Evidence that adrenaline is released from adrenergic neurones in the rectum of the fowl

Cold stress initiates catecholaminergic and serotonergic responses in the chicken gut that are associated with functional shifts in the microbiome

Climate change is one of the most significant challenges facing the sustainability of global poultry production. Stress resulting from extreme temperature swings, including cold snaps, is a major concern for food production birds. Despite being well-documented in mammals, the effect of environmental stress on enteric neurophysiology and concomitant impact on host-microbiome interactions remains poorly understood in birds. As early life stressors may imprint long-term adaptive changes in the host, the present study sought to determine whether cold temperature stress, a prominent form of early life stress in chickens, elicits changes in enteric stress-related neurochemical concentrations that coincide with compositional and functional changes in the microbiome that persist into the later life of the bird. Chicks were, or were not, subjected to cold ambient temperature stress during the first week post-hatch and then remained at normal temperature for the remainder of the study. 16S rRNA gene and shallow shotgun metagenomic analyses demonstrated taxonomic and functional divergence between the cecal microbiomes of control and cold stressed chickens that persisted for weeks following cessation of the stressor. Enteric concentrations of serotonin, norepinephrine, and other monoamine neurochemicals were elevated (P < 0.05) in both cecal tissue and luminal content of cold stressed chickens. Significant (P < 0.05) associations were identified between cecal neurochemical concentrations and microbial taxa, suggesting host enteric neurochemical responses to environmental stress may shape the cecal microbiome. These findings demonstrate for the first time that early life exposure to environmental temperature stress can change the developmental trajectory of both the chicken cecal microbiome and host neuroendocrine enteric physiology. As many neurochemicals serve as interkingdom signaling molecules, the relationships identified here could be exploited to control the impact of climate change-driven stress on avian enteric host-microbe interactions.

A neurochemical biogeography of the broiler chicken intestinal tract

The study of neurochemical-based interkingdom signaling and its impact on host-microbe interaction is called microbial endocrinology. Neurochemicals play a recognized role in determining bacterial colonization and interaction with the gut epithelium. While much attention has been devoted to the determination of neurochemical concentrations in the mammalian gut to better understand tissue and region-specific microbial endocrinology-based mechanisms of host-microbe interaction, little is known regarding the biogeography of neurochemicals in the avian gut. Greater resolution of avian gut neurochemical concentrations is needed especially as recent microbial endocrinology-based investigations into bacterial foodborne pathogen colonization of the chicken gut have demonstrated neurochemicals to affect Campylobacter jejuni and Salmonella spp. in vivo and in vitro. The aim of the present study was to determine the concentrations of stress-related neurochemicals in the tissue and luminal content of the duodenum, jejunum, ileum, cecum, and colon of the broiler intestinal tract, and to investigate if this biogeography changes with age of the bird. While all neurochemicals measured were detected in the intestinal tract, many displayed differences in regional concentrations. Whereas the catecholamine norepinephrine was detected in each region of the intestinal tract, epinephrine was present only in the cecum and colon. Likewise, dopamine, and its metabolite 3,4-dihydroxyphenylacetic acid were found in the greatest quantities in the cecum and colon. Serotonin and histamine were identified in each gut region. Region-specific age-related changes were observed (P < 0.05) for serotonin, its metabolite 5-hydroxyindole acetic acid as well as for histamine. Several neurochemicals, including norepinephrine, were found in the contents of each gut region. Epinephrine was not detected in the gut content of any region. Salsolinol, a microbial-produced neuroactive compound was detected in the gut content but not in tissue. Together, our data establish a neurochemical biogeography of the broiler chicken intestinal tract. By providing researchers with a region-by-region map of in vivo gut neurochemical concentrations of a modern broiler chicken breed, this neurochemical map is expected to inform future investigations that seek to utilize avian enteric neurochemistry.

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.

Ultrastructure of catecholamine-containing axons in the intestine of the domestic fowl

Axons in the duodenum, ileum and rectum of the domestic fowl were identified as catecholamine-containing (CA) on the basis of positive reactivity following chromaffin fixation for electron microscopy. CA-axons in association with blood vessels in all regions of the intestine and in non-vascular sites in the small intestine had a 'typical' adrenergic appearance, in that they contained many small granular vesicles (SGV) and variable numbers of large granular vesicles (LGV). In the rectum the non-vascular CA-axon profiles were atypical, in that there were many elongated LGV and few SGV, and the chromaffin reactivity was weak. The nerve profiles in the rectum were dramatically reduced following 6-hydroxydopamine and reserpine treatment and were absent in rectum cultured in the absence of extrinsic ganglia. It was concluded that the profiles, in spite of their low chromaffin reactivity, truely represent CA-axons. The possibility was raised that the atypical morphology and reduced chromaffin reactivity is due to the presence of adrenaline.

Catecholamines in the sympathetic nervous system of the domestic fowl

In order to resolve some existing uncertainties regarding the identity of the sympathetic catecholamine neurotransmitter in birds, we have measured endogenous noradrenaline (NA), adrenaline (AD) and dopamine (DA) in various peripheral tissues and in the paravertebral sympathetic chain of the domestic fowl. In all visceral tissues examined - atrium, spleen, mesenteric artery, gizzard, intestine, rectal caecum and kidney--NA concentrations were much higher than those of AD or DA. The ratios of NA:AD:DA were approximately 100:10:1 for all tissues except spleen, in which DA represented about 10% of the total catecholamines. In the paravertebral chain, the ratio of NA:DA was about 4:1, with no consistent segmental differences. Ganglionic AD was generally less than 1% of the total catecholamine, but isolated ganglia sometimes contained quite large amounts of AD. This AD was probably in chromaffin cells. The results obtained indicate that, contrary to some previous reports, NA constitutes the predominant sympathetic neurotransmitter in the fowl, and neurons in which AD is a transmitter are rare or absent. Although the relatively large amounts of DA present in the ganglia could be due to presence of dopaminergic neurons, no evidence for peripheral projections of such neurons was obtained.

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

Adrenergic depression of ganglionic transmission in non-cholinergic, non-adrenergic (NCNA) excitatory nerves was investigated in the isolated chicken rectum with its associated nerve of Remak. Preganglionic stimulation of the NCNA nerves produced contraction of the rectum, an excitatory junction potential and discharges in the postganglionic axons. Preceding stimulation of descending fibers in the nerve of Remak suppressed these responses. These inhibitory effects were almost eliminated in reserpinized preparations, and were significantly reduced by pretreatment with guanethidine and phentolamine, but not with propranolol. Exogenously-applied adrenaline and noradrenaline mimicked the inhibitory effect of nerve stimulation on the discharge in the postganglionic axons. These results indicated that the nerve of Remak contained descending adrenergic fibers, stimulation of which caused suppression of ganglionic transmission in the NCNA excitatory pathways to the rectum, by the activation of alpha-adrenoceptors on the pre- or postganglionic NCNA neuron.

Distribution of vasoactive intestinal polypeptide-, substance P-, enkephalin and neurotensin-like immunoreactive nerves in the chicken gut during development

The ontogeny and distribution of nerve cell bodies and fibres which contain vasoactive intestinal polypeptide-, substance P-, enkephalin- and neurotensin-like immunoreactivity have been studied in the chicken gastrointestinal tract, using immunocytochemistry. All four peptides were found in nerve fibres, with characteristic distribution patterns, which, in the cases of vasoactive intestinal polypeptide, substance P and methionine enkephalin were similar to those described for the mammalian gut. In addition, many of these fibres were shown to arise from intrinsic neurons, since immunoreactive nerve cell bodies for each of the peptides studied were observed. Neurotensin-immunoreactive nerves were confined to the upper part of the tract and neurotensin immunoreactive cell bodies were only observed in embryonic and newly hatched chicken gut. All four peptides were first observed at 11 days of incubation, or Hamburger-Hamilton stage 37, 20 in the upper part of the tract, particularly in the gizzard. Substance P and methionine enkephalin were subsequently seen in more caudal regions, while vasoactive intestinal polypeptide developed from each end of the tract. Adult patterns of immunoreactivity in nerve fibres were achieved during the first week after hatching. A striking observation was that immunoreactive neuronal cell bodies were much more abundant in the gut of young chickens and chicken embryos than in that of adult birds.

The effects of alpha- and beta-adrenoceptor activation on tension and membrane properties of the longitudinal smooth muscle of the chicken rectum

1. Isolated longitudinal muscle strips from the chicken rectum responded to isoprenaline, adrenaline and noradrenaline with a prolonged relaxation. The concentrations required to produce 50% of the maximum relaxation were 1.3 x 10(-8) M for isoprenaline, 1.7 x 10(-8) M for adrenaline and 10(-6) M for noradrenaline. The relaxing potency of isoprenaline is about equal to that of adrenaline, but more than 50 times that of noradrenaline. 2. Propranolol, 3.4 x 10(-6) M, blocked the isoprenaline-induced relaxation, and in the presence of this drug the responses to adrenaline and noradrenaline were converted into small, transient relaxations. The residual relaxation was blocked by phentolamine, 2.6 x 10(-6) M. 3. These catecholamines suppressed spontaneous spike discharge and produced membrane hyperpolarization. Propranolol, 3.4 x 10(-6) M, prevented the inhibitory effects of isoprenaline, and reduced but did not completely abolish those of adrenaline and noradrenaline. 4. Adrenaline and noradrenaline, but not isoprenaline, reduced membrane resistance in some preparations. 5. In the rectal muscle of the chicken, the beta-adrenoceptor mediates a prolonged relaxation and the alpha-adrenoceptor a fast and short-lasting relaxation which is usually obscured by the beta-response and unmasked only after blockade of the beta-adrenoceptors. The alpha- and beta-mediated relaxations are each associated with the suppression of spontaneous spike activity.