Demonstration of substance P in aortic nerve afferent fibers by combined use of fluorescent retrograde neuronal labeling and immunocytochemistry

Combined use of the intraaxonal retrograde transport of the fluorescent marker ‘true blue’ with substance P (SP) immunocytochemistry has been used to trace the nodose ganglion projections of SP-containing neurons of the aortic depressor nerve. It has been found that (1) SP immunoreactive (SP-I) cell bodies are clearly demonstrable in clusters in the rostral part of the nodose ganglion without the aid of colchicine pretreatment; (2) ‘true blue’ is retrogradely transported to the nodose ganglion following its application to the central cut end of the aortic nerve; (3) ‘true blue’ fluorescence and SP fluorescent immunoreactivity can be visualized in the same tissue section and certain cell bodies in the nodose ganglia contain both SP-I and retrogradely transported ‘true blue’. These results indicate that the aortic nerve which projects from the aortic arch baro- and/or chemoreceptors to brainstem vasomotor centers contains SP-I afferent fibers which emanate from the nodose ganglion.     

Neuroanatomical localization of substance p: implications for central cardiovascular control

The presence of substance P (SP) neurons in pathways known to be involved in the central control of the cardiovascular system has been studied with neuroanatomical and neurochemical techniques. SP-immunoreactive (SP-I) neurons are found in afferent baro- and chemoreceptor pathways which transmit information from peripheral receptors to the nucleus tractus solitarius. In addition, SP-I neurons located in the nucleus interfascicularis hypoglossi of the ventral medulla innervate the intermediolateral cell column, the site of origin of preganglionic sympthetic nerves. The role of these SP-I neurons in cardiovascular control remains to be determined.     

Demonstration of substance P in aortic nerve afferent fibers by combined use of fluorescent retrograde neuronal labeling and immunocytochemistry

Combined use of the intraaxonal retrograde transport of the fluorescent marker ‘true blue’ with substance P (SP) immunocytochemistry has been used to trace the nodose ganglion projections of SP-containing neurons of the aortic depressor nerve. It has been found that (1) SP immunoreactive (SP-I) cell bodies are clearly demonstrable in clusters in the rostral part of the nodose ganglion without the aid of colchicine pretreatment; (2) ‘true blue’ is retrogradely transported to the nodose ganglion following its application to the central cut end of the aortic nerve; (3) ‘true blue’ fluorescence and SP fluorescent immunoreactivity can be visualized in the same tissue section and certain cell bodies in the nodose ganglia contain both SP-I and retrogradely transported ‘true blue’. These results indicate that the aortic nerve which projects from the aortic arch baro- and/or chemoreceptors to brainstem vasomotor centers contains SP-I afferent fibers which emanate from the nodose ganglion.     

Vanilloid receptor (VR1) expression in vagal afferent neurons innervating the gastrointestinal tract

The vanilloid receptor VR1 is a nonselective cation channel activated by capsaicin as well as increases in temperature and acidity, and can be viewed as molecular integrator of chemical and physical stimuli that elicit pain. The distribution of VR1 receptors in peripheral and central processes of rat primary vagal afferent neurons innervating the gastrointestinal tract was investigated by immunohistochemistry. Forty-two percent of neurons in the nodose ganglia retrogradely labeled from the stomach wall expressed low to moderate VR1 immunoreactivity (VR1-IR). VR1-IR was considerably lower in the nodose ganglia as compared to the jugular and dorsal root ganglia. In the vagus nerve, strongly VR1-IR fibers ran in separate fascicles that supplied mainly cervical and thoracic targets, leaving only weakly VR1-IR fibers in the subdiaphragmatic portion. Vagal afferent intraganglionic laminar endings (IGLEs) in the gastric and duodenal myenteric plexus did not express VR1-IR. Similarly, VR1-IR was contained in fibers running in perfect register with vagal afferents, but was not colocalized with horseradish peroxidase in the same varicosities of intramuscular arrays (IMAs) and vagal afferent fibers in the duodenal submucosa anterogradely labeled from the nodose ganglia. Only in the gastric mucosa did we find evidence for colocalization of VR1-IR in vagal afferent terminals. In contrast, many nerve fibers coursing through the myenteric and submucosal plexuses contained detectable VR1-IR, the majority of which colocalized calcitonin gene-related peptide immunoreactivity. In the dorsal medulla there was a dense plexus of VR1-IR varicose fibers in the commissural, dorsomedial and gelatinosus subnuclei of the medial NTS and the lateral aspects of the area postrema, which was substantially reduced, but not eliminated on the ipsilateral side after supranodose vagotomy. It is concluded that about half of the vagal afferents innervating the gastrointestinal tract express low levels of VR1-IR, but that presence in most of the peripheral terminal structures is below the immunohistochemical detection threshold.     

Substance P-like immunoreactivity in rat and cat carotid bodies: light and electron microscopic studies

Substance P-immunoreactive (SP-1) structures in the carotid bodies of rats and cats were examined with the light and electron microscopes. In both species SP-I varicose nerve fibers were located singly in the interstitial connective tissue in close association with blood vessels. They were small unmyelinated fibers enveloped in a common Schwann cell sheath with other SP-negative fibers. Some of SP-I fibers contained large dense-cored granules and small clear vesicles in addition to microtubules and mitochondria and probably represented nerve fiber varicosities. The latter often were found incompletely invested by Schwann cell sheaths. SP-fibers were found occasionally in the envelopes of supporting cells at the periphery of parenchymal cell groups. However, none of the nerve terminals making synaptic contacts with glomus cells exhibited SP-like immunoreactivity. In cat carotid bodies some glomus cells showed moderate to intense SP-like immunoreactivity. The intense SP-I glomus cells displayed numerous dense-cored vesicles of 85 to 140 nm in diameter and frequently showed synaptic contacts with SP-negative nerve terminals. In rat carotid bodies we were unable to detect consistent SP-immunoreactivity in glomus cells. Our results do not favor the hypothesis that SP is a neurotransmitter/modulator in the chemoreceptor afferents synapsing on glomus cells in either the cat or rat carotid body. However our results support the hypothesis that SP in cat glomus cells may play a role in the modulation of chemoreceptor activity.     

The importance of baro- and chemoreflexes in the control of the fetal cardiovascular system

The information gained about the afferent traffic from carotid arterial baro- and chemoreceptors by direct recordings made in the sheep fetus is reviewed. Less is known about aortic baro- and chemoreceptor discharge during this period, and virtually nothing is known about the discharge of other vagal mechano- or chemoreceptor afferents. Knowledge about the functional integrity of sympathetic and parasympathetic efferent pathways is reviewed. Then the various methods which have been used for assessing fetal baro- and chemoreflexes are discussed: the crucial problem here is that there are no techniques available for either increasing or decreasing the discharge of these receptors specifically. Because they have been widely used, however, and are of clinical importance, the effects upon the fetal circulation of hypoxia and asphyxia are reviewed specifically. The relative contributions of baro- and chemoreflexes in producing these effects are considered against the background of the plethora of other processes which operate under these conditions.     

The role of substance P-containing fibers in sympathetic ganglia: Effect of capsaicin

Capsaicin was given subcutaneously to guinea pigs and the effect on substance P-immunoreactive (SP-I) fibers in the celiac/superior mesenteric and inferior mesenteric ganglia was observed at 2 day and 8–10 day intervals. Capsaicin (125 mg) treatment led to almost total disappearance of SP-I fibers from all areas examined in both short- and long-term animals. This effect applied equally to the dense network of varicose SP-I fibers and to basket-like SP-I contacts with principal ganglionic neurons. The effect of capsaicin on SP-I fibers in the mesenteric ganglia provides a strong indication that these fibers represent a homogenous population of visceral sensory afferents. This is supported by other lines of anatomical evidence in the literature. Taken together with studies that have shown axodendritic contact of SP-I terminals on principal ganglionic neurons and neuro-modulatory effects of SP on these neurons, it may be hypothesized that SP-I fibers in the mesenteric ganglia represent collaterals of visceral sensory afferents forming a subspinal feedback arc.     

Cardiovascular responses to substance P in the nucleus tractus solitarii: microinjection study in conscious rats

The cardiovascular effects of substance P (SP) microinjections in the nucleus tractus solitarii (NTS) were evaluated in conscious rats. We chose this model because it is an effective way to access some of the cardiovascular effects of neurotransmitters in the NTS without the inconvenience of blunting pathways with anesthetic agents or removing forebrain projections by decerebration. The cardiovascular responses to SP injections were also evaluated after chronic nodose ganglionectomy. We found that, in conscious rats, SP microinjections into the NTS induced hypertension and tachycardia. Unilateral and bilateral SP injections into the NTS caused a slow increase in blood pressure and heart rate that peaked 1.5-5 min after injection and lasted for 20-30 min. Nodose ganglionectomy increased the duration of the pressor and tachycardic effects of SP and enhanced the pressor response. These data show that SP in the NTS is involved in pressor pathways. The supersensitivity to SP seen after nodose ganglionectomy suggests that vagal afferent projections are involved in those pressor pathways activated by SP in the NTS.     

Simultaneous immunohistochemical demonstration of intra-axonally transported markers and neuropeptides in the peripheral nervous system of the guinea pig

Summary Projections and peptide neurotransmitter/neuromodulator content of autonomic and visceral afferent neurons of the guinea pig were studied after application of the subunit B of cholera toxin (CTB) with or without horseradish peroxidase (HRP) as retrograde and anterograde tracers and subsequent immunohistochemical processing for double staining using antibodies raised to CTB, HRP and various neuropeptides. The results demonstrate that substance P (SP)- and calcitonin gene-related peptide (CGRP)-containing dorsal root ganglion cells project to the pylorus as well as to the celiac superior mesenteric and stellate ganglia as demonstrated with both retrograde and anterograde transport methodology. Binding studies revealed that a small number of the CTB-binding dorsal root ganglion cells contains immunoreactivity to SP and CGRP. The majority of the CTB-binding cells is SP- and CGRP-negative and terminate in the deeper parts of the dorsal horn. After injection of CTB conjugated to HRP (B-HRP) into the nodose ganglion, both motor and sensory elements were labeled in the medulla oblongata. Some of the CTB labeled vagal sensory nerve fibers in the nucleus tractus solitarii (NTS) were also found to contain immunoreactivity to SP or CGRP. The tracer was also transported through the peripheral branch of the nodose ganglion cells and labeled terminals in the esophagus.     

Simultaneous immunohistochemical demonstration of intra-axonally transported markers and neuropeptides in the peripheral nervous system of the guinea pig

Projections and peptide neurotransmitter/neuromodulator content of autonomic and visceral afferent neurons of the guinea pig were studied after application of the subunit B of cholera toxin (CTB) with or without horseradish peroxidase (HRP) as retrograde and anterograde tracers and subsequent immunohistochemical processing for double staining using antibodies raised to CTB, HRP and various neuropeptides. The results demonstrate that substance P (SP)- and calcitonin gene-related peptide (CGRP)-containing dorsal root ganglion cells project to the pylorus as well as to the celiac superior mesenteric and stellate ganglia as demonstrated with both retrograde and anterograde transport methodology. Binding studies revealed that a small number of the CTB-binding dorsal root ganglion cells contains immunoreactivity to SP and CGRP. The majority of the CTB-binding cells is SP- and CGRP-negative and terminate in the deeper parts of the dorsal horn. After injection of CTB conjugated to HRP (B-HRP) into the nodose ganglion, both motor and sensory elements were labeled in the medulla oblongata. Some of the CTB labeled vagal sensory nerve fibers in the nucleus tractus solitarii (NTS) were also found to contain immunoreactivity to SP or CGRP. The tracer was also transported through the peripheral branch of the nodose ganglion cells and labeled terminals in the esophagus.     

Leptin and CCK modulate complementary background conductances to depolarize cultured nodose neurons

We have previously reported that intraceliac infusion of leptin induces a reduction of meal size that depends on intact vagal afferents. This effect of leptin is enhanced in the presence of cholecystokinin (CCK). The mechanisms by which leptin and CCK activate vagal afferent neurons are not known. In the present study, we have begun to address this question by using patch-clamp electrophysiological techniques to examine the mechanisms by which leptin and CCK activate cultured vagal afferents from adult rat nodose ganglia. We found that leptin depolarized 41 (60%) of 68 neurons. The magnitude of membrane depolarization was dependent on leptin concentration and occurred in both capsaicin-sensitive and capsaicin-insensitive neurons. We also found that a majority (16 of 22; 73%) of nodose neurons activated by leptin were also sensitive to CCK. CCK-induced depolarization was primarily associated with the increase of an inward current (11 of 12), whereas leptin induced multiple changes in background conductances through a decrease in an outward current (7 of 13), an increase in an inward current (3 of 13), or both (3 of 13). However, further isolation of background currents by recording in solutions that contained only sodium or only potassium revealed that both leptin and CCK were capable of increasing a sodium-dependent conductance or inhibiting a potassium-dependent conductance. Our results support the hypothesis that vagal afferents are a point of convergence and integration of leptin and CCK signaling for control of food intake and suggest multiple ionic mechanisms by which leptin and CCK activate vagal afferent neurons. cholecystokinin; vagal afferents; capsaicin; satiation     

Peripheral versus central modulation of gastric vagal pathways by metabotropic glutamate receptor 5

Metabotropic glutamate receptors (mGluR) are classified into group I, II, and III mGluR. Group I (mGluR1, mGluR5) are excitatory, whereas group II and III are inhibitory. mGluR5 antagonism potently reduces triggering of transient lower esophageal sphincter relaxations and gastroesophageal reflux. Transient lower esophageal sphincter relaxations are mediated via a vagal pathway and initiated by distension of the proximal stomach. Here, we determined the site of action of mGluR5 in gastric vagal pathways by investigating peripheral responses of ferret gastroesophageal vagal afferents to graded mechanical stimuli in vitro and central responses of nucleus tractus solitarius (NTS) neurons with gastric input in vivo in the presence or absence of the mGluR5 antagonist 2-methyl-6-(phenylethynyl)pyridine (MPEP). mGluR5 were also identified immunohistochemically in the nodose ganglia and NTS after extrinsic vagal inputs had been traced from the proximal stomach. Gastroesophageal vagal afferents were classified as mucosal, tension, or tension-mucosal (TM) receptors. MPEP (1-10 microM) inhibited responses to circumferential tension of tension and TM receptors. Responses to mucosal stroking of mucosal and TM receptors were unaffected. MPEP (0.001-10 nmol icv) had no major effect on the majority of NTS neurons excited by gastric distension or on NTS neurons inhibited by distension. mGluR5 labeling was abundant in gastric vagal afferent neurons and sparse in fibers within NTS vagal subnuclei. We conclude that mGluR5 play a prominent role at gastroesophageal vagal afferent endings but a minor role in central gastric vagal pathways. Peripheral mGluR5 may prove a suitable target for reducing mechanosensory input from the periphery, for therapeutic benefit.     

NMDA channels control meal size via central vagal afferent terminals

The N-methyl-D-aspartate (NMDA) ion channel blocker MK-801 administered systemically or as a nanoliter injection into the nucleus of the solitary tract (NTS), increases meal size. Furthermore, we have observed that ablation of the NTS abolishes increased meal size following systemic injection of dizocilpine (MK-801) and that MK-801-induced increases in intake are attenuated in rats pretreated with capsaicin to destroy small, unmyelinated, primary afferent neurons. These findings led us to hypothesize that NMDA receptors on central vagal afferent terminals or on higher-order NTS neurons innervated by these vagal afferents might mediate increased food intake. To evaluate this hypothesis, we examined 15% sucrose intake after 50-nl MK-801 injections ipsilateral or contralateral to unilateral nodose ganglion removal (ganglionectomy). On the side contralateral to ganglionectomy, vagal afferent terminals would be intact and functional, whereas ipsilateral to ganglionectomy vagal afferent terminals would be absent. Three additional control preparations also were included: 1) sham ganglionectomy and 2) subnodose vagotomy either contralateral or ipsilateral to NTS cannula placement. We found that rats with subnodose vagotomies increased their sucrose intake after injections of MK-801 compared with saline, regardless of whether injections were made contralateral (12.6 +/- 0.2 vs. 9.6 +/- 0.3 ml) or ipsilateral (14.2 +/- 0.6 vs. 9.7 +/- 0.4 ml) to vagotomy. Rats with NTS cannula placements contralateral to nodose ganglionectomy also increased their intake after MK-801 (12.2 +/- 0.9 and 9.2 +/- 1.1 ml for MK-801 and saline, respectively). However, rats with placements ipsilateral to ganglionectomy did not respond to MK-801 (8.0 +/- 0.5 ml) compared with saline (8.3 +/- 0.4 ml). We conclude that central vagal afferent terminals are necessary for increased food intake in response to NMDA ion channel blockade. The function of central vagal afferent processes or the activity of higher-order NTS neurons driven by vagal afferents may be modulated by NMDA receptors to control meal size.     

Secretin activates vagal primary afferent neurons in the rat: evidence from electrophysiological and immunohistochemical studies

In this study, we evaluated the vagal afferent response to secretin at physiological concentrations and localized the site of secretin's action on vagal afferent pathways in the rat. The discharge of sensory neurons supplying the gastrointestinal tract was recorded from nodose ganglia. Of 91 neurons activated by electrical vagal stimulation, 19 neurons showed an increase in firing rate in response to intestinal perfusion of 5-HT (from 1.5 +/- 0.2 to 25 +/- 4 impulses/20 s) but no response to intestinal distension. A close intra-arterial injection of secretin (2.5 and 5.0 pmol) elicited responses in 15 of these 19 neurons (from 1.5 +/- 0.2 impulses/20 s at basal to 21 +/- 4 and 43 +/- 5 impulses/20 s, respectively). Subdiaphragmatic vagotomy and perivagal application of capsaicin, but not supranodose vagotomy, completely abolished the secretin-elicited vagal nodose neuronal response. In a separate study, 9 tension receptor afferents among 91 neurons responded positively to intestinal distension but failed to respond to luminal 5-HT. These nine neurons also showed no response to administration of secretin. As expected, immunohistochemical studies showed that secretin administration significantly increased the number of Fos-positive neurons in vagal nodose ganglia. In conclusion, we demonstrated for the first time that vagal sensory neurons are activated by secretin at physiological concentrations. A subpopulation of secretin-sensitive vagal afferent fibers is located in the intestinal mucosa, many of which are responsive to luminal 5-HT.     

Distribution, origin and sensitivity to capsaicin of primary afferent substance P-immunoreactive nerves in the heart

This report is intended as an overview of the distribution, origin and sensitivity to capsaicin of substance P-immunoreactive (SP-I) primary afferent cardiac nerves. Immunohistochemical and physiological methods were employed to compare the presence and density of these nerve fibers in the guinea pig and rat hearts. SP-I fibers are numerous in the guinea pig heart including the parietal pericardium, atria, ventricles, valves, coronary arteries and around intrinsic cardiac ganglion cells. The rat heart contains few SP-I fibers. Vagotomy does not influence the number of intensity of immunoreactive fibers in the guinea pig heart. By stimulating the atrium or ventricle and recording from the second or third thoracic dorsal roots Ad1, Ad2 and C fibers were demonstrated in the atria, but only Ad fibers in the guinea pig ventricle; in addition, only Ad fibers were recorded from the vagus nerves. Only Ad1 fibers were demonstrated in the rat heart. Treatment with capsaicin depletes the SP-I and decreases the conduction velocity of C-fibers and some Ad2 fibers in the guinea pig heart. We suggest that SP-I primary afferent nerve fibers are unmyelinated (C-type) or small myelinated (Ad2-type) nerves in the guinea pig heart and that their cell bodies of origin are predominantly in dorsal root ganglia.     

Action of substance P and one of its synthetic antagonists on the nucleus tractus solitarius

The study aims to establish the nature of the chemical mediator which produces the IP (presynaptic inhibition) of the mechanoreceptive afferents reaching the NTS (nucleus tractus solitarius) of the frog. To this end we have examined the effects of the administration of SP (substance P) and of one of its antagonists in the IV ventricle, in both normal and unilaterally axotomized preparations at the level of the glossopharyngeal nerve. In particular we have examined the size of the afferent discharge of the glossopharyngeal-hypoglossus reflex arc and the PAD (primary afferent depolarization) phenomena recorded from the dorsal root of the XII. While in normal preparations the SP reduces the size of the reflex discharge, on the contrary the antagonist increases it; the electrical activity of PAD appears to be enhanced by SP and reduced by the antagonist. Lastly SP normalises the enhanced response produced by axotomy. All the observed effects favour the hypothesis that the IP, which appears in the NTS with the activation of the mechanoreceptive afferents, is brought about by the release of S.P. from their central endings.     

Amino Acid Neurotransmitters in Nucleus Tractus Solitarius: An In Vivo Microdialysis Study

Amino acid neurotransmitters in the nucleus tractus solitarius (NTS) are thought to play a key role in the mediation of visceral reflexes and glutamate has been proposed as the neurotransmitter of visceral afferent nerves projecting to this region. The present studies sought to characterize the use of in vivo microdialysis to examine extracellular fluid levels of amino acids in the NTS of anesthetized rats. Using a microdialysis probe that was 450 μm in length and a sensitive HPLC assay for amino acids, amino acids could be measured in dialysate samples collected from the NTS. Perfusion of the microdialysis probe with 60 mM K^±, to elicit depolarization of nerve terminals in the vicinity of the probe, resulted in increased dialysate fluid levels of aspartate, glutamate, glycine, taurine, and GABA. In contrast, glutamine and tyrosine were decreased and other amino acids were not significantly affected. Prior removal of the ipsilateral nodose ganglion did not alter the K^±-evoked changes in dialysate levels of any of these amino acids. Electrical stimulation of the vagus nerves, using a variety of stimulus parameters, did not significantly alter dialysate levels of glutamate or any of the other amino acids that were measured. Blockade of glutamate uptake with dihydrokainate increased dialysate levels of glutamate, aspartate, and GABA, but in the presence of dihydrokainate vagal stimulation did not alter dialysate levels of these amino acids. The results show that in vivo microdialysis can be used to examine amino acid efflux in the rat NTS and provide further evidence for amino acidergic neural transmission in the NTS. However, these studies fail to support the hypothesis that vagal afferents release glutamate or aspartate.     

Differences in neuronal lipid composition between superior cervical ganglia and nodose ganglia of the rat

The lipid content and composition of rat superior cervical ganglia containing sympathetic motor neurons and nodose ganglia containing parasympathetic sensory neurons were studied for the first time to elucidate the mechanism of the different effects of exogenous gangliosides on these neurons in the culture medium. The ganglioside content of the superior cervical ganglia was almost 3-times that of the nodose ganglia. Although both ganglia contained GM3, GD3, GD1b and GT1b as major gangliosides, the nodose ganglia additionally contained a significant amount of sialosyllactoneotetraosylceramide LM1 (10% of total sialic acids). Contrasting with nodose ganglia, vagus fiber and dorsal root ganglia of rats, superior cervical ganglia had a higher content of sulfatide than galactosylceramide. The phospholipid content was lower in superior cervical ganglia than in nodose ganglia. Superior cervical ganglia contained less ethanolamine plasmalogen and more phosphatidylcholine than nodose ganglia. Sphingomyelin in superior cervical ganglia contained mainly medium-chain fatty acids, while that in nodose ganglia contained mainly longer-chain fatty acids. Differences in the fatty acid composition of glycerophospholipids were also observed. The results indicate that the properties of neuronal cell membranes from superior cervical ganglia and nodose ganglia are quite different, and that the differences may reflect the physiological roles of these ganglia.     

孤束核内微电泳NPY对压力感受性和化学感受性激活神经元…

本实验观察了孤束核（ＮＴＳ）内微电泳神经肽Ｙ（ＮＰＹ）对压力感觉性化学感受性刺激反应神经元放电的影响。在６２个单位放电中,其中对微电泳ＮＰＹ表现兴奋反应３４个单位,１９个单位表现抑制反应,无反应单位９个。微电泳ＮＰＹ对压力感受性刺激呈兴奋反应的单位主要表现兴奋作用,对抑制反应单位主要表现抑制作用,对化学感受性刺激的兴奋单位和抑制单位均主要以兴奋为主。     

Feline Immunodeficiency Virus as a Gene Transfer Vector in the Rat Nucleus Tractus Solitarii

Gene transfer has been used to examine the role of putative neurotransmitters in the nucleus tractus solitarii (NTS). Most such studies used adenovirus vector-mediated gene transfer although adenovirus vector transfects both neuronal and non-neuronal cells. Successful transfection in the NTS has also been reported with lentivirus as the vector. Feline immunodeficiency virus (FIV), a lentivirus, may preferentially transfect neurons and could be a powerful tool to delineate physiological effects produced by altered synthesis of transmitters in neurons. However, it has not been studied in NTS. Therefore, we sought to determine whether FIV transfects rat NTS cells and to define the type of cell transfected. We found that injection of FIV encoding LacZ gene (FIVLacZ) into the NTS led to transfection of numerous NTS cells. Injection of FIVLacZ did not alter immunoreactivity (IR) for neuronal nitric oxide synthase, which we have shown resides in NTS neurons. A majority (91.7 ± 3.9%) of transfected cells contained IR for neuronal nuclear antigen, a neuronal marker; 2.1 ± 3.8% of transfected cells contained IR for glial fibrillary acidic protein, a glial marker. No transfected neurons or fibers were observed in the nodose ganglion, which sends afferents to the NTS. We conclude that FIV almost exclusively transfects neurons in the rat NTS from which it is not retrogradely transported. The cell-type specificity of FIV in the NTS may provide a molecular method to study local physiological functions mediated by potential neurotransmitters in the NTS.