Serotonergic innervation of the lateral hypothalamus: evidence from synaptosomal uptake studies

Uptake of tritiated serotonin by synaptosomes prepared from rat lateral hypothalamus was examined. Uptake of serotonin into lateral hypothalamic synaptosomes occurred by both saturable and non-saturable processes. The saturable process was a high affinity transport with kinetic parameters that agree closely with those previously reported for serotonin uptake into synaptosomes prepared from other brain regions. Fluoxetine, a selective inhibitor of uptake into serotonergic neurons, was a potent inhibitor of serotonin uptake into lateral hypothalamic synaptosomes. Desipramine and benztropine, noradrenergic and dopaminergic uptake inhibitors respectively, were much less effective. Damage to the ascending serotonergic system, by either electrolytic lesion of the dorsal or median raphe nucleus, or by 5,7 dihydroxytryptamine injections into the midbrain serotonergic pathways, significantly reduced the uptake of serotonin by lateral hypothalamic synaptosomes. Taken together, these data provide further evidence for a serotonergic terminal field within the lateral hypothalamus.