380
Brain Research, t 56 1t 978) 380-~38~ :(:~ Elsevier/North-Holland Biomedical Press
Function of nigral dopamine receptors?
S T A N L E Y D. G L I C K and L I N D A A. C R A N E
Department of Pharmacology, Mount Sinai School of Medic#ie, City University oJ New York, New York, N.Y. 10029 rU.S.A.) ) (Accepted June 29th. 1978)
Recent electrophysiological and biochemical studies have indicated that receptors within the substantia nigra have a role in regulating the activity of ascending dopaminergic neurons. Intranigral injections of D-amphetamine 4. which releases dopamine, and of apomorphine 1, which directly activates dopamine receptors, have been reported to depress the firing of neurons in the pars compacta of the substantia nigra. It has been proposed that nigral dopamine receptors function as autoreceptors on the cell bodies of ascending dopaminergic neurons 1,4. A dopamine-stimulated adenylate cyclase has been identified in the substantia nigraS,9; however, the latter does not appear to be located on dopamine-containing neurons 2,11. It has been suggested that intranigral dopamine, released from dendritic processes of ascending dopaminergic neurons, may interact with dopamine receptors on descending strionigral neurons and enhance the release of GABA l°,H. GABA would then depress neuronal firing. Dopamine receptors would still be envisioned as modulating dopaminergic activity, albeit indirectly via GABA. The present investigation was begun in an attempt to find functional evidence of such modulation. It is now well established that a dopaminergic asymmetry between left and right nigrostriatal pathways is responsible for circling behavior or rotation in rodents (e.g. ref. 3). An endogenous asymmetry in striatal dopamine metabolism is associated with spontaneous and drug-induced rotation in normal rats. More intense rotation can be elicited in animals with unilateral nigrostriatal damage or by directly administering particular drugs into one substantia nigra. Using the latter approach, evidence has been obtained that GABA (e.g. ref. 6) and substance p8 interact with ascendingdopaminergic neurons in the substantia nigra. Surprisingly, there has been little information as to what behavioral consequences might result from intranigral injections of dopaminergic agents. Accordingly, in the present study, D-amphetamine, apomorphine, haloperidol (a dopamine receptor blocking agent) as well as dopamine itself were each directly administered unilaterally into the substantia nigra in rats. Quite unexpectedly, virtually no behavioral effects were observed. Female Sprague-Dawley rats. approximately 90 days old. were implanted bilaterally with intracerebrat cannulae in the substantia nigra. The guide and injection cannulae were made of 26- and 32-gauge stainless steel tubing respectively. Rats were
381 allowed 4-5 days to recover from surgery; s t a n d a r d microinjection p r o c e d u r e s were use&. As an aid to d e t e r m i n i n g injection sites, I n d i a I n k dye was a d m i n i s t e r e d t h r o u g h each c a n n u l a p r i o r to sacrifice; brains were sectioned at 40 nm a n d stained with Luxol blue and cresyl violet for histological analysis. All p l a c e m e n t s were verified. All drugs were dissolved in physiological saline a n d a d m i n i s t e r e d unilaterally in a volume o f 0.5-1.0 #1 over 30-60 sec using a Sage infusion p u m p ( m o d e l 341); the injection cannula was r e m o v e d 30 sec after s t o p p i n g the infusion. The following drugs and d r u g doses were tested : D-amphetamine sulphate 1/~g (n = 3), 10 # g (n = 4), 20 # g (n - - 2); a p o m o r p h i n e h y d r o c h l o r i d e - - 10 ktg (n = 4), 20/~g (n = 2); haloperidol - - 0.5/~g (n = 1), 1/~g (n - - 3), 2 # g (n - - 2); d o p a m i n e h y d r o c h l o r i d e - - 10 # g (n - - 2), 20 # g (n - - 2), 50/~g (n - - 2). Rats were observed in a cylindrical enclosure (30 cm in diameter) for 1 h after drug a d m i n i s t r a t i o n . N o r o t a t o r y or other a b n o r m a l behaviors differentiable from controls (saline-injected or uninjected, n = 10) were n o t e d in any case. Bilateral a d m i n i s t r a t i o n of D - a m p h e t a m i n e (10 #g, n = 3) and h a l o p e r i d o l (1 /~g, n - - 3) were also tested. Again, no effects (e.g. s t e r e o t y p y or catalepsy might be expected) were observed. Negative results must always be interpreted with caution, since t r e a t m e n t conditions (e.g. d r u g dosages) may n o t have been optimal. However, as these experiments were nearing completion, Kelly a n d M o o r e 6 reported, similarly, that a p o m o r p h i n e (10 /~g) and D - a m p h e t a m i n e (10/~g) p r o d u c e d no circling effects after intranigral administration. The functional significance of nigral d o p a m i n e receptors is, therefore, still to be elucidated. S . D . G . is s u p p o r t e d by N I D A Research Scientist D e v e l o p m e n t A w a r d D A 70082. 1 Aghajanian, G. K. and Bunney, B. S., Central dopaminergic neurons: neurophysiological identification and resposes to drugs. In E. Usdin and S. H. Snyder (Eds.), Frontiers in Catecholamine Research, Pergamon Press, Oxford, 1973, pp. 643 648. 2 Gale, K., Guidotti, A. and Costa, E., Dopamine-sensitive adenylate cyclase : location in substantia nigra, Science, 195 (1977) 503 505. 3 Glick, S. D., Jerussi, T. P. and Fleisher, L. N., Turning in circles: the neuropharmacology of rotation, LU'e Sci., 18 (1976) 889-896. 4 Groves, P. M., Wilson, C. J., Young, S. J. and Rebec, G. V., Self-inhibition by dopaminergic neurons, Science, 190 (1975) 522-529. 5 Kebabian, J. W. and Saavedra, J. M., Dopamine-sensitive adenylate cyclase occurs in a region of substantia nigra containing dopaminergic dendrites, Science, 193 (1976) 683-685. 6 Kelly, P. H. and Moore, K. E., Dopamine concentrations in the rat brain following injections into the substantia nigra of baclofen, 7-aminobutyric acid, 7-hydroxybutyric acid, apomorphine and amphetamine, Neuropharmacology, 17 (1978) 169-174. 7 Myers, R. D., Methods for chemical stimulation of the brain. In R. D. Myers (Ed.), Methods in Psychobiology, Vol. 1, Academic Press, New York, 1972, pp. 247 280. 8 0 l p e , H.-R. and Koella, W. P., Rotatory behavior in rats by intranigral application of substance P and an eledoisin fragment, Brain Research, 126 (1977) 576-579. 9 Phillipson, O. T. and Horn, A. S., Substantia nigra of the rat contains a dopamine sensitive adenylate cyclase, Nature (Lond.), 261 (1976) 418 420. 10 Reubi, J.-C., Iversen, L. L. and Jesssell, T. M., Dopamine selectively increases [3H]GABA release from slices of rat substantia nigra in vivo, Nature (Lond.), 268 (1977) 652-654. 11 Spano, P. F., Trabucchi, M. and Di Chiara, G., Localization of nigra dopamine-sensitiveadenylate cyclase on neurons originating from the corpus striatum, Scielice, 196 (1977) 1343 1345.
Brain Research, t 56 1t 978) 380-~38~ :(:~ Elsevier/North-Holland Biomedical Press
Function of nigral dopamine receptors?
S T A N L E Y D. G L I C K and L I N D A A. C R A N E
Department of Pharmacology, Mount Sinai School of Medic#ie, City University oJ New York, New York, N.Y. 10029 rU.S.A.) ) (Accepted June 29th. 1978)
Recent electrophysiological and biochemical studies have indicated that receptors within the substantia nigra have a role in regulating the activity of ascending dopaminergic neurons. Intranigral injections of D-amphetamine 4. which releases dopamine, and of apomorphine 1, which directly activates dopamine receptors, have been reported to depress the firing of neurons in the pars compacta of the substantia nigra. It has been proposed that nigral dopamine receptors function as autoreceptors on the cell bodies of ascending dopaminergic neurons 1,4. A dopamine-stimulated adenylate cyclase has been identified in the substantia nigraS,9; however, the latter does not appear to be located on dopamine-containing neurons 2,11. It has been suggested that intranigral dopamine, released from dendritic processes of ascending dopaminergic neurons, may interact with dopamine receptors on descending strionigral neurons and enhance the release of GABA l°,H. GABA would then depress neuronal firing. Dopamine receptors would still be envisioned as modulating dopaminergic activity, albeit indirectly via GABA. The present investigation was begun in an attempt to find functional evidence of such modulation. It is now well established that a dopaminergic asymmetry between left and right nigrostriatal pathways is responsible for circling behavior or rotation in rodents (e.g. ref. 3). An endogenous asymmetry in striatal dopamine metabolism is associated with spontaneous and drug-induced rotation in normal rats. More intense rotation can be elicited in animals with unilateral nigrostriatal damage or by directly administering particular drugs into one substantia nigra. Using the latter approach, evidence has been obtained that GABA (e.g. ref. 6) and substance p8 interact with ascendingdopaminergic neurons in the substantia nigra. Surprisingly, there has been little information as to what behavioral consequences might result from intranigral injections of dopaminergic agents. Accordingly, in the present study, D-amphetamine, apomorphine, haloperidol (a dopamine receptor blocking agent) as well as dopamine itself were each directly administered unilaterally into the substantia nigra in rats. Quite unexpectedly, virtually no behavioral effects were observed. Female Sprague-Dawley rats. approximately 90 days old. were implanted bilaterally with intracerebrat cannulae in the substantia nigra. The guide and injection cannulae were made of 26- and 32-gauge stainless steel tubing respectively. Rats were
381 allowed 4-5 days to recover from surgery; s t a n d a r d microinjection p r o c e d u r e s were use&. As an aid to d e t e r m i n i n g injection sites, I n d i a I n k dye was a d m i n i s t e r e d t h r o u g h each c a n n u l a p r i o r to sacrifice; brains were sectioned at 40 nm a n d stained with Luxol blue and cresyl violet for histological analysis. All p l a c e m e n t s were verified. All drugs were dissolved in physiological saline a n d a d m i n i s t e r e d unilaterally in a volume o f 0.5-1.0 #1 over 30-60 sec using a Sage infusion p u m p ( m o d e l 341); the injection cannula was r e m o v e d 30 sec after s t o p p i n g the infusion. The following drugs and d r u g doses were tested : D-amphetamine sulphate 1/~g (n = 3), 10 # g (n = 4), 20 # g (n - - 2); a p o m o r p h i n e h y d r o c h l o r i d e - - 10 ktg (n = 4), 20/~g (n = 2); haloperidol - - 0.5/~g (n = 1), 1/~g (n - - 3), 2 # g (n - - 2); d o p a m i n e h y d r o c h l o r i d e - - 10 # g (n - - 2), 20 # g (n - - 2), 50/~g (n - - 2). Rats were observed in a cylindrical enclosure (30 cm in diameter) for 1 h after drug a d m i n i s t r a t i o n . N o r o t a t o r y or other a b n o r m a l behaviors differentiable from controls (saline-injected or uninjected, n = 10) were n o t e d in any case. Bilateral a d m i n i s t r a t i o n of D - a m p h e t a m i n e (10 #g, n = 3) and h a l o p e r i d o l (1 /~g, n - - 3) were also tested. Again, no effects (e.g. s t e r e o t y p y or catalepsy might be expected) were observed. Negative results must always be interpreted with caution, since t r e a t m e n t conditions (e.g. d r u g dosages) may n o t have been optimal. However, as these experiments were nearing completion, Kelly a n d M o o r e 6 reported, similarly, that a p o m o r p h i n e (10 /~g) and D - a m p h e t a m i n e (10/~g) p r o d u c e d no circling effects after intranigral administration. The functional significance of nigral d o p a m i n e receptors is, therefore, still to be elucidated. S . D . G . is s u p p o r t e d by N I D A Research Scientist D e v e l o p m e n t A w a r d D A 70082. 1 Aghajanian, G. K. and Bunney, B. S., Central dopaminergic neurons: neurophysiological identification and resposes to drugs. In E. Usdin and S. H. Snyder (Eds.), Frontiers in Catecholamine Research, Pergamon Press, Oxford, 1973, pp. 643 648. 2 Gale, K., Guidotti, A. and Costa, E., Dopamine-sensitive adenylate cyclase : location in substantia nigra, Science, 195 (1977) 503 505. 3 Glick, S. D., Jerussi, T. P. and Fleisher, L. N., Turning in circles: the neuropharmacology of rotation, LU'e Sci., 18 (1976) 889-896. 4 Groves, P. M., Wilson, C. J., Young, S. J. and Rebec, G. V., Self-inhibition by dopaminergic neurons, Science, 190 (1975) 522-529. 5 Kebabian, J. W. and Saavedra, J. M., Dopamine-sensitive adenylate cyclase occurs in a region of substantia nigra containing dopaminergic dendrites, Science, 193 (1976) 683-685. 6 Kelly, P. H. and Moore, K. E., Dopamine concentrations in the rat brain following injections into the substantia nigra of baclofen, 7-aminobutyric acid, 7-hydroxybutyric acid, apomorphine and amphetamine, Neuropharmacology, 17 (1978) 169-174. 7 Myers, R. D., Methods for chemical stimulation of the brain. In R. D. Myers (Ed.), Methods in Psychobiology, Vol. 1, Academic Press, New York, 1972, pp. 247 280. 8 0 l p e , H.-R. and Koella, W. P., Rotatory behavior in rats by intranigral application of substance P and an eledoisin fragment, Brain Research, 126 (1977) 576-579. 9 Phillipson, O. T. and Horn, A. S., Substantia nigra of the rat contains a dopamine sensitive adenylate cyclase, Nature (Lond.), 261 (1976) 418 420. 10 Reubi, J.-C., Iversen, L. L. and Jesssell, T. M., Dopamine selectively increases [3H]GABA release from slices of rat substantia nigra in vivo, Nature (Lond.), 268 (1977) 652-654. 11 Spano, P. F., Trabucchi, M. and Di Chiara, G., Localization of nigra dopamine-sensitiveadenylate cyclase on neurons originating from the corpus striatum, Scielice, 196 (1977) 1343 1345.
