The distribution of spinal projection neurons in the hypothalamus of the rat, studied with the HRP method

Horner syndrome as a physiological biomarker of disease in canine cervical myelopathy

BACKGROUND

Horner syndrome often occurs with cervical myelopathies and might provide insight into the underlying disease and prognosis.

OBJECTIVES

To describe the clinical and imaging features of dogs with cervical myelopathy and concurrent Horner syndrome and to determine association of Horner syndrome with diseases or magnetic resonance images (MRI).

ANIMALS

Ninety-three client-owned dogs with cervical myelopathy and concurrent Horner syndrome and 99 randomly selected client-owned dogs with cervical myelopathy without Horner syndrome (control cases).

METHODS

Retrospective study. Medical records were reviewed to identify Horner and control cases and clinical findings recorded. MRI were reviewed, and lesions characterized and recorded. Descriptive and comparative statistics were performed.

RESULTS

Non-compressive disease occurred more frequently in the Horner group compared with controls (58%; 95% CI: 48-68 vs 9%; 95% CI: 5-16; P < .0001). The most common diseases were fibrocartilaginous embolism in the Horner group (44/93; 47%) and intervertebral disc extrusion (76/99; 77%) amongst controls. On MRI, parenchymal hyperintensity was seen more commonly in the Horner group (95%; 95% CI: 88-98) compared with controls (51%; 95% CI: 41-60; P < .0001). In the Horner group, dogs that did not survive to discharge (N = 13) had more extensive MRI lesions relative to the adjacent vertebral length (200%; IQR 110%-575%) compared with survivors (N = 80; 110%; IQR 40%-250%; P = .02). Lateralization of Horner signs and MRI changes matched in 54% of cases. The overall survival rate was high in both Horner (80/93; 86%) and control (95/99; 96%) groups.

CONCLUSIONS AND CLINICAL IMPORTANCE

Horner syndrome in cervical myelopathy is commonly associated with noncompressive intraparenchymal disease.

The heart is lost without the hypothalamus

Neuroanatomic and functional studies show the paraventricular (PVN) of the hypothalamus to have a central role in the autonomic control that supports cardiovascular regulation. Direct and indirect projections from the PVN preautonomic neurons to the sympathetic preganglionic neurons in the spinal cord modulate sympathetic activity. The preautonomic neurons of the PVN adjust their level of activation in response to afferent signals arising from peripheral viscerosensory receptors relayed through the nucleus tractus solitarius. The prevailing sympathetic tone is a balance between excitatory and inhibitory influences that arises from the preautonomic PVN neurons. Under physiologic conditions, tonic sympathetic inhibition driven by a nitric oxide-γ-aminobutyric acid-mediated mechanism is dominant, but in pathologic situation such as heart failure there is a switch from inhibition to sympathoexcitation driven by glutamate and angiotensin II. Angiotensin II, reactive oxygen species, and hypoxia as a result of myocardial infarction/ischemia alter the tightly regulated posttranslational protein-protein interaction of CAPON (carboxy-terminal postsynaptic density protein ligand of neuronal nitric oxide synthase (NOS1)) and PIN (protein inhibitor of NOS1) signaling mechanism. Within the preautonomic neurons of the PVN, the disruption of CAPON and PIN signaling leads to a downregulation of NOS1 expression and reduced NO bioavailability. These data support the notion that CAPON-PIN dysregulation of NO bioavailability is a major contributor to the pathogenesis of sympathoexcitation in heart failure.

CLARITY with neuronal tracing and immunofluorescence to study the somatosensory system in rats

BACKGROUND

The CLARITY technique enables researchers to visualize different neuronal connections along the nervous system including the somatosensory system.

NEW METHOD

The present work describes the antero-lateral and dorsal column pathways until the thalamic and cortical stations, as well as descending oxytocinergic and vasopressinergic innervations by means of combined CLARITY, neuronal tracing, and immunofluorescence techniques. We used male Sprague-Dawley rats of 13, 30, and 60 days.

RESULTS

The main results are as follows: A) CLARITY is a reliable technique that can be combined with fluorescent neuronal tracers and immunofluorescence techniques without major procedure modifications; B) at spinal level, some primary afferent fibers were labeled by CGRP, as well as the presence of neuronal populations that simultaneously project to the gracile and ventral posterolateral thalamic nuclei; C) corticothalamic connections were visible when retrograde tracers were injected at thalamic level; D) oxytocin receptors were expressed in the spinal dorsal horn by GABAergic-positive neurons, reinforcing previous outcomes about the possible mechanism for oxytocin blocking the primary afferent sensory input.

COMPARISON WITH EXISTING METHODS AND CONCLUSIONS

The CLARITY technique lets us observe in a transparent way the entire processed tissue compared with classical histological methods. CLARITY is a potentially useful tool to describe neuroanatomical structures and their neurochemical stratus.

Differences in carbachol dose, pain condition, and sex following lateral hypothalamic stimulation

Lateral hypothalamic (LH) stimulation produces antinociception in female rats in acute, nociceptive pain. Whether this effect occurs in neuropathic pain or whether male-female sex differences exist is unknown. We examined the effect of LH stimulation in male and female rats using conditions of nociceptive and neuropathic pain. Neuropathic groups received chronic constriction injury (CCI) to induce thermal hyperalgesia, a sign of neuropathic pain. Nociceptive rats were naive for CCI, but received the same thermal stimulus following LH stimulation. To demonstrate that CCI ligation produced thermal hyperalgesia, males and females received either ligation or sham surgery for control. Both males and females demonstrated significant thermal hyperalgesia following CCI ligation (p<0.05), but male sham surgery rats also showed a significant left-right difference not present in female sham rats. In the second experiment, rats randomly assigned to CCI or nociceptive groups were given one of three doses of the cholinergic agonist carbachol (125, 250, or 500 nmol) or normal saline for control, microinjected into the left LH. Paw withdrawal from a thermal stimulus (paw withdrawal latency; PWL) was measured every 5 min for 45 min. Linear mixed models analysis showed that males and females in both pain conditions demonstrated significant antinociception, with the 500-nmol dose producing the greatest effect across groups compared with controls for the left paw (p<0.05). Female CCI rats showed equivalent responses to the three doses, while male CCI rats showed more variability for dose. However, nociceptive females responded only to the 500-nmol dose, while nociceptive males responded to all doses (p<0.05). For right PWL, only nociceptive males showed a significant carbachol dose response. These findings are suggestive that LH stimulation produces antinociception in male and female rats in both nociceptive and neuropathic pain, but dose response differences exist based on sex and pain condition.

Bilateral descending hypothalamic projections to the spinal trigeminal nucleus caudalis in rats

Several lines of evidence suggest that the hypothalamus is involved in trigeminal pain processing. However, the organization of descending hypothalamic projections to the spinal trigeminal nucleus caudalis (Sp5C) remains poorly understood. Microinjections of the retrograde tracer, fluorogold (FG), into the Sp5C, in rats, reveal that five hypothalamic nuclei project to the Sp5C: the paraventricular nucleus, the lateral hypothalamic area, the perifornical hypothalamic area, the A11 nucleus and the retrochiasmatic area. Descending hypothalamic projections to the Sp5C are bilateral, except those from the paraventricular nucleus which exhibit a clear ipsilateral predominance. Moreover, the density of retrogradely FG-labeled neurons in the hypothalamus varies according to the dorso-ventral localization of the Sp5C injection site. There are much more labeled neurons after injections into the ventrolateral part of the Sp5C (where ophthalmic afferents project) than after injections into its dorsomedial or intermediate parts (where mandibular and maxillary afferents, respectively, project). These results demonstrate that the organization of descending hypothalamic projections to the spinal dorsal horn and Sp5C are different. Whereas the former are ipsilateral, the latter are bilateral. Moreover, hypothalamic projections to the Sp5C display somatotopy, suggesting that these projections are preferentially involved in the processing of meningeal and cutaneous inputs from the ophthalmic branch of the trigeminal nerve in rats. Therefore, our results suggest that the control of trigeminal and spinal dorsal horn processing of nociceptive information by hypothalamic neurons is different and raise the question of the role of bilateral, rather than unilateral, hypothalamic control.

Posterior hypothalamic modulation of light-evoked trigeminal neural activity and lacrimation

Enhanced light sensitivity is a common feature of many neuro-ophthalmic conditions and some chronic headaches. Previously we reported that the bright light-evoked increases in trigeminal brainstem neural activity and lacrimation depended on a neurovascular link within the eye (Okamoto et al., 2012). However, the supraspinal pathways necessary for these light-evoked responses are not well defined. To assess the contribution of the posterior hypothalamic area (PH), a brain region closely associated with control of autonomic outflow, we injected bicuculline methiodide (BMI), a GABAa receptor antagonist, into the PH and determined its effect on the encoding properties of ocular neurons at the ventrolateral trigeminal interpolaris/caudalis transition (Vi/Vc) and caudalis/upper cervical cord junction (Vc/C1) regions and on reflex lacrimation in male rats under isoflurane anesthesia. BMI markedly reduced light-evoked (>80%) responses of Vi/Vc and Vc/C1 neurons at 10 min with partial recovery by 50 min after injection. BMI also reduced (>35%) the convergent cutaneous receptive field area of Vi/Vc and Vc/C1 ocular neurons indicating that both intra-ocular and periorbital cutaneous inputs were affected by changes in PH outflow. Light-evoked lacrimation was reduced by >35% at 10 min after BMI, while resting mean arterial pressure increased promptly and remained elevated (>20 mmHg) throughout the 50-min post-injection period. These results suggested that PH stimulation, acting in part through increased sympathetic activity, significantly inhibited light- and facial skin-evoked activity of ocular neurons at the Vi/Vc and Vc/C1 region. These data provide further support for the hypothesis that autonomic outflow plays a critical role in mediating light-evoked trigeminal brainstem neural activity and reflex lacrimation.

Nerve cells immunoreactive for p62 in select hypothalamic and brainstem nuclei of controls and Parkinson's disease cases

The protein p62 plays an important role in the proteasomal and/or autophagic clearance of misfolded and aggregation-prone proteins. Immunoreactivity for p62, however, not only characterizes pathological proteinaceous inclusions but also occurs in the form of homogeneous nerve cell labeling in brains of both healthy and diseased individuals, e.g., in the vagal dorsal motor nucleus and other subcortical nuclei. In sporadic Parkinson's disease (PD), the pathological process initially involves preganglionic neurons of the parasympathetic and sympathetic system and probably advances caudo-rostrally from there along the neuroaxis. Since all subsequently affected nuclei (lower raphe nuclei, magnocellular reticular formation, locus coeruleus, and central subnucleus of the amygdala) generate descending projections that terminate in the vagal dorsal motor nucleus and intermediolateral column, it has been conjectured that retrograde axonal transport and transsynaptic transmission of a pathogen contribute to the pathogenesis of PD. The hypothalamic paraventricular nucleus also sends projections to the preganglionic nuclei under consideration and, thus, should belong to the nuclei endangered by the pathological process. However, it remains uninvolved for the duration of the disorder. For this reason, we performed a retrospective study of the relevant nuclei in a cohort of 36 individuals, including 17 with clinically documented PD, one case with incidental Lewy body disease (ILBD), and 18 controls using p62-immunocytochemistry. Remarkably, the neurosecretory cells of the paraventricular nucleus were among the sites showing homogeneous p62-immunolabeling with the greatest consistency. Its p62-immunoreactive profile may indicate that the hypothalamic paraventricular nucleus is somehow capable of effectively metabolizing misfolded proteins and/or preventing their aggregation.

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.

Neurochemistry of the paraventricular nucleus of the hypothalamus: implications for cardiovascular regulation

The paraventricular nucleus of the hypothalamus (PVN) is an important site for autonomic and endocrine homeostasis. The PVN integrates specific afferent stimuli to produce an appropriate differential sympathetic output. The neural circuitry and some of the neurochemical substrates within this circuitry are discussed. The PVN has at least three neural circuits to alter sympathetic activity and cardiovascular regulation. These pathways innervate the vasculature and organs such as the heart, kidney and adrenal medulla. The basal level of sympathetic tone at any given time is dependent upon excitatory and inhibitory inputs. Under normal circumstances the sympathetic nervous system is tonically inhibited. This inhibition is dependent upon GABA and nitric oxide such that nitric oxide potentiates local GABAergic synaptic inputs onto the neurones in the PVN. Excitatory neurotransmitters such as glutamate and angiotensin II modify the tonic inhibitory activity. The neurotransmitters oxytocin, vasopressin and dopamine have been shown to affect cardiovascular function. These neurotransmitters are found in neurones of the PVN and within the spinal cord. Oxytocin and vasopressin terminal fibres are closely associated with sympathetic preganglionic neurones (SPNs). Sympathetic preganglionic neurones have been shown to express receptors for oxytocin, vasopressin and dopamine. Oxytocin causes cardioacceleratory and pressor effects that are greatest in the upper thoracic cord while vasopressin cause these effects but more significant in the lower thoracic cord. Dopaminergic effects on the cardiovascular system include inhibitory or excitatory actions attributed to a direct PVN influence or via interneuronal connections to sympathetic preganglionic neurones.

Distribution and neuropeptide coexistence of nucleobindin-2 mRNA/nesfatin-like immunoreactivity in the rat CNS

The protein fragment nesfatin-1 was recently implicated in the control of food intake. Central administration of this fragment results in anorexia and reduced body weight gain, whereas antisense or immunological nesfatin-1 antagonism causes increased food intake and overweight. Nesfatin-1 is derived from the precursor nucleobindin-2 (NUCB2). To identify the neurocircuitry underpinning the catabolic effects of NUCB2/nesfatin-1, we have used in situ hybridization and immunohistochemistry to map the distribution of this protein and its mRNA in the rat CNS and performed double-labeling experiments to localize its expression to functionally defined neuronal populations. These experiments confirm previous observations but also present several novel NUCB2 cell populations. Both NUCB2 mRNA and nesfatin-like immunoreactivity was most concentrated in the hypothalamus, in the supraoptic, paraventricular, periventricular and arcuate nuclei and the lateral hypothalamic area/perifornical region. Additionally, outside of the hypothalamus, labeling was observed in the thalamic parafascicular nucleus, the Edinger-Westphal nucleus, locus coeruleus, ventral raphe system, nucleus of solitary tract and in the preganglionic sympathetic intermediolateral cell column of the spinal cord, and the pituitary anterior and intermediate lobes. In neurons, immunoreactivity was almost exclusively confined to perikarya and primary dendrites with virtually no labeling of axonal terminals. Double-labeling immunohistochemistry revealed colocalization of nesfatin with vasopressin and oxytocin in magnocellular neuroendocrine neurons, thyrotropin-releasing hormone, corticotropin-releasing hormone, somatostatin, neurotensin, and growth-hormone-releasing hormone in parvocellular neuroendocrine neurons, pro-opiomelanocortin (but not neuropeptide Y) in the arcuate nucleus and melanin-concentrating hormone (but not hypocretin) in the lateral hypothalamus. Furthermore, nesfatin was extensively colocalized with cocaine- and amphetamine-regulated transcript in almost all NUCB2-expressing brain regions. These data reveal a wider distribution of NUCB2/nesfatin-1 than previously known, suggesting that the metabolic actions of this protein may involve not only feeding behavior but also endocrine and autonomic effects on energy expenditure. In addition, the subcellular distribution of nesfatin-like immunoreactivity indicates that this protein may not be processed like a conventional secreted neuromodulator.

Lateral hypothalamic-induced antinociception may be mediated by a substance P connection with the rostral ventromedial medulla

Stimulation of the lateral hypothalamus (LH) produces antinociception modified by intrathecal serotonergic receptor antagonists. Spinally-projecting serotonergic neurons in the LH have not been identified, suggesting that the LH innervates brainstem serotonergic neurons in the rostral ventromedial medulla (RVM), known to modify nociception in the spinal cord dorsal horn. To determine whether substance P (SP) plays a role in LH-induced antinociception mediated by the RVM, we conducted an anatomical experiment using retrograde tract tracing combined with double label immunocytochemistry and found that neuron profiles immunoreactive for SP in the LH project to the RVM. To further identify a functional connection between SP neurons in the LH and the RVM, the cholinergic agonist carbachol (125 nmol) was microinjected into the LH of female Sprague-Dawley rats (250-350 g) and antinociception was obtained on the tail flick or foot withdrawal tests. Cobalt chloride (100 nM) was then microinjected in the RVM to block synaptic activation of spinally-projecting RVM neurons. Within 5 min of the cobalt chloride injection, the antinociceptive effect of carbachol stimulation was blocked. In another set of experiments, the specific NK1 receptor antagonist L-703,606 (5 microg) was microinjected in the RVM following LH stimulation with carbachol and abolished LH-induced antinociception as well. Microinjection of cobalt chloride or L-703,606 in the absence of LH stimulation had no effect. These anatomical and behavioral experiments provide converging evidence to support the hypothesis that antinociception produced by activating neurons in the LH is mediated in part by the subsequent activation of spinally-projecting neurons in the RVM.

Selective inhibition from the anterior hypothalamus of C- versus A-fibre mediated spinal nociception

Modulation of spinal nociception from the anterior hypothalamus/preoptic area (AH/POA), and consequent alterations in the pain experience may contribute to integrated responses brought into play during fear or stress and as part of the sickness response. This study was designed to compare the effects of descending control from AH/POA on A- versus C-fibre-evoked spinal nociception, since any differential control is of behavioural and clinical importance given that A-fibre and C-fibre nociceptors convey different qualities of the pain signal (first and second pain, respectively), and play different roles in the development and maintenance of chronic pain states. In anaesthetised rats, electromyographic responses were recorded to monitor thresholds of withdrawal to slow (2.5 degrees Cs(-1)) or fast (7.5 degrees Cs(-1)) rates of skin heating of the hindpaw, to preferentially activate C- or A-nociceptors, respectively. Neuronal activation by microinjection of dl-homocysteic acid at sites within a specific region of AH/POA, lateral area of the anterior hypothalamus (LAAH), significantly increased response thresholds to slow heating rates (p<0.02, n=11), but not those to fast rates of heating (p=0.48, n=10). Injection of DLH adjacent to LAAH (n=9) had no significant effect on responses to slow (n=8) or fast (n=9) rates of skin heating. The functional significance of differential descending control of spinal processing of C- and A-nociceptive inputs is discussed with respect to roles both of the LAAH in pain processing, and of C- and A-nociceptive inputs in acute and chronic pain.

Organization of brain somatomotor-sympathetic circuits

Numerous physiological and emotionally motivated behaviors require concomitant activation of somatomotor and sympathetic efferents. Likewise, adaptive and maladaptive responses to stress are often characterized by simultaneous recruitment of these efferent systems. This review describes recent literature that outlines the organization of somatomotor-sympathetic circuitry in the rat. These circuits were delineated by employing recombinant pseudorabies (PRV) viral vectors as retrograde trans-synaptic tract tracers. In these studies PRV-152, a strain that expresses enhanced green fluorescent protein, was injected into sympathectomized hindlimb muscle, while PRV-BaBlu, which expresses beta-galactosidase, was injected into the adrenal gland in the same animals. Immunofluorescent methods were then used to determine the presence of putative dual-function neurons that were infected with both viral strains. These somatomotor-sympathetic neurons (SMSNs) were detected in a number of brain regions. However, the most prominent nodes in this circuitry included the paraventricular, dorsomedial, and lateral nuclei of the hypothalamus, ventrolateral periaqueductal grey and ventromedial medulla. Phenotypic studies revealed subsets of SMSNs to be capable of synthesizing serotonin, or to contain neuroactive peptides vasopressin, oxytocin, orexins, or melanin-concentrating hormone. Based on these data and the results of studies employing monosynaptic tracers a central somatomotor-sympathetic circuit is proposed. This circuitry is likely recruited in diverse situations, including stress responses, cold defense, exercise and sleep. Furthermore, activation of specific classes of SMSNs likely shapes distinct stress-coping strategies. Dysregulation in the organization and function of this circuit may also contribute to the expression of physical symptoms of affective disorders, such as major depression, anxiety and panic.

Distinct populations of presympathetic-premotor neurons express orexin or melanin-concentrating hormone in the rat lateral hypothalamus

Orexin and melanin-concentrating hormone (MCH) have been implicated in mediating a variety of different behaviors. These include sleep and wakefulness, locomotion, ingestive behaviors, and fight-or-flight response, as well as anxiety- and panic-like behaviors in rodents. Despite such diversity, all these processes require coordinated recruitment of the autonomic and somatomotor efferents. We have previously mapped the locations of presympathetic-premotor neurons (PSPMNs) in the rat brain. These putative dual-function neurons send trans-synaptic projections to somatomotor and sympathetic targets and likely participate in somatomotor-sympathetic integration. A significant portion of these neurons is found within the dorsomedial (DMH) and lateral hypothalamus (LH), areas of the brain that contain MCH- and orexin- synthesizing neurons in the central nervous system. Thus, we hypothesized that hypothalamic PSPMNs utilize MCH or orexin as their neurotransmitter. To test this hypothesis, we identified PSPMNs by using recombinant strains of the pseudorabies virus (PRV) for trans-synaptic tract tracing. PRV-152, a strain that expresses enhanced green fluorescent protein, was injected into sympathectomized gastrocnemius muscle, whereas PRV-BaBlu, which expresses beta-galactosidase, was injected into the adrenal gland in the same animals. By using immunofluorescent methods, we determined whether co-infected neurons express MCH or orexin. Our findings demonstrate that PSPMNs synthesizing either MCH or orexin are present within LH, where they form two separate populations. PSPMNs located around the fornix express orexin, whereas those located around the cerebral peduncle are more likely to express MCH. These two clusters of PSPMNs within LH likely play distinct functional roles in autonomic homeostasis and stress coping mechanisms.

Deep brain stimulation for treatment of obesity in rats

OBJECT

Given the success of deep brain stimulation (DBS) in a variety of applications (for example, Parkinson disease and essential tremor), other indications for which there is currently little effective therapy are being evaluated for clinical use of DBS. Obesity may be one such indication. Studies of the control of feeding and appetite by neurosurgical lesioning have been completed previously. This study was conducted to test the authors' hypothesis that continuous bilateral stimulatory inhibition of the rat lateral hypothalamic nucleus (LH) would lead to significant and sustained decrease in food intake and subsequent weight loss.

METHODS

Sixteen Sprague-Dawley rats were maintained on a high-fat diet. Daily food intake and weight gain were measured for 7 days, at which time the animals underwent stereotactic placement of 0.25-mm-diameter bipolar stimulating electrodes bilaterally in the LH. On postoperative Day 7, eight animals began to receive continuous stimulation of the LH. The remaining eight animals were left unstimulated as the control group. Individual animal weight, food intake, and water intake were monitored daily and continuously throughout the experiment until postoperative Day 24.

RESULTS

There was a decreased rate of weight gain after surgery in all animals, but the unstimulated group recovered and resumed a linear weight gain curve. The stimulated group, however, failed to show weight gain and remained below the mean baseline for body mass. There was a significant weight loss between the stimulated and unstimulated groups. On postoperative Day 24, compared with the day of surgery (Day 0), the unstimulated group had a mean weight gain of 13.8%, whereas the stimulated group had a 2.3% weight loss on average (p = 0.001), yielding a 16.1% weight difference between the two groups.

CONCLUSIONS

Bilateral electrical stimulatory inhibition of the LH is effective in causing significant and sustained weight loss in rats.

Branched oxytocinergic innervations from the paraventricular hypothalamic nuclei to superficial layers in the spinal cord

The paraventricular nucleus (PVN) of the hypothalamus is an interesting structure with diverse functions due to its different neuronal populations, neurotransmitters, and projections to other central nervous system structures. The PVN is a primary source of oxytocin (OT) in the central nervous system. In fact, a direct PVN projection to the spinal cord has been demonstrated by retrograde and anterograde tracers, and more than the 50% of this projection is oxytocinergic. This OT descending projection is proposed to be an endogenous system that controls the nociceptive information arriving at the spinal cord. However, we have no information about the specific organization of the OT descending innervations to the different spinal cord segments. The aim of the present study was to determine whether the projecting PVN neurons arrive at cervical regions and then continue to lumbar regions. That is, we sought to establish if the OT projecting cells have a topic or a diffuse projection in order to obtain histological data to support the endogenous OT diffuse mechanism of analgesia described elsewhere. With this purpose in mind we combined the OT immunohistochemistry technique with retrograde neuronal tracers in the spinal cord. We applied Diamidino Yellow (DY) for the superficial dorsal horn cervical segments and True Blue (TB) for the lumbar segments. Data were collected from eight rats with well-placed injections. We only used the animals in which the tracer deposits were confined to superficial layers I and II of the dorsal horn. A mainly ipsilateral projection was observed, but stained neurons were also observed in the contralateral PVN. A large fraction of the stained PVN cells was doubled labeled but some were single labeled. Combining the retrograde tracer techniques and the OT detection procedure, we observed triple-labeled neurons. The present results demonstrate that PVN neurons send collaterals at least to the superficial cervical and lumbar segments of the dorsal horn of the spinal cord. Moreover, some of these stained cells use OT as a neurotransmitter. These results are of great relevance since they demonstrate that the PVN plays an important role in the somatosensorial system, and they support anatomic evidence of an endogenous mechanism involved in analgesia. Finally, we also describe median raphe nucleus double-labeled cells (DY+TB) signaling diffuse descending projections for this largely studied nucleus that are involved in endogenous analgesia.

Rostral elements of sympatho-motor circuitry: a virally mediated transsynaptic tracing study

Numerous physiological and emotionally motivated behaviors, including locomotion, exercise, escape, and attack behaviors as well as passive coping responses, require concomitant activation of motor and sympathetic efferents. Such functional heterogeneity suggests the existence of dual function neurons that can simultaneously coordinate motor and sympathetic output. Because previous physiological investigations have implicated a number of mesencephalic and telencephalic regions in mediating these behaviors, we hypothesized the presence of dual function sympatho-motor neurons in these neural structures. To test this hypothesis, we used recombinant strains of the pseudorabies virus (PRV) for transsynaptic tract-tracing. PRV-152, a strain that expresses enhanced green fluorescent protein, was injected into sympathectomized gastrocnemius muscle, whereas PRV-BaBlu, which expresses beta-galactosidase, was injected into the adrenal gland in the same animals. Although coinfected neurons were detected in a number of mesencephalic and telencephalic regions, >50% of such neurons were located within specific subdivisions of two general areas: the hypothalamus and periaqueductal gray. These subdivisions included the ventrolateral periaqueductal gray, dorsomedial hypothalamus, dorsolateral lateral hypothalamus, and ventral portion of the medial parvocellular subdivision of the paraventricular nucleus of the hypothalamus (PVN). A subset of the sympatho-motor neurons within the PVN also contained either arginine vasopressin or oxytocin. This sympatho-motor circuitry likely plays an important role in mediating different aspects of stress responses and emotionally motivated behaviors.

Stimulation of the lateral hypothalamus produces antinociception mediated by 5-HT1A, 5-HT1B and 5-HT3 receptors in the rat spinal cord dorsal horn

The lateral hypothalamus is part of an efferent system that modifies pain at the spinal cord dorsal horn, but the mechanisms by which lateral hypothalamus-induced antinociception occur are not fully understood. Previous work has shown that antinociception produced from electrical stimulation of the lateral hypothalamus is mediated in part by spinally projecting 5-hydroxytryptamine (5-HT) neurons in the ventromedial medulla. To further examine the role of the lateral hypothalamus in antinociception, the cholinergic agonist carbamylcholine chloride (125 nmol) was microinjected into the lateral hypothalamus of female Sprague-Dawley rats and nociceptive responses measured on the tail-flick and foot-withdrawal tests. Intrathecal injections of the selective 5-HT1A, 5-HT1B, 5-HT3 receptor antagonists, WAY 100135, SB-224289, and tropisetron, respectively, and the non-specific antagonist methysergide, were given. Lateral hypothalamus stimulation with carbamylcholine chloride produced significant antinociception that was blocked by WAY 100135, tropisetron, and SB-224289 on both the tail-flick and foot-withdrawal tests. Methysergide was not different from controls on the tail flick test, but increased foot-withdrawal latencies compared with controls. These results suggest that the lateral hypothalamus modifies nociception in part by activating spinally projecting serotonin neurons that act at 5-HT1A, 5-HT1B, and 5-HT3 receptors in the dorsal horn.

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.

Evidence for a direct projection from the paraventricular nucleus of the hypothalamus to putative serotoninergic neurons of the nucleus paragigantocellularis involved in the control of erection in rats

In the male rat, serotoninergic neurons of the ventrolateral medulla send direct projections onto spinal preganglionic neurons that innervate the penis. The role of the paraventricular nucleus of the hypothalamus in the control of penile erection is well recognized. Our aim was to demonstrate anatomical relation between paraventricular neurons and medullary serotoninergic neurons innervating the penis. In adult male rats, stereotaxic iontophoretic injections of Phaseolus vulgaris leuco-agglutinin were performed in the paraventricular nucleus. Neurons in the ventrolateral medulla were retrogradely labelled using transneuronal retrograde transport of pseudorabies virus injected in the corpus cavernosum. Sections of the ventro-lateral medulla were processed for double immunofluorescence to reveal both Phaseolus vulgaris leuco-agglutinin and pseudorabies virus using specific antibodies. Sections were also processed for the simultaneous detection of pseudorabies virus and serotonin. Pseudorabies virus-infected neurons in the ventrolateral medulla were present in the nucleus paragigantocellularis, reticular formation of the medulla, raphe pallidus and raphe magnus. In the nucleus paragigantocellularis, all pseudorabies virus-infected-neurons were immunoreactive for serotonin. Some of them received Phaseolus vulgaris leuco-agglutinin-labelled varicose fibres that ran along the soma of pseudorabies virus-infected neurons. Confocal microscopy suggested the presence of several close appositions between them, which were demonstrated using three-dimensional reconstruction of serial optical sections. Our results show that paraventricular neurons send direct projections in the nucleus paragigantocellularis onto neurons that innervate the penis. They suggest a possible role of the paraventricular nucleus in penile erection through the control of descending serotoninergic raphe-spinal neurons. The neurotransmitter used in this pathway remains to be determined.

Identification of NPY-induced c-Fos expression in hypothalamic neurones projecting to the dorsal vagal complex and the lower thoracic spinal cord

Neuropeptide Y exerts profound effects on body weight and glucose homeostasis. We have investigated the effect of centrally administered neuropeptide Y on the activity of descending neurones of the hypothalamic paraventricular nucleus by combining retrograde tract tracing with c-Fos immunocytochemistry. Male rats were injected with True Blue into the dorsal vagal complex and with FluoroGold into the intermediolateral column of the lower thoracic spinal cord. One week after the last surgical procedure, animals were injected centrally with an orexigenic dose of neuropeptide Y (5 microg) and sacrificed 60 to 240 minutes following this injection. Temporal analysis of NPY-induced c-Fos expression showed a peak at 90 minutes, which was nearly returned to basal levels between 120 and 240 minutes. Expression of c-Fos was prominent in several of the subnuclei of the paraventricular nucleus and in the adjacent perifornical nucleus. Neurones projecting to the spinal cord were prominent in the dorsal, lateral, and ventral portion of the medial parvicellular subnuclei of the PVN. About 15% of IML projecting neurones of the medial parvicellular subnucleus were Fos-positive, whereas less than 5% of IML projecting neurones from other subnuclei were Fos-positive. Hardly any PVN neurones projecting to the dorsal vagal complex were concomitantly Fos-positive. A considerably larger (>10%) proportion of perifornical neurones projecting to the nucleus of the solitary tract were c-Fos-immunopositive. In conclusion, NPY induces c-Fos in paraventricular neurones projecting to intermediolateral column of the spinal cord and in neurones of the perifornical nucleus projecting to the dorsal vagal complex.

Identification of branching paraventricular neurons of the hypothalamus that project to the rostroventrolateral medulla and spinal cord

The paraventricular nucleus of the hypothalamus has efferent connections to autonomic nuclei known to ultimately regulate cardiovascular function. Studies have revealed projections to the sympathetic preganglionic neurons of the spinal cord and presympathetic motor neurons of the rostral ventrolateral medulla. This study set out to establish whether the same neurons in the paraventricular nucleus innervate both these regions. In rats the fluorescent neuroanatomical tracers FluoroGold, Fast Blue or Dextran tetramethyl rhodamine were injected into either the rostral ventrolateral medulla or T2 region of the spinal cord. After a suitable survival period (five to seven days) three populations of neurons could be identified in the paraventricular nucleus, double-labelled neurons and single-labelled neurons resulting from the injections into the spinal cord or injections into the rostral ventrolateral medulla. The neurons were of similar size regardless of the dye content. Most neurons were found in the parvocellular subdivision of the mid rostral paraventricular nucleus. The number of labelled neurons decreased in the caudal sections. This study provides an anatomical basis for three means of influence that the paraventricular nucleus can have on sympathetic activity; a hierarchical in series projection via the rostral ventrolateral medulla; a projection running in parallel with this but bypassing the rostroventrolateral medulla; and a branching population innervating neurons in both the rostral ventrolateral medulla and spinal cord. The paraventricular nucleus of the hypothalamus is an important brain area concerned with maintaining cardiovascular homeostasis. This anatomical study has not only provided confirmatory evidence that direct projections arising from the paraventricular hypothalamic nucleus do project to the rostral ventrolateral medulla and spinal cord, regions known to influence cardiovascular regulation. The study has identified a branching projection originating in the paraventricular nucleus of the hypothalamus that projects to both the rostral ventrolateral medulla and the spinal cord. Thus the paraventricular nucleus of the hypothalamus has three pathways in which to influence cardiovascular homeostasis.

Identification of an efferent projection from the paraventricular nucleus of the hypothalamus terminating close to spinally projecting rostral ventrolateral medullary neurons

The paraventricular nucleus of the hypothalamus is increasingly being viewed as an important site for cardiovascular integration because of its connections to regions in the brain and spinal cord which are known to be important in cardiovascular control. Like the vasomotor neurons of the rostral ventrolateral medulla, descending axons from paraventricular neurons can be identified that form synapses on sympathetic preganglionic neurons in the thoracic spinal cord. The purpose of this study was to determine whether paraventricular axons project to the rostral ventrolateral medulla and whether they are closely apposed to reticulospinal neurons in this region. Descending paraventricular axons were labelled with biotin dextran amine, while rostral ventrolateral medullary neurons were retrogradely labelled from the spinal cord with wheatgerm agglutinin conjugated to horseradish peroxidase. This revealed, within the rostral ventrolateral medulla, paraventricular axon and terminal varicosities closely apposed to and apparently contiguous with retrogradely labelled spinally projecting neurons. Thus our study at the light microscopical level has shown the potential for the paraventricular nucleus to directly influence rostral ventrolateral reticulospinal neurons. We suggest these connections, if confirmed by electron microscopy, could be one means by which activation of paraventricular neurons elicits alterations in blood pressure.

Hypothalamic hypocretin (orexin): robust innervation of the spinal cord

Hypocretin (orexin) is synthesized by neurons in the lateral hypothalamus and has been reported to increase food intake and regulate the neuroendocrine system. In the present paper, long descending axonal projections that contain hypocretin were found that innervate all levels of the spinal cord from cervical to sacral segments, as studied in mouse, rat, and human spinal cord and not previously described. High densities of axonal innervation are found in regions of the spinal cord related to modulation of sensation and pain, notably in the marginal zone (lamina 1). Innervation of the intermediolateral column and lamina 10 as well as strong innervation of the caudal region of the sacral cord suggest that hypocretin may participate in the regulation of both the sympathetic and parasympathetic parts of the autonomic nervous system. Double-labeling experiments in mice combining retrograde transport of diamidino yellow after spinal cord injections and immunocytochemistry support the concept that hypocretin-immunoreactive fibers in the cord originate from the neurons in the lateral hypothalamus. Digital-imaging physiological studies with fura-2 detected a rise in intracellular calcium in response to hypocretin in cultured rat spinal cord neurons, indicating that spinal cord neurons express hypocretin-responsive receptors. A greater number of cervical cord neurons responded to hypocretin than another hypothalamo-spinal neuropeptide, oxytocin. These data suggest that in addition to possible roles in feeding and endocrine regulation, the descending hypocretin fiber system may play a role in modulation of sensory input, particularly in regions of the cord related to pain perception and autonomic tone.

Modulation of exercise tachycardia by vasopressin in the nucleus tractus solitarii

Our objective was to study the role of vasopressinergic synapses at the nucleus tractus solitarii (NTS) in the modulation of exercise-induced tachycardia. We evaluated the effect of NTS administration of vasopressin (AVP) or vasopressin antagonist (AVP(ant)) on heart rate (HR) and mean arterial pressure (MAP) responses during dynamic exercise in male rats with chronic arterial and NTS cannulas. Sedentary (S) and trained (T) animals were tested at three or four exercise levels (from 0.4 up to 1.4 km/h) after NTS injection of AVP or AVP(ant) 20-30 min before treadmill exercise. Plasma and regional brain levels of AVP were measured in separate groups of S and T rats at rest and immediately after acute exercise. When administered into the NTS, exogenous AVP (20 pmol) caused a small but significant decrease in baseline HR and potentiated the tachycardiac response to mild to moderate exercise intensities (on average, increases of 35-46 beats/min over control tachycardic response). The potentiation of exercise tachycardia by AVP was long lasting and more pronounced in T than in S rats. Even 2 days after NTS AVP injection, there was evidence for an alteration in the HR response to exercise. Mediation by V1 receptors was supported by the blunted tachycardiac response to exercise after administration of a V1 antagonist d(CH2)5Tyr MeAVP into the NTS in both T and S rats (average reductions of 23-34 and 13-19 beats/min below control tachycardia, respectively). No changes were observed in baseline MAP or the exercise-induced pressor responses. There were specific changes in brain stem AVP levels that were related to the exercise treatment. T rats showed a marked increase in dorsal and ventral brain stem AVP content after acute exercise. There were no changes in hypothalamus, median eminence, posterior pituitary, or plasma AVP. These data indicate that vasopressinergic synapses and V1 receptors in the NTS are involved in the potentiation of tachycardic response to exercise. The vasopressinergic mechanism operates in both S and T rats, but training alters the sensitization of V1 receptors by AVP.

Participation of paraventricular nucleus of hypothalamus in central regulation of penile erection in the rat

PURPOSE

To investigate the possible participation of the paraventricular nucleus of hypothalamus in central regulation of penile erection.

MATERIALS AND METHODS

Male adult Sprague-Dawley rats were anesthetized and maintained with pentobarbital sodium. The intracavernous pressure (ICP) was used as an experimental index for penile erection, and was recorded alongside systemic arterial pressure and heart rate. The effect on ICP of electrical (30-s train of 30-120 microA, 40-160 Hz, 1-ms rectangular pulses) or chemical (L-glutamate, 0.5 nmol/50 nl.) activation of the paraventricular nucleus of hypothalamus (PVN) or hippocampal formation was evaluated.

RESULTS

Electrical activation of the PVN elicited both multiple and single episodes of elevation in ICP, along with visible erection and ejaculation. The former pattern exhibited an increase in ICP that was more sustained, with higher peak amplitude and longer latency. Chemical stimulation of neuronal perikarya in the PVN also resulted in similar patterns of rise in ICP and visible erection. These effects were, nonetheless, not accompanied by significant alterations in systemic arterial pressure and heart rate. Activation of the hippocampal formation, as we reported previously, similarly elicited multiple and single episodes of increase in ICP. These erectile responses, however, were substantially reduced or eliminated upon electrolytic lesion of the ipsilateral PVN.

CONCLUSION

These observations suggest that the PVN may be an important nucleus that participates in central neural regulation of penile erection in the rat. Furthermore, an efferent pathway(s) from the hippocampal formation to PVN may constitute part of the neural circuitry in the forebrain in the regulation of erectile functions.

Organization of projections from the dorsomedial nucleus of the hypothalamus: a PHA-L study in the rat

The axonal projections of the dorsomedial nucleus of the hypothalamus were investigated by using Phaseolous vulgaris-leucoagglutinin. The main conclusion of this work is that these projections are largely intrahypothalamic, with smaller components directed toward the brainstem and telencephalon. Although the intrahypothalamic pathways are very complex and intermix at various levels, we conclude that dorsomedial nucleus outputs follow three distinct ascending pathways: periventricular, coursing through the hypothalamic periventricular zone; ventral, traveling beneath the medial zone; and lateral, ascending in medial parts of the lateral hypothalamic area. Within the hypothalamus, the most densely innervated areas are the paraventricular nucleus, other dorsal regions of the periventricular zone, the preoptic suprachiasmatic nucleus, and the parastrial nucleus. Other significant terminal fields include the median preoptic, anteroventral periventricular, lateral part of the medial preoptic, and anteroventral preoptic nuclei; and the retrochiasmatic (including perisuprachiasmatic) area. Descending projections follow two pathways that also converge at various levels: a dorsal pathway in the midbrain periventricular system travels through, and primarily innervates, the periaqueductal and pontine gray, and a ventral pathway extends through ventromedial regions of the brainstem. Although sparse, fibers in the later pathway can be traced as far caudally as the nucleus of the solitary tract. The results are discussed relative to the pathways and properties of nearby hypothalamic medial zone nuclei. Dorsomedial nucleus projections are similar to certain other nuclei (e.g., anteroventral periventricular and parastrial) with predominantly intrahypothalamic projections, and different from those arising in the medial zone nuclei (medial preoptic, anterior hypothalamic, ventromedial, and mammillary.

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.

Increased firing of neurons in the posterior hypothalamus which precede classically conditioned pupillary dilations

Paralyzed cats were used as subjects in a classical conditioning experiment where each subject was exposed to 40 explicitly unpaired 1-s bursts of white noise and 0.5-s paw shocks. This training was followed by 60 trials of the two stimuli paired, where the white noise immediately preceded the paw shock. Following this training, the subjects were re-exposed to 40 trials of the explicitly unpaired procedure. The pupil was monitored as the behavior and electrodes implanted in the thalamus, the dorsal hypothalamus and the posterior hypothalamus recorded the activity of clusters of cells. Only the cells in the posterior hypothalamus showed robust changes in firing rates that preceded the pupillary behavior, both (a) on any particular trial and (b) as the learned association was being demonstrated behaviorally across trials.

Neural activity in the midbrain correlated with hindlimb extension initiated by locomotor stimulation of the hypothalamus of the anesthetized rat

Midbrain neuronal activity that correlated with the initiation of locomotion produced by hypothalamic stimulation was studied. Locomotion was elicited by electrical stimulation in the perifornical hypothalamus of 59 rats anesthetized with Nembutal. The first hindlimb extension indexed stepping onset. Single and multiple neurons were recorded ipsilateral to the stimulation site at 2230 sites in the anterior and posterior midbrain. To classify responses, activity patterns averaged around stimulation onset and around the extension onset were examined. Responses with specific correlations to extension onset were Type I; responses not specifically related to the extension onset were Type II. In the anterior midbrain, 6% of sites were Type I and 8% were Type II. The larger Type I responses were frequent in the anterior tegmentum near the central gray. The relative frequency of Type I patterns in the posterior ventrolateral tegmentum was similar. Other regions showed relatively more Type II responses; they included the ventral tegmental area, and the regions near the superior cerebellar peduncle and the posterior central gray. Regional population profiles showed that during the initiation of locomotion, neurons in the posterior peribrachial region responded early and neurons in the anterior dorsal and the posterior ventrolateral tegmentum responded later. The initiation-related activity of Type I neurons in the anterior and posterior midbrain tegmentum suggest that they warrant further study for a role in locomotor initiation.

Preoptic and hypothalamic neurons and the initiation of locomotion in the anesthetized rat

Despite its insensate condition and apparent motoric depression, the anesthetized rat can provide useful information about the systems involved in locomotor initiation. The preparation appears to be particularly appropriate for the study of the appetitive locomotor systems and may be more limited for the study of the circuits involved in exploratory and defensive locomotion. In the anesthetized rat, pharmacological evidence indicates that the preoptic basal forebrain contains neurons which initiate locomotor stepping. Mapping with low levels of electrical stimulation indicates, but does not prove, that a region centered in the lateral preoptic area might be the location of these neurons. Several lines of evidence indicate that locomotor stepping elicited by electrical stimulation of the hypothalamus is mediated by neurons in the perifornical and lateral hypothalamus. Locomotor effects of hypothalamic stimulation persist in the absence of descending fibers of passage from the ipsilateral preoptic locomotor regions but are severely impaired by kainic acid lesions in the area of stimulation. Injections of glutamate into the perifornical and lateral hypothalamus elicit locomotor stepping at short latencies. Anatomical evidence suggests that the two regions are components of a network for appetitive locomotion. The recognition that multiple systems initiate locomotion both clarifies and complicates the study of locomotion. It provides a framework that incorporates disparate findings but it also underscores the need for increased attention to behavioral issues in studies of locomotor circuitry.

Central nervous system innervation of the penis as revealed by the transneuronal transport of pseudorabies virus

Transneuronal tracing techniques were used in order to identify putative spinal interneurons and brainstem sites involved in the control of penile function. Pseudorabies virus was injected into the corpus cavernosus tissue of the penis in rats. After a four day survival period, rats were perfused with fixative and virus-labelled neurons were identified by immunohistochemistry. Postganglionic neurons were retrogradely labelled in the major pelvic ganglia. In the spinal cord, sympathetic and parasympathetic preganglionic neurons were labelled transneuronally. Presumptive interneurons were also labelled in the lower thoracic and lumbosacral spinal cord in locations consistent with what is currently known about such interneurons. In the brainstem, transneuronally labelled neurons were found in the medulla, pons and hypothalamus. Regions consistently labelled included the nucleus paragigantocellularis, parapyramidal reticular formation of the medulla, raphe pallidus, raphe magnus, A5 noradrenergic cell group, Barrington's nucleus and the paraventricular nucleus of the hypothalamus. This study confirmed previous studies from our lab and others concerning the preganglionic and postganglionic neurons innervating the penis. The number, morphology and location of these neurons were consistent with labelling seen following injection of conventional tracers into the penis. The brainstem nuclei labelled in this study were also consistent with what is currently known about the brainstem control of penile function. The labelling appeared to be highly specific, in that descending systems involved in other functions were not labelled. These results provide further evidence that the pseudorabies virus transneuronal tracing technique is a valuable method for identifying neural circuits mediating specific functions.

The lateral hypothalamic area revisited: neuroanatomy, body weight regulation, neuroendocrinology and metabolism

This article reviews findings that have accumulated since the original description of the syndrome that follows destruction of the lateral hypothalamic area (LHA). These data comprise the areas of neuroanatomy, body weight regulation, neuroendocrinology, neurochemistry, and intermediary metabolism. Neurons in the LHA are the largest in the hypothalamus, and are topographically well organized. The LHA belongs to the parasympathetic area of the hypothalamus, and connects with all major parts of the brain and the major hypothalamic nuclei. Rats with LHA lesions regulate their body weight set point in a primary manner and not because of destruction of a "feeding center". The lower body weight is not due to finickiness. In the early stages of the syndrome, catabolism and running activity are enhanced, and so is the activity of the sympathetic nervous system (SNS) as shown by increased norepinephrine excretion that normalizes one mo later. The LHA plays a role in the feedback control of body weight regulation different from ventromedial (VMN) and dorsomedial (DMN). Tissue preparations from the LHA promote glucose utilization and insulin release. Although it does not belong to the classical hypothysiotropic area of the hypothalamus, the LHA does affect neuroendocrine secretions. No plasma data on growth hormone are available following electrolytic lesions LHA but electrical stimulation fails to elicit GH secretion. Nevertheless, antiserum raised against the 1-37 fragment of human GHRF stains numerous perikarya in the dorsolateral LHA. The plasma circadian corticosterone rhythm is disrupted in LHA lesioned rats, but this is unlikely due to destruction of intrinsic oscillators. Stimulation studies show a profound role of the LHA in glucose metabolism (glycolysis, glycogenesis, gluconeogenesis), this mechanism being cholinergic. Its role in lipolysis appears not to be critical. In general, stimulation of the VMN elicits opposite effects. Lesion studies in rats show altered in vitro glucose carbon incorporation into several tissue fractions both a few days, and one mo after lesion production. Several of these changes may be due to the reduced food intake, others appear to be due to a "true" lesion effect.

Supraspinal fiber outgrowth and apparent synaptic remodelling across transected-reconstructed feline spinal cord

Following complete transection of the spinal cord at T9, 12 cats were separated into two groups: Group 1 received a collagen matrix (CM) treated with a neuroactive agent or with saline to bridge the spinal cord stumps and an omental transposition which was placed on the dorsal surface of the matrix; Group 2 received spinal cord transection only. Two cats received no spinal cord transection. After 90 days, all animals were killed and their brains and spinal cords were removed for immunohistochemical examination. Two weeks prior to sacrifice, spinal cord blood flows (SCBF) were measured and the retrograde axonal tracer Fluoro-Gold was injected below the transection site. Results show that omental transposition to the CM bridge in Group 1 animals increased SCBF an average 59% (assessed by clamping the omental blood supply to the cord). Examination of the brain 90 days after cord transection revealed Fluoro-Gold accumulation in the cytoplasm and processes of neurons located in the brainstem, midbrain, and diencephalic region which are known to contribute pathways to the spinal cord. Immunohistochemical staining with antibodies against the catecholamine synthesizing enzymes tyrosine hydroxylase and dopamine-B-hydroxylase, indicated that only Group I treated cats developed dense bundles of dopaminergic and noradrenergic fibers within the CM bridge and distal spinal cord tissue. These fibers were seen to extend 90 mm below the transection site. In addition, the synaptogenic marker synaptophysin (SYN) was observed in association with dopaminergic and noradrenergic fibers distal to the collagen matrix bridge, an indication that synaptic remodelling (regeneration) by previously denervated supraspinal axons may have occurred. Immunostaining for glial fibrillary acidic protein (GFAP) showed little to none reactive astrocytosis near the transection site of cats treated with the CM and omentum transposition (Group 1). No catecholaminergic fibers or SYN expression below the transection site were observed in Group 2 treated cats. Group 2 treated cats also showed dense immunostaining of GFAP near the transection site indicating significant astrocytic proliferation. These findings indicate that following complete spinal cord transection in cats and reconstruction with a treated collagen matrix and omental transposition, disconnected supraspinal fibers have the ability to regenerate for long anatomic distances and seemingly engage in synaptic remodelling with distal target tissue.

Projections of anterior hypothalamic neurones to the dorsal and ventral periaqueductal grey in the rat

Projections of neurones in the rostral hypothalamus to the periaqueductal grey matter (PAG) of the rat were investigated using retrograde tracing of red and green fluorescent latex microspheres. Microspheres were injected into one of 4 PAG sub-divisions, namely the dorsal, dorsolateral, ventral and ventrolateral parts. The patterns of retrogradely labelled neurones in the hypothalamus from each of the 4 PAG sub-divisions were found to differ and these are described. The precise nature of projections of neurones in the anterior hypothalamic area (AHA) was investigated and it was found that neurones within a circumscribed area of AHA, the lateral area of the anterior hypothalamus (LAAH), projected predominantly to the dorsolateral PAG while neurones in immediately adjacent areas projected to either dorsolateral or ventrolateral aspects of the PAG. Double retrograde tracing studies, where the two different colour beads were injected into different subdivisions of the PAG, gave rise to very few double labelled hypothalamic neurones, indicating that neurones in the hypothalamus project to only one sub-division of the PAG. The functional significance of these pathways is discussed in relation to mechanisms of autonomic and sensory control.

Distribution of substance P-immunoreactive elements in the preoptic area and the hypothalamus of the rat

The localization and morphology of neurons, processes, and neuronal groups in the rat preoptic area and hypothalamus containing substance P-like immunoreactivity were studied with a highly selective antiserum raised against synthetic substance P. The antiserum was thoroughly characterized by immunoblotting; only substance P was recognized by the antiserum. Absorption of the antiserum with synthetic substance P abolished immunostaining while addition of other hypothalamic neuropeptides had no effect on the immunostaining. The specificity of the observed immunohistochemical staining pattern was further confirmed with a monoclonal substance P antiserum. The distribution of substance P immunoreactive perikarya was investigated in colchicine-treated animals, whereas the distribution of immunoreactive nerve fibers and terminals was described in brains from untreated animals. In colchicine-treated rats, immunoreactive cells were reliably detected throughout the preoptic area and the hypothalamus. In the preoptic region, labeled cells were found in the anteroventral periventricular and the anteroventral preoptic nuclei and the medial and lateral preoptic areas. Within the hypothalamus, immunoreactive cells were found in the suprachiasmatic, paraventricular, supraoptic, ventromedial, dorsomedial, supramammillary, and premammillary nuclei, the retrochiasmatic, medial hypothalamic, and lateral hypothalamic areas, and the tuber cinereum. The immunoreactive cell groups were usually continuous with adjacent cell groups. Because of the highly variable effect of the colchicine treatment, it was not possible to determine the actual number of immunoreactive cells. Mean soma size varied considerably from one cell group to another. Cells in the magnocellular subnuclei of the paraventricular and supraoptic nuclei were among the largest, with a diameter of about 25 microns, while cells in the supramammillary and suprachiasmatic nuclei were among the smallest, with a diameter of about 12 microns. Immunoreactive nerve fibers were found in all areas of the preoptic area and the hypothalamus. The morphology, size, density, and number of terminals varied considerably from region to region. Thus, some areas contained single immunoreactive fibers, while others were innervated with such a density that individual nerve fibers were hardly discernible. During the last decade, knowledge about neural organization of rodent hypothalamic areas and mammalian tachykinin biochemistry has increased substantially. In the light of these new insights, the present study gives comprehensive morphological evidence that substance P may be centrally involved in a wide variety of hypothalamic functions. Among these could be sexual behavior, pituitary hormone release, and water homeostasis.

Meso-diencephalic regions projecting to spinal cord and dorsal column nuclear complex in the hedgehog-tenrec, Echinops telfairi

The distribution of neurons projecting to the spinal cord and dorsal column nuclear complex was investigated in the mesodiencephalic regions of the lesser hedgehog-tenrec, Echinops telfairi (Insectivora) by using the retrograde flow technique. While only few neurons projected to the dorsal column nuclear complex, numerous cells were found to give rise to spinal projections. Rubro-spinal neurons of various sizes were distributed over the entire rostrocaudal extent of the contra-lateral nucleus; a few neurons were also located ipsilaterally, Unlike that of the opossum, the projection appeared to be somatotopically organised. Interstitio-spinal neurons were differentiated into several subpopulations according to their location and laterality of projection. In the ipsilateral periventricular grey, in addition, there was a distinct population of cells possibly corresponding to the nucleus of Darkschewitsch. The mesencephalic central grey contained relatively few labeled neurons, the great majority of them being mesencephalic trigeminal, ectopic cuneiform or midline cells. Labeled cuneiform and midline cells, on the other hand, were quite numerous, extending both from a level just caudal to the trochlear nucleus to levels far beyond the rostral tip of the somatic oculomotor nucleus. The discrepancy between the poorly differentiated oculomotor nuclei and the apparently well-developed Edinger-Westphal complex is discussed. Hypothalamo-spinal neurons were essentially restricted to dorsal regions: the hypothalamic paraventricular nucleus (PAV), the dorso-medial (DmHy) and dorso-intermediate cell groups as well as the lateral hypothalamic zone. The latter two cell groups were bilaterally labeled, while the labeled neurons in DmHy and PAV were located predominantly ipsilaterally. Labeled neurons in the amygdala, colliculus superior and mesencephalic trigeminal nucleus were only found following cervical injections; all other mentioned areas and the posterior commissure complex projected to, at least, midthoracic level.

Locomotor sites mapped with low current stimulation in intact and kainic acid damaged hypothalamus of anesthetized rats

To determine whether local neurons mediated the locomotor effects of electrical stimulation of the lateral hypothalamus, kainic acid injections (0.5-1.25 micrograms), intended to destroy neural somata as opposed to fibers of passage, were made unilaterally in the tuberal-posterior hypothalamus of 22 rats. The area of lesion and its contralateral homolog were mapped for locomotor stepping sites in Nembutal-anesthetized rats mounted in a stereotaxic apparatus such that locomotor stepping rotated a wheel. Stimulation (25 and 50 microA, 50 Hz, 0.5-ms cathodal pulses, 10-s trains) was delivered through 50-80 microns glass pipettes filled with 2 M saline. Contralateral to the lesion, locomotor stepping sites were common in the perifornical lateral and medial hypothalamus and less dense in the zona incerta. On the side of the kainic-acid lesion, locomotor sites were generally absent in the central part of the damaged area. If they did appear within the area of lesion, they tended to be near the border with intact tissue. In a few cases, locomotor stepping sites were found centrally located in the lesion amidst widespread loss of somata. In four rats, additional maps of anterior locomotor regions in the preoptic area ipsilateral to the lesion suggested that their descending fibers were largely spared by the kainic lesions. Local neurons appear to be major contributors to the locomotion elicited by electrical stimulation of the lateral hypothalamus, but fibers of passage may also participate.

Projections of the paraventricular nucleus of the hypothalamus to the sexually dimorphic lumbosacral region of the spinal cord

Lumbar regions L5-L6 of the spinal cord of the male rat contain the sexually dimorphic motor nuclei, the spinal nucleus of the bulbocavernosus (SNB) and the dorsolateral nucleus (DLN), which innervate perineal muscles, the bulbocavernosus and the ischiocavernosus, respectively. This neuromuscular system controls penile reflexes which are essential to male reproductive success. Oxytocin has been shown to induce penile reflexes and the site of action for these effects is the PVN. Since PVN is known to project to cervical and thoracic levels of spinal cord, the present study examined projections of the PVN to the L5-L6 region of the spinal cord. WGA-HRP was injected into the region of L5-L6, aimed at the SNB and DLN and their dendritic extents, in intact male, castrated male and female rats. WGA-HRP-labelled cells bodies were found in the parvocellular subnuclei of PVN, as well as regions of the lateral hypothalamus and the dorsal area of the hypothalamus. These results demonstrate that the PVN projects to lumbar levels of the spinal cord that are sexually dimorphic and androgen-dependent. This suggests that PVN may modulate the activity of these motoneurons.

Stimulation of the hypothalamic paraventricular nucleus produces analgesia not mediated by vasopressin or endogenous opioids

The analgesic effect of electrical stimulation of the hypothalamic paraventricular nucleus (PVN) was studied. Additionally, the involvement of vasopressin and opioid peptides in this process was examined by comparing vasopressin-deficient (Brattleboro) and Long-Evans rats and by administering the opiate antagonist naloxone. Rats were chronically implanted with a stimulating electrode in the parvocellular (PVN-Pc) and magnocellular (PVN-Mg) divisions of the PVN. At least 10 days after surgery, the analgesic effects of PVN stimulation were examined in lightly anesthetized rats, using the tail-flick method, and in unanesthetized rats, using the hot-plate test. PVN stimulation produced marked analgesia in both tests. Current threshold for analgesia was lower from PVN-Pc than from PVN-Mg. Threshold did not differ significantly between Brattleboro and Long-Evans rats and was not affected by naloxone administration. The results indicate that the PVN is part of the brain's pain inhibitory system, and show that the analgesia induced by PVN stimulation is not mediated by either vasopressin or opioid peptides.

Activation of brown adipose tissue thermogenesis by chemical stimulation of the posterior hypothalamus

The posterior hypothalamus (PH) is involved in the generation of behavioral thermoregulatory responses, but the importance of the PH in the control of autonomic thermoregulatory responses such as heat production in brown adipose tissue (BAT) is not well defined. In the present study, selective stimulation of PH neurons by local application of the excitatory amino acid glutamate (250 nl of 1 M solution, unilaterally) caused a sharp, transient increase in interscapular BAT (IBAT) and core temperature in urethane-anesthetized rats. This effect was blocked by pretreatment with the sympathetic ganglionic blocker, chlorisondamine chloride (2 mg/kg) or the beta-adrenergic receptor blocker, propranolol (2 mg/kg), implicating the involvement of the sympathetic system. The effect of intra-PH injection of glutamate on IBAT and core temperatures could be mimicked by injection of the gamma-aminobutyric acid (GABA) receptor antagonist, bicucullin methiodide (BMI, 50 ng), into the same PH site. This effect of BMI could be blocked by co-injection of the GABA(A) receptor agonist, muscimol (25 ng). Further, BMI co-injection potentiated the effect of intra-PH injection of glutamate on IBAT and core temperatures. Conversely, muscimol co-injection prevented the stimulatory effect of intra-PH injection of glutamate. Taken together, the results indicate that direct chemical stimulation of neurons in the PH can activate an autonomic mechanism controlling heat production in BAT. Further, they suggest the neural mechanism in the PH mediating this effect is tonically inhibited by GABA, as blockade of GABAergic function in the PH produces an effect similar to that observed after direct stimulation of PH neurons with glutamate.(ABSTRACT TRUNCATED AT 250 WORDS)

Supraspinal projections to the ventromedial lumbar spinal cord in adult male rats

In the present study, the fluorescent tract tracing compound Fluorogold was used to study the afferents of the SNB (spinal nucleus of the bulbocavernosus), which is found in the ventromedial spinal grey and innervates penile muscles of the male rat. Fluorogold was iontophoretically injected into the SNB, which was located by recording antidromic activation of the motoneurons after stimulating the bulbocavernosus muscle. Retrogradely labeled cells were found in laminae I, V-IX, and area X of the lumbar spinal cord, suggesting segmental input to the SNB. Supraspinally, the greatest number of labeled cells were in the medulla oblongata, particularly in the lateral vestibular nucleus, gigantocellular reticular nucleus, and ventral and alpha divisions of the gigantocellular reticular nucleus. Labeled cells were also observed in the medullary raphe nuclei, the ventral medullary nucleus, and the spinal vestibular nucleus. In the pons, labeled cells were observed in the nucleus locus coeruleus, nucleus subcoeruleus, and caudal pontine reticular nucleus. No labeled cells were present in the cerebellum, rostral pons, mesencephalon, and cerebral cortex. The most rostral occurrence of labeled cells was in the medial parvicellular division of the hypothalamic paraventricular nucleus. These potential afferents to the SNB identified in male rats imply that the inputs to motoneurons that innervate sex-specific muscles involved in male reproductive behavior may be similar to the inputs to lumbar motoneurons described in the female rat that innervate muscles involved in female sexual behavior.

Oxytocinergic innervation of the rat spinal cord. An electron microscopic study

Pre- and postembedding immunocytochemical procedures were used, together with antisera raised against oxytocin or its neurophysin, to characterize oxytocinergic pathways in the rat spinal cord, at the electron microscopic level. Pre-embedding immunoperoxidase staining performed on vibratome sections revealed oxytocin- and neurophysin-positive axonal profiles and terminals scattered predominantly in laminae I and II of the dorsal horn and in the central gray (lamina X). They were also visible, but to a lesser extent, in the intermediolateral columns, at thoracic and lumbar levels. Postembedding immunogold staining performed directly on ultrathin sections of the same areas, fixed in osmium and embedded in resin, permitted to show clearly that the oxytocinergic axons made symmetrical and asymmetrical synaptic contacts onto dendritic profiles. It also allowed subcellular localization of the neuropeptide immunoreactivities which were restricted to relatively large, electron-dense vesicles in the immunopositive terminals. Oxytocinergic terminals were never seen to participate in glomerular configurations in the superficial layers of the dorsal horn nor were immunoreactive cell bodies visible in any spinal area. Our results provide direct morphological evidence that oxytocinergic pathways make synapses in several regions of the spinal cord, thus supporting the contention that oxytocin may exert neurotransmitter/neuromodulator actions in this area of the CNS.

Locomotor stepping elicited by electrical stimulation of the hypothalamus persists after lesion of descending fibers of passage

Locomotion initiated by electrical stimulation of the lateral hypothalamus could be due to activation of local neurons or of fibers of passage descending from locomotor regions in the basal forebrain. This study mapped hypothalamic sites for electrically elicited locomotion in six rats with electrolytic lesions of the ipsilateral basal forebrain sources of descending fibers of passage. For mapping, anesthetized rats were held in a stereotaxic apparatus supported by a sling so that stepping movements rotated a wheel. Anesthesia was maintained by periodic injections of Nembutal (7 mg/kg) supplemented by lidocaine injections. Stimulation (25 and 50 microA, 50 Hz, 0.5 msec cathodal pulses, 10 sec trains) was applied through 50-80 microns diameter pipettes filled with 2 M saline. In all cases, locomotor stepping could be elicited by stimulation in sites ipsilateral to the lesion at currents of 50 microA or less. In the one case in which 25-microA sites were not found in the lateral hypothalamus, the lesion extended caudally to within 1 mm of the stimulation sites. These findings do not exclude a locomotor role for fibers of passage but they suggest that activation of lateral hypothalamic neurons is sufficient to initiate locomotion.