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Role of dorsal mesencephalic reticular formation and deep layers of superior colliculus in turning behaviour elicited from the striatum
Brain Research, 215 (1981) 337-341 © Elsevier/North-Holland Biomedical Press
337
Role of dorsal mesencephalic reticular formation and deep layers of superior colliculus in turning behaviour elicited from the striatum
M. MORELLI, A. IMPERATO, M. L. PORCEDDU and G. DI CHIARA* Institute of Pharmacology, University of Cagliari, Cagliari (Italy) (Accepted February 19th, 1981) Key words: reticular formation - - turning behaviour - - kainic acid - - superior colliculus Kainate or electrolytic lesions were placed unilaterally in the dorsal mesencephalic reticular formation (MRF) or in the deep layers of the superior colliculus (DLSC) on the same side of a unilateral lesion of the medial forebrain bundle with 6-OHDA. Before the lesions the rats turned contralaterally when challenged with 0.25 mg/kg of apomorphine. After lesions of the MRF most rats turned ipsilaterally in response to the same dose of apomorphine. After lesions of the DLSC apomorphine-induced contralateral turning was significantly reduced but not abolished. The results indicate that the MRF and DLSC play a primary role in the expression of turning originated from the striatum.
Turning behaviour (i.e. circling in a head to tail posture) can be elicited by peripheral administration o f apomorphine, a DA-receptor agonist, to rats bearing unilateral lesions o f nigrostriatal D A - n e u r o n e s made by local infusion o f 6-OHdopamine ( 6 - O H D A ) 18. The turning thus elicited is contralateral i.e. directed to the side opposite to the 6 - O H D A lesion and is currently regarded as due to prevalence o f striatal D A - r e c e p t o r stimulation on the lesioned side made supersensitive by the dopaminergic denervation 13. This condition can be considered as a rather pure behavioural model o f striatal dopaminergic activity and for this reason is currently a d o p t e d in studies on striatal function and on the neural pathways which mediate its behavioural expression. Using this model it was first shown that the strio-nigral tract 7 and the substantia nigra pars reticulata neurones 4 are out-put pathways for behavioural responses arising in the striatum. Since pars reticulata neurones project in turn to the ventro-medial thalamus, superior colliculus (SC) and mesencephalic reticular formation ( M R F ) 1,11, one might expect that lesions o f these areas would influence behavioural syndromes originating in the striatum. We have recently reported that unilateral kainate-induced lesions o f the dorsal M R F result in m o t o r asymmetries ipsilateral to the lesioned side u p o n peripheral apomorphine administration 8. These results indicate that this area plays an important role in the maintenance o f postural balance between the two sides o f the body. In order to * To whom correspondence should be addressed at the Institute of Pharmacology, University of Cagliari, Via Porcell, 4-09100 Cagliari. Italy.
338 study more specifically the role of the dorsal M R F as an out-put station for striatal functions we studied the effect of unilateral kainate-induced and electrolytic lesions of" the M R F and of the SC on the contralateral turning behaviour elicited by apomorphine in rats unilaterally lesioned with 6 - O H D A in the medial forebrain bundle (MFB). Male Charles River Sprague-Dawley rats (280-320 g)were anaesthetized with ether, placed in a K o p f stereotaxic apparatus and infused through stainless steel cannulas (0.36 m m external diameter) with 6 - O H D A (8 #g in 4 #1 of saline with 0.1 ascorbic acid) in the rostral tip of the substantia nigra, where nigrostriatal neurones course en route to the striatum (A 2.2, L 2.0, V 7.8 of Pellegrino and Cushman)L Seven days later, the rats were administered with apomorphine (0.25 mg/kg s.c.) and the turning behaviour was recorded and estimated by counting the number of turns performed in 3 min at 10 and 20 min after drug-administration. The test was repeated every 5 days until stable turning values were obtained. At this time, i.e. 15-20 days post-6-OHDA, the rats were randomly divided into 3 groups: one group was anaesthetized with Equithesin and infused in the dorsal M R F (coordinates A 5.0, V 5.5, L 1.7) of Pellegrino and Cushman 9 with 0.5/~g of kainate dissolved in 0.25 #1 of saline buffered to p H 7.2 with phosphate at a speed of 1/tl/3 min. After the end of infusion, cannulas were left in place for 2 min in order to reduce reflux. The second group was infused with kainate at the same dose and under the same conditions in the SC 1.5 m m dorsal to the M R F site. The third group was infused in the M R F with vehicle alone. At the end of surgery all rats were administered with 10 mg/kg i.p. of diazepam (Valium, Roche) in order to prevent convulsions and the related distant brain damageL In an additional series of animals lesioned with 6 - O H D A and similarly selected double unilateral electrolytic lesions were performed by passing anodal current (0.5 m A for 20 sec) through stainless steel electrodes (0.23 m m diameter) insulated except at the tip. The rats were randomly divided into 3 groups: in one group current was passed at two sites in the M R F (A 4.6, L 1.7, V 6.0 and A 5.4, L 1.7, V 5.5)9; in another group the current was passed at two sites in the deep layers of SC located 1.5 mm dorsally to those in the M R F ; in a third group the electrodes were inserted in the M R F but no current was passed. The spontaneous behaviour of rats was observed for four days in their home cages. At the 4th day the rats were placed in plexiglas cylinders, administered with 0.25 mg/kg of apomorphine and the direction and number of turns recorded (see above). This test was repeated every week for 3 weeks and then the animals were sacrificed by perfusion with formalin, the mesencephalon dissected and processed for histology and stained with Luxol Fast Blue--cresyl violet. Table I shows the turning behaviour elicited by apomorphine in control rats and in rats infused unilaterally with kainic acid or electrolesioned in the dorsal M R F or in the SC on the same side of a 6 - O H D A lesion. In the prelesion period all groups showed turning contralateral to 6 - O H D A lesions with mean intensities varying from 12 to 18 rpm. The control groups injected with vehicle or sham-electrolesioned in the dorsal M R F showed a consistent and tight turning contralateral to the 6-OHDA lesion. In contrast, most of the rats infused with kainate and all the rats electrolesioned in the M R F showed a consistent turning ipsilateral to the 6-OHDA lesion. These chan-
339 TABLE I Effect of unilateral kainate-induced and electrolytic lesions of the mesencephalic reticular formation (MRF) and of the superior colliculus (SC) on apomorphine-induced turning behaviour in the 6-OHDA model N = number of rats for each group; n = number of rats turning; D = direction of turning; C = contralateral turning; I = ipsilateral turning (in respect to lesions). Results are the means 4- S.E.M. of the turning intensity (rpm) obtained in each rat at 10 and 20 min after apomorphine. Area N Vehicle MRF SC Sham MRF SC
D
~m
Prekainate 15 C 1 4 ± 3 14 C 17 4- 4 16 C 16 4-3 Preelectrolesion 12 C 15 4-3 14 C 13 4- 3 14 C 1 8 ± 4
1st Week
2rid Week
3rd Week
n
n
n
D
~m
Postkainate 15 C 174-3 14 I 8.54- 1.8 14 C 6.0dzl.5" Postelectrolesion 12 C 14 4-3 14 I 8.54- 1.6 14 C 6 . 6 ~ 1 . 3 "
D
~m
D
~m
15 C 12 I 16 C
13 + 3 15 C 7.54- 1.3 12 I 6.34- 1.4" 16 C
164-3 6.34- 1.5 8.0± 1.8"
12 C 14 I 14 C
164-3 12 C 6.54- 1.5 14 I 8.54- 1.7" 14 C
17 4-3 7.04- 1.5 7.34- 1.6"
* P < 0.05 (Student's t-test) in respect to vehicle or sham-operated group and to prelesion values. ges w e r e a l r e a d y p r e s e n t o n e w e e k a f t e r M R F - l e s i o n s a n d w e r e m a i n t a i n e d t h r o u g h the 3 w e e k s o f t h e o b s e r v a t i o n p e r i o d . T h e ipsilateral t u r n i n g was n o t as t i g h t as t h a t o f t h e c o n t r o l g r o u p b u t still it w a s a s s o c i a t e d to b e n d i n g o f t h e h e a d t o w a r d s t h e tail. T h e rats l e s i o n e d in t h e S C still t u r n e d c o n t r a l a t e r a l l y t o t h e 6 - O H D A lesion, b u t t h e i r t u r n i n g i n t e n s i t y was significantly l o w e r t h a n t h a t o f t h e c o n t r o l g r o u p a n d o f t h e i r p r e - l e s i o n values.
s
[ ======================== ..:... /r,~........:.:.r.:.. (c,F) ',',
\
" e v ^' "":::::::"e.'.~ ~'::':"'.~ .::.""~ ,..H.v.v.'.v.v
=======================
Fig. 1. Location and extent of representative kainate-induced (top-figure) and electrolytic (lower figure) lesions in the mesencephalic reticular formation and in the superior colliculus. Top left: distance in mm caudally to bregma. Abbreviations: BC, decussatio brachii congiuntivi; CIF, inferior colliculus; CT, central tegmental nucleus; LM, lemniscus medialis; PVG: periaqueductal grey; RF, reticular formation; TCS, cortico-spinal tract.
340 Histological examination of the mesencephalon of rats infused with kainate in the dorsal M R F showed loss of neurons and gliosis in an area about 2.0-2.5 m m wide in its largest dimension. Within this area, myelinated tracts of passage appeared normal. As shown in Fig. 1, the lesioned area was centred in the dorsal M R F but invariably involved also the deepest grey layer (striatum griseum profundum) of the SC. The lateralmost aspect of the periaqueductal grey (lateral nucleus of Hamilton) was also lesioned in some cases. Cranially, the lesions did not reach the posterior nuclei of the thalamus and the pretectal nuclei and ventrally did not extend further than a depth of 6.5 mm from the dura. The substantia nigra was always totally spared. As shown in Fig. l, infusion of kainic acid 1.5 mm from this site, i.e. in the SC, resulted in damage to most collicular layers and often impinged upon the M R F ; the dorsolateral aspect of the periaqueductal grey was often lesioned. The electrolytic lesions involved the entire cranio-caudal extent of the dorsal M R F or the SC. In transverse sections the lesions appeared remarkably discrete, as those aimed at the dorsal M RF lesioned this area but spared the periaqueductal grey and lesioned the deepest layer of the SC to a variable extent. The electrolytic lesions of the SC variably involved the stratum griseum superficiale but consistently lesioned the stratum opticum and the deeper layers of the SC. The exact degree of involvement of the M R F is difficult to be evaluated in view of the difficulty to define the boundary between the stratum griseum profundum and the dorsal MRF, however it was estimated to be only marginal. Our results show that kainate-induced and electrolytic lesions of the dorsal M R F on the same side o f a 6 - O H D A lesion in the MFB is capable to reduce drastically or even reverse the contralateral turning elicited by apomorphine. The effects produced by the lesions on turning behaviour cannot be explained as dependent on a general effect on motility because the rats did appear, since the first week postlesion, in good physical conditions, had normal exploratory behaviour when placed in the open field and failed to show signs of akinesia in their spontaneous behaviour. Indeed the reduction of circling intensity (revolutions × min) is not due to reduction of motility but rather to the fact that the circles described by the rats are much larger and therefore more time is necessary to complete them than in the prelesion period or in the sham-operated groups. In fact none of these lesions appear to interfere with the motility component of turning behaviour but rather with the postural one. To our knowledge such a drastic influence on turning behaviour has been reported only for electrolytic lesions of the out-put pathway from the striatum to the substantia nigra pars reticulata 7 or for kainate lesions of the pars reticulata itself 4. In view of this and of the fact that apomorphine-induced contralateral turning behaviour in the 6-OHDA rat is a pure expression of postsynaptic striatal activity secondary to stimulation of DA-receptors, our data strongly indicate that the dorsal M R F plays a crucial role in the behavioural expression of striatal function. The lesions which abolish contralateral turning are not restricted exclusively to the dorsal M R F since they impinge also upon the deep layers of the SC. However, lesions centred in the deep layers of the SC, which involve only marginally the dorsal M R F , are less effective than lesions of M R F in reducing turning behaviour. Therefore, although the deep layers of the SC seem to have a critical function in the expression of
341 t u r n i n g behaviour, their role a p p e a r s to be s e c o n d a r y in respect to t h a t o f the d o r s a l MRF. Indeed, in view o f the strict c o n t i g u i t y (indeed c o n t i n u i t y ) between these two areas a n d o f their a n a t o m o - f u n c t i o n a l similarity (which has led E d w a r d s 5 to consider the deep collicular layers as the d o r s a l m o s t extension o f the M R F ) , we p r o p o s e to consider t h e m as a u n i t a r y c o m p l e x o f p r i m a r y i m p o r t a n c e in p o s t u r e a n d in the b e h a v i o u r a l expression o f striatal functions. I n particular, these areas m i g h t receive, t h r o u g h b r a n c h e d n i g r o - r e t i c u l a r a n d nigro-collicular p r o j e c t i o n s 11, the i n f o r m a t i o n arisen in the s t r i a t u m a n d convey it to the spinal cord12, ~4. This conclusion is at variance with t h a t o f o t h e r w o r k e r s who excluded a role of the s u p e r i o r colliculus in t u r n i n g behaviour3,10. This difference p r o b a b l y derives at least in p a r t f r o m the t o p o g r a p h y o f their collicular lesions, which a p p e a r to be m o r e m e d i a l a n d superficial a n d m o r e restricted in their c r a n i o - c a u d a l extent t h a n ours a n d p r o b a b l y failed to d e s t r o y to a sufficient degree the deep collicular layers.
1 Beckstead, R. M., Domesick, V. B. and Nauta, W. J. H., Efferent connections of the substantia nigra and ventral tegmental area in the rat, Brain Research, 175 (1979) 191-217. 2 Ben-Ari, Y., Tremblay, E., Ottersen, O. P. and Naquet, R., Evidence suggesting secondary epileptogenic lesions after kainic acid: pretreatment with diazepam reduces distant but not local brain damage, Brain Research, 165 (1979) 362-365. 3 Crossman, A. R. and Sambrook, M. A., The neurological basis of motor asymmetry following unilateral nigrostriatal lesions in the rat: the effect of secondary superior colliculus lesions, Brain Research, 159 (1979) 211-213. 4 Di Chiara, G., Porceddu, M. L., Morelli, M., Mulas, M. L. and Gessa, G. L., Substantia nigra as an output station for striatal dopaminergic responses: role of a GABA-mediated inhibition of pars reticulata neurons, Naunyn-Schmiedeberg's Arch. Pharmacol., 306 (1979) 153-159. 5 Edwards, S. B., The deep cell layers of the superior colliculus: their reticular characteristics and structural organization. In J. A. Hobson and M. A. Brazier (Eds.), The Reticular Formation Revisited, Raven Press, New York, 1980. 6 Deniau, J. M., Grovofa, I., Steindler, D. and Kitai, S. T., Axonal arborizations of nigrothalamic and nigrotectal cells: anatomical and electrophysiological studies, Neurosci. Abstr., (1980) Abstract 273.5. 7 Marshall, J. F. and Ungerstedt, U., Striatal efferent fibers play a role of maintaining rotational behaviour in the rat, Science, 198 (1977) 62-64. 8 Mulas, A., Longoni, R., Spina, L., Del Fiacco, M. and Di Chiara, G., lpsiversive turning behaviour after discrete unilateral lesions of the dorsal mesencephalic reticular formation by kainic acid, Brain Research, 208 (1981) 468-472. 9 Pellegrino, L. J. and Cushman, A. J., A Stereotaxic Atlas of the Rat Brain, Meredith, New York, 1971. 10 Reavill, C., Leigh, N., Jenner, P. and Marsden, C. D., Dopamine-mediated circling behaviour does not involve the nigro-tectal pathway, Exp. Brain Res. 37 (1979) 309-316. 11 Rinvik, E., Grovof/t, 1. and Ottersen, O. P., Demonstration of nigrotectal and nigro-reticular projections in the cat by axonal transport of proteins, Brain Research, 112 (1976) 388-394. 12 Tohyama, M., Sakai, K., Salvert, D., Touret, M. and Jouvet, M., Spinal projections from the lower brain stem in the cat as demonstrated by the horseradish peroxidase technique. I. Origins of the reticulospinal tracts and their funicular trajectories, Brain Research, 173 (1979) 383-403. 13 Ungerstedt, U., Postsynaptic supersensitivity after 6-hydroxydopamine induced degeneration of the nigro-striatal dopamine system, Acta physiol, scand., Suppl. 367 (1971) 69-93. 14 Waldron, H. A. and Gwyn, D. G., Descending nerve tracts in the spinal cord of the rat. I. Fibers from the midbrain, J. comp. Neurol., 137 (1969) 143-154.
337
Role of dorsal mesencephalic reticular formation and deep layers of superior colliculus in turning behaviour elicited from the striatum
M. MORELLI, A. IMPERATO, M. L. PORCEDDU and G. DI CHIARA* Institute of Pharmacology, University of Cagliari, Cagliari (Italy) (Accepted February 19th, 1981) Key words: reticular formation - - turning behaviour - - kainic acid - - superior colliculus Kainate or electrolytic lesions were placed unilaterally in the dorsal mesencephalic reticular formation (MRF) or in the deep layers of the superior colliculus (DLSC) on the same side of a unilateral lesion of the medial forebrain bundle with 6-OHDA. Before the lesions the rats turned contralaterally when challenged with 0.25 mg/kg of apomorphine. After lesions of the MRF most rats turned ipsilaterally in response to the same dose of apomorphine. After lesions of the DLSC apomorphine-induced contralateral turning was significantly reduced but not abolished. The results indicate that the MRF and DLSC play a primary role in the expression of turning originated from the striatum.
Turning behaviour (i.e. circling in a head to tail posture) can be elicited by peripheral administration o f apomorphine, a DA-receptor agonist, to rats bearing unilateral lesions o f nigrostriatal D A - n e u r o n e s made by local infusion o f 6-OHdopamine ( 6 - O H D A ) 18. The turning thus elicited is contralateral i.e. directed to the side opposite to the 6 - O H D A lesion and is currently regarded as due to prevalence o f striatal D A - r e c e p t o r stimulation on the lesioned side made supersensitive by the dopaminergic denervation 13. This condition can be considered as a rather pure behavioural model o f striatal dopaminergic activity and for this reason is currently a d o p t e d in studies on striatal function and on the neural pathways which mediate its behavioural expression. Using this model it was first shown that the strio-nigral tract 7 and the substantia nigra pars reticulata neurones 4 are out-put pathways for behavioural responses arising in the striatum. Since pars reticulata neurones project in turn to the ventro-medial thalamus, superior colliculus (SC) and mesencephalic reticular formation ( M R F ) 1,11, one might expect that lesions o f these areas would influence behavioural syndromes originating in the striatum. We have recently reported that unilateral kainate-induced lesions o f the dorsal M R F result in m o t o r asymmetries ipsilateral to the lesioned side u p o n peripheral apomorphine administration 8. These results indicate that this area plays an important role in the maintenance o f postural balance between the two sides o f the body. In order to * To whom correspondence should be addressed at the Institute of Pharmacology, University of Cagliari, Via Porcell, 4-09100 Cagliari. Italy.
338 study more specifically the role of the dorsal M R F as an out-put station for striatal functions we studied the effect of unilateral kainate-induced and electrolytic lesions of" the M R F and of the SC on the contralateral turning behaviour elicited by apomorphine in rats unilaterally lesioned with 6 - O H D A in the medial forebrain bundle (MFB). Male Charles River Sprague-Dawley rats (280-320 g)were anaesthetized with ether, placed in a K o p f stereotaxic apparatus and infused through stainless steel cannulas (0.36 m m external diameter) with 6 - O H D A (8 #g in 4 #1 of saline with 0.1 ascorbic acid) in the rostral tip of the substantia nigra, where nigrostriatal neurones course en route to the striatum (A 2.2, L 2.0, V 7.8 of Pellegrino and Cushman)L Seven days later, the rats were administered with apomorphine (0.25 mg/kg s.c.) and the turning behaviour was recorded and estimated by counting the number of turns performed in 3 min at 10 and 20 min after drug-administration. The test was repeated every 5 days until stable turning values were obtained. At this time, i.e. 15-20 days post-6-OHDA, the rats were randomly divided into 3 groups: one group was anaesthetized with Equithesin and infused in the dorsal M R F (coordinates A 5.0, V 5.5, L 1.7) of Pellegrino and Cushman 9 with 0.5/~g of kainate dissolved in 0.25 #1 of saline buffered to p H 7.2 with phosphate at a speed of 1/tl/3 min. After the end of infusion, cannulas were left in place for 2 min in order to reduce reflux. The second group was infused with kainate at the same dose and under the same conditions in the SC 1.5 m m dorsal to the M R F site. The third group was infused in the M R F with vehicle alone. At the end of surgery all rats were administered with 10 mg/kg i.p. of diazepam (Valium, Roche) in order to prevent convulsions and the related distant brain damageL In an additional series of animals lesioned with 6 - O H D A and similarly selected double unilateral electrolytic lesions were performed by passing anodal current (0.5 m A for 20 sec) through stainless steel electrodes (0.23 m m diameter) insulated except at the tip. The rats were randomly divided into 3 groups: in one group current was passed at two sites in the M R F (A 4.6, L 1.7, V 6.0 and A 5.4, L 1.7, V 5.5)9; in another group the current was passed at two sites in the deep layers of SC located 1.5 mm dorsally to those in the M R F ; in a third group the electrodes were inserted in the M R F but no current was passed. The spontaneous behaviour of rats was observed for four days in their home cages. At the 4th day the rats were placed in plexiglas cylinders, administered with 0.25 mg/kg of apomorphine and the direction and number of turns recorded (see above). This test was repeated every week for 3 weeks and then the animals were sacrificed by perfusion with formalin, the mesencephalon dissected and processed for histology and stained with Luxol Fast Blue--cresyl violet. Table I shows the turning behaviour elicited by apomorphine in control rats and in rats infused unilaterally with kainic acid or electrolesioned in the dorsal M R F or in the SC on the same side of a 6 - O H D A lesion. In the prelesion period all groups showed turning contralateral to 6 - O H D A lesions with mean intensities varying from 12 to 18 rpm. The control groups injected with vehicle or sham-electrolesioned in the dorsal M R F showed a consistent and tight turning contralateral to the 6-OHDA lesion. In contrast, most of the rats infused with kainate and all the rats electrolesioned in the M R F showed a consistent turning ipsilateral to the 6-OHDA lesion. These chan-
339 TABLE I Effect of unilateral kainate-induced and electrolytic lesions of the mesencephalic reticular formation (MRF) and of the superior colliculus (SC) on apomorphine-induced turning behaviour in the 6-OHDA model N = number of rats for each group; n = number of rats turning; D = direction of turning; C = contralateral turning; I = ipsilateral turning (in respect to lesions). Results are the means 4- S.E.M. of the turning intensity (rpm) obtained in each rat at 10 and 20 min after apomorphine. Area N Vehicle MRF SC Sham MRF SC
D
~m
Prekainate 15 C 1 4 ± 3 14 C 17 4- 4 16 C 16 4-3 Preelectrolesion 12 C 15 4-3 14 C 13 4- 3 14 C 1 8 ± 4
1st Week
2rid Week
3rd Week
n
n
n
D
~m
Postkainate 15 C 174-3 14 I 8.54- 1.8 14 C 6.0dzl.5" Postelectrolesion 12 C 14 4-3 14 I 8.54- 1.6 14 C 6 . 6 ~ 1 . 3 "
D
~m
D
~m
15 C 12 I 16 C
13 + 3 15 C 7.54- 1.3 12 I 6.34- 1.4" 16 C
164-3 6.34- 1.5 8.0± 1.8"
12 C 14 I 14 C
164-3 12 C 6.54- 1.5 14 I 8.54- 1.7" 14 C
17 4-3 7.04- 1.5 7.34- 1.6"
* P < 0.05 (Student's t-test) in respect to vehicle or sham-operated group and to prelesion values. ges w e r e a l r e a d y p r e s e n t o n e w e e k a f t e r M R F - l e s i o n s a n d w e r e m a i n t a i n e d t h r o u g h the 3 w e e k s o f t h e o b s e r v a t i o n p e r i o d . T h e ipsilateral t u r n i n g was n o t as t i g h t as t h a t o f t h e c o n t r o l g r o u p b u t still it w a s a s s o c i a t e d to b e n d i n g o f t h e h e a d t o w a r d s t h e tail. T h e rats l e s i o n e d in t h e S C still t u r n e d c o n t r a l a t e r a l l y t o t h e 6 - O H D A lesion, b u t t h e i r t u r n i n g i n t e n s i t y was significantly l o w e r t h a n t h a t o f t h e c o n t r o l g r o u p a n d o f t h e i r p r e - l e s i o n values.
s
[ ======================== ..:... /r,~........:.:.r.:.. (c,F) ',',
\
" e v ^' "":::::::"e.'.~ ~'::':"'.~ .::.""~ ,..H.v.v.'.v.v
=======================
Fig. 1. Location and extent of representative kainate-induced (top-figure) and electrolytic (lower figure) lesions in the mesencephalic reticular formation and in the superior colliculus. Top left: distance in mm caudally to bregma. Abbreviations: BC, decussatio brachii congiuntivi; CIF, inferior colliculus; CT, central tegmental nucleus; LM, lemniscus medialis; PVG: periaqueductal grey; RF, reticular formation; TCS, cortico-spinal tract.
340 Histological examination of the mesencephalon of rats infused with kainate in the dorsal M R F showed loss of neurons and gliosis in an area about 2.0-2.5 m m wide in its largest dimension. Within this area, myelinated tracts of passage appeared normal. As shown in Fig. 1, the lesioned area was centred in the dorsal M R F but invariably involved also the deepest grey layer (striatum griseum profundum) of the SC. The lateralmost aspect of the periaqueductal grey (lateral nucleus of Hamilton) was also lesioned in some cases. Cranially, the lesions did not reach the posterior nuclei of the thalamus and the pretectal nuclei and ventrally did not extend further than a depth of 6.5 mm from the dura. The substantia nigra was always totally spared. As shown in Fig. l, infusion of kainic acid 1.5 mm from this site, i.e. in the SC, resulted in damage to most collicular layers and often impinged upon the M R F ; the dorsolateral aspect of the periaqueductal grey was often lesioned. The electrolytic lesions involved the entire cranio-caudal extent of the dorsal M R F or the SC. In transverse sections the lesions appeared remarkably discrete, as those aimed at the dorsal M RF lesioned this area but spared the periaqueductal grey and lesioned the deepest layer of the SC to a variable extent. The electrolytic lesions of the SC variably involved the stratum griseum superficiale but consistently lesioned the stratum opticum and the deeper layers of the SC. The exact degree of involvement of the M R F is difficult to be evaluated in view of the difficulty to define the boundary between the stratum griseum profundum and the dorsal MRF, however it was estimated to be only marginal. Our results show that kainate-induced and electrolytic lesions of the dorsal M R F on the same side o f a 6 - O H D A lesion in the MFB is capable to reduce drastically or even reverse the contralateral turning elicited by apomorphine. The effects produced by the lesions on turning behaviour cannot be explained as dependent on a general effect on motility because the rats did appear, since the first week postlesion, in good physical conditions, had normal exploratory behaviour when placed in the open field and failed to show signs of akinesia in their spontaneous behaviour. Indeed the reduction of circling intensity (revolutions × min) is not due to reduction of motility but rather to the fact that the circles described by the rats are much larger and therefore more time is necessary to complete them than in the prelesion period or in the sham-operated groups. In fact none of these lesions appear to interfere with the motility component of turning behaviour but rather with the postural one. To our knowledge such a drastic influence on turning behaviour has been reported only for electrolytic lesions of the out-put pathway from the striatum to the substantia nigra pars reticulata 7 or for kainate lesions of the pars reticulata itself 4. In view of this and of the fact that apomorphine-induced contralateral turning behaviour in the 6-OHDA rat is a pure expression of postsynaptic striatal activity secondary to stimulation of DA-receptors, our data strongly indicate that the dorsal M R F plays a crucial role in the behavioural expression of striatal function. The lesions which abolish contralateral turning are not restricted exclusively to the dorsal M R F since they impinge also upon the deep layers of the SC. However, lesions centred in the deep layers of the SC, which involve only marginally the dorsal M R F , are less effective than lesions of M R F in reducing turning behaviour. Therefore, although the deep layers of the SC seem to have a critical function in the expression of
341 t u r n i n g behaviour, their role a p p e a r s to be s e c o n d a r y in respect to t h a t o f the d o r s a l MRF. Indeed, in view o f the strict c o n t i g u i t y (indeed c o n t i n u i t y ) between these two areas a n d o f their a n a t o m o - f u n c t i o n a l similarity (which has led E d w a r d s 5 to consider the deep collicular layers as the d o r s a l m o s t extension o f the M R F ) , we p r o p o s e to consider t h e m as a u n i t a r y c o m p l e x o f p r i m a r y i m p o r t a n c e in p o s t u r e a n d in the b e h a v i o u r a l expression o f striatal functions. I n particular, these areas m i g h t receive, t h r o u g h b r a n c h e d n i g r o - r e t i c u l a r a n d nigro-collicular p r o j e c t i o n s 11, the i n f o r m a t i o n arisen in the s t r i a t u m a n d convey it to the spinal cord12, ~4. This conclusion is at variance with t h a t o f o t h e r w o r k e r s who excluded a role of the s u p e r i o r colliculus in t u r n i n g behaviour3,10. This difference p r o b a b l y derives at least in p a r t f r o m the t o p o g r a p h y o f their collicular lesions, which a p p e a r to be m o r e m e d i a l a n d superficial a n d m o r e restricted in their c r a n i o - c a u d a l extent t h a n ours a n d p r o b a b l y failed to d e s t r o y to a sufficient degree the deep collicular layers.
1 Beckstead, R. M., Domesick, V. B. and Nauta, W. J. H., Efferent connections of the substantia nigra and ventral tegmental area in the rat, Brain Research, 175 (1979) 191-217. 2 Ben-Ari, Y., Tremblay, E., Ottersen, O. P. and Naquet, R., Evidence suggesting secondary epileptogenic lesions after kainic acid: pretreatment with diazepam reduces distant but not local brain damage, Brain Research, 165 (1979) 362-365. 3 Crossman, A. R. and Sambrook, M. A., The neurological basis of motor asymmetry following unilateral nigrostriatal lesions in the rat: the effect of secondary superior colliculus lesions, Brain Research, 159 (1979) 211-213. 4 Di Chiara, G., Porceddu, M. L., Morelli, M., Mulas, M. L. and Gessa, G. L., Substantia nigra as an output station for striatal dopaminergic responses: role of a GABA-mediated inhibition of pars reticulata neurons, Naunyn-Schmiedeberg's Arch. Pharmacol., 306 (1979) 153-159. 5 Edwards, S. B., The deep cell layers of the superior colliculus: their reticular characteristics and structural organization. In J. A. Hobson and M. A. Brazier (Eds.), The Reticular Formation Revisited, Raven Press, New York, 1980. 6 Deniau, J. M., Grovofa, I., Steindler, D. and Kitai, S. T., Axonal arborizations of nigrothalamic and nigrotectal cells: anatomical and electrophysiological studies, Neurosci. Abstr., (1980) Abstract 273.5. 7 Marshall, J. F. and Ungerstedt, U., Striatal efferent fibers play a role of maintaining rotational behaviour in the rat, Science, 198 (1977) 62-64. 8 Mulas, A., Longoni, R., Spina, L., Del Fiacco, M. and Di Chiara, G., lpsiversive turning behaviour after discrete unilateral lesions of the dorsal mesencephalic reticular formation by kainic acid, Brain Research, 208 (1981) 468-472. 9 Pellegrino, L. J. and Cushman, A. J., A Stereotaxic Atlas of the Rat Brain, Meredith, New York, 1971. 10 Reavill, C., Leigh, N., Jenner, P. and Marsden, C. D., Dopamine-mediated circling behaviour does not involve the nigro-tectal pathway, Exp. Brain Res. 37 (1979) 309-316. 11 Rinvik, E., Grovof/t, 1. and Ottersen, O. P., Demonstration of nigrotectal and nigro-reticular projections in the cat by axonal transport of proteins, Brain Research, 112 (1976) 388-394. 12 Tohyama, M., Sakai, K., Salvert, D., Touret, M. and Jouvet, M., Spinal projections from the lower brain stem in the cat as demonstrated by the horseradish peroxidase technique. I. Origins of the reticulospinal tracts and their funicular trajectories, Brain Research, 173 (1979) 383-403. 13 Ungerstedt, U., Postsynaptic supersensitivity after 6-hydroxydopamine induced degeneration of the nigro-striatal dopamine system, Acta physiol, scand., Suppl. 367 (1971) 69-93. 14 Waldron, H. A. and Gwyn, D. G., Descending nerve tracts in the spinal cord of the rat. I. Fibers from the midbrain, J. comp. Neurol., 137 (1969) 143-154.