Responses of rat lateral hypothalamic neuron activity to vestibular nuclei stimulation

Effects of lateral vestibular nucleus (LVN) stimulation on neuronal activity in the rat lateral hypothalamic area (LHA), including specific glucose-sensitive neurons, were investigated by extracellular and intracellular recordings in vivo. Stimulation of the contralateral LVN evoked 3 types of response in 46% (111/240) of the neurons recorded extracellularly: long latency (38.1 +/- 23.6 ms) excitation (62/111, 56%), short latency (6.9 +/- 3.1 ms) excitation-inhibition (33/111, 30%), and inhibition with 20.1 +/- 11.1 ms latency (16/111, 14%). Glucose-sensitive neurons, which were identified by electrophoretic application of glucose, did not respond specifically to such stimulation. Neuronal activity was recorded intracellularly from 31 LHA neurons, of which 13 responded to LVN stimulation. Seven of the 13 neurons showed a long latency EPSP (10.4 +/- 5.5 ms) and the remaining 6 exhibited an EPSP-IPSP sequence with shorter latency (4.5 +/- 3.0 ms). The amplitude of these responses was graded with a change in stimulus intensity. The EPSPs of both types of response were considered to be polysynaptic because of shortening of latencies by higher current stimulation. Since the LHA is implicated in the regulation of autonomic nerve activity, the present results showing polysynaptic pathways from the LVN to the LHA suggest functional involvement of the LHA in vestibulo-autonomic responses.