Sympathetic activation: a potential link between comorbidities and COVID-19.

In coronavirus disease 2019 (COVID-19), higher morbidity and mortality are associated with age, male gender, and comorbidities, such as chronic lung diseases, cardiovascular pathologies, hypertension, kidney diseases, diabetes mellitus, and obesity. All of the above conditions are characterized by increased sympathetic discharge, which may exert significant detrimental effects on COVID-19 patients, through actions on the lungs, heart, blood vessels, kidneys, metabolism, and/or immune system. Furthermore, COVID-19 may also increase sympathetic discharge, through changes in blood gases (chronic intermittent hypoxia, hyperpnea), angiotensin-converting enzyme (ACE)1/ACE2 imbalance, immune/inflammatory factors, or emotional distress. Nevertheless, the potential role of the sympathetic nervous system has not yet been considered in the pathophysiology of COVID-19. In our opinion, sympathetic overactivation could represent a so-far undervalued mechanism for a vicious circle between COVID-19 and comorbidities.

A Central Role for Sympathetic Nerves in Herpes Stromal Keratitis in Mice.

PURPOSE: Herpes simplex virus type 1 (HSV-1) is a neurotrophic virus that can cause herpes stromal keratitis (HSK), a severe corneal inflammation that can lead to corneal scarring and blindness. This study identified neurologic changes that occur in HSV-1-infected corneas and related them to HSV-1-induced immunopathology. METHODS: Corneas of BALB/c and C57BL/6 mice were infected with HSV-1 strains that induce HSK. Changes in sensory nerves were identified by immunofluorescence staining of sensory and sympathetic nerves for substance P (SP) and tyrosine hydroxylase (TH), respectively, and confocal microscopic examination. Some mice received superior cervical ganglionectomy (SCGx) to eliminate sympathetic nerves from the cornea. RESULTS: Normal corneas exclusively expressed sensory nerves that entered the stroma as large nerve stalks, branched to form a plexus at the epithelial/stromal interface, and extended termini into the epithelium. These nerves completely retracted from the infected cornea and were replaced by sympathetic nerves that sprouted extensively to hyperinnervate the corneal stroma but failed to form a plexus or extend termini into the epithelium. The hyperinnervating nerves expressed the sympathetic nerve marker TH and their invasion was blocked by performing SCGx. Moreover, the corneal opacity and neovascularization that normally characterizes HSK in this mouse model were largely abrogated by SCGx. Sensory nerves reinnervated infected corneas following SCGx, reformed a nerve plexus, and extended termini into the epithelium resulting in recovery of corneal sensitivity. CONCLUSIONS: Sympathetic nerves have a central role in HSK in mice, preventing reinnervation by sensory nerves and promoting severe and persistent corneal inflammation.

Inhibition of catecholamine degradation ameliorates while chemical sympathectomy aggravates the severity of acute Friend retrovirus infection in mice.

Several lines of evidence indicate that the sympathetic nervous system (SNS) might be involved in the pathogenesis and progression of retroviral infections. However, experimental data are scarce and findings inconsistent. Here, we investigated the role of the SNS during acute infection with Friend virus (FV), a pathogenic murine retrovirus that causes polyclonal proliferation of erythroid precursor cells and splenomegaly in adult mice. Experimental animals were infected with FV complex, and viral load, spleen weight, and splenic noradrenaline (NA) concentration was analyzed until 25 days post infection. Results show that FV infection caused a massive but transient depletion in splenic NA during the acute phase of the disease. At the peak of the virus-induced splenomegaly, splenic NA concentration was reduced by about 90% compared to naïve uninfected mice. Concurrently, expression of the catecholamine degrading enzymes monoamine oxidase A (MAO-A) and catechol-O-methyltransferase (COMT) was significantly upregulated in immune cells of the spleen. Pharmacological inhibition of MAO-A and COMT by the selective inhibitors clorgyline and 3,5-dinitrocatechol, respectively, efficiently blocked NA degradation and significantly reduced viral load and virus-induced splenomegaly. In contrast, chemical sympathectomy prior to FV inoculation aggravated the acute infection and extended the duration of the disease. Together these findings demonstrate that catecholamine availability at the site of viral replication is an important factor affecting the course of retroviral infections.

The p75 neurotrophin receptor is required for the major loss of sympathetic nerves from islets under autoimmune attack.

Our goal was to determine the role of the p75 neurotrophin receptor (p75NTR) in the loss of islet sympathetic nerves that occurs during the autoimmune attack of the islet. The islets of transgenic (Tg) mice in which ß-cells express a viral glycoprotein (GP) under the control of the insulin promotor (Ins2) were stained for neuropeptide Y before, during, and after virally induced autoimmune attack of the islet. Ins2-GP(Tg) mice injected with lymphocytic choriomeningitis virus (LCMV) lost islet sympathetic nerves before diabetes development but coincident with the lymphocytic infiltration of the islet. The nerve loss was marked and islet-selective. Similar nerve loss, chemically induced, was sufficient to impair sympathetically mediated glucagon secretion. In contrast, LCMV-injected Ins2-GP(Tg) mice lacking the p75NTR retained most of their islet sympathetic nerves, despite both lymphocytic infiltration and development of diabetes indistinguishable from that of p75NTR wild-type mice. We conclude that an inducible autoimmune attack of the islet causes a marked and islet-selective loss of sympathetic nerves that precedes islet collapse and hyperglycemia. The p75NTR mediates this nerve loss but plays no role in mediating the loss of islet ß-cells or the subsequent diabetes. p75NTR-mediated nerve loss may contribute to the impaired glucose counterregulation seen in type 1 diabetes.

Analysis of the mechanism of reactivation of latently infecting pseudorabies virus by acetylcholine.

In this study, the effect of cholinergic or adrenergic inhibitors on the reactivation of latent Pseudorabies virus (PRV) was analyzed to clarify the mechanism of the reactivation of latent PRV by acetylcholine. For acetylcholine inhibition, latently infected mice were injected with scopolamine or succynilcholine before acetylcholine stimulation. For sympathetic blocking, mice were preinjected intraperitoneally with phenoxybenzamine or propranolol. The signals to both acetylcholine receptors had no relationship to the reactivation of latent PRV, and both sympathetic blockers showed inhibition of PRV reactivation by acetylcholine. In our reactivation model, a large amount of acetylcholine may stimulate the sympathetic nerve system in some way to reactivate the virus.

Potential role of HPA axis and sympathetic nervous responses in depletion of B cells induced by H9N2 avian influenza virus infection.

Except severe pulmonary disease caused by influenza virus infection, an impaired immune system is also a clinic characteristic. However, the mechanism(s) of influenza virus infection-induced depletion of B cells was unknown. Here, we compared the effect of two variant virulence H9N2 virus infections on mouse B cells. Our study found that the infection with highly pathogenic virus (V) of led to depletion of spleen B cells and bone marrow (BM) early B cells, compared to lowly pathogenic virus (Ts). Moreover, high apoptosis and cell cycle arrest in spleen and BM were detected, suggesting important factors for the reduction of B cells in both organs. Further, this effect was not caused by virus replication in spleen and BM. Compared to Ts virus infection, V virus resulted in higher glucocorticoids (GCs) and lower leptin level in plasma. Intraperitoneal GCs receptor antagonist RU486 injection was sufficient to prevent the loss of spleen B cell and BM pro- and immature B cells, but similar result was not observed in leptin-treated mice. Depletion of spleen B cells and BM pro-B cells was also reversed by chemical sympathectomy mediated by the norepinephrine (NE) analog 6-hydroxydopamine (6-OHDA), but the treatment didn't affect the GCs level. This study demonstrated that depletion of B cells induced by H9N2 AIV was dependent on HPA axis and sympathetic response.

Anterograde transneuronal viral tract tracing reveals central sensory circuits from brown fat and sensory denervation alters its thermogenic responses.

Brown adipose tissue (BAT) thermogenic activity and growth are controlled by its sympathetic nervous system (SNS) innervation, but nerve fibers containing sensory-associated neuropeptides [substance P, calcitonin gene-related peptide (CGRP)] also suggest sensory innervation. The central nervous system (CNS) projections of BAT afferents are unknown. Therefore, we used the H129 strain of the herpes simplex virus-1 (HSV-1), an anterograde transneuronal viral tract tracer used to delineate sensory nerve circuits, to define these projections. HSV-1 was injected into interscapular BAT (IBAT) of Siberian hamsters and HSV-1 immunoreactivity (ir) was assessed 24, 48, 72, 96, and 114 h postinjection. The 96- and 114-h groups had the most HSV-1-ir neurons with marked infections in the hypothalamic paraventricular nucleus, periaqueductal gray, olivary areas, parabrachial nuclei, raphe nuclei, and reticular areas. These sites also are involved in sympathetic outflow to BAT suggesting possible BAT sensory-SNS thermogenesis feedback circuits. We tested the functional contribution of IBAT sensory innervation on thermogenic responses to an acute (24 h) cold exposure test by injecting the specific sensory nerve toxin capsaicin directly into IBAT pads and then measuring core (T(c)) and IBAT (T(IBAT)) temperature responses. CGRP content was significantly decreased in capsaicin-treated IBAT demonstrating successful sensory nerve destruction. T(IBAT) and T(c) were significantly decreased in capsaicin-treated hamsters compared with the saline controls at 2 h of cold exposure. Thus the central sensory circuits from IBAT have been delineated for the first time, and impairment of sensory feedback from BAT appears necessary for the appropriate, initial thermogenic response to acute cold exposure.

Generalized anhidrosis in a child following presumptive H1N1 influenza.

We report an 8-year-old girl who developed generalized anhidrosis following presumptive H1N1 infection. Pure autonomic dysfunction is an unusual complication following H1N1 infection and specially generalized anhidrosis without other autonomic dysfunction have not been reported before.

SIV infection decreases sympathetic innervation of primate lymph nodes: the role of neurotrophins.

The sympathetic nervous system regulates immune responses in part through direct innervation of lymphoid organs. Recent data indicate that viral infections can alter the structure of lymph node innervation. To determine the molecular mechanisms underlying sympathetic denervation during Simian Immunodeficiency Virus (SIV) infection, we assessed the expression of neurotrophic factors and neuromodulatory cytokines within lymph nodes from experimentally infected rhesus macaques. Transcription of nerve growth factor (NGF), brain-derived neurotropic factor (BDNF) and neurotrophin-4 (NT4) decreased significantly in vivo during chronic SIV infection, whereas expression of the neuro-inhibitory cytokine interferon-gamma (IFN gamma) was up-regulated. Acute SIV infection of macaque leukocytes in vitro induced similar changes in the expression of neurotrophic and neuro-inhibitory factors, indicative of an innate immune response. Statistical mediation analyses of data from in vivo lymph node gene expression suggested that coordinated changes in expression of multiple neuromodulatory factors may contribute to SIV-induced depletion of catecholaminergic varicosities within lymphoid tissue. Given previous evidence that lymph node catecholaminergic varicosities can enhance SIV replication in vivo, these results are consistent with the hypothesis that reduced expression of neurotrophic factors during infection could constitute a neurobiological component of the innate immune response to viral infection.

Social stress enhances sympathetic innervation of primate lymph nodes: mechanisms and implications for viral pathogenesis.

Behavioral processes regulate immune system function in part via direct sympathetic innervation of lymphoid organs, but little is known about the factors that regulate the architecture of neural fibers in lymphoid tissues. In the present study, we find that experimentally imposed social stress can enhance the density of catecholaminergic neural fibers within axillary lymph nodes from adult rhesus macaques. This effect is linked to increased transcription of the key sympathetic neurotrophin nerve growth factor and occurs predominately in extrafollicular regions of the paracortex that contain T-lymphocytes and macrophages. Functional consequences of stress-induced increases in innervation density include reduced type I interferon response to viral infection and increased replication of the simian immunodeficiency virus. These data reveal a surprising degree of behaviorally induced plasticity in the structure of lymphoid innervation and define a novel pathway by which social factors can modulate immune response and viral pathogenesis.

New developments in tracing neural circuits with herpesviruses.

Certain neurotropic viruses can invade the nervous system of their hosts and spread in chains of synaptically connected neurons. Consequently, it is possible to identify entire hierarchically connected circuits within an animal. In this review, we discuss the use of neurotropic herpesviruses as neuronal tract tracers. Although a variety of tract tracing viruses are available, each with its own unique infection characteristics, we focus on the widespread use of attenuated strains of pseudorabies virus (PRV), a swine herpesvirus with a broad host range. In particular, we focus on new applications of PRV for tract tracing including use of multiple infections by PRV reporter viruses to test for circuit convergence/divergence within the same animal. We provide examples of these combined application techniques within the context of an animal model to study the naturally occurring reversal of seasonal obesity in Siberian hamsters.

A spinal cord pathway connecting primary afferents to the segmental sympathetic outflow system.

The sympathetic innervation of lumbar dorsal root ganglia (DRGs) and the possible presence of spinal cord circuits connecting primary sensory afferents to the sympathetic outflow to DRGs were investigated. We used simultaneous tracing of the sympathetic input to and sensory output from DRGs. Adult male rats received unilateral microinjections of the Bartha strain of pseudorabies virus into four lumbar DRGs. At 24 h post-inoculation, productive infection was detected in both DRG neurons and sympathetic postganglionic neurons. Infection of spinal cord neurons was first observed in sympathetic preganglionic neurons of the intermediolateral column. Subsequently, the infection spread to the contralateral intermediolateral column, the area around the central canal and the superficial dorsal horn layers. To investigate the relationship between infected spinal cord neurons and primary afferents from the corresponding DRGs, we injected pseudorabies virus for retrograde tracing together with cholera toxin B for anterograde tracing. We found that infected LIV/LV and LX neurons were in close apposition to cholera toxin B labeled afferents. Importantly, immunohistochemical detection of bassoon, a pre-synaptic zone protein, identified such contacts as synapses. Together, this suggests synaptic contacts between primary sensory afferents and neurons regulating sympathetic outflow to corresponding DRGs.

Modulation of host immunity by HIV may be partly achieved through usurping host autonomic functions.

Modulation of host immunity has been observed in human immunodeficiency virus (HIV) infections. HIV is believed to influence host immunity through a variety of mechanisms including direct effects on host T cell survival, indirect effects on cytokine profile through modulation of immune cells, and modulation of endocrine functions that affect immunity such as steroids. We hypothesize that HIV infection may also alter host immunity through modulation of host sympatho-vagal balance. Specifically, we propose that HIV drives autonomic balance towards sympathetic bias, which can contribute to a T helper (Th)2 type immunity. A variety of paraviral syndromes associated with HIV infection such as QT prolongation, cachexia, cardiomyopathy, and lipodystrophy are consistent with evidence of autonomic dysfunction. Immunomodulatory effects of autonomic dysfunction toward Th2 bias are presented. A plausible mechanism by which HIV can influence autonomic balance through hypothalamic manipulation is offered. Shift to Th2 dominance is associated with HIV disease progression and can be viewed as a viral adaptation to promote its own survival. Autonomic remodeling by HIV may exemplify this phenomenon. Our hypothesis has implications for treatment of HIV and its associated syndromes.

Brainstem substrates of sympatho-motor circuitry identified using trans-synaptic tracing with pseudorabies virus recombinants.

Previous physiological investigations have suggested the existence of a neural circuit that coordinates activation of motor and autonomic efferents before or at the onset of exercise. Traditionally these circuits have been postulated to involve forebrain areas. However, overlapping populations of medullary reticular formation neurons that participate in motor or autonomic control have been described previously, suggesting that individual pontomedullary reticular formation neurons may coordinate both motor and autonomic responses. We tested this hypothesis by conducting transneuronal retrograde tracing of motor and sympathetic nervous system pathways in rats using recombinant strains of pseudorabies virus (PRV). A PRV strain expressing the green fluorescent protein (PRV-152) was injected into the left gastrocnemius muscle, which was surgically sympathectomized, whereas another recombinant (PRV-BaBlu) was injected into the left adrenal gland. Immunofluorescence methods using monospecific antisera and distinct fluorophores identified neurons infected with one or both of the recombinants. Brainstem neurons coinfected with both PRV recombinants, which presumably had collateralized projections to both adrenal sympathetic preganglionic neurons and gastrocnemius motoneurons, were observed in several areas of the pontomedullary reticular formation. The largest number of such neurons was located in the rostral ventromedial medulla within the ventral gigantocellular nucleus, gigantocellular nucleus pars alpha, raphe obscurus, and raphe magnus. These neurons are candidates for relaying central command signals to the spinal cord.

Separate urinary bladder and prostate neurons in the central nervous system of the rat: simultaneous labeling with two immunohistochemically distinguishable pseudorabies viruses.

BACKGROUND: This work examines the central nervous system distribution of virus-labeled neurons from the rat urinary bladder and the prostate simultaneously within the same tissue sections. Two immunohistochemically distinct pseudorabies virus strains were simultaneously injected into male Sprague Dawley rats (approximately 280 gm). One virus was injected into the bladder and the other into the prostate. After incubation intervals of 2.25, 2.5, 2.75, 3 and 4 days, sections from the spinal cord and brain were processed immunohistochemically to detect cells, within a single section, which were labeled separately by each virus or were labeled by both viruses. RESULTS: Each strain of virus labeled a separate population of neurons and some neurons were labeled by both strains. The majority of neurons labeled by virus from the urinary bladder were found in the L6-S1 spinal cord segments within the dorsal gray commissure, the intermediolateral area and the superficial dorsal horn. Neurons labeled by virus from the prostate were mainly found in the L1-L2 spinal cord segments in the dorsal gray commissure and the intermediolateral areas. Double-labeled interneurons in L1-L2 were mainly located in the intermediolateral area. In L6-S1 they were divided between the dorsal gray commissure and the intermediolateral area. CONCLUSIONS: Spinal neurons innervating the bladder are clearly separate and different from those innervating the prostate. This difference also persists in the brain. In disagreement with previous reports, no direct anatomical evidence of parasympathetic innervation of the prostate was observed.

Distribution of sympathetic preganglionic neurons innervating the kidney in the rat: PRV transneuronal tracing and serial reconstruction.

The organization of spinal motor circuitry to the kidney is not well-characterized and changes in renal innervation have been associated with disease states such as hypertension found in the spontaneously hypertensive rat or renal hypertension. Here, we describe the segmental and intra-segmental organization of the spinal motor circuitry that was resolved after neurotropic viral injection into the kidney and retrograde transneuronal transport to the spinal cord. In the first experiment, the serial reconstruction of infected neurons in the thoracolumbar spinal cord from T8-L1 was performed following injection of pseudorabies virus (PRV, Bartha strain) into either the cranial pole, the caudal pole or both the cranial and caudal poles of the left kidney in male rats. In the second experiment, rats received injections of two different PRV strains that were genetically engineered to express unique reporter molecules; one of the engineered strains was injected into the cranial pole and the other was injected into the caudal pole. Either 3- or 4-day post-infection, the animals were anesthetized and sacrificed by transcardial perfusion. PRV-infected neurons were located by immunocytochemistry against either PRV itself (experiment 1) or the unique marker proteins (experiment 2). After injection of both poles of the kidney, the majority of the infected neurons were found in the ipsilateral intermediolateral cell column (IML) from T10 to T12 with the mode at T11. Infected neurons were found in discrete neuron clusters in the intermediolateral cell column along the longitudinal axis in a repeating pattern of high and low density that has been called "beading". Three observations indicated a topographic distribution of renal sympathetic preganglionic neurons (SPN). First, after injection into either the cranial or caudal poles of the kidney, the mode of infected cells was located in segments T11 and T12, respectively. The one spinal segment shift in the mode suggested a topographic distribution. Second, in spinal segments T8-L1, comparison of the distributions of the neurons innervating each pole of the left kidney revealed an overlap in the distribution, except in the T11 segment. In the T11 segment, the neurons projecting to each pole tended to segregate into separate populations. Third, in rats that received injections of two PRV strains that were genetically engineered to express unique markers into opposite poles of the kidney, a segregation of neurons projecting to the cranial and caudal poles of the kidney was noted again in the T11 spinal segment and the segregation at adjacent spinal levels was obvious. The analysis of the distribution of infected neurons within each spinal cord segment (intra-segmental distribution) revealed three different patterns along the cranial-caudal dimension. In segments T8-T10, >60% of the infected neurons were located in the caudal half of the spinal segment. In segments T12-L1, >60% of the infected neurons were located in the cranial half of the spinal segment. In segment T11, the neurons were more evenly distributed throughout the segment. These intra-segmental distribution patterns were found after both 3- or 4-day survival periods post-infection and were found in most animals. The distribution of clusters of neurons revealed a similar intra-segmental pattern. Thus, as was described previously for the sympathetic postganglionic neurons that innervate the kidney, the present work indicates a topographic organization in the second-order neurons in the renal sympathetic efferent pathway. The physiological significance of this anatomical organization remains to be determined.

Neural circuitry of the kidney: NO-containing neurons.

The neurons synthesizing nitric oxide (NO) that are part of the renal sympathetic pathways were located by double-staining for the neuronal isoform of nitric oxide synthase (nNOS) using immunocytochemistry to identify NO-synthesizing neurons and transneuronal tracing following infection of the left kidney with pseudorabies virus (PRV). Following kidney injection with PRV, the animals survived 4-day post-inoculation prior to sacrifice and tissue processing. PRV-infected neurons that double-stained for nNOS were found in the paraventricular hypothalamic nucleus (PVN), the raphe obscurus nucleus (ROb), the ventromedial medulla (VMM), the rostral ventrolateral medulla (rVLM) and the A5 cell group. In the thoracolumbar spinal cord, nNOS neurons co-localized with PRV-infected cells in the dorsal horn in laminae I, III-V ipsilateral to the injected kidney and in lamina X, the intermediolateral cell column, the lateral funiculus, the intercalated nucleus and the central autonomic area. We conclude that NO synthesizing cells may significantly affect renal autonomic pathways in the rat by interacting with the renal sensory and sympathomotor circuitry at multiple sites.

A novel link between stress and human cytomegalovirus (HCMV) infection: sympathetic hyperactivity stimulates HCMV activation.

Recently, inflammatory mediators such as TNFalpha were identified as triggering active human cytomegalovirus (HCMV) infection. Here, we demonstrate that a highly stressful event in the absence of systemic inflammation, as observed in patients with acute myocardial infarction, leads to the development of an active HCMV infection in latently infected patients. Elucidating the molecular mechanism of virus activation, we could show that catecholamines directly stimulate the HCMV immediate-early (IE) enhancer/promoter in monocytic cells via beta-2 adrenergic receptors. Subsequent activation of the cAMP/PK-A-signaling pathway results in enhanced synthesis and binding of the transcription factor CREB-1/ATF-1 to the cAMP-responsive elements within the IE enhancer. Epinephrine also enhanced HCMV gene expression in infected THP-1 cells by about 50% in three of four experiments. These data suggest that HCMV, like HSV-1 and VZV, can be (re)activated under stress conditions.

Connections of Barrington's nucleus to the sympathetic nervous system in rats.

Barrington's nucleus (BN) has been considered a pontine center related exclusively to the control of pelvic parasympathetic activity. The present study demonstrates an anatomical linkage between BN and autonomic outflow to visceral targets innervated exclusively by the sympathetic division of the autonomic nervous system. Temporal analysis of infection after injection of pseudorabies virus (PRV), a retrograde transynaptic tracer, into two sympathetically innervated organs, the spleen and the kidney, revealed the presence of infected neurons in BN at early post-inoculation survival intervals. Immunohistochemical localization of PRV after spleen injections showed that a small subpopulation of BN neurons became labeled in a time frame coincident with the appearance of infected neurons in other brain regions known to project to sympathetic preganglionic neurons (SPNs) in the thoracic spinal cord; a larger number of infected neurons appeared in BN at intermediate intervals after PRV injections into the spleen or kidney. Coinjection of the retrograde tracer Fluoro-Gold i.p. and PRV into the spleen demonstrated that parasympathetic preganglionic neurons in the caudal medulla or lumbo-sacral spinal cord were not infected, indicating that infected BN neurons were not infected via a parasympathetic route. Thus, BN neurons become infected after PRV injections into the spleen or kidney either directly through BN projections to SPNs, or secondarily via BN projections to infected pre-preganglionic neurons. These results demonstrate an anatomical linkage, either direct or indirect, between BN and sympathetic activity. Because BN receives numerous inputs from diverse brain regions, the relation of BN with both branches of the autonomic nervous system suggests that this nucleus might play a role in the integration of supraspinal inputs relevant to the central coordination of sympathetic and parasympathetic activity.

Spinal and brain circuits to motoneurons of the bulbospongiosus muscle: retrograde transneuronal tracing with rabies virus.

Retrograde transneuronal tracing with rabies virus from the left bulbospongiosus muscle (BS) was used to identify the neural circuits underlying its peripheral and central activation. Rats were killed at 2, 3, 4, and 5 days post-inoculation (p.i.). Rabies immunolabelling was combined with immunohistochemical detection of choline acetyltransferase and oxytocin. Virus uptake was restricted to ipsilateral BS motoneurons (2 days p.i.). The onset of transfer (3 days p.i.) visualized interneurons in the dorsal grey commissure (DGC), intermediate zone, and sacral parasympathetic nucleus (SPN), mainly in DGC at L5-S1, and revealed synaptic connections between BS and external urethral sphincter motoneurons. At 4 and 5 days p.i., higher-order interneurons were labelled in other spinal areas and segments. Supraspinal labelling initially involved only Barrington's nucleus, nucleus reticularis magnocellularis, and paragigantocellularis lateralis (4 days p.i.). Later, labelling extended to other populations traditionally associated with control of sexual activity and micturition (periaqueductal grey, paraventricular nucleus, medial preoptic area, prefrontal cortex), but also indicated the intervention of somatic descending motor pathways (vestibulospinal and reticulospinal neurons, "hindlimb" regions of sensorimotor cortex and red nucleus) and cerebellar nuclei in multisynaptic innervation of the labelled motoneurons. Dual color immunofluorescence disclosed multisynaptic links between these motoneurons and thoracolumbar medial sympathetic (choline acetyltransferase-immunoreactive) neurons. In contrast, preganglionic neurons in SPN and most oxytocinergic neurons in paraventricular hypothalamic nucleus remained unlabelled, suggesting that parasympathetic and somatic outflow to pelvic organs are probably controlled by separate interneuronal populations and that oxytocinergic spinal projections are more likely to influence sacral autonomic rather than somatic outflow.