Opioid binding in the rostral hypothalamus is reduced following lesion of the ventral noradrenergic tract in female rats.
Experiments were undertaken to establish whether opioid receptors exert a direct presynaptic influence on noradrenergic (NA) terminals in the preoptic/anterior hypothalamus (PO/AH) of the female rat. Thus, opioid binding studies were performed in rats with lesions of the ventral NA tract (VNAT; the main NA projection to the hypothalamus) to assess whether a loss of NA terminals may also result in a decrease in opioid binding in the PO/AH. In the first experiment, unilateral electrolytic lesions of the VNAT caused a significant reduction in both the NA content and specific [3H]-diprenorphine binding to membrane homogenates in the ipsilateral PO/AH. In the second experiment bilateral 6-hydroxydopamine (6-OHDA)-induced lesions of the VNAT caused a significant reduction in NA levels in the PO/AH as well as significant decreases in the density of [3H]-diprenorphine binding to tissue sections of the PO/AH when compared to control animals. These results strongly suggest that the NA input to the PO/AH is regulated by endogenous opioid peptides, and provide an anatomical substrate to explain opioid-NA interactions in the control of gonadotrophin releasing hormone (GnRH) and gonadotrophin secretion.
Dyer
R G
RG
Department of Neuroendocrinology, AFRC Institute of Animal Physiology and Genetics Research, Babraham, Cambridge, UK.
Parvizi
N
N
Hollingsworth
S
S
Mansfield
S
S
Heavens
R P
RP
Bicknell
R J
RJ
Sirinathsinghji
D J
DJ
D000818:Animals; D001345:Autoradiography; D004174:Diprenorphine / Q000378:metabolism; D005260:Female; D006892:Hydroxydopamines / Q000494:pharmacology; D007031:Hypothalamus / Q000378:metabolism*; D007032:Hypothalamus, Anterior / Q000502:physiology*; D009638:Norepinephrine / Q000502:physiology*; D016627:Oxidopamine; D051381:Rats; D011919:Rats, Inbred Strains; D011957:Receptors, Opioid / Q000378:metabolism*
D006892:Hydroxydopamines; D011957:Receptors, Opioid; D004174:Diprenorphine; D016627:Oxidopamine; D009638:Norepinephrine