Neuropeptide Y-like immunoreactivity is absent from most perivascular noradrenergic axons in a marsupial, the brush-tailed possum

Galanin modulates cholinergic neurotransmission in the heart

The role of galanin (Gal) in the modulation of cholinergic neurotransmission in the heart in wild-type (129 SvJ), and GALR1 knockout mice has been studied. The mice were anaesthetised and ventilated. Blood pressure (BP) and the increase in pulse interval evoked by stimulation of the vagus nerve (deltaPI) were recorded. Resting BP and PI were not different in control and GALR1-KO mice. In control mice an intravenous, bolus injection of Gal (0.8-13 nmol/kg; n = 4-6) attenuated the deltaPI, dose dependently from 33 +/- 7% to 78 +/- 9.5%. In GALR1-KO mice, Gal (0.8-13 nmol/kg) did not attenuate deltaPI at any dose (n = 3-4). In control mice intravenous, bolus injection of neuropeptide Y (NPY; 0.5-10 nmol/kg, n = 5-7) attenuated the deltaPI by 13 +/- 10% to 67 +/- 7% with a half time to recovery of 0.5-5 +/- 1 min. In control mice, following activation of the cardiac sympathetic nerve (10 Hz for 2 min; n = 3) the deltaPI was attenuated by 92 +/- 2% with a half time to recovery of 7 +/- 1 min. In control mice in the presence of the beta-adrenoceptor antagonist propranolol (1 mg/kg), and 1 micromol/kg BIIE0426 (an NPY Y2 receptor antagonist) the deltaPI was 57+/-3% with a half time to recovery of 2.5+/-0.5 min. In GALR1-KO mice, in the presence of propranolol and BIIE0426 there was no inhibition of deltaPI. In mice, it is proposed that both Gal and NPY contribute to the prolonged attenuation of parasympathetic slowing of the heart following activation of the cardiac sympathetic nerve.

Two populations of sympathetic neurons project selectively to mesenteric artery or vein

The objective of this study was to determine whether sympathetic neurons of the inferior mesenteric ganglion (IMG) projecting to mesenteric arteries could be distinguished by their localization, neurochemical phenotype, and electrophysiological properties from neurons projecting to mesenteric veins. In an in vitro intact vasculature-IMG preparation, neurons were labeled following intraluminal injection of Fluoro-Gold or rhodamine beads into the inferior mesenteric artery (IMA) or vein (IMV). The somata of neurons projecting to IMA were localized in the central part of the IMG, whereas those projecting to IMV were localized more peripherally. None of the labeled neurons was doubly labeled. Neuropeptide Y immunoreactivity was found in 18.9% of neurons innervating the IMA, but not in neurons innervating the IMV. Identified neurons were dissociated and characterized using whole cell patch-clamp recording. After direct soma depolarization, all of the labeled arterial and venous neurons were classified as tonic firing, compared with only 40% of unlabeled neurons; the remaining 60% of unlabeled neurons were phasic firing. The results indicate that IMG neurons projecting to mesenteric arteries are distinct from neurons projecting to mesenteric veins.

Substance P stimulates sphincter of Oddi motility and inhibits trans-sphincteric flow in the Australian brush-tailed possum

Substance P containing nerves are widely distributed throughout the gastrointestinal tract. The aims of this study were to determine the distribution of substance P containing nerves in the extrahepatic biliary tree of the Australian brush-tailed possum and to characterize the effect of exogenous substance P on the sphincter of Oddi (SO) motility and transphincteric flow in vivo. Immunohistochemical staining of fixed specimens (n = 8) found moderate numbers of substance P containing nerve cell bodies and fibres throughout the neural plexuses of the SO, in particular in the serosal and intraluminal nerve trunks of the SO and gallbladder. Synthetic porcine substance P (1-2000 ng kg-1), administered by close intra-arterial injection (i.a.; n = 7), produced a dose-dependent elevation in basal pressure [P < 0.01] and an associated dose-dependent reduction in trans-sphincteric flow [P < 0.0001]. Substance P had no significant dose-dependent effect on SO phasic contraction amplitude or frequency. Tetrodotoxin (9 micrograms kg-1, i.a.) did not inhibit the effect of substance P on SO motility and trans-sphincteric flow (n = 5). In conclusion, substance P containing nerves are found throughout the possum extrahepatic biliary tree. Exogenous substance P stimulates SO motility and reduces trans-sphincteric flow in vivo by acting directly on the sphincter smooth muscle.

Non-noradrenergic sympathetic neurons project to extramuscular feed arteries and proximal intramuscular arteries of skeletal muscles in guinea-pig hindlimbs

This study set out to examine the non-noradrenergic sympathetic innervation of extramuscular and intramuscular arterial vessels supplying hindlimb muscles of guinea-pigs, using multiple-labelling fluorescence immunohistochemistry. Non-noradrenergic axons, identified by their immunoreactivity (IR) to vasoactive intestinal peptide (VIP) and neuropeptide Y (NPY), innervated nearly all (> or = 88%) extramuscular feed arteries supplying muscles of the medial thigh. The distribution of non-noradrenergic axons along extramuscular feed arteries was often patchy, with increased density near some branch points. The density of axons with VIP-IR and NPY-IR at the adventitia-medial junction of the largest extramuscular arteries was similar to the density of noradrenergic axons identified by IR to tyrosine hydroxylase (TH) and NPY. The proportion of arterial vessels innervated by VIP-IR axons decreased in more distal, intramuscular arterial segments, and when present, the VIP-IR axons were fewer in number than TH-IR axons innervating the same segments. Distal arterioles (< 20 microns diameter) were never innervated by VIP-IR axons, but always by TH-Ir axons. The non-noradrenergic sympathetic neurons are almost certainly vasodilator neurons. The prominent innervation of extramuscular feed arteries by sympathetic non-noradrenergic neurons has not been reported previously, even in cats and dogs where there is good physiological evidence for a sympathetic vasodilator response in skeletal muscles. The present morphological results provide compelling reasons for re-evaluating the functional role of sympathetic vasodilation in skeletal muscles of rodents, particularly in relation to the role of feed arteries in neural regulation of muscle blood flow.

Selective regional vasoconstriction underlying pressor effects of galanin in anaesthetized possums compared with cats

1. Intravenous administration of porcine galanin (5 nmol kg-1) caused a rise in mean blood pressure in the brush-tailed possum, Trichosurus vulpecula, from 58 +/- 1.6 to 106 +/- 1.6 mmHg. This effect is in contrast to the cat, in which no significant change in blood pressure was recorded in response to galanin (88 +/- 2.3 vs. 86 +/- 2.4 mmHg). 2. Cardiac output and regional blood flow distribution were assessed by distribution of radioactive microspheres in four anaesthetized possums and four cats, before and after administration of galanin. 3. Cardiac output was 289.8 +/- 14.0 ml min-1 in the cat and 189.9 +/- 25.5 ml min-1 in the possum. Galanin administration did not significantly change cardiac output in either species. 4. In the possum, galanin administration caused large increases in resistance to flow in the spleen, gut, adrenal glands, kidney, skin and carcass. The largest increase was in the kidneys, where renal blood flow fell to 6% of control levels. 5. In the cat, changes in resistance were small. Small increases in resistance to flow in muscle and carcass were offset by small decreases in resistance in the lungs and kidneys. 6. The results suggest that the pressor effect of galanin in the possum is the result of direct vasoconstrictor action in several vascular beds, in contrast to the cat, in which such effects are few and weak.

Innervation of the monotreme gastrointestinal tract: a study of peptide and catecholamine distribution

The distribution of neurons and endocrine cells containing various peptides or catecholamines was examined in the digestive tracts of the echidna (Tachyglossus aculeatus) and the platypus (Ornithorhynchus anatinus). Comparisons were made with published studies in other species in order to obtain a broader view of the phylogenetic distribution and possible functions of gut peptides and catecholamines. Further comparisons between the echidna and platypus were made in light of their different dietary features and gut histology. The distribution of neurons and axons containing catecholamines or various peptides resembled that in other species (such as the frequent appearance of axons containing substance P and vasoactive intestinal peptide in the intestinal mucosa, and axons containing substance P or enkephalins in the circular muscle). In both species, the stomach histologically resembles the esophagus, being aglandular and lined with stratified squamous epithelium. Innervation of these two organs was similar but not identical, with a greater array of peptides found in the gastric muscle. The intestinal mucosa was densely innervated in both species. The platypus small intestine is unusual in having a thick and deeply folded mucosa (but no villi), in which the superficial epithelium is absent or incomplete at many sites; many axons travel close to these luminal surfaces. Many (putative noradrenergic) axons associated with blood vessels contained neuro-peptide Y, but there was no evidence for intrinsic catecholamine-containing neurons. Somatostatin and cholecystokinin were present in some endocrine cells, but unlike many mammals, absent in neuronal tissue. These studies have shown that there are many strong similarities between monotremes and other mammals in the distribution and array of peptides found within nervous and endocrine tissues of the digestive tract. However, numerous small differences of the echidna and platypus innervation may be correlated with their different digestive structures.

Inhibition of cardiac vagal action by galanin but not neuropeptide Y in the brush-tailed possum Trichosurus vulpecula

1. Stimulation of the right cardiac sympathetic nerve for 2 min at 16 Hz in the presence of either beta- or alpha- and beta-adrenoceptor blockade evoked attenuation of cardiac vagal action in eight possums: 31.3 +/- 10.3% maximum inhibition of cardiac vagal action on prolonging pulse interval, with a time to half-recovery of 4.9 +/- 1.1 min. 2. Intravenous injection of galanin (2-3.5 nmol kg-1) evoked similar inhibition of cardiac vagal action: 41.3 +/- 4.1% maximum inhibition of cardiac vagal action on pulse interval, with a time to half-recovery of 13.4 +/- 2.3 min. 3. Intravenous injection of neuropeptide Y (NPY) at greater molar doses (6.5-10 nmol kg-1) caused no inhibition of cardiac vagal action. 4. The galanin injections caused a powerful pressor response: 57.1 +/- 4.9 mmHg increase in systolic blood pressure. NPY caused a smaller pressor response, despite administration of higher molar doses: 36.7 +/- 3.0 mmHg increase in systolic blood pressure. 5. In the possum, galanin but not NPY can mimic the effects of cardiac sympathetic nerve stimulation on vagal action. Galanin also causes large pressor effects.

The distribution and colocalization of neuropeptides in perivascular nerves innervating the large arteries and veins of the snake, Elaphe obsoleta

Single- and dual-labelling immunohistochemistry were used to determine the distribution and coexistence of neuropeptides in perivascular nerves of the large arteries and veins of the snake, Elaphe obsoleta, using antibodies for vasoactive intestinal polypeptide, substance P, calcitonin gene-related peptide, neuropeptide Y, galanin, somatostatin, and leu-enkephalin. Blood vessels were sampled from four regions along the body of the snake: region 1, arteries and veins anterior to the heart; region 2, central vasculature 5 cm anterior and 10 cm posterior to the heart; region 3, arteries and veins in a 30-cm region posterior to the liver; and region 4, dorsal aorta and renal arteries, renal and intestinal veins, 5-30 cm cephalad of the vent. A moderate to dense distribution of vasoactive intestinal polypeptide-like immunoreactive fibres was found in most arteries and veins of regions 1-3, but fibres were absent from the vessels of region 4. The majority of vasoactive intestinal polypeptide-like immunoreactive fibres contained colocalized substance P-like immunoreactivity, and these fibres were unaffected by either capsaicin or 6-hydroxydopamine (6-OHDA) pretreatment. In the anterior section of the snake, the vagal trunks contained many cell bodies with colocalized vasoactive intestinal polypeptide and substance P-like immunoreactivity. It is suggested that the vasoactive intestinal polypeptide/substance P-like immunoreactive cell bodies and fibres are parasympathetic postganglionic nerves. Neuropeptide Y-like immunoreactive fibres were observed in all arteries and veins, being most dense in regions 3 and 4. The majority of these fibres also contained colocalized galanin-like immunoreactivity, and were absent in tissues from 6-OHDA pretreated snakes, suggesting that neuropeptide Y and galanin are colocalized in adrenergic nerves. A small number of neuropeptide Y-like immunoreactive fibres contained vasoactive intestinal polypeptide but not galanin, and were unaffected by 6-OHDA treatment. All calcitonin gene-related peptide-like immunoreactive fibres contained colocalized substance P-like immunoreactivity, and these fibres were observed in all vessels, being particularly dense in the carotid artery and jugular veins. All calcitonin gene-related peptide/substance P-like immunoreactive fibres appeared damaged after capsaicin treatment suggesting they represent fibres from afferent sensory neurons. A sparse plexus of somatostatin-like immunoreactive fibres was observed in the vessels only from region 4. No enkephalin-like immunoreactive fibres were found in any blood vessels from any region. This study provides morphological evidence to suggest that there is considerable functional specialization within the components of the rat snake peripheral autonomic system controlling the circulation, in particular the regulation of venous capacitance.

Projections and pathways of submucous neurons to the mucosa of the guinea-pig small intestine

Double-labelling immunohistochemistry and retrograde transport of the carbocyanine dye, DiI, were used to establish the pathways of submucous neurons to the mucosa of the guinea-pig small intestine. Following the application of DiI to a villus, DiI-labelled nerve cell bodies were found in the submucous plexus up to 8.3 mm circumferentially and 3.8 mm longitudinally. The size of each of the four characterised classes of submucous neurons was determined and their distributions and projections mapped. Cells characterised by vasoactive intestinal polypeptide immunoreactivity accounted for 52% of DiI-labelled cells and had the longest projections. Cells characterised by neuropeptide Y (19%) or by calretinin immunoreactivity (13% of all DiI-labelled neurons) had relatively short projections and cells with substance P immunoreactivity (20%) had intermediate lengths of projection. When DiI was applied directly to the submucous plexus, filled neurons of all classes had significantly shorter projections, indicating that they must run for considerable distances in other pathways to the mucosa, probably via the non-ganglionated plexus. On average, each villus is innervated by at least 70 submucous neurons. From quantitative estimates there are 9 submucous neurons per villus. Thus, each submucous neuron is likely to supply about 8 villi. This demonstrates a high degree of convergence and divergence in the innervation of the mucosa.

Vasoconstrictor, vasodilator and pilomotor pathways in sympathetic ganglia of guinea-pigs

Triple-labelling immunofluorescence and retrograde axonal tracing with fluorescent dyes have been combined to identify and characterize the neuropeptide content of vasoconstrictor, vasodilator and pilomotor neurons in the lumbar sympathetic ganglia of guinea-pigs. Postganglionic noradrenergic pilomotor neurons lacked immunoreactivity to neuropeptide Y and comprised up to about 30% of postganglionic neurons. Most post-ganglionic noradrenergic neurons that contained neuropeptide Y immunoreactivity were likely to be vasoconstrictor neurons, although some noradrenergic neurons containing neuropeptide Y projected to pelvic viscera. Vasoconstrictor neurons comprised up to about 60% of postganglionic neurons. About 15% of postganglionic neurons were non-noradrenergic and contained immunoreactivity to vasoactive intestinal peptide, neuropeptide Y and dynorphin. They mostly innervated blood vessels supplying skeletal muscles and were likely to be vasodilator neurons. Endings of presumed preganglionic neurons containing immunoreactivity to substance P were exclusively associated with vasodilator neurons. Conversely, presumed preganglionic endings containing immunoreactivity to calcitonin gene-related peptide were exclusively associated with vasoconstrictor neurons, although not all vasoconstrictor neurons had such endings associated with them. Presumed preganglionic terminals containing immunoreactivity to enkephalin were associated with some postganglionic neurons in each functional class. These results show that preganglionic and postganglionic sympathetic neurons lying in different functional pathways can be distinguished by their neuropeptide content as well as their projections. The identification of neurochemically distinct functional pathways begins to explain how the sympathetic nervous system is organized to allow the precise control of discrete target tissues.

Galanin is more common than NPY in vascular sympathetic neurons of the brush-tailed possum

The distribution of galanin (Gal) in sympathetic vascular neurons of adult and juvenile brush-tailed possums (Trichosurus vulpecula), was examined using double-labelling immunohistochemistry. This was compared with the distribution of neuropeptide Y (NPY) in the same tissues. Immunoreactivity (IR) to galanin was present in the majority (64-99%) of nerve cell bodies in paravertebral sympathetic ganglia, where it mostly co-existed with IR to the catecholamine-synthesizing enzyme, tyrosine hydroxylase (TH). Gal-IR also was present in most, if not all, TH-IR perivascular axons supplying systemic arteries and veins. NPY-IR was less common than Gal-IR in all sympathetic ganglia and perivascular axons examined. Some sympathetic, TH-IR axons supplying the abdominal aorta and renal artery contained both Gal-IR and NPY-IR, while TH-IR axons supplying cephalic and thoracic vessels contained Gal-IR but not NPY-IR. Limited observations on sympathetic neurons in two species of wallabies indicated that Gal-IR also was more common than NPY-IR in other marsupial species, but the incidence of NPY-IR was higher in these wallabies than in the brush-tailed possum. Together with previous studies, this work suggests that the coexistence of galanin and NPY may be the primitive condition for sympathetic neurons in tetrapods. The differential expression of these peptides in specific populations of sympathetic neurons may have important functional consequences in the autonomic control of the circulation.

Vasomotor, pilomotor and secretomotor neurons distinguished by size and neuropeptide content in superior cervical ganglia of mice

Populations of postganglionic sympathetic neurons projecting to cranial targets from the superior cervical ganglia of mice were identified by retrograde axonal tracing with Fast blue combined with double-labelling immunofluorescence to detect immunoreactivity to tyrosine hydroxylase and neuropeptide Y. Nearly all neurons in the ganglion contained tyrosine hydroxylase immunoreactivity, but only about 50% of them also contained immunoreactivity to neuropeptide Y. The maximum diameter of cells with immunoreactivity to neuropeptide Y was significantly smaller than that of cells without it. Terminal axons containing immunoreactivity to both neuropeptide Y and tyrosine hydroxylase occurred around blood vessels supplying most cranial tissues, including the skin. Axons with immunoreactivity to tyrosine hydroxylase but not to neuropeptide Y innervated the piloerector muscles and the acini of the salivary glands. After injection of Fast blue into the skin or the submandibular salivary gland, populations of vasomotor, pilomotor and secretomotor neurons could be distinguished by soma size and by neuropeptide Y immunoreactivity. Neurons projecting to the salivary glands were the largest (mean diameter: 32 microns) and lacked immunoreactivity to neuropeptide Y; neurons projecting to cutaneous blood vessels were the smallest (mean diameter: 19 microns) and contained immunoreactivity to neuropeptide Y; neurons projecting to piloerector muscles were intermediate in size (mean diameter: 23 microns) and lacked neuropeptide Y immunoreactivity. A cluster analysis procedure confirmed that soma size and peptide content together identify major functional populations of neurons in the superior cervical ganglia of mice.

Effects of cervical sympathetic nerve stimulation and neuropeptide Y (NPY) on cranial blood flow in the cat

Effects of cervical sympathetic nerve stimulation (SNS) at 10 Hz and intravenous infusion of neuropeptide Y (NPY), 10 and 100 pmol x kg body wt-1 x min-1 for 5 min, on regional blood flow in the cat were investigated with radioactive microspheres. Sympathetic nerve stimulation caused significant reductions in blood flows in the facial tissues including the eye. Alpha-adrenoceptor blockade with phenoxybenzamine and combined beta- and alpha-adrenoceptor blockade with propranolol and phenoxybenzamine abolished the effects of sympathetic nerve stimulation in most facial tissues except in the tongue, upper eyelid and masseter muscle. In most cranial tissues, neuropeptide Y reduced regional blood flow and increased vascular resistance. No effect of neuropeptide Y on vascular resistance was observed in the choroid. In the present study, evidence for a non-adrenergic component in sympathetic vasoconstriction was found in the tongue, upper eyelid and masseter muscle but not in the majority of feline facial tissues. Neuropeptide Y was a potent vasoconstrictor in many cranial tissues, while in parts of the uvea, the effects of neuropeptide Y were less pronounced.

Calretinin immunoreactivity in cholinergic motor neurones, interneurones and vasomotor neurones in the guinea-pig small intestine

Immunoreactivity for calretinin, a calcium-binding protein, was studied in neurones in the guinea-pig small intestine. 26 +/- 1% of myenteric neurones and 12 +/- 3% of submucous neurones were immunoreactive for calretinin. All calretinin-immunoreactive neurones were also immunoreactive for choline acetyltransferase and hence are likely to be cholinergic. In the myenteric plexus, two subtypes of Dogiel type-I calretinin-immunoreactive neurones could be distinguished from their projections and neurochemical coding. Some calretinin-immunoreactive myenteric neurones had short projections to the tertiary plexus, and hence are likely to be cholinergic motor neurones to the longitudinal muscle. Some of these cells were also immunoreactive for substance P. The remaining myenteric neurones, immunoreactive for calretinin, enkephalin, neurofilament protein triplet and substance P, are likely to be orad-projecting, cholinergic interneurones. Calretinin immunoreactivity was also found in cholinergic neurones in the submucosa, which project to the submucosal vasculature and mucosal glands, and which are likely to mediate vasodilation. Thus, calretinin immunoreactivity in the guinea-pig small intestine is confined to three functional classes of cholinergic neurones. It is possible, for the first time, to distinguish these classes of cells from other enteric neurones.

Three types of neurochemically defined autonomic fibres innervate the carotid baroreceptor and chemoreceptor regions in the guinea-pig

The innervation of the carotid body, carotid sinus, and neighbouring arteries (common carotid artery; external carotid artery; occipital artery; ascending pharyngeal artery) was investigated in guinea-pigs by means of glyoxylic acid-induced catecholamine-fluorescence and immunohistochemistry using a variety of antisera against neuropeptides and tyrosine hydroxylase (TH). Fibres displaying catecholamine-fluorescence, TH- and neuropeptide Y-like immunoreactivity (NPY-LI) were less numerous in the carotid sinus than in all other arterial segments. Vasoactive intestinal polypeptide (VIP)-LI axons were almost lacking in the common carotid, external carotid and occipital arteries, consistently found in the carotid sinus, and more numerous in the ascending pharyngeal artery. Catecholaminergic, TH-, NPY- and VIP-LI fibres were observed deep in the media of the carotid sinus, where the baroreceptor terminals are located. In contrast, they did not enter the media in the adjacent arterial segments. All these fibres disappeared following excision of the superior cervical ganglion, but were unaffected by combined transection of the carotid sinus nerve and resection of the no-dose ganglion, suggesting a sympathetic origin. Double-staining immunofluorescence revealed at least three types of autonomic, presumably sympathetic fibres in the carotid sinus: 1) TH+/NPY+, 2) NPY+/VIP+, and 3) VIP+ fibres. This points to a non-noradrenergic efferent innervation of the carotid sinus in addition to the hitherto known noradrenergic sympathetic fibres. The three populations of autonomic fibres seen in the carotid sinus were also observed in the carotid body, but the paucity of NPY+/VIP+ double-labelled fibres raises doubt as to the functional significance of this particular fibre type in modulating arterial chemoreception. The multiplicity of neurochemically defined autonomic nerves to the carotid baro- and chemoreceptor regions probably reflects functionally separate pathways that are differently regulated and exert different effects.

Sympathetic noradrenergic neurons containing dynorphin but not neuropeptide Y innervate small cutaneous blood vessels of guinea-pigs

We have used double-labelling immunofluorescence techniques and retrograde axonal transport of Fast Blue to characterize three populations of sympathetic noradrenergic neurons innervating blood vessels in the hairless skin of the ears and paws of guinea-pigs. Each population of neurons innervated a specific level of the vascular bed, and had a distinctive content of neuropeptides. Sympathetic noradrenergic neurons innervating large distributing arteries contained immunoreactivity to neuropeptide Y. Neurons innervating smaller cutaneous arteries contained immunoreactivity to prodynorphin-derived peptides in addition to neuropeptide Y. Finally, sympathetic neurons innervating the smallest arterioles, and arterio-venous anastomoses, contained immunoreactivity to prodynorphin-derived peptides, but had no detectable neuropeptide Y. Although the major form of dynorphin immunoreactivity in perivascular sympathetic axons was dynorphin A(1-8), immunoreactivity to both dynorphin A(1-8) and dynorphin A(1-17) occurred in the cell bodies of these neurons, suggesting that dynorphin A is processed during axonal transport to the terminals. The perivascular sympathetic neurons containing prodynorphin-derived peptides but not neuropeptide Y are most likely to be involved in the regulation of thermoregulatory cutaneous vascular circuits.

Opioid-like immunoreactive neurons in secretomotor pathways of the guinea-pig ileum

In this study we sought to establish the distribution, projections and neurochemical coding of opioid immunoreactive neurons in secretomotor pathways of the guinea-pig ileum. Non-cholinergic secretomotor neurons in the submucous ganglia have been shown to be immunoreactive for dynorphin A 1-8, dynorphin A 1-17, dynorphin B and alpha neo-endorphin while cholinergic neurons have been shown to be immunoreactive for dynorphin A 1-8 only. Thus all submucous neurons in the guinea-pig ileum are immunoreactive for prodynorphin-derived peptides. Two major populations of opioid immunoreactive fibres projecting to the submucous ganglia have been established. Firstly, neurons immunoreactive for prodynorphin-derived peptides and vasoactive intestinal peptide project anally from the myenteric plexus to the submucous ganglia. Secondly, a substantial proportion of sympathetic postganglionic fibres immunoreactive for tyrosine hydroxylase, and projecting from the coeliac ganglion to submucous ganglia, have been shown to be immunoreactive for prodynorphin-derived peptides. Other smaller populations of opioid-immunoreactive neurons include fibres immunoreactive for substance P, enkephalin and dynorphin A 1-8 which project from the myenteric plexus to the non-ganglionated plexus of the submucosa. These fibres are probably excitatory motor neurons to the muscularis mucosae. The present paper has described several distinct populations of opioid immunoreactive neurons in secretomotor pathways of the guinea-pig ileum. Furthermore we have shown that these enteric or postganglionic sympathetic neurons contain opioid peptides in combination with other neurotransmitter substances. These results should provide a firmer basis on which to plan functional experiments to elucidate the physiological role of opioid peptides in the enteric nervous system.

Substance P immunoreactivity in the superior cervical ganglia of normotensive and genetically hypertensive rats

Substance P-like immunoreactivity (SPI) was investigated in the superior cervical ganglion of normotensive and genetically hypertensive (GH) Otago Wistar rats aged 1, 2, 8-10 and 50-60 weeks, by used of an indirect immunoperoxidase method. SPI was not seen in neuronal cell bodies but a subpopulation of ganglion cells was supplied by SP-positive terminals which closely invested the cell surface. This subpopulation showed no particular topographical distribution. The number of SP-positive terminal varicosities per unit area was several times higher in GH rats than in normotensive rats at all ages over 2-60 weeks. The proportion of neurons supplied by SP-positive terminals (sampled in 8-10 week-old rats) was also greater in GH than in normotensive rats. Decentralization of the ganglion or chronic capsaicin treatment removed all SP-immunoreactive terminals around the cell bodies, indicating that the SP-positive terminals are collaterals of thoracic sensory afferents. As SP has been reported to have an excitatory effect in sympathetic ganglia, intraganglionic release of SP might contribute to the development of hypertension in the GH strain.

Co-localization and plasticity of transmitters in peripheral autonomic and sensory neurons

Immunohistochemical studies have shown that most peripheral autonomic and sensory ganglia are heterogeneous, consisting of several populations of neurons which can be distinguished by their content of peptide and non-peptide transmitters, and transmitter-associated enzymes. Many neurons contain several different potential transmitters, especially neuropeptides. Some neuropeptides have been localized in more than one population of autonomic and sensory neurons. However, the peptide often occurs together with a distinctive combination of additional transmitters in each neuronal class. The precise combination of transmitters found in any individual neuron is highly correlated with the peripheral target of the neuron. This indicates that immunohistochemically defined neuronal populations represent distinct functional classes of neurons. In an increasing number of cases, many of the potential transmitters contained in a particular neuron have been shown to be released from the nerve terminals, and to contribute to presynaptic or postsynaptic effects of nerve activation. Despite this association between the combination of potential transmitters contained in a neuron, and the function of the neuron, not all transmitters or transmitter-associated enzymes are expressed equally at all times in the life of a neuron: the levels of some substances change dramatically during development; some are detected only after experimental alteration of the environment of the developing or mature neurons. Taken together, these results indicate that, during development, pathway-specific information influences the differentiation of peripheral autonomic and sensory neurons. Furthermore, the expression of neuropeptides and transmitter-associated enzymes in a particular neuron appears to be under continuous regulation. These phenomena demonstrate the complexity and precision involved in development and maintenance of the peripheral autonomic and sensory nervous systems.

Increased dopamine-beta-hydroxylase-like immunoreactivity in non-noradrenergic axons supplying the guinea-pig uterine artery after 6-hydroxydopamine treatment

We have reinvestigated the immunohistochemistry of autonomic axons supplying the guinea-pig uterine artery to determine whether non-noradrenergic paracervical ganglion neurons projecting to the artery contain immunoreactivity to dopamine-beta-hydroxylase (DBH) or somatostatin (SOM) in addition to neuropeptide Y (NPY) and vasoactive intestinal peptide (VIP). In untreated arteries no VIP axons had immunoreactivity to tyrosine hydroxylase (TH), although 9% had immunoreactivity to DBH. Somatostatin immunoreactivity was detected in 25% of non-noradrenergic axons containing NPY and VIP. After in vivo treatment with 6-hydroxydopamine (6-OHDA), noradrenergic axons containing immunoreactivity to NPY, DBH and TH were absent from the adventitia-medial junction. However, 65-70% of the non-noradrenergic axons with NPY and VIP showed DBH immunoreactivity after 6-OHDA. These axons did not show catecholamine fluorescence after incubation with pargyline together with noradrenaline, dopamine or L-DOPA. The number of axons with SOM immunoreactivity increased by 44% after 6-OHDA treatment, but only 24% of SOM axons had DBH immunoreactivity. Surgical destruction of the non-noradrenergic autonomic axons in 6-OHDA-treated animals led to the loss of all DBH immunoreactivity. These results demonstrate that DBH immunoreactivity can be detected in a small proportion of non-noradrenergic axons supplying uterine arteries from untreated animals. After chemical sympathectomy with 6-OHDA, the levels of DBH immunoreactivity in axons of non-noradrenergic neurons increased, and more axons with DBH immunoreactivity were detected. DBH immunoreactivity seemed to increase preferentially in axons with NPY and VIP, but not SOM. The number of NPY, VIP axons containing SOM also increased after 6-OHDA. These findings demonstrate that peripheral neurons containing several different potential neurotransmitters can change their levels of neuropeptides and transmitter-synthesizing enzymes in response to local environmental changes.

Co-existence of neuropeptides in sympathetic, cranial autonomic and sensory neurons innervating the iris of the guinea-pig

We have used double-labelling immunofluorescence to identify the peptide content of autonomic and sensory neurons innervating the iris of albino guinea-pigs. Four major classes of neurons were identified on the basis of their distributions, origins and immunohistochemical characteristics. A dense plexus of noradrenergic axons in the constrictor and dilator muscles of the iris originated from the superior cervical ganglion, and contained immunoreactivity (IR) to both neuropeptide Y (NPY) and dynorphin (DYN). The constrictor and dilator muscles were also supplied with a dense plexus of axons with IR to substance P (SP). These axons probably originated from SP-IR nerve cell bodies located along the ciliary nerves, and are almost certainly the same axons as those producing cholinergic pupilloconstriction. The iris was also innervated by unmyelinated, capsaicin-sensitive axons with IR to both SP and calcitonin gene-related peptide. Most of these axons also contained IR to DYN and some were also IR for cholecystokinin. These axons are almost certainly sensory. Axons containing IR to both NPY and vasoactive intestinal peptide (VIP) were common in the ciliary processes, and also formed a sparse plexus near the ciliary margin of the dilator muscle. Following surgical sympathetic denervation these axons showed IR for dopamine-beta-hydroxylase; they seemed to originate from the sphenopalatine ganglion. These results demonstrate that there are well-defined patterns of coexistence of neuropeptides in the autonomic and sensory neurons supplying the iris of guinea-pigs. To understand the physiological roles of these peptides, it will be necessary to consider the possibility of complex interactions between them.