Preoptic projections to Barrington's nucleus and the pericoerulear region: architecture and terminal organization

Somatostatin Neurons in the Mouse Pontine Nucleus Activate GABAA Receptor Mediated Synaptic Currents in Locus Coeruleus Neurons

The pontine nuclei comprising the locus coeruleus (LC) and Barrington’s nucleus (BRN) amongst others form the neural circuitry(s) that coordinates arousal and voiding behaviors. However, little is known about the synaptic connectivity of neurons within or across these nuclei. These include corticotropin-releasing factor (CRF⁺) expressing neurons in the BRN that control bladder contraction and somatostatin expressing (SST⁺) neurons whose role in this region has not been discerned. To determine the synaptic connectivity of these neurons, we employed optogenetic stimulation with recordings from BRN and LC neurons in brain stem slices of channelrhodopsin-2 expressing SST or CRF neurons. Optogenetic stimulation of CRF⁺ BRN neurons of Crf^Cre;chr2-yfp mice had little effect on either CRF⁺ BRN neurons, CRF^– BRN neurons, or LC neurons. In contrast, in Sst^Cre;chr2-yfp mice light-activated inhibitory postsynaptic currents (IPSCs) were reliably observed in a majority of LC but not BRN neurons. The GABA_A receptor antagonist, bicuculline, completely abolished the light-induced IPSCs. To ascertain if these neurons were part of the neural circuitry that controls the bladder, the trans-synaptic tracer, pseudorabies virus (PRV) was injected into the bladder wall of Crf^Cre;tdTomato or Sst^Cre;tdTomato mice. At 68–72 h post-viral infection, PRV labeled neurons were present only in the BRN, being preponderant in CRF⁺ neurons with few SST⁺ BRN neurons labeled from the bladder. At 76 and 96 h post-virus injection, increased labeling was observed in both BRN and LC neurons. Our results suggest SST⁺ neurons rather than CRF⁺ neurons in BRN can regulate the activity of LC neurons.

The Brain and the Bladder: Forebrain Control of Urinary (In)Continence

Neural circuits extending from the cerebral cortex to the bladder maintain urinary continence and allow voiding when it is socially appropriate. Injuries to certain brain regions produce a specific disruption known as urge incontinence. This neurologic symptom is distinguished by bladder spasticity, with sudden urges to void and frequent inability to maintain continence. The precise localization of neural circuit disruptions responsible for urge incontinence remains poorly defined, partly because the brain regions, cell types, and circuit connections that normally maintain continence are unknown. Here, we review what is known about the micturition reflex circuit and about forebrain control of continence from experimental animal studies and human lesion data. Based on this information, we hypothesize that urge incontinence results from damage to a descending pathway that normally maintains urinary continence. This pathway begins with excitatory neurons in the prefrontal cortex and relays subcortically, through inhibitory neurons that may help suppress reflex micturition during sleep and until it is safe and socially appropriate to void. Identifying the specific cell types and circuit connections that constitute the continence-promoting pathway, from the forebrain to the brainstem, will help us better understand why some brain lesions and neurodegenerative diseases disrupt continence. This information is needed to pave the way toward better treatments for neurologic patients suffering from urge incontinence.

Barrington's nucleus: Neuroanatomic landscape of the mouse "pontine micturition center"

Barrington's nucleus (Bar) is thought to contain neurons that trigger voiding and thereby function as the "pontine micturition center." Lacking detailed information on this region in mice, we examined gene and protein markers to characterize Bar and the neurons surrounding it. Like rats and cats, mice have an ovoid core of medium-sized Bar neurons located medial to the locus coeruleus (LC). Bar neurons express a GFP reporter for Vglut2, develop from a Math1/Atoh1 lineage, and exhibit immunoreactivity for NeuN. Many neurons in and around this core cluster express a reporter for corticotrophin-releasing hormone (BarCRH ). Axons from BarCRH neurons project to the lumbosacral spinal cord and ramify extensively in two regions: the dorsal gray commissural and intermediolateral nuclei. BarCRH neurons have unexpectedly long dendrites, which may receive synaptic input from the cerebral cortex and other brain regions beyond the core afferents identified previously. Finally, at least five populations of neurons surround Bar: rostral-dorsomedial cholinergic neurons in the laterodorsal tegmental nucleus; lateral noradrenergic neurons in the LC; medial GABAergic neurons in the pontine central gray; ventromedial, small GABAergic neurons that express FoxP2; and dorsolateral glutamatergic neurons that express FoxP2 in the pLC and form a wedge dividing Bar from the dorsal LC. We discuss the implications of this new information for interpreting existing data and future experiments targeting BarCRH neurons and their synaptic afferents to study micturition and other pelvic functions.

Neuropeptide S and Its Receptor: A Newly Deorphanized G Protein–Coupled Receptor System

Neuropeptide S (NPS) is a recently discovered bioactive peptide that has shed new light on the neurobiology of sleep/wakefulness regulation and anxiety-like behavior. NPS can potently promote arousal and suppress all stages of sleep. This effect might be modulated by NPS receptors expressed in thalamic centers that are relays for transmitting arousing stimuli originating from the brainstem to the cortex. The peptide precursor is expressed most prominently in a novel nucleus located directly adjacent to the nora-drenergic locus coeruleus, a brain structure with well-defined functions in arousal, stress, and anxiety. NPS was also found to induce anxiolytic-like behavior in a battery of four different tests of innate responses to stress. This unique pharmacological profile of NPS offers significant potential for developing new drugs for the treatment of sleep and/or anxiety disorders.

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.

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.

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.

Role of the lateral preoptic area and the bed nucleus of stria terminalis in the regulation of penile erection

To elucidate the role of the preoptic area (POA) in the regulation of penile erection, we examined the effects of electrical stimulation in and around the POA on penile erection in rats, which was assessed by changes in pressure in the corpus spongiosum of the penis (CSP) and electromyography (EMG) of the bulbospongiosus (BS) muscle. In unanesthetized and anesthetized rats, four types of responses were induced by stimulation in and around the POA; (1) normal type responses, which were similar to spontaneously occurring erections, characterized by slow increase in CSP pressure and sharp peaks concurrent with BS muscle bursting; (2) muscular type responses, which included sharp CSP pressure peaks (muscular component) with almost no vascular component; (3) mixed type responses, which included a sequence of high-frequency CSP peaks followed by low-frequency CSP peaks; and (4) micturition type responses, which had higher-frequency and lower-amplitude CSP peaks than other responses which were identical to those of normal micturition. In unanesthetized condition, erections were evoked by stimulation of the lateral preoptic area (LPOA), medial preoptic area (MPOA), bed nucleus of the stria terminalis (BST), paraventricular nucleus (PVN), reuniens thalamic nucleus (Re) and lateral septum (LS). Lower-intensity stimulation evoked erections from the LPOA, BST, PVN and RE, but not the MPOA. In anesthetized condition, stronger stimuli were required and effective sites were restricted to the LPOA, MPOA and BST. These findings suggest that the lateral and medial subdivisions of the preoptic area play different roles in mediating penile erection.

Dissecting natural sensory plasticity: hormones and experience in a maternal context

There is a growing consensus that the auditory system is dynamic in its representation of behaviorally relevant sounds. The auditory cortex in particular seems to be an important locus for plasticity that may reflect the memory of such sounds, or functionally improve their processing. The mechanisms that underlie these changes may be either intrinsic because they depend on the receiver's physiological state, or extrinsic because they arise from the context in which behavioral relevance is gained. Research in a mouse model of acoustic communication between offspring and adult females offers the opportunity to explore both of these contributions to auditory cortical plasticity in a natural context. Recent works have found that after the vocalizations of infant mice become behaviorally relevant to mothers, auditory cortical activity is significantly changed in a way that may improve their processing. Here we consider the hypothesis that maternal hormones (intrinsic factor) and sensory experience (extrinsic factor) contribute together to drive these changes, focusing specifically on the evidence that well-known experience-dependent mechanisms of cortical plasticity can be modulated by hormones.

Estrogen-sensitive projections from the medial preoptic area to the dorsal pontine tegmentum, including Barrington's nucleus, in the rat

AIM

Urinary incontinence affects a significant number of post-menopausal women. There is conflicting evidence whether voiding symptoms in these women are related to hypoestrogenism or aging itself. This neuroanatomical study was designed to determine whether a specific central nervous system (CNS) pathway that projects to the pontine micturition center (PMC, also known as "Barrington's nucleus") is estrogen sensitive in a rat model.

METHODS

A fluorescent retrograde tracer was injected into the dorsal pontine tegmentum of adult female Sprague-Dawley rats to identify neurons in the medial preoptic area (MPA) that project to the PMC. Immunohistochemistry was performed using antibodies directed against estrogen receptor-alpha (ERalpha) and estrogen receptor-beta (ERbeta) to identify estrogen-sensitive neurons. The brain sections were examined using fluorescence microscopy to identify cells that project to the PMC (contain fluorescent tracer) and also express ER (are immunoreactive for ER).

RESULTS

There are neurons in the MPA that are double labeled (contain fluorescent tracer and express ERalpha, but not ERbeta), showing that a subset of neurons projecting from the MPA to the PMC is estrogen sensitive.

CONCLUSIONS

A subset of estrogen-sensitive neurons projects from the MPA to the PMC in rats, raising the possibility that indirect estrogenic regulation of forebrain neuronal function may modulate the micturition reflex. Future development of drugs that alter the function of this estrogen-sensitive CNS pathway may provide therapeutic strategies to treat post-menopausal incontinence.

Penile erection and micturition events triggered by electrical stimulation of the mesopontine tegmental area

The cholinergic neurons in the laterodorsal tegmental nucleus (LDT) play a crucial role in the regulation of rapid eye movement (REM) sleep. Because penile erection occurs during REM sleep, the involvement of the LDT in penile erection was examined in unanesthetized head-restrained rats. To detect penile erection, corpus spongiosum of the penis (CSP) pressure was measured through a telemetric device with simultaneous bulbospongiosum (BS) muscle EMG recording through stainless wires. Electrical stimulation in and around the LDT induced the following three CSP pressure patterns: 1) a full erection pattern indistinguishable from the nonevoked or spontaneous erection, characterized by a slow increase in CSP pressure with additional sharp CSP peaks associated with BS muscle bursts, 2) a muscular pattern characterized by sharp CSP pressure peaks but in the absence of a vascular component, i.e., without an increase in baseline CSP pressure, and 3) a mixed-type response characterized by high-frequency CSP pressure peaks followed by a full erection response. Full erections were evoked in and around the LDT, including more medially and ventrally. The sites for inducing mixed-type events were intermingled with the sites that triggered full erections in the anterior half of the LDT, whereas they were separated in the posterior half. The sites for muscular responses were lateral to the sites for full erections. Finally, a CSP pressure response identical to micturition was evoked in and around the Barrington's nucleus and in the dorsal raphe nucleus. These results suggest that the LDT and surrounding region are involved in the regulation of penile erection. Moreover, different anatomical areas in the mesopontine tegmentum may have specific roles in the regulation of penile erection and micturition.

Distribution of neuropeptide S receptor mRNA and neurochemical characteristics of neuropeptide S-expressing neurons in the rat brain

Neuropeptide S (NPS) and its receptor (NPSR) constitute a novel neuropeptide system that is involved in regulating arousal and anxiety. The NPS precursor mRNA is highly expressed in a previously undescribed group of neurons located between the locus coeruleus (LC) and Barrington's nucleus. We report here that the majority of NPS-expressing neurons in the LC area and the principal sensory trigeminal nucleus are glutamatergic neurons, whereas many NPS-positive neurons in the lateral parabrachial nucleus coexpress corticotropin-releasing factor (CRF). In addition, we describe a comprehensive map of NPSR mRNA expression in the rat brain. High levels of expression are found in areas involved in olfactory processing, including the anterior olfactory nucleus, the endopiriform nucleus, and the piriform cortex. NPSR mRNA is expressed in several regions mediating anxiety responses, including the amygdaloid complex and the paraventricular hypothalamic nucleus. NPSR mRNA is also found in multiple key regions of sleep neurocircuitries, such as the thalamus, the hypothalamus, and the preoptic region. In addition, NPSR mRNA is strongly expressed in major output and input regions of hippocampus, including the parahippocampal regions, the lateral entorhinal cortex, and the retrosplenial agranular cortex. Multiple hypothalamic nuclei, including the dorsomedial and the ventromedial hypothalamic nucleus and the posterior arcuate nucleus, express high levels of NPSR mRNA, indicating that NPS may regulate energy homeostasis. These data suggest that the NPS system may play a key role in modulating a variety of physiological functions, especially arousal, anxiety, learning and memory, and energy balance.

Parabrachial nucleus influences the control of normal urinary bladder function and the response to bladder irritation in rats

The contribution of the parabrachial nucleus to the mediation of bladder contraction was examined in the rat. Constant infusion (0.1 ml/min) of saline or 0.2% acetic acid evoked normal or abnormal bladder contractions, respectively. Single unit activity was recorded in the parabrachial nucleus with tungsten microelectrodes. Seven units with activity that was correlated with bladder contraction during saline infusion were located in the lateral subnuclei and three units were located in the medial subnuclei of the parabrachial nucleus. Twelve units with activity that was correlated with abnormal bladder contractions were found widely distributed in the parabrachial nucleus. An inverse correlation of activity to normal or abnormal bladder contractions was identified in 11 units in the parabrachial nucleus. Pressure injection of 5 mM CoCl(2) into the parabrachial nucleus was used to block synaptic transmission unilaterally. Normal bladder contractions evoked by saline infusion were disrupted by 5 of 10 injections, 4 of them in the medial subnuclei of the parabrachial nucleus and one in the lateral subnuclei. Abnormal bladder contractions were converted to a normal pattern in nine experiments where CoCl(2) injections lay in the lateral subnuclei of the parabrachial nucleus. In five experiments, CoCl(2) disrupted abnormal bladder contractions; four effective sites were located in the lateral subnucleus and one lay in the medial subnucleus of the parabrachial nucleus. These data demonstrated that single units responding to both normal and abnormal contractions were located throughout the parabrachial nuclei whereas the lateral subnuclei play a predominant role in mediation of abnormal bladder contractions and the medial subnuclei play a predominant role in the mediation of normal bladder contractions.

Projections from bed nuclei of the stria terminalis, magnocellular nucleus: implications for cerebral hemisphere regulation of micturition, defecation, and penile erection

The basic structural organization of axonal projections from the small but distinct magnocellular and ventral nuclei (of the bed nuclei of the stria terminalis) was analyzed with the Phaseolus vulgaris leucoagglutinin anterograde tract tracing method in adult male rats. The former's overall projection pattern is complex, with over 80 distinct terminal fields ipsilateral to injection sites. Innervated regions in the cerebral hemisphere and brainstem fall into nine general functional categories: cerebral nuclei, behavior control column, orofacial motor-related, humorosensory/thirst-related, brainstem autonomic control network, neuroendocrine, hypothalamic visceromotor pattern-generator network, thalamocortical feedback loops, and behavioral state control. The most novel findings indicate that the magnocellular nucleus projects to virtually all known major parts of the brain network that controls pelvic functions, including micturition, defecation, and penile erection, as well as to brain networks controlling nutrient and body water homeostasis. This and other evidence suggests that the magnocellular nucleus is part of a corticostriatopallidal differentiation modulating and coordinating pelvic functions with the maintenance of nutrient and body water homeostasis. Projections of the ventral nucleus are a subset of those generated by the magnocellular nucleus, with the obvious difference that the ventral nucleus does not project detectably to Barrington's nucleus, the subfornical organ, the median preoptic and parastrial nuclei, the neuroendocrine system, and midbrain orofacial motor-related regions.

Plateau Potentials in Developing Antennal-Lobe Neurons of the Moth,Manduca sexta

Using whole cell recordings from antennal-lobe (AL) neurons in vitro and in situ, in semi-intact brain preparations, we examined membrane properties that contribute to electrical activity exhibited by developing neurons in primary olfactory centers of the brain of the sphinx moth, Manduca sexta. This activity is characterized by prolonged periods of membrane depolarization that resemble plateau potentials. The presence of plateau potential–generating mechanisms was confirmed using a series of tests established earlier. Brief depolarizing current pulses could be used to trigger a plateau state. Once triggered, plateau potentials could be terminated by brief pulses of hyperpolarizing current. Both triggering and terminating of firing states were threshold phenomena, and both conditions resulted in all-or-none responses. Rebound excitation from prolonged hyperpolarizing pulses could also be used to generate plateau potentials in some cells. These neurons were found to express a hyperpolarization-activated inward current. Neither the generation nor the maintenance of plateau potentials was affected by removal of Na+ions from the extracellular medium or by blockade of Na+currents with TTX. However, blocking of Ca2+currents with Cd2+(5 × 10−4M) inhibited the generation of plateau potentials, indicating that, in Manduca AL neurons, plateau potentials depend on Ca2+. Examining Ca2+currents in isolation revealed that activation of these currents occurs in the absence of experimentally applied depolarizing stimuli. Our results suggest that this activity underlies the generation of plateau potentials and characteristic bursts of electrical activity in developing AL neurons of M. sexta.

Indirect projections from the suprachiasmatic nucleus to major arousal-promoting cell groups in rat: implications for the circadian control of behavioural state

The circadian clock housed in the suprachiasmatic nucleus (SCN) controls various circadian rhythms including daily sleep-wake cycles. Using dual tract-tracing, we recently showed that the medial preoptic area (MPA), subparaventricular zone (SPVZ) and dorsomedial hypothalamic nucleus (DMH) are well positioned to relay SCN output to two key sleep-promoting nuclei, namely, the ventrolateral and median preoptic nuclei. The present study examined the possibility that these three nuclei may link the SCN with wake-regulatory neuronal groups. Biotinylated dextran-amine with or without cholera toxin B subunit was injected into selected main targets of SCN efferents; the retrograde labeling in the SCN was previously analyzed. Here, anterograde labeling was analyzed in immunohistochemically identified cholinergic, orexin/hypocretin-containing and aminergic cell groups. Tracer injections into the MPA, SPVZ and DMH resulted in moderate to dense anterograde labeling of varicose fibers in the orexin field and the tuberomammillary nucleus. The locus coeruleus, particularly the dendritic field, contained moderate anterograde labeling from the MPA and DMH. The ventral tegmental area, dorsal raphe nucleus, and laterodorsal tegmental nucleus all showed moderate anterograde labeling from the DMH. The substantia innominata showed moderate anterograde labeling from the MPA. These results suggest that the MPA, SPVZ and DMH are possible relay nuclei for indirect SCN projections not only to sleep-promoting preoptic nuclei as previously shown, but also to wake-regulatory cell groups throughout the brain. In the absence of major direct SCN projections to most of these sleep/wake-regulatory regions, indirect neuronal pathways probably play an important role in the circadian control of sleep-wake cycles and other physiological functions.

Afferent projections to the pontine micturition center in the cat

The pontine micturition center (PMC) or Barrington's nucleus controls micturition by way of its descending projections to the sacral spinal cord. However, little is known about the afferents to the PMC that control its function and may be responsible for dysfunction in patients with urge-incontinence and overactive bladder. In five female cats, wheatgerm agglutinin-conjugated horseradish peroxidase (WGA-HRP) injections were made in the PMC and adjoining dorsolateral pontine tegmentum. Retrogradely labeled neurons were found in a large area, including the medullary and pontine medial and lateral tegmental field; dorsomedial, lateral, and ventrolateral periaqueductal gray matter (PAG); posterior hypothalamus; medial preoptic area (MPO); bed nucleus of the stria terminalis; central nucleus of the amygdala; and infralimbic, prelimbic, and insular cortices. To verify whether these areas indeed project specifically to the PMC or perhaps only to adjacent structures in the pontine tegmentum, in 67 cats (3)H-leucine or WGA-HRP injections were made in each of these regions. Five cell groups appeared to have direct connections to the PMC, the ventromedial pontomedullary tegmental field, the ventrolateral and dorsomedial PAG, the MPO, and the posterior hypothalamus. The possible functions of these projections are discussed. These results indicate that all other parts of the brain that influence micturition have no direct connection with the PMC.

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.

Neuropeptide S: a neuropeptide promoting arousal and anxiolytic-like effects

Arousal and anxiety are behavioral responses that involve complex neurocircuitries and multiple neurochemical components. Here, we report that a neuropeptide, neuropeptide S (NPS), potently modulates wakefulness and could also regulate anxiety. NPS acts by activating its cognate receptor (NPSR) and inducing mobilization of intracellular Ca2+. The NPSR mRNA is widely distributed in the brain, including the amygdala and the midline thalamic nuclei. Central administration of NPS increases locomotor activity in mice and decreases paradoxical (REM) sleep and slow wave sleep in rats. NPS was further shown to produce anxiolytic-like effects in mice exposed to four different stressful paradigms. Interestingly, NPS is expressed in a previously undefined cluster of cells located between the locus coeruleus (LC) and Barrington's nucleus. These results indicate that NPS could be a new modulator of arousal and anxiety. They also show that the LC region encompasses distinct nuclei expressing different arousal-promoting neurotransmitters.

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.

Comparison of different computer models of the neural control system of the lower urinary tract

This paper presents a series of five models that were formulated for describing the neural control of the lower urinary tract in humans. A parsimonious formulation of the effect of the sympathetic system, the pre-optic area, and urethral afferents on the simulated behavior are included. In spite of the relative simplicity of the five models studied, behavior that resembles normal lower urinary tract behavior as seen during an urodynamic investigation could be simulated. The models were tested by studying their response to disturbances of the afferent signal from the bladder. It was found that the inhibiting reflex that results from including the sympathetic system or the pre-optic area (PrOA) only counteracts the disturbance in the storage phase. Once micturition has started, these inhibiting reflexes are suppressed. A detrusor contraction that does not result in complete micturition similar to an unstable detrusor contraction could be simulated in a model including urethral afferents. Owing to the number of uncertainties in these models, so far no unambiguous explanation of normal and pathological lower urinary tract behavior can be given. However, these models can be used as an additional tool in studies of the mechanisms of the involved neural control.

Neural activity in the horizontal limb of the diagonal band of broca can be modulated by electrical stimulation of the olfactory bulb and cortex in rats

Previously published theoretical models of olfactory processing suggest that cholinergic modulatory inputs to the olfactory system should be regulated by neural activity in the olfactory bulb. We tested these predictions using in vivo electrophysiology in rats. We show that the activity of approximately 20% of neurons recorded in the horizontal limb of the diagonal band of Broca (HDB), which is the source of cholinergic projections to the olfactory system, can be modulated by electrical stimulation of either the lateral olfactory tract or the cell body layer of piriform cortex. These data suggest a possible physiological pathway for the proposed regulation of neural activity in the HDB by activity in the olfactory bulb or cortex.

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.

Sexual motivation--an inquiry into events determining the occurrence of sexual behavior

For the individual engaged in it, sexual behavior has no finality or purpose other than its own execution. Data are presented showing that the execution of sexual reflexes can promote learning, i.e. it functions as reinforcement. Furthermore, positive affect is generated. Based on these principles, a model of sexual motivation has been elaborated. The conceptual framework is the incentive motivation theory previously proposed by Bindra D, A motivational view of learning, performance, and behavior modification, Psychol Rev 1974: 81:199-213; A Theory of Intelligent Behavior, New York: Wiley, 1976; How adaptive behavior is produced: a perceptual-motivational alternative to response reinforcement, Behav Brain Sci 1978; 1:41-52. Although the model is intended for application to most mammals, the rat is used as example. Essentially, sexual approach behaviors are activated by appropriate incentives (conditioned in the male, unconditioned in the female). Approach is, in the inexperienced male, followed by the execution of copulatory reflexes as a consequence of accidentally obtained tactile stimulation of the perineal region. In the female, copulatory acts are activated by tactile stimulation of the flanks and hinds provided by the mounting male. The role of conditioning for the execution of copulatory reflexes and for the acquisition of incentive value of neutral stimuli is analyzed. It is also shown that the incentive properties of sexual acts are not substantially different from those of other incentives. Sexual exhaustion is suggested to be either a case of negative alliesthesia or of stimulus habituation and the Coolidge effect is, in consequence, an example of dishabituation. Studies in women and men support this proposal. It is emphasized that sexual behavior is best understood as being entirely mechanistic albeit not deterministic.

Social stress effects on territorial marking and ultrasonic vocalizations in mice

Acute social defeat (SD) leads to transient and persistent physiological and behavioral changes. We examined the effects of acute SD on territorial urine marking and ultrasonic courtship vocalizations in DBA/2 male mice. Both behaviors are considered androgen dependent and are influenced by social status, with dominant mice displaying more of both behaviors. In Experiment 1, male mice that received SD displayed prolonged inhibition of territorial urine marking, relative to nondefeated control mice (NOSD). In addition, territorial marking increased with repeated tests. In Experiment 2, male mice that received 3 successive days of SD displayed fewer ultrasonic courtship vocalizations at 30 min. post-SD1 and 30 min. post-SD2, relative to NOSD mice. In Experiment 2, we also observed decreased territorial marking 4 weeks post-SD. In sum, SD induced prolonged inhibition of territorial marking, but had only transient effects on ultrasonic courtship vocalizations, suggesting that different mechanisms may mediate the maintenance of these behaviors.

Rewiring cortex: the role of patterned activity in development and plasticity of neocortical circuits

Visually driven activity is not required for the establishment of ocular dominance columns, orientation columns, and long-range horizontal connections in visual cortex, although spontaneous activity appears to be necessary. The role of activity may be instructive or simply permissive; evidence for an instructive role requires inquiry into the role of the pattern of activity in shaping cortical circuits. The few experiments that have probed the role of patterned activity include the effects of artificial strabismus, artificial stimulation of the optic nerve, and rewiring visual projections from the retina to the auditory thalamus and cortex. These experiments demonstrate that patterned activity is vital for the maintenance of thalamocortical, local intracortical, and long-range horizontal connections in cortex.

Efferent projections of the nucleus of the solitary tract to peri-locus coeruleus dendrites in rat brain: evidence for a monosynaptic pathway

Locus coeruleus (LC) neurons respond to autonomic influences, are activated by physiological stressors, and discharge in parallel with peripheral sympathetic nerves. The circuitry underlying modulation of LC activity by physiological manipulations (i.e., hemodynamic stress, hypovolumia) remains unclear. Specifically, monosynaptic projections from primary baroreceptor centers to the LC have been suggested by electrophysiological studies but have not been unequivocally established. Light microscopic anterograde tract-tracing studies have previously shown that neurons originating in the nucleus of the solitary tract (NTS) project to a region of the rostrodorsal pontine tegmentum, which contains noradrenergic dendrites of the LC; however, it is not known whether these NTS efferents specifically target LC dendrites. Therefore, we combined peroxidase labeling of biotinylated dextran amine (BDA) or Phaseolus vulgaris-leucoagglutinin (PHA-L) from the NTS with gold-silver labeling for tyrosine hydroxylase (TH) in the rostrolateral peri-LC region. Injections placed into neighboring nuclei (nucleus gracilis, hypoglossal nucleus) served as controls. Only injections centered in the NTS produced anterograde labeling in peri-LC regions containing TH processes. By electron microscopy, BDA- or PHA-L-labeled axon terminals originating from the NTS contained small, clear, and some large dense-core vesicles and formed heterogeneous synaptic contacts characteristic of both excitatory- and inhibitory-type transmitters. Approximately 19% of the BDA and PHA-L axon terminals examined originating from the commissural portion of the NTS formed synaptic specializations with dendrites exhibiting TH immunoreactivity in the peri-LC. These results demonstrate that neurons projecting from the cardiovascular-related portion of the NTS target noradrenergic dendrites, indicating that barosensitive NTS neurons may directly modulate the activity of LC neurons and may serve to integrate autonomic responses in brain by influencing the widespread noradrenergic projections of the LC. In addition, these findings demonstrate that extranuclear dendrites are an important termination site for afferents to the LC.

Direct projections from the medial preoptic area to spinally-projecting neurons in Barrington's nucleus: an electron microscope study in the rat

Direct projections from the medial preoptic area (MPO) to the pontine micturition center neurons directly projecting to the lumbosacral spinal cord were revealed electron microscopically in the rat by a double labeling method. Biotinylated dextran amine (BDA) was injected into the MPO and horseradish peroxidase (HRP) was injected into the lumbosacral cord segments. At light microscopic level, BDA-labeled presumptive axon terminals completely overlapped with HRP-labeled neurons in Barrington's nucleus. Electron microscopic observation showed that some BDA-labeled axon terminals made synaptic contacts with dendrites of HRP-labeled neurons in Barrington's nucleus. The present results indicated that the MPO may be involved in the modulation of the pontine micturition reflex in the rat.

Cross-modal reorganization of callosal connectivity without altering thalamocortical projections

Mammalian cerebral cortex is composed of a multitude of different areas that are each specialized for a unique purpose. It is unclear whether the activity pattern and modality of sensory inputs to cortex play an important role in the development of cortical regionalization. The modality of sensory inputs to cerebral cortex can be altered experimentally. Neonatal diversion of retinal axons to the auditory thalamus (cross-modal rewiring) results in a primary auditory cortex (AI) that resembles the primary visual cortex in its visual response properties and topography. Functional reorganization could occur because the visual inputs use existing circuitry in AI, or because the early visual inputs promote changes in AI's circuitry that make it capable of constructing visual receptive field properties. The present study begins to distinguish between these possibilities by exploring whether the callosal connectivity of AI is altered by early visual experience. Here we show that early visual inputs to auditory thalamus can reorganize callosal connections in auditory cortex, causing both a reduction in their extent and a reorganization of the pattern. This result is distinctly different from that in deafened animals, which have widespread callosal connections, as in early postnatal development. Thus, profound changes in cortical circuitry can result simply from a change in the modality of afferent input. Similar changes may underlie cortical compensatory processes in deaf and blind humans.

A computer model for describing the effect of urethral afferents on simulated lower urinary tract function

A computer model of mechanical properties of the bladder, the urethra and the rhabdosphincter, as well as their neural control is presented in this paper. The model has a rather simple design and processes sensory information from both the bladder wall tension and urethral stretch. It is assumed that afferent signals from the urethra are involved in a sacral excitatory reflex and a supraspinal inhibitory reflex. Pressure and flow signals that resemble experimentally measured normal human behaviour could be simulated with this model. From these simulations the relation between the neural control mechanisms used in the model and the neural control mechanism in vivo cannot be judged entirely because similar behaviour could be simulated with models that are bas ed on different neural control mechanisms. Also behaviour that resembles detrusor overactivity was simulated with our model after an externally induced rise in detrusor pressure was added. Detrusor overactivity, sometimes in combination with urethral relaxation, can occur during a urodynamic investigation. A possible explanation for this detrusor overactivity might be that the micturition reflex is triggered by unknown disturbances and is inhibited immediately after by the same mechanism that normally ceases voiding. The described model provides such a mechanism. Based on these simulations, therefore, it is concluded that urethral afferent signals might be important in lower urinary tract control.

CNS location of uterine-related neurons revealed by trans-synaptic tracing with pseudorabies virus and their relation to estrogen receptor-immunoreactive neurons

Retrograde, transneuronal tracing with Bartha's strain of pseudorabies virus was used in rats to identify spinal cord, brainstem and hypothalamic loci of uterine-related neurons that could function in the regulation of uterine activity. Based on the premise that estrogen might influence such uterine-related neurons, the existence of estrogen receptors in neurons in these same loci was examined. Viral injections were made into the uterine cervix, body and cervical end of the uterine horns, and the rats allowed to survive for four to six days. After four days, mainly the spinal cord, medulla and pons contained virus-infected neurons. After longer survival times, progressively higher levels of the neuraxis contained viral-labeled neurons, so that by six days hypothalamic uterine-related neurons were identified. First-order virus-infected neurons were visualized by immunohistochemistry in the pelvic paracervical parasympathetic ganglia and in inferior mesenteric sympathetic ganglia. Preganglionic and putative interneurons were labeled in the lumbosacral spinal cord and thoracic spinal cord mainly in the lateral horn area (sacral parasympathetic nucleus and intermediolateral nucleus), lateral aspect of the dorsal horn, intermediate gray, lamina X and dorsal gray commissural area. In the brainstem, labeling was most evident and consistent in the nucleus tractus solitarius, ventrolateral medulla, raphe magnus and pallidus nuclei, parapyramidal area, A5 cell group, Barrington's nucleus of the pons and periaqueductal gray of the midbrain. In the hypothalamus, virus-infected neurons were most marked in the paraventricular nucleus, with fewer in the medial preoptic area and ventromedial hypothalamic nucleus. Estrogen receptor-immunoreactive neurons were most often present among the virus-labeled uterine-related neurons of the spinal cord, nucleus tractus solitarius, ventrolateral medulla, periaqueductal gray, medial preoptic area and ventromedial hypothalamic nucleus. These results identify a multisynaptic pathway of neurons whose eventual output is involved in uterine functions, whose distribution is similar to that revealed by pseudorabies virus tracing from other visceral organs, and which are often mixed among estrogen-responsive neurons.

The region of the pontine parabrachial nucleus is a major target of dehydration-sensitive CRH neurons in the rat lateral hypothalamic area

Neurons in a restricted part of the lateral hypothalamic area (LHA) show increased expression of corticotropin-releasing hormone (CRH) mRNA as a consequence of cellular dehydration. In the present study, we have investigated the organization of their efferent projections by using anterograde and retrograde tracing techniques. Additionally, we have compared the distribution of CRH mRNA-containing neurons after cellular dehydration and intraventricular (i.c.v.) colchicine injections. Our results show that cellular dehydration activates a more restricted neuronal population than does i.c.v. colchicine. Iontophoretic injections of Phaseolus vulgaris leucoagglutinin (PHAL) were placed in the LHA of animals drinking hypertonic saline and their proximity to activated CRH neurons determined by in situ hybridization for CRH mRNA. Although labelled fibers from these injections were seen throughout the brain, the region of the parabrachial nucleus and nucleus of the solitary tract (NTS) were most conspicuous in also having CRH immunoreactive fibers. Injections of Fluoro-Gold placed in these two structures were used to confirm these findings in dehydrated animals. Significant numbers of neurons containing both Fluoro-Gold and CRH mRNA were seen in the lateral hypothalamus after injections in the lateral and medial parts of the parabrachial nucleus; far fewer were seen after injections in the NTS. These results strongly suggest that the CRH neurons in the LHA activated by cellular dehydration provide an input to the region of the parabrachial nucleus. The altered biochemical composition of this pathway may well be able to modify sensory and motor patterns both during and after dehydration.

Fos expression in rat pontine tegmental neurons following activation of the medial preoptic area

Fos immunohistochemistry was used to map the distribution of pontine neurons excited by activation of the medial preoptic area (MPO). Although we have previously shown that Barrington's nucleus receives a very dense focal input from the MPO, electrical stimulation of the preoptic area unexpectedly induced very little Fos expression in Barrington's neurons. These results suggest that the MPO-->Barrington's projection utilizes a transmitter(s) that does not involve transduction of the Fos protein; alternatively, MPO afferents to Barrington's nucleus may be inhibitory in nature. As Barrington's nucleus plays a critical role in micturition, MPO projections to Barrington's nucleus may regulate voiding reflexes during sexual behavior. Interestingly, while the locus coeruleus (LC) proper receives only a sparse projection from the MPO, extensive Fos expression was present in LC. The finding of Fos immunoreactive LC neurons suggests that the excitatory influence of MPO may regulate LC neuronal activity and NE release during reproductive behaviors.

Direct projections from the periaqueductal gray to pontine micturition center neurons projecting to the lumbosacral cord segments: an electron microscopic study in the rat

Direct projections from the periaqueductal gray (PAG) to the pontine micturition center neurons directly projecting to the lumbosacral cord segments were observed electron microscopically in the rat by a double labeling method. Biotinylated dextran amine (BDA) was injected into the PAG and horseradish peroxidase (HRP) was injected into the lumbosacral cord segments. After injection of BDA into the ventrolateral part of the PAG, many BDA-labeled axons were seen light microscopically in Barrington's nucleus; a moderate number of them were found in the pontine tegmental region just ventral to Barrington's nucleus (D-region [Ding, Y-Q., Takada, M., Tokuno, H. and Mizuno, N., J. Comp. Neurol., 357 (1996) 318-330]). On the other hand, after injection of BDA into the dorsolateral part of the PAG, only a few BDA-labeled axons were seen in Barrington's nucleus or the D-region. BDA-labeled axon terminals were electron microscopically confirmed to be in synaptic contact with HRP-labeled dendrites and somata in Barrington's nucleus and the D-region. The results indicate that the ventrolateral part of the PAG is implicated in regulation of the micturition reflex.

Metabotropic glutamate receptor in GHRH and beta-endorphin neurones of the hypothalamic arcuate nucleus

Growth hormone-releasing hormone (GHRH) and beta-endorphin are mainly synthesized in neurones of the hypothalamic arcuate nucleus. Arcuate neurones also contain both ionotropic and metabotropic glutamate receptors. The aim of present study was to investigate whether glutamate receptors are present in GHRH and beta-endorphin containing nerve cells of this hypothalamic area. Using double-label immunocytochemistry as well as the mirror technique, we found that almost all GHRH and beta-endorphin immunoreactive arcuate neurones contain the metabotropic glutamate receptor la. The observations provide morphological evidence for the view that glutamate, which appears to be a major excitatory neurotransmitter in the hypothalamus, may directly stimulate GHRH and beta-endorphin neurones of the medial hypothalamus.

Discrete subregions of the rat midbrain periaqueductal gray project to nucleus ambiguus and the periambigual region

We investigated the organization of projections from the rat midbrain periaqueductal gray to nucleus ambiguus and the periambigual region using retrograde and anterograde tract tracing techniques. Retrograde tracing results revealed that neurons that project to nucleus ambiguus arise from three discrete, longitudinally organized columns of neurons located in the supraoculomotor central gray, lateral and ventrolateral periaqueductal gray. Anterograde tracing studies demonstrated that projections from these three columns of periaqueductal gray neurons terminate with topographic specificity in nucleus ambiguus and the periambigual region. Double-labelling studies demonstrated that periaqueductal gray neurons terminate in close contiguity to cholinergic neurons in the compact, semicompact, loose and external formations of nucleus ambiguus. The present results suggest that projections from periaqueductal gray to nucleus ambiguus may mediate, in part, certain cardiovascular adjustments and vocalizations produced by stimulation of periaqueductal gray.

Projections from the lateral part of the central amygdalar nucleus to the postulated fear conditioning circuit

The lateral part of the central nucleus projects densely to only three regions: the medial part of the central nucleus, restricted parts of the bed nuclei of the stria terminalis, and the parabrachial nucleus in the pons. The possible role of the lateral central amygdalar nucleus in circuitry mediating conditioned emotional responses is discussed; changing neuropeptide levels in the lateral part may act as a 'gain control' for reversible long-term modulation (LTM) of medial part output.

Modulation of inhibition in a model of olfactory bulb reduces overlap in the neural representation of olfactory stimuli

In a neural model of olfactory bulb processing, we demonstrate the putative role of the modulation of two types of inhibition, inspired by electrophysiological data on the effect of acetylcholine and noradrenaline on olfactory bulb synaptic transmission. Feedback regulation of modulation based on bulbar activity serves to 'normalize' the activity of output neurons in response to different levels of input activities. This mechanism also decreases the overlap between pairs of output patterns (Mitral cell activities), enhancing the discrimination between overlapping olfactory input patterns. The effect of the modulation at the two levels of interneurons is complementary: while an increase in periglomerular inhibition decreases the number of responding output neurons, a decrease in granule cell inhibition increases the firing frequencies of these neurons.

Neurons in the rat brain and spinal cord labeled after pseudorabies virus injected into the external urethral sphincter

Male Sprague-Dawley rats, with their pelvic and hypogastric nerves transected, were infected with pseudorabies virus (PRV) injected into the external urethral sphincter. Animals were sacrificed at 2, 2.5, 3, and 4 days postinfection. Spinal cord and brain tissue were sectioned and processed by immunohistochemical techniques with antisera against PRV and choline acetyl transferase (CAT). At 2 days postinfection, virus-labeled neurons were found in the ventrolateral divisions of Onuf's nucleus and in the dorsal gray commissure (DGC). At progressively later incubation times, labeled neurons were found in the intermediolateral regions, the superficial layer of the dorsal horn, and the brainstem, in particular, the pontine micturition center. PRV/CAT-positive neurons were only found in Onuf's nucleus. Preganglionic neurons in the L6-S1 intermediolateral regions were CAT positive but PRV negative, thus suggesting that they are interneurons, not sacral parasympathetic preganglionic neurons. After 4 days, virus had spread to neurons in the paraventricular, preoptic, and even cortical regions. The distribution of these PRV-labeled brain neurons strongly resembled that obtained after the injection of PRV into the urinary bladder (Nadelhaft et al. [1992] Neurosci. Lett. 143:271-274). In both cases, neurons were labeled in the DGC in the spinal cord. The data therefore suggest that neurons in the DGC may be involved in the integrated control of the bladder and the external urethral sphincter.

Evidence for divergent projections to the brain noradrenergic system and the spinal parasympathetic system from Barrington's nucleus

The present study was designed to determine whether Barrington's nucleus, which lies ventromedial to the locus coeruleus (LC) and projects to the sacral parasympathetic nucleus, is a source of afferent projections to the LC. Restricted injections of the anterograde tracer, biocytin, into Barrington's nucleus labeled varicose fibers that extended from the injection site into the LC. Consistent with this, injections of the retrograde tracers, wheatgerm agglutinin conjugated to horseradish peroxidase coupled to gold particles (WGA-Au-HRP) or fluorescein-conjugated latex beads, into the LC labeled numerous (approximately 10%) Barrington's neurons that were also retrogradely labeled by Fluoro-Gold (FG) injections in the spinal cord. Retrograde tracing from the LC combined with corticotropin-releasing hormone (CRH) immunohistochemistry revealed that at least one third of the retrogradely labeled neurons in Barrington's nucleus were CRH-immunoreactive (CRH-IR). Finally, in triple labeling studies, CRH-Barrington's neurons were consistently observed that were retrogradely labeled from both the and spinal cord. These findings implicate Barrington's nucleus as an LC afferent and a source of CRH-IR fibers in the LC. Additionally, the results suggest that some Barrington's neurons diverge to innervate both the spinal cord and the LC. This divergent innervation may serve to coregulate the sacral parasympathetic nervous system and brain noradrenergic system, thus providing a mechanism for coordinating pelvic visceral functions with forebrain activity.

Single neurons in Barrington's nucleus projecting to both the paraventricular thalamic nucleus and the spinal cord by way of axon collaterals: a double labeling study in the rat

Barrington's nucleus, a center for the micturition reflex in the pontine tegmentum, was recently reported to send projection fibers to the paraventricular thalamic nucleus (PVT). In the present study, we examined whether or not Barrington's nucleus neurons projecting to the PVT issue axon collaterals to the lowest lumbar cord segment (L6) containing the spinal micturition center. Our retrograde double-labeling study revealed that a subset of Barrington's nucleus neurons send projection fibers to both the L6 and the thalamic midline including the PVT via axon collaterals. Such neurons projecting directly to the thalamic midline and L6 by way of axon collaterals were additionally scattered in the locus coeruleus, subcoeruleus nucleus and sublaterodorsal nucleus.

Dendrites of locus coeruleus neurons extend preferentially into two pericoerulear zones

The intrinsic cytoarchitecture and neurochemical organization of the nucleus locus coeruleus have been characterized extensively, but there is little information about the organization of locus coeruleus neuronal processes extending outside of the nucleus proper. Light and electron microscopic immunocytochemical techniques were used to investigate the distribution of dopamine-beta-hydroxylase- or tyrosine-hydroxylase-labeled extranuclear processes in the rat pericoerulear region. The vast majority of these processes extended preferentially into two zones: (1) the pontine tegmentum medial and rostral to locus coeruleus, here termed the rostromedial pericoerulear region; and (2) a narrow region adjacent to the IVth ventricle caudomedial to locus coeruleus, designated here as the caudal juxtaependymal pericoerulear region. Far fewer labeled processes extended into the lateral and ventral pericoerulear regions. Seventy-seven percent of the labeled profiles in the pericoerulear region were dendrites. All labeled profiles in the rostromedial pericoerulear region and 94% of the labeled profiles in the caudal juxtaependymal zone were dendrites. By contrast, in the rostroventral pericoerulear region, 25% of the labeled profiles were axons. Locus coeruleus extranuclear dendrites were never presynaptic to other structures but were often contacted by several unlabeled presynaptic terminals. These results indicate that the dendrites of locus coeruleus neurons extend preferentially into two pericoerulear zones. Extranuclear dendrites in all pericoerulear regions receive extensive, nonnoradrenergic synaptic contacts. Thus, pericoerulear dendrites, particularly in the rostromedial and caudal juxtaependymal zones, are important sites for the integration of inputs to locus coeruleus neurons.