Ca2+/calmodulin-dependent protein kinase II in the rat cranial sensory ganglia

Immunohistochemistry for Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) was performed on the rat cranial sensory ganglia. More than one half of neurons was immunoreactive for the enzyme in the trigeminal (60%), jugular (70%), petrosal (55%) and nodose ganglia (63%). These neurons were mainly small to medium-sized. The co-expression study demonstrated that one half of CaMKII-immunoreactive (ir) neurons was also immunoreactive for calcitonin gene-related peptide (CGRP) or the vanilloid receptor subtype 1 (VR1) in the trigeminal, jugular and petrosal ganglia. In the nodose ganglion, CaMKII-ir neurons were mostly devoid of CGRP-immunoreactivity (ir) (8.2%) whereas the co-expression with VR1-ir was common among such neurons (72%). In the facial skin, nasal mucosa and palate, the epithelium and taste bud were innervated by CaMKII-ir nerve fibers. In addition, the retrograde tracing study demonstrated that 39.6% and 44.8% of trigeminal neurons which were retrogradely traced with fluorogold from the facial skin and nasal mucosa exhibited CaMKII-ir. Forty-six percent of petrosal neurons which innervated the soft palate were immunoreactive for the enzyme.

Streptozotocin-induced diabetes causes metabolic changes and alterations in neurotrophin content and retrograde transport in the cervical vagus nerve

Abnormal availability of neurotrophins, such as nerve growth factor (NGF), has been implicated in diabetic somatosensory polyneuropathy. However, the involvement of neurotrophins in diabetic neuropathy of autonomic nerves, particularly the vagus nerve which plays a critical role in visceral afferent and in autonomic motor functions, is unknown. To assess the effects of hyperglycemia on the neurotrophin content and transport in this system, cervical vagus nerves of streptozotocin (STZ)-induced diabetic rats were studied at 8, 16, and 24 weeks after the induction of diabetes. Elevations in vagus nerve hexose (glucose and fructose) and polyol levels (sorbitol), and their normalization with insulin treatment, verified that the STZ treatment resulted in hyperglycemia-induced metabolic abnormalities in the nerve. Neurotrophin (NGF and neurotrophin-3; NT-3) content and axonal transport were assessed in the cervical vagus nerves from nondiabetic control rats, STZ-induced diabetic rats, and diabetic rats treated with insulin. The NGF, but not the NT-3, content of intact vagus nerves from diabetic rats was increased at 8 and 16 weeks (but not at 24 weeks). Using a double-ligation model to assess the transport of endogenous neurotrophins, the retrograde transport of both NGF and NT-3 was found to be significantly reduced in the cervical vagus nerve at later stages of diabetes (16 and 24 weeks). Anterograde transport of NGF or NT-3 was not apparent in the vagus nerve of diabetic or control rats. These data suggest that an increase in vagus nerve NGF is an early, but transient, response to the diabetic hyperglycemia and that a subsequent reduction in neuronal access to NGF and NT-3 secondary to decreased retrograde axonal transport may play a role in diabetes-induced damage to the vagus nerve.

Attenuation of the afferent limb of the baroreceptor reflex in streptozotocin-induced diabetic rats

Diabetic autonomic neuropathy is a common complication following prolonged diabetes. Alterations of cardiovascular reflexes contribute to the increased cardiovascular morbidity and mortality seen in diabetic patients. This study sought to better characterize these complications by investigating the afferent limb of the baroreceptor reflex in an experimental rat model of diabetes. Streptozotocin (STZ)-induced diabetic and euglycemic control rats were studied at 8- and 16-week time points after initiation of the experiment. Activation of the afferent limb of the baroreceptor reflex was assessed by measuring the numbers of c-Fos-immunoreactive (ir) neurons in the CNS site of termination of the baroreceptor afferent neurons, the nucleus of the solitary tract (NTS). Initial experiments established that baseline cardiovascular parameters and NTS expression of c-Fos-ir neurons were not different between diabetic and control rats at either time point. Phenylephrine (PE)-induced activation of baroreceptors resulted in a significant elevation in the numbers of c-Fos-ir neurons in the NTS of control rats. Although diabetic rats showed similar pressor responses to PE, the activation of c-Fos-ir neurons in the NTS of diabetic rats was significantly attenuated. At both 8 and 16 weeks, STZ-induced diabetic rats had significantly fewer c-Fos-ir neurons in the commissural NTS and in the caudal subpostrernal NTS when compared to the non-diabetic control animals receiving PE. These data suggest that STZ-induced diabetes, for a period of 8 and 16 weeks, results in reduced activity in the afferent baroreceptor input to the NTS, and are consistent with diabetes-induced damage to baroreceptor afferent nerves.

Axotomy alters neurotrophin and neurotrophin receptor mRNAs in the vagus nerve and nodose ganglion of the rat

Neurotrophins and neurotrophin receptors play an important role in survival and growth of injured peripheral nerves. To study the injury-mediated neurotrophic response in autonomic nerves, we investigated changes in mRNA expression of neurotrophins and their receptors in the transected vagus nerve and nodose ganglion. Studies using in situ hybridization histochemistry showed that axotomy of the cervical vagus nerve resulted in increased expression of mRNAs for nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin-3 (NT-3), and for TrkA, TrkB, and TrkC receptors in non-neuronal cells at both the proximal and distal segments of the transected cervical vagus nerve. Moreover, NGF protein was increased in the distal end, and NT-3 protein was increased in both the proximal and the distal ends of the transected nerve 3 days after axotomy. No change of p75(NTR) mRNA was detected in the transected vagus nerve. The induction of each neurotrophin and Trk receptor mRNA was apparent within 1 day after the axotomy and was sustained at least 14 days. By 45 days after the axotomy, a time when axonal reconnection with target tissue is made (integrity of the nerve-target connection was confirmed by the retrograde transport of FluoroGold from the stomach to vagal cell bodies), the levels of neurotrophin and Trk mRNAs in the vagus nerve declined to pre-axotomy levels. TrkA, TrkC, and p75(NTR) mRNA-containing vagal sensory neurons in the nodose ganglion were reduced in number after cervical vagotomy. Neurotrophin-mRNA-containing neurons were not found in the nodose ganglia from either intact or vagotomized rats. The axotomy-induced up-regulation of neurotrophins and Trk receptors mainly in the non-neuronal cells at or near the site of transection suggests that neurotrophins are involved in the survival and regeneration process of the vagus nerve after injury.

Neurotrophins alter the numbers of neurotransmitter-ir mature vagal/glossopharyngeal visceral afferent neurons in vitro

Mature nodose and petrosal ganglia neurons (placodally derived afferent neurons of the vagal and glossopharyngeal nerves) contain TrkA and TrkC, and transport specific neurotrophins [nerve growth factor (NGF), neurotrophin-3 (NT-3), neurotrophin-4 (NT-4)]. This study evaluated neurotrophin influences on the presence of neuropeptides and/or neurotransmitter enzymes in these visceral sensory neurons. NGF, NT-3 and NT-4 (10-100 ng/ml) were applied (5 days) to dissociated, enriched, cultures of mature nodose/petrosal ganglia neurons, and the neurons processed for tyrosine hydroxylase (TH), vasoactive intestinal peptide (VIP), calcitonin gene-related peptide (CGRP) and neurofilament (NF-200) immunocytochemistry. Addition of NGF to nodose/petrosal ganglia neuron-enriched cultures significantly increased the number of TH-immunoreactive (ir) neurons, decreased the number of VIP-ir neurons in the cultures, and did not affect the numbers of CGRP-ir neurons. The addition of an NGF neutralizing antibody attenuated the effects of NGF on TH and VIP-ir neurons. NT-3 increased the number of VIP-ir neurons in the nodose/petrosal ganglia cultures and did not alter the numbers of TH-, or CGRP-ir neurons. The addition of an NT-3 neutralizing antibody attenuated the effects of NT-3 on VIP-ir neurons. NT-4 had no significant effects on the numbers of TH, VIP and CGRP-ir neurons. The absence of neurotrophin-induced changes in the numbers of NF-200-ir neurons in culture showed the lack of neurotrophin-mediated changes in survival of mature vagal afferent neurons. These data demonstrate that specific neurotrophins influence the numbers of neurons labeled for specific neurochemicals in nodose/petrosal ganglia cultures. These data, coupled with previous evidence for the presence of TrkA and TrkC mRNA and of the retrograde transport of NGF and NT-3, suggest important roles for NGF and NT-3 in the maintenance of transmitter phenotype of these mature visceral afferent neurons.

The coexistence of TrkA with putative transmitter agents and calcium-binding proteins in the vagal and glossopharyngeal sensory neurons of the adult rat

The presence of the neurotrophin receptor, TrkA, in neurochemically identified vagal and glossopharyngeal sensory neurons of the adult rat was examined. TrkA was colocalized with calcitonin gene-related peptide (CGRP), parvalbumin, or calbindin D-28k in neurons of the nodose, petrosal and/or jugular ganglia. In contrast, no TrkA-immunoreactive (ir) neurons in these ganglia colocalized tyrosine hydroxylase-ir. About one-half of the TrkA-ir neurons in the jugular and petrosal ganglia contained CGRP-ir, whereas only a few of the numerous TrkA-ir neurons in the nodose ganglion contained CGRP-ir. Although 43% of the TrkA-ir neurons in the nodose ganglion contained calbindin D-28k-ir, few or no TrkA-ir neurons in the petrosal or jugular ganglia were also labeled for either calcium-binding protein. These data show distinct colocalizations of TrkA with specific neurochemicals in vagal and glossopharyngeal sensory neurons, and suggest that nerve growth factor (NGF), the neurotrophin ligand for TrkA, plays a role in functions of specific neurochemically defined subpopulations of mature vagal and glossopharyngeal sensory neurons.

Coexistence of s100beta and putative transmitter agents in vagal and glossopharyngeal sensory neurons of the rat

The coexistence of S100beta with calcitonin gene-related peptide (CGRP), substance P (SP), somatostatin (SOM), nicotinamide adenosine dinucleotide phosphate-diaphorase (NADPH-d), and tyrosine hydroxylase (TH) was examined in the glossopharyngeal and vagal sensory ganglia. S100beta immunoreactive (-ir) neurons in the jugular and petrosal ganglia frequently colocalized CGRP- or SP-ir, whereas S100beta-ir neurons in the nodose ganglion infrequently contained CGRP- or SP-ir. No S100beta-ir neurons in the jugular and petrosal ganglia showed SOM-ir while the small number of SOM-ir neurons in the nodose ganglion colocalized S100beta-ir. Many neurons in the nodose ganglion colocalized S100beta-ir and NADPH-d activity, whereas S100beta-ir neurons in the jugular and nodose ganglia infrequently contained NADPH-d activity. S100beta- and TH-ir were frequently colocalized in nodose ganglion but not in petrosal or jugular ganglion neurons. These findings suggest relationships between S100beta and specific putative transmitters in functions of subpopulations of vagal and glossopharyngeal sensory neurons.

Axonal transport of neurotrophins by visceral afferent and efferent neurons of the vagus nerve of the rat

The receptor-mediated axonal transport of [125I]-labeled neurotrophins by afferent and efferent neurons of the vagus nerve was determined to predict the responsiveness of these neurons to neurotrophins in vivo. [125I]-labeled neurotrophins were administered to the proximal stump of the transected cervical vagus nerve of adult rats. Vagal afferent neurons retrogradely transported [125I]neurotrophin-3 (NT-3), [125I]nerve growth factor (NGF), and [125I]neurotrophin-4 (NT-4) to perikarya in the ipsilateral nodose ganglion, and transganglionically transported [125I]NT-3, [125I]NGF, and [125I]NT-4 to the central terminal field, the nucleus tractus solitarius (NTS). Vagal afferent neurons showed minimal accumulation of [125I]brain-derived neurotrophic factor (BDNF). In contrast, efferent (parasympathetic and motor) neurons located in the dorsal motor nucleus of the vagus and nucleus ambiguus retrogradely transported [125I]BDNF, [125I]NT-3, and [125I]NT-4, but not [125I]NGF. The receptor specificity of neurotrophin transport was examined by applying [125I]-labeled neurotrophins with an excess of unlabeled neurotrophins. The retrograde transport of [125I]NT-3 to the nodose ganglion was reduced by NT-3 and by NGF, and the transport of [125I]NGF was reduced only by NGF, whereas the transport of [125I]NT-4 was significantly reduced by each of the neurotrophins. The competition profiles for the transport of NT-3 and NGF are consistent with the presence of TrkA and TrkC and the absence of TrkB in the nodose ganglion, whereas the profile for NT-4 suggests a p75 receptor-mediated transport mechanism. The transport profiles of neurotrophins by efferent vagal neurons in the dorsal motor nucleus of the vagus and nucleus ambiguus are consistent with the presence of TrkB and TrkC, but not TrkA, in these nuclei. These observations describe the unique receptor-mediated axonal transport of neurotrophins in adult vagal afferent and efferent neurons and thus serve as a template to discern the role of specific neurotrophins in the functions of these visceral sensory and motor neurons in vivo.

Coexistence of calcium-binding proteins in vagal and glossopharyngeal sensory neurons of the rat

The presence and coexistence of the calcium-binding proteins (CaBPs), calbindin D-28k, parvalbumin and S100 protein, were immunohistochemically examined in the glossopharyngeal and vagal sensory ganglia, the carotid body and taste buds. The CaBPs were found in each ganglion with the nodose ganglion containing the largest number of CaBP-immunoreactive (ir) cells (calbindin D-28k > or = S100 >> parvalbumin). The coexistence of CaBPs was found in neurons of the nodose, petrosal, and jugular ganglia. Calbindin D-28k-ir neurons in the nodose and petrosal ganglia frequently colocalized S100-ir whereas calbindin D-28k-ir neurons in the jugular ganglion less frequently contained S100-ir. Only small percentages of calbindin D-28k-ir neurons in each ganglion colocalized parvalbumin. Similarly, S100-ir neurons in the nodose and petrosal ganglia frequently colocalized calbindin D-28k-ir whereas S100-ir neurons in the jugular ganglion less frequently contained calbindin D-28k-ir. Moderate to small percentages of S100-ir neurons in each ganglion colocalized parvalbumin. Parvalbumin-ir neurons nearly always colocalized S100-ir in the nodose, petrosal and jugular ganglia. Moderate to small percentages of parvalbumin-ir neurons in each ganglion colocalized calbindin D-28k. Whereas calbindin D-28k- and S100-ir were colocalized in nerve fibers and cells within taste buds of circumvallate papilla of the tongue, the coexistence of these CaBPs could not be determined in the carotid body. These findings suggest a co-operative role for CaBPs in the functions of subpopulations of nodose and petrosal ganglia neurons.

Neurochemistry of the nodose ganglion

Placode-derived general visceral afferent neurons of the nodose ganglion transmit visceral sensory information from specialized sensory endings of the vagus nerve and its branches to the nucleus of the solitary tract. These neurons are critical in relaying information such as elevations in blood pressure, changes in blood oxygenation, passage of contents through the esophagus and intestines, and distention of the heart, stomach, and lungs to the CNS for reflex maintenance of visceral functions. Multiple neurotransmitters, neuropeptides, calcium binding proteins, and other neuroactive substances are associated with neurons of the nodose ganglion. Many neurons colocalize 2 or more neuroactive substances creating the potential for complex interactions of neurochemical signals in the NTS. Neurons of the nodose ganglion also contain a variety of receptors which respond to transmitters, inflammatory mediators, and neurotrophic factors. The contents of these neurochemicals and receptors are not static as alterations in their expression are noted in response to epigenetic influences. Although not yet well understood, potential factors and mechanisms regulating neurochemical events in the nodose ganglion neurons are discussed.

Immunocytochemical studies of the 5-HT(1A) receptor in ventral medullaryneurons that project to the intermediolateral cell column and contain serotonin or tyrosine hydroxylase immunoreactivity

Activation of serotonin-1A receptors (5-HT(1A)R) in the medulla oblongata lowers sympathetic nerve discharge and blood pressure. Binding sites for 5-HT(1A)R ligands are present in ventral medullary nuclei [e.g., rostral ventrolateral medulla (RVLM), raphe pallidus (RPa), and parapyramidal region (PPR)] that project to sympathetic preganglionic neurons in the intermediolateral cell column (IML). However, the projections and the neurochemical contents of the ventral medullary neurons that are likely to be involved in the hypotensive actions of 5-HT(1A) agonists are unclear. Using a sheep antibody to a fragment of the third intracellular loop of the 5-HT(1A)R, we localized 5-HT(1A)R immunoreactivity (ir) to IML-projecting neurons that were retrogradely labeled with rhodamine beads injected into the IML of adult male rats. The percentages of IML-projecting neurons containing 5-HT(1A)R-ir were 49% in RPa, 34% in PPR, and 44% in RVLM. Using multiple-immunofluorescence labeling, we also demonstrated 5-HT(1A)R-ir in serotonergic (5-HT) and in catecholaminergic (tyrosine hydroxylase; TH-ir) neurons of the ventral medulla. The percentages of 5-HT-ir neurons containing 5-HT(1A)R-ir were 28% in RPa, 18% in PPR, and 31% in raphe obscurus. In addition, 5-HT(1A)R-ir was present in 14% of TH-ir neurons of the RVLM. Moreover, some IML-projecting neurons in the PPR and RPa were doubly immunolabeled for 5-HT(1A)R-ir and 5-HT, and some IML-projecting neurons in the RVLM were doubly immunolabeled for 5-HT(1A)R-ir and TH-ir. These data provide anatomical evidence for the presence of 5-HT(1A)R on serotonergic and catecholaminergic bulbospinal neurons and for their potential role in directly modifying the activity of these ventral medullary neurons.

A novel technique for producing antibody-coated microprobes using a thiol-terminal silane and a heterobifunctional crosslinker

Antibody-coated microprobes are used to measure neuropeptide release in the central nervous system. Although they are not quantitative, they provide the most precise spatial resolution of the location of in vivo release of any currently available method. Previous methods of coating antibody microprobes are difficult and time-consuming. Moreover, using these methods we were unable to produce evenly coated antibody microprobes. This paper describes a novel method for the production of antibody microprobes using thiol-terminal silanes and the heterobifunctional crosslinker, 4-(4-N-maleimidophenyl)butyric acid hydrazide HCl 1/2 dioxane (MPBH). Following silation, glass micropipettes are incubated with antibody to substance P (SP) that has been conjugated to MPBH. This method results in a dense, even coating of antibody without decreasing the biological activity of the antibody. Additionally, this method takes considerably less time than previously described methods without sacrificing the use of antibody microprobes as micropipettes. The sensitivity of the microprobes for SP is in the picomolar range, and there is a linear correlation between the log of SP concentration (M) and B/B0 (r2 = 0.98). The microprobes are stable for up to 3 weeks when stored in 0.1 M sodium phosphate buffer with 50 mM NaCl (pH 7.4) at 5 degrees C. Finally, insertion into the exposed spinal cord of an anesthetized rat for 15 min produces no damage to the antibody coating.

Coexistence of calbindin D-28k and NADPH-diaphorase in vagal and glossopharyngeal sensory neurons of the rat

The presence and coexistence of calbindin D-28k-immunoreactivity (ir) and nicotinamide adenosine dinucleotide phosphate (NADPH)-diaphorase activity (a marker of neurons that are presumed to convert L-arginine to L-citrulline and nitric oxide) were examined in the glossopharyngeal and vagal sensory ganglia (jugular, petrosal and nodose ganglia) of the rat. Calbindin D-28k-ir nerve cells were found in moderate and large numbers in the petrosal and nodose ganglia, respectively. Some calbindin D-28k-ir nerve cells were also observed in the jugular ganglion. NADPH-diaphorase positive nerve cells were localized to the jugular and nodose ganglia and were rare in the petrosal ganglion. A considerable portion (33-51%) of the NADPH-diaphorase positive neurons in these ganglia colocalized calbindin D-28k-ir. The presence and colocalization of calbindin D-28k-ir and NADPH-diaphorase activity in neurotransmitter-identified subpopulations of visceral sensory neurons were also studied. In all three ganglia, calcitonin gene-related peptide (CGRP)-ir was present in many NADPH-diaphorase positive neurons, a subset of which also contained calbindin D-28k-ir. In the nodose ganglion, many (42%) of tyrosine hydroxylase (TH)-ir neurons also contained NADPH diaphorase activity but did not contain calbindin D-28k-ir. These data are consistent with a potential co-operative role for calbindin D-28k and NADPH-diaphorase in the functions of a subpopulation of vagal and glossopharyngeal sensory neurons.

Characterization of substance P release from the intermediate area of rat thoracic spinal cord

Substance P (SP) nerve terminals innervate the intermediolateral cell column (IML) of the thoracic spinal cord, where SP coexists with serotonin (5-HT), neurokinin A (NKA) and thyrotropin-releasing hormone (TRH). Neither the depolarization-induced release of SP nor the presence of other neurochemicals in the regulation of SP release has been directly studied in this system. In the present study, basal and K(+)-stimulated release of SP from the microdissected intermediate area (including the IML, intercalated nucleus and central autonomic nucleus) of the rat thoracic spinal cord, and the regulation of SP release by presynaptic autoreceptors and by coexisting neurochemicals (5-HT, NKA and TRH) were studied using an in vitro superfusion system. Potassium evoked a concentration- and extracellular Ca(2+)-dependent release of SP. In rats pretreated with the serotoninergic neurotoxin, 5,7-dihydroxytryptamine (5,7-DHT), both SP content and the absolute amount of SP released were decreased. However, the fraction of the remaining tissue content of SP released by K+ depolarization was not changed subsequent to 5,7-DHT treatment. Moreover, 5-HT, 5-HT1B agonists (CGS-12066B and RU 24969) and a 5-HT3 agonist (2-methyl-5-HT) did not alter the K(+)-evoked release of SP. These data demonstrate that SP is released from the intermediate area of the rat thoracic spinal cord and some of the SP released comes from serotoninergic nerve terminals. Although 5-HT coexists with SP in the IML, neither endogenous 5-HT nor 5-HT receptor ligands appear to regulate the release of SP. Other colocalized neuropeptides (NKA and TRH) are not involved in the regulation of SP release because neither NKA, a NK2 agonist (GR 64349) nor a TRH analog (MK-771) changed the K(+)-evoked release of SP. A neurokinin-1 (NK1) antagonist (GR 82334) dose-dependently (10(-9)-10(-7) M) increased the K(+)-stimulated release of SP. These data suggest the presence of presynaptic inhibitory NK1 autoreceptors. Whereas, NK1 agonists, [GR 73632 (10(-9)-10(-6) M) and [Sar9, Met (O2)11]SP (10(-8)-10(-6) M)], increased the basal and K(+)-stimulated release of SP, the excitatory effects of GR 73632 were not blocked by the NK1 antagonist. Moreover, GR 73632 increased the efflus of SP to a greater extent in the absence of peptidase inhibitors. Thus, the effect of NK1 agonists on the release of SP may be related to an inhibition of peptide degradation rather than activation of NK1 autoreceptors.

Presence and localization of neurotrophin receptor tyrosine kinase (TrkA, TrkB, TrkC) mRNAs in visceral afferent neurons of the nodose and petrosal ganglia

The presence of mRNAs to the high affinity tyrosine kinase (Trk) receptors for neurotrophins was studied in visceral afferent neurons of the nodose and petrosal ganglia of adult and neonatal rats using in situ hybridization histochemistry. Neurons containing TrkA mRNA were found in the adult nodose and petrosal ganglia. About 10% of nodose ganglion neurons and 38% of petrosal ganglion neurons contained TrkA mRNA. The nodose and petrosal ganglia from 1 day old neonates also expressed TrkA mRNA. No TrkB mRNA-containing neurons were detected in the adult nodose and petrosal ganglia, whereas TrkB mRNA was detected in 1 day old neonatal nodose and petrosal ganglia. TrkC mRNA was found in about 9% of nodose ganglion neurons and 11% of petrosal ganglion neurons of adult rats. Likewise, low but detectable levels of TrkC mRNA were seen in 1 day old neonatal nodose and petrosal ganglia. These data demonstrate the presence of TrkA and TrkC in the adult nodose and petrosal ganglia and provide a substrate for the ongoing neurotrophin-induced regulation of these placodally derived visceral afferent neurons. The altered expression of Trk receptor mRNAs in the nodose and petrosal ganglia between the adult and neonatal rats may reflect developmentally regulated changes in neurotrophin responsiveness.

Inhibition of axoplasmic transport in the rat vagus nerve alters the numbers of neuropeptide and tyrosine hydroxylase messenger RNA-containing and immunoreactive visceral afferent neurons of the nodose ganglion

Previous work showed that axotomy-induced deafferentation of the placode-derived visceral afferent neurons of the nodose ganglion altered their expression of some neuropeptides and tyrosine hydroxylase. The present studies were designed to selectively evaluate the loss of axonal transport on the numbers of vasoactive intestinal polypeptide, tyrosine hydroxylase, and calcitonin gene-related peptide mRNA-containing and immunoreactive neurons in the nodose ganglion of the adult rat. Vinblastine (0.15 mM) application to the cervical vagus nerve was used to block axonal transport between ganglionic perikarya and peripheral targets. In situ hybridization histochemistry with 35S-labeled oligonucleotide probes was used to both quantify the number of mRNA-containing neurons and to assess the density of mRNA expression per neuron, and immunocytochemistry was used to visualize the number of immunoreactive neurons. The efficacy of vinblastine to inhibit axonal transport was verified by evaluating the build-up of calcitonin gene-related peptide immunoreactive in the vagus nerve immediately rostral to the site of drug application. The absence of vinblastine-induced neuronal damage was verified by the relative absence of degenerating nerves in the vagus nerve caudal to the site of drug application. Vinblastine treatment of the vagus nerve increased the numbers of vasoactive intestinal peptide mRNA-containing neurons and vasoactive intestinal peptide-immunoreactive neurons in the nodose ganglion at three, seven and 14 days, and increased the numbers of calcitonin gene-related peptide mRNA-containing and calcitonin gene-related peptide-immunoreactive neurons in the nodose ganglion at one, three and seven days. The average labeling density of vasoactive intestinal peptide mRNA-containing neurons was also increased following vinblastine treatment. Vinblastine treatment of the cervical vagus nerve, however, led to the appearance of low-labeling density calcitonin gene-related peptide mRNA-neurons and resulted in reduction of the average labeling density for calcitonin gene-related peptide mRNA-containing neurons. In contrast, application of vinblastine to the cervical vagus nerve, decreased the number of tyrosine hydroxylase mRNA-containing and tyrosine hydroxylase-immunoreactive neurons in the nodose ganglion. In summary, inhibition of the axoplasmic transport between the periphery and the visceral sensory perikarya appeared to alter vasoactive intestinal peptide, calcitonin gene-related peptide, and tyrosine hydroxylase expression and content in visceral sensory neurons of the nodose ganglion. These data suggest the presence of an axonally transported influence on the regulation of neuropeptide and neurotransmitter enzyme synthesis in mature placode-derived visceral sensory neurons.

Parvalbumin and calbindin D-28k in vagal and glossopharyngeal sensory neurons of the rat

Parvalbumin- and calbindin D-28k-immunoreactivities (ir) were examined in the glossopharyngeal and vagal sensory ganglia (petrosal, nodose and jugular ganglia), the carotid sinus nerve and the carotid body. Parvalbumin-ir nerve cells were mostly localized in the petrosal and nodose ganglia and were rare in the jugular ganglion. Calbindin D-28k-ir nerve cells were found in moderate and large numbers in the petrosal and nodose ganglia, respectively. Only a few calbindin D-28k-ir nerve cells were observed in the jugular ganglion. The carotid sinus nerve and carotid body contained numerous calbindin D-28k-ir nerve fibers but few parvalbumin-ir nerve fibers. Studies of the coexistence of these calcium-binding proteins with calcitonin gene-related peptide (CGRP)- and tyrosine hydroxylase (TH)-ir showed that CGRP-ir was rarely colocalized in parvalbumin- or calbindin D-28k-ir nerve cells in the petrosal or nodose ganglion. Moreover, TH-ir was not generally contained in parvalbumin-ir nerve cells in the petrosal, nodose and jugular ganglia while a portion (15-19%) of calbindin D-28k-ir neurons in the petrosal and nodose ganglia colocalized TH-ir. These findings are consistent with the involvement of calcium-binding proteins, particularly calbindin D-28k, in the function of visceral sensory neural systems of the glossopharyngeal and vagus nerves and, perhaps, in baro- and chemoreceptor neurotransmission.

Tachykinin receptors in the spinal cord

In summary, all three tachykinin receptors appear to be important modulators of physiological systems in the spinal cord. However, although there is a good deal of data concerning binding characteristics in peripheral tissues, work done in the spinal cord is scanty, leading to a number of unanswered questions. Firstly, Lui et al. (1993) have suggested a discrepancy between the location of SP binding sites and SP containing terminals. This might explain the conflicting evidence on the role of NK1 receptors in the dorsal horn. Furthermore, evidence that NK2 receptors are involved in nociception is increasing, however binding sites for these receptors in the spinal cord have not been demonstrated. This appears to be due to the difficulty in locating an ideal receptor specific ligand. The role of NK2 receptors in autonomic function is also unclear, perhaps for the same reason. Finally, there is evidence indicating that NK3 binding sites are increased following transection of the LIV-VI dorsal roots, however, studies on the effects of inflammation have not been done, as they have with the NK1 and NK2 receptors. All of these and many more unanswered questions require further investigation.

Plasticity of tyrosine hydroxylase and vasoactive intestinal peptide messenger RNAs in visceral afferent neurons of the nodose ganglion upon axotomy-induced deafferentation

The nodose ganglion contains placode-derived visceral sensory neurons of the vagus nerve. Previous study showed that axotomy-induced deafferentation reduced the number of tyrosine hydroxylase-immunoreactive and increased the number of vasoactive intestinal peptide-immunoreactive neurons in the ganglion. The present study was conducted to determine whether the changes in neuropeptide/neurotransmitter enzyme content are associated with changes in the expression of tyrosine hydroxylase and vasoactive intestinal peptide messenger RNAs in the nodose ganglion. We used in situ hybridization histochemistry with 35S-labeled oligonucleotide probes for tyrosine hydroxylase and vasoactive intestinal peptide precursor messenger RNAs. Peripheral axotomy of visceral afferent inputs reduced tyrosine hydroxylase messenger RNA and increased vasoactive intestinal peptide messenger RNA expression in neurons of the nodose ganglion of the rat. The number of tyrosine hydroxylase messenger RNA-containing neurons was significantly reduced at three, seven and 14 days after axotomy-induced deafferentation compared with intact and sham-operated controls. Labeling density of tyrosine hydroxylase messenger RNA-containing neurons was significantly reduced at three and seven days. Conversely, the number of vasoactive intestinal peptide messenger RNA-containing neurons increased significantly at three, seven and 14 days, while the labeling density of vasoactive intestinal peptide messenger RNA-containing neurons also increased at one, three, seven and 14 days. The results of the present study indicate that the axotomy-induced down-regulation of tyrosine hydroxylase and up-regulation of vasoactive intestinal peptide in the neurons of the nodose ganglion are associated with changes in their messenger RNAs in response to axotomy-induced deafferentation.

Release of [3H]5-hydroxytryptamine from the intermediate area of rat thoracic spinal cord is modulated by presynaptic autoreceptors

Serotonin (5-HT) nerve terminals innervate sympathetic preganglionic neurons of the intermediolateral cell column (IML); however, neither the depolarization-induced release of 5-HT nor the presence of presynaptic modulatory autoreceptors have been directly studied in this system. We used in vitro superfusion of the microdissected intermediate area (including the intermediolateral cell column, intercalated nucleus, and central autonomic nucleus) of the rat thoracic spinal cord to measure basal and stimulated release of preloaded [3H]5-HT. Elevated K+ evoked a concentration- and Ca(2+)-dependent release of [3H]5-HT. Exogenous 5-HT and the 5-HT1B agonist, CGS-12066B, both decreased the K(+)-stimulated release of [3H]5-HT. A 5-HT1B antagonist (methiothepin) blocked the 5-HT- and the CGS-12066B-induced inhibition of K(+)-evoked release of [3H]5-HT. A 5-HT1A antagonist (NAN-190) did not alter the inhibitory actions of exogenous 5-HT. Moreover, a 5-HT1A agonist (8-OH-DPAT), a 5-HT2A/2C agonist [(+/-)-DOI hydrochloride), and a 5-HT3 agonist (2-methyl-5-HT) did not alter the K(+)-evoked release of [3H]5-HT. These data demonstrate that 5-HT is released from the intermediate area of the rat thoracic spinal cord. The 5-HT receptor subtype involved in the inhibition of the evoked release of [3H]5-HT is of the 5-HT1B subtype. These findings may help clarify the complex role of 5-HT in spinal regulation of the sympathetic nervous system.

Peripheral deafferentation alters calcitonin gene-related peptide mRNA expression in visceral sensory neurons of the nodose and petrosal ganglia

Visceral sensory neurons of the glossopharyngeal and vagus nerves are located in the petrosal and nodose ganglia, respectively. Our previous studies showed that peripheral axotomy which removes afferent input to visceral sensory perikarya decreased the number of calcitonin gene-related peptide (CGRP)-immunoreactive (ir) neurons in the petrosal but not the nodose ganglion. To evaluate axotomy-induced changes in CGRP mRNA expression, we used in situ hybridization histochemistry with 35S-labeled oligonucleotide probes. CGRP mRNA-containing neurons were studied 1, 3, 7 and 14 days after peripheral deafferentation of the left nodose and petrosal ganglia via transection of the left cervical vagus, superior laryngeal, glossopharyngeal and carotid sinus nerves. The numbers of CGRP mRNA-containing neurons in the deafferented petrosal ganglion were significantly reduced at 3, 7 and 14 days compared to either intact or sham-operated control ganglia. However, the density of hybridization product in the positively-labeled petrosal ganglion cells was not significantly changed. The numbers of CGRP mRNA-containing neurons in the deafferented nodose ganglion were significantly reduced at 3 and 7 days. These data suggest that axotomy-induced changes in CGRP-ir neurons of the petrosal ganglion correlate with changes in CGRP mRNA and probably result from altered CGRP gene expression. In addition, in situ hybridization histochemistry revealed changes in CGRP neurons of the nodose ganglion which were not apparent with immunocytochemistry.

Neurokinin A coexists with substance P and serotonin in ventral medullary spinally projecting neurons of the rat

The coexistence of neurokinin A (NKA) with substance P (SP) and serotonin (5-HT) in ventral medullary neurons of the parapyramidal region and nucleus raphe pallidus of the rat was studied using multiple immunofluorescence labeling. Nearly all of the NKA-immunoreactive (IR) cells in the parapyramidal region and raphe pallidus were SP-IR nd 5-HT-IR, whereas about 70% of the SP-IR neurons and about 60% of the 5-HT-IR neurons contained NKA-IR. There were no apparent differences in the patterns of coexistence between parapyramidal and raphe pallidus neurons. NKA-IR neurons, which colocalized SP-IR and 5-HT-IR, were studied for projections to the lumbar and thoracic spinal cord by use of retrograde transport of fluorescent tracer. Whereas about 50% of the retrogradely labeled neurons of the parapyramidal region and raphe pallidus contained NKA-IR, nearly all of the NKA-IR neurons projected to the thoracic and lumbar spinal cord. In addition, some NKA-IR neurons in the ventral medulla were retrogradely labeled with tracer from localized injections into the thoracic intermediolateral cell column. In summary, this study demonstrated that NKA-IR is colocalized with SP-IR in bulbospinal serotonergic neurons of the parapyramidal region and raphe pallidus, which are known to regulate sensory, motor, and autonomic activities of the spinal cord.

Autoradiographic localization of 5-hydroxytryptamine1A, 5-hydroxytryptamine1B and 5-hydroxytryptamine1C/2 binding sites in the rat spinal cord

Autoradiographic techniques revealed that 5-hydroxytryptamine1A, 5-hydroxytryptamine1B and 5-hydroxytryptamine1C/2 binding sites are differentially distributed in the spinal cords of adult male rats. In the dorsal horn, 5-hydroxytryptamine1A sites were dense in all laminae; 5-hydroxytryptamine1B sites were more dense in laminae I, III and IV than in lamina II; while 5-hydroxytryptamine1C/2 sites were very sparse. The dorsal commissure gray matter also exhibited very dense 5-hydroxytryptamine1A and 5-hydroxytryptamine1B binding. In the intermediate and central gray matter, all three sites were moderately dense at autonomic levels, with exceptionally dense1C/2 binding restricted to the intermediolateral nucleus at rostral thoracic levels. In the ventral horn, 5-hydroxytryptamine1A and 5-hydroxytryptamine1B sites were very sparse (except for very dense 5-hydroxytryptamine1A sites located in the dorsolateral nucleus of the pudendal nerve), while 5-hydroxytryptamine1C/2 sites were relatively dense in motor nuclei. Surprisingly, 5-hydroxytryptamine1B sites were moderately dense in the dorsal column corticospinal tract. These studies will provide an anatomical perspective for interpretation of the complex role of 5-hydroxytryptamine in regulating spinal cord function.

Presence and coexistence of putative neurotransmitters in carotid sinus baro- and chemoreceptor afferent neurons

The presence and coexistence of tyrosine hydroxylase (TH), vasoactive intestinal polypeptide (VIP), calcitonin gene-related peptide (CGRP), substance P (SP) and galanin (GAL) were studied in the petrosal and jugular neurons innervating the carotid body and carotid sinus of the rat. The retrograde labeling of the carotid sinus nerve with Fluoro-gold (FG) demonstrated that most (94.5%) FG-labeled ganglionic neurons were observed in the petrosal ganglion. Fewer (5.2%) FG-labeled neurons were seen in the jugular ganglion and very few (0.3%) were observed in the nodose ganglion. Immunohistochemistry revealed that subpopulations of TH-, VIP-, CGRP-, SP- and GAL-immunoreactive (-ir) neurons in the petrosal ganglion projected to the carotid sinus nerve. Approximately 4% of FG-labeled neurons contained TH-ir and were predominantly found in the caudal portion of the petrosal ganglion. Nearly 90% of total TH-ir neurons in the petrosal ganglion were labeled with FG. Less than 1% of FG-labeled neurons were immunoreactive for VIP in this ganglion. In the petrosal ganglion, 25% of FG-labeled neurons contained CGRP-ir, and 16.7% of FG-labeled neurons contained SP-ir. 30% of CGRP-ir or SP-ir neurons in the petrosal ganglion were labeled with FG. In the jugular ganglion, no TH- or VIP-ir neurons projected to the carotid sinus nerve and only small populations of CGRP- or SP-ir neurons projected to the carotid sinus nerve. Many FG-labeled and GAL-ir neurons were observed in the petrosal and jugular ganglia.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypotensive effects of 5-HT1A receptor activation: ventral medullary sites and mechanisms of action in the rat

Serotonin-1A (5-HT1A) binding sites were previously localized in several regions of the ventral medulla associated with neural regulation of the cardiovascular system. Some of these binding sites were associated with serotonergic neurons of the ventral medulla. The purpose of these studies was to assess and characterize hypotensive responses to a 5-HT1A agonist, (8-hydroxy-dipropylaminotetraline, 8-OH-DPAT), administered to the ventral medulla of the rat, to correlate the responsive ventral medullary sites with the distribution of 3H-8-OH-DPAT binding sites, and to assess the role of serotonergic systems in mediating the hypotensive responses. Ventral medullary application of 8-OH-DPAT caused dose-related reductions in mean arterial pressure and heart rate which were mediated by the autonomic nervous system. The hypotensive response to 8-OH-DPAT was attenuated by pretreatment with the 5-HT1A antagonists, spiperone or NAN-190. Microinjections of 8-OH-DPAT into ventral medullary structures revealed that 8-OH-DPAT responsive sites included the raphe pallidus, the parapyramidal region, and the rostral ventrolateral medulla. The role of serotonergic terminals in mediating the responses of 8-OH-DPAT was evaluated in animals pretreated with the serotonin nerve toxin, 5,7-dihydroxytryptamine (5,7-DHT). Cardiovascular responses to ventral medullary application of 8-OH-DPAT were unaffected by the selective depletion of serotonin. Thus, whereas the hypotensive responses elicited by 8-OH-DPAT in the raphe pallidus and parapyramidal region may involve serotonergic neurons, other non-serotonergic sites (e.g. the rostral ventrolateral medulla) can mediate the hypotensive actions of 8-OH-DPAT.

Distribution, origin and plasticity of galanin-immunoreactivity in the rat carotid body

The distribution, origin and plasticity of galanin immunoreactivity in the rat carotid body was examined using an indirect immunofluorescence method. Galanin-immunoreactive nerve fibers were observed around the blood vessels as well as around the clusters of glomus and sustentacular cells. A double-immunofluorescence method revealed the coexistence of galanin- and calcitonin gene-related peptide-immunoreactivities in these nerve fibers. In the jugular, petrosal and nodose ganglia which supply the sensory nerve fibers to the carotid body, subpopulations of neurons showed both galanin- and calcitonin gene-related peptide-immunoreactivities. In the superior cervical ganglion, a few neurons were immunoreactive for galanin but not calcitonin gene-related peptide. While the nerve fibers showing both galanin- and calcitonin gene-related peptide-immunoreactivities disappeared after transection of the carotid sinus nerve, many galanin-immunoreactive nerve fibers without calcitonin gene-related peptide-immunoreactivity appeared throughout the operated carotid body. In addition, galanin-immunoreactive glomus cells which were not observed in the normal carotid body, were apparent at one and three days after transection of the carotid sinus nerve. At seven days after the carotid sinus nerve transection, the galanin-immunoreactive glomus cells disappeared. In the superior cervical ganglion, the number of galanin-immunoreactive neurons increased from one day after transection of the carotid sinus nerve. Within three days after the carotid sinus nerve transection in combination with superior cervical ganglion-ectomy, all galanin-immunoreactive nerve fibers disappeared, while many galanin-immunoreactive glomus cells appeared in the operated carotid body. At seven days after this operation, the number of galanin-immunoreactive glomus cells decreased and a few galanin-immunoreactive nerve fibers with or without calcitonin gene-related peptide-immunoreactivities appeared. Transection of the vagus nerve had no effect on the number or distribution of galanin-immunoreactivity in the carotid body. Disappearance of galanin- and calcitonin gene-related peptide-immunoreactive nerve fibers after transection of the carotid sinus nerve suggests that the majority of those nerve fibers originate from petrosal neurons which colocalize galanin- and calcitonin gene-related peptide-immunoreactivity. In addition, the carotid sinus nerve transection may cause the acquisition of galanin-immunoreactivity in originally immunonegative glomus cells, and in nerve fibers which probably originate from the superior cervical ganglion.

Neurokinin B peptide-2 neurons project from the hypothalamus to the thoracolumbar spinal cord of the rat

The presence and location of CNS neurokinin B peptide-2-like immunoreactive neurons that project to the spinal cord were studied by a combination of retrograde transport of fluorescent dye (FluoroGold) and fluorescence immunocytochemistry. After injections of FluoroGold into the thoracic or lumbar segments of the rat spinal cord, serial sections of brain were stained with antisera directed against neurokinin B peptide-2. The results of the study showed that neurokinin B peptide-2-like immunoreactive neurons were located in the nucleus arcuate, median eminence, ventral and external bed nuclei of the stria terminalis, dorsal hypothalamic area, and medial habenula. Neurokinin B peptide-2 neurons that give rise to the long descending projections from the hypothalamus to thoracolumbar spinal cord were found only in the dorsal hypothalamic area. Approximately 36% of the neurokinin B peptide-2 neurons in the dorsal hypothalamic area projected to the spinal cord, whereas about 28% of the spinal projecting neurons in the dorsal hypothalamic area contained neurokinin B peptide-2-like immunoreactivity. Most of the spinal projecting neurokinin B peptide-2 neurons in the dorsal hypothalamic area had a cell size of 15 x 25 microns. In the spinal cord, immunoreactive neurokinin B peptide-2 fibers and terminals were distributed mainly in the superficial dorsal horn and the central autonomic area, with the highest density in laminae II and X, with less density in laminae IV and V. A few neurokinin peptide-2 fibers and terminals were also found in the ventral horn of the spinal cord. The results of the present study show that hypothalamic neurokinin B peptide-2 neurons are the main source of the spinal neurokinin B peptide-2.

Cytochrome oxidase activity in vagal and glossopharyngeal visceral sensory neurons of the rat: effect of peripheral axotomy

Cytochrome oxidase (CO) activity, an endogenous metabolic marker, was examined in visceral sensory neurons of the rat nodose and petrosal ganglia by using enzyme histochemistry. In the normal nodose and petrosal ganglia, nerve cells showed various degrees of staining intensity. The population of darkly stained neurons in the nodose ganglion was higher than in the petrosal ganglion. Axotomy of the peripheral axons of these bipolar sensory neurons was used to study potential changes in ganglionic cellular metabolism associated with loss of afferent inputs and/or injury. Peripheral axotomy had a significant effect on CO activity in the nodose ganglion. By 3 days after axotomy, darkly stained neurons decreased in number and lightly stained neurons, which were not observed in the normal ganglion, appeared in the nodose ganglion. At 7 days after axotomy, the average population of these lightly stained neurons increased to 29% in the nodose ganglion. Subsequently, the population decreased so that at 14 days and 21 days, 19% and 7% respectively of neurons were stained lightly. Even at 28 days after axotomy, the lightly stained neurons were still observed. In the petrosal ganglion, no remarkable change was observed at any stage after axotomy. These results suggest that metabolic activity decreases in some nodose neurons after peripheral nerve section.

Autoradiographic localization of 5HT1 binding sites in autonomic areas of the rat dorsomedial medulla oblongata

Serotonin (5HT) binding sites in autonomic portions of the dorsomedial medulla oblongata of the rat were localized using autoradiographic techniques with radioactive ligands that express high affinity for the 5HT1 (3H-5HT), 5HT1A (3H-8OH-DPAT), or 5HT1B (125I-CYP with isoproterenol) receptor subtypes. 5HT1A sites were densely distributed in the nucleus tractus solitarius (NTS), with the highest densities localized to the interstitial subnucleus and the central subnucleus. 5HT1B sites were also found in the NTS, with the highest densities localized to the substantia gelatinosa subnucleus. The dorsal motor nucleus of the vagus nerve and nucleus ambiguus exhibited low densities of 5HT1B sites. However, the nucleus intercalatus, a cerebellar relay nucleus that also contains dendrites of vagal parasympathetic preganglionic neurons and receives autonomic forebrain afferent input, showed very dense 5HT1B sites. The promontorium, paratrigeminal islands, and the dorsomedial portion of the trigeminal nucleus (DM5), which are areas of viscerosomatic integration, exhibited high densities of both 5HT1A and 5HT1B sites. The area postrema contained low levels of both 5HT1A and 5HT1B sites. Visceral deafferentation via cervical vagotomy or nodose ganglionectomy caused a significant decrease in 5HT1A sites in the interstitial subnucleus of the NTS ipsilateral to the lesion. No changes were seen in 5HT1B sites. These studies suggest that 5HT1A and 5HT1B sites are involved in the processing of visceral sensory information in the NTS and associated areas. Based upon viscerotopic organization of the NTS, 5HT1A sites appear preferentially distributed in portions of the NTS that are associated with the coordination of swallowing, respiration, and cardiovascular function, while 5HT1B sites appear preferentially distributed in areas of the NTS associated with gastrointestinal, hepatic, pancreatic, and cardiovascular function. However, since these association were not absolute and there was a great deal of overlap between the two sites, speculation regarding their specific functions in autonomic control must await pharmacological examination.

Autoradiographic localization of 5HT1 binding sites in the medulla oblongata of the rat

Serotonin (5HT) binding sites in the medulla oblongata of the rat were localized using autoradiographic techniques with radioactive ligands that express high affinity for the 5HT1 (3H-5HT), 5HT1A (3H-80H-DPAT), or 5HT1B (125I-CYP with isoproterenol) receptor subtypes. 5HT1A sites were concentrated primarily in certain sensory regions of the medulla and in regions that contain serotonergic neurons. 5HT1B sites were diffusely distributed throughout the reticular formation and motor regions as well as being localized to certain sensory regions. A surprising finding was an association of 5HT1B binding sites with the corticospinal tract. 3H-5HT binding generally reflected the combined pattern of 5HT1A and 5HT1B sites but was also extremely dense in the choroid plexus, which exhibited virtually no 5HT1A or 5HT1B ligand binding. Presumably this binding, which was blocked by ketanserin, corresponds to 5HT1C sites. Administration of the serotonergic neurotoxin 5,7-dihydroxytryptamine reduced 5HT1A binding sites in regions of the medulla that contain serotonergic neuronal cell bodies. 5HT1B binding was not significantly altered in any area of the medulla. These studies indicate an important role for 5HT1A ligands in the processing of visceral and somatic sensory information, in regulation of certain cerebellar afferent projections, and in the regulation of serotonergic neuronal activity. 5HT1B ligands would be expected to regulate visceral and somatic efferent activity, as well as sensory information and reticular efferent activity, and might presynaptically regulate cortical inputs to the brain stem and spinal cord.

5-Hydroxytryptamine1C/2 agonists in the thoracic spinal cord: cardiovascular effects and binding sites in the intermediolateral cell column

The presence of 5-hydroxytryptamine (5-HT)1C/2 binding sites in autonomic regions of the thoracic spinal cord and their role in the regulation of sympathetic outflow to the cardiovascular system were examined. Light microscopic receptor autoradiography was used to visualize the binding of the 5-HT1C/2 ligand, [125I]-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane [( 125I]DOI). In thoracic spinal cord, a discrete and preferential localization of specific [125I]DOI binding sites was found in the intermediolateral cell column. To determine the mean arterial pressure (MAP) and heart rate (HR) effects resulting from activation of 5-HT1C/2 receptors in spinal cord, DOI and alpha-methyl-5-HT were administered intrathecally (i.t.) to anesthetized, artificially ventilated rats. DOI (1-100 micrograms) caused initial decreases followed by increases in MAP and HR, whereas alpha-methyl-5-HT (1-30 micrograms) only decreased MAP and HR. The distribution of [125I]DOI after i.t. administration and the effects of a peripherally administered 5-HT1C/2 antagonist 6-methyl-1-(1-methylethyl)-ergoline-8 beta-carboxylic acid, 2-hydroxyl-1-methyl propyl ester and maleate salt (LY53857) showed that the pressor effects of i.t. DOI were due to peripheral leakage and suggested that the depressor effects were due to a spinal site of action. The depressor effects of DOI were prevented by peripheral administration of phentolamine. Pretreatment with i.t. administration of 5-HT1C/2 antagonists (LY53857, ketanserin and mianserin) did not block the depressor or bradycardic effects of i.t. administration of DOI. Only LY53857 was effective in blocking the depressor effects of i.t. administration of alpha-methyl-5-HT.(ABSTRACT TRUNCATED AT 250 WORDS)

Calretinin-immunoreactivity in vagal and glossopharyngeal sensory neurons of the rat: distribution and coexistence with putative transmitter agents

Immunoreactivity for the calcium binding protein, calretinin (calretinin-ir), was demonstrated in cell bodies of vagal and glossopharyngeal sensory ganglia (jugular, petrosal, and nodose ganglia) and in associated nerve fibers. In the jugular and petrosal ganglia, many calretinin-ir neurons were also immunoreactive for calcitonin gene-related peptide and substance P. In the nodose ganglion, most of the calretinin-ir neurons lacked these peptides. None of the calretinin-ir neurons in these ganglia were also immunoreactive for tyrosine hydroxylase.

Axotomy alters putative neurotransmitters in visceral sensory neurons of the nodose and petrosal ganglia

Acute peripheral axotomy of the visceral sensory neurons of the vagus and glossopharyngeal nerves removes peripheral depolarizing and trophic influences to their sensory ganglia. To study axotomy-induced changes in the putative neurotransmitters of visceral sensory neurons, rats were sacrificed 1, 3, 7 or 14 days after transection of either the cervical vagus and superior laryngeal nerves (to affect peripheral axotomy of the nodose ganglion) or the glossopharyngeal and carotid sinus nerves (to affect peripheral axotomy of the petrosal ganglion). The numbers of tyrosine hydroxylase (TH)-immunoreactive (ir), vasoactive intestinal peptide (VIP)-ir, calcitonin-gene-related peptide (CGRP)-ir, and substance P (SP)-ir neurons in the respective ganglia were analyzed in axotomized and control ganglia. In the nodose ganglion, axotomy of the cervical vagus resulted in a rapid (by 1 day) reduction in the number of TH-ir cells, whereas VIP-ir neurons were dramatically increased in number by 3 days. CGRP- and SP-ir cells in the nodose ganglion were relatively unaffected by axotomy. In the petrosal ganglion, axotomy of the glossopharyngeal and carotid sinus nerves greatly reduced the number of TH-ir cells but did not alter the number VIP-ir neurons. CGRP- and SP-ir neurons in the petrosal ganglion were reduced in number by axotomy. Thus, axotomy of visceral sensory neurons differentially changed the content and perhaps the expression of putative transmitters. Differential changes were seen among transmitters in a single ganglia and between ganglia. These data demonstrate the plasticity of putative neurotransmitter systems in visceral afferent systems of adult rats.

Diversity in mammalian tachykinin peptidergic neurons: multiple peptides, receptors, and regulatory mechanisms

The tachykinins comprise a family of closely related peptides that participate in the regulation of diverse biological processes. The tachykinin peptides substance P, neurokinin A, neurokinin A(3-10), neuropeptide K, and neuropeptide gamma are produced from a single preprotachykinin gene as a result of differential RNA splicing and differential posttranslational processing. Another tachykinin, neurokinin B, is produced from a separate preprotachykinin gene. These preprotachykinin mRNAs and peptide products are differentially distributed throughout the nervous system. Three distinct G protein-coupled tachykinin receptors exist for these tachykinin peptides. The three receptors interact differentially with the tachykinin peptides and are uniquely distributed throughout the nervous system. The NK-1 receptor preferentially interacts with substance P, the NK-2 receptor prefers neurokinin A, neuropeptide K, and neuropeptide gamma, and the NK-3 receptor interacts best with neurokinin B. Examples of the roles of tachykinin peptidergic neuronal systems are taken from the spinal cord sensory system and the nigrostriatal extrapyramidal motor system. Analysis of the functional significance of multiple tachykinin peptide systems, receptor-second messenger coupling mechanisms, and developmental and regulatory mechanisms underlying peptide mRNA and receptor expression represent areas of current and future investigation.

Discrete localization of high-density 5-HT1A binding sites in the midline raphe and parapyramidal region of the ventral medulla oblongata of the rat

Serotonergic agonists that interact with the 5-HT1A receptor subtype cause marked decreases in blood pressure when administered to the medulla oblongata. In the present study, specific binding of the 5-HT1A-specific ligand, [3H]8-OH-DPAT, was determined in sections of the rat medulla oblongata using autoradiographic techniques. The highest density of binding was associated with the midline raphe nuclei and the parapyramidal regions of the rostral ventral medulla, areas that contain serotonergic neurons. Administration of the serotonergic neurotoxin, 5,7-dihydroxytryptamine (5,7-DHT), 2 weeks prior to sacrifice, resulted in a marked loss of binding in the medullary raphe nuclei and the parapyramidal region. These results demonstrate the presence of 5-HT1A binding sites in discrete regions of the ventral medulla and are consistent with the hypothesis that 5-HT1A agonists reduce blood pressure by directly suppressing the activity of serotonergic neurons in the ventral medulla.

Evidence for co-existence of thyrotropin-releasing hormone, substance P and serotonin in ventral medullary neurons that project to the intermediolateral cell column in the rat

The present study was conducted to determine if substance P-, thyrotropin-releasing hormone- and/or serotonin-immunoreactivities coexist in ventral medullary neurons that project to the intermediolateral cell column in the rat. Neurons that projected to the intermediolateral cell column were identified by the presence of retrogradely transported rhodamine bead-labeled microspheres in the cell body after an injection of the microspheres into the intermediolateral cell column of the third thoracic spinal cord segment. Co-existence was determined by using a combination of dual color immunohistochemistry and serial 4-microns sections that were immunostained with different antibodies. Antibodies to substance P, serotonin, and pre-pro-thyrotropin releasing hormone160-169 were used to identify substance P, serotonin and thyrotropin-releasing hormone, respectively. Neurons that contained substance P-, thyrotropin-releasing hormone- and/or serotonin-immunoreactivities and that projected to the intermediolateral cell column were present in the nucleus raphe magnus, the nucleus raphe pallidus, the nucleus reticularis magnocellularis pars alpha, the paragigantocellular reticular nucleus and the parapyramidal region. Neurons that projected to the intermediolateral cell column, in each of these regions, were found to contain each of the following combinations of immunoreactive neurochemicals: substance P and thyrotropin-releasing hormone: substance P and serotonin; thyrotropin-releasing hormone and serotonin; or substance P, thyrotropin-releasing hormone and serotonin. In addition, most of the regions also contained neurons that appeared to contain only one of the neurochemicals and that also projected to the intermediolateral cell column. The greatest number of neurons that projected to the intermediolateral cell column and that also contained two or more co-existing neurochemicals was present in the midline regions. This study demonstrates the presence of neurons in the ventral medulla that project to the intermediolateral cell column and contain three co-existing neurochemicals. This study also demonstrates the use of a new method for the localization of three neurochemicals in single projection-specific neurons.

Studies on the coexistence of substance P with other putative transmitters in the nodose and petrosal ganglia

Visceral afferent neurons of the nodose and petrosal ganglia are immunoreactive (ir) for many neurotransmitters [e.g., substance P (SP), neurokinin A (NKA), calcitonin gene-related peptide (CGRP), and dopamine (tyrosine hydroxylase-ir; TH)]. Coexistence of SP-ir with NKA-, CGRP-, or TH-ir was studied in individual neurons of the rat ganglia using fluorescence immunocytochemistry. SP- and NKA-ir were present in equal numbers of cells and were consistently colocalized. SP- and CGRP-ir were found to be similarly distributed in scattered cells, concentrated mostly in the rostral pole of the nodose ganglion and in the petrosal ganglion. SP-ir completely coexisted with CGRP-ir. However, there was at least twice the number of CGRP-ir neurons as SP-ir neurons, and thus CGRP-ir neurons that did not contain SP-ir were also present. In contrast, SP- and TH-ir had different distributions in both the nodose and the petrosal ganglia. SP-ir was located in the more rostral regions of both the nodose and petrosal ganglia, whereas TH-ir was detected throughout the entire nodose ganglion and only in the most caudal region of the petrosal ganglion. There was no coexistence of SP- and TH-ir. These data demonstrate the differential localization and coexistence of putative transmitters in visceral sensory neurons in the nodose and petrosal ganglia.

Enkephalin-immunoreactive neuronal projections from the medulla oblongata to the intermediolateral cell column: relationship to substance P-immunoreactive neurons

The present study investigated the ventral medullary distribution of enkephalin-immunoreactive neurons that project to the intermediolateral cell column and the relationship of these neurons to substance P-immunoreactive neurons. Neurons that projected to the intermediolateral cell column were identified by the presence of rhodamine-labeled microspheres within the neuronal cell body after an injection of the microspheres into the intermediolateral cell column of the third thoracic spinal cord segment. Enkephalin- and substance P-immunoreactivities were identified by dual-color immunohisto-chemistry. Enkephalin-immunoreactive neurons that projected to the intermediolateral cell column were present in the raphe magnus, the nucleus reticularis magnocellularis pars alpha, the paragigantocellular reticular nucleus, and the parapyramidal region. These neurons were present throughout the rostrocaudal extent of each of these nuclei. However, in the raphe magnus the greatest number was present at more rostral levels of the nucleus. The morphology and distribution of enkephalin-immunoreactive neurons that projected to the intermediolateral cell column were similar to those of enkephalin-immunoreactive neurons that were not observed to contain rhodamine-labeled microspheres. Substance P- and enkephalin-immunoreactive neurons that projected to the intermediolateral cell column were present in similar distributions in each of the nuclei studied, except the raphe magnus. The raphe magnus contained more enkephalin- than substance P-immunoreactive neurons at rostral levels and more substance P-immunoreactive neurons than enkephalin-immunoreactive neurons at caudal levels. Coexistence of substance P- and enkephalin-immunoreactivities in ventral medullary neurons that projected to the intermediolateral cell column was rarely seen. These studies support the hypothesis that ventral medullary enkephalinergic neurons project to the intermediolateral cell column where they could act to modulate preganglionic sympathetic activity.

Serotonin and substance P colocalization in medullary projections to the nucleus tractus solitarius: dual-colour immunohistochemistry combined with retrograde tracing

Serotonin (5HT) and substance P (SP) are colocalized in terminals within the nucleus tractus solitarius (NTS). The purpose of the present study was to determine the origin of these terminals. 5HT- and SP-immunoreactivities (IR) were visualized using dual-colour immunofluorescence histochemistry with amino-4-methylcoumarin-3-acetic acid- and fluorescein isothiocyanate-conjugated secondary antisera, while NTS-afferent neurons were visualized by retrograde labelling with rhodamine beads. Extensive colocalization of 5HT- and SP-IR was seen in NTS-afferent neurons located in the nucleus raphe pallidus, nucleus raphe obscurus, nucleus raphe magnus, and in the parapyramidal region. Over 80 per cent of the SP-IR NTS-afferent neurons contained 5HT-IR, while 68 per cent of the 5HT-IR neurons contained SP-IR. Thus, 5HT- and SP-IR are extensively colocalized in NTS-afferent neurons in the medullary raphe nuclei and associated areas of the ventral medulla.

Substance P antagonist-induced spinal cord vasoconstriction: effects of thyrotropin-releasing hormone and substance P agonists

Local spinal cord vasomotor effects of 3 substance P (SP) antagonists were studied in the rat following intrathecal (IT) administration. Each SP antagonist (3.3 nmol) increased spinal cord vascular resistance and reduced blood flow. A LH-RH antagonist analog (10 nmol) of similar molecular weight and which also contained multiple D-Trp residues did not cause spinal cord vasoconstriction. The vasoconstrictor action of the SP antagonist, [D-Arg1, D-Pro2, D-Trp7,9, Leu11]-SP [( D-Arg]-SP) was unaffected by pretreatment with a stable SP receptor agonist (5 nmol IT). Given evidence for a cerebral vasodilator action of TRH agonists, the effects of TRH (IV) and a stable TRH analog (MK-771, IT) on [D-Arg]-SP-induced vasoconstriction were also assessed. Neither TRH nor MK-771 prevented the [D-Arg]-SP-induced vasoconstriction. However, TRH (IV) but not MK-771 (IT) partially opposed [D-Arg]-SP-induced reduction in thoracic spinal cord blood flow. Thus, SP antagonists cause spinal cord vasoconstriction by a non-SP receptor mediated phenomenon. In addition, the attenuation of SP-antagonist-induced neuropathological changes previously reported with IV. TRH administration is likely due to less severe consequences of vasoconstriction in the presence of a higher initial baseline blood flow rather than direct prevention of the vasoconstriction.

Immunohistochemical study of neuropeptides in vagal and glossopharyngeal afferent neurons in the rat

The presence and distribution of multiple neuropeptides in vagal and glossopharyngeal afferent ganglia of the rat were studied using immunohistochemistry. Substance P-, calcitonin-gene related peptide-, cholecystokinin-, neurokinin A-, vasoactive intestinal polypeptide-, and somatostatin-immunoreactive neurons were detected in each visceral afferent ganglion. Neurotensin-immunoreactive cells were not observed. In the nodose ganglion (inferior ganglion of the vagus nerve) occasional immunoreactive cells were scattered throughout the main (caudal) portion of the ganglion with small clusters of cells seen in the rostral portion. The pattern of distribution of the various peptides in the nodose ganglion was similar, with the exception of vasoactive intestinal polypeptide-immunoreactive neurons which exhibited a more caudal distribution. The relative numbers of immunoreactive cells varied, with the greatest numbers being immunoreactive for substance P or vasoactive intestinal polypeptide, and the lowest numbers being immunoreactive for neurokinin A and somatostatin. A build-up of immunoreactivity for each of the peptides, except somatostatin and neurotensin, was detected in vagal nerve fibers of colchicine-injected ganglia. Numerous peptide-immunoreactive cells were also found in the petrosal (inferior ganglion of the glossopharyngeal nerve) and jugular (superior ganglion of the vagus nerve) ganglia. No specific intraganglionic distribution was noted although the relative numbers of cells which were immunoreactive for the different peptides varied considerably. Substance P and calcitonin-gene related peptide were found in large numbers of cells, cholecystokinin was seen in moderate numbers of cells, and neurokinin A, vasoactive intestinal polypeptide and somatostatin were seen in fewer cells. These data provide evidence for the presence and non-uniform distribution of multiple peptide neurotransmitters in vagal and glossopharyngeal afferent neurons. In general, relatively greater numbers of immunoreactive cells were located in the rostral compared with caudal nodose ganglion, and in the petrosal and jugular ganglia compared with the nodose ganglion. Thus, multiple neuropeptides may be involved as afferent neurotransmitters in the reflexes mediated by vagal and glossopharyngeal sensory nerves.

Bulbospinal thyrotropin-releasing hormone projections to the intermediolateral cell column: a double fluorescence immunohistochemical-retrograde tracing study in the rat

Whereas the neurochemistry of the peripheral autonomic nervous system has been well characterized, less is known concerning the neurotransmitters utilized by medullary projections onto sympathetic preganglionic neurons residing in the thoracolumbar spinal intermediolateral cell column. Retrograde transport of rhodamine-labeled fluorescent microspheres following discrete microinjection into the thoracic intermediolateral cell column was combined with immunohistochemistry to determine neuroanatomic location of thyrotropin-releasing hormone-immunoreactive neurons which project to the intermediolateral cell column in the rat. The ventromedial group of raphe nuclei including the nucleus raphe pallidus, obscurus, and magnus possessed the greatest number of medullary thyrotropin-releasing hormone-immunoreactive neurons which also contained rhodamine-labeled microspheres. High numbers of intermediolateral cell column-projecting thyrotropin-releasing hormone-immunoreactive neurons were also observed in nucleus reticularis paragigantocellularis lateralis and magnocellularis, the lateral reticular nucleus, and the superficial ventral (arcuate) medullary surface. Despite the observations that nucleus reticularis gigantocellularis, paramedianus, and ventralis pars beta project to the intermediolateral cell column, double-labeled cells were not observed in these nuclei. Furthermore, whereas the nucleus reticularis magnocellularis and gigantocellularis, and the lateral reticular nucleus displayed strong ipsilateral predominance in projecting to the intermediolateral cell column, other medullary reticular and raphe nuclei displayed bilateral projections. The present findings support the hypothesis that thyrotropin-releasing hormone-containing neurons in the ventral medulla project to the intermediolateral cell column, and may influence sympathetic preganglionic neurons.

Thyrotropin-releasing hormone receptor activation in the spinal cord increases blood pressure and sympathetic tone to the vasculature and the adrenals

Cardiovascular and regional hemodynamic effects of the intrathecal (i.t.) administration of a thyrotropin-releasing hormone (TRH) analog, MK-771 (L-pyro-2-aminoadipyl-histidyl-thiazolidine-4-carboxamide), were studied in rats. MK-771 (0.01-5.0 micrograms i.t.) caused dose-related increases in mean arterial pressure (MAP) and heart rate (HR). TRH (10 micrograms i.t.), but not TRH-free acid, produced similar cardiovascular effects. The MAP response to MK-771 (i.t.) remained primarily intact after cervical spinal cord transection, whereas the HR response was attenuated (37% of control). The MAP response to MK-771 was blocked by peripheral administration of pentolinium or phentolamine, and was partially attenuated by adrenalectomy. The HR response was reduced by pentolinium or atropine. Assessment of changes in regional blood flow and vascular resistance with the radioactive microsphere technique showed that MK-771 increased total peripheral resistance and vasoconstricted cutaneous, skeletal muscle, adrenal, renal and intestinal vascular beds. Cardiac output and stroke volume were not altered. MK-771 had no effect on vascular resistance locally or in other central nervous system structures. However, blood flow was elevated by MK-771 in spinal cord and brain. These data show that TRH receptor activation in the thoracic spinal cord, presumably in the intermediolateral cell column, elevated MAP by increased sympathetic activity to the peripheral vasculature and the adrenals. However, the HR response to TRH receptor activation required a supra-spinal component and was mediated in part by vagal inhibition.

Catecholamine-synthesizing neuronal projections to the nucleus tractus solitarii of the rat

The objective of the present study was to determine the location of the neurons that give rise to catecholamine-containing terminals in the nucleus tractus solitarii. This was done by injecting rhodamine-filled latex microspheres into the nucleus tractus solitarii of rats to retrogradely label neuronal cell bodies and by processing sections from the brains of these animals to determine if the labelled neurons were immunoreactive for the catecholamine-synthesizing enzymes, dopamine-beta-hydroxylase (DBH) and phenylethanolamine-N-methyl transferase (PNMT). Approximately 60% of the DBH-immunoreactive neurons that projected to the nucleus tractus solitarii belonged to the A1/C1 cell group, while an additional 20% belonged to the A5 cell group. Thus, these two ventrolateral rhombencephalic cell groups accounted for nearly 80% of the total number of rhodamine-bead-labelled DBH-immunoreactive neurons in this series of experiments. Only a small number of DBH-immunoreactive neurons of the A2/C2 cell group contained rhodamine-filled latex microspheres. Rarely, DBH-immunoreactive neurons in the locus coeruleus and the nucleus subcoeruleus were found to project to the nucleus tractus solitarii. The majority of the PNMT-immunoreactive neurons that projected to the nucleus tractus solitarii belonged to the C1 cell group. Only small numbers of PNMT-immunoreactive neurons of the C2 and C3 groups were found to contain rhodamine-filled latex microspheres. It is concluded that neurons in the ventrolateral medulla and pons, some of which presumably utilize norepinephrine and/or epinephrine as a transmitter, could regulate autonomic function via direct projections to the nucleus tractus solitarii.

Immunohistochemical and biochemical analysis of serotonin and substance P colocalization in the nucleus tractus solitarii and associated afferent ganglia of the rat

In a previous study of afferent projections to the nucleus tractus solitarii (NTS), it was shown that over half of the retrogradely-labelled neurons in the nucleus raphe pallidus contained serotonin-immunoreactivity and over half of these neurons contained substance P-immunoreactivity, suggesting that these two putative neurotransmitters are colocalized in NTS-afferent neurons. The objectives of the present study were to 1) directly determine if varicosities in the NTS, the area postrema (AP), and the dorsal motor nucleus of the vagus nerve (DMN) do contain both transmitters, 2) determine if primary afferent neurons in the nodose and pretrosal ganglia might also colocalize serotonin and substance P, and 3) quantify the amount of substance P that is contained in serotonergic varicosities in the NTS. Distributions and colocalization of substance P and serotonin in the NTS were studied using dual-color immunohistochemistry, while the quantity of substance P in serotonergic varicosities was assessed by radioimmunoassay (RIA) using micropunches from the NTS of 5,7-dihydroxytryptamine-(5,7 DHT-) and vehicle-treated rats. Varicosities that contained both serotonin- and substance P-immunoreactivity were found in the NTS, the DMN, and the AP. Double-labelled varicosities were common in the NTS and DMN (i.e., qualitatively similar to the density seen in the hypoglossal nucleus and in the ventral horn of the cervical spinal cord); however, the vast majority of the varicosities in these autonomic areas only displayed immunoreactivity for one or the other of these transmitters. This paucity of doubly-labelled varicosities, in comparison to the number of singly-labelled varicosities, was reflected in the lack of a significant decrease in substance P levels as determined by RIA of micropunches taken from caudal and intermediate levels of the NTS in 5,7 DHT- and vehicle-treated rats.(ABSTRACT TRUNCATED AT 250 WORDS)