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Presynaptic adrenergic facilitation of parasympathetic neurotransmission in sympathectomized rat smooth muscle
Author(s) -
KrizsanAgbas Dora,
Zhang Renjie,
Marzban Farshid,
Smith Peter G.
Publication year - 1998
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1998.841bd.x
Subject(s) - medicine , endocrinology , cholinergic , bethanechol , phentolamine , phenylephrine , guanethidine , adrenergic , stimulation , prazosin , neurotransmission , parasympathetic nervous system , chemistry , muscarinic acetylcholine receptor , biology , autonomic nervous system , receptor , antagonist , blood pressure , heart rate
1 Parasympathetic innervation of rat eyelid tarsal smooth muscle normally inhibits sympathetic neurotransmission prejunctionally without significant direct postjunctional effects. Following surgical sympathectomy, parasympathetic stimulation elicits smooth muscle contraction. This study examined the relative contributions of cholinergic and adrenergic mechanisms mediating these contractions. 2 Electrical stimulation of the superior salivatory nucleus, which activates tarsal muscle parasympathetic nerves, elicited large contractions at 2 days postsympathectomy, which were abolished by atropine and were decreased by 65 % by α 1 ‐adrenoceptor blockade or spinal cord transection. 3 Contractions in response to direct cholinergic stimulation by bethanechol at 2 days postsympathectomy were increased following spinal cord transection (C2) and suppressed by the α 1 ‐adrenoceptor agonist phenylephrine, indicating that adrenoceptors on smooth muscle attenuate cholinergic contractions. However, phenylephrine infusion enhanced contractile responses to parasympathetic stimulation. 4 Reverse transcription‐polymerase chain reaction revealed α 1D ‐adrenoceptor mRNA within pterygopalatine ganglia. 5 At 5 weeks and 14 months postsympathectomy, adrenergic facilitation was significantly less than at 2 days, whereas prazosin‐insensitive muscarinic contraction was increased. 6 We conclude that degeneration of sympathetic innervation is followed rapidly by adrenoceptor‐mediated prejunctional enhancement of parasympathetic nerve‐smooth muscle neurotransmission, which occurs prior to neuroeffector junction formation as determined previously by electron microscopy. Subsequently, noradrenergic enhancement is diminished as cholinergic neurotransmission becomes established.