Journal of Neuroscience, Vol 7, 3827-3839, Copyright © 1987 by Society for Neuroscience
Cholinergic innervation of the smooth muscle cells in the choroid coat of the chick eye and its development
SD Meriney and G Pilar
Department of Physiology and Neurobiology, University of Connecticut, Storrs 06268.
The mechanical and pharmacological characteristics of the cholinergic
activation of the smooth muscle in the choroidal coat of the chick eye have
been assessed in tissues isolated from birds 1 d posthatching using
histological, electrophysiological, and immunological techniques. The
choroidal coat is innervated by a dense network of cholinergic nerves that
make en passant synapses with smooth muscle. Thirty-hertz stimulation of
these nerves initiates red blood cell (RBC) movement in the vessels of the
choroidal coat, and this activation is blocked by muscarinic ACh receptor
(AChR) antagonists. Force-transducer recordings of nerve-induced
contractions of this tissue have a slow onset and relaxation time course
similar to those of smooth muscle contractions. Furthermore, since nearly
half the cholinergic neurons innervating the choroid die within a defined
period during development, the onset and pharmacology of this innervation
were studied during embryogenesis. With a neural cytoskeletal-like
immunostain, we demonstrated that choroid axons are present in peripheral
tissue by stage (St) 29. Extracellular electrical recordings made after
choroid nerve stimulation allowed us to distinguish axon from muscle
responses. These procedures permitted us to examine the time course of the
innervation of the smooth muscle. However, to visualize the postsynaptic
smooth muscle response, it was necessary to treat the isolated preparation
with tetraethylammonium chloride (TEA). Accordingly, TEA-enhanced
electrical smooth muscle responses to single-nerve stimuli could be
recorded only after St 39. Treatment of the nerve-muscle preparation with
prostigmine allowed the recording of TEA-enhanced electrical activity as
early as St 36 (1 d after the beginning of the normal choroid neuron death
period). This synaptic activation was completely blocked by atropine or
quinuclidinyl benzylate (QNB), and was not affected by alpha bungarotoxin
(alpha BTX), indicating that, as in the posthatching tissue, neuromuscular
transmission is mediated by muscarinic receptors. These results show that
cholinergic muscarinic activation of the choroidal coat can occur as early
as St 36, but that it is not as efficient as transmission later in
embryogenesis.
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