| Abstract: | ![]()
The putative peptide neurotransmitter cholecystokinin (CCK) is co-localized witsubstance 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 wita bursting pattern and at other times witfairly regular rates whicvary generally from 1 to 7 Hz. These neurons respond to noxious stimuli, sucas toe pinch, witan 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 botthe spontaneous firing rate and the toe pinch-induced increase in firing rate. Naloxone is able to reverse the effects of morphine. Althougwe 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 througafferent systems. |
