Neuronal nitric oxide synthase and calbindin expression in sympathetic preganglionic neurons following capsaicin treatment

Along with well-known data on the neurochemical mechanisms of nociceptor activation, there are still no clear data regarding changes in the cellular composition and morphological characteristics of spinal preganglionic neurons (SPN) after capsaicin treatment. The mechanism of capsaicin toxicity differs in developing and mature nerve cells. This study aimed to determine the number of SPN in the autonomic nuclei on spinal cord (SC) sections and their cross-sectional area, the localization, percentage, and profile area of SPN containing neuronal nitric oxide synthase (nNOS) and calbindin (CB) in the thoracic SC of rats of different ages (from birth to 1-year-old) after capsaicin treatment. Neonatal capsaicin treatment generally decreased the cross-sectional area of the SPN pericarya. However, the cross-sectional area of the CB-immunoreactive (IR) SPN increased in the central autonomic area in rats aged 10-30 days old after capsaicin treatment. The number of SPN decreased only in the central autonomic area of rats aged <20 days. The proportion of nNOS-IR neurons remained steady and did not change during development. The cross-sectional area of nNOS-IR SPN in capsaicin-treated rats was less than that in control rats. The results obtained will promote further studies on the mechanisms of sensory processing in the SC and the development of the sympathetic nervous system.

Development of nNOS-positive preganglionic sympathetic neurons in the rat thoracic spinal cord

To gain a better understanding of the neuroplasticity of sympathetic neurons during postnatal ontogenesis, the distribution of neuronal nitric oxide synthase (nNOS) immunoreactivity was studied in sympathetic preganglionic neurons (SPN) in the spinal cord (Th2 segment) of female Wistar rats at different ages (newborn, 10-, 20-, 30-day-old; 2-, 6-month-old; 3-year-old). In all age groups, the majority of nNOS-immunoreactive (IR) neurons was observed in the nucleus intermediolateralis thoracolumbalis pars principalis. In the first month, the proportion of nNOS-IR neurons decreased significantly from 92 ± 3.4% in newborn to 55 ± 4.6% in 1-month-old, while the number of choline acetyltransferase (ChAT)-IR neurons increased from 74 ± 4.2% to 99 ± 0.3% respectively. Decreasing nNOS expression in the first 10 days of life was also confirmed by western blot analysis. Some nNOS-IR SPN also colocalized calbindin (CB) and cocaine and amphetamine-regulated transcript (CART). The percentage of NOS(+)/CB(-) SPN increased from 23 ± 3.6% in 10-day-old to 36 ± 4.2% in 2-month-old rats. Meanwhile, the proportion of NOS(+)/CART(-) neurons decreased from 82 ± 4.7% in newborn to 53 ± 6.1% in 1-month-old rats. The information provided here will also serve as a basis for future studies investigating the mechanisms of autonomic neuron development.

Brain-to-stomach transfer of α-synuclein via vagal preganglionic projections

Detection of α-synuclein lesions in peripheral tissues is a feature of human synucleinopathies of likely pathogenetic relevance and bearing important clinical implications. Experiments were carried out to elucidate the relationship between α-synuclein accumulation in the brain and in peripheral organs, and to identify potential pathways involved in long-distance protein transfer. Results of this in vivo study revealed a route-specific transmission of α-synuclein from the rat brain to the stomach. Following targeted midbrain overexpression of human α-synuclein, the exogenous protein was capable of reaching the gastric wall where it was accumulated into preganglionic vagal terminals. This brain-to-stomach connection likely involved intra- and inter-neuronal transfer of non-fibrillar α-synuclein that first reached the medulla oblongata, then gained access into cholinergic neurons of the dorsal motor nucleus of the vagus nerve and finally traveled via efferent fibers of these neurons contained within the vagus nerve. Data also showed a particular propensity of vagal motor neurons and efferents to accrue α-synuclein and deliver it to peripheral tissues; indeed, following its midbrain overexpression, human α-synuclein was detected within gastric nerve endings of visceromotor but not viscerosensory vagal projections. Thus, the dorsal motor nucleus of the vagus nerve represents a key relay center for central-to-peripheral α-synuclein transmission, and efferent vagal fibers may act as unique conduits for protein transfer. The presence of α-synuclein in peripheral tissues could reflect, at least in some synucleinopathy patients, an ongoing pathological process that originates within the brain and, from there, reaches distant organs innervated by motor vagal projections.

Synaptic connections between endomorphin 2-immunoreactive terminals and μ-opioid receptor-expressing neurons in the sacral parasympathetic nucleus of the rat

The urinary bladder is innervated by parasympathetic preganglionic neurons (PPNs) that express μ-opioid receptors (MOR) in the sacral parasympathetic nucleus (SPN) at lumbosacral segments L6-S1. The SPN also contains endomorphin 2 (EM2)-immunoreactive (IR) fibers and terminals. EM2 is the endogenous ligand of MOR. In the present study, retrograde tract-tracing with cholera toxin subunit b (CTb) or wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) via the pelvic nerve combined with immunohistochemical staining for EM2 and MOR to identify PPNs within the SPN as well as synaptic connections between the EM2-IR terminals and MOR-expressing PPNs in the SPN of the rat. After CTb was injected into the pelvic nerve, CTb retrogradely labeled neurons were almost exclusively located in the lateral part of the intermediolateral gray matter at L6-S1 of the lumbosacral spinal cord. All of the them also expressed MOR. EM2-IR terminals formed symmetric synapses with MOR-IR, WGA-HRP-labeled and WGA-HRP/MOR double-labeled neuronal cell bodies and dendrites within the SPN. These results provided morphological evidence that EM2-containing axon terminals formed symmetric synapses with MOR-expressing PPNs in the SPN. The present results also show that EM2 and MOR might be involved in both the homeostatic control and information transmission of micturition.

Electrophysiological, pharmacological and molecular profile of the transient outward rectifying conductance in rat sympathetic preganglionic neurons in vitro

Transient outward rectifying conductances or A-like conductances in sympathetic preganglionic neurons (SPN) are prolonged, lasting for hundreds of milliseconds to seconds and are thought to play a key role in the regulation of SPN firing frequency. Here, a multidisciplinary electrophysiological, pharmacological and molecular single-cell rt-PCR approach was used to investigate the kinetics, pharmacological profile and putative K+ channel subunits underlying the transient outward rectifying conductance expressed in SPN. SPN expressed a 4-aminopyridine (4-AP) sensitive transient outward rectification with significantly longer decay kinetics than reported for many other central neurons. The conductance and corresponding current in voltage-clamp conditions was also sensitive to the Kv4.2 and Kv4.3 blocker phrixotoxin-2 (1-10 μM) and the blocker of rapidly inactivating Kv channels, pandinotoxin-Kα (50 nM). The conductance and corresponding current was only weakly sensitive to the Kv1 channel blocker tityustoxin-Kα and insensitive to dendrotoxin I (200 nM) and the Kv3.4 channel blocker BDS-II (1 μM). Single-cell RT-PCR revealed mRNA expression for the α-subunits Kv4.1 and Kv4.3 in the majority and Kv1.5 in less than half of SPN. mRNA for accessory β-subunits was detected for Kvβ2 in all SPN with differential expression of mRNA for KChIP1, Kvβ1 and Kvβ3 and the peptidase homologue DPP6. These data together suggest that the transient outwardly rectifying conductance in SPN is mediated by members of the Kv4 subfamily (Kv4.1 and Kv4.3) in association with the β-subunit Kvβ2. Differential expression of the accessory β subunits, which may act to modulate channel density and kinetics in SPN, may underlie the prolonged and variable time-course of this conductance in these neurons.

Defining the pupillary component of the perioculomotor preganglionic population within a unitary primate Edinger-Westphal nucleus

The primate Edinger-Westphal nucleus (EW) contains perioculomotor preganglionic (pIII(PG)) motoneurons that control the lens and pupil. Separate subdivisions have been described in EW and termed visceral columns, with the lateral visceral column (lvc) reportedly receiving pretectal inputs for the pupillary light reflex. However, choline acetyl transferase staining reveals a single paired column of cells dorsal to the oculomotor nucleus, suggesting the EW is not subdivided. We investigated this issue by transneuronal retrograde labelling of pIII(PG) neurons in three monkey species. In all three, pIII(PG) neurons were contained in a single column. We have also examined which part of the macaque pIII(PG) population receives pretectal input. Injections of biocytin into the pretectum anterogradely labelled terminals that lay in close association with pIII(PG) motoneurons retrogradely labelled by ciliary ganglion injections of WGA-HRP. These close associations were concentrated in the ventromedial portion of the middle third of EW, suggesting this pIII(PG) region mediates pupillary control. In other cases, pretectal WGA-HRP injections, in addition to labelling terminals in the EW, produced a circular field of labelled neurons, and terminals in the periaqueductal grey, dorsolateral to EW. This region may represent the previously designated lvc, but it does not contain pIII(PG) motoneurons.

[Alteration of trachea and bronchi smooth muscles constriction under long inhalation of dioxide nitrogen by rats]

On insulated preparation of trachea and bronchi, change of the smooth muscles constriction was studied in rats inhaling dioxide nitrogen during 15, 30 and 60 days. The inhalation enhanced 1.5-fold and bronchi 2.5-fold responses of tracheal smooth muscles to stimulation of preganglionic nerve. The delay of the response in both events increased 1.3-fold. Long repeated stimulation caused a further increase of the constriction of tracheas and bronchi (1.32-fold). Blocking receptor with Novocain (1.0 mcg/ml) reduced the amplitude of the constriction and enhanced the response delay. After 30 days of inhalation, repeated nerve stimulations enhanced the amplitude of the constriction up to 120%, but after 60 days it reduced the amplitude of the constriction to 71 and 77% in preparations of tracheas and bronchi, respectively. In our opinion, long inhalation of dioxide nitrogen broke functioning of local lung nervous system controlling activity of the smooth muscles. The research results indicate important role of neuron functional module in pathology of the respiratory ways caused inhalation of dioxide nitrogen.

VGLUT1 and VGLUT2 innervation in autonomic regions of intact and transected rat spinal cord

Fast excitatory neurotransmission to sympathetic and parasympathetic preganglionic neurons (SPN and PPN) is glutamatergic. To characterize this innervation in spinal autonomic regions, we localized immunoreactivity for vesicular glutamate transporters (VGLUTs) 1 and 2 in intact cords and after upper thoracic complete transections. Preganglionic neurons were retrogradely labeled by intraperitoneal Fluoro-Gold or with cholera toxin B (CTB) from superior cervical, celiac, or major pelvic ganglia or adrenal medulla. Glutamatergic somata were localized with in situ hybridization for VGLUT mRNA. In intact cords, all autonomic areas contained abundant VGLUT2-immunoreactive axons and synapses. CTB-immunoreactive SPN and PPN received many close appositions from VGLUT2-immunoreactive axons. VGLUT2-immunoreactive synapses occurred on Fluoro-Gold-labeled SPN. Somata with VGLUT2 mRNA occurred throughout the spinal gray matter. VGLUT2 immunoreactivity was not noticeably affected caudal to a transection. In contrast, in intact cords, VGLUT1-immunoreactive axons were sparse in the intermediolateral cell column (IML) and lumbosacral parasympathetic nucleus but moderately dense above the central canal. VGLUT1-immunoreactive close appositions were rare on SPN in the IML and the central autonomic area and on PPN. Transection reduced the density of VGLUT1-immunoreactive axons in sympathetic subnuclei but increased their density in the parasympathetic nucleus. Neuronal cell bodies with VGLUT1 mRNA occurred only in Clarke's column. These data indicate that SPN and PPN are densely innervated by VGLUT2-immunoreactive axons, some of which arise from spinal neurons. In contrast, the VGLUT1-immunoreactive innervation of spinal preganglionic neurons is sparse, and some may arise from supraspinal sources. Increased VGLUT1 immunoreactivity after transection may correlate with increased glutamatergic transmission to PPN.

Allergic lung inflammation affects central noradrenergic control of cholinergic outflow to the airways in ferrets

Brain stem noradrenergic cell groups mediating autonomic responses to stress project to airway-related vagal preganglionic neurons (AVPNs). In ferrets, their activation produces withdrawal of cholinergic outflow to the airways via release of norepinephrine and activation of alpha(2A)-adrenergic receptors (alpha(2A)-AR) expressed by AVPNs. In these studies, we examined the effects of allergen exposure of the airway (AE) with ovalbumin on noradrenergic transmission regulating the activity of AVPNs and, consequently, airway smooth muscle tone. Experiments were performed in vehicle control (Con) and AE ferrets. Microperfusion of an alpha(2A)-AR agonist (guanabenz) in close proximity to AVPNs elicited more pronounced effects in Con than AE ferrets, including a decrease in unit activity and reflexly evoked responses of putative AVPN neurons with a corresponding decrease in cholinergic outflow to the airways. Although no differences were found in the extent of noradrenergic innervation of the AVPNs, RT-PCR and Western blot studies demonstrated that AE and repeated exposure to antigen significantly reduced expression of alpha(2A)-ARs at message and protein levels. These findings indicate that, in an animal model of allergic asthma, sensitization and repeated challenges with a specific allergen diminish central inhibitory noradrenergic modulation of AVPNs, possibly via downregulation of alpha(2A)-AR expression by these neurons.

Vagally mediated, nonparacrine effects of cholecystokinin-8s on rat pancreatic exocrine secretion

Cholecystokinin (CCK) has been proposed to act in a vagally dependent manner to increase pancreatic exocrine secretion via actions exclusively at peripheral vagal afferent fibers. Recent evidence, however, suggests the CCK-8s may also affect brain stem structures directly. We used an in vivo preparation with the aims of 1) investigating whether the actions of intraduodenal casein perfusion to increase pancreatic protein secretion also involved direct actions of CCK at the level of the brain stem and, if so, 2) determining whether, in the absence of vagal afferent inputs, CCK-8s applied to the dorsal vagal complex (DVC) can also modulate pancreatic exocrine secretion (PES). Sprague-Dawley rats (250-400 g) were anesthetized and the common bile-pancreatic duct was cannulated to collect PES. Both vagal deafferentation and pretreatment with the CCK-A antagonist lorglumide on the floor of the fourth ventricle decreased the casein-induced increase in PES output. CCK-8s microinjection (450 pmol) in the DVC significantly increased PES; the increase was larger when CCK-8s was injected in the left side of the DVC. Protein secretion returned to baseline levels within 30 min. Microinjection of CCK-8s increased PES (although to a lower extent) also in rats that underwent complete vagal deafferentation. These data indicate that, as well as activating peripheral vagal afferents, CCK-8s increases pancreatic exocrine secretion via an action in the DVC. Our data suggest that the CCK-8s-induced increases in PES are due mainly to a paracrine effect of CCK; however, a relevant portion of the effects of CCK is due also to an effect of the peptide on brain stem vagal circuits.

Cholecystokinin-8s excites identified rat pancreatic-projecting vagal motoneurons

It is known that cholecystokinin (CCK) acts in a paracrine fashion to increase pancreatic exocrine secretion via vagal circuits. Recent evidence, however, suggests that CCK-8s actions are not restricted to afferent vagal fibers, but also affect brain stem structures directly. Within the brain stem, preganglionic neurons of the dorsal motor nucleus of the vagus (DMV) send efferent fibers to subdiaphragmatic viscera, including the pancreas. Our aims were to investigate whether DMV neurons responded to exogenously applied CCK-8s and, if so, the mechanism of action. Using whole cell patch-clamp recordings we show that perfusion with CCK-8s induced a concentration-dependent excitation in approximately 60% of identified pancreas-projecting DMV neurons. The depolarization was significantly reduced by tetrodotoxin, suggesting both direct (on the DMV membrane) and indirect (on local synaptic circuits) effects. Indeed, CCK-8s increased the frequency of miniature excitatory currents onto DMV neurons. The CCK-A antagonist, lorglumide, prevented the CCK-8s-mediated excitation whereas the CCK-B preferring agonist, CCK-nonsulfated, had no effect, suggesting the involvement of CCK-A receptors only. In voltage clamp, the CCK-8s-induced inward current reversed at -106 +/- 3 mV and the input resistance increased by 150 +/- 15%, suggesting an effect mediated by the closure of a potassium conductance. Indeed, CCK-8s reduced both the amplitude and the time constant of decay of a calcium-dependent potassium conductance. When tested with pancreatic polypeptide (which reduces pancreatic exocrine secretion), cells that responded to CCK-8s with an excitation were, instead, inhibited by pancreatic polypeptide. These data indicate that CCK-8s may control pancreas-exocrine secretion also via an effect on pancreas-projecting DMV neurons.

Glucagon-like peptide-1 excites pancreas-projecting preganglionic vagal motoneurons

Glucagon-like peptide-1 (GLP-1) increases pancreatic insulin secretion via a direct action on pancreatic beta-cells. A high density of GLP-1-containing neurons and receptors is also present in brain stem vagal circuits; therefore, the aims of the present study were to investigate 1) whether identified pancreas-projecting neurons of the dorsal motor nucleus of the vagus (DMV) respond to exogenously applied GLP-1, 2) the mechanism(s) of action of GLP-1, and 3) whether the GLP-1-responsive neurons (putative modulators of endocrine secretion) could be distinguished from DMV neurons responsive to peptides that modulate pancreatic exocrine secretion, specifically pancreatic polypeptide (PP). Whole cell recordings were made from identified pancreas-projecting DMV neurons. Perfusion with GLP-1 induced a concentration-dependent depolarization in approximately 50% of pancreas-projecting DMV neurons. The GLP-1 effects were mimicked by exendin-4 and antagonized by exendin-(9-39). In approximately 60% of the responsive neurons, the GLP-1-induced depolarization was reduced by tetrodotoxin (1 microM), suggesting both pre- and postsynaptic sites of action. Indeed, the GLP-1 effects were mediated by actions on potassium currents, GABA-induced currents, or both. Importantly, neurons excited by GLP-1 were unresponsive to PP and vice versa. These data indicate that 1) GLP-1 may act on DMV neurons to control pancreatic endocrine secretion, 2) the effects of GLP-1 on pancreas-projecting DMV neurons are mediated both via a direct excitation of their membrane as well as via an effect on local circuits, and 3) the GLP-1-responsive neurons (i.e., putative endocrine secretion-controlling neurons) could be distinguished from neurons responsive to PP (i.e., putative exocrine secretion-controlling neurons).

Neurally released pituitary adenylate cyclase-activating polypeptide enhances guinea pig intrinsic cardiac neurone excitability

Intracellular recordings were made in vitro from guinea-pig cardiac ganglia to determine whether endogenous neuropeptides such as pituitary adenylate cyclase-activating polypeptide (PACAP) or substance P released during tetanic neural stimulation modulate cardiac neurone excitability and/or contribute to slow excitatory postsynaptic potentials (sEPSPs). When nicotinic and muscarinic receptors were blocked by hexamethonium and atropine, 20 Hz stimulation for 10 s initiated a sEPSP in all innervated neurones. In 40% of the cells, excitability was enhanced after termination of the sEPSP. This suggested that non-cholinergic receptor-mediated mechanisms contributed to the sEPSP and modulated neuronal excitability. Exogenous PACAP and substance P initiated a slow depolarization in the neurones whereas neuronal excitability was only increased by PACAP. When ganglia were treated with the PAC1 antagonist PACAP6-38 (500 nM), the sEPSP evoked by 20 Hz stimulation was reduced by approximately 50% and an enhanced excitability occurred in only 10% of the cells. These observations suggested that PACAP released from preganglionic nerve terminals during tetanic stimulation enhanced neuronal excitability and evoked sEPSPs. After addition of 1 nM PACAP to the bath, 7 of 9 neurones exhibited a tonic firing pattern whereas in untreated preparations, the neurons had a phasic firing pattern. PACAP6-38 (500 nM) diminished the increase in excitability caused by 1 nM PACAP so that only 4 of 13 neurones exhibited a tonic firing pattern and the other 9 cells retained a phasic firing pattern. These findings indicate that PACAP can be released by tetanic neural stimulation in vitro and increase the excitability of intrinsic cardiac neurones. We hypothesize that in vivo PACAP released during preganglionic firing may modulate neurotransmission within the intrinsic cardiac ganglia.

Gamma-aminobutyric acid-containing sympathetic preganglionic neurons in rat thoracic spinal cord send their axons to the superior cervical ganglion

Gamma-aminobutyric acid (GABA)-containing fibers have been observed in the rat superior cervical ganglion (SCG) and, to a lesser extent, in the stellate ganglion (STG). The aim of present study is to clarify the source of these fibers. No cell body showed mRNAs for glutamic acid decarboxylases (GADs) or immunoreactivity for GAD of 67 kDa (GAD67) in the cervical sympathetic chain. Thus, GABA-containing fibers in the ganglia are suggested to be of extraganglionic origin. GAD67-immunoreactive fibers were found not in the dorsal roots or ganglia, but in the ventral roots, so GABA-containing fibers in the sympathetic ganglia were considered to originate from the spinal cord. Furthermore, almost all GAD67-immunoreactive fibers in the sympathetic ganglia showed immunoreactivity for vesicular acetylcholine transporter, suggesting that GABA was utilized by some cholinergic preganglionic neurons. This was confirmed by the following results. 1) After injection of Sindbis/palGFP virus into the intermediolateral nucleus, some anterogradely labeled fibers in the SCG were immunopositive for GAD67. 2) After injection of fluorogold into the SCG, some retrogradely labeled neurons in the thoracic spinal cord were positive for GAD67 mRNA. 3) When the ventral roots of the eighth cervical to the fourth thoracic segments were cut, almost all GAD67- and GABA-immunoreactive fibers disappeared from the ipsilateral SCG and STG, suggesting that the vast majority of GABA-containing fibers in those ganglia were of spinal origin. Thus, the present findings strongly indicate that some sympathetic preganglionic neurons are not only cholinergic but also GABAegic.

Choline acetyl transferase and neuropeptide immunoreactivities are colocalized in somata, but preferentially localized in distinct axon fibers and boutons of cat sympathetic preganglionic neurons

Cholinergic sympathetic preganglionic neurons (SPN) coexpress the biosynthetic enzyme for acetylcholine, choline acetyl-transferase (ChAT), and neuropeptides such as enkephalin (ENK) in their cell bodies. However, it is not clear whether they also coexpress ChAT and neuropeptides in axon fibers and boutons. To explore coexpression of ChAT and neuropeptides in somata and axon processes of SPN, we investigated, using immunohistochemistry, retrograde labeling, confocal analysis, and tridimensional reconstruction, whether ChAT and the peptides neurotensin, methionine-ENK, somatostatin, calcitonin gene-related peptide, and vasoactive intestinal peptide colocalize in somata, axons fibers, and boutons of cat SPN. Practically, complete colocalization for these peptides and ChAT was observed in SPN somata. Conversely, in most instances we observed independent localization of immunoreactivity (IR) for ChAT and the peptides in axon fibers and boutons. The minor colocalization between ChAT- and peptide-IR in preganglionic fibers could correspond to a sequential axonal transport of ChAT and peptides, since we observed coexistence of these transmitters after blocking axonal transport. Contrary to Dale's principle, our results suggest that SPN can synthesize ChAT and peptides in their cell bodies and route them to distinct axon boutons or terminals in sympathetic ganglia. Presence of axon boutons containing either ChAT or neuropeptides lead us to suggest a new neurochemical pattern of cotransmission in sympathetic ganglia based on the concurrent release of transmitters and cotransmitters from distinct presynaptic boutons, rather than in the corelease of these mediators from the same axon process. The possibility that cellular segregation could be transient and depend on functional requirements is considered.

The autonomic facial nerve pathway in birds: a tracing study in chickens

PURPOSE

In birds, the parasympathetic innervation of the choroid is via the ciliary (cranial nerve III) and pterygopalatine (cranial nerve VII) ganglia, the latter consisting of a chain of microganglia within the orbit. Because of the scattered nature of these microganglia, lesions of this nerve pathway in birds have not been attempted, making interpretation of the functional contribution of this parasympathetic input to the avian eye uncertain. The purpose of this study was to find an extraorbital approach to the preganglionic part of cranial nerve VII and to reveal its peripheral terminals and its site of origin in the brain stem.

METHODS

The radix autonomica cranial nerve VII was accessed via the tympanic cavity and injected with dextran coupled to Texas red (DTxR). Orbital structures and the brain stem were prepared for tracer detection and immunohistochemistry for neuronal nitric oxide synthase (nNOS), choline acetyl transferase (ChAT), vasoactive intestinal polypeptide (VIP), calcitonin gene-related peptide (CGRP), galanin (GAL), and somatostatin (SOM). For documentation, fluorescence and confocal laser scanning microscopy were used.

RESULTS

Anterogradely labeled DTxR-positive nerve fibers were detected within the orbital pterygopalatine microganglionic chain, forming boutons closely associated with nNOS-positive neurons. Retrogradely labeled DTxR-positive neurons with cell diameters of approximately 20 microm were found in the brain stem. These were positive for ChAT, but negative for nNOS, VIP, SOM, GAL, and CGRP. They most likely represent the preganglionic neurons of the superior salivatory nucleus. In close proximity, there were larger (40 microm) unlabeled neurons that were positive for ChAT and CGRP, but negative for GAL. These most likely represent motoneurons of the facial nerve.

CONCLUSIONS

This surgical approach offers excellent opportunities for lesioning experiments for the study of the autonomic facial nerve pathway in birds in terms of both its anatomic organization and its function.

Immunoreactivity for cocaine- and amphetamine-regulated transcript in rat sympathetic preganglionic neurons projecting to sympathetic ganglia and the adrenal medulla

Many sympathetic preganglionic neurons (SPN) in the intermediolateral cell column (IML) contain cocaine- and amphetamine-regulated transcript (CART), but the function of these CART-immunoreactive (IR) neurons is unknown. To test the possibility that CART might mark SPN involved in cardiovascular regulation, we first established whether all CART neurons in the spinal cord were SPN by double-immunofluorescent labelling for CART and choline acetyltransferase (ChAT). All autonomic subnuclei contained SPN immunoreactive for ChAT plus CART. Occasional ChAT-negative, CART-positive neurons occurred adjacent to the IML, indicating the existence of CART-IR interneurons. We then retrogradely labelled SPN with cholera toxin subunit B (CTB) from a variety of targets and used double immunofluorescence to detect CTB and CART. Among SPN in the IML, 43% projecting to the coeliac ganglion, 34% projecting to the major pelvic ganglion, and about 15% projecting to the superior cervical ganglion or adrenal medulla contained CART. CART also occurred in most SPN projecting to the major pelvic ganglion from either the central autonomic area (63%) or the intercalated nucleus (58%). Finally, we used drug-induced hypotension in conscious rats to evoke Fos immunoreactivity in barosensitive SPN and immunostained to reveal Fos and CART. CART immunoreactivity was present in 41% of the Fos-IR barosensitive neurons, which were concentrated in the IML of segments T5-T13. CART-positive, Fos-negative neurons also occurred in the same segments. These results indicate that CART occurs in barosensitive SPN, nonbarosensitive SPN, and interneurons. Thus, CART is not an exclusive marker for cardiovascular SPN but is likely to influence many autonomic activities.

Expression of ghrelin receptor mRNA in the rat and the mouse brain

Ghrelin is a hormone that stimulates growth hormone secretion and signals energy insufficiency via interaction with its receptor, the growth hormone secretagogue receptor (GHSR). The GHSR is located in both the central nervous system and the periphery. Its distribution in the CNS, as assessed by in situ hybridization histochemistry (ISHH), has been described previously in a few mammalian species, although these studies were limited by either the detail provided or the extent of the regions examined. In the present study, we systematically examined the distribution of GHSR mRNA in the adult rat and mouse brains and cervical spinal cords by using ISHH with novel cRNA probes specific for the mRNA encoding functional GHSR (the type 1a variant). We confirmed GHSR mRNA expression in several hypothalamic nuclei, many of which have long been recognized as playing roles in body weight and food intake. GHSR also was found in several other regions previously unknown to express GHSR mRNA, including many parasympathetic preganglionic neurons. Additionally, we found GHSR mRNA within all three components of the dorsal vagal complex, including the area postrema, the nucleus of the solitary tract, and the dorsal motor nucleus of the vagus. Finally, we examined the coexpression of GHSR with tyrosine hydroxylase and cholecystokinin and demonstrate a high degree of GHSR mRNA expression within dopaminergic, cholecystokinin-containing neurons of the substantia nigra and ventral tegmental area.

Segmental organization of spinal reflexes mediating autonomic dysreflexia after spinal cord injury

Spinal cord injuries above mid-thoracic levels can lead to a potentially life-threatening hypertensive condition termed autonomic dysreflexia that is often triggered by distension of pelvic viscera (bladder or bowel). This syndrome is characterized by episodic hypertension due to sudden, massive discharge of sympathetic preganglionic neurons in the thoracolumbar spinal cord. This hypertension is usually accompanied by bradycardia, particularly if the injury is caudal to the 2nd to 4th thoracic spinal segments. The development of autonomic dysreflexia is correlated with aberrant sprouting of peptidergic afferent fibers into the spinal cord below the injury. In particular, sprouting of nerve growth factor-responsive afferent fibers has been shown to have a major influence on dysreflexia, perhaps by amplifying the activation of disinhibited sympathetic neurons. Using a model of noxious bowel distension after complete thoracic spinal transection at the 4th thoracic segment in rats, we selectively altered C-fiber sprouting, at specified spinal levels caudal to the injury, with microinjections of adenovirus encoding the growth-promoting nerve growth factor or the growth-inhibitory semaphorin 3A. This was followed by assessment of physiological responses to colorectal distension and subsequent histology. Additionally, anterograde tract tracers were injected into the lumbosacral region to compare the extent of labeled propriospinal rostral projections in uninjured cords to those in cords after complete 4th thoracic transection. In summary, overexpression of chemorepulsive semaphorin 3A impeded C-fiber sprouting in lumbosacral segments and mitigated hypertensive autonomic dysreflexia, whereas the opposite results were obtained with nerve growth factor overexpression. Furthermore, compared to naïve rats, there were significantly more labeled lumbosacral propriospinal projections rostrally after thoracic injury. Collectively, our findings suggest that distension of pelvic viscera increases the excitation of expanded afferent terminals in the disinhibited lumbosacral spinal cord. This, in turn, triggers excitation and sprouting of local propriospinal neurons to relay visceral sensory stimuli and amplify the activation of sympathetic preganglionic neurons in the thoracolumbar cord, to enhance transmission in the spinal viscero-sympathetic reflex pathway. These responses are manifested as autonomic dysreflexia.

The anti-inflammatory effect of peripheral bee venom stimulation is mediated by central muscarinic type 2 receptors and activation of sympathetic preganglionic neurons

The anti-inflammatory effect (AI) induced by peripheral injection of diluted bee venom (dBV) involves activation of spinal cord circuits and is mediated by catecholamine release from adrenal medulla, but the precise neuronal mechanisms involved are not fully understood. In a recent study, we demonstrated that an increase in spinal acetylcholine is involved in mediating the anti-inflammatory effect of dBV and that this mediation also involves adrenomedullary activation. The present study utilized the mouse air pouch inflammation model to evaluate the involvement of spinal acetylcholine receptors and sympathetic preganglionic neurons (SPNs) in dBV's anti-inflammatory effect (dBVAI). Intrathecal (IT) pretreatment with atropine (muscarinic cholinergic antagonist) but not hexamethonium (nicotinic cholinergic antagonist) significantly suppressed dBVAI on zymosan-evoked leukocyte migration. Subsequent experiments showed that IT pretreatment with methoctramine (a muscarinic receptor type 2; M(2) antagonist), but not pirenzepine (an M(1) antagonist) or 4-DAMP (an M(3) antagonist), suppressed the dBVAI. In addition, dBV stimulation specifically increased Fos expression in SPNs of the T7-T11, but not the T1-T6 or T12-L2 spinal cord segments, in animals with zymosan-induced inflammation. Moreover, IT methoctramine pretreatment suppressed this dBV-induced Fos expression specifically in SPNs of T7-T11 level. Peripheral sympathetic denervation using 6-hydroxydopamine (6-OHDA) treatment (which spares sympathetic adrenal medullary innervation) did not alter dBVAI. Collectively these results indicate that dBV stimulation leads to spinal cord acetylcholine release that in turn acts on spinal M(2) receptors, which via a hypothesized disinhibition mechanism activates SPNs that project to the adrenal medulla. This activation ultimately leads to the release of adrenal catecholamines that contribute to dBVAI.

Chronic ether stress-induced response of urocortin 1 neurons in the Edinger-Westphal nucleus in the mouse

Urocortin 1 (Ucn1) neurons, most abundantly expressed in the Edinger-Westphal nucleus (E-WN), respond to various acute challenges. In a recent study, we found that acute ether stress resulted in the strongest activation of E-WN Ucn1 cells, as revealed by immunohistochemistry for Fos (often used as a marker for neuronal activation). Although the acute stress responsiveness of E-WN Ucn1 neurons has been widely studied, the activation pattern of Fos in these neurons in response to repeated challenges has not yet been investigated. Therefore, we quantitatively studied Fos activation in E-WN neurons and measured Ucn1 mRNA levels in E-WN neurons after acute and chronic ether stress in mice. Acute stress resulted in a robust Fos response and an increase in Ucn1 mRNA as compared to non-stressed mice. In the chronic stress paradigm, Fos expression was unchanged, whereas after 2 and 3 weeks of daily ether exposure Ucn1 mRNA expression had strongly declined in the E-WN. Fos and Ucn1 mRNA were co-expressed in E-WN neurons in both acutely and chronically stressed animals. This paper is the first to demonstrate that Ucn1 mRNA-expressing neurons in the E-WN show a non-habituating Fos response to a chronic homotypic ether challenge that also resulted in a reliable down-regulation of E-WN Ucn1 mRNA levels vs. acutely stressed animals. Based on these results, we propose that the E-WN-Ucn1 system represents a novel stress adaptation pathway, which may play an important role in coping with chronic challenges.

Enkephalins and functionally specific vagal preganglionic neurons to the heart: Ultrastructural studies in the cat

In cat, distinct populations of vagal preganglionic and postganglionic neurons selectively modulate heart rate, atrioventricular conduction and left ventricular contractility, respectively. Vagal preganglionic neurons to the heart originate in the ventrolateral part of nucleus ambiguus and project to postganglionic neurons in intracardiac ganglia, including the sinoatrial (SA), atrioventricular (AV) and cranioventricular (CV) ganglia, which selectively modulate heart rate, AV conduction and left ventricular contractility, respectively. These ganglia receive projections from separate populations of vagal preganglionic neurons. The neurochemical anatomy and synaptic interactions of afferent neurons which mediate central control of these preganglionic neurons is incompletely understood. Enkephalins cause bradycardia when microinjected into nucleus ambiguus. It is not known if this effect is mediated by direct synapses of enkephalinergic terminals upon vagal preganglionic neurons to the heart. The effects of opioids in nucleus ambiguus upon AV conduction and cardiac contractility have also not been studied. We have tested the hypothesis that enkephalinergic nerve terminals synapse upon vagal preganglionic neurons projecting to the SA, AV and CV ganglia. Electron microscopy was used combining retrograde labeling from the SA, AV or CV ganglion with immunocytochemistry for enkephalins in ventrolateral nucleus ambiguus. Eight percent of axodendritic synapses upon negative chronotropic, and 12% of axodendritic synapses upon negative dromotropic vagal preganglionic neurons were enkephalinergic. Enkephalinergic axodendritic synapses were also present upon negative inotropic vagal preganglionic neurons. Thus enkephalinergic terminals in ventrolateral nucleus ambiguus can modulate not only heart rate but also atrioventricular conduction and left ventricular contractility by directly synapsing upon cardioinhibitory vagal preganglionic neurons.

A part of cholinergic fibers in mouse superior cervical ganglia contain GABA or glutamate

The localizations and functions of glutamate and GABA, the major amino acid neurotransmitters in the central nervous system, are still unclear in the peripheral nervous system. We immunohistochemically double-stained mouse superior cervical ganglia with antibodies for the vesicular acetylcholine transporter (VAchT), GAD65, the vesicular glutamate transporters 1-3 (VGluTs1-3), the marker of the sympathetic preganglionic neuron (SPN), GABAergic, and glutamatergic terminals, respectively. All GAD65-positive terminals showed VAchT immunoreactivity, indicating that GABAergic fibers originate from SPNs. VGluT2-immunoreactive terminals showing colocalization with VAchT were observed, but VGluT1 and 3 immunoreactive terminals were not. Colocalization of GAD65 and VGluT2 was rarely found. All VGluT2-immunopositive terminals were also immunopositive for neuronal nitric oxide synthase (nNOS), a marker for the subpopulation of the SPNs, while about half of the GABA-immunopositive fibers were immunopositive for nNOS. The origin of these fibers was discussed.

Airway-related vagal preganglionic neurons express brain-derived neurotrophic factor and TrkB receptors: implications for neuronal plasticity

Recent evidence indicates that brain-derived neurotrophic factor (BDNF) is present in neurons and may affect neurotransmitter release, cell excitability, and synaptic plasticity via activation of tyrosine kinase B (TrkB) receptors. However, whether airway-related vagal preganglionic neurons (AVPNs) produce BDNF and contain TrkB receptors is not known. Hence, in ferrets, we examined BDNF and TrkB receptor expression in identified AVPNs using in situ hybridization and immunohistochemistry. BDNF protein levels were measured within the rostral nucleus ambiguus (rNA) region by ELISA. We observed that the subpopulation of AVPNs, identified by neuroanatomical tract tracing, within the rNA region express BDNF mRNA, BDNF protein, as well as TrkB receptor. In addition, brain tissue from the rNA region contained measurable amounts of BDNF that were comparable to the hippocampal region of the brain. These data indicate, for the first time, that the BDNF-TrkB system is expressed by AVPNs and may play a significant role in regulating cholinergic outflow to the airways.

Phosphorylated extracellular signal-regulated kinase 1/2 immunoreactivity identifies a novel subpopulation of sympathetic preganglionic neurons

Distinct chemical codes are thought to reflect functional specificity in sympathetic preganglionic neurons (SPN). Although a number of chemical candidates have been identified including neurotransmitter-related, calcium-binding and other proteins, signal transduction proteins have been largely neglected. Not only might these chemicals allow discrimination of functionally unique chemical signatures, but they may also identify activated neurons. Immunoreactivity (ir) to phosphorylated extracellular signal-regulated kinase 1/2 (p-ERK1/2) was differentially located within the thoracic spinal cord depending upon which of three forms of killing was used: the only exception to this was the intermediolateral cell column (IML) which was consistently, densely labeled. The presence or absence of p-ERK1/2 in SPN (n=17,541) within the IML of the thoraco-lumbar spinal cord was determined in seven rats. SPN were identified on the basis of their location, size and that they contained choline acetyltransferase ir. On average, 58% of SPN contained p-ERK1/2, however, more SPN in both the upper (72%; C8-T4) and lower (78%; T11-L3) thoraco-lumbar spinal cord contained p-ERK1/2-ir than the middle thoracic region (47%; T4-T10). p-ERK1/2-ir was also examined in SPN (n=1895) innervating the adrenal medulla (identified by retrograde tracing using cholera toxin B subunit) combined with localization of neuronal nitric oxide synthase (nNOS) in three rats. On average, 64% of adrenal SPN contain p-ERK1/2-ir, and it was confirmed that all adrenal SPN contain nNOS-ir. It appears that p-ERK1/2-ir SPN, described in this study, have tonically activated receptors that are coupled to intracellular signal transduction pathways that lead to the phosphorylation of ERK1/2.

Chemical profile of vagal preganglionic motor cells innervating the airways in ferrets: the absence of noncholinergic neurons

In ferrets, we investigated the presence of choline acetyltransferase (ChAT), vasoactive intestinal peptide (VIP), and markers for nitric oxide synthase (NOS) in preganglionic parasympathetic neurons innervating extrathoracic trachea and intrapulmonary airways. Cholera toxin β-subunit, a retrograde axonal transganglionic tracer, was used to identify airway-related vagal preganglionic neurons. Double-labeling immunohistochemistry and confocal microscopy were employed to characterize the chemical nature of identified airway-related vagal preganglionic neurons at a single cell level. Physiological experiments were performed to determine whether activation of the VIP and ChAT coexpressing vagal preganglionic neurons plays a role in relaxation of precontracted airway smooth muscle tone after muscarinic receptor blockade. The results showed that 1) all identified vagal preganglionic neurons innervating extrathoracic and intrapulmonary airways are acetylcholine-producing cells, 2) cholinergic neurons innervating the airways coexpress ChAT and VIP but do not contain NOS, and 3) chemical stimulation of the rostral nucleus ambiguus had no significant effect on precontracted airway smooth muscle tone after muscarinic receptor blockade. These studies indicate that vagal preganglionic neurons are cholinergic in nature and coexpress VIP but do not contain NOS; their stimulation increases cholinergic outflow, without activation of inhibitory nonadrenergic, noncholinergic ganglionic neurons, stimulation of which induces airway smooth muscle relaxation. Furthermore, these studies do not support the possibility of direct inhibitory innervation of airway smooth muscle by vagal preganglionic fibers that contain VIP.

Autonomic microganglion cells: a source of acetylcholine in the rat carotid body

Hypoxic chemosensitivity of peripheral arterial chemoreceptors and the ventilatory response to O2 deprivation increases with postnatal development. Multiple putative neurotransmitters, which are synthesized in the carotid body (CB), are thought to mediate signals generated by hypoxia. Acetylcholine (ACh) is believed to be a major excitatory neurotransmitter participating in hypoxic chemosensitivity. However, it is not known whether ACh originates from type I cells in the CB. In these studies, we tested the hypothesis that choline acetyltransferase (ChAT) and vesicular ACh transporter (VAChT) mRNAs are expressed in the CB and that mRNA levels would increase with postnatal maturation or exposure to hypoxia. Semiquantitative in situ hybridization histochemistry and immunohistochemistry were used to localize cholinergic markers within neurons and cells of the rat CB, the nodose-petrosal-jugular ganglion complex, and the superior cervical ganglion up to postnatal day 28. We show that the pattern of distribution, in tissue sections, is similar for both ACh markers; however, the level of VAChT mRNA is uniformly greater than that of ChAT. VAChT mRNA and immunoreactivity are detected abundantly in the nodose-petrosal-jugular ganglion complex in a number of microganglion cells embedded in nerve fibers innervating the CB for all postnatal groups, whereas ChAT mRNA is detected in only a few of these cells. Contrary to our hypothesis, postnatal maturation caused a reduction in ACh trait expression, whereas hypoxic exposure did not induce the upregulation of VAChT and ChAT mRNA levels in the CB, microganglion, or within the ganglion complex. The present findings indicate that the source of ACh in the CB is likely within autonomic microganglion cells and cholinergic nerve terminals.

Differential expression of calcium channels in sympathetic and parasympathetic preganglionic inputs to neurons in paracervical ganglia of guinea-pigs

Neurons in pelvic ganglia receive nicotinic excitatory post-synaptic potentials (EPSPs) from sacral preganglionic neurons via the pelvic nerve, lumbar preganglionic neurons via the hypogastric nerve or both. We tested the effect of a range of calcium channel antagonists on EPSPs evoked in paracervical ganglia of female guinea-pigs after pelvic or hypogastric nerve stimulation. omega-Conotoxin GVIA (CTX GVIA, 100 nM) or the novel N-type calcium channel antagonist, CTX CVID (100 nM) reduced the amplitude of EPSPs evoked after pelvic nerve stimulation by 50-75% but had no effect on EPSPs evoked by hypogastric nerve stimulation. Combined addition of CTX GVIA and CTX CVID was no more effective than either antagonist alone. EPSPs evoked by stimulating either nerve trunk were not inhibited by the P/Q calcium channel antagonist, omega-agatoxin IVA (100 nM), nor the L-type calcium channel antagonist, nifedipine (30 microM). SNX 482 (300 nM), an antagonist at some R-type calcium channels, inhibited EPSPs after hypogastric nerve stimulation by 20% but had little effect on EPSPs after pelvic nerve stimulation. Amiloride (100 microM) inhibited EPSPs after stimulation of either trunk by 40%, while nickel (100 microM) was ineffective. CTX GVIA or CTX CVID (100 nM) also slowed the rate of action potential repolarization and reduced afterhyperpolarization amplitude in paracervical neurons. Thus, release of transmitter from the terminals of sacral preganglionic neurons is largely dependent on calcium influx through N-type calcium channels, although an unknown calcium channel which is resistant to selective antagonists also contributes to release. Release of transmitter from lumbar preganglionic neurons does not require calcium entry through either conventional N-type calcium channels or the variant CTX CVID-sensitive N-type calcium channel and seems to be mediated largely by a novel calcium channel.

Orexin-immunoreactive inputs to rat sympathetic preganglionic neurons

Orexin increases blood pressure and orexin-immunoreactive (IR) axons robustly innervate the spinal cord. Seeking anatomical evidence for direct effects of orexin on sympathetic preganglionic neurons (SPN), we used immunohistochemistry to study the relationships between orexin-IR axons and SPN identified by immunoreactivity for choline acetyltransferase (ChAT) or for cholera toxin B retrogradely transported from the superior cervical ganglion (SCG). In the intermediolateral cell column (IML), varicose, orexin-positive axons closely apposed almost all SPN in segments T1 and T2, but appositions were rare in T4-L2. Orexin fibers also apposed ChAT-IR cell bodies in the intercalated nucleus and the central autonomic area from T1 to L2. Orexin-IR synapses were identified ultrastructurally on SPN projecting to the SCG. Since SPN involved in cardiovascular control cluster in the IML of mid- and lower thoracic cord, these findings suggest that orexin affects blood pressure by acting on supraspinal neurons rather than SPN.

The suprachiasmatic nucleus balances sympathetic and parasympathetic output to peripheral organs through separate preautonomic neurons

Opposing parasympathetic and sympathetic signals determine the autonomic output of the brain to the body and the change in balance over the sleep-wake cycle. The suprachiasmatic nucleus (SCN) organizes the activity/inactivity cycle and the behaviors that go along with it, but it is unclear how the hypothalamus, in particular the SCN, with its high daytime electrical activity, influences this differentiated autonomic balance. In a first series of experiments, we visualized hypothalamic pre-sympathetic neurons by injecting the retrograde tracer Fluoro-Gold into the thoracic sympathetic nuclei of the spinal cord. Pre-parasympathetic neurons were revealed by injection of the retrograde trans-synaptic tracer pseudorabies virus (PRV) into the liver and by sympathetic liver denervation, forcing the virus to infect via the vagus nerve only. This approach revealed separate pre-sympathetic and pre-parasympathetic neurons in the brainstem and hypothalamus. Next, selective retrograde tracing with two unique reporter PRV strains, one injected into the adrenal and the other into the sympathetic denervated liver, demonstrated that there are two separate populations of pre-sympathetic and pre-parasympathetic neurons within the paraventricular nucleus of the hypothalamus. Interestingly, this segregation persists into the SCN, where, as a result, the day-night balance in autonomic function of the organs is affected by specialized pre-sympathetic or pre-parasympathetic SCN neurons. These separate preautonomic SCN neurons provide the anatomical basis for the circadian-driven regulation of the parasympathetic and sympathetic autonomic output.

Localization of preganglionic neurons that innervate choroidal neurons of pterygopalatine ganglion

PURPOSE

The pterygopalatine ganglion (PPG) receives preganglionic input from the superior salivatory nucleus (SSN) of the facial motor complex and is the main source of parasympathetic input to the choroid in mammals. The present study was undertaken to determine in rats the location and neurotransmitters of SSN neurons innervating those PPG neurons that target the choroid and to determine the location and neurotransmitters of the PPG choroidal neurons themselves.

METHODS

Retrograde labeling from rat choroid using a fluorescent tracer, in combination with immunofluorescence labeling for nitric oxide synthase (NOS), vasoactive intestinal polypeptide (VIP), and choline acetyltransferase (ChAT), was used to characterize the location and neurotransmitters of choroidal PPG neurons. To identify SSN neurons that innervate the choroidal PPG neurons, the Bartha strain of the retrograde transneuronal tracer pseudorabies virus (PRV-Ba) was injected into rat choroid, and immunolabeling for NOS or ChAT was used to characterize their neurochemistry.

RESULTS

Fluorescent retrograde labeling showed that PPG neurons projecting to the choroid contained NOS, VIP, and ChAT and were widely distributed in PPG and its preganglionic root, the greater petrosal nerve. SSN neurons were ChAT(+), and a subset of them was found to contain NOS. PRV-Ba transneuronal retrograde labeling revealed that choroidal preganglionic neurons were localized to the rostral medioventral part of the ipsilateral SSN. The choroidal SSN neurons were ChAT(+) and appeared largely to correspond to the NOS(+) neurons of the SSN.

CONCLUSIONS

These results show that preganglionic neurons in rats that are presumed to regulate choroidal blood flow through the PPG reside within the rostral medioventral SSN, and that NOS is a marker for these SSN neurons.

Prenatal development of peptidergic primary afferent projections to mouse lumbosacral autonomic preganglionic cell columns

To examine the prenatal development of spinal visceral reflexes, primary sensory nerve fibers immunoreactive for calcitonin gene-related peptide (CGRP) were examined in the spinal cord, particularly in the autonomic preganglionic nuclei of mouse embryos. On embryonic day 16 (E16), CGRP-immunoreactive fibers were first observed in the sacral intermediolateral nucleus (IML) of the parasympathetic division as well as in the lumbar central autonomic nucleus (CA) of the sympathetic division, where they appeared in proximity to preganglionic neuronal perikarya immunoreactive for choline acetyltransferase or nitric oxide synthase. Most of the CGRP-immunoreactive varicosities were negative for substance P. Substance P-immunoreactive varicosities were scattered in these nuclei, but no appositions were seen on the preganglionic neuronal perikarya. On E18, CGRP-immunoreactive fibers were more abundant in the sacral IML and the lumbar CA. Co-expression of substance P and CGRP was frequently observed in the varicosities very close to the preganglionic neuronal perikarya on E18. CGRP-immunoreactive fibers were also observed in the lumbar IML on E18, although significantly fewer were found in this nucleus compared with the sacral IML. In contrast to the upper lumbar level, no fibers immunoreactive for CGRP were observed in the IML at the thoracic level. These results suggest that peptidergic primary sensory fibers grow to project to the selective targets of autonomic preganglionic neurons during the embryonic period. The potential direct connections between the peptidergic primary sensory fibers and preganglionic neurons innervating the pelvic viscera might provide a circuit for spinal visceral reflexes active in embryos.

Evidence for a glutamatergic input to pontine preganglionic neurons of the superior salivatory nucleus in rat

Parasympathetic preganglionic neurons of the superior salivatory nucleus (SSN), which projects to the pterygopalatine ganglion (PPG), modulate salivation, lacrimation, and cerebrovascular tone. Our previous studies suggest that excitatory projections from the nucleus tractus solitarii modulate cerebrovascular tone by actions on SSN neurons. In this study we sought to test the hypothesis that N-methyl-D-aspartate (NMDA) type glutamate receptors and vesicular glutamate transporters (VGLUT) are present in the SSN and that SSN neurons receive glutamatergic input. In six rats we injected tetramethylrhodamine dextran (TRD), a fluorescent tracer, unilaterally into the PPG to label SSN neurons. Four days later, rats were perfused and brain stem sections containing the SSN were processed for fluorescent immunohistochemistry for N-methyl-D-aspartate receptor subunit 1 (NMDAR1) and vesicular glutamate transporters (VGLUT1 and VGLUT2). Confocal laser scanning microscopy showed that 88+/-3% of TRD-labeled SSN neurons contained NMDAR1-immunoreactivity (IR). The surrounding neuropil contained numerous fibers labeled for VGLUT2-IR, but not VGLUT1-IR. Double fluorescent immunohistochemistry for NMDAR1 and VGLUT2 revealed that fibers containing VGLUT2-IR were often in close proximity to cell bodies or proximal dendrites of TRD-labeled SSN neurons that were positive for NMDAR1-IR. These studies support our hypothesis that NMDA receptors and VGLUT are present in the SSN. They further provide support for the suggestion that there are glutamatergic inputs to SSN neurons and would be consistent with an excitatory input that could regulate cerebrovascular tone.

Ectopic sympathetic preganglionic neurons maintain proper connectivity in the reeler mutant mouse

The location of sympathetic preganglionic neurons (SPN) in the spinal cord of the reeler mouse mutant is abnormal. Instead of their normal location in the intermediolateral column, the majority of SPN in the reeler cluster around the central canal. To determine whether ectopically located SPN in the reeler form appropriate synaptic connections with their pre- and postsynaptic partners, we examined 1). whether the axons of descending neural pathways that normally terminate on SPN follow them to their ectopic location, and 2). whether the central autonomic neural circuit that controls sympathetic output to the kidney is organized normally in the reeler. Using antibodies against tyrosine hydroxylase, serotonin, neuropeptide Y, substance P and calcitonin gene-related peptide as markers for adrenergic, serotonergic and peptidergic terminals, we found that axons which normally innervate SPN follow these neurons to their ectopic spinal location in the reeler. Injection of pseudorabies virus into the kidney of wild type and reeler mutant mice revealed similar patterns of renal sympathetic and pre-sympathetic control circuits in the spinal cord, brainstem and forebrain. These results indicate that the presynaptic inputs and postsynaptic targets of SPN in the reeler are normal, despite the ectopic spinal location of their cell bodies.

Ionotropic glutamate receptor subunit immunoreactivity of vagal preganglionic neurones projecting to the rat heart

The ionotropic glutamate receptor subunits expressed by vagal preganglionic neurones in the rat medulla oblongata were examined by using fluorescence immunolabelling combined with retrograde neuronal tracing. The general population of these neurones in the medulla was identified by intraperitoneal injections of Fluorogold and also with choline acetyltransferase antibodies. Cardiac projecting neurones were specifically identified by applying the fluorescent tracer 1,1'-dioctadecyl-3,3,3',3'-tetramethyl-indocarbocyanine (DiI) to the heart or by injecting cholera toxin B-subunit into the pericardium. Both tracers labelled populations of neurones lying in the dorsal vagal nucleus, intermediate reticular formation and nucleus ambiguus, and when both tracers were applied simultaneously, approximately 50% of cells were dual-labelled. Control experiments established that the labelling was specific for neurones projecting to the heart. Most vagal preganglionic neurones, including those projecting to the heart, irrespective of their location in the medulla, had a similar profile of glutamate receptor immunoreactivity. Labelling of somata for the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic (AMPA) subunit GluR1 was weak or absent, while labelling with antibodies directed to GluR2, a common sequence of GluR2 and GluR3, and GluR4 was moderate or intense. All neurones studied appeared to express the N-methyl-D-aspartate (NMDA) receptor subunit NR1, and while antibodies recognising the NR2A and NR2B splice variants gave strong labelling, immunoreactivity with a NR2B specific antibody was weaker. Weak to moderate labelling was seen in some neurones using antibodies to the kainate receptor subunits KA2 and GluR5-7. These results are consistent with neurophysiological data indicating the presence of AMPA, NMDA and kainate responses in cardiac vagal preganglionic neurones, and suggest that these neurones are similar to other vagal parasympathetic preganglionic neurones in expressing mainly AMPA receptor subunits GluR2-4.

Age-associated changes in the monoaminergic innervation of rat lumbosacral spinal cord

The effects of ageing on the innervation patterns of lumbosacral spinal nuclei involved in controlling lower urinary tract functions, including micturition, were studied using immunohistochemistry for serotonin (5-HT) and tyrosine hydroxylase (TH) in male Wistar rats of 3 and 24 months. Quantitative image analysis revealed significant age-associated declines in the innervation of most regions including the intermediolateral cell nucleus, sacral parasympathetic nucleus, dorsal grey commissure and in the ventral horn including the dorsolateral nucleus which in the rat is one of the component nuclei homologous to Onuf's nucleus in man. Notable exceptions to this generalised decline were observed in the 5-HT innervation of the sacral parasympathetic nucleus, which was maintained, and in the region of the dorsolateral motor nucleus where TH-like immunoreactivity did not significantly decline. These results suggest that the changes in micturition characteristics observed in aged rats may in part be a consequence of the alterations in, and decline of, aminergic inputs to both autonomic and somatic spinal nuclei associated with bladder function.

Suckling-induced activation of neural c-fos expression at lower thoracic rat spinal cord segments

Suckling stimulation is essential for neuroendocrine and sympathetic reflex activation during lactation. In the present study, the induction of c-fos gene expression was used to identify neuronal populations in the spinal cord activated by acute 5 min suckling or by electrical stimulation of the central stump of the first abdominal mammary nerve in lactating rats previously separated from their litters for 6 or 18 h. In addition, to investigate whether spinal sympathetic preganglionic neurons are activated by suckling, dual immunostaining (Fos and choline acetyltransferase) was performed. Fos was expressed at low levels in continuously suckled and 6 h nonsuckled mothers, but no expression was found after 18 h of nonsuckling. On the other hand, in 6 h nonsuckled rats, significant increments in Fos expression occurred in several regions after acute suckling and after electrical stimulation. Also, the pattern of Fos expression in each spinal laminae was different for the two stimuli, i.e. more intense effects of suckling in deep laminae V-X and more intense effects in laminae I-IV with electrical stimulation. Double-labeling after suckling was found only in sympathetic preganglionic neurons from the intermedio-medial cell column, whereas after electrical stimulation, double label was observed only in neurons from the intermedio-lateral cell column. On the other hand, no effect upon Fos protein expression was observed after suckling and only a minor effect after electrical stimulation of mammary nerve in 18 h nonsuckled rats. These results are consistent with previous findings on the sympathetic reflex regulation of the mammary gland, as well as on the importance of the nonsuckling interval for optimal functioning of lactation.

Neurochemistry of nerve fibers apposing sympathetic preganglionic neurons activated by sustained hypotension

Sympathetic preganglionic neurons (SPN) in rat spinal cord were activated by the reflex stimulation of bulbospinal sympathetic neuronal pathways after a nitroprusside-induced hypotension. Hypotension-sensitive SPN, identified by immunoreactivity (IR) to the product of the immediate early gene c-fos and to choline acetyltransferase, were localized in the intermediolateral cell column of thoracic and upper lumbar cord, particularly middle to lower thoracic cord. Putative neurotransmitters, or their markers, in varicose fiber networks around SPN were identified. Nearly all hypotension-sensitive (Fos-IR) SPN were apposed by varicose fibers immunoreactive for tyrosine hydroxylase, serotonin, substance P, or enkephalin. Neuropeptide Y (NPY)- or phenylethanolamine-N-methyl transferase (PNMT)-IR varicose fibers apposed Fos-IR SPN in the upper and middle thoracic spinal cord, but in lower thoracic segments some Fos-IR SPN lacked these appositions. In thoracic segment 12, 51% +/- 5% of Fos-IR SPN (n = 9 rats) lacked PNMT contacts and 25% +/- 3% of Fos-IR SPN (n = 8 rats) lacked NPY contacts. In contrast to other chemically defined afferents, galanin-IR varicose fibers apposed fewer than half of the Fos-IR SPN in the middle to lower thoracic cord. Neurotransmitters/neuromodulators that might influence the activity of SPN acting in the baroreflex-mediated control of blood pressure have been identified. Uniformity in the neurochemistry of some fibers making connections with Fos-IR SPN, regardless of their segmental origin, suggests that common sets of neurons provide convergent inputs to all hypotension-sensitive SPN. Other fibers show topographic differences in their contacts with Fos-IR SPN, suggesting that subgroups of hypotension-sensitive SPN are targeted by particular neuron groups.

Glutamate and GABA content of calbindin-immunoreactive nerve terminals in the rat intermediolateral cell column

Immunoreactivity for calbindin-D28K (calbindin) occurs in some bulbospinal vasopressor neurons in the rostral ventrolateral medulla and calbindin-immunoreactive terminals form synapses in the intermediolateral cell column (IML), where the cell bodies of sympathetic preganglionic neurons are located. In this study, we used post-embedding immunogold labelling to determine whether calbindin terminals in the IML contained the excitatory amino acid neurotransmitter glutamate. We also assessed GABA immunoreactivity in semi-serial sections through the same terminals since this inhibitory amino acid transmitter is present in the inputs to sympathetic preganglionic neurons that lack glutamate. Analysis of 42 calbindin-positive terminals whose postsynaptic targets were not identified revealed two major groups on the basis of amino acid content. One group was immunoreactive for glutamate; and the other, for GABA. In addition, about 20% of the calbindin terminals were positive for both glutamate and GABA. Our anatomical methods cannot differentiate whether this third group is a subset of the GABAergic terminals or a separate population capable of co-releasing the two amino acids.

GABA in the control of sympathetic preganglionic neurons

1. Amino acid neurotransmitters are critical for controlling the activity of most central neurons, including sympathetic preganglionic neurons (SPN), the spinal cord neurons involved in controlling blood pressure and other autonomic functions. 2. In studies reviewed here, SPN were identified either by retrograde tracing from a peripheral target (superior cervical ganglion or adrenal medulla) or by detection of immunoreactivity for choline acetyltransferase (ChAT), the acetylcholine-synthesizing enzyme that is a marker for all SPN, in intact or completely transected rat spinal cord. 3. Postembedding immunogold labelling on ultrathin sections was then used to detect GABA and sometimes glutamate in nerve terminals on SPN or near them in the neuropil of the lateral horn. 4. In some cases, the terminals were prelabelled to show an anterograde tracer or immunoreactivity for ChAT or neuropeptide Y. 5. This anatomical work has provided information that is helpful in understanding how SPN are influenced by their GABAergic innervation. 6. Immunogold studies showed that the proportion of input provided by GABAergic terminals varies between different groups of SPN. For some groups, this input may be preferentially targeted to cell bodies. 7. Anterograde tracing demonstrated that supraspinal as well as intraspinal GABAergic neurons innervate SPN and investigations on completely transected cord suggested that supraspinal neurons may provide a surprisingly large proportion of the GABAergic terminals that contact SPN. 8. The double-labelling studies in which other amino acids, ChAT or neuropeptide Y were localized along with GABA indicate that GABAergic terminals contain other neurochemicals that could modulate the actions of GABA, depending on the complement of receptors that are present pre- and post-synaptically. 9. Taken together, these data indicate that GABAergic transmission to SPN may be much more complicated than suggested by the currently available electrophysiological studies.

Pre- and postsynaptic actions of ATP on neurotransmission in rat submandibular ganglia

The pre- and postsynaptic actions of exogenously applied ATP were investigated in intact and dissociated parasympathetic neurones of rat submandibular ganglia. Nerve-evoked excitatory postsynaptic potentials (EPSPs) were not inhibited by the purinergic receptor antagonists, suramin and pyridoxal-phosphate-6-azophenyl-2',4'-disulphonic acid (PPADS), or the desensitising agonist, alpha,beta-methylene ATP. In contrast, EPSPs were abolished by the nicotinic acetylcholine receptor antagonists, hexamethonium and mecamylamine. Focal application of ATP (100 microM) had no effect on membrane potential of the postsynaptic neurone or on the amplitude of spontaneous EPSPs. Taken together, these results suggest the absence of functional purinergic (P2) receptors on the postganglionic neurone in situ. In contrast, focally applied ATP (100 microM) reversibly inhibited nerve-evoked EPSPs. Similarly, bath application of the non-hydrolysable analogue of ATP, ATP gamma S, reversibly depressed EPSPs amplitude. The inhibitory effects of ATP and ATP gamma S on nerve-evoked transmitter release were antagonised by bath application of either PPADS or suramin, suggesting ATP activates a presynaptic P2 purinoceptor to inhibit acetylcholine release from preganglionic nerves in the submandibular ganglia. In acutely dissociated postganglionic neurones from rat submandibular ganglia, focal application of ATP (100 microM) evoked an inward current and subsequent excitatory response and action potential firing, which was reversibly inhibited by PPADS (10 microM). The expression of P2X purinoceptors in wholemount and dissociated submandibular ganglion neurones was examined using polyclonal antibodies raised against the extracellular domain of six P2X purinoceptor subtypes (P2X(1-6)). In intact wholemount preparations, only the P2X(5) purinoceptor subtype was found to be expressed in the submandibular ganglion neurones and no P2X immunoreactivity was detected in the nerve fibres innervating the ganglion. Surprisingly, in dissociated submandibular ganglion neurones, high levels of P2X(2) and P2X(4) purinoceptors immunoreactivity were found on the cell surface. This increase in expression of P2X(2) and P2X(4) purinoceptors in dissociated submandibular neurones could explain the increased responsiveness of the neurones to exogenous ATP. We conclude that disruption of ganglionic transmission in vivo by either nerve damage or synaptic blockade may up-regulate P2X expression or availability and alter neuronal excitability.

Phosphorylation of CREB in thoracolumbar spinal neurons and dorsal root ganglia after renal artery occlusion in rat

These studies have demonstrated that ipsilateral renal artery occlusion (RAO) in rat results in the phosphorylation of cyclic AMP (cAMP) response element binding protein (p-CREB) in the thoracolumbar (T8-L2) spinal cord and associated dorsal root ganglia (DRG). p-CREB-immunoreactivity (IR) was expressed bilaterally in the thoracolumbar spinal cord, whereas expression in the DRG was ipsilateral relative to RAO. p-CREB-IR was primarily expressed in four distinct regions of the spinal cord: medial or lateral dorsal horn (MDH or LDH), dorsal commissural nucleus (DCN) and the region of the intermediolateral cell column (IML). After RAO, p-CREB-IR was greatest in the T13-L2 spinal segments. Within the T13-L1 spinal segments, p-CREB-IR was greatest in the MDH, LDH and DCN and expression in each of these regions was comparable within a segment. Following RAO, there was a significant (p < or = 0.001) increase in the percentage (86-98%) of p-CREB-IR spinal neurons expressing choline acetyltransferase (ChAT)-IR (a marker of preganglionic neurons) in the IML of the T10, T12 and L1 spinal segments examined. After ipsilateral RAO, expression of p-CREB-IR was increased in the ipsilateral, T8-L2 DRG with the greatest number of p-CREB-IR dorsal root ganglion cells being located in the L1 dorsal root ganglion. Retrograde tracing with Fluorogold (FG) to label renal afferent cells in the DRG revealed a significant (p < or = 0.01) increase in the percentage (75-86%) of renal afferent cells expressing p-CREB-IR after ipsilateral RAO. These studies demonstrate that p-CREB-IR is a useful tool for examining the distribution of spinal neurons and DRG involved in reflexes of renal origin. In addition, expression of p-CREB-IR may be coupled to late response genes that may exert long-term changes in neuronal function after RAO.

Neurokinin-1 receptor immunoreactivity in hypotension sensitive sympathetic preganglionic neurons

Substance P activation of neurokinin-1 (NK1) receptors on spinal sympathetic preganglionic neurons (SPN) influences blood pressure. We identified SPN likely to subserve the baroreceptor reflex and established if these neurons showed NK1 receptor-immunoreactivity. Nitroprusside (NP) infusion or inferior vena cava (IVC) constriction activated similar numbers of SPN. Of these, about 40% were NK1 receptor-immunoreactive after NP infusion, but only about 20% were NK1 receptor-immunoreactive after IVC constriction. The distribution of Fos/NK1 receptor SPN suggested that substance P may preferentially target sympathoadrenal SPN.

Bidirectional modulation of P2X receptor-mediated response by divalent cations in rat dorsal motor nucleus of the vagus neurons

The modulatory effects of Zn(2+) and other divalent cations on the ATP-induced responses of preganglionic neurons acutely dissociated from the rat dorsal motor nucleus of the vagus (DMV) were examined using a nystatin-perforated patch technique under voltage-clamp. DMV neurons were identified by back-filling of DiI placed on the vagal bundle at the neck. Zn(2+) exerts a concentration-dependent effect on P2X receptor-mediated current (I(ATP)): a potentiation by low concentrations of Zn(2+) (< or = 50 microM) and an inhibition by high concentrations (> 50 microM). Inhibition of the ATP response was associated with a prolongation of the rising phase of I(ATP). Cu(2+) mimicked Zn(2+) regarding the biphasic modulation of I(ATP). On the other hand, Ni(2+) potentiated, but failed to inhibit, the ATP response even at a concentration of 3 mM. Quantitative RT-PCR revealed the similarity of P2X(2) mRNA expression between the DMV and superior cervical ganglion (SCG) but not in the dorsal root ganglion (DRG) and hypoglossal nucleus (XII). The results from the electrophysiological and molecular approaches suggest that functional P2X receptors expressed in DMV neurons are characterized mainly by the P2X(2) and P2X(2/6) subtype. DMV neurons possess similar P2X receptor characteristics to SCG neurons.

Increased innervation of rat preganglionic sympathetic neurons by substance P containing nerve fibers in response to spinal cord injury

Substance P (SP) is elevated in the intermediate zone caudal to a spinal cord lesion presumably due to sprouting of intraspinal and primary afferent axons. It is unclear, however, if axon terminals are in direct contact with preganglionic neurons located within the different autonomic subnuclei. Therefore, the innervation of preganglionic sympathetic neurons by SP was quantified using confocal imaging and morphometric image analysis. The number of SP-immunoreactive varicosities apposed to nitric oxide synthase-positive neurons significantly increased bilaterally in all sympathetic areas of segment T2 one week after low cervical hemisection at C6/7. Consequently, direct excitatory effects of SP on preganglionic neurons may play an important role in the dysregulation of arterial blood pressure observed in patients with spinal cord injury at the cervical or upper thoracic level.

Lack of neurotrophin-4 causes selective structural and chemical deficits in sympathetic ganglia and their preganglionic innervation

Neurotrophin-4 (NT-4) is perhaps the still most enigmatic member of the neurotrophin family. We show here that NT-4 is expressed in neurons of paravertebral and prevertebral sympathetic ganglia, i.e., the superior cervical (SCG), stellate (SG), and celiac (CG) ganglion. Mice deficient for NT-4 showed a significant reduction (20-30%) of preganglionic sympathetic neurons in the intermediolateral column (IML) of the thoracic spinal cord. In contrast, neuron numbers in the SCG, SG, and CG were unchanged. Numbers of axons in the thoracic sympathetic trunk (TST) connecting the SG with lower paravertebral ganglia were also reduced, whereas axon numbers in the cervical sympathetic trunk (CST) were unaltered. Axon losses in the TST were paralleled by losses of synaptic terminals on SG neurons visualized by electron microscopy. Furthermore, immunoreactivity for the synaptic vesicle antigen SV2 was clearly reduced in the SG and CG. Levels of catecholamines and tyrosine hydroxylase immunoreactivity were dramatically reduced in the SG and the CG but not in the SCG. Despite this severe phenotype in the sympathetic system, blood pressure levels were not reduced and displayed a pattern more typical of deficits in baroreceptor afferents. Numbers of IML neurons were unaltered at postnatal day 4, suggesting a postnatal requirement for their maintenance. In light of these and previous data, we hypothesize that NT-4 provided by postganglionic sympathetic neurons is required for establishing and/or maintaining synapses of IML neurons on postganglionic cells. Impairment of synaptic connectivity may consequently reduce impulse flow, causing a reduction in transmitter synthesis in postganglionic neurons.

Nitric oxide synthase neurons in the rodent spinal cord: distribution, relation to Substance P fibers, and effects of dorsal rhizotomy

The indirect immunofluorescent method was employed to investigate the distribution of neuronal nitric oxide synthase-like immunoreactivity(nNOS-LI) in the spinal cord of the golden hamster and to compare it to data obtained from rats. Immunoreactive neurons were found throughout the cervico-sacral extent in the dorsal horn (mainly in laminae I-III) and in the preganglionic autonomic regions, i.e., the sympathetic intermediolateral nucleus (IML), lateral funicle (LF), intercalated region (IC), the area surrounding the central canal (CA), and the sacral preganglionic parasympathetic cell group. While the distribution of immunoreactive cells was generally similar in both species, some differences were observed. For example in the hamster LF, a higher percentage of stained neurons was seen than in the IML, while the situation was rather inverse in the rat. In order to study the coincidence of nNOS-LI in the population of preganglionic sympathetic neurons (PSN) that innervate the superior cervical ganglion (SCG), these were identified by retrograde axonal transport of fluoro-gold (FG) following unilateral injection into the SCG. PSN were localized ipsilateral to the injection site mainly in the IML and LF of spinal segments C7-Th4. The portion of double-labeled neurons of the IML were lower in hamster (17% in C7, 34% in C8) of FG-labeled cells) than in rat (47% in C8, 77% in Th2), while in the LF of segments C8-Th2 in both species the majority of FG-neurons contained nNOS. While only very few double-labeled neurons were detected in the IC in hamster and rat, a striking difference was observed in the CA, where no double-labeled neurons were found in hamster, but up to 50% in rat. Double immunofluorescence detection of nNOS and substance P (SP) showed that in both the autonomic regions and the dorsal horn, SP-LI fibers and puncta were present in close spatial relationship to nNOS-LI cell bodies. These results were basically identical in the hamster and rat. Unilateral transection of the dorsal roots of segments C6-Th2 in rats resulted in a clear reduction of SP-LI structures in the dorsal horn 5 days after rhizotomy, but not in the autonomic regions. Compared to the unlesioned side, the numbers of nNOS-LI neurons in the superficial laminae of the dorsal horn were reduced to 32-46% in the lesioned segments, and to 53% and 87%, respectively, in the two segments cranial to the rhizotomized segments but remained unchanged caudally to the lesion. Numbers of nNOS-LI cell bodies in the autonomic regions were not altered following dorsal root transection. The present study provides data on the widespread distribution of nNOS in the spinal cord of golden hamster and describes the partial coincidence of the enzyme in PSN. The effects of dorsal rhizotomy on nNOS-LI neurons in the dorsal horn reveal that primary-afferent fibers provide a stimulatory influence on neurons of the dorsal horn to generate the gaseous neuroactive substance, nitric oxide.

Differential regulation of trkA and p75 in noradrenergic pelvic autonomic ganglion cells after deafferentation of their cholinergic neighbours

In rats, following lesion of lumbar or sacral preganglionic axons, many pelvic ganglion cells undergo axogenesis to form baskets of terminals around select populations of nearby ganglion cells. The aim of the current study was to address mechanisms underlying initiation of this sprouting, focusing on a possible role for nerve growth factor (NGF). Immunohistochemical localization of NGF receptors (trkA and p75) showed that virtually all noradrenergic and a minority of cholinergic pelvic neurons expressed both receptors. Terminals immunoreactive for each substance were found in pelvic viscera. In pelvic ganglia, many glial cells expressed p75 but not trkA, and very few lumbar or sacral preganglionic neurons expressed either receptor. Lumbar and/or sacral preganglionic inputs were removed from ganglion cells by cutting the hypogastric, pelvic or both nerves, and tissues analysed 8 days later. Levels of receptor expression in noradrenergic pelvic ganglion cells were estimated by calculating the proportion that were receptor-immunopositive, and quantifying the intensity of trkA or p75 immunofluorescence. No lesion had a significant effect on trkA expression, however, a marked decrease in p75 occurred after cutting pelvic nerves, i.e. after deafferentation of neighbouring cholinergic neurons. These injuries appeared to cause little overall change in glial p75 expression. This study shows that manipulations that trigger sprouting from noradrenergic pelvic neurons cause downregulation of p75 but not trkA. Interestingly, this is occurring while some of their target organs are synthesizing high levels of NGF. This contrasts with other NGF-sensitive cells, in which one or both receptor types are upregulated by increased exposure to the ligand. The current study is also the first to show a change in p75 expression in neurons that are neither deafferented nor axotomized.

Differential distribution of nerve terminals immunoreactive for substance P and cholecystokinin in the sympathetic preganglionic cell column of the filefish Stephanolepis cirrhifer

Immunoreactivity for substance P and cholecystokinin-8 was examined in the nerve fibers in the central autonomic nucleus, a cell column for sympathetic preganglionic neurons, in the filefish Stephanolepis cirrhifer. Substance P-immunoreactive fibers were distributed throughout the entire rostrocaudal extent, but were more abundant in the caudal part of the column, where substance P-immunoreactive varicosities sometimes made contacts with the sympathetic preganglionic neurons. Cholecystokinin-8-immunoreactive fibers were found almost entirely in the rostral part of the column, where a dense network of varicosities was in close apposition to a considerable number of the sympathetic preganglionic neurons. Double labeling immunohistochemistry showed that substance P fibers and cholecystokin-8 fibers were entirely different, and distinct from serotonin-immunoreactive fibers. By using immunoelectron microscopy, synaptic specialization was sometimes observed between the dendrites of preganglionic neurons and varicosities immunoreactive for substance P and cholecystokinin-8. Substance P- and cholecystokinin-8 fibers were seen from the descending trigeminal tract, through the dorsolateral funiculus and the ventral portion of the dorsal horn, to the central autonomic nucleus. After colchicine treatment, substance P-immunoreactive perikarya were found in the cranial and spinal sensory ganglia. These results suggest that the sympathetic preganglionic neurons of the filefish receive innervation by substance P fibers and cholecystokinin fibers, and that the former might be of primary sensory origin. Topographical distribution of cholecystokinin-8-immunoreactive terminals in the central autonomic nucleus along the rostrocaudal extent might underlie the differential regulation of sympathetic activity via a distinct population of sympathetic preganglionic neurons.