Cannabinoid receptor binding did not vary in several hypothalamic nuclei after hypothalamic deafferentation.

Cannabinoid receptors are sparsely distributed in the hypothalamic nuclei, although they seem to be located on key neurons because their activation produces important neuroendocrine effects. In the present study, we have examined whether cannabinoid receptor-containing hypothalamic neurons are intrinsic or extrinsic to this brain region. To this end, we have examined whether the hypothalamic deafferentation was followed by a general loss of cannabinoid receptor binding, thus suggesting that cannabinoid receptor-containing neurons would have their cell bodies outside the hypothalamus, or whether this was followed by no changes in binding, thus suggesting that cannabinoid receptors would be located on intrinsic neurons. Three experimental groups were then analyzed: (i) animals with complete hypothalamic deafferentation in both sides; (ii) hemideafferentated animals; and (iii) sham-operated animals. In the three cases, cannabinoid receptor binding did not vary among these three groups in any of the hypothalamic nuclei analyzed. These were the arcuate nucleus, ventromedial hypothalamic nucleus, lateral and dorsal hypothalamic areas, paraventricular nucleus and medial preoptic area. This clearly supports the view that cannabinoid receptor-containing neurons into the hypothalamus are all intrinsic to this brain region.