Afferent fiber connections from lower brain stem to hypothalamus studied by the horseradish peroxidase method with special reference to noradrenaline innervation

Effect of Noradrenaline on the Facial Stimulation-Evoked Mossy Fiber-Granule Cell Synaptic Transmission in Mouse Cerebellar Cortex

Noradrenaline is an important neuromodulator in the cerebellum. We previously found that noradrenaline depressed cerebellar Purkinje cell activity and climbing fiber–Purkinje cell synaptic transmission in vivo in mice. In this study, we investigated the effect of noradrenaline on the facial stimulation-evoked cerebellar cortical mossy fiber–granule cell synaptic transmission in urethane-anesthetized mice. In the presence of a γ-aminobutyrate_A (GABA_A) receptor antagonist, air-puff stimulation of the ipsilateral whisker pad evoked mossy fiber–granule cell synaptic transmission in the cerebellar granular layer, which expressed stimulus onset response, N1 and stimulus offset response, N2. Cerebellar surface perfusion of 25 μM noradrenaline induced decreases in the amplitude and area under the curve of N1 and N2, accompanied by an increase in the N2/N1 ratio. In the presence of a GABA_A receptor blocker, noradrenaline induced a concentration-dependent decrease in the amplitude of N1, with a half-maximal inhibitory concentration of 25.45 μM. The noradrenaline-induced depression of the facial stimulation-evoked mossy fiber–granule cell synaptic transmission was reversed by additional application of an alpha-adrenergic receptor antagonist or an alpha-2 adrenergic receptor antagonist, but not by a beta-adrenergic receptor antagonist or an alpha-1 adrenergic receptor antagonist. Moreover, application of an alpha-2 adrenergic receptor agonist, UK14304, significantly decreased the synaptic response and prevented the noradrenaline-induced depression. Our results indicate that noradrenaline depresses facial stimulation-evoked mossy fiber–granule cell synaptic transmission via the alpha-2 adrenergic receptor in vivo in mice, suggesting that noradrenaline regulates sensory information integration and synaptic transmission in the cerebellar cortical granular layer.

Pancreas-Brain Crosstalk

The neural regulation of glucose homeostasis in normal and challenged conditions involves the modulation of pancreatic islet-cell function. Compromising the pancreas innervation causes islet autoimmunity in type 1 diabetes and islet cell dysfunction in type 2 diabetes. However, despite the richly innervated nature of the pancreas, islet innervation remains ill-defined. Here, we review the neuroanatomical and humoral basis of the cross-talk between the endocrine pancreas and autonomic and sensory neurons. Identifying the neurocircuitry and neurochemistry of the neuro-insular network would provide clues to neuromodulation-based approaches for the prevention and treatment of diabetes and obesity.

Modulation of cardiorespiratory function mediated by the paraventricular nucleus

The hypothalamic paraventricular nucleus (PVN) coordinates autonomic and neuroendocrine systems to maintain homeostasis and to respond to stress. Neuroanatomic and neurophysiologic experiments have provided insight into the mechanisms by which the PVN acts. The PVN projects directly to the spinal cord and brainstem and, specifically, to sites that control cardio-respiratory function: the intermediolateral cell columns and phrenic motor nuclei in the spinal cord and rostral ventrolateral medulla (RVLM) and the rostral nuclei in the ventral respiratory column (rVRC) in the brainstem. Activation of the PVN increases ventilation (both tidal volume and frequency) and blood pressure (both heart rate and sympathetic nerve activity). Excitatory and inhibitory neurotransmitters including glutamate and GABA converge in the PVN to influence its neuronal activity. However, a tonic GABAergic input to the PVN directly modulates excitatory outflow from the PVN. Further, even within the PVN, microinjection of GABA(A) receptor blockers increases glutamate release suggesting an indirect mechanism by which GABA control contributes to PVN functions. PVN activity alters blood pressure and ventilation during various stresses, such as maternal separation, chronic intermittent hypoxia (CIH), dehydration and hemorrhage. Among the several PVN neurotransmitters and neurohormones, vasopressin and oxytocin modulate ventilation and blood pressure. Here, we review our data indicating that increases in vasopressin and vasopressin type 1A (V(1A)) receptor signalling in the RVLM and rVRC are mechanisms increasing blood pressure and ventilation after exposure to CIH. That blockade of V(1A) receptors in the medulla normalizes baseline blood pressure as well as blunts PVN-evoked blood pressure and ventilatory responses in CIH-conditioned animals indicate the role of vasopressin in cardiorespiratory control. In summary, morphological and functional studies have found that the PVN integrates sensory input and projects to the sympathetic and respiratory control systems with descending projections to the medulla and spinal cord.

Effect of lidocaine administration at the nucleus locus coeruleus level on lateral hypothalamus-induced antinociception in the rat

Several lines of evidence have shown that stimulation or inactivation of lateral hypothalamus (LH) produces antinociception. In this study, we assessed the role of nucleus locus coeruleus (LC) in antinociceptive response induced by LH stimulation or inactivation in the rat. The cholinergic agonist carbachol (125 nmol/0.5 microl saline) or lidocaine (2%; 0.5 microl) was unilaterally microinjected into the LH with the LC inactivation concurrently. Antinociceptive responses were obtained by tail-flick test and represented as maximal possible effect (MPE) at 5, 10, 15, 20, 30 and 60 min after drug administration. The results showed that microinjection of carbachol into the LH significantly induced antinociception at 5 and 10 min (p<0.001). This effect was significantly blocked by microinjection of lidocaine into the LC. On the other hand, microinjection of lidocaine into LH-induced antinociception at 5 (p<0.01) and 10 (p<0.05) min after administration. However, inactivation of the LC following the LH inactivation increased MPE at 5 min after injection. These findings support the conclusion that antinociception produced by LH stimulation or inactivation involves two separate mechanisms. It seems that analgesic response induced by LH stimulation is mediated in part by the subsequent activation of spinally projecting noradrenergic neurons in the LC cell group.

Acute changes in 3H-PAC and 125I-PYY binding in the nucleus tractus solitarii and hypothalamus after a hypertensive stimulus

Activation of alpha-2-adrenergic and neuropeptide Y (NPY) receptors in the nucleus tractus solitarii (NTS) induces hypotension and bradycardia. On the contrary, activation of angiotensin II (Ang II) receptors leads to hypertension. Acute changes in binding parameters of alpha-2-adrenergic, NPY and Ang II receptors were evaluated in the NTS and paraventricular hypothalamic nucleus (PVN) of rats after a hypertensive stimulus employing quantitative receptor autoradiography. Saturation experiments showed a decrease in the number (Bmax) of alpha-2-adrenergic binding sites in the NTS 6 hours after coarctation-induced hypertension. Furthermore, the affinity of NPY receptors was diminished as seen by the increase in the KD value of 125I-PYY. Tyrosine hydroxylase and NPY immunoreactivities were increased in the NTS and ventral medulla. Binding of 125I-Ang II was not changed in the NTS. Binding of all ligands analyzed was not altered in the PVN. The results suggest an acute down-regulation of alpha-2-adrenergic and NPY receptors involved with hypotension in response to hypertensive stimulus, which might be related to an increased availability of catecholamines and NPY in the NTS.

Cytoarchitectonic subdivisions of the parabrachial nucleus in the Japanese monkey (Macacus fuscatus) with special reference to spinoparabrachial fiber terminals

The cytoarchitectonic subnuclear organization of the parabrachial nucleus (PB) surrounding the brachium conjunctivum (BC) in the monkey was examined using the Nissl method and the anterograde axonal flow method. PB of the monkey could be divided into the following subnuclei: the dorsal area (DPBM) along the medial surface of the medial three-fourths of BC in the caudal half of medial PB (PBM), the ventral area (VPBM) along the medial surface of the lateral one-fourth of BC in the rostral two-thirds of PB, the ventrolateral part of lateral PB (PBL) lateral to BC throughout PB (EL), the ventral part of the rostral half of PBL ventral to EL (EXL), the medial part of middle PBL along the dorsal surface of BC (VL), the dorsal and lateral marginal part of PBL in the rostral two-thirds of PB (DL), the cell cluster in the dorsomedial part of the rostral half of PBL between VL and DL (CL), the dorsocentral part appearing at the level of root exit of the trochlear nerve between DL and CL and extending to the rostral end of PBL (IL), the area between DL and IL in the rostral one-seventh of PBL (SL), and Kölliker-Fuse nucleus (KF) ventral to EL and BC in the middle one-third of PB and lateral to the lateral pontine tegmentum. After the injection of biotinylated dextran amine into the upper cervical segments, labeled fibers terminated in each subdivision of PB with different densities; most heavily in IL, more heavily in DL and KF, moderately in EL and VPBM, and scarcely in the rest of PB. The present study demonstrated for the first time the subdivisions of PB in the monkey, which were essentially common to those of the rat based on the cytoarchictecture of PB and spinal fiber terminals in it.

Neuronal projections to the lateral retrochiasmatic area of sheep with special reference to catecholaminergic afferents: immunohistochemical and retrograde tract-tracing studies

The retrochiasmatic area contains the A15 catecholaminergic group and numerous monoaminergic afferents whose discrete cell origins are unknown in sheep. Using tract-tracing methods with a specific retrograde fluorescent tracer, fluorogold, we examined the cells of origin of afferents to the retrochiasmatic area in sheep. The retrogradely labeled cells were seen by observation of the tracer by direct fluorescence or by immunohistochemistry with specific antibodies raised in rabbits or horses. Among the retrogradely labeled neurons, double immunohistochemistry for tyrosine hydroxylase, dopamine-beta-hydroxylase, and serotonin were used to characterize catecholamine and serotonin FG labeled neurons. The retrochiasmatic area, which included the A15 dopaminergic group and the accessory supraoptic nucleus (SON), received major inputs from the lateral septum (LS), the bed nucleus of the stria terminalis (BNST), the thalamic paraventricular nucleus, hypothalamic paraventricular and supraoptic nuclei, the perimamillary area, the amygdala, the ventral part of the hippocampus and the parabrachial nucleus (PBN). Further, numerous scattered retrogradely labeled neurons were observed in the preoptic area, the ventromedial part of the hypothalamus. the periventricular area, the periaqueductal central gray (CG), the ventrolateral medulla and the dorsal vagal complex. Most of the noradrenergic afferents came from the ventro-lateral medulla (Al group), and only a few from the locus coeruleus complex (A6/A7 groups). A few dopaminergic neurons retrogradely labeled with flurogold were observed in the periventricular area of the hypothalamus. Rare serotoninergic fluorogold labeled neurons belonged to the dorsal raphe nucleus. Most of these afferents came from both sides of the brain, except for hypothalamic supraoptic and paraventricular nuclei. In the light of these anatomical data, we compared our results with data obtained from rats, and we discussed the putative role of these afferents in sheep in the regulation of several specific functions in which the retrochiasmatic area may be involved, such as reproduction.

Localization of angiotensin II AT1 receptor-like immunoreactivity in catecholaminergic neurons of the rat medulla oblongata

There exist at least two distinct subtypes of angiotensin II receptors in the brain, namely the AT1 and AT2 subtypes. The high density of angiotensin II AT1 receptors is present in the medulla oblongata. The AT1 subtype of angiotensin II receptors mainly mediates central cardiovascular events. In the present study a polyclonal antibody against the angiotensin II AT1 receptor and a monoclonal antibody against tyrosine hydroxylase were employed to evaluate the possible presence of angiotensin II AT1 receptor-like immunoreactivity in the catecholaminergic neurons of the rat medulla oblongata by means of the double colour immunofluorescence technique. A weak, diffuse cytoplasmic angiotensin II AT1 receptor-like immunoreactivity was observed in almost all the catecholaminergic cell bodies of the A2, C1, C2 and C3 cell groups, except those of the A1 cell group containing moderately intense, diffuse cytoplasmic angiotensin II AT1 receptor-like immunoreactivity, occasionally found in the noradrenergic dendrites of the A1 cell group. There was a higher density of the angiotensin II AT1 receptor-like immunoreactive profiles in the A2 cell group area than in other catecholaminergic cell group areas. In addition, the angiotensin II AT1 receptor-like immunoreactivity was seen in non-catecholaminergic neurons. The present results provide evidence for the existence of the specific angiotensin II AT1 receptor-like immunoreactivity in the noradrenergic and adrenergic neurons of the rat medulla oblongata known to have a cardiovascular role. Thus, the findings support the view that angiotensin II AT1 receptors in the medulla oblongata participate in cardiovascular control and indicate a cellular substrate for the documented interaction between the angiotensin II and adrenergic transmission lines in cardiovascular function at the level of the nucleus tractus solitarii.

Gonadal steroids regulate behavioral responses to pheromones by actions on a subdivision of the medial preoptic nucleus

Mating behavior in male hamsters is initiated by pheromones, detected by two chemosensory systems which converge on the medial nucleus of the amygdala and the bed nucleus of the stria terminalis. Neurons in these areas project to the medial preoptic nucleus. All three of these areas contain androgen receptors. Using Fos as a marker of stimulation we have found that pheromones stimulate neurons in all three areas in intact males but fail to stimulate the magnocellular division of the medial preoptic nucleus of castrates. As this area plays a critical role in the regulation of male mating behavior our results suggest that steroids regulate mating by maintaining the responsiveness of the magnocellular division of the medial preoptic nucleus to pheromones.

Localization of neuropeptide Y Y1 receptor-like immunoreactivity in catecholaminergic neurons of the rat medulla oblongata

Neuropeptide Y receptors in the medulla oblongata participate in central cardiovascular control. The neuropeptide Y1 receptor subtype gene and amino acid sequence have been identified by molecular cloning studies. In this study, a C-terminal peptide representing amino acids 355-382 of the neuropeptide Y1 receptor was synthesized and cross-linked to thyroglobulin to produce an antibody against a partial sequence of the neuropeptide Y1 receptor, used to localize neuropeptide Y1 receptor-like immunoreactivity in the catecholaminergic neurons of the medulla oblongata. The double colour immunofluorescence technique with a polyclonal antibody against the neuropeptide Y1 receptor and a monoclonal antibody against tyrosine hydroxylase revealed that in the rat medulla oblongata, a weak (the C3 cell group) to moderately intense (the A1, A2, C1 and C2 cell groups), diffuse cytoplasmic neuropeptide Y1 receptor-like immunoreactivity was distributed primarily in the noradrenergic and adrenergic cell bodies and occasionally seen in the noradrenergic and adrenergic cell processes. Almost all tyrosine hydroxylase-like immunoreactive cell bodies in the A1, A2, C1, C2 and C3 cell groups showed neuropeptide Y1 receptor-like immunoreactivity. The neuropeptide Y1 receptor-like immunoreactivity in the A2 cell group was somewhat stronger. The present findings show localization of specific neuropeptide Y1 receptor-like immunoreactivity in the vast majority of the noradrenergic and adrenergic cell bodies of the A1, A2, C1, C2 and C3 cell groups, which are putative cardiovascular regions. The results support the view that neuropeptide Y1 receptors in the medulla oblongata are involved in central cardiovascular control and may coexist with another important receptor, the alpha 2A-adrenoceptor, also involved in central, cardiovascular regulation, since the alpha 2A-adrenoceptor-like immunoreactivity has been shown to exist in almost all noradrenergic and adrenergic cell bodies in the brainstem. In conclusion, centrally administered neuropeptide Y may act in part via neuropeptide Y1 receptors located on the soma and dendrites of noradrenergic and adrenergic neurons, where it may interact with alpha 2-adrenoceptors at least in the noradrenergic A2 neurons. This noradrenaline system may be involved in at least part of the vasodepressor actions of neuropeptide Y, noradrenaline and adrenaline in the nucleus tractus solitarii in view of the present findings.

Evidence for corticotropin-releasing hormone projections from Barrington's nucleus to the periaqueductal gray and dorsal motor nucleus of the vagus in the rat

The present study used anterograde and retrograde tract tracing and immunohistochemistry to determine the efferent projections of corticotropin-releasing hormone (CRH) neurons of Barrington's nucleus in the rat. Injections of Phaseolus vulgaris-leucoagglutinin into Barrington's nucleus resulted in anterograde labeling in the dorsal motor nucleus of the vagus, periaqueductal gray, medial thalamic nuclei, lateral hypothalamus, paraventricular nucleus of the hypothalamus, lateral preoptic area, and lateral septum. The retrograde tract tracer, fluorogold, injected into the lumbosacral spinal cord labeled many, but not all, CRH-immunoreactive neurons in Barrington's nucleus. Moreover, some Barrington's neurons that were retrogradely labeled from the spinal cord were not CRH-immunoreactive. Several CRH-immunoreactive Barrington's neurons were retrogradely labeled by fluorogold injections into the periaqueductal gray, and these were located predominantly in the dorsal part of the nucleus. Additionally, some CRH-immunoreactive Barrington's neurons were retrogradely labeled from fluorogold injections into the dorsal motor nucleus of the vagus. In contrast, fluorogold injections into the lateral hypothalamus, lateral preoptic area, or lateral septum did not result in double labeling of CRH-immunoreactive neurons in Barrington's nucleus. These results suggest that many, but not all, CRH-containing neurons of Barrington's nucleus project to the lumbosacral spinal cord. In addition to their previously documented projections to the spinal cord, these neurons may be a source of CRH in the periaqueductal gray and dorsal motor nucleus of the vagus. CRH projections of Barrington's nucleus may play a role in behavioral or autonomic aspects of stress responses, in addition to their proposed role in micturition.

Involvement of the noradrenergic afferents from the nucleus tractus solitarii to the supraoptic nucleus in oxytocin release after peripheral cholecystokinin octapeptide in the rat

Activation of abdominal vagal afferents by peripheral injection of cholecystokinin octapeptide induces oxytocin release into the circulation. To test the hypothesis that cholecystokinin increases oxytocin release via activation of noradrenergic afferents from the brainstem, we injected rats with 5-amino-2,4-dihydroxy-alpha-methylphenylethylamine, a selective neurotoxin to noradrenergic fibres, into a lateral cerebral ventricle. The neurotoxin treatment reduced the noradrenaline content in the hypothalamus by 75% and reduced the oxytocin secretion in response to cholecystokinin by over 90%. In separate experiments, the neurotoxin was injected unilaterally in the vicinity of the supraoptic nucleus to test whether direct noradrenergic afferents to the supraoptic nucleus are involved in the response to cholecystokinin. The injection reduced the immunoreactivity for dopamine beta-hydroxylase in the supraoptic nucleus and significantly decreased the number of the supraoptic neurons expressing Fos-like protein after cholecystokinin but not after hypertonic saline. In further experiments, rhodamine-conjugated latex microspheres were injected into the supraoptic nucleus to retrogradely label afferent neurons, and the brains were processed with double-immunohistochemistry for tyrosine hydroxylase and Fos-like protein. In the C2/A2 but not the C1/A1 region of the brainstem, cholecystokinin increased the expression of Fos-like protein in the population of retrogradely-labelled catecholaminergic cells. In the C2/A2 region, the majority of retrogradely labelled cells expressing Fos-like protein after cholecystokinin were catecholaminergic. We conclude that noradrenergic afferents from the A2 but not from the A1 region of the brainstem to the hypothalamus mediate, at least in part, oxytocin release following cholecystokinin.

Fos expression within regions of the preoptic area, hypothalamus and brainstem during pregnancy and parturition

Vaginocervical stimulation, that occurs during mating or with the birth of pups, is believed to induce specific sexual and maternal behaviours in the rat as well as stimulating a number of neuroendocrine responses including the secretion of oxytocin, prolactin and luteinizing hormone. Since the medial preoptic area has been implicated in the induction of maternal behaviour, the expression of the immediate-early gene product Fos was compared between non-pregnant, late pregnant and parturient rats. Although no difference was detected in the number of Fos-positive neuronal profiles in the preoptic area of non-pregnant and late-pregnant rats, a large increase was observed in the medial preoptic nucleus and the anteroventral periventricular region, as well as in the hypothalamic supraoptic nucleus, of parturient rats. Double labelling for Fos and tyrosine hydroxylase immunoreactivity in the brainstem of parturient rats showed the activation of catecholaminergic neurons in both the nucleus of the tractus solitarius and in the ventrolateral medulla that may form part of the afferent pathway from the uterus and cervix to the preoptic area and hypothalamus.

Modelling the luteinizing hormone-releasing hormone pulse generator

Pituitary hormones are released in pulses as a result of episodic patterns of electrical activity in neuroendocrine neurons. The mechanisms underlying such pulsatility have, however, been difficult to elucidate. For example, the luteinizing hormone-releasing hormone neurons regulating reproductive functioning have a sparse and scattered distribution within the hypothalamus which has made definitive electrophysiological investigation impracticable. Little is known not only of their electrical characteristics, but also of the critical neural components with which they interact to form the so-called "luteinizing hormone-releasing hormone pulse generator". We have used here a neural modelling approach, based on the FitzHugh-Nagumo model of a single neuron, to provide a simple dynamical network model of this neuroendocrine pulse generator. We have found that the minimal components required to generate pulsatile luteinizing hormone secretion arise from combining luteinizing hormone-releasing hormone neurons with reciprocally connected inhibitory interneurons and an external stimulatory input. Local GABA neurons and ascending noradrenergic and/or adrenergic inputs have been used as the biological basis for these respective components. The network displays a wide repertoire of behaviours comparable with experimental observations, including some thought previously to be paradoxical. The capacity of this model network to display complex behavioural features interpretable against experimental evidence suggests that this type of modelling may become a necessary adjunct to empirical studies of pulsatile neuroendocrine systems.

Analysis of brainstem A1 and A2 noradrenergic inputs to the preoptic area using microdialysis in the rat

Noradrenergic inputs to the preoptic area (POA) are involved in regulating a variety of homeostatic functions. However, the accurate measurement of endogenous noradrenaline (NA) release in the POA has been difficult to achieve and consequently little has been done to characterise the different noradrenergic pathways. By combining the technique of intracranial microdialysis with tissue pre-loading of [3H]NA we have developed a sensitive index of NA release in the POA [8]. Using this method we have now examined and compared the effects of electrical stimulation of the brainstem A1 and A2 cell groups on NA release in the POA. Anaesthetised proestrus rats were implanted with microdialysis probes either unilaterally or bilaterally in the POA and stimulating electrodes positioned in either the A1 or A2 regions. Electrical stimulation (10 Hz, 10s on/off for 20 min) of the A1 region resulted in repeatable, calcium-dependent increases in radioactivity outflow from the ipsilateral POA (P < 0.01). A1-evoked release was twice as large as that observed after equivalent 10 Hz electrical stimulation of the A2 region (P < 0.05). In experiments using bilateral POA microdialysis and A1 stimulation, a significant increase in release from the contralateral POA, amounting to approximately 80% of that observed in the ipsilateral POA, was observed. Experiments involving the blockade of A1-stimulated release in the ipsilateral POA by perfusion with a calcium-free medium demonstrated that increases in radioactivity measured in the contralateral POA were not originating from the ipsilateral POA.(ABSTRACT TRUNCATED AT 250 WORDS)

Catecholaminergic projections from the solitary tract nucleus to the perifornical hypothalamus

The source of adrenergic and other catecholaminergic fibers innervating the perifornical lateral hypothalamus was localized in the medulla after combination of Fluoro-Gold retrograde tracing and immunohistochemistry for either tyrosine-hydroxylase or phenylethanolamine-N-methyltransferase. Following perifornical injections, Fluoro-Gold-labeled neurons were observed mainly in regions including the noradrenergic and adrenergic cell groups. In the caudal solitary tract nucleus, two kinds of doubly labeled neurons were found: a) numerous noradrenergic neurons in the A2 group at the level of, or caudal to the area postrema; b) some adrenergic neurons in the C2 group at a level immediately rostral to the area postrema. These catecholaminergic neurons connecting the caudal solitary tract nucleus to the perifornical hypothalamus might convey feeding relevant information such as glycemic level or satiety signals.

Medullary synaptic inputs to thyrotropin-releasing hormone (TRH)-containing neurons in the hypothalamus: an ultrastructural study combining WGA-HRP anterograde tracing with TRH immunocytochemistry

Ascending projections from the A1/C1 cell group and from the A2 cell group in the medulla oblongata was studied in the light microscope by anterograde tracing of Phaseolus vulgaris leucoagglutinin and in the electron microscope by anterograde tracing of wheat germ agglutinin-coupled horseradish peroxidase (WGA-HRP) combined with thyrotropin-releasing hormone (TRH) immunocytochemistry in the hypothalamic paraventricular nucleus (PVN). WGA-HRP-labeled axon terminals originating from neurons in the A1/C1 or the A2 cell group were found to make synaptic contacts with TRH-containing cell bodies and dendrites in the medial parvocellular part of the PVN, usually forming axo-dendritic synapses. Of all the afferent synapses on TRH neurons in the PVN, 9.8-20.9% of the presynaptic axon terminals were WGA-HRP-positive. This indicates that each brain stem catecholaminergic cell group that contribute to innervation of the PVN is in a position to modulate the activity of TRH neurons.

Characterization of tritiated noradrenaline release from the rat preoptic area with microdialysis in vivo

Present techniques are unable to provide a sensitive and accurate index of noradrenergic activity in the rat preoptic area. In this study, we have examined the brainstem A1 noradrenergic input to the preoptic area using a new technique whereby [3H]noradrenaline is preloaded into the preoptic area and release of radioactivity from this region is measured subsequently using microdialysis in vivo. Electrical stimulation of the ipsilateral A1 area for 20 min at 5, 10, and 15 Hz evoked significant increases in dialysate radioactivity that were repeatable and frequency-dependent. After removal of calcium from the perfusion medium, basal release of radioactivity was markedly reduced and the effect of A1 stimulation abolished. Changing to a 100 mM K+ medium evoked an increase in the release of radioactivity that was sixfold greater than that seen after A1 stimulation. Separation of the dialysate with HPLC showed that 33% of the increase in measured radioactivity after A1 stimulation was directly attributable to [3H]noradrenaline and the remainder to the metabolites vanillylmandelic acid, 3,4-dihydroxymandelic acid, and 3,4-dihydroxyphenylglycol. In contrast, the increase in radioactivity after K+ depolarization was due almost completely to [3H]noradrenaline. Addition of 10 microM clonidine to the perfusion medium markedly reduced basal release of radioactivity, but had no effect on evoked release following A1 stimulation. Conversely, perfusion with 10 microM yohimbine had no effect on basal release, but significantly increased evoked release after A1 stimulation. These results now provide a characterization of noradrenergic activity in the preoptic area and indicate the importance of the A1 noradrenergic input to this region. The technique of measuring radioactivity with microdialysis after preloading with [3H]noradrenaline provides a relatively simple, sensitive index of noradrenergic activity in vivo with good temporal resolution.

Neuronal projections to the medial preoptic area of the sheep, with special reference to monoaminergic afferents: immunohistochemical and retrograde tract tracing studies

The preoptic area contains most of the luteinizing hormone releasing hormone immunoreactive neurons and numerous monoaminergic afferents whose cell origins are unknown in sheep. Using tract tracing methods with a specific retrograde fluorescent tracer, fluorogold, we examined the cells of origin of afferents to the medial preoptic area in sheep. Among the retrogradely labeled neurons, immunohistochemistry for tyrosine hydroxylase, dopamine-beta-hydroxylase, phenylethanolamine N-methyltransferase, and serotonin was used to characterize catecholamine and serotonin fluorogold labeled neurons. Most of the afferents came from the ipsilateral side to the injection site. It was observed that the medial preoptic area received major inputs from the diagonal band of Broca, the lateral septum, the thalamic paraventricular nucleus, the lateral hypothalamus, the area dorsolateral to the third ventricle, the perimamillary area, the amygdala, and the ventral part of the hippocampus. Other numerous, scattered, retrogradely labeled neurons were observed in the ventral part of the preoptic area, the vascular organ of the lamina terminalis, the ventromedial part of the hypothalamus, the periventricular area, the area lateral to the interpeduncular nucleus, and the dorsal vagal complex. Noradrenergic afferents came from the complex of the locus coeruleus (A6/A7 groups) and from the ventro-lateral medulla (group A1). However, dopaminergic and adrenergic neuronal groups retrogradely labeled with fluorogold were not observed. Serotoninergic fluorogold labeled neurons belonged to the medial raphe nucleus (B8, B5) and to the serotoninergic group situated lateral to the interpeduncular nucleus (S4). In the light of these anatomical data we hypothesize that these afferents have a role in the regulation of several functions of the preoptic area, particularly those related to reproduction. Accordingly these afferents could be involved in the control of luteinizing hormone releasing hormone (LHRH) pulsatility or of preovulatory LHRH surge.

Morphological relationships between tyrosine hydroxylase-immunoreactive neurons and dopamine-beta-hydroxylase-immunoreactive fibres in dopamine cell group A15 of the sheep

Double immunocytochemical labelling with antibodies raised against tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase was used on semi-thin sections of sheep hypothalamus to investigate possible morphological relationships between dopamine neurons of group A15 and noradrenaline afferents to this area. Dopamine-beta-hydroxylase-immunoreactive (IR) fibres were found in the close proximity of dendrites of TH-IR neurons. At electron microscopic level, single immunocytochemical staining with TH antibodies revealed the presence of synaptic contacts between labelled or unlabelled axon terminals and anti-TH labelled dendrites. These observations suggest that in the sheep, TH-IR neurons of group A15 are controlled by non-catecholaminergic and catecholaminergic afferents. Catecholamine inputs could contain either dopamine or noradrenaline. The hypothesis of noradrenaline inputs to A15 is strongly supported by the results obtained after double labelling on semi-thin sections. Tyrosine hydroxylase-immunoreactive perikarya and dendrites often seemed to be partly surrounded by glial processes. This latter observation suggests that the synaptic investment of these neurons might be controlled by glial cells.

Ultrastructural studies of medullary synaptic inputs to vasopressin-immunoreactive neurons in the supraoptic nucleus of the rat hypothalamus

Direct projections from the A1/C1 catecholaminergic cell group in the caudal ventrolateral medulla oblongata to neurons containing vasopressin (VP) in the supraoptic nucleus (SON) were studied electron microscopically by a double-labeling technique which combines anterograde tracing after injection of wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) into the A1/C1 cell group with VP immunocytochemistry. WGA-HRP-labeled axon terminals originating from neurons in the A1/C1 cell group were found to make synaptic contacts with VP-immunoreactive cell bodies and dendrites in the SON, most often forming axo-dendritic synapses. This indicates that VP-containing neurosecretory neurons in the SON receive monosynaptic catecholaminergic input from the A1/C1 cell group.

Changes in the release of gamma-aminobutyric Acid and catecholamines in the preoptic/septal area prior to and during the preovulatory surge of luteinizing hormone in the ewe

Abstract The technique of intracranial microdialysis was used to monitor changes in the outflow of the catecholamines, noradrenaline, adrenaline and dopamine and the inhibitory amino-acid gamma-aminobutyric acid (GABA) in the preoptic/septal area of the conscious ewe during an oestradiol-induced surge of luteinizing hormone (LH). The same animals were sampled twice from an identical brain site, once in the presence of oestradiol and once in its absence, when no surge occurred and LH levels remained low. Changes in the outflow of GABA, noradrenaline and adrenaline (but not dopamine) were related to changes in LH secretion. Specifically, GABA outflow was maximal in the hours following oestradiol administration but began a sustained fall some 10 h before the surge began, to level off just before the first increment in LH secretion. Low GABA concentrations were maintained until after gonadotrophin levels had once more returned to baseline. The release of all three catecholamines was pulsatile. Noradrenergic activity was greater in the presence of oestradiol although activity did not alter over the 20 h of sampling. The pulse frequency of adrenaline was maximal in the hours immediately prior to the LH surge and minimal in the hours following its initiation. These data suggest that a decrease in GABAergic transmission in the vicinity of the LH-releasing hormone cell bodies is a necessary component of the neural mechanism by which the oestradiol-induced surge of LH is generated. A general increase in noradrenergic activity coupled with changes in the release of adrenaline at the time of the surge may be additional prerequisites for successful ovulation.

Dynorphin A-containing neural elements in the nucleus of the solitary tract of the rat. Light and electron microscopic immunohistochemistry

Distribution of dynorphin A (DyA) immunoreactivity in the nucleus of the solitary tract (NTS) was examined in rats after various surgical transections by light and electron microscopic immunohistochemistry. In colchicine-treated animals DyA immunostained perikarya were seen in each subdivision of the NTS. In intact rats, dense network of immunopositive nerve fibers was localized light microscopically, and synaptic contacts were found between DyA immunopositive structures (axo-axonic, axo-dendritic synapses), electron microscopically. Surgical transections medial, caudal or rostral to the nucleus did not alter the distribution pattern of DyA in the NTS. Lesion immediately lateral to the nucleus resulted in an ipsilateral appearance of immunostained cell bodies. Vagal and glossopharyngeal afferents (including baroreceptor fibers) terminate in the medial and commissural subnucleus of the NTS. Two days after extracranial vagotomy, synaptic contacts between degenerated presynaptic boutons and DyA immunopositive postsynaptic elements were observed in both medial and commissural part of the NTS. These observations provide morphological evidence suggesting that (1) axons of dynorphin A-containing cell bodies form an intrinsic network inside the nucleus; (2) these DyA cells receive direct peripheral inputs through the vagus nerve, and (3) projecting DyA neurons may exist in the NTS, they may innervate medullary, rather than forebrain, higher brainstem or spinal cord neurons.

Neuropeptides and catecholamines in efferent projections of the nuclei of the solitary tract in the rat

This study focuses on the involvement of catecholamines and nine different peptides in efferents of the nucleus of the solitary tract to the central nucleus of the amygdala, the bed nucleus of the stria terminalis, and different parabrachial and hypothalamic nuclei in the rat. A double-labeling technique was used that combines a protein-gold complex as the retrograde tracer with immunohistochemistry. Catecholaminergic projection neurons were the most numerous type observed and projected mainly ipsilaterally to all targets studied. Most projections arose from areas overlying the dorsal motor nucleus, mainly the medial nucleus. Neurons synthesizing somatostatin, met-enkephalin-Arg-Gly-Leu, dynorphin B, neuropeptide Y, and neurotensin projected to all structures examined. Somatostatin and enkephalin immunoreactive projection cells were the most numerous. They were located in close proximity to each other, including all subnuclei immediately surrounding the solitary tract, bilaterally. Most dynorphin and neuropeptide Y immunoreactive projection cells were found rostral to that of enkephalinergic and somatostatinergic projections, and mainly in the ipsilateral medial nucleus. Neurotensinergic projections were sparse and from dorsal and dorsolateral nuclei. Substance P and cholecystokinin contribute to parabrachial afferents. The location of substance P immunoreactive projection cells closely resembled that of enkephalinergic and somatostatinergic projections. Projecting cholecystokinin immunoreactive cells were observed in dorsolateral nucleus. Bombesin immunoreactive cells in dorsal nucleus projected to either the parabrachial or hypothalamic nuclei. No vasoactive intestinal polypeptide-containing cells were detected. Thus, most catecholaminergic and neuropeptidergic efferents originated from different populations of cells. It is proposed that catecholaminergic neurons constitute the bulk of solitary efferents and that they may contribute to autonomic neurotransmission. Peptidergic neurons mainly form other subgroups of projections and may play a role in modulating the physiological state of the target nuclei.

Lower brainstem afferents to the cat posterior hypothalamus: a double-labeling study

Using a double-immunostaining technique with cholera toxin (CT) as a retrograde tracer, the authors examined the cells of origin and the histochemical nature of lower brainstem afferents to the cat posterior hypothalamus. The posterior hypothalamus, in particular the lateral hypothalamic area, receives substantial afferent projections from: substantia nigra, peripeduncular nucleus, ventral tegmental area, periaqueductal grey, mesencephalic reticular formation, peribrachial region including the locus coeruleus complex, rostral raphe nuclei and the rostral part of the nucleus magnus. In addition, a moderate number of retrogradely labeled neurons was found in: Edinger-Westphal nucleus, nucleus reticularis pontis oralis, nucleus reticularis magnocellularis, caudal lateral bulbar reticular formation around the nucleus ambiguus and lateral reticular nucleus and the nucleus of the solitary tract. The posterior hypothalamus receives: 1) dopaminergic inputs from A8, A9 and A10 cell groups; 2) noradrenergic inputs from A6 and A7 pontine, as well as A1 and A2 bulbar cell groups; 3) adrenergic inputs from C1 cell group in the caudal medulla; 4) serotoninergic inputs from the rostral raphe nuclei (B6, B7 and B8 cell groups); 5) cholinergic inputs from the peribrachial region of the dorsal pontine tegmentum as well as from the nucleus reticularis magnocellularis of the medulla; 6) peptidergic inputs such as methionine-enkephalin, substance P, corticotropin-releasing factor and galanin that originate mainly in the mesencephalic periaqueductal grey, the dorsal raphe nucleus and the peribrachial region of the dorsal pontine tegmentum.

Afferent connections of the rat's supraoptic nucleus

Neurons projecting to the supraoptic nucleus (SON) have been identified following stereotaxic injections of either horseradish peroxidase or fast blue into the SON region of adult rats. The subfornical organ, median preoptic nucleus, organum vasculosum of the lamina terminalis and medial septal nucleus were the source of the largest numbers of supraoptic-projecting neurons. Several smaller projections also originate from the ipsilateral locus coeruleus, preoptic area, lateral parolfactorial area, dorsomedial nucleus of the hypothalamus, lateral parabrachial nucleus and ventrolateral medulla. Several other areas appeared to project only to the region immediately dorsal to the SON: lateral septal nucleus, diagonal band of Broca, ventral tegmental nucleus, and the supramamillary nucleus. These areas may influence SON neurosecretory function by way of interneurons found immediately dorsal to SON. Additional areas were identified with retrograde fluorescent label only, and these projected to the area immediately dorsal to SON and/or to SON itself.

Demonstration of extensive brainstem projections to medial and lateral thalamus and hypothalamus in the rat

We use the method of retrograde transport of colloidal gold with silver intensification to map locations of brainstem neurons projecting to various nuclei of the medial and lateral thalamus (Menetrey, Histochemistry 83, 391-395, 1985; Seeley and Field, Brain Res. 449, 177-191, 1988). In rats injections of less than 1.0 microliters of a gold-wheatgerm agglutinin-horseradish peroxidase complex were restricted to the centrum medianum, centralis lateralis, medialis dorsalis, zona incerta, ventrobasal thalamic complex, or medial or lateral hypothalamus. Injections in the centralis lateralis, with some involvement of centrum medianum and medial medialis dorsalis, labeled numerous neurons throughout the rostrocaudal extent of the midbrain periaqueductal gray, and adjacent reticular formation, dorsal raphe nucleus and substantia nigra. These labeled neurons were distributed bilaterally, but with a preponderance ipsilaterally. Numerous neurons in the deep layers of the ipsilateral superior colliculus and in the anterior pretectal nucleus were also labeled. Many neurons in the pontomedullary raphe nuclei (including nucleus raphe magnus), locus coeruleus and dorsolateral parabrachial nuclei, and in the pontomedullary reticular formation, were labeled bilaterally. Fewer were seen bilaterally in the lateral reticular nucleus and nucleus of the solitary tract, with relatively few in the dorsal aspect of the trigeminal nucleus caudalis. Injections restricted largely to the centrum medianum labeled fewer cells in the brainstem, but with similar distributions. An injection restricted to the centralis lateralis also resulted in a similar distribution of labeled neurons in midbrain and nucleus raphe magnus but did not label neurons at more caudal medullary levels. An injection restricted to zona incerta labeled numerous neurons in a distribution similar to that following medial thalamic injections, except that many more were observed in the contralateral sensory trigeminal nucleus and in the dorsal column nuclei. Injections of the ventrobasal thalamic nucleus labeled many neurons in the trigeminal and dorsal column nuclei, but many fewer neurons in the midbrain, periaqueductal gray and reticular formation compared with medial thalamic injections. Labeled neurons were also seen in the superior and inferior colliculi, due presumably to involvement by the injection of the lateral posterior and magnocellular medial geniculate nuclei, respectively. Injections in the lateral hypothalamus labeled numerous neurons in a distribution similar to that seen following medial thalamic injections.(ABSTRACT TRUNCATED AT 400 WORDS)

Electrical stimulation of specific brainstem nuclei suppresses growth hormone-releasing hormone-induced growth hormone secretion in the pentobarbital anaesthetized rat

Abstract To clarify the neural mechanism related to suppression of growth hormone (GH) secretion, biphasic electrical stimulation was delivered into several brainstem nuclei in the pentobarbital anaesthetized rat. A concentric bipolar stimulating electrode was implanted chronically one week prior to the electrical stimulation. Ninety min before the electrical stimulation, the rats were anaesthetized by ip injection of pentobarbital and a silastic cannula was inserted into the right atrium for blood sampling. Blood samples were withdrawn five times (0, 10, 20, 30 and 60 min) during the experiment. Electrical stimulation was delivered for 10 min just after the first blood sampling. One min after the onset of the stimulation, human GH-releasing hormone was injected iv to induce GH secretion. Electrical stimulation of several brainstem nuclei, i.e. the locus coeruleus, the rostral portion of the nucleus tractus solitarius and the lateral reticular nucleus suppressed GH secretion and the central gray of the pons showed a tendency for the suppression of GH secretion. On the other hand, electrical stimulation of the parabrachial nucleus and the caudal portion of the nucleus tractus solitarius did not suppress GH secretion. These suppressions were nullified by prior electrolytic lesioning of the hypothalamic periventricular nucleus where the major cell bodies of somatostatin immunoreactive fibres in the median eminence originate. These results indicate that electrical stimulation of several brainstem nuclei excites somatostatin neurons in the periventricular nucleus which are responsible for the suppression of GH secretion.

Immunohistochemical analysis of the neurotoxic effects of DSP-4 identifies two populations of noradrenergic axon terminals

N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) is a potent and highly selective neurotoxin which induces degeneration of noradrenergic axons. The effects of DSP-4 vary considerably in different brain regions: the drug produces nearly complete depletion of noradrenaline in neocortex, hippocampus, cerebellum and spinal cord, but only partial depletion in hypothalamus and brainstem. In this study we have employed an immunohistochemical method to assess the neurotoxic effects of DSP-4 on the structural integrity of central noradrenergic neurons in the rat, and to identify those noradrenergic axons that remain in the central nervous system 2-4 weeks after DSP-4 treatment. The staining results identified noradrenergic axon terminals as the principal site of action of DSP-4; noradrenergic cell bodies and preterminal axons were not noticeably affected. DSP-4 produced an almost all or none neurotoxic effect on noradrenergic axon terminals in different brain regions. Nearly all noradrenergic axon terminals were destroyed in the neocortex, hippocampus, olfactory bulb, thalamus, tectum, cerebellum and spinal cord dorsal horn. In contrast, most noradrenergic axons were unaffected in the basal forebrain, hypothalamus, reticular formation, brainstem motor nuclei and spinal cord ventral horn. These remaining noradrenergic axon terminals differed morphologically from sensitive axons by their thickness, size and spacing of their varicosities and their dense arborizations within terminal fields. The distribution of noradrenergic axons susceptible to DSP-4 correlates very closely with the distribution of locus coeruleus axons and possibly all regions in which noradrenergic terminals are unaffected by DSP-4 receive their major noradrenergic input from non-locus coeruleus neurons. This study provides the first direct evidence that DSP-4 destroys noradrenergic axon terminals from the locus coeruleus, but not those from non-locus coeruleus neurons. This profound differential sensitivity of noradrenergic axons to DSP-4 is matched by distinct differences in their morphology and their topographic projections. The results support the view that locus coeruleus and non-locus coeruleus noradrenergic neurons constitute two separate subsystems, which differ not only in their projections but also with respect to the pharmacological properties of their axon terminals.

Interconnections between hypothalamus and cerebellum

The cerebellum and hypothalamus are interconnected through a multitude of direct (monosynaptic) and indirect (polysynaptic) pathways. Direct hypothalamocerebellar fibres are mainly uncrossed and reach all parts of the cerebellar cortex and nuclei. They are neither mossy fibres nor climbing fibres, but appear to terminate in all layers of the cerebellar cortex as multilayered fibres. At least some of the hypothalamocerebellar fibres are histaminergic, and it appears that a small proportion of the hypothalamocerebellar neurons contain GABA. Indirect hypothalamocerebellar connections may be relayed through various brain stem nuclei. The hypothalamo-ponto-cerebellar pathway, which has a contralateral predominance, appears to be the quantitatively most important of these. The direct cerebellohypothalamic projection originates from the cerebellar nuclei and terminates in the posterior hypothalamus, in the same regions where the direct hypothalamocerebellar pathway has its main origin. Indirect cerebellohypothalamic connections with brain stem relays have also been demonstrated. The functions of hypothalamocerebellar circuits are so far unknown. However, these pathways are probably involved in the coordination and integration of somatic as well as non-somatic responses to a given set of inputs.

Cardiovascular significance of neuropeptide Y in the caudal ventrolateral medulla of the rat

The cardiovascular effects of intracisternal and intraparenchymal injection of neuropeptide Y (NPY) into the caudal ventrolateral medulla (CVLM) were investigated in anaesthetized normotensive rats. Intracisternal administration of 1.25 nmol NPY gave rise to a significant fall in blood pressure and heart rate, maximal 1 h postinjection. More localized microinjections of NPY into the CVLM similarly produced dose-dependent falls in blood pressure and heart rate. The bradycardia was significantly reduced or abolished by cardiac vagal blockade induced by: (1) pretreatment with the peripheral muscarinic antagonist methylatropine; or (2) ipsilateral vagotomy. These procedures also gave rise to a small reduction in the hypotensive response to NPY but the remaining component of the response was still significantly different from control, saline responses which were without significant haemodynamic effects. The results of this study provide further evidence for a central role for NPY in cardiovascular control. In the CVLM NPY responses appear to involve at least two different mechanisms: the fall in heart rate results from activation of cardiac vagal neurons in the nucleus ambiguus. The hypotensive response is more complex. The fall in blood pressure may be due in part to an activation of A1 noradrenergic neurons resulting in reduced sympathetic outflow but a small component of the response is a result of the profound slowing of the heart.

Convergence of thermal, osmotic and cardiovascular signals on preoptic and anterior hypothalamic neurons in the rat

Responsiveness of thermosensitive neurons in the preoptic and anterior hypothalamus (PO/AH) to osmotic and cardiovascular signals have been shown to be responsible, at least partly, for the reduced thermoregulation during dehydration and the hypothermia after acute blood loss. The responsiveness to local and peripheral (hepatoportal) osmotic stimuli were found in about 60% of PO/AH thermosensitive neurons and 12% of thermally insensitive neurons in tissue slices in vitro and in urethane-anesthetized rats. Since hyperosmotic stimuli predominantly decreased the activity of both warm-sensitive and cold-sensitive neurons, the reduced heat loss and heat production during dehydration may be explained by altered activity of PO/AH thermosensitive neurons induced by hyperosmolality. About 42% of 250 PO/AH neurons (66.3% of thermosensitive neurons and 30% of thermally insensitive neurons) exhibited the responsiveness to changes in blood pressure by less than 15 mmHg, which was found to be mediated by baro/volume receptors. Hypotensive stimuli predominantly increased the activity of warm-sensitive neurons and decreased the activity of cold-sensitive neurons. The neuronal responses may explain, at least in part, the hypothermia after acute bleeding.

Identification of the hypothalamic site through which locus coeruleus axons decussate to reach and stimulate contralateral LH-RH neurons

Recently we reported that locus coeruleus (LC) electrical stimulation (ES) amplifies the quantity of LH released after prior medial preoptic nucleus (MPN)-electrochemical stimulation (ECS). In these studies we also observed that amplification of LH release occurred only when we activated those LC neurons whose cell bodies reside contralateral to the site of MPN-ECS. Seemingly, stimulatory LC axons decussate to reach contralateral hypothalamic regions which contain LH-RH neurons. The purpose of the present study was to identify the site(s) at which such decussation(s) occur. To accomplish this we used a special knife blade to make gross transsections in hypothalamic regions previously described by others as regions where LC decussations occur. Transection 1 (T1) interrupted axons coursing through the medial forebrain bundle (MFB) in the region of the posterior lateral hypothalamus. This transection was placed ipsilateral to the side of LC-ES and it had no effect on LH patterns or concentrations which were released by MPN-ECS. However, T1 completely blocked the amplifying effects of LC stimulation on LH secretion after MPN-ECS. Transection 2 (T2) was placed in the region of the MPN, parallel to the superior sagittal sinus. The knife blade was lowered in midline to the top of the 3rd ventricle and transected all fibers which cross midline within and around the anterior commissure. LH release following MPN-ECS was not appreciably affected in these rats nor did T2 alter the amplifying effects of LC-ES on LH. However, while plasma LH peaked between 60 and 75 min and then declined towards baseline in MPN + LC-stimulated rats, it remained significantly elevated throughout the remainder of the blood collection periods (180 min) in rats receiving combined MPN + LC and T2. Transection 3 (T3) also was placed in the MPN region and differed from T2 only in that we lowered the knife to the base of the sphenoid bone. Thus, T3 disrupted all fibers which cross midline in the AC region and dorsal to the optic chiasm (dorsal supraoptic decussation of LC axons). This transection did not affect LH release evoked by MPN-ECS but completely eliminated the amplifying effects of LC stimulation after MPN-ECS on LH secretion. These data indicate that stimulatory LC axons which affect LH-RH neuronal activity enter the hypothalamus ipsilateral to the site of LC-ES and then project rostrally in the MFB to the lateral preoptic area.(ABSTRACT TRUNCATED AT 400 WORDS)

Projections of the medial preoptic nucleus: a Phaseolus vulgaris leucoagglutinin anterograde tract-tracing study in the rat

The projections of the medial preoptic nucleus (MPN) were examined by making injections of the anterogradely transported lectin Phaseolus vulgaris leucoagglutinin (PHA-L) into the MPN and charting the distribution of labeled fibers. The evidence indicates that the MPN projects extensively to widely distributed regions in both the forebrain and brainstem, most of which also supply inputs to the nucleus. An important neuroendocrine role for the MPN is underscored by its extensive projections to almost all parts of the periventricular zone of the hypothalamus, including the anteroventral periventricular, anterior part of the periventricular, paraventricular (PVH), and arcuate nuclei, and a role in autonomic mechanisms is indicated by projections to such regions as the dorsal and lateral parvicellular parts of the PVH, the lateral parabrachial nucleus, and the nucleus of the solitary tract. Other projections of the MPN suggest participation in the initiation of specific motivated behaviors. For example, inputs to two nuclei of the medial zone of the hypothalamus, the ventromedial and dorsomedial nuclei, may be related to the control of reproductive and ingestive behaviors, respectively, although the possible functional significance of a strong projection to the ventral premammillary nucleus is presently unclear. The execution of these behaviors may involve activation of somatomotor regions via projections to the substantia innominata, zona incerta, ventral tegmental area, and pedunculopontine nucleus. Similarly, inputs to other regions that project directly to the spinal cord, such as the periaqueductal gray, the laterodorsal tegmental nucleus, certain medullary raphe nuclei, and the magnocellular reticular nucleus may also be involved in modulating somatic and/or autonomic reflexes. Finally, the MPN may influence a wide variety of physiological mechanisms and behaviors through its massive projections to areas like the ventral part of the lateral septal nucleus, the bed nucleus of the stria terminalis, the lateral hypothalamic area, the supramammillary nucleus, and the ventral tegmental area, all of which have extensive connections with regions along the medial forebrain bundle. Although the PHA-L method does not allow a clear demonstration of possible differential projections from each subdivision of the MPN, our results suggest that each of them does give rise to a unique pattern of outputs.(ABSTRACT TRUNCATED AT 400 WORDS)

Immunocytochemical localization of peptides and other neurochemicals in the rat laterodorsal tegmental nucleus and adjacent area

The laterodorsal tegmental nucleus (ntdl) contains a cluster of cells located just medial to the locus coeruleus in the pontine brainstem. The ntdl has been shown to project both rostrally to the forebrain and diencephalon and caudally to the spinal cord. In an effort to characterize this region neurochemically, the present study was conducted to identify a variety of neurochemicals localized within perikarya and fibers of the ntdl and surrounding nuclei. Rats were perfused with formalin, and brain sections were processed for fluorescence immunocytochemistry and acetylcholinesterase (AChE). Of the neurochemicals screened, atrial natriuretic factor (ANF), choline acetyltransferase (ChAT), cholecystokinin (CCK), calcitonin gene-related peptide (CGRP), dynorphin B (Dyn B), galanin, somatostatin, substance P, neurotensin (NT), neuropeptide Y (NPY), vasopressin, vasoactive intestinal polypeptide (VIP), serotonin (5HT), glutamic acid decarboxylase (GAD), and tyrosine hydroxylase (TH) were studied. AChE and ChAT staining revealed that the ntdl contains mostly cholinergic neurons. In addition, brightly reactive substance P and galanin and paler staining CRF, ANF, CGRP, NT, VIP, and Dyn B cell bodies were found within the ntdl. Varicose fibers in this nucleus also contained these peptides in addition to CCK, GAD, TH, 5HT, and NPY. The dorsal tegmental nucleus, dorsal raphe nucleus, locus coeruleus, and the parabrachial region contained a dense and varied assortment of peptides with distinct positions and patterns. This multiplicity of neurochemicals within this area suggests a possible influence on a variety of functions modulated by the ntdl and other closely associated tegmental nuclei.

Brainstem afferents to the basal forebrain in the rat

Brainstem afferents to various nuclei of the basal forebrain of the rat were examined using the retrograde transport of wheat germ agglutinin-horseradish peroxidase. These forebrain nuclei included the medial septum-vertical limb of the diagonal band nucleus, the lateral septum, the nucleus of the horizontal limb of the diagonal band, the medial preoptic area and the magnocellular preoptic nucleus/substantia innominata. Medial septal-vertical limb of the diagonal band injections produced dense cell labeling in: raphe obscurus, nucleus incertus, central gray-pars alpha, locus coeruleus, raphe pontis, median raphe, nucleus of Darkschewitsch, a compact cell group within the mesencephalic gray dorsolateral to the nucleus of Darkschewitsch and the supramammillary nucleus. Lateral septal injections produced the heaviest cell labeling in the A1 and A2 areas (of Dahlstrom and Fuxe), the lateral parabrachial nucleus, the Kolliker-Fuse nucleus, the ventral tegmental area and the supramammillary nucleus. There were considerably fewer labeled cells overall with lateral septal as compared with medial septal injections. Brainstem projections to the horizontal limb of the diagonal band were pronounced. The most heavily labeled nuclei were A1, locus coeruleus, laterodorsalis (dorsolateral tegmental nucleus of Castaldi), raphe pontis, median raphe, lateral parabrachial nucleus, ventral tegmental area, nucleus of Darkschewitsch and the supramammillary nucleus. Medial preoptic area injections produced pronounced labeling in: A1 and A2 areas, raphe magnus, locus coeruleus, laterodorsalis, lateral parabrachial nucleus, pedunculopontine nucleus, peripenduncular nucleus and the supramammillary nucleus. The pattern of brainstem labeling obtained with magnocellular preoptic/substantia innominata injections was considerably different from the patterns seen with the other injections. Specifically, relatively few cell groups, essentially confined to the upper brainstem (rostral pons and midbrain), were densely labeled following magnocellular preoptic/substantia innominata injections. These included the medial parabrachial nucleus, the pedunculopontine nucleus, the dorsal raphe nucleus, the ventral tegmental area and the supramammillary nucleus. With the exception of the supramammillary nucleus, each of these cell groups was more heavily labeled with magnocellular preoptic/substantia innominata injections than with others of this series. The above describes the major brainstem projections to each of the forebrain sites.(ABSTRACT TRUNCATED AT 400 WORDS)

A1 noradrenergic action on medial preoptic-medial septal neurons: a neuropharmacological study

In an attempt to determine whether the excitatory and inhibitory orthodromic responses of single medial preoptic-medial septal (MPO-S) neurons to discrete electrical stimulation of the A1 noradrenergic region were mediated specifically by norepinephrine (NE) and involved different types of adrenoreceptors, a series of electrophysiological and neuropharmacological experiments was conducted. Extracellular single unit recording and local drug application techniques were used in female rats under urethane anesthesia. Chemical lesion of the catecholaminergic nerve terminal plexus in the medial preoptic area with 6-hydroxydopamine abolished both excitatory and inhibitory orthodromic effects of A1 region stimulation on MPO-S neurons, suggesting the noradrenergic nature of the effects. This conclusion was corroborated by the observation that the orthodromic effects were mimicked by locally applied exogenous NE. The excitatory effects were reliably mimicked by a low concentration of NE (0.5 mM; in-barrel concentration) and methoxamine (1.0 mM, an alpha-1 agonist), but not by either low or high concentrations (1 and 100 mM) of clonidine (an alpha-2 agonist) and isoproterenol (a beta agonist). The inhibitory orthodromic effects of A1 region stimulation were reliably mimicked by a high concentration of NE (50 mM), clonidine (100 mM) and isoproterenol (100 mM), but not by a low concentration of NE (0.5 mM), methoxamine (1 mM), clonidine (1 mM) or isoproterenol (1 mM). A high concentration (100 mM) of methoxamine mimicked the inhibitory effects less than 40% of the time. The low concentration (0.5 mM) NE-induced excitation that matched the excitatory orthodromic effect of A1 region stimulation was blocked by phentolamine (100 mM), an alpha blocker, but not by timolol (100 mM), a beta blocker. On the other hand, the high concentration (50 mM) NE-induced inhibition that matched the inhibitory orthodromic effect of A1 region stimulation was blocked by timolol, but not by phentolamine. Taken together, the present results are consistent with the hypotheses that the ascending noradrenergic projections from the A1 region affect the excitability of MPO-S neurons directly through NE and that the excitatory and inhibitory orthodromic effects involve different types of adrenoreceptors, i.e., alpha-1 and beta receptors, respectively.

Analgesia produced by injection of lidocaine into the lateral hypothalamus

The local anesthetic lidocaine was injected into the lateral hypothalamus (LH) of awake, freely moving rats immediately prior to pain testing with either the formalin or the foot-flick test. Regional anesthesia of the LH resulted in a significant bilateral reduction of pain scores in the formalin test but had no effect in the foot-flick test. The decreased pain in the formalin test was not due to the diffusion of lidocaine into areas surrounding the LH or other possible artifacts. The results provide further evidence of hypothalamic involvement in pain perception and indicate that different neural systems subserve different types of pain.

Responses of preoptic thermosensitive neurons to changes in blood pressure

Effects of changes in arterial blood pressure were studied on the neuronal activity of 56 thermosensitive and 122 thermally insensitive neurons of the preoptic and anterior hypothalamus (PO/AH) in the urethane-anesthetized rat. Falls in blood pressure by 15 mmHg or less, which were induced by hemorrhage or by IV injection of vasoactive drug, resulted in the increased activity of warm-sensitive neurons (53.3%) and the decreased activity of cold-sensitive neurons (45.5%). However, the majority (71.3%) of thermally insensitive neurons were not affected by a rise or a fall in blood pressure by as large as 30 mmHg. Bilateral sections of glossopharyngeal, vagus and sympathetic nerves abolished the neuronal responses to blood pressure changes, indicating that the responses are mediated largely by peripheral baro/volume receptors. Increased and decreased activities of warm-sensitive neurons and cold-sensitive neurons during hypotension respectively suggest that at least a part of hypothermia observed during acute hemorrhage is a centrally induced response having a survival value.

Effect of selective lesions of medullary catecholamine nuclei on experimental cerebral vasospasm in the rat

Intracisternal injection of blood in the rat induces an angiographically demonstrable, biphasic cerebral vasospasm of the vertebrobasilar system, with a maximal acute spasm at 10 min and a maximal late spasm at 2 days after the subarachnoid hemorrhage (SAH). Selective lesioning of the A1 nuclei in the medulla oblongata prior to the SAH prevents the development of the late spasm, but the acute spasm develops to the same extent as in sham-lesioned animals. Lesions of the medullary A2 nuclei not only prevent the development of both acute and late spasm, but give rise to a dilatation of the vertebrobasilar arteries at day 2 post-SAH. The study indicates that both the A1 and A2 nuclei participate in the development of vasospasm post-SAH. The contrasting patterns of spasm after A1 and A2 lesions suggest a different mechanism for acute and late spasm.

The distribution of neurotransmitter-specific cells and fibers in the anteroventral periventricular nucleus: implications for the control of gonadotropin secretion in the rat

The anteroventral periventricular nucleus (AVPv), which lies in the periventricular zone of the preoptic region, is critical for normal phasic gonadotropin secretion since lesions of this nucleus abolish the progesterone-induced surge of luteinizing hormone secretion from the anterior pituitary, block ovulation, and induce persistent vaginal estrus in female rats. However, very little is known about the neurotransmitter-specific pathways associated with this nucleus. In the present study we evaluated the distribution of biochemically specific cells and fibers within the AVPv and adjacent regions by using an indirect immunohistochemical method with antisera to serotonin (5-HT), dopamine beta-hydroxylase (DBH), tyrosine hydroxylase (TH), neuropeptide Y (NPY), cholecystokinin-8 (CCK), vasoactive intestinal polypeptide (VIP), substance P (SP), neurotensin (NT), corticotropin-releasing factor (CRF), luteotropin-releasing hormone (LRH), somatostatin (SS), thyrotropin-releasing hormone (TRH), oxytocin (OXY), vasopressin (VAS), adrenocorticotropic hormone (ACTH1-24), alpha-melanocyte-stimulating hormone (alpha-MSH), leucine-enkephalin (L-ENK), and calcitonin gene-related peptide (CGRP). Our findings indicate that both cells and fibers containing these putative neurotransmitters are differentially distributed in and around the AVPv in accordance with the cytoarchitectonic organization of this part of the preoptic region. The AVPv itself appears to receive strong inputs from SP-, VAS-, CCK-, and SS-containing pathways, whereas the highest densities of L-ENK-, NT-, 5-HT-, NPY-, and DBH-immunoreactive fibers were found in the cell-sparse zone just lateral to the AVPv. The suprachiasmatic preoptic nucleus (PSCh), a small group of cells located ventral to the AVPv just dorsal to the optic chiasm, contained high densities of alpha-MSH- and ACTH-immunoreactive fibers, as well as substantial numbers of fibers containing catecholamines or NPY. In contrast, a dense plexus of VAS-stained fibers was distributed fairly evenly throughout the AVPv and PSCh. Numerous L-ENK-immunoreactive cell bodies, and moderate numbers of CCK-, NT-, and CRF-stained cell bodies were found in the AVPv. The PSCh contained many TH-stained cells (presumably dopaminergic), in addition to a moderate number of CCK-containing cell bodies, while a high density of NT- and CRF-stained cells were found in the cell-sparse zone lateral to the AVPv, in addition to several CCK-, SP-, VIP-, and TH-containing cells.(ABSTRACT TRUNCATED AT 400 WORDS)

The relationship between descending serotonin projections and ascending projections in the nucleus raphe magnus: a double labeling study

The nucleus raphe magnus and rostral parts of the nucleus raphe obscurus were found to have extensive efferent projections: a major ascending non-serotonergic (5-HT) projection through the median forebrain bundle, and a descending system consisting of both 5-HT and non-5-HT neurons. Differences in the localizations of their cells of origin suggest that they form two distinct efferent systems from the caudal medullary raphe nuclei.

Efferent projections of nucleus locus coeruleus: morphologic subpopulations have different efferent targets

This study quantitatively addresses the hypothesis that there is a systematic relationship between the morphologic characteristics of locus neurons and the particular target regions they innervate. Following horseradish peroxidase injections into selected terminal fields, locus coeruleus cell bodies are heavily labeled by retrograde transport so that somata size and shape, and in many cases primary dendritic pattern can be observed. This allows the classification of neurons as one of six cell types: large multipolar cells within ventral locus coeruleus, large multipolar cells in the anterior pole of locus coeruleus, fusiform cells in dorsal LC, posterior pole cells, medium-sized multipolar cells (termed core cells in this report), and small round cells. It was found that while core cells contribute to the innervation of all terminal fields examined, other cell types project to more restricted sets of targets. The contributions of each type to selected efferents are presented in detail. In particular, fusiform cells project to hippocampus and cortex, large multipolar cells in ventral locus coeruleus project to spinal cord and cerebellum, and small round cells in central and anterior locus coeruleus, as well as large multipolar cells in anterior locus coeruleus, project to hypothalamus. These results, in conjunction with those described in the preceding report, indicate that locus coeruleus is intrinsically organized with respect to efferent projections with much more specificity than has previously been evident. This high degree of organization is consistent with other recent demonstrations of functional specificity exhibited by locus coeruleus neurons.

Fetal noradrenergic transplants into amine-depleted basal forebrain nuclei restore drinking to angiotensin

6-Hydroxydopamine-induced catecholamine denervations in the organum vasculosum of the lamina terminalis and the median preoptic nucleus attenuate drinking responses to systemic angiotensin II (ANG II) injections. Transplanting catecholamines in these nuclei using fetal noradrenergic (NE) cell suspension restores ANG II-elicited thirst. These results emphasize the functional importance of NE neuronal systems in nuclei of the anteroventral third ventricle (AV3V) in mediating ANG II-induced drinking behaviors.

Neurotransmitter specificity of cells and fibers in the medial preoptic nucleus: an immunohistochemical study in the rat

The medial preoptic nucleus (MPN) is a sexually dimorphic complex with three major subdivisions. The cell-dense central (MPNc) and medial (MPNm) subdivisions are larger in male rats, while the cell-sparse lateral subdivision (MPNl) occupies a majority of the nucleus in females. In the present study we evaluated the distribution of possible monoaminergic and peptidergic cells and fibers within the MPN, as well as in adjacent regions of the medial preoptic area of the adult male rat. For this, we used an indirect immunohistochemical method with antisera to serotonin (5HT), dopamine beta-hydroxylase (DBH), tyrosine hydroxylase (TH), neuropeptide Y (NPY), cholecystokinin (CCK), vasoactive intestinal polypeptide (VIP), substance P (SP), neurotensin (NT), corticotropin-releasing factor (CRF), luteotropin-releasing hormone (LRH), somatostatin (SS), thyrotropin-releasing hormone (TRH), oxytocin (OXY), vasopressin (VAS), adrenocorticotropic hormone (1-24; ACTH), alpha-melanocyte-stimulating hormone (alpha-MSH), leucine-enkephalin (L-ENK), and calcitonin gene-related peptide (CGRP). The results suggest that cell bodies and/or fibers crossreacting with all of these putative neurotransmitters are differentially distributed within the MPN. Within the MPNm, the densest plexuses of fibers were stained with antisera to SP and NPY, while moderate densities of fibers were stained with anti-DBH, SS, CCK, CGRP, ACTH, and alpha-MSH, and only a few fibers were stained with anti-5HT, TH, NT, VAS, and L-ENK. Moderate numbers of SP- and L-ENK-immunoreactive cell bodies, and a few SS-, NT-, CRF-, and TRH-stained cell bodies were also found within the MPNm. The MPNc contained a dense plexus of CCK-immunoreactive fibers, as well as a few CRF-immunoreactive fibers. Both fiber types were localized almost exclusively to this subdivision, while most of the others studied here appeared to avoid it selectively. This suggests that there are relatively few inputs to the MPNc, and that they tend to avoid other parts of the nucleus, although moderate densities of DBH- and NPY-immunoreactive fibers were found in both the MPNm and MPNc. The MPNc contained several CCK-immunoreactive cell bodies as well as a moderate number of TRH-stained cell bodies. Both cell types were nearly completely localized to the MPNc. The major inputs to the MPNl studied here appear to be stained with antisera to 5HT and L-ENK, although moderate numbers of NT- and CRF- immunoreactive fibers were also found in this part of the nucleus.(ABSTRACT TRUNCATED AT 400 WORDS)

The organization of neural inputs to the medial preoptic nucleus of the rat

There is general agreement that the medial preoptic nucleus (MPN) receives projections from widespread regions of the brain, although there are significant discrepancies in the literature with regard to certain specific inputs. Therefore, we have reexamined the inputs to this nucleus with both retrograde and anterograde axonal transport techniques. First, injections of the retrograde tracers true blue, SITS, or wheat germ agglutinin were made into the region of the MPN and the distribution of retrogradely labeled cells was charted. Then, autoradiographic material was used to confirm the results of the retrograde studies, to identify the route taken by fibers projecting to the MPN, and to describe the distribution of projections with respect to the three cytoarchitectonic subdivisions of the nucleus. The results indicate that the MPN receives inputs from widely distributed areas in both the forebrain and brainstem, and that these inputs appear to be distributed topographically within the three cytoarchitectonic subdivisions of the nucleus. Direct inputs to the MPN arise from all major areas of the hypothalamus (except for the median and magnocellular preoptic nuclei, the supraoptic and suprachiasmatic nuclei, and the medial and lateral mammillary nuclei). Projections from nuclei within the periventricular zone of the hypothalamus end primarily in the medial part of the MPN, while inputs from the lateral zone are mainly confined to the lateral part of the nucleus, as are projections from the nuclei within the medial zone, except for those from the anterior and ventromedial nuclei, which appear to be more widespread. The MPN receives major inputs from limbic regions including the amygdala, ventral subiculum, and ventral lateral septal nucleus, all of which end preferentially in the lateral part of the MPN. In contrast, the projection from the encapsulated part of the bed nucleus of the stria terminalis appears to end preferentially in the central part of the MPN and in immediately adjacent regions of the medial subdivision. In addition, the MPN may receive relatively sparse inputs from infralimbic and insular cortical areas, the nucleus accumbens, and the substantia innominata. Finally, ascending serotoninergic projections from the raphe nuclei appear to terminate principally in the lateral part of the MPN, whereas inputs from regions containing noradrenergic cell groups are chiefly distributed to the central and medial parts of the nucleus. Other brainstem regions that appear to provide modest inputs include the ventral tegmental area, central tegmental field, periaqueductal gray, pedunculopontine nucleus, and the peripeduncular nucleus.(ABSTRACT TRUNCATED AT 400 WORDS)

Rostral pontine and caudal mesencephalic control of arterial pressure and iliac, celiac and renal vascular resistance. I. Anatomic regions

The rostral pons and caudal mesencephalon in 26 cats were electrically stimulated (greater than 2400 sites) while measuring arterial pressure and iliac, celiac and renal vascular resistance. Areas active in control of arterial pressure and iliac vasoconstriction were located in the marginal nucleus of the brachium conjunctivum (BCM) and in parts of the central tegmental fields (FTC) of the mesencephalon. Areas active in control of celiac and renal vasoconstriction were confined to the BCM. Areas active in control of iliac and celiac vasodilation were generally found ventral to the constrictor areas in the FTC of the mesencephalon. Stimulation of the caudal periaqueductal grey, locus caeruleus and underlying reticular formation elicited no change in any parameter measured. These findings suggest that multiple pathways for control of arterial pressure and vasoconstriction pass through or synapse in a discrete region of the dorsal rostral pons that is limited to the BCM.