Analysis of functional connection of the dorsomedial hypothalamic nucleus for themoregulation

下丘脑的视前区(POA)在体温调节神经回路中占有重要地位。最近，有报道称下丘脑背内侧核(DMH)参与了热量产生的控制。因此，在本研究中，我们用霍乱毒素b逆行注射到大鼠背内侧下丘脑的免疫组织化学方法，研究了热(33℃)或冷(10℃)暴露对Fos表达的影响，研究了与下丘脑背内侧有功能传入联系以调节体温的脑区。双标细胞被定义为与DMH具有与体温调节有关的功能联系的神经元。热暴露大鼠仅在正中视前区(MnPO)可见双标记细胞。冷暴露大鼠下丘脑前部可见双标记细胞，尤其是内侧部和腹侧部。Fos和CTB的研究结果表明，DMH神经元可能受到MnPO神经元的抑制，而MnPO内的CTB-IR神经元可能是GABA能的，并直接调节DMH神经元的活动。为了检验这种可能性，我们进一步研究了GABA能神经元的标记物GAD67在CTB-IR MnPO神经元中的mRNA表达。我们发现在MnPO中有79.6%的CTB-IR细胞表达GAD67基因。这些结果表明，POA中的神经元，尤其是MnPO中的神经元，接受来自皮肤的热输入，并通过GABA能突触向DMH发送抑制信号，以抑制热产生；而AH中的神经元从皮肤接收冷信号，并向DMH发送兴奋信号，以激活热产生。

The preoptic area(POA) in the hypothalamus occupies a crucial position in the neuronal circuit for thermoregulation. Recently, the dorsomedial hypothalamus(DMH) was reported to be involved in the control of heat production. Therefore, in the present study, we investigated the brain areas that had functional afferent connections with the dorsomedial hypothalamus(DMH) for thermoregulation in rats, using immuno-histochemical analyses of a retrograde tracer, cholera toxin-b(CTb), injected into the DMH and Fos expression in response to warm (33℃) or cold (10℃) exposure. A double-labeled cell was defined as the neuron had functional connection with the DMH in relation to thermoregulation. In the warm-exposed rats, double-labeled cells were obtained only in the median preoptic area(MnPO). In the cold exposed rats, double-labeled cells were obtained in the anterior hypothalamus(AH), especially in its medial and ventral parts. The results in the Fos and CTb studies raised a possibility that the DMH neurons would be inhibited by the MnPO neurons, and CTb-IR neurons in the MnPO would be GABAergic and directly regulate activity of the DMH neurons. To examine this possibility, we further investigated an expression of mRNA for GAD67,a marker for GABAergic neuron, in CTB-IR MnPO neuron. We found that 79.6% of CTb-IR cells in the MnPO exhibited signals for GAD67 mRNA. These results suggest that the neurons in the POA, especially in the MnPO, receive warm inputs from the skin and send inhibitory signals, via GABAergic synapses, to the DMH to suppress heat production, and the neurons in the AH receive cold signals from the skin and send excitatory signals to the DMH, to activate heat production.