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Br J Pharmacol. 1974 Oct; 52(2): 175–190.
PMCID: PMC1776873

The rabbit rectococcygeus

A ganglion-free, parasympathetically innervated preparation


1 Isolated, desheathed preparations of the rabbit rectococcygeus muscle were relatively insensitive to spasmogens other than muscarinic drugs. Transmural stimulation with 1-50 pulses (0.2-0.4 ms at 10 Hz) elicited graded twitches which were abolished by tetrodotoxin and were therefore neurogenic; longer pulses sometimes triggered tetrodotoxin-resistant myogenic contractions.

2 Twitches elicited by 0.2-0.4 ms pulses were due to post-ganglionic excitation because they were not reduced by hexamethonium, pentolinium or dimethyltubocurarine, or by ganglion-paralyzing concentrations of nicotine.

3 The acetyl- and butyryl-cholinesterase activities of the rectococcygeus were determined manometrically and could be selectively inhibited by BW 284C51 (1:5-bis-(4-allyl-dimethylammonium-phenyl)-pentan-3-one dibromide) and iso-OMPA (tetramonoisopropylpyrophosphortetramide), respectively. Single-pulse twitches were greatly potentiated in amplitude and duration only when both cholinesterases were inhibited.

4 The preparations could not be made to contract by nicotine (2.1-21 μM) even after cholinesterase inhibition, suggesting an absence of ganglion-cells; with nicotine (105-210 μM) small, atropine-susceptible responses were elicited, which were non-ganglionic because they were not reduced by tetrodotoxin.

5 Rectococcygeus preparations that had been treated with physostigmine released acetylcholine into the bath fluid on electrical stimulation.

6 The motor transmission was paralyzed by botulinum toxin (Type A) and abolished by atropine; the block of muscarinic receptors by atropine was effective against both endogenous and exogenous acetylcholine.

7 Inhibitory adrenoceptors and scanty motor α-adrenoceptors were detected in the smooth muscle.

8 Strong inhibitions of motor transmission and of rhythmic activity were produced by noradrenaline (but not by tyramine), by isoprenaline, and, after phentolamine, also by adrenaline and phenylephrine. These inhibitions were only slightly reduced by propranolol and rather more by pindolol.

9 Experiments on preparations retaining their extrinsic nerve supply suggest an absence of ganglionic relays in the last 1-2 cm of the motor nerve pathway to this muscle.

10 Some contrasting properties of the adjacent caudo-anal muscle, including the poor motor responses to transmural stimulation, are described.

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Selected References

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  • Ambache N, Freeman MA, Hobbiger F. Distribution of acetylcholinesterase and butyrylcholinesterase in the myenteric plexus and longitudinal muscle of the guinea-pig intestine. Biochem Pharmacol. 1971 Jun;20(6):1123–1132. [PubMed]
  • Ambache N, Verney J, Zar MA. Evidence for the release of two atropine-resistant spasmogens from Auerbach's plexus. J Physiol. 1970 May;207(3):761–782. [PMC free article] [PubMed]
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  • McKirdy HC. Functional relationship of longitudinal and circular layers of the muscularis externa of the rabbit large intestine. J Physiol. 1972 Dec;227(3):839–853. [PMC free article] [PubMed]
  • PATON WD. The action of morphine and related substances on contraction and on acetylcholine output of coaxially stimulated guinea-pig ileum. Br J Pharmacol Chemother. 1957 Mar;12(1):119–127. [PMC free article] [PubMed]
  • Paton WD, Vizi ES. The inhibitory action of noradrenaline and adrenaline on acetylcholine output by guinea-pig ileum longitudinal muscle strip. Br J Pharmacol. 1969 Jan;35(1):10–28. [PMC free article] [PubMed]
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  • SCHAUMANN W. Influence of atropine and morphine on the liberation of acetylcholine from the guinea pig's intestine. Nature. 1956 Nov 17;178(4542):1121–1122. [PubMed]
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