Morairty S, Rainnie D, McCarley R, Greene R
SRI International, Menlo Park, CA, USA.
Neuroscience. 2004;123(2):451-7. doi: 10.1016/j.neuroscience.2003.08.066.
The ventrolateral preoptic area of the hypothalamus (VLPO) contains a population of sleep-active neurons and is hypothesized to be an important part of the somnogenic process. Adenosine (AD) is an endogenous sleep-promoting factor and may play an important role in promoting natural sleep. We hypothesize that AD may promote sleep, in part, by activating the VLPO sleep-active neurons. Although, in the CNS, AD is generally regarded as an inhibitory neuromodulator, it is possible for AD to be directly excitatory via A2 receptors or indirectly via disinhibition. In order to test the hypotheses that AD can excite VLPO neurons we made intracellular recordings from the VLPO in vitro and examined the effects of AD on VLPO neural activity. Whole cell patch-clamp recordings were obtained from rat brain slices and drugs were bath applied. VLPO neurons were electrophysiologically heterogeneous. Depolarizing current steps elicited rhythmic firing (25 of 57), spike frequency adaptation or accommodation (24 of 57), or an unusual burst firing response (eight of 57). Spontaneous synaptic activity was pronounced in most recorded neurons and consisted of either fast excitatory post-synaptic potentials/currents (EPSP/C's) and/or fast inhibitory post-synaptic potentials/currents (IPSP/C's). The IPSC's were fully blocked by 30 microM bicuculline suggesting they are GABA(A)-mediated events, and the EPSC's were blocked by 40 microM DNQX suggesting they are mediated by the AMPA subtype of glutamate receptor (five of five). AD (20-100 microM) reduced the frequency of spontaneous IPSC's in 11 of 17 VLPO neurons (28-100%; mean reduction=63%) without significant effects on resting membrane potential. IPSC was unaffected in five neurons and one neuron displayed increases in spontaneous IPSC's. In contrast, AD decreased EPSC frequency in seven cells (36-73%; mean=59%), increased frequency in five cells (30-236%; mean 83%) and had no effect in six cells. AD application increased the firing rate in two of four cells tested. These data are consistent with the hypothesis that one mechanism which AD may promote sleep is by blocking inhibitory inputs on VLPO sleep-active neurons.
下丘脑腹外侧视前区（VLPO）含有一群睡眠活跃神经元，被认为是睡眠发生过程的重要组成部分。腺苷（AD）是一种内源性促睡眠因子，可能在促进自然睡眠中发挥重要作用。我们假设AD可能部分通过激活VLPO睡眠活跃神经元来促进睡眠。虽然在中枢神经系统中，AD通常被视为一种抑制性神经调质，但AD有可能通过A2受体直接产生兴奋性作用，或通过去抑制间接产生兴奋性作用。为了验证AD能兴奋VLPO神经元的假设，我们在体外对VLPO进行细胞内记录，并研究AD对VLPO神经活动的影响。从大鼠脑片中获得全细胞膜片钳记录，并将药物浴加应用。VLPO神经元在电生理上具有异质性。去极化电流阶跃引发节律性放电（57个中有25个）、动作电位频率适应或适应（57个中有24个），或异常的爆发性放电反应（57个中有8个）。大多数记录的神经元中自发突触活动明显，由快速兴奋性突触后电位/电流（EPSP/C）和/或快速抑制性突触后电位/电流（IPSP/C）组成。IPSC被30μM荷包牡丹碱完全阻断，表明它们是GABA（A）介导的事件，而EPSC被40μM DNQX阻断，表明它们由谷氨酸受体的AMPA亚型介导（5个中有5个）时。AD（20 - 100μM）使17个VLPO神经元中的11个自发IPSC频率降低（28 - 100%；平均降低 = 63%），对静息膜电位无显著影响。5个神经元中的IPSC未受影响，1个神经元的自发IPSC增加。相反，AD使7个细胞的EPSC频率降低（36 - 73%；平均 = 59%），5个细胞的频率增加（30 - 236%；平均83%），6个细胞中无影响。施加AD使4个测试细胞中的2个放电率增加。这些数据与以下假设一致，即AD促进睡眠的一种机制可能是通过阻断VLPO睡眠活跃神经元上的抑制性输入。
