INDUCTION OF FOS-IMMUNOREACTIVITY IN PROLACTIN-LIKE CONTAINING NEURONS OF THE RAT LATERAL HYPOTHALAMUS AFTER INSULIN-TREATMENT

The role of the lateral hypothalamus (LHT) in the regulation of feedin g behavior has long been established. The major contribution of LHT gl ucose-sensitive neurons, activated by low glucose concentration, is we ll accepted. Two peptidergic neuron populations, whose perikarya are e xclusively located within this area, have been recently described. The y respectively produce peptides derived from the melanin-concentrating hormone (MCH) precursor and prolactin-like immunoreactive peptide (PL I). In the present study, hypoglycemia-induced neuron stimulation was assessed in the rat LHT, by using Fos immunocytochemistry 1 to 5 h aft er a single insulin injection. In control animals, very scarce Fos-lik e immunoreactivity (FLI)-containing nuclei were observed in LHT. Insul in treatment induced an important and progressive increase in the numb er and staining intensity of neuron nuclei detected by Fos antiserum. Five hours after injection, few MCH neurons exhibited FLI, but about 8 0% of PLI-containing neurons expressed FLI and more than 50% of the FL I-containing nuclei belonged to PLI neurons. It was thus concluded tha t PLI-expressing neurons, which dramatically responded to insulin trea tment, might correspond to a subpopulation of the glucose-sensitive LH T neurons.