【Purpose】There are glucose sensing neurons in the ventromedial hypothalamus (VMH). Although sympathetic nerve activity (SNA) is regulated by the VMH, it is not known whether glucose sensing neurons in the VMH mediate the SNA. On the other hand, the VMH neurons expresses receptors of various neuropeptides that are involved in regulation of feeding behavior. In preliminary experiments, we found a group of strong burst generating neurons in the VMH, which might be involved in SNA. Therefore, we examined responses of the burst generator in the VMH to feeding peptides as well as glucose.
【Method】Electrophysiological properties and optical imagings on both side of neurons in the VMH were observed on slice preparations of the hypothalamus from 5- to 14-day-old Wistar rats. Glucose sensing neurons in the VMH were confirmed by change of glucose concentration in ringer solutions at 2-, 10-, 30mM. Neuronal activity of glucose sensing neurons in the preparation was detected as a change by superfusion with feeding neuropeptide.
【Result】We found novel oscillations (0.039-0.089 Hz, average 0.063 Hz) in the VMH. Frequency of oscillation was increased by low glucose, and decreased by high glucose, neuropeptide Y, Ghrelin, Galanin, and Isopreterenol. The simultaneous recordings from the left and right side VMH indicated that both rhythmic activities were not synchronized.
【Discussion】The frequency of oscillation in the VMH neurons was very similar to low frequency of heart rate variability which is one of the index of SNA. Our findings about glucose sensing properties detected in oscillation suggested that the burst generating neurons consist of glucose-inhibited neurons. Oscillation within the VMH may mediate SNA, because frequency change of oscillation in response to application of feeding peptides and glucose were similar pattern with those of SNA.