Nerve pathways involved in adrenergic regulation of electrical and mechanical activities in the chicken rectum

Abstract

1 Peripheral nerve pathways responsible for adrenergic inhibition of mechanical and electrical activities in the chicken rectum and receptors mediating the adrenergic inhibition were investigated in isolated extrinsically-innervated rectum of the chicken. 2 Electrical stimulation ofthe anal end (Ra) or the ileal cut end (Ri) of Remak's nerve, or perivascular nerves (P) elicited relaxation of the rectum pretreated with atropine (0.5 JM) and hexamethonium (0.3 mM) to block the cholinergic and non-cholinergic, non-adrenergic excitatory innervations. Ri stimulation was much less effective than Ra and P stimulations. The relaxation was shown to be related to cessation of spontaneous spike discharge of the longitudinal muscle which was accompanied by membrane hyperpolarization. 3 The inhibitory effects elicited by Ra and P stimulations, which were prolonged beyond the period of the stimulation, were converted to transient ones by propranolol (3.4 fAM). Phentolamine (2.6 pM) reduced effectively the residual effects. In contrast, the effects of Ri stimulation were little affected by these drugs. 4 The present results provide evidence for the existence of two nerve pathways responsible for direct adrenergic inhibitory innervation to the chicken rectum, one running orally in Remak's nerve trunk, leaving it and descending in the branches to the rectum, and the other running as the perivascular nerves along the arterial supplies ofthe rectum. The direct innervation is mediated predominantly by 1-adrenoceptors.

Some membrane properties of the circular muscle of chicken rectum and its non‐adrenergic non‐cholinergic innervation.

“…The resting membrane potential ranged between -42 and -68 mV, giving a mean of -55-0±0-6 mV (n = 95). This value was somewhat larger than that of the longitudinal muscle of the chicken rectum (Komori & Ohashi, 1987). Some preparations (70%) were spontaneously active and exhibited spontaneous membrane depolarizations in the early period of each experiment, during which the resting membrane potential was -55 mV or more.…”

“…The membrane depolarizations (referred to as slow action potentials in the Results), which are spontaneous or electrically evoked, in the circular muscle of chicken rectum are similar in temporal parameters and amplitude to the slow waves in other gastrointestinal smooth muscles of many species (see . The slow depolarization is unlikely to be electrotonic spread from the longitudinal muscle, because such slow changes in membrane potential have not been observed in the longitudinal muscle of chicken rectum (Komori et al 1980;Komori & Ohashi, 1987). The effectiveness of D600 in suppressing discharge of the slow depolarization can be interpreted as an indication for involvement of a Ca21 inward current in the generation.…”

“…Nonadrenergic, non-cholinergic neurones whose cell bodies are located in Remak's ganglia (Kanazawa, Ohashi & Takewaki, 1980) are mainly responsible for the excitatory innervation, and excitatory junction potentials are recorded intracellularly from the smooth muscle cells Komori & Ohashi, 1982). Adrenergic nerve fibres innervating the muscle have been also demonstrated in the electrophysiological studies, and electrical stimulation of these fibres at a relatively high frequency produces membrane hyperpolarization, inhibits discharges of the action potentials and in turn causes relaxation (Komori & Ohashi, 1987). Although the circular muscle of chicken rectum has been suggested to play an essential role in storing and expelling the contents, little is known about the electrical membrane properties or about its innervation.…”

Morphology and projections of neurons in Remak's nerve of the domestic fowl revealed by intracellular injection of biocytin

“…Ten birds were killed by an overdose of halothane anaesthetic. The rectum, jejunum and attached mesentery with Remak's nerve and blood vessels were quickly excised and immersed into cold modified Krebs'-Henseleit solution: 118.9 mM NaCl, 4.6 mM KCl, 1.8 mM CaCl 2 , 2.4 mM MgSO 4, 1.2 mM KH 2 PO 4 , 25.0 mM NaHCO 3 and 11.1 mM glucose bubbled with 5% CO 2 and 95% O 2 (Komori and Ohashi 1987) maintained at 4°C. The gut contents were flushed from the lumen and the tissue washed in several changes of fresh Krebs' solution.…”

“…Electrophysiological and pharmacological studies have demonstrated that Remak's nerve participates in the regulation of gut motility (Bartlet and Hassan 1971;Hodgkiss 1984a,b;Komori et al 1986Komori et al , 1988Komori and Ohashi 1987). The nature of this control is unknown.…”