BACKGROUND & AIMS:
Hippocampal GABAergic interneurons are responsible for controlling the output and efficacy of synaptic input of large principal cell populations and, thereby, determine the oscillatory discharge patterns and synaptic plasticity in the hippocampus. Single interneurons are able to prevent repetitive firing of postsynaptic pyramidal cells (R. Miles, K. Tóth, A.I. Gulyás, N. Hájos, and T.F. Freund. Neuron, 16815-823, 1996), whereas on occasion a single pyramidal cell may be able to activate an interneuron under in vitro conditions (A.I. Gulyás, R. Miles, A. Sik, K. Tóth, N. Tamamaki, and T.F. Freund.
Nature (London), 366683-687, 1993). Inhibition is therefore extremely powerful. Transient suppression of interneuronal activity allows the precise timing and synchronization of inhibitory postsynaptic potentials arriving at principal cells.
A rhythmic suppression or modulation of interneuron discharge may be brought about by input from at least two major sources(i) from other local interneurons or (ii) from subcortical centers. Of the possible local sources, in the present review particular attention will be paid to GABAergic neurons specialized to innervate other interneurons. Subcortical pathways known to modulate specific inhibitory functions in the hippocampus, i.e., the GABAergic and cholinergic septohippocampal and the serotonergic raphe hippocampal pathways, will also be reviewed. Roles of these control mechanisms may include the generation of theta and higher frequency oscillations and the selective removal of inhibition from the termination zone of specific excitatory afferents, thereby increasing their efficacy and (or) plasticity.
背景与目标:
海马GABA能性神经元负责控制大量主细胞群的输出和突触输入的功效,从而确定海马中的振荡放电模式和突触可塑性。单个中间神经元能够阻止突触后锥体细胞的反复发射(R. Miles,K.Tóth,AIGulyás,N.Hájos和TF Freund。Neuron,16815-823,1996),而有时单个锥体细胞可能是能够在体外条件下激活中间神经元(AIGulyás,R.Miles,A.Sik,K.Toth,N.Tamamaki和TF Freund。
Nature(London),366683-687,1993) 。因此抑制作用非常强大。神经元间活动的瞬时抑制可以使到达主细胞的抑制性突触后电位的精确定时和同步。
至少从两个主要来源(i)的输入可以实现对神经元放电的节律性抑制或调节。其他局部中间神经元;或(ii)来自皮层下中心。在可能的本地来源中,在本综述中,将特别关注专门用于支配其他中间神经元的GABA能神经元。也将审查已知可调节海马中特定抑制功能的皮层下途径,即GABA能和胆碱能的海马途径和血清素能的罗非鱼海马途径。这些控制机制的作用可能包括产生theta和更高频率的振荡,以及选择性地消除特定兴奋性传入传入末端区域的抑制作用,从而提高其功效和(或)可塑性。