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At least 523 records · Page 29Linked to original sources
PubMed1993

A retrograde labeling technique for the functional study of airway-specific visceral afferent neurons.

The development of a method is described whereby primary afferent neurons that specifically innervate the airways in the guinea pig can be retrogradely labeled, acutely dissociated and studied functionally with electrophysiological techniques. Following administration of either dextran-tetramethylrhodamine, Fast Blue, or Fluorogold dye into the tracheal lumen, dye-labeled neurons can be visualized in 100 microns serial nodose ganglion sections. Control experiments show that labeling does not result from the undesirable spread of the dyes to target innervation fields in the gastrointestinal (GI) or cardiovascular (CV) systems. Neuronal somata retain dye label when acutely dissociated. Microelectrode studies provide evidence that the presence of the Rhodamine dye label and its fluorescent excitation neither alter basic electrophysiological membrane parameters nor the chemoreceptive properties of isolated neurons. Thus this new method will allow the isolation of individual airway-specific primary visceral afferent neurons for functional studies with multidisciplinary techniques.

Amidines↗
PubMed1995

Neuroanatomical tract tracing provides histological verification of neuron loss following cytotoxic lesions.

In the present study we report a neuroanatomical procedure that provides direct histological verification of the extent of neuron loss following cytotoxic lesions of the lateral subdivision of the habenular complex (Lhb). Following kainic acid-induced lesions of Lhb neurons, the fluorescent retrograde tracer Fluoro-Gold was injected into the ventral midbrain where many medial habenula (Mhb) and Lhb neurons project. The absence of retrogradely labeled neurons in the Lhb indicated the extent of neuron loss there, and the presence of Fluoro-Gold-labeled neurons in the Mhb indicated that its neurons were intact. The extent of neuron loss in the Lhb was significantly correlated with behavioral data. Retrograde tract tracing can be used as an effective histological tool to verify the extent of neuron loss following a lesion procedure.

Animals↗
PubMed1994

Immunolabeling of retrogradely transported Fluoro-Gold: sensitivity and application to ultrastructural analysis of transmitter-specific mesolimbic circuitry.

Fluorescence microscopy shows extensive filling of perikarya and distal dendrites following injections of Fluoro-Gold (FG) into their terminal fields. However, elucidation of synaptic contacts onto identified projection neurons has been limited by the lack of compatibility between electron-dense markers required for ultrastructural analysis and morphology preservation. The recent advent of antisera to FG has revealed numerous potential applications for analyzing chemically defined synaptic circuitry. To take advantage of the high sensitivity of this retrograde tracer in ultrastructural studies, we extended and detailed the original description of single immunocytochemical labeling of FG by comparing the advantages of immunodetection of an antiserum against FG using 2 distinct electron-dense markers: (1) avidin-biotin peroxidase (ABC) reacted with 3,3'-diaminobenzidine and darkened with osmium tetroxide, or (2) silver-intensified 1 nm colloidal gold particles. We subsequently examined the utility of combining these markers in single sections for detection of transmitters (e.g., gamma-aminobutyric acid (GABA) and 5-hydroxytryptamine (5-HT)) in axon terminals presynaptic to retrogradely labeled neurons. Both analyses were carried out on the well-characterized mesolimbic pathway originating from perikarya in the ventral tegmental area (VTA) that project to the nucleus accumbens. Injections of FG were stereotaxically placed in the nucleus accumbens of anesthetized adult rats. From these animals, vibratome sections of aldehyde-fixed brains were examined for light-microscopic detection of FG using: (1) epi-fluorescence without immunocytochemistry, (2) immunoperoxidase, or (3) immunogold-silver. All 3 methods revealed circumscribed injections in the nucleus accumbens. Additionally, both immunocytochemical methods appeared to be as sensitive as epi-fluorescence in light-microscopic detection of retrogradely labeled perikarya and fine-caliber dendrites extending for 2-3 branch points beyond the soma. Electron microscopy showed that the FG was detectable not only in lysosomes but also throughout the cytoplasmic matrix of perikarya and dendrites using either immunoperoxidase or immunogold-silver labeling methods. In the second part of this analysis, single sections of tissue were processed for dual labeling using either immunoperoxidase or immunogold-silver for detection of FG in conjunction with the converse label for GABA or 5-HT, respectively. Regardless of the labeling combinations, the peroxidase and gold-silver reactions were readily distinguished within sections examined by light or electron microscopy. Synaptic junctions from unlabeled or from GABA or 5-HT labeled terminals were most readily identified when the targets were lightly immunoreactive for peroxidase or labeled using silver-intensified colloidal gold.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Efficacy of seven retrograde tracers, compared in multiple-labelling studies of feline motoneurones.

The labelling efficacies of 7 retrograde tracers were evaluated following cut nerve exposure or intramuscular injection into the serially compartmentalized neck muscle, biventer cervicis. Tested tracers included Fast Blue (FB), Fluorogold (FG), dextran conjugated to fluorescein (FD), dextran conjugated to rhodamine (Fluororuby (FR), 3000 and 10,000 MW), fluorescent latex microspheres, horseradish peroxidase coupled to colloidal gold, and 1,1'-dioctadecyl-3,3,3',3'-tetramethyl indocarbocyanine perchlorate (DiI). In 2 animals, horseradish peroxidase was also employed and spinal cords were processed for peroxidase activity to evaluate its effect on the appearance of cells labelled with fluorescent tracers. Four tracers, FB, FG, FD and FR, could be observed in motoneurones under the conditions of our study. FB and FG labelled comparable numbers of motoneurones following cut nerve exposure, but dissimilar numbers following intramuscular injection. FG diffused extensively following injection and was found in motoneurones not only in the appropriate ipsilateral segment but also adjacent ipsilateral and contralateral segments. Intramuscular injections of FB usually labelled fewer cells than cut nerve exposure, but evidence for spurious labelling following intramuscular injection could also be found. FD or FR labelled motoneurones following cut nerve exposure but not following intramuscular injection. The conjugated dextrans labelled more variable numbers of cells than FB or FG, but the labelled cells had similar patterns of distribution. The remaining tracers were ineffective as retrograde markers in our study, and the possible reasons for these failures are discussed.

Amidines↗
PubMed1994

Intraperitoneal injections of Fluorogold reliably labels all sympathetic preganglionic neurons in the rat.

The ability of intraperitoneal injections of a retrograde neuronal tracer, Fluorogold, to label the entire population of sympathetic preganglionic neurones was tested with a double-labelling strategy. Animals were injected intraperitoneally (i.p.) with Fluorogold, while Fast Blue or subunit B of cholera toxin were injected into a peripheral autonomic ganglion or into the adrenal gland. Sympathetic preganglionic neurones were then examined for retrogradely transported tracers. In all cases, preganglionic neurones labelled with Fast Blue or cholera toxin also contained Fluorogold, indicating that i.p. injections of Fluorogold do reliably label the entire population of sympathetic preganglionic neurones.

Adrenal Glands↗
PubMed1995

A constant current source for extracellular microiontophoresis.

A sophisticated constant-current source suitable for extracellular microiontophoresis of tract-tracing substances, such as Phaseolus vulgaris leucoagglutinin, Biocytin or Fluoro-Gold, is described. This design uses a flyback switched-mode power supply to generate controllable high-voltage and operational amplifier circuitry to regulate current and provide instrumentation. Design features include a fast rise time, +/- 2000 V supply (stable output in < 250 ms), simultaneous load current and voltage monitoring, and separate pumping and holding current settings. Three features of this constant-current source make it especially useful for extracellular microiontophoresis. First, the output voltage monitor permits one to follow changes in the microelectrode resistance during current injection. Second, the voltage-limit (or out-of-compliance) indicator circuitry will sound an alarm when the iontophoretic pump is unable to generate the desired current, such as when the micropipette is blocked. Third, the high-compliance voltage power supply insures up to +/- 20 microA of current through 100 M omega resistance. This device has proven itself to be a reliable constant-current source for extracellular microiontophoresis in the laboratory.

Brain↗
PubMed1991

Origin of galanin-immunoreactive nerve fibers in the rat paracervical autonomic ganglia and uterine cervix.

Retrograde axonal tracing with fluorogold in conjunction with immunohistochemistry was used to examine the source of galanin-immunoreactive nerve fibers in the paracervical ganglia and uterine cervix of the female rat. Immunohistochemistry revealed galanin-immunoreactive neuron somata in lumbosacral dorsal root ganglia and around the central canal of the lumbosacral spinal cord (lamina X). Injection of fluorogold into the paracervical ganglia resulted in labelled cells in dorsal root ganglia and the sacral parasympathetic nucleus of the spinal cord; but fluorogold-labelled, galanin-immunoreactive cells were found only in dorsal root ganglia. Injection of the tracer in the cervix resulted in labelled cells in the paracervical ganglia and dorsal root ganglia; however, fluorogold-labelled, galanin-immunoreactive cells were again evident only in dorsal root ganglia. It is suggested that the galanin-immunoreactive nerve fibers and varicosities in the paracervical ganglia and uterine cervix are sensory fibers from spinal dorsal root ganglia. The galanin-immunoreactive varicosities in the ganglia could play a role in the modulation of pelvic visceral activity, while those in the musculature of the cervix could influence contractility.

Animals↗
PubMed1991

Neurotensin-like immunoreactivity in presumptive baroreceptor neurons innervating the guinea pig carotid sinus.

This study was carried out to determine the ultrastructure and origin of previously described neurotensin-like immunoreactive (NT-LI) nerve fibres in the wall of the carotid sinus of the guinea pig. In our degeneration experiments, these NT-LI axons were unaffected by surgical sympathectomy but disappeared in response to transection of the carotid sinus nerve, thus suggesting a sensory origin. This assumption could be supported by combined retrograde tracing and immunohistochemistry. Primary afferent neurons of the sensory glossopharyngeal (petrosal) ganglion projecting to the carotid sinus were identified by injecting the retrograde fluorescent tracer, Fluoro-Gold, into the sinus wall, and some of these neurons displayed NT-LI. Within the carotid sinus, the terminals of these NT-LI sensory neurons exhibited ultrastructural features characteristic of baroreceptor endings, i.e. axonal swellings filled with mitochondria and closely associated to elastin. However, many endings also fulfilling the ultrastructural criteria for baroreceptors were devoid of immunolabelling. Thus, we conclude that the NT-LI terminals constitute a subgroup rather than the entire population of baroreceptor endings within the guinea pig carotid sinus. With respect to the established pharmacological effects of NT in guinea pig, we propose an involvement of NT-LI fibres in the modulation of baroreception at the peripheral level.

Animals↗
PubMed1991

Viscerotopic representation of preganglionic efferent vagus nerve in the brainstem of the rat: a Fluoro-Gold study.

To investigate the viscerotopic distribution of the cells of origin of preganglionic vagus nerve in rats, Fluoro-Gold was injected into various visceral tissues. After injections into the gastroesophageal junction and the gastric corpus, labelled cells were localized in the medial half of the dorsal motor nucleus of the vagus (dmnX). Cells in the nucleus ambiguous (nA) were also labelled after injections into the gastroesophageal junction. After injections into the pancreatic head and the celiac plexus, labelled cells were located bilaterally in the lateral part of the caudal dmnX. In the rostral dmnX, however, the pancreatic head was represented in the medial segment. After injections into the lung, duodenum, liver and ascending colon, no labelling was observed in the brainstem.

Adhesives↗
PubMed1992

Location and peptide content of pelvic neurons supplying the muscle and lamina propria of the rat vas deferens.

Retrograde tracing and immunohistochemistry have identified the location within the rat pelvic plexus of neurons which project to the vas deferens, and their neurochemical properties. The fluorescent tracers, Fast Blue and FluoroGold, were injected into the wall of the vas deferens and labelled neurons located within the ventral part of the major pelvic ganglion (MPG) and the adjacent accessory ganglia (AG). Most neurons were located in ganglia ipsilateral to the injection site. Noradrenergic neurons were defined as those containing immunoreactivity for tyrosine hydroxylase (TH). Five groups of dye-labelled neurons could be identified immunohistochemically, noradrenergic neurons containing neuropeptide Y (NPY) (60-70%), and four types of non-noradrenergic neurons, NPY-only neurons (5-10%), NPY neurons containing vasoactive intestinal peptide (VIP) (3-5%), neurons containing only VIP (15-25%) and neurons containing galanin (GAL) (2-5%). Noradrenergic axons, and axons containing NPY or GAL were primarily located within the muscle, whereas most VIP axons were found as a dense plexus within the lamina propria. Very few peptide-containing varicose nerve terminals surrounded dye-labelled (vas deferens-projecting) pelvic neurons. Thus, no peptide marker was found for most of the preganglionic inputs supplying postganglionic neurons which project to the vas deferens. These studies have shown that pelvic neurons supplying the vas deferens have a discrete location within the rat pelvic ganglia and that they comprise at least five neurochemical groups, providing innervation to the muscle and lamina propria. The preganglionic connections with these noradrenergic and non-noradrenergic (possible cholinergic) pathways, and further examination of the role of mucosal innervation remain to be determined.

Amidines↗
PubMedDate not supplied

Topographical distribution and immunocytochemical features of colonic neurons that project to the cranial mesenteric ganglion in the pig.

Using the retrograde neuronal tracers Fast blue and Fluorogold, the topographical distribution and morphological features of porcine colonic neurons projecting to the cranial (superior) mesenteric ganglion have been investigated. Two to four weeks after injection of the tracer into the cranial mesenteric ganglion of immature pigs, labelled neurons were found throughout the colon. In the myenteric and outer submucous plexuses, they were present in ganglia situated to the side of the mesenteric attachment. The highest density of labelled neurons was observed at the end of the ascending colon, which in the pig represents 78-80% of the total colon length. The viscerofugal neurons had a multidendritic appearance and part of them were immunoreactive for calcitonin gene-related peptide or serotonin. This study has revealed similarities but also significant differences in the colono-sympathico-colonic pathways between the pig and small laboratory animals such as the guinea-pig.

Amidines↗
PubMed1993

Characterization of vagal innervation to the rat celiac, suprarenal and mesenteric ganglia.

In order to shed light on the controversial issue of vagal innervation of the solar plexus ganglia, vagal efferent preganglionic fibers were anterogradely labeled by injecting the fluorescent carbocyanine dye Dil into the dorsal motor nucleus (dmnX). Additionally, Fluorogold was used to label the ganglia in toto, providing a counterstain and the possibility of UV light-guided dissection of the various ganglia. Using optical sectioning of whole mounted intact ganglia by means of laser scanning confocal microscopy, a considerable number of Dil-labeled vagal terminal-like structures were found in the major ganglia (celiac, superior mesenteric and suprarenal). Additionally, vagal efferent terminals were regularly found in microganglia associated with the periarterial plexuses of the celiac and superior mesenteric arteries, and in a few cases in small ganglia of the intermesenteric and renal plexuses. By using animals with prior selective vagal branch vagotomies, leaving only one (or a pair) of the three major abdominal divisions intact, it was concluded that the two celiac branches contribute the bulk of this vagal innervation, with the two gastric and the unpaired hepatic branch providing a small contribution mostly limited to the celiac ganglia. From control experiments, which involved Dil injections (1) into the dmnX in animals whose visceral afferents had been previously destroyed by capsaicin; (2) into the nodose ganglia, in order to anterogradely label vagal afferents; and (3) into the cervical vagus nerve as a control for uptake by fibers of passage, it was concluded that the identified terminal-like structures were vagal efferents and not inadvertently labeled afferents. We suggest that these vagal terminals have to be regarded either as ectopic parasympathetic junctions, or as part of a vagal mechanism for gating of sympathetic ganglionic transmission. Functionally, the parasympathetic innervation of the solar plexus may provide not only the classic vagal influence on gastrointestinal targets, but also vagal control of the adrenal glands and possibly other abdominal organs that have not been traditionally regarded as vagal targets.

Afferent Pathways↗
PubMed1993

The effect of chronic decentralization on the enkephalin immunoreactive plexus around penile ganglionic neurons.

Target organ responses to sympathetic nerve stimulation are altered following partial decentralization of the pelvic plexus in the rat. One possible explanation for the new responses is that nerve injury has led to a reorganization of synaptic connections within pelvic ganglia. Since one measure of synaptic influence is the occurrence of a pericellular plexus of varicose fibers around autonomic ganglion cells, the present study has used immunocytochemistry for enkephalin (ENK), a peptide present in nerve fibers in the pelvic plexus, to follow changes in the innervation of penile ganglionic neurons after interruption of preganglionic pathways. Penile ganglion cells were located by the injection of the tracer Fluorogold into the penile crura. Four days after lesion of the pelvic nerve, innervation of penile neurons falls from 76% to 20%. This number increases however, to 31% in chronically (6 weeks) lesioned animals. In the totally decentralized ganglia, ENK immunoreactive (IR) fibers enclose fewer than 12% of the penile neurons 4 days after nerve lesion. However, this value rises to 35% in the chronically decentralized pelvic ganglion. Therefore, recovery of an enkephalin plexus occurs irrespective of whether the pelvic nerve, or both the hypogastric and pelvic nerve have been cut. Although these findings suggest sprouting within partially decentralized ganglia, the similar incidence of an ENK plexus in ganglia subjected to chronic partial or total decentralization indicates that preganglionic fibers are not responsible for the emergent fibers.

Animals↗
PubMed1993

Contribution of bed nucleus of the stria terminalis to the cardiovascular responses elicited by stimulation of the amygdala.

Anatomical and physiological studies were done in the rat to investigate the possibility that the cardiovascular responses elicited by stimulation of central nucleus of the amygdala (ACe) were mediated via projections to bed nucleus of the stria terminalis (BST). In the first series, to determine the distribution of neurons in ACe that projected to the cardiovascular region of BST, the retrograde tracer Fluorogold (FG) or rhodamine latex micro-beads (Rd) were injected into BST. FG and Rd injections that overlapped the cardiovascular region of BST resulted in retrogradely labelled neurons throughout the amygdala. In ACe, retrogradely labelled neurons were observed primarily in the lateral subdivision of the rostral ACe compared to the caudal ACe. The medial subdivision of ACe was found to have very few retrogradely labelled neurons. In the second series, the effect of either blocking synaptic transmission in BST with CoCl2, chemical lesions of BST with ibotenic acid (IBO), or electrolytic lesions of BST on the depressor response elicited by either electrical or chemical stimulation of ACe was investigated in the chloralose-anesthetized, artificially ventilated and paralysed rat. Microinjections of CoCl2 into BST significantly attenuated the depressor responses to stimulation of the rostral components of the lateral subnucleus of ACe, but not those to stimulation of the caudal and medial components of ACe. Microinjections of IBO into BST or electrolytic lesions of BST resulted in similar effects on the depressor responses to ACe stimulation. Taken together, these data indicate that neurons within the rostral components of the lateral subnucleus of ACe project to the cardiovascular region of BST and mediate in part the depressor responses to stimulation of the rostral ACe. On the other hand, the depressor responses elicited from the caudal ACe are not mediated through BST. These results suggest that at least two independent pathways originate in the ACe that influence the circulation.

Amygdala↗
PubMed1995

A light-microscopic study of the intermediolateral nucleus following injection of CB-HRP and fluorogold into the superior cervical ganglion of the rat.

Sympathetic preganglionic neurons in the intermediolateral nucleus of the thoracic spinal cord of the adult rat which innervate the superior cervical ganglion (SPN-scg) were identified by means of retrograde transport of cholera subunit B-conjugated horseradish peroxidase and fluorogold. In horizontal sections of the spinal cord, the SPN-scg were observed to be arranged in clusters which displayed a characteristic triangular configuration. Within this triangle, the cells showed no preferential orientation for their long axes were oriented obliquely, transversely or longitudinally. The dendrites arising from these clusters were oriented either longitudinally, medially, or laterally. The medially-oriented dendrites formed a subependymal plexus and some have been observed to cross the midline to the opposite side. The most significant finding was the presence of the white matter dendritic plexus which was formed by the laterally-directed bundles of dendrites. The present findings thus suggested that SPN-scg may be regulated by means of two circuits: the classical (medial) core circuit and a paralateral circuit which may convey supraspinal afferent inputs to the SPN-scg.

Animals↗
PubMed1994

Alterations in neural pathways to the urinary bladder of the rat in response to streptozotocin-induced diabetes.

Voiding dysfunction in diabetics has been attributed to a variety of causes including an axonopathy in autonomic pathways to the urinary bladder. The present study was undertaken to determine whether changes occurred in afferent and efferent neurons supplying bladders of streptozotocin (STZ)-induced diabetic rats. Nine weeks after STZ treatment, the mean cross-sectional area for retrogradely labeled (Fluoro-Gold) bladder neurons in the major pelvic ganglion (MPG) was greater in diabetics (364 microns 2) than controls (300 microns 2). The number of labeled neurons was similar in these groups. In contrast, mean cross-sectional areas of bladder afferent neurons labeled with WGA-HRP in the L6 and S1 dorsal root ganglia (DRG) were smaller (393 microns 2) in diabetics than in normal rats (528 microns 2). In addition, very few DRG neurons were labeled in STZ-treated rats and transganglionic labeling of bladder afferent projections in the L6 and S1 spinal cord with WGA-HRP was sparse. Radioimmunoassay studies revealed that substance P was reduced by 70% in the MPG and by 40% in L6 DRG, yet this peptide was unchanged in the bladders of diabetic rats. The amounts of VIP in the MPG and DRG of diabetics and controls were similar, while VIP in the bladder was increased in diabetics. These observations indicate that both afferent and efferent neurons innervating the urinary bladder are altered in the STZ-induced diabetic rat. In addition, axonal transport in visceral afferent pathways may be disrupted.

Afferent Pathways↗
PubMed1994

Distribution of extrinsic enkephalin-containing nerve fibers in the rat rectum and their origin in the major pelvic ganglion.

The distribution of nerve fibers containing enkephalin (ENK)-like immunoreactivity was examined in the rectum of aganglionosis rats (AGRs) which completely lack the intramural ganglion cells in the large intestine, and was compared with that of their normal littermates. Furthermore, Met5-enkephalin-Arg6-Gly7-Leu8 (MEAGL)-like immunoreactive neurons projecting to the rectum were examined using retrograde tracing combined with immunohistochemistry in the major pelvic ganglion of normal male rats. In the intermuscular space of the aganglionic rectum of AGRs, unlike the pattern of the normal intermuscular plexus, moderate numbers of ENK-like-immunoreactive fibers were arranged in an irregular, coarse network; greatly diminished numbers of immunoreactive fibers were found in the submucosa. No ENK-like-immunoreactive fibers were seen in the circular muscle layer and mucosa. In the normal rat rectum, ENK-like-immunoreactive fibers were seen throughout all layers, and immunoreactive nerve cells were found predominantly in the myenteric plexus of colchicine-treated animals. Fluoro-Gold injected into the upper rectum labelled numerous principal ganglion neurons in the major pelvic and inferior mesenteric ganglia. Less than 10% of tracer-labelled neurons were positive for fluorescein immunolabelling of MEAGL in the major pelvic ganglion; no immunoreactive neurons were found in the inferior mesenteric ganglion. In the major pelvic ganglion of the colchicine-treated normal rats, about 5% of principal ganglion neurons were immunoreactive for MEAGL. Comparison of serial paraffin sections of the major pelvic ganglion stained for tyrosine hydroxylase (TH), MEAGL and vasoactive intestinal polypeptide (VIP), respectively, revealed that more than half of MEAGL-like immunoreactive neurons were also positive for TH; there was no case showing co-existence of MEAGL with VIP in the principal neurons. These results indicate that a small number of enkephalin-containing neurons in the major pelvic ganglion project to the rectum, and that more than half of these neurons are postganglionic sympathetic. They may terminate mainly in the myenteric ganglia in the rectum.

Animals↗
PubMed1994

Projections from the prevertebral and major pelvic ganglia to the ileum and large intestine of the male rat.

The sympathetic innervation of the gut arises from the prevertebral and pelvic ganglia, and to a variable extent, from neurons located in the paravertebral ganglia, the splanchnic and intermesenteric nerves. In this study we have injected retrograde tracers into the wall of the ileum and several regions of the large intestine to determine the proportion of neurons supplying these regions from each of the ganglia and nerves. The sympathetic supply to the ileum arises primarily from neurons in the splanchnic nerves and the paravertebral ganglia T9-T11 (SPL) and the coeliaco-mesenteric ganglion complex (CG/SMG), with a small supply from the proximal intermesenteric nerves (IMN). The distribution of neurons projecting to the proximal colon is very similar, although some labelled neurons are found throughout the length of the IMN and also in the inferior mesenteric ganglion (IMG). The middle colon is primarily supplied by the IMN and the IMG, although this region receives innervation from all the ganglia and nerves investigated, including the major pelvic ganglia (MPG). Neurons located in the distal two-thirds on the IMN and more caudal structures were labelled from the distal colon. The distal colon is the only region of gut to receive a relatively large innervation from the MPG, with approximately one third of labelled neurons in each of the IMN, IMG and the MPG. These studies also compared two retrograde tracers, Fast Blue and Fluorogold. Fluorogold was found specifically to label neurons projecting to each region of intestine injected. However, when injected into the middle colon, Fast Blue labelled neurons that project to this region as well as many neurons that Fluorogold studies indicate project to other regions; Fast Blue should therefore be used only with caution.

Amidines↗