Paré D, Steriade M, Deschênes M, Bouhassira D
Laboratoire de Neurophysiologie, Faculté de Médecine, Université Laval, Québec, Canada.
J Neurosci. 1990 Jan;10(1):20-33. doi: 10.1523/JNEUROSCI.10-01-00020.1990.
This study describes the effects of brain-stem cholinergic laterodorsal tegmental (LDT) stimulation on the synaptic responsiveness of anterior thalamic (AT) neurons. A sample of AT cells, physiologically identified by their short-latency (less than 6.5 msec) response to mammillary body (MB) stimulation, was recorded in unanesthetized, chronically implanted cats and in urethane-anesthetized cats. In chronic experiments, LDT stimulation evoked a short-latency (10-20 msec) excitation in most AT cells. Moreover, brief LDT trains (3 shocks at 300 Hz, every 3 sec) enhanced the responsiveness of AT cells to both MB (orthodromic) and cortical (ortho- and antidromic) stimuli. This effect did not vary as a function of the interval between LDT conditioning and MB or cortical testing shocks, but as a function of the number of trials. The effects of LDT stimuli resisted reserpine treatment (0.75 mg/kg), suggesting that they were not dependent on the coactivation of monoaminergic fibers. Finally, LDT trains did not suppress inhibitory processes in AT neurons when conditioning-testing intervals were longer than 60 msec. Intracellular recordings performed in urethane-anesthetized cats revealed that LDT stimulation induced a short-latency depolarization which increased with membrane hyperpolarization and was associated with an increase in apparent membrane conductance. Usually, isolated LDT trains did not evoke lasting changes in membrane potential or conductance. However, when LDT trains were applied every 3 sec, they gradually decreased the apparent membrane conductance without altering the membrane potential. This conductance change had a time course similar to the LDT-induced potentiation of responsiveness observed in the chronic experiments. In some neurons, LDT conditioning trains also induced a marked increase in the probability of fast prepotentials being triggered by subthreshold MB or cortical orthodromic volleys. In order to distinguish the cumulative effects of repeated LDT trains from the possibly slow time course of LDT influences, we studied the effects of a unique 1 sec LDT train (at 30 Hz) on the synaptic responsiveness of AT cells recorded extracellularly in reserpine-treated, urethane-anesthetized animals. Such LDT trains induced a 2.9-fold increase in synaptic responsiveness, reaching its peak 40-50 sec after the LDT train and lasting up to 4 min. Iontophoretic application of the muscarinic blocker scopolamine blocked these long-lasting potentiating effects of LDT stimuli. Removal of cortical and basal forebrain inputs to the AT nuclear complex by appropriate transections did not abolish the potentiating effects of LDT trains.(ABSTRACT TRUNCATED AT 400 WORDS)
本研究描述了脑干胆碱能背外侧被盖区（LDT）刺激对丘脑前核（AT）神经元突触反应性的影响。在未麻醉的慢性植入猫和乌拉坦麻醉的猫中，记录了通过对乳头体（MB）刺激的短潜伏期（小于6.5毫秒）反应生理鉴定的AT细胞样本。在慢性实验中，LDT刺激在大多数AT细胞中诱发了短潜伏期（10 - 20毫秒）的兴奋。此外，短暂的LDT串刺激（300赫兹，每3秒3次电击）增强了AT细胞对MB（顺向）和皮质（顺向和逆向）刺激的反应性。这种效应并不随LDT条件刺激与MB或皮质测试电击之间的间隔而变化，而是随试验次数而变化。LDT刺激的效应抵抗利血平治疗（0.75毫克/千克），表明它们不依赖于单胺能纤维的共同激活。最后，当条件刺激 - 测试间隔长于60毫秒时，LDT串刺激并未抑制AT神经元中的抑制过程。在乌拉坦麻醉的猫中进行的细胞内记录显示，LDT刺激诱导了短潜伏期的去极化，该去极化随膜超极化而增加，并与表观膜电导的增加相关。通常，孤立的LDT串刺激不会引起膜电位或电导的持久变化。然而，当每3秒施加LDT串刺激时，它们逐渐降低表观膜电导而不改变膜电位。这种电导变化的时间进程与在慢性实验中观察到的LDT诱导的反应性增强相似。在一些神经元中，LDT条件刺激串也诱导了由阈下MB或皮质顺向冲动触发快速前电位的概率显著增加。为了区分重复LDT串刺激的累积效应与LDT影响可能的缓慢时间进程，我们研究了在利血平处理的、乌拉坦麻醉的动物中，对细胞外记录的AT细胞施加独特的1秒LDT串刺激（30赫兹）的影响。这种LDT串刺激诱导突触反应性增加2.9倍，在LDT串刺激后40 - 50秒达到峰值，并持续长达4分钟。毒蕈碱阻断剂东莨菪碱的离子导入应用阻断了LDT刺激的这些持久增强效应。通过适当的横断术去除AT核复合体的皮质和基底前脑输入并未消除LDT串刺激的增强效应。（摘要截断于400字）
