Ryan J W, Waldrop T G
Department of Physiology and Biophysics, University of Illinois, Urbana 61801, USA.
Respir Physiol. 1995 Jun;100(3):185-94. doi: 10.1016/0034-5687(95)00010-b.
Previous studies have demonstrated that the caudal hypothalamus modulates the respiratory responses to hypoxia and hypercapnia. In addition, many of the neurons in this area have a basal discharge related to the cardiac and/or respiratory cycles and are stimulated by hypoxia or hypercapnia. The purpose of the present study was to determine if these hypothalamic neurons project to a known cardiorespiratory area, the periaqueductal gray in the rat. In a first set of experiments, rhodamine-tagged microspheres were injected into the periaqueductal gray (PAG) to determine the areas of the caudal hypothalamus that project to the PAG. These studies revealed that the caudal hypothalamus sends strong ipsilateral and weak contralateral projections to the PAG. In a second set of experiments, single unit recordings were made from neurons in the caudal hypothalamus; the basal discharge of these neurons were examined with signal averaging techniques. Each neuron (n = 79) was tested for a response to inhalation of a hypoxic (10% O2) and a hypercapnic (5% CO2) gas. Antidromic activation techniques were then used to determine if neurons in the caudal hypothalamus send projections to or through the PAG. Nineteen percent (n = 15) of the hypothalamic neurons studied could be activated from the PAG; approximately 53% (n = 8) of these were excited by hypoxia and 27% (n = 4) by hypercapnia. Most of these neurons tested (42 of 64 neurons) had a basal discharge related temporally to the cardiac and/or respiratory cycles. These findings suggest that a caudal hypothalamic to periaqueductal gray projection is involved in the integrated response to hypoxia.
先前的研究表明，下丘脑尾部可调节对低氧和高碳酸血症的呼吸反应。此外，该区域的许多神经元具有与心脏和/或呼吸周期相关的基础放电，并受到低氧或高碳酸血症的刺激。本研究的目的是确定这些下丘脑神经元是否投射到大鼠中一个已知的心肺区域——导水管周围灰质。在第一组实验中，将罗丹明标记的微球注入导水管周围灰质（PAG），以确定投射到PAG的下丘脑尾部区域。这些研究表明，下丘脑尾部向PAG发出强烈的同侧投射和微弱的对侧投射。在第二组实验中，对下丘脑尾部的神经元进行单单位记录；用信号平均技术检查这些神经元的基础放电。测试每个神经元（n = 79）对吸入低氧（10% O2）和高碳酸（5% CO2）气体的反应。然后使用逆向激活技术来确定下丘脑尾部的神经元是否投射到PAG或通过PAG投射。所研究的下丘脑神经元中有19%（n = 15）可从PAG被激活；其中约53%（n = 8）被低氧兴奋，27%（n = 4）被高碳酸血症兴奋。这些测试的大多数神经元（64个神经元中的42个）具有与心脏和/或呼吸周期在时间上相关的基础放电。这些发现表明，下丘脑尾部到导水管周围灰质的投射参与了对低氧的综合反应。
