Analysis of functional connection of the dorsomedial hypothalamic nucleus for themoregulation

下丘脑视前区（POA）在体温调节神经回路中占有重要地位。最近，下丘脑背内侧核（DMH）被报道参与控制产热。因此，在本研究中，我们研究了与背内侧下丘脑（DMH）有功能性传入联系的脑区的温度调节，使用逆行示踪剂，霍乱毒素-b（CTb）的免疫组织化学分析，注射到DMH和Fos表达的反应，温暖（33℃）或寒冷（10℃）暴露。双标记细胞是指与DMH有体温调节功能联系的神经元。在热暴露大鼠中，双标记细胞仅在正中视前区（MnPO）获得。冷暴露大鼠下丘脑前部（AH），尤其是其内侧部和腹侧部出现双标细胞。Fos和CTb的研究结果提示DMH神经元可能受到MnPO神经元的抑制，MnPO中的CTb阳性神经元可能是GABA能的，直接调节DMH神经元的活动。为了验证这种可能性，我们进一步研究了CTB-IR MnPO神经元中GABA能神经元的标志物GAD 67的mRNA表达。我们发现，在MnPO中，79.6%的CTb-IR细胞表现出GAD 67 mRNA的信号。这些结果表明，POA的神经元，特别是MnPO，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，以抑制产热; AH的神经元接受来自皮肤的冷信号，并向DMH发送兴奋信号，以激活产热。

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.