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

AE McEachern, JF Margiotta, DK Berg
1985 Journal of Neuroscience  
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 enkephalin-and 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
more » ... (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
doi:10.1523/jneurosci.05-10-02690.1985 pmid:2995607 fatcat:acxv426rhnc5zeh3rx344z3rje