Electrophysiological effects of cholecystokinin octapeptide on identified rat nigrostriatal dopaminergic neurons.
Cholecystokinin octapeptide (CCK-8) exists in a subpopulation of midbrain dopaminergic (DA) neurons and has been shown to affect the activity of unidentified DA cells. This study describes the effects of the sulfated (CCK-8S) and unsulfated (CCK-8US) peptides (8 micrograms/kg, i.v.) on the ability of apomorphine to inhibit the firing rate of nigrostriatal DA cells identified by antidromic activation from the caudate nucleus of anesthetized rats. CCK-8S excited 9/25 DA cells while CCK-8US was without effect on firing rate (n = 9). CCK-8S pretreatment resulted in complex changes in the sensitivity of nigrostriatal DA cells to apomorphine which were related to whether an initial excitatory response was elicited by CCK-8S. CCK-8US did not alter apomorphine sensitivity. These results suggest that CCK-8S can exert modulatory effects on DA cells independent of a direct excitatory action. The effect of acute CCK-8 injection on the number of spontaneously active DA cells in stereotaxically defined regions of the substantia nigra and ventral tegmental area was also determined. CCK-8S doubled the number of active cells in these areas; CCK-8US did not alter the population activities.
Freeman
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AS
Center for Cell Biology, Sinai Research Institute, Detroit, MI 48235-2899.
Chiodo
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LA
D000818:Animals; D001058:Apomorphine / Q000494:pharmacology; D003342:Corpus Striatum / Q000187:drug effects / Q000502:physiology*; D004298:Dopamine / Q000502:physiology; D004558:Electric Stimulation; D008297:Male; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D012844:Sincalide / Q000494:pharmacology*; D013378:Substantia Nigra / Q000187:drug effects / Q000502:physiology*
D012844:Sincalide; D001058:Apomorphine; D004298:Dopamine