gamma-Aminobutyric acid receptors on chick ciliary ganglion neurons in vivo and in cell culture

Abstract

In the chick ciliary ganglion, preganglionic terminals maintain cholinergic synapses on the choroid neurons and both cholinergic and electrical synapses on the ciliary neurons. The preganglionic terminals also contain enkephalinand substance P-like immunoreactivity, suggesting that transmission through the ganglion is more complicated than is indicated by the known synaptic connections.We report here that embryonic chick ciliary ganglion neurons also have yaminobutyric acid (GABA) receptors and that GABA applied to the ganglion can block transmission elicited by preganglionic stimulation.Studies on the neurons in cell culture indicate that the GABA response is mediated by GABAn receptors: GABA activates a Cl-conductance, and the response can be mimicked by muscimol and blocked by bicuculline or picrotoxin. The GABA receptors are regulated independently from acetylcholine (ACh) receptors on the neurons since the levels of ACh and GABA sensitivity are influenced differently by culture age and by chronic exposure to GABA or elevated K+ concentrations.Application of GABA to intact ciliary ganglia increases the membrane conductance of ganglionic neurons (as in culture), reduces to subthreshold the amplitude of excitatory postsynaptic potentials in the neurons elicited by preganglionic stimulation and completely blocks transmission through the ganglion.A native source of ligand for the receptors in viva has yet to be identified.Autonomic ganglia have been likened to simple relay stations in which little processing or modification of the signal occurs as it is transmitted from preganglionic to postganglionic neurons. This once seemed particularly true for the chick ciliary ganglion where no interneurons or synapses between ganglionic neurons have been identified in vivo. The ganglion contains two populations of neurons: choroid neurons that innervate smooth muscle in the choroid layer, and ciliary neurons that innervate striated muscle in the iris and ciliary body. Both populations of neurons are in turn innervated by preganglionic neurons located in the Edinger-Westphal nucleus of

Sequential Interplay of Nicotinic and GABAergic Signaling Guides Neuronal Development

“…An informative example is the chick ciliary ganglion (CG), which receives nicotinic synaptic input from the accessory oculomotor nucleus and innervates smooth and striated muscle in the eye (7). In addition to nAChRs, CG neurons express GABA A receptors (8) and, we find, receive GABAergic input ( fig. S1).…”

Patch‐clamp analysis of glycine‐induced currents in chick ciliary ganglion neurons.

“…The ability of d-tubocurarine and hexamethonium to block chemical transmission through the ganglion demonstrates the importance of nicotinic receptors in ganglionic function (Landmesser & Pilar 1972, 1974. The neurons also express GABAA receptors capable of blocking ganglionic transmission when activated with micromolar concentrations of exogenous GABA (McEachern, Margiotta & Berg, 1985). Endogenous sources of GABA in the ganglion have yet to be identified.…”

Calcium‐activated chloride current in cultured sensory and parasympathetic quail neurones.

“…Nevertheless, most sensory neurones have ICI(Ca) and most ciliary ganglion neurones do not. It is interesting to mention that chick ciliary ganglion neurones cultured under similar conditions can express another type of chloride channel (McEachern, Margiotta & Berg, 1985). These channels mediate the GABAA response in these neurones.…”