Boudaba C, Schrader L A, Tasker J G
Department of Cell and Molecular Biology, Tulane University, New Orleans, Louisiana 70118, USA.
J Neurophysiol. 1997 Jun;77(6):3396-400. doi: 10.1152/jn.1997.77.6.3396.
We conducted whole cell voltage-clamp and current-clamp recordings in slices of rat hypothalamus to test for local excitatory synaptic circuits. Local excitatory inputs to neurons of the paraventricular nucleus (PVN) and supraoptic nucleus (SON) were studied with the use of electrical and chemical stimulation. Extracellular electrical stimulation provided indirect evidence of local excitatory circuits. Single stimuli evoked multiple excitatory postsynaptic potentials (EPSPs) or excitatory postsynaptic currents (EPSCs) in some PVN and SON cells, invoking polysynaptic excitatory inputs. Repetitive stimulation (10-20 Hz, 2-10 s) elicited long afterdischarges of EPSPs/EPSCs, suggesting a potentiation of upstream synapses in a polysynaptic circuit. Bath application of metabotropic glutamate receptor agonists provided more conclusive evidence for local excitatory circuits. Metabotropic receptor activation caused an increase in the frequency of EPSPs/EPSCs that was blocked by tetrodotoxin, suggesting that it was mediated by activation of local presynaptic excitatory neurons. The local excitatory inputs to SON and PVN neurons were mediated by glutamate release, because the EPSPs/EPSCs elicited with electrical stimulation and metabotropic receptor activation were blocked by ionotropic glutamate receptor antagonists. Finally, glutamate microstimulation furnished the most direct demonstration of local excitatory synaptic circuits. Glutamate microstimulation of perinuclear sites elicited an increase in the frequency of EPSPs/EPSCs in 13% of the PVN and SON neurons tested. Two sites provided most of the local excitatory synaptic inputs to PVN neurons, the dorsomedial hypothalamus and the perifornical region. These experiments provide converging physiological evidence for local excitatory synaptic inputs to hypothalamic neurons, inputs that may play a role in pulsatile hormone release.
我们在大鼠下丘脑切片中进行了全细胞电压钳和电流钳记录，以测试局部兴奋性突触回路。通过电刺激和化学刺激研究了室旁核（PVN）和视上核（SON）神经元的局部兴奋性输入。细胞外电刺激提供了局部兴奋性回路的间接证据。单个刺激在一些PVN和SON细胞中诱发了多个兴奋性突触后电位（EPSP）或兴奋性突触后电流（EPSC），引发了多突触兴奋性输入。重复刺激（10 - 20 Hz，2 - 10 s）引发了EPSP/EPSC的长时间后放电，表明多突触回路中上游突触的增强。代谢型谷氨酸受体激动剂的浴应用为局部兴奋性回路提供了更确凿的证据。代谢型受体激活导致EPSP/EPSC频率增加，这被河豚毒素阻断，表明它是由局部突触前兴奋性神经元的激活介导的。SON和PVN神经元的局部兴奋性输入是由谷氨酸释放介导的，因为电刺激和代谢型受体激活引发的EPSP/EPSC被离子型谷氨酸受体拮抗剂阻断。最后，谷氨酸微刺激提供了局部兴奋性突触回路最直接的证据。对核周部位的谷氨酸微刺激在13%的测试PVN和SON神经元中引起了EPSP/EPSC频率的增加。两个部位为PVN神经元提供了大部分局部兴奋性突触输入，即背内侧下丘脑和穹窿周区域。这些实验为下丘脑神经元的局部兴奋性突触输入提供了一致的生理学证据，这些输入可能在脉冲式激素释放中起作用。
