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Localisation of arginine vasopressin V1a receptors on sympatho-adrenal preganglionic neurones.

Vasopressin-containing nerve terminals are present in the spinal cord of several species. This study was designed to determine whether sympatho-adrenal preganglionic neurones (SPN) express vasopressin receptors (VPRs). SPN in the spinal cord were revealed by retrograde labelling of Fluorogold following its unilateral injection into the adrenal medulla of 12-20 day postnatal rats. VPRs were simultaneously visualised in the Fluorogold-labelled slices of spinal cord using a recently developed biotinylated vasopressin receptor antagonist [1-phenylacetyl,2-O-methyl-D-tyrosine,6-arginine,8-arginine,9-lysinam ide(Nepsilon-biotinamidocaproamide)]vasopressin, PhAcAL(Btn)VP. The VPR:PhAcAL(Btn)VP complexes were visualised either with Texas Red-conjugated avidin or with a Vectastain avidin:alkaline phosphatase detection kit. These dual-labelling experiments revealed VPRs to be present in the spinal grey matter and to be particularly dense in the intermediate grey matter and adjacent regions of the ventral horn. Many SPN were associated with receptor-specific labelling of PhAcAL(Btn)VP, thereby demonstrating that VPRs are expressed by these neurones. These VPRs were pharmacologically defined as the V1a subtype. It is concluded that sympatho-adrenal preganglionic neurones express VPRs and that these are of the V1a subtype. The distribution of VPRs is not, however, restricted to these SPN in the spinal cord.

Adrenal Glands↗

Relationships between thalamostriatal neurons and pedunculopontine projections to the thalamus: a neuroanatomical tract-tracing study in the rat.

The present study aimed to investigate whether the pedunculopontine projection to the thalamus overlaps with identified thalamostriatal neurons. These projections were studied using a dual tract-tracing procedure combining anterogradely transported biotinylated dextran amine (pedunculopontine projections) and retrogradely transported Fluoro-Gold (thalamostriatal projections). Overlapping thalamic territories between thalamostriatal neurons and the axon terminals arising from the pedunculopontine tegmental nucleus were observed in the midline (paraventricular) and in the intralaminar (centrolateral, central medial, paracentral and parafascicular) thalamic nuclei. Other thalamic nuclei, such as the ethmoid, intermediodorsal, mediodorsal, paratenial, posteromedian, ventromedian, ventrolateral and rhomboid thalamic nuclei, displayed a lesser degree of overlap. These observations suggest the existence of presumptive contacts between thalamostriatal neurons and axons emerging from the pedunculopontine tegmental nucleus, therefore supporting the possible existence of feedback circuits in the rat basal ganglia in which the tegmento-thalamic projection would play a major role.

Animals↗

Multiple axonal tracing: simultaneous detection of three tracers in the same section.

Multiple neuroanatomical tract-tracing methods are important tools for elucidating the connectivity between different populations of neurons. Evaluation of the question as to whether two specific fiber inputs converge on a particular, identified population of projection neurons requires the application of a triple-staining procedure that allows the unequivocal detection of three markers in a single section. The present report deals with a combination of tracing methods using anterogradely transported Phaseolus vulgaris leucoagglutinin and biotinylated dextran amine in conjunction with retrogradely transported Fluoro-Gold. These tracers were simultaneously detected according to a three-color paradigm, which includes the use of three different peroxidase substrates (nickel-enhanced diaminobenzidine, diaminobenzidine, and Vector VIP), thus resulting in three distinct precipitates: black, brown, and purple. We illustrate this method by showing convergence of projections arising from neurons located in two separate basal ganglia-related nuclei onto identified thalamostriatal projection neurons.

Agglutinins↗

Olfactory-hypoglossal connections.

Natural olfactory stimulation with amyl acetate significantly modulates the electrical activity of hypoglossal neurons and the electromyographic responses of the tongue musculature. The aim of the present study was to identify and characterize, using neuroanatomical and neurophysiological approaches, the pathways involved in the transmission of the olfactory information to the hypoglossal nucleus (XIIn). The neuroanatomical findings provided the initial demonstration that olfactory information is conveyed from the olfactory bulb to the hypoglossal nucleus via the interpeduncular nucleus (IPn) by both fast disynaptic and different polysynaptic pathways. The latter, in particular, involve many of the brain structures that process olfactory information. The electrophysiological studies demonstrated that the IPn neurons respond with a variety of patterns to natural stimulation of the olfactory receptors, thus supporting the hypothesis that the IPn is a crucial relay station for the elaboration and transmission of olfactory stimuli to XIIn.

Animals↗

The origin of sensory innervation of the peritoneum in the rat.

The distribution of sensory neurons innervating the peritoneum was studied using axonal transport of fluoro-gold. The tracer was injected into parietal peritoneum, diaphragm, mesentery, mesocolon, visceral peritoneum covering the stomach, small intestine, colon, liver, spleen, kidney, urinary bladder or uterus. After ten days of survival bilateral dorsal root ganglia from C2 to S6, and the nodose ganglia were dissected. The cryostat sections of these ganglia were mounted on glass slides and observed with a fluorescence microscope. In cases where the tracer was placed on the peritoneum covering the abdominal wall, labeled neurons were observed only in the ipsilateral dorsal root ganglia. A small number of neurons in nodose and cervical dorsal root ganglia of both sides were labeled after placing the tracer on the central part of the diaphragm. When fluoro-gold was applied to the peripheral part of the diaphragm, nodose ganglion was negative, and dorsal root ganglia from T6 to T12 were positive. Many neurons in the nodose ganglia in addition to somata in the dorsal root ganglia from T4 to T13 were labeled when the tracer was placed on the peritoneum lining the stomach, small intestine or caecum. After applying the tracer onto the colon, labeled neurons were observed in the dorsal root ganglia from T13 to L2 and L5 to S1. Ganglion cells in the nodose and dorsal root ganglia from T5 to T13 were positive when fluoro-gold was placed on the mesentery. No labeled neurons were observed in any ganglia when the tracer was applied to the peritoneum covering the spleen, kidney, uterus, urinary bladder and liver. These results suggest that most of the parietal peritoneum receives sensory nerves from dorsal root ganglia and the visceral peritoneum from both spinal nerves and the vagus nerve.

Animals↗

Cells of origin of vagal motor neurons projecting to different parts of the stomach in the rat: confocal laser scanning and electron microscopic study.

Parasympathetic motor neurons in the dorsal motor nucleus of the vagus (DMV) innervate the stomach by way of the gastric and hepatic branches of the vagus nerve. To investigate whether single neurons of the DMV provide collateral innervations to various parts of the stomach, we injected the retrograde tracer Fluoro-Gold (FG) into the cardia and the retrograde tracer cholera toxin subunit b (CTb) into the antrum or the pylorus of the same animal. Both retrogradely FG-labeled and CTb-labeled neurons were found throughout the DMV. Almost all CTb-labeled neurons (97%) were double-labeled with FG after injection of FG into the cardia and CTb into the antrum, while only a few CTb-labeled neurons (11%) were double-labeled with FG after injection of FG into the cardia and CTb into the pylorus. Thus, the cardia and the antrum received collateral projections, but the pylorus received projections mainly from different neurons in the DMV. These results indicate that different neurons in the DMV activate either the cardia or the pyloric sphincter muscles. We also labeled, retrogradely, the neurons projecting to the cardia and the pylorus in the DMV with cholera toxin-conjugated horseradish peroxidase (CT-HRP) to examine their ultrastructural characteristics. Although the neurons projecting to the cardia (21.6x15.0 microm, 248.0 microm2 per section) were significantly smaller than the neurons projecting to the pylorus (27.5x15.9 microm, 323.2 microm2 per section), their ultrastructural appearances were similar. Both types of neurons were small-to-medium sized, round or oval in shape, and generally had a small amount of cytoplasm containing a few Nissl bodies and a round nucleus. The average number of axosomatic terminals per section was low in the neurons projecting to the cardia (2.3) and the neurons projecting to the pylorus (3.0). Almost all axon terminals contacting these motor neurons contained round synaptic vesicles and made asymmetric synaptic contacts (Gray's type I).

Animals↗

Neurons in the dorsal column nuclei of the rat emit a moderate projection to the ipsilateral ventrobasal thalamus.

The dorsal column nuclei (DCN; gracile and cuneate nuclei) give rise to the medial lemniscus, the fibre system that provides an organised somatosensory input to the thalamus. Unlike the spinothalamic and trigeminothalamic tracts that project, also to the ipsilateral thalamus, the medial lemniscus system is believed to be entirely crossed. We demonstrate that DCN emit a small number of axons that reach the ipsilateral thalamus. As retrograde fluorescent neuronal tracer Fluoro-gold was stereotaxically injected in the ventrobasal thalamus of nine young adult Wistar rats. The injection foci were voluminous and encroached upon adjacent nuclei, but the periphery of the injection halo never spilled over to the contralateral thalamus. All sections of the contralateral gracile and cuneate nuclei and the midline nucleus of Bischoff contained abundant retrogradely labelled neurons. The comparison with the Nissl-stained parallel sections suggests that approximately 70-80% of the DCN neurons project to the contralateral thalamus. Counting of retrogradely labelled neurons in two cases revealed 4,809 and 4,222 neurons in the contralateral and 265 and 214 in the ipsilateral DCN, respectively. Thus, although less prominent than the ipsilateral spinothalamic tract, the lemniscal system also emits an ipsilateral projection that accounts for about 5% of the neuronal population in DCN that innervates the ventrobasal thalamus.

Afferent Pathways↗

Brain stem afferent connections of the amygdala in the rat with special references to a projection from the parabigeminal nucleus: a fluorescent retrograde tracing study.

A recently revealed important function of the amygdala (Am) is that it acts as the brain's "lighthouse", which constantly monitors the environment for stimuli which signal a threat to the organism. The data from patients with extensive lesions of the striate cortex indicate that "unseen" fearful and fear-conditioned faces elicit increased Am responses. Thus, also extrageniculostriate pathways are involved. A multisynaptic pathway from the retina to the Am via the superior colliculus (SC) and the pulvinar was recently suggested. We here present data based on retrograde neuronal labeling following injection of the fluorescent tracer Fluoro-Gold in the rat Am that the parabigeminal nucleus (Pbg) emits a substantial, bilateral projection to the Am. This small cholinergic nucleus (Ch8 group) in the midbrain tegmentum is a subcortical relay visual center that is reciprocally connected with the SC. We suggest the existence of a second extrageniculostriate multisynaptic connection to Am: retina-SC-Pbg-Am, that might be very effective since all tracts listed above are bilateral. In addition, we present hodological details on other brainstem afferent connections of the Am, some of which are only recently described, and some others that still remain equivocal. Following selective injections of Fluoro-Gold in the Am, retrogradely labeled neurons were observed in parasubthalamic nucleus, peripeduncular nucleus, periaqueductal gray, dopaminergic nuclear complex (substantia nigra pars lateralis and pars compacta, paranigral, parabrachial pigmented and interfascicular nuclei, rostral and caudal linear nuclei, retrorubral area), deep mesencephalic nucleus, serotoninergic structures (dorsal, median and pontine raphe nuclei), laterodorsal and pedunculopontine tegmental nuclei (Ch6 and Ch5 groups), parabrachial nuclear complex, locus coeruleus, nucleus incertus, ventrolateral pontine tegmentum (A5 group), dorsomedial medulla (nucleus of the solitary tract, A2 group), ventrolateral medulla (A1/C1 group), and pars caudalis of the spinal trigeminal nucleus. A bilateral labeling of the upper cervical spinal cord was also observed.

Amygdala↗

Differential uptake of molecules from the circulation and CSF reveals regional and cellular specialisation in CNS detection of homeostatic signals.

The uptake of hydroxystilbamidine (OHSt, FluoroGold equivalent) and wheat germ agglutinin (WGA), into the hypothalamus, two hours after injections into either the circulation or the cerebrospinal fluid, were compared in adult rats. Following intravenous injection, OHSt was found in astrocytes of the median eminence and medial part of the arcuate nucleus whereas WGA intensely labelled the blood vessels and ependymal cells throughout the hypothalamus. In complete contrast, intracerebroventricular (icv) injection into the lateral ventricle resulted in OHSt uptake by ependymocytes and astrocytes in the area adjacent to the third ventricle, with virtually no uptake in regions taking up this dye following systematic injections, i.e., the median eminence and medial arcuate. Following icv injection WGA labelling was intense in all parts of the ependymal layer of the third ventricle, including the alpha- and beta-tanycytes. Injections into the cisterna magna gave a different pattern of uptake with OHSt being found only in astrocytes in the ventral part of the hypothalamus lateral to the arcuate nucleus whilst WGA uptake was virtually absent. This highlights the regional and cellular specialisation for uptake of molecules from the circulation and CSF. The median eminence and medial arcuate take up molecules from the circulation, with different cell types taking up different molecules. As the CSF flows through the ventricular system, different cells lining the ventricular and subarachnoid spaces take up molecules differentially. Molecules in the CSF appear to be excluded from the median eminence and medial arcuate region.

Animals↗

Immunfluorescence study of neuropeptides in identified neurons of the rat auditory superior olivary complex.

The present study was conducted to investigate the distribution and immunohistochemical characteristics of ascending and descending projection neurons of the rat superior olivary complex (SOC), a group of interrelated brainstem nuclei. Ascending neurons were identified by injection of cholera toxin B subunit (CTB) into the central nucleus of the inferior colliculus (IC), descending neurons were labeled by application of Fluoro-Gold (FG) into the scala tympani of the cochlea, ipsilaterally to the IC injection. In accordance with the literature, we observed neurons innervating the IC located in the lateral superior olivary nucleus (LSO) and dorsal periolivary groups (DPO) on both sides, in the superior paraolivary nucleus (SPO) predominantly ipsilateral, as well as in the ipsilateral medial superior olivary nucleus (MSO) and the medial nucleus of the trapezoid body (MNTB). Cochlear projection neurons were found predominantly in the ipsilateral LSO as well as in the bilateral SPO, DPO, MSO and MNTB. In addition, a considerable population of neurons in the ipsilateral LSO and SPO were identified as being both ascending and descending. To further characterize these double-projecting neurons, brainstem sections were incubated in antisera directed against different neuroactive substances. The majority of ascending/descending cells in the LSO contained calcitonin gene-related peptide, but not substance P (SP), met-enkephalin (ENK) or tyrosine hydroxylase (TH). Some of these neurons apparently were contacted by ENK- or SP-immunoreactive fibers and terminals. In addition, we found TH-immunoreactive neurons in the lateral MNTB region. These neurons, which were labeled upon tracer injection into the cochlea (but not upon IC injection), probably belong to the C1 catecholaminergic cell group and may represent a division of the uncrossed olivocochlear bundle. The present results reveal the existence of a previously unknown subpopulation of SOC neurons that project to both the cochlea and the inferior colliculus. Their CGRP immunoreactivity and their uncrossed projection pattern provide evidence that they may belong to the cholinergic, putatively excitatory cell group.

Animals↗

Calcitonin gene-related peptide immunoreactive DRG neurons innervating the cervical facet joints show phenotypic switch in cervical facet injury in rats.

Patients with cervical facet lesions and facet joint injury sometimes experience diffuse neck pain, headache, and arm and shoulder pain. However, the pathophysiology of the intensity and expansion of facet joint pain has not yet been investigated. Retrograde transport of fluoro-gold (F-G) and immunohistochemistry of calcitonin gene-related peptide (CGRP) was used in 20 rats (control group, n=10; injured group, n=10). For the injured group, the whole facet capsule was incised. Of the total F-G labelled dorsal root ganglion (DRG) neurons innervating the C5/6 facet joint, the number and the cross-sectional area of cell profiles of F-G labelled CGRP-ir neurons were evaluated in the bilateral DRGs of both groups. The numbers of CGRP-ir F-G labelled DRG neurons as a percentage of all F-G labelled DRG neurons at C3, C4, C5, C6, C7, C8, T1, T2, and T3 respectively were 30, 22, 43, 47, 21, 19, 25, 36 and 30% in the control group, and 13, 15, 23, 17, 15, 8, 16, 28 and 35% in the injured group, with the injured group showing a significantly lower percentage of CGRP-ir F-G labelled neurons than the control group at C5 and C6 (P<0.05). However, the mean cross-sectional area of F-G labelled CGRP-ir cells from C3 to C8 DRGs increased from 625+/-22 micro m(2) to 878+/-33 micro m(2) in the injured group (P<0.001). Associated with the injured facet joints, the phenotypic switch to large neurons may complicate the mechanism of injured facet pain.

Animals↗

Calcitonin gene-related peptide immunoreactive neurons with dichotomizing axons projecting to the lumbar muscle and knee in rats.

Dorsal root ganglion (DRG) neurons with dichotomizing axons have been reported in several species and are thought to be related to referred pain. However, these neurons, which have dichotomizing axons to the lumbar muscles and to the knee, have not been investigated. Clinically, pain from the lumbar muscles is sometimes referred to the lower extremities. Two kinds of neurotracers [1,1'-dioctadecyl-3,3,3',3'-tetramethyl-indocarbocyanine perchlorate (DiI) and fluoro-gold (FG)] were used in the present double-labelling study. DiI crystals were placed in the left lower back muscle, and FG was applied to the medial side of the knee. Bilateral DRGs from L1 through L6 were immunoreacted with calcitonin gene-related peptide (CGRP) antibodies and observed under a fluorescence microscope. DRG neurons double-labelled with DiI and FG were recognized only in the ipsilateral DRGs from levels L1 to L6. Approximately 1% of DRG neurons innervating the low back muscles had other axons to the medial side of the knee. In double-labelled neurons, the ratio of CGRP-immunoreactive DRG neurons was 60%. This finding provides a possible neuroanatomical explanation for referred knee pain from the lower back since CGRP is a marker of sensory neurons typically involved with pain perception. However, these neurons are rare, and mechanisms of referred pain may be explained by the convergence-projection hypothesis.

Animals↗

Characteristics of sensory DRG neurons innervating the lumbar facet joints in rats.

The rat L5/6 facet joint, from which low-back pain can originate, is multisegmentally innervated from the L1 to L5 dorsal root ganglions (DRGs). Sensory fibers from the L1 and L2 DRGs are reported to non-segmentally innervate the paravertebral sympathetic trunks, whilst those from the L3 to L5 DRGs segmentally innervate the L5/6 facet joint. In the current study, characteristics of sensory DRG neurons innervating the L5/6 facet joint were investigated in rats, using a retrograde neurotransport method, lectin affinity- and immuno-histochemistry. We used four markers: (1) calcitonin gene-related peptide (CGRP) as a marker of small peptide containing neurons, (2) the glycoprotein binding the isolectin from Griffonia simplicifolia (IB4) or (3 the purinergic P2X(3) receptor for small, non-peptide containing neurons, and (4) neurofilament 200 (NF200) for small and large myelinated fibers. IB4-binding and CGRP and P2X(3) receptor containing neurons are typically involved in pain sensation, whereas NF200 is associated with pain and proprioception. Neurons innervating the L5/6 facet joints, retrogradely-labeled with fluoro-gold (FG), were distributed throughout DRGs from L1 to L5. Of FG-labeled neurons, the ratios of NF200 immunoreactive (IR) neurons and CGRP-IR neurons were 37% and 35% respectively. The ratio of IB4-binding and P2X(3) receptor-IR neurons was 10%, significantly less than the ratio of CGRP-IR neurons to FG-labeled neurons. The ratios of IB4-binding and P2X(3) receptor-IR neurons were significantly higher, and that of CGRP-IR neurons was significantly less in L1 and L2 DRGs than those in L3, L4 or L5 DRGs. Under physiological conditions in rats, DRG neurons transmit several types of sensations, such as proprioception or nociception of the facet joint. Most neurons transmitting pain are CGRP-IR peptide-containing neurons. They may have a more significant role in pain sensation in the facets via peptidergic DRG neurons.

Animals↗

Up-regulation of TNFalpha in DRG satellite cells following lumbar facet joint injury in rats.

The rat L5/6 facet joint, from which low back pain can originate, is multisegmentally innervated from the L1 to L5 dorsal root ganglia (DRG). Sensory fibers from the L1 and L2 DRG are reported to non-segmentally innervate the paravertebral sympathetic trunks, while those from the L3 to L5 DRGs segmentally innervate the L5/6 facet joint. Tumor necrosis factor alpha (TNFalpha) is a mediator of peripheral and central nervous system inflammatory response and plays a crucial role in injury and its pathophysiology. In the current study, change in TNFalpha in sensory DRG neurons innervating the L5/6 facet joint following facet joint injury was investigated in rats using a retrograde neurotransport method and immunohistochemistry. Neurons innervating the L5/6 facet joints, retrogradely labeled with fluoro-gold (FG), were distributed throughout DRGs from L1 to L5. Most DRG FG-labeled neurons innervating L5/6 facet joints were immunoreactive (IR) for TNFalpha before and after injury. In the DRG, glial fibrillary acidic protein (GFAP)-IR satellite cells emerged and surrounded neurons innervating L5/6 facet joints after injury. These satellite cells were also immunoreactive for TNFalpha. The numbers of activated satellite cells and TNFalpha-IR satellite cells were significantly higher in L1 and L2 DRG than in L3, L4, and L5 DRG. These data suggest that up-regulation of glial TNFalpha may be involved in the pathogenesis of facet joint pain.

Animals↗

Calcitonin gene-related peptide immunoreactive sensory DRG neurons innervating the cervical facet joints in rats.

The rat C5/6 facet joint is innervated multisegmentally from the C3 to the T3 dorsal root ganglia. Sensory fibers from the C3, C4, and C7-T3 dorsal root ganglia were reported to be innervated nonsegmentally through the paravertebral sympathetic trunks, while those from the C5 and C6 dorsal root ganglia were reported to segmentally innervate the C5/6 facet joint. The presence of calcitonin gene-related peptide-immunoreactive nerve fibers has been proved in the facet joints, but their ratios have not been studied. Fluoro-gold-labeled neurons innervating the C5/6 facet joint were distributed throughout the dorsal root ganglia from the C3 to T3 levels. Of the fluoro-gold-labeled neurons, the ratios of calcitonin gene-related peptide-immunoreactive C3, C4, C45 C6, C7, C8, T1, T2, and T3 dorsal root ganglion neurons were 30%, 22%, 43%, 47%, 21%, 19%, 25%, 36%, and 40%, respectively. The ratios of calcitonin gene-related peptide-immunoreactive neurons in the C5 and C6 dorsal root ganglia were significantly higher than those in the C3, C4, C7, and C8 dorsal root ganglia. In the physiological condition in rats, the neurons of the C5 and C6 dorsal root ganglia may have a more significant role in pain sensation of the facets than other dorsal root ganglion neurons.

Animals↗

The effects of anti-nerve growth factor on retrograde labelling of superior cervical ganglion neurones projecting to the molar pulp in the rat.

The aims were to demonstrate sympathetic ganglion neurones projecting to the rat molar pulp and to determine whether deprivation of nerve growth factor (NGF) in neonatal rats eliminates this source of pulpal innervation. Newborn Sprague-Dawley rats were given subcutaneous injections of rabbit anti-mouse-NGF serum for 1 month. Control animals included litter mates treated with preimmune serum and untreated, age-matched rats. AT 4 months of age, Fluoro-gold (FG) was applied to the pulp chamber of the right first maxillary molar. One week later, the animals were perfusion fixed, and the superior cervical ganglia (SCG) were removed, embedded in paraffin, and serially sectioned at 10 microns. FG-labelled cells were detected by epifluorescence microscopy with a u.v. filter set. Control animals had 5-10 FG-labelled neurones widely distributed throughout the SCG ipsilateral to the injection site and no labelled cells in the contralateral SCG. NGF-deprived animals had either no FG-labelled cells or a single labelled cell in the ipsilateral SCG. These results indicate that, in rats, (1) the number of SCG neurones projecting to the molar pulp is rather low, (2) SCG neurones that innervate the dental pulp of the maxillary molar pulp are dispersed throughout the ganglion, (3) the projection from SCG to the molar is exclusively ipsilateral, and (4) neonatal NGF deprivation induces a permanent, almost total, loss of sympathetic neurones projecting to the dental pulp.

Animals↗