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

Prevalence, Risk Factors, Pathophysiology, Potential Biomarkers and Management of Feline Idiopathic Cystitis: An Update Review

Feline idiopathic cystitis is a widespread disease in small animal clinics, which mainly presents with urinary signs like dysuria, stranguria, hematuria, pollakiuria, and periuria. The etiopathogenesis of the disease may involve interactions between the environmental stressors, neuroendocrine system and bladder of affected cats. Diagnostic biomarkers have not been tested in clinical studies though they are theoretically feasible, and since the clinical signs of the disease assemble those of other feline lower urinary diseases, its diagnosis is a procedure of exclusion. The primary treatment of the disease is long-term multimodal environmental modification (or enrichment) while anti-anxiety drugs and nutritional supplements are recommended for chronic recurrent cases. Still, many medicines need to be evaluated for their efficacy and safety. This review aims to provide readers with a comprehensive understanding of feline idiopathic cystitis by summarizing and updating studies concerning the prevalence, risk factors, etiological hypotheses, diagnostic procedures, possible treatments, and prognosis of the disease.

Chronic Social Defeat Stress Up-Regulates Spexin in the Brain of Nile Tilapia (Oreochromis niloticus)

Spexin (SPX), a neuropeptide evolutionarily conserved from fish to mammals, is widely distributed in the brain and peripheral tissues and associated with various physiological functions. Recently SPX has been suggested to be involved in neurological mechanism of stress. The current study investigates the involvement of SPX in chronic social defeat stress, using male teleost, the Nile tilapia (Oreochromis niloticus) as an animal model due to its distinct social hierarchy of dominant and subordinate relationship. The tilapia genome has SPX1a and SPX1b but has no SPX2. In the Nile tilapia, we localized SPX1a and SPX1b in the brain using in-situ hybridization. Next, using qPCR we examined gene expression of SPX1a and SPX1b in chronically stress (socially defeated) fish. SPX1a expressing cells were localized in the semicircular torus of the midbrain region and SPX1b expressing cells in the telencephalon. Chronically stress fish showed elevated plasma cortisol levels; with an upregulation of SPX1a and SPX1b gene expression in the brain compared to non-stress (control) fish. Since social defeat is a source of stress, the upregulated SPX mRNA levels during social defeat suggests SPX as a potentially inhibitory neuropeptide capable of causing detrimental changes in behaviour and physiology.

Synaptic Inputs to the Mouse Dorsal Vagal Complex and Its Resident Preproglucagon Neurons

Stress responses are coordinated by widespread neural circuits. Homeostatic and psychogenic stressors activate preproglucagon (PPG) neurons in the caudal nucleus of the solitary tract (cNTS) that produce glucagon-like peptide-1; published work in rodents indicates that these neurons play a crucial role in stress responses. While the axonal targets of PPG neurons are well established, their afferent inputs are unknown.

Stress responses are coordinated by widespread neural circuits. Homeostatic and psychogenic stressors activate preproglucagon (PPG) neurons in the caudal nucleus of the solitary tract (cNTS) that produce glucagon-like peptide-1; published work in rodents indicates that these neurons play a crucial role in stress responses. While the axonal targets of PPG neurons are well established, their afferent inputs are unknown. Here we use retrograde tracing with cholera toxin subunit b to show that the cNTS in male and female mice receives axonal inputs similar to those reported in rats. Monosynaptic and polysynaptic inputs specific to cNTS PPG neurons were revealed using Cre-conditional pseudorabies and rabies viruses. The most prominent sources of PPG monosynaptic input include the lateral (LH) and paraventricular (PVN) nuclei of the hypothalamus, parasubthalamic nucleus, lateral division of the central amygdala, and Barrington's nucleus (Bar). Additionally, PPG neurons receive monosynaptic vagal sensory input from the nodose ganglia and spinal sensory input from the dorsal horn. Sources of polysynaptic input to cNTS PPG neurons include the hippocampal formation, paraventricular thalamus, and prefrontal cortex. Finally, cNTS-projecting neurons within PVN, LH, and Bar express the activation marker cFOS in mice after restraint stress, identifying them as potential sources of neurogenic stress-induced recruitment of PPG neurons. In summary, cNTS PPG neurons in mice receive widespread monosynaptic and polysynaptic input from brain regions implicated in coordinating behavioral and physiological stress responses, as well as from vagal and spinal sensory neurons. Thus, PPG neurons are optimally positioned to integrate signals of homeostatic and psychogenic stress.

SIGNIFICANCE STATEMENT Recent research has indicated a crucial role for glucagon-like peptide-1-producing preproglucagon (PPG) neurons in regulating both appetite and behavioral and autonomic responses to acute stress. Intriguingly, the central glucagon-like peptide-1 system defined in rodents is conserved in humans, highlighting the translational importance of understanding its anatomical organization. Findings reported here indicate that PPG neurons receive significant monosynaptic and polysynaptic input from brain regions implicated in autonomic and behavioral responses to stress, as well as direct input from vagal and spinal sensory neurons. Improved understanding of the neural pathways underlying the recruitment of PPG neurons may facilitate the development of novel therapies for the treatment of stress-related disorders.

Shared Autonomic Pathways Connect Bone Marrow and Peripheral Adipose Tissues Across the Central Neuraxis

Bone marrow adipose tissue (BMAT) is increased in both obesity and anorexia. This is unique relative to white adipose tissue (WAT), which is generally more attuned to metabolic demand. It suggests that there may be regulatory pathways that are common to both BMAT and WAT and also those that are specific to BMAT alone. The central nervous system (CNS) is a key mediator of adipose tissue function through sympathetic adrenergic neurons. Thus, we hypothesized that central autonomic pathways may be involved in BMAT regulation. To test this, we first quantified the innervation of BMAT by tyrosine hydroxylase (TH) positive nerves within the metaphysis and diaphysis of the tibia of B6 and C3H mice. We found that many of the TH+ axons were concentrated around central blood vessels in the bone marrow. However, there were also areas of free nerve endings which terminated in regions of BMAT adipocytes. Overall, the proportion of nerve-associated BMAT adipocytes increased from proximal to distal along the length of the tibia (from ~3-5 to ~14-24%), regardless of mouse strain. To identify the central pathways involved in BMAT innervation and compare to peripheral WAT, we then performed retrograde viral tract tracing with an attenuated pseudorabies virus (PRV) to infect efferent nerves from the tibial metaphysis (inclusive of BMAT) and inguinal WAT (iWAT) of C3H mice. PRV positive neurons were identified consistently from both injection sites in the intermediolateral horn of the spinal cord, reticular formation, rostroventral medulla, solitary tract, periaqueductal gray, locus coeruleus, subcoeruleus, Barrington's nucleus, and hypothalamus. We also observed dual-PRV infected neurons within the majority of these regions. Similar tracings were observed in pons, midbrain, and hypothalamic regions from B6 femur and tibia, demonstrating that these results persist across mouse strains and between skeletal sites. Altogether, this is the first quantitative report of BMAT autonomic innervation and reveals common central neuroanatomic pathways, including putative "command" neurons, involved in coordinating multiple aspects of sympathetic output and facilitation of parallel processing between bone marrow/BMAT and peripheral adipose tissue.

Evolution of Structural and Functional Diversity of Spexin in Mammalian and Non-mammalian Vertebrate Species

Spexin (SPX) is a novel neuropeptide, which was first identified in the human genome using bioinformatics. Since then, orthologs of human SPX have been identified in mammalian and non-mammalian vertebrates. The mature sequence of SPX, NWTPQAMLYLKGAQ, is evolutionally conserved across vertebrate species, with some variations in teleost species where Ala at position 13 is substituted by Thr. In mammals, the gene structure of SPX comprises six exons and five introns, however, variation exists within non-mammalian species, goldfish and zebrafish having five exons while grouper has six exons. Phylogenetic and synteny analysis, reveal that SPX is grouped together with two neuropeptides, kisspeptin (KISS) and galanin (GAL) as a family of peptides with a common evolutionary ancestor. A paralog of SPX, termed SPX2 has been identified in non-mammalians but not in the mammalian genome. Ligand-receptor interaction study also shows that SPX acts as a ligand for GAL receptor 2 (2a and 2b in non-mammalian vertebrates) and 3. SPX acts as a neuromodulator with multiple central and peripheral physiological roles in the regulation of insulin release, fat metabolism, feeding behavior, and reproduction. Collectively, this review provides a comprehensive overview of the evolutionary diversity as well as molecular and physiological roles of SPX in mammalian and non-mammalian vertebrate species.

Neuroimmune Communication in Health and Disease

The immune and nervous systems are tightly integrated, with each system capable of influencing the other to respond to infectious or inflammatory perturbations of homeostasis. Recent studies demonstrating the ability of neural stimulation to significantly reduce the severity of immunopathology and consequently reduce mortality have led to a resurgence in the field of neuroimmunology. Highlighting the tight integration of the nervous and immune systems, afferent neurons can be activated by a diverse range of substances from bacterial-derived products to cytokines released by host cells. While activation of vagal afferents by these substances dominates the literature, additional sensory neurons are responsive as well. It is becoming increasingly clear that although the cholinergic anti-inflammatory pathway has become the predominant model, a multitude of functional circuits exist through which neuronal messengers can influence immunological outcomes. These include pathways whereby efferent signaling occurs independent of the vagus nerve through sympathetic neurons. To receive input from the nervous system, immune cells including B and T cells, macrophages, and professional antigen presenting cells express specific neurotransmitter receptors that affect immune cell function. Specialized immune cell populations not only express neurotransmitter receptors, but express the enzymatic machinery required to produce neurotransmitters, such as acetylcholine, allowing them to act as signaling intermediaries. Although elegant experiments have begun to decipher some of these interactions, integration of these molecules, cells, and anatomy into defined neuroimmune circuits in health and disease is in its infancy. This review describes these circuits and highlights continued challenges and opportunities for the field.

Characterization of the neuroinvasive profile of a pseudorabies virus recombinant expressing the mTurquoise2 reporter in single and multiple injection experiments

BACKGROUND

Viral transneuronal tracing has become a well established technology used to define the synaptic architecture of polysynaptic neural networks.

NEW METHOD

In this report we define the neuroinvasive profile and reporter expression of a new recombinant of the Bartha strain of pseudorabies virus (PRV). The new recombinant, PRV-290, expresses the mTurquoise2 fluorophor and is designed to complement other isogenic recombinants of Bartha that express different reporters of infection. Results & Comparison with Existing Methods: PRV-290 was injected either alone or in combination with isogenic recombinants of PRV that express enhanced green fluorescent protein (EGFP; PRV-152) or monomeric red fluorescent protein (mRFP; PRV-614). Circuits previously defined using PRV-152 and PRV-614 were used for the analysis. The data demonstrate that PRV-290 is a retrograde transneuronal tracer with temporal kinetics similar to those of its isogenic recombinants. Stable expression of the diffusible mTurquoise2 reporter filled infected neurons, with the extent and intensity of labeling increasing with advancing post inoculation survival. In multiple injection experiments, PRV-290 established productive infections in neurons also replicating PRV-152 and/or PRV-614. This novel demonstration of three recombinants infecting individual neurons represents an important advance in the technology.

CONCLUSION

Collectively, these data demonstrate that PRV-290 is a valuable addition to the viral tracer toolbox for transneuronal tracing of neural circuitry.

Distribution of catecholaminergic presympathetic-premotor neurons in the rat lower brainstem

We previously characterized the organization of presympathetic-premotor neurons (PSPMNs), which send descending poly-synaptic projections with collaterals to skeletal muscle and the adrenal gland. Such neurons may play a role in shaping integrated adaptive responses, and many of them were found within well-characterized regions of noradrenergic cell populations suggesting that some of the PSPMNs are catecholaminergic. To address this issue, we used retrograde trans-synaptic tract-tracing with attenuated pseudorabies virus (PRV) recombinants combined with multi-label immunofluorescence to identify PSPMNs expressing tyrosine hydroxylase (TH). Our findings indicate that TH-immunoreactive (ir) PSPMNs are present throughout the brainstem within multiple cell populations, including the A1, C1, C2, C3, A5 and A7 cell groups along with the locus coeruleus (LC) and the nucleus subcoeruleus (SubC). The largest numbers of TH-ir PSPMNs were located within the LC and SubC. Within SubC and the A7 cell group, about 70% of TH-ir neurons were PSPMNs, which was a significantly greater fraction of neurons than in the other brain regions we examined. These findings indicate that TH-ir neurons near the pontomesencephalic junction that are distributed across the LC, SubC, and the A7 may play a prominent role in somatomotor-sympathetic integration, and that the major functional role of the A7 and SubC noradrenergic cell groups maybe in the coordination of concomitant activation of somatomotor and sympathetic outflows. These neurons may participate in mediating homeostatic adaptations that require simultaneous activation of sympathetic and somatomotor nerves in the periphery.

Regulation of the renal sympathetic nerves in heart failure

Heart failure (HF) is a serious debilitating condition with poor survival rates and an increasing level of prevalence. HF is associated with an increase in renal norepinephrine (NE) spillover, which is an independent predictor of mortality in HF patients. The excessive sympatho-excitation that is a hallmark of HF has long-term effects that contribute to disease progression. An increase in directly recorded renal sympathetic nerve activity (RSNA) has also been recorded in animal models of HF. This review will focus on the mechanisms controlling sympathetic nerve activity (SNA) to the kidney during normal conditions and alterations in these mechanisms during HF. In particular the roles of afferent reflexes and central mechanisms will be discussed.

Autonomic consequences of spinal cord injury

Spinal cord injury (SCI) results not only in motor and sensory deficits but also in autonomic dysfunctions. The disruption of connections between higher brain centers and the spinal cord, or the impaired autonomic nervous system itself, manifests a broad range of autonomic abnormalities. This includes compromised cardiovascular, respiratory, urinary, gastrointestinal, thermoregulatory, and sexual activities. These disabilities evoke potentially life-threatening symptoms that severely interfere with the daily living of those with SCI. In particular, high thoracic or cervical SCI often causes disordered hemodynamics due to deregulated sympathetic outflow. Episodic hypertension associated with autonomic dysreflexia develops as a result of massive sympathetic discharge often triggered by unpleasant visceral or sensory stimuli below the injury level. In the pelvic floor, bladder and urethral dysfunctions are classified according to upper motor neuron versus lower motor neuron injuries; this is dependent on the level of lesion. Most impairments of the lower urinary tract manifest in two interrelated complications: bladder storage and emptying. Inadequate or excessive detrusor and sphincter functions as well as detrusor-sphincter dyssynergia are examples of micturition abnormalities stemming from SCI. Gastrointestinal motility disorders in spinal cord injured-individuals are comprised of gastric dilation, delayed gastric emptying, and diminished propulsive transit along the entire gastrointestinal tract. As a critical consequence of SCI, neurogenic bowel dysfunction exhibits constipation and/or incontinence. Thus, it is essential to recognize neural mechanisms and pathophysiology underlying various complications of autonomic dysfunctions after SCI. This overview provides both vital information for better understanding these disorders and guides to pursue novel therapeutic approaches to alleviate secondary complications.

Central nervous system control of gastrointestinal motility and secretion and modulation of gastrointestinal functions

Although the gastrointestinal (GI) tract possesses intrinsic neural plexuses that allow a significant degree of autonomy over GI functions, the central nervous system (CNS) provides extrinsic neural inputs that regulate, modulate, and control these functions. While the intestines are capable of functioning in the absence of extrinsic inputs, the stomach and esophagus are much more dependent upon extrinsic neural inputs, particularly from parasympathetic and sympathetic pathways. The sympathetic nervous system exerts a predominantly inhibitory effect upon GI muscle and provides a tonic inhibitory influence over mucosal secretion while, at the same time, regulates GI blood flow via neurally mediated vasoconstriction. The parasympathetic nervous system, in contrast, exerts both excitatory and inhibitory control over gastric and intestinal tone and motility. Although GI functions are controlled by the autonomic nervous system and occur, by and large, independently of conscious perception, it is clear that the higher CNS centers influence homeostatic control as well as cognitive and behavioral functions. This review will describe the basic neural circuitry of extrinsic inputs to the GI tract as well as the major CNS nuclei that innervate and modulate the activity of these pathways. The role of CNS-centered reflexes in the regulation of GI functions will be discussed as will modulation of these reflexes under both physiological and pathophysiological conditions. Finally, future directions within the field will be discussed in terms of important questions that remain to be resolved and advances in technology that may help provide these answers.

Functional role of Barrington's nucleus in the micturition reflex: relevance in the surgical treatment of Parkinson's disease

The pontine micturition center or Barrington's nucleus (BN) - besides regulating micturition - co-regulates the activity of other pelvic viscera such as the colon and genitals. At present, this issue is gaining particular importance due to: (i) recent findings of α-synuclein in BN, (ii) known urinary dysfunction in parkinsonian patients (part of the so-called non-motor symptoms), other patients with dementia and as in very old individuals; and (iii) its proximity to the pedunculopontine nucleus, a surgical target in deep brain stimulation for Parkinson's disease (PD). The structural and functional organization of the micturition reflex comprises a coordinating action of somatic motor activity with both divisions of the autonomic nervous system, modulated by trunk encephalic and cortical centers that involve the BN as locus coeruleus and periaqueductal gray matter, among other trunk encephalic structures. The involvement of dopaminergic activity (physiologic inhibition of the micturition reflex mediated by dopaminergic D1 activity) that diminishes in Parkinsonism and leads to overactivity of the micturition reflex is also well known. In this review, the integrating role of the BN in the context of vesical and gastrointestinal behavior is revisited, and the principal morpho-functional findings that associate dysfunction with the urinary disorders that appear during the pre-motor stages of PD are summarized.

Autonomic regulation of cellular immune function

The nervous system and the immune system (IS) are two integrative systems that work together to detect threats and provide host defense, and to maintain/restore homeostasis. Cross-talk between the nervous system and the IS is vital for health and well-being. One of the major neural pathways responsible for regulating host defense against injury and foreign antigens and pathogens is the sympathetic nervous system (SNS). Stimulation of adrenergic receptors (ARs) on immune cells regulates immune cell development, survival, proliferative capacity, circulation, trafficking for immune surveillance and recruitment, and directs the cell surface expression of molecules and cytokine production important for cell-to-cell interactions necessary for a coordinated immune response. Finally, AR stimulation of effector immune cells regulates the activational state of immune cells and modulates their functional capacity. This review focuses on our current understanding of the role of the SNS in regulating host defense and immune homeostasis. SNS regulation of IS functioning is a critical link to the development and exacerbation of chronic immune-mediated diseases. However, there are many mechanisms that need to be further unraveled in order to develop sound treatment strategies that act on neural-immune interaction to resolve or prevent chronic inflammatory diseases, and to improve health and quality of life.

Identification of CNS neurons innervating the levator ani and ventral bulbospongiosus muscles in male rats

INTRODUCTION

The pelvic striated muscles play an important role in mediating erections and ejaculation, and together these muscles compose a tightly coordinated neuromuscular system that is androgen sensitive and sexually dimorphic.

AIM

To identify spinal and brains neurons involved in the control of the levator ani (LA) and bulbospongiosus (BS) in the male adult and preadolescent rat.

METHODS

Rats were anesthetized, and the transsynaptic retrograde tracer pseudorabies virus (PRV) was injected into the LA muscle of adults or the ventral BS muscle in 30-day-old rats. After 3-5 days rats were sacrificed, and PRV-labeled neurons in the spinal cords and brains were identified using immunohistochemistry. The presence of gastrin-releasing peptide (GRP) in the lumbar spinal neurons was examined.

MAIN OUTCOMES MEASURES

The location and number of PRV-labeled neurons in the spinal cord and brain and GRP colocalization in the lumbar spinal cord.

RESULTS

PRV-labeled spinal interneurons were found distributed throughout T11-S1 of the spinal cord, subsequent to dorsal medial motoneuron infection. The majority of spinal interneurons were found in the lumbosacral spinal cord in the region of the dorsal gray commissure and parasympathetic preganglionic neurons. Preadolescent rats had more PRV-labeled spinal interneurons at L5-S1 where the motoneurons were located but relatively less spread rostrally in the spinal cord compared with adults. Lumbar spinothalmic neurons in medial gray of L3-L4 co-localized PRV and GRP. In the brain consistent labeling was seen in areas known to be involved in male sexual behavior including the ventrolateral medulla, hypothalamic paraventricular nucleus, and medial preoptic area.

CONCLUSION

Common spinal and brain pathways project to the LA and BS muscles in the rat suggesting that these muscles act together to coordinate male sexual reflexes. Differences may exist in the amount of synaptic connections/neuronal pathways in adolescents compared with adults.

Synaptic and extrasynaptic transmission of kidney-related neurons in the rostral ventrolateral medulla

The rostral ventrolateral medulla (RVLM) is a critical component of the sympathetic nervous system regulating homeostatic functions including arterial blood pressure. Using the transsynaptic retrograde viral tracer PRV-152, we identified kidney-related neurons in the RVLM. We found that PRV-152-labeled RVLM neurons displayed an unusually large persistent, tonic current to both glutamate, via N-methyl-d-aspartate (NMDA) and 2-amino-3-(3-hydroxy-5-methyl-isoxazol-4-yl)propanoic acid (AMPA)/kainate receptors, and to γ-aminobutyric acid (GABA), via GABAA receptors, in the absence of large-scale phasic neurotransmission with whole cell patch-clamp recordings. A cocktail of potent NMDA and AMPA/kainate ionotropic glutamate receptor antagonists AP-5 (50 μM) and CNQX (10 μM) revealed a two-component somatic tonic excitatory current with an overall amplitude of 42.6 ± 13.4 pA. Moreover, application of the GABAA receptor blockers gabazine (15 μM) and bicuculline (30 μM) revealed a robust somatic tonic inhibitory current with an average amplitude of 196.3 ± 39.3 pA. These findings suggest that the tonic current plays a role in determining the resting membrane potential, input resistance, and firing rate of RVLM neurons. The magnitude of the tonic inhibitory current demonstrates that GABAergic inhibition plays a critical role in regulation of kidney-related RVLM neurons. Our results indicate that the GABAergic tonic current may determine the basal tone of firing activity in kidney-related RVLM neurons.

Critical evaluation of the anatomical location of the Barrington nucleus: relevance for deep brain stimulation surgery of pedunculopontine tegmental nucleus

Deep brain stimulation (DBS) has become the standard surgical procedure for advanced Parkinson's disease (PD). Recently, the pedunculopontine tegmental nucleus (PPN) has emerged as a potential target for DBS in patients whose quality of life is compromised by freezing of gait and falls. To date, only a few groups have published their long-term clinical experience with PPN stimulation. Bearing in mind that the Barrington (Bar) nucleus and some adjacent nuclei (also known as the micturition centre) are close to the PPN and may be affected by DBS, the aim of the present study was to review the anatomical location of this structure in human and other species. To this end, the Bar nucleus area was analysed in mouse, monkey and human tissues, paying particular attention to the anatomical position in humans, where it has been largely overlooked. Results confirm that anatomical location renders the Bar nucleus susceptible to influence by the PPN DBS lead or to diffusion of electrical current. This may have an undesirable impact on the quality of life of patients.

Distinct intrinsic and synaptic properties of pre-sympathetic and pre-parasympathetic output neurons in Barrington's nucleus

Barrington's nucleus (BN), commonly known as the pontine micturition center, controls micturition and other visceral functions through projections to the spinal cord. In this study, we developed a rat brain slice preparation to determine the intrinsic and synaptic mechanisms regulating pre-sympathetic output (PSO) and pre-parasympathetic output (PPO) neurons in the BN using patch-clamp recordings. The PSO and PPO neurons were retrogradely labeled by injecting fluorescent tracers into the intermediolateral region of the spinal cord at T13-L1 and S1-S2 levels, respectively. There were significantly more PPO than PSO neurons within the BN. The basal activity and membrane potential were significantly lower in PPO than in PSO neurons, and A-type K(+) currents were significantly larger in PPO than in PSO neurons. Blocking A-type K(+) channels increased the excitability more in PPO than in PSO neurons. Stimulting μ-opioid receptors inhibited firing in both PPO and PSO neurons. The glutamatergic EPSC frequency was much lower, whereas the glycinergic IPSC frequency was much higher, in PPO than in PSO neurons. Although blocking GABAA receptors increased the excitability of both PSO and PPO neurons, blocking glycine receptors increased the firing activity of PPO neurons only. Furthermore, blocking ionotropic glutamate receptors decreased the excitability of PSO neurons but paradoxically increased the firing activity of PPO neurons by reducing glycinergic input. Our findings indicate that the membrane and synaptic properties of PSO and PPO neurons in the BN are distinctly different. This information improves our understanding of the neural circuitry and central mechanisms regulating the bladder and other visceral organs.

Prenatal expression of MET receptor tyrosine kinase in the fetal mouse dorsal raphe nuclei and the visceral motor/sensory brainstem

Signaling via MET receptor tyrosine kinase (MET) has been implicated in a number of neurodevelopmental events, including cell migration, dendritic and axonal development and synaptogenesis. Related to its role in the development of forebrain circuitry, we recently identified a functional promoter variant of the MET gene that is associated with autism spectrum disorder (ASD). The association of the MET promoter variant rs1858830 C allele is significantly enriched in families with a child who has ASD and co-occurring gastrointestinal conditions. The expression of MET in the forebrain had been mapped in detail in the developing mouse and rhesus macaque. However, in mammals, its expression in the developing brainstem has not been studied extensively throughout developmental stages. Brainstem and autonomic circuitry are implicated in ASD pathophysiology and in gastrointestinal dysfunction. To advance our understanding of the neurodevelopmental influences of MET signaling in brainstem circuitry development, we employed in situ hybridization and immunohistochemistry to map the expression of Met and its ligand, Hgf, through prenatal development of the mouse midbrain and hindbrain. Our results reveal a highly selective expression pattern of Met in the brainstem, including a subpopulation of neurons in cranial motor nuclei (nVII, nA and nXII), B6 subgroup of the dorsal raphe, Barrington's nucleus, and a small subset of neurons in the nucleus of solitary tract. In contrast to Met, neither full-length nor known splice variants of Hgf were localized in the prenatal brainstem. RT-PCR revealed Hgf expression in target tissues of Met-expressing brainstem neurons, suggesting that MET in these neurons may be activated by HGF from peripheral sources. Together, these data suggest that MET signaling may influence the development of neurons that are involved in central regulation of gastrointestinal function, tongue movement, swallowing, speech, stress and mood.

Rapid Glucocorticoid-Induced Activation of TRP and CB1 Receptors Causes Biphasic Modulation of Glutamate Release in Gastric-Related Hypothalamic Preautonomic Neurons

Glucocorticoids rapidly regulate synaptic input to neuroendocrine cells in the hypothalamic paraventricular nucleus (PVN) by inducing the retrograde release of endogenous messengers. Here we investigated the rapid effects of dexamethasone (DEX) on excitatory synaptic input to feeding-related, preautonomic PVN neurons using whole-cell patch-clamp recordings. In ∼50% of identified gastric-related preautonomic PVN neurons, DEX elicited a biphasic synaptic response characterized by an initial rapid and transient increase in the frequency of miniature excitatory postsynaptic currents (mEPSCs), followed by a decrease in mEPSC frequency within 9 min; remaining cells displayed only a decrease in mEPSC frequency. The late-phase decrease in mEPSC frequency was mimicked by the cannabinoid receptor agonists anandamide (AEA) and WIN 55,212-2, and it was blocked by the CB1 receptor antagonist AM251. The biphasic DEX effect was mimicked by AEA. The early increase in mEPSCs was mimicked by activation of transient receptor potential vanilloid type 1 (TRPV1) receptors with capsaicin and by activation of TRPV4 receptors with 4-α-PDD. The increase was reduced, but not blocked, by selective TRPV1 antagonists and in TRPV1 knockout mice; it was blocked completely by the broad-spectrum TRPV antagonist ruthenium red and by combined application of selective TRPV1 and TRPV4 antagonists. The DEX effects were prevented entirely by intracellular infusion of the G-protein inhibitor, GDPβS. Thus, DEX biphasically modulates synaptic glutamate onto a subset of gastric-related PVN neurons, which is likely mediated by induction of a retrograde messenger. The effect includes a TRPV1/4 receptor-mediated transient increase and subsequent CB1 receptor-mediated suppression of glutamate release. Multiphasic modulation of glutamate input to PVN neurons represents a previously unappreciated complexity of control of autonomic output by glucocorticoids and endogenous cannabinoids.

Preproglucagon (PPG) neurons innervate neurochemically identified autonomic neurons in the mouse brainstem

Preproglucagon (PPG) neurons produce glucagon-like peptide-1 (GLP-1) and occur primarily in the nucleus tractus solitarius (NTS). GLP-1 affects a variety of central autonomic circuits, including those controlling the cardiovascular system, thermogenesis, and most notably energy balance. Our immunohistochemical studies in transgenic mice expressing YFP under the control of the PPG promoter showed that PPG neurons project widely to central autonomic regions, including brainstem nuclei. Functional studies have highlighted the importance of hindbrain receptors for the anorexic effects of GLP-1. In this study, we assessed YFP innervation of neurochemically identified brainstem neurons in transgenic YFP-PPG mice. Immunoreactivity for YFP plus choline acetyltransferase (ChAT), tyrosine hydroxylase (TH) and/or serotonin (5-HT) was visualised with two- or three-colour immunoperoxidase labelling using black (YFP), brown and blue-grey reaction products. In the dorsal motor nucleus of the vagus (DMV), terminals from fine YFP-immunoreactive axons closely apposed a small proportion of ChAT-positive and rare TH-positive/ChAT-positive motor neurons, mostly ventral to AP. YFP-immunoreactive innervation was virtually absent from the compact and loose formations of the nucleus ambiguus. In the NTS, some TH-immunoreactive neurons were closely apposed by YFP-containing axons. In the A1/C1 column in the ventrolateral medulla, close appositions on TH-positive neurons were more common, particularly in the caudal portion of the column. A single YFP-immunoreactive axon usually provided 1-3 close appositions on individual ChAT- or TH-positive neurons. Serotonin-immunoreactive neurons were most heavily innervated, with the majority of raphé pallidus, raphé obscurus and parapyramidal neurons receiving several close appositions from large varicosities of YFP-immunoreactive axons. These results indicate that GLP-1 neurons innervate various populations of brainstem autonomic neurons. These include vagal efferent neurons and catecholamine neurons in areas linked with cardiovascular control. Our data also indicate a synaptic connection between GLP-1 neurons and 5-HT neurons, some of which might contribute to the regulation of appetite.

Peptides derived from the prohormone proNPQ/spexin are potent central modulators of cardiovascular and renal function and nociception

Computational methods have led two groups to predict the endogenous presence of a highly conserved, amidated, 14-aa neuropeptide called either spexin or NPQ. NPQ/spexin is part of a larger prohormone that contains 3 sets of RR residues, suggesting that it could yield more than one bioactive peptide; however, no in vivo activity has been demonstrated for any peptide processed from this precursor. Here we demonstrate biological activity for two peptides present within proNPQ/spexin. NPQ/spexin (NWTPQAMLYLKGAQ-NH(2)) and NPQ 53-70 (FISDQSRRKDLSDRPLPE) have differing renal and cardiovascular effects when administered intracerebroventricularly or intravenously into rats. Intracerebroventricular injection of NPQ/spexin produced a 13 ± 2 mmHg increase in mean arterial pressure, a 38 ± 8 bpm decrease in heart rate, and a profound decrease in urine flow rate. Intracerebroventricular administration of NPQ 53-70 produced a 26 ± 9 bpm decrease in heart rate with no change in mean arterial pressure, and a marked increase in urine flow rate. Intraventricular NPQ/spexin and NPQ 53-70 also produced antinociceptive activity in the warm water tail withdrawal assay in mice (ED(50)<30 and 10 nmol for NPQ/spexin and NPQ 53-70, respectively). We conclude that newly identified peptides derived from the NPQ/spexin precursor contribute to CNS-mediated control of arterial blood pressure and salt and water balance and modulate nociceptive responses.

Early life experience shapes the functional organization of stress-responsive visceral circuits

Emotions are closely tied to changes in autonomic (i.e., visceral motor) function, and interoceptive sensory feedback from body to brain exerts powerful modulatory control over motivation, affect, and stress responsiveness. This manuscript reviews evidence that early life experience can shape the structure and function of central visceral circuits that underlie behavioral and physiological responses to emotive and stressful events. The review begins with a general discussion of descending autonomic and ascending visceral sensory pathways within the brain, and then summarizes what is known about the postnatal development of these central visceral circuits in rats. Evidence is then presented to support the view that early life experience, particularly maternal care, can modify the developmental assembly and structure of these circuits in a way that impacts later stress responsiveness and emotional behavior. The review concludes by presenting a working hypothesis that endogenous cholecystokinin signaling and subsequent recruitment of gastric vagal sensory inputs to the caudal brainstem may be an important mechanism by which maternal care influences visceral circuit development in rat pups. Early life experience may contribute to meaningful individual differences in emotionality and stress responsiveness by shaping the postnatal developmental trajectory of central visceral circuits.

Noxious colorectal distention in spinalized rats reduces pseudorabies virus labeling of sympathetic neurons

The retrograde transsynaptic tracer pseudorabies virus (PRV) has been widely used as a marker for synaptic connectivity in the spinal cord. Notably, the PRV-152 construct expresses enhanced green fluorescent protein (EGFP). We recently reported a significant attenuation of PRV-152 labeling of the intermediolateral cell column (IML) and celiac ganglia after complete T4 spinal cord transection versus sham injury in rats at 96 h after PRV-152 inoculation of the left kidney. Here we found a significant increase in noxious colorectal distention (CRD)-evoked c-Fos expression in spinal cords of injured versus sham rats without PRV infection. In order to assess whether enhancing neuronal activity in spinalized rats might increase PRV-152 labeling, we subjected awake spinalized rats to 1.5 h of intermittent noxious CRD either: (1) just prior to inoculation, or (2) 96 h after inoculation (n = 3/group). Equal numbers of spinalized rats in both groups received PRV-152 inoculations without CRD (non-stimulated; n = 3/group). At 96 h post-inoculation fixed spinal cords and left celiac ganglionic tissues were assessed for the distribution and quantification of EGFP-labeled cells. The injured cohort that received CRD just prior to PRV injection showed a significant reduction in EGFP-labeled cells in both the IML and left celiac ganglion compared to non-stimulated injured rats. In contrast, the injured cohort that received CRD 96 h after PRV-152 inoculation showed no differences in EGFP-labeled cell numbers in the IML or celiac ganglia versus non-stimulated injured rats. Interestingly, microglia near c-Fos-positive cells after acute CRD appeared more reactive compared to non-stimulated spinalized rats, and activated microglial cells markedly reduce viral transduction and progression following PRV inoculation of the CNS. Hence our results imply that increased CRD-induced c-Fos expression in the injured paradigm, prior to but not after PRV injection, further attenuates PRV-152 uptake, perhaps through changes in neuronal activity and/or innate neuro-immune responses.

Distinct patterns of neuronal inputs and outputs of the juxtaparaventricular and suprafornical regions of the lateral hypothalamic area in the male rat

We have analyzed at high resolution the neuroanatomical connections of the juxtaparaventricular region of the lateral hypothalamic area (LHAjp); as a control and in comparison to this, we also performed a preliminary analysis of a nearby LHA region that is dorsal to the fornix, namely the LHA suprafornical region (LHAs). The connections of these LHA regions were revealed with a coinjection tract-tracing technique involving a retrograde (cholera toxin B subunit) and anterograde (Phaseolus vulgaris leucoagglutinin) tracer. The LHAjp and LHAs together connect with almost every major division of the cerebrum and cerebrospinal trunk, but their connection profiles are markedly different and distinct. In simple terms, the connections of the LHAjp indicate a possible primary role in the modulation of defensive behavior; for the LHAs, a role in the modulation of ingestive behavior is suggested. However, the relation of the LHAjp and LHAs to potential modulation of these behaviors, as indicated by their neuroanatomical connections, appears to be highly integrative as it includes each of the major functional divisions of the nervous system that together determine behavior, i.e., cognitive, state, sensory, and motor. Furthermore, although a primary role is indicated for each region with respect to a particular mode of behavior, intermode modulation of behavior is also indicated. In summary, the extrinsic connections of the LHAjp and LHAs (so far as we have described them) suggest that these regions have a profoundly integrative role in which they may participate in the orchestrated modulation of elaborate behavioral repertoires.

Evolutionary sequence modeling for discovery of peptide hormones

There are currently a large number of "orphan" G-protein-coupled receptors (GPCRs) whose endogenous ligands (peptide hormones) are unknown. Identification of these peptide hormones is a difficult and important problem. We describe a computational framework that models spatial structure along the genomic sequence simultaneously with the temporal evolutionary path structure across species and show how such models can be used to discover new functional molecules, in particular peptide hormones, via cross-genomic sequence comparisons. The computational framework incorporates a priori high-level knowledge of structural and evolutionary constraints into a hierarchical grammar of evolutionary probabilistic models. This computational method was used for identifying novel prohormones and the processed peptide sites by producing sequence alignments across many species at the functional-element level. Experimental results with an initial implementation of the algorithm were used to identify potential prohormones by comparing the human and non-human proteins in the Swiss-Prot database of known annotated proteins. In this proof of concept, we identified 45 out of 54 prohormones with only 44 false positives. The comparison of known and hypothetical human and mouse proteins resulted in the identification of a novel putative prohormone with at least four potential neuropeptides. Finally, in order to validate the computational methodology, we present the basic molecular biological characterization of the novel putative peptide hormone, including its identification and regional localization in the brain. This species comparison, HMM-based computational approach succeeded in identifying a previously undiscovered neuropeptide from whole genome protein sequences. This novel putative peptide hormone is found in discreet brain regions as well as other organs. The success of this approach will have a great impact on our understanding of GPCRs and associated pathways and help to identify new targets for drug development.

Noradrenergic axon terminals contact gastric preautonomic neurons in the paraventricular nucleus of the hypothalamus in rats

Hypothalamic neural activity is modulated by viscerosensory signals that are carried in large part by noradrenergic (NA) inputs to the paraventricular nucleus of the hypothalamus (PVN). The present study examined the ultrastructural relationship of NA axon varicosities with the somata and dendrites of identified gastric preautonomic PVN neurons in adult male rats. NA varicosities were visualized by immunoperoxidase labeling of dopamine beta hydroxylase (DbH), and gastric preautonomic PVN neurons were identified by immunogold labeling of pseudorabies virus (PRV) transported retrogradely and transneuronally from injection sites in the stomach wall. Among 1,136 DbH-positive varicosities identified within the parvocellular PVN in four rats, approximately 36% formed either a close apposition or a synaptic contact with a somatic or dendritic profile. The majority of identified contacts between DbH- and PRV-positive profiles were classified as close appositions that lacked clear synaptic specializations. Approximately 65% of identified synaptic contacts between DbH- and PRV-positive profiles were classified as symmetric (Gray's type II) synapses. DbH-positive terminals formed close appositions and synaptic contacts with dendritic and somatic compartments of PRV-positive neurons, although dendrites were contacted nearly five times more often than somata. These findings invite continued work to delineate the functional role of NA signaling pathways in conveying interoceptive signals to preautonomic PVN neurons under normal and pathophysiological conditions.

Projections from bed nuclei of the stria terminalis, dorsomedial nucleus: implications for cerebral hemisphere integration of neuroendocrine, autonomic, and drinking responses

The overall projection pattern of a tiny bed nuclei of the stria terminalis anteromedial group differentiation, the dorsomedial nucleus (BSTdm), was analyzed with the Phaseolus vulgaris-leucoagglutinin anterograde pathway tracing method in rats. Many brain regions receive a relatively moderate to strong input from the BSTdm. They fall into eight general categories: humeral sensory-related (subfornical organ and median preoptic nucleus, involved in initiating drinking behavior and salt appetite), neuroendocrine system (magnocellular: oxytocin, vasopressin; parvicellular: gonadotropin-releasing hormone, somatostatin, thyrotropin-releasing hormone, corticotropin-releasing hormone), central autonomic control network (central amygdalar nucleus, BST anterolateral group, descending paraventricular hypothalamic nucleus, retrochiasmatic area, ventrolateral periaqueductal gray, Barrington's nucleus), hypothalamic visceromotor pattern-generator network (five of six known components), behavior control column (ingestive: descending paraventricular nucleus; reproductive: lateral medial preoptic nucleus; defensive: anterior hypothalamic nucleus; foraging: ventral tegmental area, along with interconnected nucleus accumbens and substantia innominata), orofacial motor control (retrorubral area), thalamocortical feedback loops (paraventricular, central medial, intermediodorsal, and medial mediodorsal nuclei; nucleus reuniens), and behavioral state control (subparaventricular zone, ventrolateral preoptic nucleus, tuberomammillary nucleus, supramammillary nucleus, lateral habenula, and raphé nuclei). This pattern of axonal projections, and what little is known of its inputs suggest that the BSTdm is part of a striatopallidal differentiation involved in coordinating the homeostatic and behavioral responses associated thirst and salt appetite, although clearly it may relate them to other functions as well. The BSTdm generates the densest known inputs directly to the neuroendocrine system from any part of the cerebral hemispheres.

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.

Time-dependent alterations in mRNA expression of brain neuropeptides regulating energy balance and hypothalamo-pituitary-adrenal activity after withdrawal from intermittent morphine treatment

Chronic stressors alter brain function and may leave traces after their relief. We used intermittent morphine treatment to examine the relationships between stress-induced changes in energy balance and hypothalamo-pituitary-adrenal (HPA) activity and the recovery thereafter. We studied the effects of morphine injections on energy balance, hormones and fat stores, brain neuropeptide expression, and the ACTH and corticosterone responses to restraint 12 hr after the final injection and 8 d later during recovery. Weight gain, food intake, and caloric efficiency decreased at morphine onset, and these were maintained throughout the morphine injections. At 12 hr, fat stores, leptin, insulin, and testosterone concentrations were reduced. Subsequently, body weight gain and food intake increased and caloric efficiency was above control during the final days. By the eighth recovery day, fat stores and peripheral hormones were no longer depressed. At 12 hr, an over-response of CRF mRNA to restraint occurred in the hypothalamus, similar to the facilitated ACTH and corticosterone responses. On day 8, the hypothalamic CRF mRNA response to restraint was still facilitated, opposite to inhibited ACTH responses. Hypothalamic CRF mRNA correlated highly with mesenteric fat weight in morphine-treated rats. We conclude that there is a prolonged recovery from chronic stressors involving interrelated changes in energy balance and HPA activity. Nonetheless, 8 d after withdrawal from morphine, rats still display facilitated central stress responses, similar to the HPA symptoms described in posttraumatic stress disorder patients. Repeated partial withdrawal associated with intermittent morphine treatment, compounded by complete withdrawal associated with termination of the treatment, is likely required for these metabolic and HPA derangements.

Identification of neural pathways involved in genital reflexes in the female: a combined anterograde and retrograde tracing study

The medial preoptic area (MPOA) is important for reproductive behavior in females. However, the descending pathways mediating these responses to the spinal motor output are unknown. The MPOA does not directly innervate the spinal cord. Therefore, pathways mediating MPOA-induced changes in sexual behavior must relay in the brain. The nucleus paragigantocellularis (nPGi) projects heavily to spinal circuits involved in female sexual reflexes and is involved in the tonic inhibition of genital reflexes. However, the periaqueductal gray (PAG) is also important for female sexual behavior. The present study examined the hypothesis that the MPOA output relays through PAG and the nPGi before descending to the spinal cord. We used anterograde and retrograde tracing techniques to examine the descending pathways and relay sites from the MPOA to the spinal cord and the nPGi in the female rat. Injection of biotinylated dextran amine into the MPOA produced dense labeling in specific regions of the PAG and Barrington's nucleus; anterogradely labeled fibers terminated close to neurons retrogradely labeled from the spinal cord in the PAG, Barrington's nucleus, nPGi, lateral hypothalamus and paraventricular nucleus (PVN). Anterogradely labeled fibers and varicosities were also found close to neurons retrogradely labeled from the nPGi in the PAG, lateral hypothalamus and PVN. These results suggest that the major MPOA output relays in the PAG and nPGi before descending to innervate spinal circuits regulating female genital reflexes and that the MPOA plays a multifaceted role in female reproductive behavior through its modulation of PAG output systems.

Serotonergic collateralized projections from Barrington's nucleus to the medial preoptic area and lumbo-sacral spinal cord

In this study, we employed triple fluorescent labelling to reveal the distribution of the direct serotonergic neurons within Barrington's nucleus (BN) that supply branching collateral input to the medial preoptic area (MPA) and to the lumbo-sacral spinal cord (LSC). Immunocytochemical detection of the monoclonal antibody raised against serotonin was used for identification of the neurons. The projections were defined by injections of two retrograde tracers: fluoro gold and rhodamine in the MPA and LSC, respectively. The aim of this study is to identify the direct projections to BN and MPA and/or LSC. The present study confirms findings of others describing BN-LSC projections and extends previous findings by demonstrating an single or collateralized fibers with MPA, and serotonergic immunoreactive fibers.

Dual viral transneuronal tracing of central autonomic circuits involved in the innervation of the two kidneys in rat

The neural control of renal function is exerted by the central nervous system via sympathetic innervation of the kidneys. To determine the extent to which the control of the two kidneys is provided by the same brain neurons, the central circuitry involved in the innervation of both kidneys was characterized in individual rats by dual viral transneuronal tracing using isogenic recombinant strains (PRV-152 and BaBlu) of pseudorabies virus. Prior to dual tracing, the neuroinvasive properties of PRV-152 and BaBlu were characterized by conducting parametric studies, using the two kidneys as an anatomical model, and comparing the pattern of infection with that obtained following injection of the parental strain, PRV-Bartha, into the left kidney. Once the optimal concentrations of virus required to obtain equivalent infection were established, PRV-152 and BaBlu were injected into the left and right kidney, respectively, in the same rats. Immunocytochemical localization of viral reporter proteins at different postinoculation times allowed us to determine the sequence of infection in the brain, as well as to quantify dual- and single-labeled neurons in each infected area. Neurons that influence autonomic outflow to one or both kidneys coexist in all brain areas involved in the control of the sympathetic outflow to the kidneys at every hierarchical level of the circuit. The proportions of dual-infected neurons with respect to the number of total infected neurons varied across regions, but they were maintained at different survival times. The pattern of infection suggests that the activity of each kidney is controlled independently by organ-specific neurons, whereas the functional coordination of the two kidneys results from neurons that collaterize to modulate the sympathetic outflow to both organs. The advantages of using an anatomical symmetrical system, such as the two kidneys, as an experimental approach to characterize PRV recombinants in general are also discussed.

Projections from bed nuclei of the stria terminalis, posterior division: implications for cerebral hemisphere regulation of defensive and reproductive behaviors

The posterior division of the bed nuclei of the stria terminalis has three major nuclei: principal, interfascicular, and transverse, which receive topographically ordered inputs from the medial amygdalar nucleus. The overall pattern of axonal projections from each nucleus was determined in male rats with the Phaseolus vulgaris-leucoagglutinin method. Together, these nuclei project topographically back to the medial amygdalar nucleus, to the adjacent lateral septal nucleus, to the nucleus accumbens and substantia innominata, to hypothalamic parts of the behavior control column, and to the hypothalamic periventricular region, which controls patterned neuroendocrine and autonomic responses. The principal nucleus preferentially innervates septal and hypothalamic regions that control reproductive behavior and visceromotor responses, confirming a similar analysis by Gu et al. (J Comp Neurol [2003] 460:542-562). In contrast, the interfascicular and transverse nuclei differentially innervate septal and hypothalamic regions that control defensive as well as reproductive behaviors. In addition, the transverse nucleus projects significantly to midbrain parts of the behavior control column concerned with foraging/exploratory behavior. All three posterior division nuclei also project to thalamocortical feedback loops (by means of the nucleus reuniens and paraventricular nucleus). These structural data may be interpreted to suggest that the bed nuclei posterior division forms part (pallidal) of a corticostriatopallidal system involved in controlling two major classes of social (defensive and reproductive) behavior.

Convergent responses of Barrington's nucleus neurons to pelvic visceral stimuli in the rat: a juxtacellular labelling study

Barrington's nucleus impacts on bladder and distal colon function and relays pelvic visceral information to the forebrain. This study investigated processing of information from the bladder and the distal colon by Barrington's nucleus in the rat. The responses of individual Barrington's nucleus neurons to bladder and/or colon distention were characterized using extracellular recording and the recorded neurons were identified using juxtacellular labelling. Most neurons within Barrington's nucleus (79%) were activated by bladder distention, consistent with its role as a pontine micturition centre. Although no neurons were selectively responsive to colon distention, the majority of bladder-responsive neurons (73%) were also activated by colon distention. In a second study, Barrington's nucleus neurons were characterized with respect to their response to colon distention and their immunoreactivity for the stress-related neuropeptide corticotropin-releasing factor (CRF). Of 30 labelled neurons in the central part of Barrington's nucleus, 53% were activated by colon distention and 63% of these were CRF-ir. This is the first report demonstrating that Barrington's nucleus neurons are responsive to colon distention. The results provide evidence for convergence of information from the bladder and the colon onto individual Barrington's nucleus neurons. Taken with evidence that many Barrington's nucleus neurons are synaptically linked to the bladder and colon, the present study suggests a role for these neurons in coordinating peripheral parasympathetic and central responses to both viscera and implicate CRF as a neurotransmitter in this function. Dysfunctions in this circuit may underlie the coexistence of colon and bladder symptoms observed in functional bowel disorders.

Central representation of bladder and colon revealed by dual transsynaptic tracing in the rat: substrates for pelvic visceral coordination

The neurocircuitry underlying regulation of bladder and distal colon function by Barrington's nucleus (the pontine micturition centre) was investigated in rats by identifying neurons which were transsynaptically labelled from these viscera, with pseudorabies virus (PRV) or genetically modified forms of PRV [PRV-beta-galactosidase (PRV-beta-Gal) and PRV-green fluorescent protein (PRV-GFP)]. PRV injection into the bladder or the colon of separate rats suggested an overlap in the distribution of bladder- and colon-related neurons in Barrington's nucleus, as well as a topographical arrangement whereby dorsal neurons were bladder-related and ventral neurons were colon-related. In rats injected with PRV-beta-Gal into one viscera and PRV-GFP into another, neurons in the major pelvic ganglion and lumbosacral spinal cord were primarily single-labelled at relatively early survival times. With longer survival times many double-labelled neurons (>70%) appeared in Barrington's nucleus, suggesting that individual Barrington's nucleus neurons are synaptically linked to preganglionic parasympathetic neurons which independently innervate the colon or the bladder. In addition to these dual-labelled neurons, Barrington's nucleus neurons which were single-labelled from either viscera were observed and these exhibited a viscerotopic organization consistent with the single-labelling studies. Together, these findings suggest the existence of three neuronal populations in Barrington's nucleus, one which is synaptically linked to both the bladder and the colon and the other two populations which are specifically linked to either viscera. These anatomical substrates may underlie the central coordination of bladder and colon function and play a role in disorders characterized by a coexistence of bladder and colonic symptoms.

Intermittent morphine administration induces dependence and is a chronic stressor in rats

Although constant treatment with morphine (implanted pellets) does not activate the hypothalamic-pituitary-adrenal (HPA) axis, intermittent injections of morphine may constitute a chronic stressor in rats. To test this hypothesis, we compared the effects of morphine in escalating doses (10-40 mg/kg, s.c.) or saline injected twice daily for 4 days on energy balance, hormones, HPA responses to novel restraint and central corticotropin-releasing factor (CRF) mRNA 12 h and 8 days after the last morphine injection in adult male Sprague-Dawley rats. Weight gain stopped at the onset of morphine, weight loss was marked 36 h postmorphine; thereafter, body weight gain paralleled saline controls. At 12 h, insulin, leptin, and testosterone concentrations were reduced but normalized by 8 days. Restraint and tail nicks caused facilitated ACTH responses at 12 h, under-responsiveness at 8 days. CRF mRNA, measured only at 12 h, was increased in the paraventricular (PVN) and Barrington's nuclei (BAR), decreased in the bed nuclei of the stria terminalis (BNST) and unchanged in the amygdala (CeA) in morphine-treated rats. After stress, CRF mRNA increased in PVN in both groups, increased in BAR and decreased in BNST in saline but not morphine groups, and was unchanged in CeA in both groups. Results from all variables characterize intermittent morphine injections as a chronic stressor. In contrast to constant treatment, injected morphine probably allows some withdrawal during each 12 h interval, causing repeated stress. Drug addicts treat themselves intermittently, and stress causes relapse after withdrawal. Thus, intermittent morphine, itself, may promote relapse.

Voluntary freewheel running selectively modulates catecholamine content in peripheral tissue and c-Fos expression in the central sympathetic circuit following exposure to uncontrollable stress in rats

Modulation of sympathetic drive to the spleen is one potential mechanism whereby physical activity prevents stress-induced splenic immune suppression in rats. The current study tested the hypothesis that voluntary freewheel running reduces peripheral sympathetic drive by modulating stress-induced activity of brain regions synaptically linked to sympathetically innervated peripheral organs, including the adrenals and spleen. To this end, adrenal and splenic catecholamine content and activity of the central sympathetic circuit indexed by c-Fos protein induction, elicited by acute exposure to inescapable tail shock, were measured. Stressor exposure depleted adrenal and splenic norepinephrine content and elicited a robust increase in c-Fos in the brains of sedentary rats. Physical activity status had no effect on adrenal norepinephrine content. Indicative of attenuated sympathetic drive to the spleen, however, 6 weeks of voluntary freewheel running diminished stress-induced splenic norepinephrine depletion, and significantly attenuated stress-induced c-Fos in specific brain regions responsible for sympathetic regulation, including tyrosine hydroxylase-immunoreactive neurons of the locus coeruleus, A5 cell group and rostral ventrolateral medulla. Results suggest that voluntary activity attenuates sympathetic drive to the spleen during stressor exposure by selectively modulating stress-induced activity of the central sympathetic circuit. The attenuation of sympathetic responses observed in this study may be one important mechanism for the protective effect of physical activity against stress-related illness and immunosuppression.

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.

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.

Efferent control of different visceral pelvic organs by spinal and supraspinal centres

A growing number of patients with pelvic organ dysfunction and failing response to standard treatment concepts are referred to special neuro-urology services. New therapeutic options are available, such as unilateral and bilateral sacral nerve stimulation, and the use of different neurotoxins for the overactive bladder. However, a lack of knowledge and understanding in central innervation and modulation of pelvic organ function prevents a striking progress in this clinical area. A concept of efferent innervation of pelvic organs based on experimental animal studies, using the retrograde, transneuronal and self-amplifying tracer Pseudorabiesvirus, is discussed in a clinical context.

Modifications to central neural circuitry during heart failure

AIM

During heart failure (HF), excess sodium retention is triggered by increased plasma renin-angiotensin-aldosterone activity and increased basal sympathetic nerve discharge (SND). Enhanced basal SND in the renal nerves plays a role in sodium retention. Therefore, as a hypothetical model for the central sympathetic control pathways that are dysregulated as a consequence of HF, the central neural pathways regulating the sympathetic motor output to the kidney are reviewed in the context of their role during HF.

CONCLUSION

From these findings, a model of the neuroanatomical circuitry that may be affected during HF is constructed.

Spinal cord neural organization controlling the urinary bladder and striated sphincter

The storage and elimination of urine requires the coordination of activity between the autonomic nervous system (thoracolumbar sympathetic and sacral parasympathetic divisions) controlling the urinary bladder and urethra and the lumbosacral somatic motoneurons innervating the striated sphincter and pelvic floor muscles. These three efferent systems involved in the control of lower urinary tract function receive segmental sensory information from various visceral organs and the perineum, as well as inputs from supraspinal regions. Ascending and descending connections between the various spinal segments levels and supraspinal regions provide the reflex substrates participating in normal bladder continence and micturition reflexes. Many of the actions of descending and segmental reflexes are mediated by excitatory and inhibitory sacral spinal interneurons located within the region of the parasympathetic preganglionic autonomic neurons and the sphincter ventral horn motoneurons. This review will: (1) discuss the basic organization and spinal elements of the reflex pathways subserving continence and micturition; (2) describe features of the identified sacral interneuronal circuitry contributing to the control of the bladder and sphincter function; and (3) discuss how changes in the control of these reflex pathways and neurons may contribute to abnormal patterns of bladder and sphincter function commonly observed following spinal cord injury.

The locus coeruleus, Barrington's nucleus, and neural circuits of stress

Much attention has focused on the role of the locus coeruleus (LC) as a component of the central neural circuitry involved in stress. Many, though not all, stressful stimuli produce activation of LC neurons, as reflected by increased Fos expression in these neurons. Stimulation of the LC elicits many stress-like responses, including increased ACTH secretion, though not all responses to LC stimulation are readily interpretable in the context of stress. In particular, stimulation of the LC, at least in anesthetized rats, elicits a decrease in blood pressure and heart rate. Inhibition of the LC has been reported to inhibit certain responses to stress, including inhibition of ACTH release in response to certain stressors. Furthermore, local inhibition of the LC prevents foot shock-evoked Fos expression in certain brain areas. In the studies of the role of the LC in stress, one complicating factor has been the inadequate attention given to Barrington's nucleus (BN), which is located adjacent to the LC. Although BN is best recognized for its role in the control of micturition, the fact that it is activated by a great variety of stressful stimuli, and that it is anatomically connected to multiple output systems involved in stress responses, suggest that it may play a role in the neural circuitry subserving responses to stress.

Fos expression in non-catecholaminergic neurons in medullary and pontine nuclei after volume depletion induced by polyethylene glycol

Fos immunocytochemistry was combined with immunolabeling for dopamine-beta-hydroxylase (DBH) to examine neuronal activation in the medulla and pons after administration of polyethelene glycol (PEG), which produces volume depletion without altering arterial blood pressure. Increased Fos immunoreactivity was observed in the area postrema, nucleus of the solitary tract, rostral ventrolateral medulla, lateral parabrachial nucleus, and the dorsomedial pons at the level of the locus coeruleus. Fos immunolabeling in the caudal nucleus of the solitary tract, rostral ventrolateral medulla, and the dorsomedial pons occurred primarily in neurons that did not contain DBH. Thus, PEG activates non-catecholaminergic neurons in medullary and pontine areas associated with cardiovascular and body fluid regulation.

Characterization of the central nervous system innervation of the rat spleen using viral transneuronal tracing

Splenic immune function is modulated by sympathetic innervation, which in turn is controlled by inputs from supraspinal regions. In the present study, the characterization of central circuits involved in the control of splenic function was accomplished by injecting pseudorabies virus (PRV), a retrograde transynaptic tracer, into the spleen and conducting a temporal analysis of the progression of the infection from 60 hours to 110 hours postinoculation. In addition, central noradrenergic cell groups involved in splenic innervation were characterized by dual immunohistochemical detection of dopamine-beta-hydroxylase and PRV. Infection in the CNS first appeared in the spinal cord. Splenic sympathetic preganglionic neurons, identified in rats injected with Fluoro-Gold i.p. prior to PRV inoculation of the spleen, were located in T(3)-T(12) bilaterally; numerous infected interneurons were also found in the thoracic spinal cord (T(1)-T(13)). Infected neurons in the brain were first observed in the A5 region, ventromedial medulla, rostral ventrolateral medulla, paraventricular hypothalamic nucleus, Barrington's nucleus, and caudal raphe. At intermediate survival times, the number of infected cells increased in previously infected areas, and infected neurons also appeared in lateral hypothalamus, A7 region, locus coeruleus, subcoeruleus region, nucleus of the solitary tract, and C3 cell group. At longer postinoculation intervals, infected neurons were found in additional hypothalamic areas, Edinger-Westphal nucleus, periaqueductal gray, pedunculopontine tegmental nucleus, caudal ventrolateral medulla, and area postrema. These results demonstrate that the sympathetic outflow to the spleen is controlled by a complex multisynaptic pathway that involves several brainstem and forebrain nuclei.

Contributions of the medullary raphe and ventromedial reticular region to pain modulation and other homeostatic functions

The raphe magnus is part of an interrelated region of medullary raphe and ventromedial reticular nuclei that project to all areas of the spinal gray. Activation of raphe and reticular neurons evokes modulatory effects in sensory, autonomic, and motor spinal processes. Two physiological types of nonserotonergic cells are observed in the medullary raphe and are thought to modulate spinal pain processing in opposing directions. Recent evidence suggests that these cells may modulate stimulus-evoked arousal or alerting rather than pain-evoked withdrawals. Nonserotonergic cells are also likely to modulate spinal autonomic and motor circuits involved in thermoregulation and sexual function. Medullary serotonergic cells have state-dependent discharge and are likely to contribute to the modulation of pain processing, thermoregulation, and sexual function in the spinal cord. The medullary raphe and ventromedial reticular region may set sensory, autonomic, and motor spinal circuits into configurations that are appropriate to the current behavioral state.

Increased plasma norepinephrine concentration in cats with interstitial cystitis

PURPOSE

Interstitial cystitis is a chronic urological syndrome affecting humans and domestic animals, including cats (feline interstitial cystitis). The symptoms of interstitial cystitis seem to be exacerbated by stress, suggesting involvement of the sympathetic nervous system and/or hypothalamic-pituitary-adrenal axis. Others have described sympathetic nervous system abnormalities in patients with interstitial cystitis but to our knowledge no data on plasma catecholamine concentrations or hypothalamic-pituitary-adrenal axis function in such patients have been reported. To evaluate the role of these systems in cats with feline interstitial cystitis we simultaneously measured baseline plasma concentrations of catecholamines and their metabolites to assess sympathetic activity, and the response of plasma adenocorticotropic hormone and cortisol concentrations to the infusion of corticotropin-releasing factor.

MATERIALS AND METHODS

Eight healthy cats and 8 with feline interstitial cystitis were anesthetized and a catheter was placed in the external jugular vein. Four hours after recovery samples were obtained for high performance liquid chromatography analysis of plasma norepinephrine, dihydroxyphenylglycol, epinephrine, dihydroxyphenylalanine, dopamine and dihydroxyphenylacetic acid. In 4 cats per group 1 microg. ovine corticotropin-releasing factor per kg. body weight was infused and blood samples were collected at intervals for 120 minutes for determining adenocorticotropic hormone and cortisol.

RESULTS

Significant increases in plasma norepinephrine and dihydroxyphenylglycol as well as a trend toward increased epinephrine were found, whereas no effect on dihydroxyphenylalanine, dopamine, dihydroxyphenylacetic acid, adenocorticotropic hormone or cortisol was identified in cats with feline interstitial cystitis.

CONCLUSIONS

These results support and extend previous studies identifying an increase in sympathetic activity in cats with feline interstitial cystitis.