OPIOID EFFECTS ON HYPOTHALAMIC NEURONAL EXCITABILITY

Although it has been known for decades that opiates inhibit the
reproductive cycle of the mammal via direct actions on the
hypothalamus, little research has been done on the cellular
mechanism of their action. The present proposal will evaluate
firstly the physiological effects of the endogenous opioids on
hypothalamic neurons, and secondly, the effects of chronic
morphine on these same cells. Hypothalamic slices will be
prepared from cycling female guinea pigs, and single electrode
voltage clamp experiments will be done in order to elucidate the
acute and chronic effects of opioids on the membrane properties
of arcuate and cell-poor zone (ARC-CPZ) neurons. Dose response
curves will be generated based on the changes in membrane
current caused by specific opioid agonists. Schild analysis will be
utilized to characterize the specific receptor(s) involved in the
direct actions of the opioids, and the specific K+ and/or Ca+2
conductance(s) coupled to the receptor(s) will be ascertained.
LHRH release from hypothalamic slices will be measured and
Schild analysis of the inhibition of peptide release by specific
agonists will be correlated with the voltage clamp data on single
ARC-CPZ neurons. The effects of 17beta-estradiol (E2) on the
acute actions of the opioids will be ascertained by using slices
prepared from ovariectomized females and ovariectomized
females that have received E2 replacement. Dose response
curves will be established for specific opioid agonists mesuring ion
conductances. LHRH release will also be measured in these same
slices and shifts in the dose response curve and any changes in
receptor affinity ascertained. Once the physiological role of the
endogenous opioids in regulating the activity of ARC-CPZ neurons
has been assessed, then studies will be initiated to determine the
effects of chronic morphine on the electrophysiological properties
of these cells and on the release of LHRH. Slices will be prepared
from physically dependent and tolerant guinea pigs, and the
changes in the opioid dose response and in their coupling to
specific membrane conductances determined in ARC-CPZ
neurons. It is envisioned that these studies will elucidate the
physiological role of the opioids in the control of the mammalian
reproductive cycle and the basis for the inhibition of the cycle
with chronic abuse.