Direct effects of the adrenergic neurotoxin DSP4 on central opiate receptors: implications for neuroendocrine studies.

We have shown that the noradrenergic neurotoxin DSP4 can acutely abolish naloxone-induced secretion of LH in the rat. A part of this influence is clearly related to an unexpected interaction with hypothalamic opiate ( [3H]-naloxone) binding sites. Injection of DSP4 (50 mg/kg) can severely reduce opiate binding assayed in vitro. In addition, the drug is very potent in blocking opiate receptors in vitro, as determined in slice and homogenate assays. Consideration must now be given to the possibility that many previous studies on acute effects of DSP4 undoubtedly involved the opiatergic system in addition to noradrenergic terminals. Thus, DSP4 is not the drug of choice for experiments designed to probe catecholamine-opiate interactions in the control of LH release.