Evidence for adrenergic modulation of ganglionic transmission in the ganglia of the nerve of Remak of the chicken

Distribution of vasoactive intestinal peptide and substance P messenger ribonucleic acid in intestinal nerve of Remak of chicken

The intestinal nerve of Remak (INR) is unique to birds. The exact distributions and secretions of the peptide transmitters in the INR that innervate the intestine, and the patterns of their projections to the nerve plexus of the intestinal wall, are still unclear. In the present study, the distributions of chicken vasoactive intestinal peptide (VIP) mRNA and substance P (SP) mRNA in the chicken INR were demonstrated by means of in situ hybridization histochemistry, using sense and antisense digoxigenin-labeled RNA probes. The in situ hybridization histochemistry results suggested that VIP mRNA-positive neurons were mainly distributed in ganglions, whereas some of the INR fibers were weakly positive. The proportion of VIP mRNA-positive cells among total neurons was 75% in the juxta-jejunoileum portion and 87% in the juxta-rectal portion of the INR. Most SP mRNA-positive cells were sporadically distributed in layers or small groups within the ganglions, as well as in nerve trunks between ganglions. Moreover, the proportion of positive cells among total neurons was 83% in the juxta-jejunoileum portion and 98% in the juxta-rectal portion of the INR, which suggests that both VIP and SP mRNA are coexpressed in the chicken INR. Our results provide an approach to further study of the locations of VIP and SP in nerve tissue.

The sympathetic postganglionic and sensory innervation of oviducal magnum in hen: a choleratoxin subunit B-conjugated horseradish peroxidase study

The anatomy of the extrinsic innervation of the avian magnum has not been accurately demonstrated previously. In the present study, choleratoxin subunit B-conjugated horseradish peroxidase (CB-HRP) was used as a retrograde tracer to determine the sympathetic postganglionic and sensory innervation of the magnum of hens. With regard to the sympathetic postganglionic innervation, following CB-HRP injections under the serosa of the magnum, CB-HRP-positive neurons were found bilaterally in the C12-LS13 ganglia of the sympathetic chain, splanchnic ganglia and adrenal ganglia. The number of labelled neurons in the left ganglia of the sympathetic chain and splanchnic ganglia was approximately 2.1 times that in the right ganglia. This suggests that the unilateral magnum is bilaterally innervated with sympathetic postganglionic nerves, the left nerves being predominant. With regard to the sensory innervation, following tracer injections, CB-HRP-positive neurons were found bilaterally in the spinal ganglia C13-LS12, jugular ganglia and nodose ganglia. The number of positive cells in the left ganglia was about 2.2 times that in the right ganglia. In the spinal ganglia, 85.6% of the labelled neurons were in the T5-LS2 and LS8-LS11 ganglia. These results suggest that the sensory nerve fibres of the magnum reach the central nervous system principally via two groups of spinal ganglia and vagus nerves, and that the innervation is bilateral although the left-hand route predominates. Moreover, 45.7% of all the CB-HRP-labelled neurons were found in the rectal region of the intestinal nerve of Remak (INR), which suggests that the INR plays a very important role in the functional regulation of the magnum.

Electrical characteristics and responses to jejunal distension of neurons in Remak's juxta-jejunal ganglia of the domestic fowl

1. Remak's nerve is a ganglionated nerve trunk found only in birds that runs parallel to the gut from the duodenal-jejunal junction to the cloaca. We report the first electrophysiological characterization of these neurons and their responses to gut distension. 2. A segment of chicken jejunum with attached Remak's nerve was pinned in an electrophysiological chamber. Neurons in Remak's ganglia were impaled with microelectrodes. The adjacent segment of gut was distended with fluid. 3. One hundred and thirty neurons were characterized into three electrophysiological classes: (i) tonic neurons (74%) fired action potentials spontaneously (frequency 3.5 Hz) and continuously (up to 40 Hz) throughout a depolarizing current pulse; (ii) AD neurons (22%) fired a brief burst of action potentials (1-10), which were followed by a prolonged after-depolarization (AD) of duration 2.8 +/- 0.3 s; and (iii) phasic neurons (4%) fired an initial burst of action potentials followed by an after-hyperpolarization (duration, 520.0 +/- 32.0 ms). Tetrodotoxin (1 microM) abolished action potentials in tonic and AD neurons as well as the after-depolarization. 4. Spontaneous fast excitatory postsynaptic potentials (FEPSPs) occurred in all classes of neurons; they were not observed, however, in ganglia isolated from the jejunum. 5. Intracellular injection of biocytin revealed that neurons could be characterized into four morphological classes. Tonic neurons, which had long and extensive dendritic trees, were Remak's Type I, II and IV neurons. AD neurons also comprised Remak's type II neurons. Phasic neurons were Remak's Type III neurons. Most neurons had axons that projected orally along Remak's nerve. 6. Distension of the jejunum evoked FEPSPs and action potentials in tonic neurons, and repetitive bursts of action potentials (1-4) followed by an after-depolarization in AD neurons. All responses to distension were blocked by hexamethonium (300 microM) and tetrodotoxin (1 microM). 7. In conclusion, neurons in Remak's juxta-jejunal nerve appear to regulate gut motility. Three distinct electrophysiological classes of neurons were observed, all of which appear to be activated by distension sensitive cholinergic intestinofugal neurons in the jejunum.

Calbindin, tyrosine hydroxylase and opioid-like immunoreactivity in the intestinal nerve of Remak of the domestic fowl

Four classes of neurons were identified in both juxta-jejunal and juxta-rectal ganglia of Remak's nerve of the domestic fowl using double-labeling immunohistochemistry. Neurons immunoreactive (IR) for tyrosine hydroxylase (TH) formed a mutually exclusive subpopulation from neurons displaying calbindin (CaBP)-IR. Between 48-72% of juxta-jejunal neurons labeled for TH whereas 36-57% of juxta-rectal neurons displayed TH-IR. CaBP-IR was present in 18-40% of juxta-jejunal neurons; this increased to 31-46% in juxta-rectal neurons. The majority of CaBP-IR neurons (78-85%) also displayed opioid (beta-EP)-IR. Within each ganglion a small percentage of neurons (4-18%) were non-IR with any of the three antibodies. This is the first report of an immunohistochemically identified subpopulation of non-catecholaminergic neurons within the juxta-jejunal ganglia of Remak's nerve. It is proposed that these perikarya are a major source of the CaBP-IR and opioid-IR nerve fibers found in the chicken gut.

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

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. Electrical stimulation of the 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 microM) 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. 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 microM). Phentolamine (2.6 microM) reduced effectively the residual effects. In contrast, the effects of Ri stimulation were little affected by these drugs. 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 of the rectum. The direct innervation is mediated predominantly by beta-adrenoceptors.

A study of pre- and postganglionic fibres in the intestinal nerve (Remark's nerve) of the chicken

The mean peak CV's of two electrophysiologically defined groups of fibres in the intestinal nerve of the chicken have been determined. One group of fibres is constituted by the processes of enteric cholinergic neurones which project along the side branches of the intestinal nerve and synapse within the nerve trunk. These preganglionic fibres have a mean peak CV (at 40 degrees C) of 0.31 m x s-1. The other group is made up of fibres of postganglionic neurones which project orally along the nerve trunk. The results suggest that some postganglionic neurones project only as far as the next ganglion whilst others project beyond the next two ganglia for distances greater than 5 mm. The postganglionic fibres have a mean peak CV (at 40 degrees C) of 0.71 m X s-1. These figures demonstrate that both pre- and postganglionic fibres are unmyelinated. The temperature coefficient (Q10) for the CV of unmyelinated fibres in the intestinal nerve was 1.57.

The conduction velocity, number, and diameter of unmyelinated fibers in Remak's nerve

Remak's nerve in the chicken was examined ultrastructurally and electrophysiologically to determine the characteristics of fibers in the nerve trunk. The ration of unmyelinated fibers to myelinated ones was 111:1. The mean number of unmyelinated fibers was 3555 plus/minus 232 (SEM, n=5) and they had a mean diameter of 0.502 plus/minus 0.034 (SEM) micron. The compound action potential consisted almost entirely of a large diphasic waveform which had a mean peak conduction velocity of 0.62 plus/minus 0.031 (SEM, n=5) m.s-1 at 37 degrees C.