"Electrical Transmission" at an Excitatory Synapse in a Vertebrate Brain

Abstract

A type of excitatory synaptic transmission which is novel for the vertebrate brain has been found in the ner neuron (M-cell) by means of the passive spread of their action currents across the synaptic membrane. After stimulating the ipsilateral eighth cranial nerve, an excitatory postsynaptic potential (EPSP) appears in the M-cell with a latency which is very brief ( about 0.1 msec) and which proba; bly represents a negligible synaptic delay. This response is attributed to the club endings: there were steep gradients of potential along the lateral dendrite of the M-cell during activity and the early EPSP was maximal in the distal part of the dendrite where the club endings predominate. Potential changes in the M-cell spread (passively) backwards into certain eighth-nerve fibers (probably club endings) indicating the presence of special low-resistance connections between them and the M-cell.

Colocalization of somatostatin with GABA or glutamate in distinct afferent terminals presynaptic to the Mauthner cell

“…The density of gold particles was the highest in LMCEs. These endings transmit both electrically and chemically (Furshpan, 1964;Korn and Faber, 1976;Lin and Faber, 1988) in agreement with electron microscopic (Roberston et al, 1963;Nakajima, 1974) and freezefracture (Tuttle et al, 1986) data. Previous iontophoretic (Diamond and Roper, 1973) and pharmacological (Wolszon and Faber, 1988) studies suggest that the chemical component of LMCEs is mediated by glutamate.…”

“…Further, this cyclic neuropeptide may coexist with GABA in the lamprey spinal cord (Christenson et al, 1991). The extremity of the M-cell lateral dendrite is richly innervated by glutamic acid decarboxylase (GAD)-immunoreactive boutons (Petrov et al,199 1) and the corresponding GABAergic boutons are adjacent to the large myelinated club endings (LMCEs) that comprise the main electrical and chemical excitatory inputs to this neuron (Furshpan, 1964;Korn and Faber, 1976;Faber and Kern, 1978) a spatial relationship between excitatory and inhibitory afferents comparable to that for distal dendrites and dendritic spines of hippocampal (Somogyi et al, 1984) and neostriatal (Takagi et al, 1983) neurons. In this article, we show that some of these inhibitory afferents contain both somatostatin and GABA.…”

Voltage-Dependent Enhancement of Electrical Coupling by a Subthreshold Sodium Current

“…1 A). The AD coupling is a distinctive feature of the club endings (Furshpan, 1964) and a convenient way to study retrograde transmission; it was used instead of that produced by activating other VIIIth nerve afferents to avoid possible complications attributable to local responses produced by changes in axonal excitability after the nerve stimulation. The voltage dependence of AD coupling potential was investigated by pairing this potential with presynaptic depolarizing and hyperpolarizing currents (Ϯ0.9 nA) (Fig.…”

“…To demonstrate that this amplification operates under these conditions, we tested the effect of QX-314 on the amplitude of the retrogradely transmitted coupling potential attributable to the dendritic depolarization produced by the activation of a population of these afferents; that is, the characteristic intradendritically recorded mixed, electrical, and chemical, synaptic potential in response to VIIIth nerve stimulation (Fig. 9A) (Furshpan, 1964) can be recorded simultaneously as a coupling potential in nearby terminals for which the stimulus strength is subthreshold (Fig. 9B, VIIIth N. coup) (Pereda et al, 1995).…”

“…Auditory afferents terminating as mixed (electrical and chemical) synapses known as large myelinated club endings on the goldfish Mauthner (M-) cells ("club endings") (Bartelmez, 1915;Furshpan, 1964;Nakajima, 1974;Lin and Faber, 1988) provide a convenient in vivo model in the vertebrate CNS, amenable to experimental manipulation, to study how efficient bi-directional communication is achieved despite unfavorable electrical and geometrical conditions. This relatively homogeneous group of synaptic contacts is tightly segregated to the distal portion of the lateral dendrite of the M-cells (Bartelmez, 1915), a pair of large reticulospinal neurons responsible for the organization of escape responses evoked by sound and other senses (Eaton et al, 2001).…”