helpful advice in the course of the work, Andr4 Boyer for technical assistance, and Franqoise Farnarier for correcting the English. REFERENCES
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