Feeding related lateral hypothalamic neuron responses to odors depend on food deprivation in rats.

It has been investigated feeding related LHA neuronal activity and responses to odor stimulation in rats at various levels of satiation. Extracellular responses of 168 neurons to three odors, isoamylacetate (AA), cineole (CL), and isovaleric acid (VA), were recorded from 168 LHA neurons of Wistar-SPF male rats. Of 168 units, 107 (63.7%) responded to from one to three odors, but not to light or phonic stimulation. Of the responding units, 94.4% (101/107) were excited, and 5.6% were inhibited. In response to a single electrical stimulation (0.5 msec, 1-10 V) of the OB, 61 units were excited with latencies of 6-43 msec (19.8 +/- 12.0 msec, mean +/- S.D.) indicating compound OB-LHA relations--mono- and polysynaptic through myelinated and nonmyelinated fibers. The results suggest predominantly excitatory effects of both electrical stimulation of the OB and odor stimulation on the LHA. Firing frequency in response to AA or VA was significantly (p less than 0.05) greater for the long fasting group (38 hr, LF, n = 8) than for the NF (nonfasting, n = 12) group; differences between the LF and MF (24 hr, n = 6) groups were not significant. Glucose-sensitive neurons (GSN, n = 19) responded more to odors than non-GSNs (n = 86), and discharge frequency increase depended markedly on food deprivation. Food deprivation results suggest that responsiveness of feeding related LHA neurons to odors depends on the degree of satiation. In conclusion, it was confirmed that olfactory functions are important in the responses of hypothalamic feeding related neurons.