Chemically defined collateral projections from the pons to the central nucleus of the amygdala and hypothalamic paraventricular nucleus in the rat

Triple fluorescence labelling was employed to reveal the distribution of chemically identified neurons within the pontine laterodorsal tegmental nucleus and dorsal raphe nucleus which supply branching collateral input to the central nucleus of the amygdala and hypothalamic paraventricular nucleus. The chemical identity of neurons in the laterodorsal tegmental nucleus was revealed by immunocytochemical detection of choline-acetyltransferase or substance P; in the dorsal raphe nucleus, the chemical content of the neurons was revealed with antibody recognizing serotonin. The projections were defined by injections of two retrograde tracers, rhodamine- and fluorescein-labelled latex microspheres, in the central nucleus of the amygdala and paraventricular nucleus, respectively. Neurons projecting to both the central nucleus of the amygdala and the paraventricular nucleus were distributed primarily within the caudal extensions of the laterodorsal tegmental nucleus and dorsal raphe nucleus. Approximately 11% and 7% of the labelled cells in the laterodorsal tegmental nucleus and dorsal raphe nucleus projected via branching collaterals to the paraventricular nucleus and central nucleus of the amygdala. About half of these neurons in the laterodorsal tegmental nucleus were cholinergic, and one-third were substance-P-ergic; in the dorsal raphe nucleus, approximately half of the neurons containing both retrograde tracers were serotonergic. These results indicate that pontine neurons may simultaneously transmit signals to the central nucleus of the amygdala and paraventricular nucleus and that several different neuroactive substances are found in the neurons participating in these pathways. This coordinated signalling may lead to synchronized responses of the central nucleus of the amygdala and paraventricular nucleus for the maintenance of homeostasis.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of c-fos protein in rat brain elicited by electrical and chemical stimulation of the hypothalamic paraventricular nucleus

The functional connectivity of the paraventricular nucleus of the hypothalamus (PVN) was studied by assessing the expression of the immediate early gene, c-fos, after unilateral stimulation of this structure in urethane-anesthetized rats. Electrical stimulation for 1 h (10 s on, 10 s off; 15-40 microA at 20 Hz) was accompanied by increases in mean arterial pressure (13-29 mm Hg). In these animals, ipsilateral increases in numbers of neurons with Fos-like immunoreactivity (FLI) were immunohistochemically demonstrated in the insular cortex, lateral septum, medial amygdala, hypothalamus, lateral division of the parabrachial nucleus (PBN) of the pons and the nucleus of the tractus solitarius (NTS) and ventrolateral medulla (VLM). Numbers of cells with FLI were quantitated in five areas known for their roles in autonomic function: arcuate nucleus, ventromedial hypothalamus, lateral PBN, NTS (at three levels) and VLM (caudal and rostral). In each case, stimulation of the PVN led to significant differences in number of neurons with FLI on the side ipsilateral to the stimulation compared to the contralateral side. To eliminate effects associated with stimulation of fibers of passage in the vicinity of the PVN, the results after electrical stimulation were compared to those obtained in animals in which the PVN was chemically stimulated unilaterally with the excitatory amino acid L-glutamate (5 one-minute infusions of 50 nl, 0.5 M glutamate over 1 h). Mean arterial pressure was increased after each injection (7-13 mm Hg), and significant differences in numbers of neurons with FLI between sides were maintained in all five areas except the NTS caudal to, and at, the level of the area postrema. An increase in neurons with FLI in the piriform cortex of all animals including controls may be due to injury-induced activation of target neurons from the PVN. These data illustrate that electrical and chemical stimulation of the PVN leads to simultaneous activation of neurons in many targets. All of the target areas studied receive direct projections from the PVN, although multisynaptic projections may also contribute to activation of target neurons.

Electrical stimulation of the central nucleus of the amygdala induces fos-like immunoreactivity in the hypothalamus of the rat: a quantitative study

The effect of electrical stimulation of an important forebrain autonomic structure, the central nucleus of the amygdala (CNA), on c-fos expression in three hypothalamic nuclei was studied in rat with immunocytochemistry to reveal the protein (Fos) encoded by the immediate early gene (IEG). Image analysis was used to quantify the Fos immunoreactive neurons within the supraoptic (SON), paraventricular (PVN), and arcuate (AN) nuclei. Stimulation for 60 min induced a statistically significant increase of the number of Fos immunoreactive neurons in all three nuclei ipsilateral to the CNA stimulation site. Double immunocytochemical staining (Fos and vasopressin or Fos and oxytocin) was employed to evaluate the participation of different subpopulations of neurons within the SON and PVN in response to CNA stimulation. In the SON, the increased number of Fos immunoreactive nuclei following the stimulation was observed in the vasopressin and oxytocin-secreting cells within this nucleus. In the PVN, the increase in the number of Fos immunoreactive neurons was predominantly within the parvocellular compartment. These studies demonstrate that IEG expression in hypothalamic neurons can be evoked as a result of afferent stimulation from the CNA. Activation of peptide- and hormone-containing neurons within the SON, PVN and AN, through mono- or multisynaptic pathways, may play a role in hormonal and autonomic responses.

Reinnervation of isolated islets of Langerhans transplanted beneath the kidney capsule in the rat

Neural regulation of islets of Langerhans mediates responses to stress and food ingestion. Transplantation of isolated islets offers hope to patients with insulin dependent diabetes mellitus but denervation of isolated islets may affect the capacity for appropriate metabolic control. Previous examination of the endocrine response to stress in islet autografted dogs revealed differences consistent with loss of neural regulation. Therefore, in the present study, islets grafted in rats were examined for extent and nature of reinnervation. Islets isolated from syngeneic donors were grafted under the kidney capsule of Wistar-Furth rats (n = 7) after 3 wk of streptozotocin induced diabetes. After 4 mo, graft-bearing kidneys were recovered and processed for double immunofluorescence. Antibodies were directed against (a) neuron associated proteins: synapsin (SYN) and L1; (b) neurotransmitters; tyrosine hydroxylase (TH), neuropeptide Y (NPY), vasoactive intestinal peptide (VIP), and calcitonin gene-related peptide (CGRP); and (c) islet hormones: insulin and somatostatin. SYN and L1 immunoreactivities in nerve fibres suggested reinnervation of the grafted islets although fibres were not associated with structures within the transplanted islets as in intact islets. CGRP immunoreactivity was observed in fibres and in a subpopulation of cells within intact islets but only in cells of the grafted islets. VIP, TH, and NPY immunoreactivities were found in nerve fibres of intact islets but only VIP was observed in fibres of grafted islets suggesting an absence of sympathetic reinnervation. In conclusion, transplanted islets of Langerhans become reinnervated but with a distribution and complement of neurotransmitters distinct from intact islets.

Distribution of the tight junction-associated protein ZO-1 in circumventricular organs of the CNS

The immunofluorescent distribution of ZO-1, a tight junction-associated protein, was studied in murine circumventricular organs. These regions generally express a less restrictive blood-brain barrier than is found in other areas of the CNS. In the remaining brain parenchyma, where a characteristic blood-brain barrier exists, ZO-1 was localized in discrete, continuous lines along blood vessels, presumably in association with endothelial cell tight junctions. The ependymal cells in the ventricular walls displayed a more punctate pattern of ZO-1 distribution, indicative of discontinuous tight junctions. In two of the circumventricular organs examined, the median eminence and the subfornical organ, many capillaries lacked detectable ZO-1 immunoreactivity while the apical aspects of the specialized ependymal cells (tanycytes) revealed an unbroken ZO-1 distribution. Scant labelling of ZO-1 in blood vessels was found in the area postrema, and only weak and discontinuous ZO-1 labelling was present in the ventricular wall. Capillaries of the organum vasculosum laminae terminalis expressed ZO-1 immunoreactivity which was comparable to the pattern observed in CNS regions with typical blood-brain barrier. The subcommissural organ, known to contain a blood-brain barrier, also displayed continuous ZO-1 staining in blood vessels. Unbroken ZO-1 distribution was observed in the specialized ependymal cells adjacent to both the organum vasculosum laminae terminalis and subcommissural organ. These immunocytochemical data demonstrate a distribution of ZO-1 in CNS parenchyma outside the circumventricular organs that is consistent with an organization of tight junctions which prevent free paracellular exchange of substances between blood and neuropil but which allow for continuity between CSF and the neuronal environment. The ZO-1 staining pattern in blood vessels and ventricular walls of the circumventricular organs is heterogeneous despite the prevalent absence of a functional blood-brain barrier.

Alterations in brain hexokinase activity associated with heart failure in rats

This study examined the activity of discrete regions of the brain as assessed with histological localization and photodensitometric quantification of the metabolic enzyme hexokinase in a group of rats with coronary occlusion (HF) and in sham-operated control rats. Three weeks after surgery, the mean left ventricular end diastolic pressure and right atrial pressure were elevated, and left ventricular peak systolic pressure was decreased in the HF group compared with the sham group; these findings are also observed during heart failure. In addition, histological data indicated that there was a 37.6 +/- 2.8% outer and 40.8 +/- 3.1% inner infarct of the myocardium in the group of rats with HF (n = 6). Rats in the control group had no observable damage to the myocardium (n = 6). Accompanying these symptoms of heart failure were significant increases in hexokinase activity in the parvocellular (pPVN, 16.3%) and magnocellular (mPVN, 17.6%) divisions of the paraventricular nucleus of the hypothalamus, and in the locus ceruleus (LC, 17.1%). No changes in hexokinase activity were observed in the median preoptic area, supraoptic nucleus (SON), subfornical organ, or posterior hypothalamus. These results reinforce the idea that heart failure (with coronary occlusion) is associated with changes in specific areas in the brain and that metabolic alterations in the pPVN, mPVN, and LC are likely related to alterations in vasopressin production, blood volume regulation, and sympathoexcitation observed in the heart failure state.

Effects of renal denervation and reinnervation on ganglionic gene expression of neurotransmitter proteins and c-fos in rat

To investigate the molecular basis for reno-renal interactions, Northern blot analyses of sympathetic ganglia were used to study the changes in levels of mRNA encoding tyrosine hydroxylase (TH), neuropeptide Y (NPY), and c-fos at 4, 14, 21, and 56 days after denervation of the left kidney, and of c-fos mRNA at 1 and 4 h after denervation. Ganglia included in the study were right and left paravertebral chain ganglia (PVG, T11 to L2), celiac-mesenteric plexus (CMP), and right and left superior cervical ganglia (SCG). Levels of TH mRNA in the left PVG and CMP were decreased at 4 and 14 days compared to controls. Levels were elevated at 21 days and similar to control levels at 56 days. In the right PVG, TH mRNA levels were elevated at 4 and 14 days, diminished from this elevated level at 21 days, and similar to control levels at 56 days. No differences were found in TH mRNA levels of left or right SCG compared to controls. In long-term experiments (days), no differences in NPY or c-fos mRNA levels were found in any of the ganglia from experimental rats compared to controls. Levels of c-fos mRNA in the left PVG and CMP were decreased at 1 hour compared to control levels. By 4 h, differences in mRNA levels were no longer apparent. In the right PVG, c-fos mRNA levels were elevated at 1 hour and no longer different from control levels at 4 h. No differences were found in c-fos mRNA levels of left or right SCG compared to controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Branching projections of catecholaminergic brainstem neurons to the paraventricular hypothalamic nucleus and the central nucleus of the amygdala in the rat

In this study, we have employed triple fluorescent-labelling to reveal the distribution of catecholaminergic neurons within three brainstem areas which supply branching collateral input to the central nucleus of the amygdala (CNA) and the hypothalamic paraventricular nucleus (PVN): the ventrolateral medulla (VLM), the nucleus of the solitary tract (NTS) and the locus coeruleus (LC). The catecholaminergic identity of the neurons was revealed by immunocytochemical detection of the biosynthetic enzyme, tyrosine hydroxylase. The projections were defined by injections of two retrograde tracers, rhodamine- and fluorescein-labelled latex microspheres, in the CNA and PVN, respectively. In the VLM and NTS, the greatest incidence of neurons which contained both retrograde tracers was found at the level of the area postrema. These neurons were mainly located within the confines of the A1/C1 (VLM) and A2 (NTS) catecholaminergic neuronal groups. Double-projecting neurons in the LC (A6) were distributed randomly within the nucleus. It was found that 15% in the VLM, 10% in the NTS and 5% in the LC of the retrogradely labelled cells projected via branching collaterals to the PVN and CNA. One half of these neurons in the VLM and NTS were catecholaminergic, in contrast to the LC where virtually all double-retrogradely labelled neurons revealed tyrosine hydroxylase immunoreactivity. In the other brainstem catecholaminergic cell groups (A5, A7, C3), no catecholaminergic neurons were found that supplied branching collaterals to the CNA and PVN. Our results indicate that brainstem neurons may be involved in the simultaneous transmission of autonomic-related signals to the CNA and the PVN. Catecholamines are involved in these pathways as chemical messengers. Brainstem catecholaminergic and non-catecholaminergic neurons, through collateral branching inputs may provide coordinated signalling of visceral input to rostral forebrain sites. This may lead to a synchronized response of the CNA and PVN for the maintenance of homeostasis.

Efferent projections from the parabrachial nucleus demonstrated with the anterograde tracer Phaseolus vulgaris leucoagglutinin

Efferent projections from the parabrachial complex (PBN) were studied in the rat using the anterograde tracer, Phaseolus vulgaris leucoagglutinin (PHA-L). Projections to the hypothalamus (ventromedial, dorsomedial, paraventricular, and supraoptic nuclei) originate primarily in the lateral PBN (1PBN). The amygdalar central nucleus (ACE) receives strong projections from all parts of the PBN although the external 1PBN projects primarily to the lateral ACE. Whereas the projections to the lateral bed nucleus of the stria terminalis, median preoptic nucleus, diagonal band of Broca, and lateral preoptic area originate primarily from the 1PBN, those to the insular cortex arise from the medial PBN (mPBN). The mPBN projects to the ventral posteromedial thalamus and the 1PBN and mPBN project to the zona incerta. Descending projections from the mPBN and Kölliker-Fuse area target the commissural nucleus tractus solitarius (NTS); the mPBN projects to the more rostral NTS. Similarly, the caudal parvicellular reticular formation (RF) receives projections from the mPBN and 1PBN, whereas input to the rostral RF arises from the former. All compartments of the PBN project to the ventrolateral medulla, although the projections arising from the 1PBN are densest. Finally, the raphe nuclei and periaqueductal gray receive some projections from most PBN divisions. These pathways provide a potential means whereby autonomic information can be relayed through the PBN to other structures important in regulating autonomic functions.

Expression of c-fos protein in rat brain after electrical stimulation of the aortic depressor nerve

To reveal central nervous system (CNS) structures involved in the baroreceptor reflex we studied the distribution of Fos protein-like immunoreactivity in the rat brain after one hour of electrical stimulation of the aortic depressor nerve (ADN). In 13 male Wistar rats under urethane the ADN was cut on both sides and the central ends were placed on stimulating electrodes. Intermittent (11 s on, 6 s off) electrical stimulation at parameters set to elicit a drop in mean arterial pressure of 15-30 mmHg was applied to one, both or neither ADNs for 1 h. CNS sections were incubated for 48 h in anti-Fos antibody and prepared for visualization of the reaction product using the ABC immunoperoxidase technique. Label was found in several discrete brain nuclei primarily on the side ipsilateral to the side of stimulation. In the medulla labelled nuclei were found in the nucleus tractus solitarius, area postrema, rostral and caudal ventrolateral medulla, nucleus ambiguus and medullary reticular formation. In the pons labelled neurons were found in the lateral and ventrolateral parabrachial nucleus, locus coeruleus, pontine reticular field and A5 region. In the forebrain labelled nuclei were observed in the peri- and paraventricular hypothalamus, supraoptic nucleus, subfornical organ, preoptic area, central nucleus of the amygdala, median preoptic area, horizontal limb of the diagonal band, bed nucleus of the stria terminalis and islands of Calleja. In control animals moderate amounts of label were present in the supraoptic nucleus and periventricular hypothalamus bilaterally. These results define central pathways involved in mediating the baroreceptor reflex.

Characterization of peptidergic efferents from the lateral parabrachial nucleus to identified neurons in the rat dorsal raphe nucleus

The peptidergic content of the lateral parabrachial nucleus (LPB) efferents to the dorsal raphe nucleus (DRN) was studied by combining visualization of the anterogradely transported tracer Phaseolus vulgaris leucoagglutinin within fibers that were immunocytochemically stained for neurotensin (NT), calcitonin gene-related peptide (CGRP) or galanin (GAL). The identity of DRN target neurons was determined with simultaneous immunocytochemical labelling for serotonin, the major transmitter within the nucleus. Within the DRN, we estimated that about two-thirds of the anterogradely labelled fibers arising from the LPB also showed peptidergic immunoreactivity. NT was the most commonly observed neuropeptide in LPB neuronal efferents directed to the DRN, followed by CGRP and GAL. The peptidergic afferents in the DRN were oriented preferentially in the dorsoventral plane. Peptidergic fibers from the LPB possessed varicosities (diameters not exceeding 3 microns) and were apposed on serotoninergic neuronal somata. Some of the anterogradely labelled peptidergic fibers were not associated with cells showing immunoreactivity for serotonin. The present results suggest that NT-ergic, CGRP-ergic and GAL-ergic neurons within the LPB are in contact with serotoninergic and non-serotoninergic neurons within the DRN. Since the DRN is known to project to the LPB, it is likely that bi-directional interconnections between these nuclei exist. Such linkages may provide anatomical substrates for coordinated autonomic responses.

Expression of c-fos protein in rat brain elicited by electrical stimulation of the pontine parabrachial nucleus

The expression of Fos, the protein product of the primary response gene c-fos, was used metabolically to map the short-term (1 hr) effects of urethane and sodium pentobarbital anesthesia in rat. Subsequently, urethane-anesthetized rats were used to study the integrated response to electrical stimulation (1-1.5 hr) of the pontine parabrachial nucleus (PBN), an important center for relay of autonomic information in the brain. Immunohistochemistry was used to localize Fos-like immunoreactivity (FLI) in the brain. To approximate amounts of FLI in the conscious animal, rats were killed immediately after attaining surgical anesthesia with sodium pentobarbital (50 mg/kg) or urethane (1.2-1.7 gm/kg). No FLI was found in the brains of these rats. In rats killed 1 hr after anesthesia with sodium pentobarbital, FLI was found only in the habenulae. After 1 h of urethane anesthesia, low levels of FLI were found in the following areas: nucleus of the tractus solitarius (NTS); caudal and rostral ventrolateral medulla (VLM); lateral PBN; ventromedial, paraventricular, and supraoptic nuclei (SON) of the hypothalamus; medial preoptic area; central nucleus of the amygdala (ACE); endopiriform cortex; insular cortex; piriform cortex; and islands of Calleja. Electrical stimulation of the PBN (10 sec on, 10 sec off; 15-50 microA at 20 Hz for 60-90 min) in rats anesthetized with urethane led to increases in mean arterial pressure (10-30 mm Hg) and to ipsilateral increases of FLI in the lateral PBN, dorsal division of SON, ACE, endopiriform nucleus, insular cortex, piriform cortex, and islands of Calleja. In two animals, ipsilateral increases were found in the ventromedial hypothalamus and medial amygdaloid nucleus.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of the parabrachial nucleus input to the hypothalamic paraventricular nucleus in the rat

The brainstem parabrachial nucleus (PBN) is viewed as an increasingly important site for the transfer of autonomic-related information to more rostral structures in the forebrain including the hypothalamus. In this study, we examined electrophysiologically in vivo and anatomically the nature of PBN input to the hypothalamic paraventricular nucleus (PVN) and particularly to the vasopressin-and oxytocin-secreting magnocellular neurosecretory cells within this nucleus. In urethane-anaesthetized rats, extracellular recordings from 108 antidromically identified neurosecretory PVN cells revealed an excitatory (37/43 cells) and less frequently an inhibitory (6/43 cells) response consequent to electrical stimulation in the PBN. Both vasopressin (12/37 cells)-and oxytocin (9/37 cells)-secreting neurons appear to respond to the PBN stimulus. Four cells projecting to the neurohypophysis could also be antidromically activated from PBN, and this observation may be indicative of collateral branching in some PVN neurosecretory neurons. In addition, recordings from 60 non-magnocellular (i.e. non-neurohypophysially-projecting) PVN cells revealed a facilitatory response (43/60 cells) following PBN stimulation, Iontophoretic injections of the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L) were made within the rat lateral PBN and brains prepared for immunocytochemical examination of projections to the PVN region. PHA-L-labelled fibres and terminals were visualized within both the parvocellular and magnocellular divisions of the PVN. In addition, labelled fibres were also seen in a region immediately dorsal to the PVN. PHA-L-labelled fibres with axonal varicosities and boutons were visualized over immunocyto-chemically-identified vasopressin and oxytocin neurons within the magnocellular PVN. These convergent electrophysiological and anatomical data provide evidence for a PBN projection to the PVN that is predominantly excitatory to both magnocellular neurosecretory and non-magnocellular cells. Moreover, with respect to vasopressin-and oxytocin-secreting cells, the PBN input appears to be directed at both populations of peptidergic neurons.

The hypothalamic paraventricular and lateral parabrachial nuclei receive collaterals from raphe nucleus neurons: a combined double retrograde and immunocytochemical study

Retrograde tracer injections of fluorescein- and rhodamine-labelled latex microspheres centered in the parvicellular zone of the hypothalamic paraventricular nucleus and pontine lateral parabrachial nucleus revealed that 36% of the labelled neurons in the dorsal raphe nucleus send collaterals to both structures. These cells were organized in a well-distinguishable cluster within the dorsal raphe nucleus. By combining retrograde tracing with immunocytochemistry, it was found that less than 8% of the double-labelled cells stained positively for serotonin. Of the remaining raphe nuclei that were examined, only the median raphe nucleus contributed a minor nonserotoninergic projection to the paraventricular or lateral parabrachial nuclei. Few of the retrogradely labelled cells in the median raphe nucleus contained both tracers. These results suggest that nonserotoninergic and serotoninergic neurons in the dorsal raphe nucleus, via collateral branching, may simultaneously influence the activity of two central nervous system nuclei involved in autonomic control.

Neurons in the rat medulla oblongata containing neuropeptide Y-, angiotensin II-, or galanin-like immunoreactivity project to the parabrachial nucleus

Projections from the medulla to the parabrachial complex of the rat were examined for their content of neuropeptide Y-, angiotensin II- or galanin-like immunoreactivity using combined retrograde tracing and immunohistochemical techniques. Rhodamine-labelled latex microspheres were stereotaxically injected into discrete nuclei of the parabrachial complex. After survival of two to five days, colchicine (100 micrograms in 10 microliters saline) was injected into the cisterna magna. One day later, rats were perfused and the brainstems were prepared for visualization of the retrograde tracer and immunoreactivity of one of the three peptides. Retrograde labelling verified that the area postrema, nucleus of the tractus solitarius, caudal spinal nucleus of the trigeminal nerve, parvocellular reticular nucleus, and ventrolateral medulla including the rostral ventrolateral medulla and nucleus paragigantocellularis project to the lateral parabrachial and Kölliker-Fuse nuclei. While most projections were primarily ipsilateral, a small proportion of the projections from the ventrolateral medulla was bilateral. Neurons containing neuropeptide Y-like immunoreactivity were found in the caudal and intermediate nucleus of the tractus solitarius, dorsal to the lateral reticular nucleus and in the nucleus paragigantocellularis. After bilateral microsphere injections into the lateral parabrachial and Kölliker-Fuse nuclei, double-labelled neurons were found dorsal to the lateral reticular nucleus of caudal and intermediate medullary levels, at the ventral surface of the medulla at intermediate levels and in the nucleus paragigantocellularis at rostral levels. Neurons with angiotensin II-like immunoreactivity were observed at the dorsomedial border of the caudal and intermediate nucleus of the tractus solitarius, in the area postrema and in the lateral reticular nucleus and nucleus paragigantocellularis. Of these neurons, small numbers in the nucleus of the tractus solitarius and ventrolateral medulla also projected to the lateral parabrachial and Kölliker-Fuse nuclei. Neurons containing galanin-like immunoreactivity were found in the caudal nucleus of the tractus solitarius, the area postrema, the spinal trigeminal nucleus, the raphe nuclei (pallidus and obscurus), the nucleus paragigantocellularis and dorsal to the lateral reticular nucleus. Of these cells, double-labelled neurons were found in the commissural and medial subdivisions of the caudal nucleus of the tractus solitarius and in the rostral ventrolateral medulla including the ventral surface and the nucleus paragigantocellularis. The results suggest that neuropeptide Y, angiotensin II and galanin may serve as neurochemical messengers in pathways from the medulla to the parabrachial complex. The location of double-labelled neurons suggests that the information relayed by these neurons is related to autonomic activity.

Gene expression of tyrosine hydroxylase and neuropeptide Y in prevertebral ganglia of renal hypertensive rats

The gene expression of tyrosine hydroxylase (TH) and neuropeptide Y (NPY) was studied in prevertebral ganglia and adrenal glands of adult male rats during the development of renal hypertension (removal of 1 kidney/constriction of other kidney). Only tissues from rats with arterial pressures significantly elevated by day 3 were compared with those from controls. At 4 or 5 days after renal surgery, superior cervical ganglia, celiac-mesenteric plexus, adrenal glands, and stellate ganglia were surgically removed from nonfixed rats for Northern blot analysis or from perfusion-fixed rats for in situ hybridization. In all tissues, levels of TH mRNA were decreased in hypertensive rats; cells with decreased levels were scattered throughout each tissue. In contrast, levels of NPY mRNA were unchanged in hypertensive rats compared with controls. Changes in TH mRNA levels suggest that the developing phase of renal hypertension is associated with a decrease in sympathetic outflow to the periphery. In contrast, the failure of NPY mRNA levels to change suggests a different regulatory mechanism for NPY expression or a different role for NPY in sympathetic neurotransmission.

Parabrachial nucleus projection towards the hypothalamic supraoptic nucleus: electrophysiological and anatomical observations in the rat

It has been proposed that the pontine parabrachial nucleus (PBN) participates in the regulation of body fluid balance and the release of vasopressin from the neurohypophysis, although the pathways mediating the latter response are uncertain. This study in the rat, utilizing anatomical and electrophysiological methods, describes a projection from the lateral PBN towards the hypothalamic supraoptic nucleus (SON). Rats received iontophoretic injections of the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L, 2% solution). After 14-17 days, rats were sacrificed and their brains prepared for immunofluorescent visualization of projections to the SON region. PHA-L-labelled terminals were found primarily in perinuclear regions immediately dorsal to the SON. In contrast, injections within the medial PBN and the nearby Kölliker-Fuse nucleus did not reveal labelling in or around the SON. Extracellular recordings from 86 of 118 antidromically identified neurons in anaesthetized rats revealed a set of complex synaptic responses after stimulation in the PBN. Excitatory responses (in 82 of 86 cells) of short (less than 100 msec, 39/82 cells) and long (greater than 100 msec, 43/82) duration were observed in both vasopressin- and oxytocin-secreting cells of the SON, while 4/86 cells displayed a depressant response to PBN stimulation. In the adjacent perinuclear zone, 22/39 nonneurosecretory cells responded with an increase in their excitability consequent to an identical stimulus. These data suggest a predominantly facilitatory influence of lateral PBN neurons on SON neurosecretory cells in the rat, and that the PBN-SON projection is an indirect one that utilizes an interneuronal network located in the perinuclear zone adjacent to the SON.

Effects of neonatal sympathectomy with 6-hydroxydopamine or guanethidine on survival of neurons in the intermediolateral cell column of rat spinal cord

The effects of removing target cells on survival of, and inputs to, sympathetic preganglionic neurons were studied in rats that were sympathectomized with 6-hydroxydopamine (6-OHDA) or guanethidine sulfate. Separate groups of neonatal and 1-week male rats were given injections of 6-OHDA for 10 days and of guanethidine for 3 weeks (5 days/week), respectively. Histofluorescence results suggest that catecholaminergic neurons in most ganglia are destroyed with treatment except for adrenal medulla, which is unaffected [14], and the pelvic ganglion where only partial destruction occurs. Cells in the intermediolateral cell column from representative spinal cord segments of treated and control adult rats were counted. In 6-OHDA-treated rats, cells decreased in number in all segments compared to controls. In guanethidine-treated rats, cells were also decreased in number; in some segments the decrease was significantly greater than with 6-OHDA. Sympathectomy had no effect on neurons in the intermediate gray of L5 or in the ventral horn of T3. The results of this study demonstrate that peripheral sympathectomy causes loss of sympathetic preganglionic neurons and that guanethidine is slightly more effective than 6-OHDA.

Alterations in brain hexokinase activity associated with streptozotocin-induced diabetes mellitus in the rat

The effects of streptozotocin-induced diabetes mellitus on the activity of discrete regions of the brain were studied with histochemical localization and photodensitometric quantification of the metabolic enzyme, hexokinase. Two weeks after a single injection of streptozotocin (65 mg/kg, i.p.), plasma glucose and osmolarity levels were elevated, and plasma sodium concentrations were depressed. These changes were reversed in diabetic rats treated with insulin. Accompanying these symptoms of diabetes were significant increases in hexokinase activity in the magnocellular division of the paraventricular nucleus of the hypothalamus (mPVH, 12.1%), the medial subdivision of the nucleus of the tractus solitarius (mNTS, 15.5%), and the commissural subdivision of the NTS (cNTS, 10.9%). An increase, though just below the level of significance, was also observed in the supraoptic nucleus of the hypothalamus (SON, 11.5%). The increases in hexokinase activity were completely reversed in the cNTS (and SON) and only partly reversed in the mPVH and mNTS of insulin-treated diabetic rats. No changes in hexokinase activity were seen in the subfornical organ, medial preoptic area, parvocellular division of the PVH, locus coeruleus, or dorsal motor nucleus of the vagus of diabetic rats. These results reinforce the idea that the brain is not exempt from changes associated with diabetes mellitus and suggest that metabolic alterations in the mPVH (and SON) and two divisions of the NTS are likely related to changes in vasopressin production and blood volume, respectively.

Metabolic alterations in discrete regions of the rat brain during development of spontaneous hypertension

Hexokinase histochemistry was used to identify brain regions that undergo metabolic changes during the development of hypertension in the spontaneously hypertensive rat (SHR). Photodensitometric measurements of reaction product were made in the commissural subdivision of the nucleus of the tractus solitarius, medial subfornical organ, supraoptic nucleus, magnocellular division of the parvocellular division of the paraventricular nucleus, anterior hypothalamic area, and posterior hypothalamus of prehypertensive SHR (4 weeks) and SHR with developing hypertension (8 weeks). These values were compared with those obtained from age-matched Sprague-Dawley and Wistar-Kyoto rats. At 4 weeks, significantly lower levels of hexokinase were observed in the commissural subdivision of the nucleus of the tractus solitarius and the magnocellular division of the paraventricular nucleus of SHR; a higher level was seen in the posterior hypothalamus. At 8 weeks, significantly higher levels of hexokinase were observed in the anterior hypothalamic area and the posterior hypothalamus. These results can be compared to those from adult SHR where lower levels of activity were found in the parvo- and magnocellular divisions of the paraventricular nucleus. Together these results suggest that, while the role of the magnocellular division of the paraventricular nucleus remains unclear, the commissural subdivision of the nucleus of the tractus solitarius and posterior hypothalamus may participate in the initial events leading to hypertension whereas the parvocellular division of the paraventricular nucleus does not.

Effects of colchicine on hexokinase activity in the paraventricular and supraoptic nuclei of spontaneously hypertensive and normotensive rats

The effects of intracerebroventricular (ICV) colchicine (70 micrograms per rat) on systolic pressures and levels of hexokinase activity in the hypothalamic paraventricular (PVH) and supraoptic (SON) nuclei were investigated in adult normotensive and spontaneously hypertensive rats (SHR). One day after colchicine injection, systolic pressures had dropped significantly in Sprague-Dawley (SD) rats, Wistar-Kyoto (WKY) rats, and SHR; the largest decrease was seen in SHR. Postinjection pressures in SHR were within the normotensive range. No further decreases were observed two days after injections. Quantitative analysis of hexokinase activity in control animals verified that the parvo- and magnocellular PVH (but not SON) of SHR contained significantly lower levels of hexokinase than in WKY or SD rats. Two days after colchicine injection, hexokinase activities in pPVH and mPVH were similar in all three strains. Activity had decreased significantly in SD and WKY rats. In SHR, no differences between control and postinjection values were found. Hexokinase activity in SON was significantly decreased to the same extent in all strains. As metabolic activity in the pPVH, mPVH, and SON decreased after colchicine injection in normotensive rats whereas no such decreases occurred in the pPVH and mPVH of SHR, the findings suggest that colchicine may have differential effects on the metabolic activity of specific cell groups in brain depending on the physiological state of the animal.

Regional alterations in hexokinase activity within rat brain during dehydration and rehydration

Histochemical localization and photodensitometric quantification of the metabolic enzyme, hexokinase (HK), were used to study changes in brain metabolic activity that occur during the development of (5 days) and recovery from (7 days) dehydration. In water-deprived (WD) rats, HK activity increased after 2 days in the subfornical organ (SFO, 22%), nucleus circularis (NC, 36%), parvo- and magnocellular divisions of the paraventricular nucleus (pPVH, 17%; mPVH, 46%) and supraoptic nucleus (SON, 46%). Activity in SFO declined to control levels at 3 days but increased again thereafter. In pPVH, mPVH, and SON, activity was elevated until the end of the experiment. In NC, activity returned to control levels within 2 days of drinking by the rats. In salt-loaded (2% NaCl in water) rats, changes were similar to those of WD rats up to 2 days of dehydration (SFO, 25%; NC, 20%; pPVH, 16%; mPVH, 38%; SON, 50%). Activity in SFO and pPVH returned to control levels after 3 days and remained unchanged. In mPVH, SON, and NC, activity remained elevated and declined to control levels when salt-free water was provided. Results confirm that water deprivation is a stronger dehydrating stimulus than salt loading. In addition, metabolic activity, as measured by HK activity, varies daily during periods of dehydration and rehydration. These changes cannot always be predicted from results obtained only at the end of a period of dehydration. It is concluded that it is necessary to study dehydration-induced changes in brain metabolism on a daily basis to more fully understand the roles of discrete brain regions in the regulation of body fluids.

Decreased hexokinase activity in paraventricular nucleus of adult SHR and renal hypertensive rats

Metabolic activity was assessed in the brains of spontaneously hypertensive rats (SHR) using the histochemical hexokinase (HK) technique and photodensitometric analysis. Of eight regions known to play a role in cardiovascular regulation, only the paraventricular nucleus of the hypothalamus (PVH) exhibited alterations in HK activity. Significantly lower levels of HK activity in SHR than in control Sprague-Dawley and Wistar-Kyoto rats were measured in both the parvo- and magnocellular divisions of the PVH. No differences in HK activity were found in the anterior hypothalamic nucleus, posterior hypothalamic nucleus, supraoptic nucleus, subfornical organ, central nucleus of the amygdala, or the medial nucleus of the tractus solitarius of SHR. Similar results were obtained in renal hypertensive rats; furthermore, a positive correlation was found between levels of arterial pressure and densitometric readings. These latter results strongly suggest that metabolic alterations in the PVH of SHR are directly related to the increases in arterial pressure and are not due to the genetic makeup of SHR. In light of studies by others, the data from the present study have been interpreted to suggest that the decreases in metabolic activity in the PVH of the adult SHR are the result of a central attempt to bring the level of the arterial pressure down to normal levels and not to the altered activity of a region that might be acting to keep arterial pressure elevated.