Cholecystokinin-containing and nociceptive neurons in rat Edinger-Westphal nucleus.
The putative peptide neurotransmitter cholecystokinin (CCK) is co-localized with substance P (SP) in a dense cluster of neurons located in the rat Edinger-Westphal (EW) nucleus. In an attempt to record electrophysiologically from these CCK-containing neurons, we have identified a group of nociceptive neurons located within the confines of the EW nucleus. The firing pattern of these nociceptive neurons is erratic, sometimes with a bursting pattern and at other times with fairly regular rates which vary generally from 1 to 7 Hz. These neurons respond to noxious stimuli, such as toe pinch, with an increase in rate and sometimes enter an apparent depolarization blockade (preceded by an increase in the duration and a decrease in the amplitude of the action potential). Systemically administered morphine suppresses both the spontaneous firing rate and the toe pinch-induced increase in firing rate. Naloxone is able to reverse the effects of morphine. Although we have identified in the EW area a moderate density of terminals containing enkephalin-like immunoreactivity, morphine locally applied via microiontophoresis is largely without effect on the firing of these neurons. We hypothesize that the opiate-induced suppression of these nociceptive neurons is not mediated directly on the EW cells, but rather indirectly through afferent systems.
D000818:Animals; D002697:Chloral Hydrate / Q000494:pharmacology; D002766:Cholecystokinin / Q000378:metabolism*; D008238:Lysergic Acid Diethylamide / Q000494:pharmacology; D008297:Male; D008854:Microscopy, Electron; D009020:Morphine / Q000494:pharmacology; D009619:Nociceptors / Q000502:physiology*; D010146:Pain / Q000503:physiopathology*; D051381:Rats; D013477:Superior Colliculi / Q000166:cytology / Q000187:drug effects / Q000502:physiology*
D002697:Chloral Hydrate; D009020:Morphine; D008238:Lysergic Acid Diethylamide; D002766:Cholecystokinin