Role of the lateral hypothalamus in modulating responses of parabrachial gustatory neurons in the rat.

The lateral hypothalamus (LH) receives projections from the parabrachial nucleus (PBN) gustatory neurons and sends efferent projections to the PBN. To examine if the LH is involved in modulating activity of gustatory neurons in the PBN, we examined the effects of electrical stimulation and electrolytic lesions of the LH on the response of PBN gustatory neurons, using extracellular recording techniques. Among 45 PBN taste neurons recorded, 60% were affected by LH stimulation and 73% were affected by LH lesions. During LH stimulation, the responses of most affected PBN neurons were inhibited with the magnitude significantly lower than that obtained before stimulation (P<0.05). In contrast, LH lesions facilitated the response. Based on the best-stimulus category, the responses of the NaCl-best neurons to NaCl and HCl and the QHCl-best neurons to HCl and QHCl were significantly suppressed during LH stimulation (P<0.05). After lesions of the LH, however, the response to HCl in NaCl-best PBN neurons was significantly increased (P<0.05). Analysis of across-unit patterns indicated that LH stimulation decreased the correlations between NaCl and other stimuli, and increased those between QHCl and other stimuli. After LH lesions, the correlations between NaCl and other tastants were higher than those before lesions. These findings suggest that the LH mediates feeding and taste via modulating the activity and chemical selectivity of PBN gustatory neurons.