Paraventricular nucleus: a site for the integration of neuroendocrine and autonomic mechanisms

Lesions of the paraventricular nucleus area of the hypothalamus disrupt the suprachiasmatic leads to spinal cord circuit in the melatonin rhythm generating system

The circadian rhythm in melatonin production in mammals is regulated by a suprachiasmatic (SCN) leads to spinal cord leads to pineal circuit. In the present investigation the possible participation of the paraventricular nucleus of the hypothalamus (PVN) in the SCN leads to spinal cord segment of this circuit was investigated in the rat. Bilateral lesions of the PVN area were produced and one to two weeks later melatonin production was evaluated by measuring the activities of the two pineal enzymes required for the formation of melatonin from serotonin, indoleamine N-acetyltransferase (NAT) and hydroxyindole-O-methyltransferase (HIOMT), and urinary 6-hydroxymelatonin, the major melatonin metabolite. In some cases pineal melatonin was also measured. Control animals received sham-PVN lesions. Histological examination of the lesions indicated that the PVN were bilaterally destroyed 100% in 12 animals. The nighttime pineal melatonin and urinary 6-hydroxymelatonin values in this group were reduced about 90%, nighttime pineal NAT activity was reduced about 98%, and HIOMT activity about 75%. The urinary 6-hydroxymelatonin values of PVN-lesioned animals and animals with denervated pineal glands were similar. In animals with hypothalamic lesions involving less than 30% of the PVN, nighttime values of NAT, HIOMT, and urinary 6-hydroxymelatonin were normal; in animals with 30 to 95% PVN damage these parameters were altered to a small degree. These studies, together with histochemical observations, indicate the SCN neurons responsible for pineal circadian rhythms project to the PVN area of the hypothalamus.

A combined vascular-catecholamine fluorescence method reveals the relative vascularity of rat locus coeruleus and the paraventricular and supraoptic nuclei of the hypothalamus

Vascular perfusion with a fluorescent dye, Pontamine sky blue, was combined with glyoxylic acid-induced catecholamine fluorescence to produce simultaneous staining of intracerebral blood vessels and catecholamine-containing cells and fibers. Quantitative measurements of blood vessels per unit area revealed that the vascular density of rat locus coeruleus did not differ from the surrounding neuropil but was significantly lower than that of the hypothalamic supraoptic and paraventricular (PVN) nuclei. Moreover, the density of blood vessels in the magnocellular portion of PVN was not uniform throughout its rostrocaudal extent but was dense only in a specific subdivision of lateral PVN, which is predominantly vasopressinergic and is also heavily innervated by catecholamine terminals.

Quantitative histological studies on the hypothalamic paraventricular nucleus in rats. II. Number of local and certain afferent nerve terminals

The total number and the numerical ratio of extrinsic and intrinsic (local) innervations of magnocellular neurons in the paraventricular nucleus (mPVN) were determined after surgical isolation of the nucleus in rats. Various lesions and transections of fibers running to the mPVN were performed to determine the number and possible sources of septal, hippocampal and caudal periventricular fibers to the mPVN. The relatively high proportion of possibly intrinsic connections (43%) suggests a local, integrative function of neuronal activity in the PVN. On the average, 57% of the total number of presynaptic boutons have been found to originate from outside the nucleus (extrinsic afferentation). Only 7% of these fibers ascend from caudal through the periventricular area. mPVN afferents originating from the ventral subiculum and from the lateral septal nucleus comprise about 3 and 5% of the extrinsic afferentation, respectively.

Quantitative histological studies on the hypothalamic paraventricular nucleus in rats: I. Number of cells and synaptic boutons

Quantitative histological analysis of serial sections of the adult male rat brain gives mean total estimates of the numbers of cells in the magnocellular and parvicellular divisions of the paraventricular hypothalamic nuclei (PVN) of 6600 and 11,500, respectively. The numbers and densities (number/mm3) of presynaptic bouton profiles have been measured and calculated on electron micrographs of the magnocellular paraventricular nucleus (mPVN). There are approximately 18 x 10(6) presynaptic boutons in the magnocellular subdivision: 76% of the synaptic boutons are axodendritic, 17% axosomatic and 7% are unidentified but include a few axo-axonic contacts. One third of the boutons contain dense-core vesicles although their postsynaptic contacts do not differ from other boutons. The estimated ratio of the number of boutons per neuron in the magnocellular paraventricular nucleus is 2820:1.

Effects of lesions in the paraventricular nucleus of the hypothalamus on vasopressin and oxytocin contents in brainstem and spinal cord of rat

The effects of lesions of the paraventricular nucleus in rat hypothalamus (PVN) on the vasopressin (AVP) and oxytocin (OT) contents of the brainstem and spinal cord, as measured by radioimmunoassay, were studied. AVP decreased by 50% and 80% in brainstem and spinal cord of lesioned animals, whereas OT disappeared almost completely. Therefore, in contrast to OT, the PVN is not the only site of origin of AVP-containing nerve fibers projecting to the brainstem.

Hypothalamic pathways involved in metabolic regulatory functions, as identified by track-tracing methods

The present review of the fiber connections of the hypothalamus has been concerned basically with recent data obtained by the aid of the autoradiographic and HRP tracer techniques. Evidence presented has shown that, besides confirming many of the older data, recent studies have resulted in the introduction of several conceptual modifications into the classic picture of hypothalamic hodological relationships. Among these conceptual modifications, the following can be mentioned: (1) the medially placed nuclei of the hypothalamus have a great number of long efferent and afferent connections with many extrahypothalamic structures; (2) many hypothalamic nuclei send direct projections to cell territories in the brainstem and spinal cord that contain preganglionic autonomic motor neurons; (3) several neural districts that lie caudal to the mesencephalon send direct projections to the hypothalamus; (4) in addition to the olfactory channel, other sensory pathways (including interoceptive and gustatory conduction lines) have a relatively direct access to hypothalamic mechanisms; (5) the hypothalamus sends fibers to several brainstem territories that give rise to widespread monoaminergic projections; and (6) there are anatomical pathways that establish reciprocal connections between the hypothalamus and the basal ganglia. Some of the possible physiological correlates of these anatomical findings in the context of metabolic regulatory functions have been briefly indicated.

Pituitary blood flow

The direction of pituitary blood flow, the amount of pituitary blood flow, its regional control, and the role of the median eminence microcirculation are the subjects of this review. Present concepts of pituitary blood flow are focused almost entirely on its direction and arouse from studies of pituitary vascular anatomy performed almost 50 years ago. The development of new anatomic techniques has led to a reappraisal of pituitary angioarchitecture, stimulated physiological studies to clarify the pattern of blood flow within the entire gland, and led to a reappraisal of accepted concepts of directional pituitary blood flow. The availability of techniques to accurately measure organ blood flow has permitted study of pituitary blood flow; and, when combined with knowledge of pituitary anatomy, the application of these techniques promises to provide a means to develop insight into control of the mechanisms by which chemical messengers are delivered to the pituitary to control its function. New anatomic techniques promise to develop new understanding of the three-dimensional arrangement of median eminence microvasculature and yield new concepts of blood flow regulation within the median eminence that can be tested by physiological means.

The organization of noradrenergic pathways from the brainstem to the paraventricular and supraoptic nuclei in the rat

Axonal transport and immunohistochemical methods have been used to clarify the organization of pathways from noradrenergic and adrenergic cell groups in the brainstem to the paraventricular (PVH) and supraoptic (SO) nuclei of the hypothalamus. First, the location of such cells was determined with a combined retrograde tracer-immunofluorescence method. The fluorescent tracer, True Blue, was injected into the PVH or the SO, and sections through the brainstem were stained with anti-(rat) DBH, a specific marker for noradrenergic and adrenergic neurons. It was found that, after injections in the PVH, doubly labeled neurons were confined almost exclusively to 3 cell groups, the A1 region of the ventral medulla, which contained a majority of such cells, the A2 region in the dorsal vagal complex, and the locus coeruleus (A6 region). After injections centered in the SO an even greater proportion of doubly labeled cells were found in the A1 region, although some were also found in the A2 and A6 regions. The topography of doubly labeled cells indicates that these projections arise primarily from noradrenergic neurons, although adrenergic cells in both the C1 and the C2 groups probably contribute as well. Because well over 80% of the retrogradely labeled cells in these three regions were also DBH-positive, we next placed injections of [3H]amino acids into each of them in different groups of animals, and traced the course and distribution of the ascending (presumably DBH-positive) projections to the PVH and SO in the resulting autoradiograms. Injections centered in the A1 region labeled a substantial projection to most parts of the parvocellular division of the PVH, and was most dense in the dorsal and medial parts. In addition, terminal fields were labeled on those parts of the magnocellular division of the PVH, and of the SO, in which vasopressinergic cell bodies are concentrated. Injections centered in the A2 region also labeled a projection to the parvocellular division of the PVH that was topographically similar, but less dense, than that from the A1 region. In contrast, [3H]amino acid injections centered in the locus coeruleus labeled a moderately dense projection to the PVH that was limited to the medialmost part of the parvocellular division. Neither the A2 nor the A6 cell groups project to the magnocellular parts of PVH, or to the SO. The autoradiographic material, and additional double-labeling experiments, were used to identify and to characterize projections that interconnect the A1, A2 and A6 regions, as well as possible projections from these cell groups to the spinal cord. These results may be summarized as follows: a substantial projection from the nucleus of the solitary tract to the A1 region was identified, but this pathway does not arise from catecholaminergic neurons in the A2 cell group. DBH-stained cells in the A1 region project back to the dorsal vagal complex, as well as quite massively to the locus coeruleus (A6 region)...

Brain stem innervation of the caudal neurosecretory system

The innervation of the caudal neurosecretory system of Poecilia sphenops (black molly) was studied by use of the retrograde horseradish peroxidase (HRP) method. The structure of the caudal neurosecretory system in this species was well suited for application of HRP procedures. Acrylamide/HRP gel implants were placed in the nucleus of the caudal neurosecretory system. Two neuronal groups which contained HRP filled cells were found in the brains tem. Bilateral projections originate from the dorsal tegmentum of the midbrain and the reticular nucleus of the medulla.

Vasopressin-reversible increase in angiotensin-converting enzyme in specific hypothalamic nuclei of Brattleboro rats

The activity of the angiotensin-converting enzyme (ACE) (kininase II, EC 3.4.15.1) was examined in 5 discrete hypothalamic nuclei of rats lacking vasopressin (homozygous Brattleboro rats, DI, di/di) and their corresponding controls (heterozygous Brattleboro rats, HZ, di/+, and Long Evans, LE, +/+ rats), with and without hormonal replacement with arginine-vasopressin (AVP). DI rats showed a vasopressin-reversible increased ACE activity when compared with LE controls, HZ rats showing intermediate activity. These changes occurred only in the supraoptic and periventricular hypothalamic nuclei, and were absent in other hypothalamic areas studied, including the paraventricular nucleus. These results provide biochemical evidence in support of previous anatomical and physiological data, for an interaction between the brain vasopressin and angiotensin systems in discrete hypothalamic nuclei, and suggest that vasopressin could regulate the formation of brain angiotensin II by modulating the activity of the converting enzyme.

Angiotensin-converting enzyme in discrete areas of the rat forebrain and pituitary gland

With the use of a sensitive radioisotopic method we have examined the activity of the angiotensin-converting enzyme (ACE, E.C. 3.4.15.1) in specific nuclei of the rat forebrain and in the anterior, intermediate and posterior lobes of the pituitary gland of the rat. We reported that ACE activity is heterogeneously distributed in the rat forebrain, with a 200-fold difference between the lowest and the highest values. Highest enzyme activities were found in the subfornical organ and in the posterior lobe of the pituitary gland. High ACE activity was also detected in the intermediate and anterior lobes of the pituitary gland, the caudate nucleus, and the medial habenular nucleus. Substantial activity also existed in the globus pallidus, the median eminence, the supraoptic and paraventricular nuclei, the lateral habenular nucleus and the organon vasculosum laminae terminalis. Our results demonstrate that one of the components of the renin-angiotensin system, the angiotensin-converting enzyme, is highly localized to a few discrete brain structures and the pituitary gland. These findings suggest that angiotensin II could be formed locally in some of these structures, supporting previous immunohistochemical data.

The tuberoinfundibular system of the rat as demonstrated by immunohistochemical localization of retrogradely transported wheat germ agglutinin (WGA) from the median eminence

The origin of neuronal perikarya which project to the external zone of the median eminence (the tuberoinfundibular neuronal system) was determined in the rat after injection or diffusion of wheat germ agglutinin (WGA) into the median eminence. The retrogradely transported lectin was detected in neurons using an immunohistochemical method based on the peroxidase-antiperoxidase technique. Immunoreactive cell bodies were found both in hypothalamic and extrahypothalamic regions. Within the hypothalamus, the majority of peroxidase-positive cells were present in the dorsomedial and basolateral portions of the arcuate nucleus, regions of the periventricular nucleus, and the preoptic region, particularly at the level of the organum vasculosum of the lamina terminalis (OVLT). Within the extrahypothalamic regions, WGA-positive perikarya were found in the diagonal band of Broca, the region of the medical septum and the brainstem. Only rare cells were labeled in the ventromedial nucleus of the hypothalamus and no cells were labeled in any region of the amygdala. These data demonstrate that neurons with afferent projections to the median eminence are more widely distributed in the rat brain than previously recognized and therefore, that the concept of the tuberoinfundibular neuronal system must be expanded.

Differential distribution of immunoreactive angiotensin and angiotensin-converting enzyme in rat brain

To help resolve the controversy about the brain renin-angiotensin system, the distribution of immunoreactive angiotensin in the brains of male rats was analyzed using twelve different antibodies to angiotensin II, two of which had previously been reported to stain nerve fibers in the central nervous system. The distribution of angiotensin-converting enzyme immunoreactivity was also examined using an antibody to rabbit lung converting enzyme, and the distribution of this immunoreactivity was compared to that of immunoreactive angiotensin. Weak angiotensin-like immunoreactivity was found in cell bodies of the hypothalamic magnocellular nuclei of colchicine-treated rats and in nerve terminals of the median eminence, neurohypophysis, central nucleus of the amygdala, bed nucleus of the stria terminalis and various other sites in the brain and spinal cord of untreated rats. Staining could be demonstrated with only three antisera. Antigenic specificity was carefully studied in these antisera. Each was similar in that staining could be blocked with angiotensins I, II or III and tetradecapeptide renin substrate, although angiotensins II and III were most potent. Because of the relatively few angiotensin II antisera which could stain brain and because they are blockable with angiotensin I and tetradecapeptide renin substrate, the precise nature of immunoreactive angiotensin remains an open question. Intense converting enzyme-like activity was localized in endothelial cells of capillaries throughout the brain, in the subfornical organ and in the 'brush border' of choroidal epithelial cells in contact with cerebrospinal fluid. No activity was detected in neural tissue other than the subfornical organ and occasional weak activity in some ependymal elements elsewhere. These findings indicate that angiotensin and converting enzyme immunoreactivities are not co-distributed and raises several questions regarding the nature of, and pathway for, formation of immunoreactive angiotensin in the brain.

Relationship of the central ACTH-immunoreactive opiocortin system to the supraoptic and paraventricular nuclei of the hypothalamus of the rat

ACTH-immunoreactive (ir) fibers of the central opiocortin system are present in high density in the mid-portion of the paraventricular nucleus (PVN). ACTH-ir fibers, however, do not appear to directly contact oxytocin-ir vasopressin-ir, containing perikarya or axons of vasopressinergic neurons. Magnocellular neurons located more anteriorly and posteriorly in the PVN as well as those located laterally have few ACTH-ir fibers associated with them. No ACTH-ir fibers are present in the supraoptic nucleus.

Central neurohypophyseal peptide pathways: interactions with endocrine and other autonomic functions

Electrophysiological and pharmacological studies have been carried out in rats and rabbits to attempt to identify possible functional roles for neurohypophyseal peptides in brain. In anesthetized rats, single unit recordings and antidromic activation criteria were utilized to identify projections of the paraventricular nucleus (PVN) to neurohypophysis and to extrahypothalamic areas (amygdala or nucleus tractus solitarius). None of the cells tested innervated more than one of these areas and, when tested for their responses to haemorrhage, increased body osmolarity, or suckling of pups, only the osmotic stimulus caused increased activity in some cells projecting to amygdala or nucleus tractus solitarius. Indirect evidence as well as direct measurement by radioimmunoassay of arginine vasopressin (AVP) in brain perfusates revealed probable central release of AVP in response to stimuli known to activate pituitary secretion of this peptide. These observations raise the possibility that certain brain and pituitary peptidergic systems may function in a co-ordinated manner.

The identification of specific brain nuclei in which catecholamine turnover is increased by left ventricular receptors during acute myocardial infarction in the rat

Central catecholaminergic nerves have been shown to participate in the integration of cardio-cardiac reflexes induced by coronary artery ligation in the rat. In this study we measured the turnover of dopamine, norepinephrine and epinephrine in microdissected brain regions to identify some of the specific neural loci involved in this integration. Three groups of rats, treated with alpha-methyltyrosine, an inhibitor of catecholamine biosynthesis were examined: left coronary artery ligation, left coronary artery ligation with the left ventricle painted with lidocaine, and sham operation. An untreated group of resting rats was also examined. Dopamine, norepinephrine and epinephrine turnover was increased in ligated rats in nucleus tractus solitarius (right and left), nucleus commissuralis, A1-region, locus coeruleus, nucleus cuneatus, and area postrema in the pons-medulla and nucleus dorsomedialis in the hypothalamus. Norepinephrine and dopamine (but not epinephrine) turnover was increased in nucleus ambiguus in the brain stem and nucleus paraventricularis in the hypothalamus. A ligation-induced increase in norepinephrine turnover, alone, was exhibited by the A2-region and nucleus gigantocellularis in the medulla and nucleus supraopticus and nucleus hypothalamicus posterior in the hypothalamus. Dopaminergic nerves to the nucleus gigantocellularis appeared to be inhibited following coronary ligation. The catecholamine stores of 11 nuclear regions were not influenced by coronary artery occlusion. Topical lidocaine, applied to the ischemic left ventricle, only, of ligated rats, completely restored regional brain catecholamine turnover to that found in sham-operated animals. In conclusion, we have identified discrete loci in the brain in which catecholamine turnover (as measured by alpha-methyltyrosine induced disappearance) is increased by the stimulation of left ventricular receptors during acute myocardial ischemia in the rat.

Immunohistochemical identification of neurons in the paraventricular nucleus of the hypothalamus that project to the medulla or to the spinal cord in the rat

A method that allows the concurrent localization of an antigen and a retrogradely transported fluorescent dye (true blue) was used to identify, immunohistochemically, cells in the paraventricular nucleus of the hypothalamus (PVH) that project to autonomic centers in the brainstem or in the spinal cord of the adult albino rat. After placing injections of true blue in the dorsal vagal complex or in upper thoracic segments of the spinal cord, series of evenly spaced sections through the PVH were stained with antisera directed against oxytocin, vasopressin, somatostatin, methionine-enkephalin, or leucine-encephalin. The results indicate that both oxytocin- and vasopressin-stained cells in the PVH project to the spinal cord and (or) to the dorsal vagal complex, although about three times as many oxytocin-stained cells were doubly labeled after injections centered in either terminal field. The oxytocin- and vasopressin-stained cells that give rise to these long descending projections were found primarily in caudal part of the parvocellular division of the PVH, where immunoreactive cells were shown to be significantly smaller than oxytocin- and vasopressin-stained cells in parts of the nucleus that project to the posterior pituitary. Small populations of cells in the PVH that cross-react with antisera against somatostatin, leucine-enkephalin, or methionine-enkephalin were also shown to project directly to the region of the dorsal vagal complex and to the spinal cord, and to have a unique distribution within the PVH. Collectively, the total number of doubly labeled cells that were identified in these experiments accounts for only about one-fourth of the total number of PVH neurons with long descending projections, thus suggesting that additional neuroactive substances are contained within these pathways.

The distribution and cells of origin of ACTH(1-39)-stained varicosities in the paraventricular and supraoptic nuclei

ACTH(1-39)-immunoreactive fibers and varicosities were localized using indirect immunofluorescence histochemistry in normal rats, and were found to be distributed in specific parts of the parvocellular division of the paraventricular nucleus, and in regions of the magnocellular division of the paraventricular and supraoptic nuclei in which oxytocinergic cells predominate. A combined retrograde transport-immunohistochemical method was used to confirm that these projections arise from a group of ACTH(1-39)-stained cells in the arcuate nucleus (and in adjacent regions along the base of the hypothalamus), and to describe their distribution within this region.

Synaptic inputs and action potentials of magnocellular neuropeptidergic cells: intracellular recording and staining in slices of rat hypothalamus

Excitatory postsynaptic potentials (EPSPs) and action potentials of magnocellular neuropeptidergic cells (MNCs) in the paraventricular (PVN) and supraoptic nuclei (SON) were studied with intracellular recording in coronal slices of rat hypothalamus. The fluorescent dye Lucifer Yellow (LY) was injected intracellularly and the cells were subsequently identified as magnocellular (somata greater than 15 x 15 micrometer). These cells generally had a large cytoplasm-to-nucleus ratio. In PVN it was frequently possible to trace filled dendrites to the ependyma of the third ventricle, and occasionally dendritic spines could be seen. Electrical stimuli in areas dorsolateral and ventrolateral to the fornix column evoked EPSPs in some anatomically identified MNCs of PVN, which indicates that presynaptic fibers innervating MNCs approach PVN from this region. Short-latency (less than 1 msec) spikes could be evoked in many MNCs of PVN by stimulation near SON, which is consistent with the known projection to the neurohypophysis of many MNCs. Action potentials in MNCs of PVN and SON had significantly longer durations at one-third spike height (mean +/- S.D. = 2.06 +/- 0.6 msec) than hippocampal CA1 pyramidal cells (1.17 +/- 0.29 msec). This suggests that neuroendocrine cells in mammals and some lower vertebrates and invertebrates are similar in this regard.

The milk ejection reflex in the pig

1. The milk ejection reflex in response to suckling was studied in conscious sows by continuous recording of intramammary pressure, radioimmunoassay of plasma concentrations of neurohypophysial hormones, and observation of the behaviour of the sows and piglets.2. A regular pattern of nursing, suckling and milk ejection was observed. The mean duration of the suckling period was 6.3 min. Over 144 suckling periods, 113 milk ejections were recorded. Each milk ejection was characterized by a sudden rise in intramammary pressure reaching 20-49 mmHg, and lasting 8-41 sec. Milk ejections occurred only once per suckling period, at a mean interval of 44.3 min.3. Each milk ejection occurred with a mean latency of 2.4 min from the onset of a period of initial massage of the udders by the piglets, and was coincident with a period of quiet suckling when the piglets were consuming milk. The onset of nursing was signalled by the sows grunting in a rhythmic manner. In most cases, the frequency of grunts, at first low, increased suddenly 23 sec before milk ejection.4. During eighteen suckling periods leading to milk ejection, neurohypophysial hormone assays performed on serial blood samples showed an increase in plasma concentration of oxytocin up to 30 sec before milk ejection. The concentration of lysine-vasopressin did not rise above basal levels.5. In 21.4% of the suckling periods, no rise in intramammary pressure was observed. In these ;incomplete sucklings', the sow usually failed to grunt rapidly, and the piglets obtained no milk. For three of these periods, hormone assay showed no increase in oxytocin or vasopressin concentrations in blood.6. Oxytocin given intravenously produced variations in intramammary pressure which depended on the dose and the rate of injection. Rapid injections of 25-50 m-u. oxytocin, caused milk ejections similar to those induced by suckling. When oxytocin was administered at different rates, the faster the injection, the shorter the latency and the higher the amplitude of the response. Plasma concentrations of oxytocin after injection of 25 m-u. were similar to those observed during reflex milk ejection.7. Trains of electrical pulses were applied to the posterior pituitary of four anaesthetized sows. At frequencies of stimulation above 10 Hz, a rise in intramammary pressure and an increase in plasma oxytocin and vasopressin concentrations were observed. At frequencies of stimulation of 30-50 Hz, the response of the mammary gland and the time course of the variations in oxytocin plasma concentrations were similar to those observed during natural reflex milk ejection.8. It is concluded that reflex milk ejections during suckling in the pig are caused by the intermittent and spurt-like release of about 25 m-u. oxytocin, without concomitant vasopressin release. It is postulated that the release of oxytocin is probably precipitated by a brief and massive activation of oxytocin-secreting neurones in the hypothalamus. Central mechanisms controlling the intermittent release of oxytocin are discussed.

Stimulation by thyrotropin-releasing hormone of vagal outflow to the thyroid gland

An intracerebroventricular (i.c.v.) injection of TRH to the urethane anesthetized rat stimulates the activity of the superior laryngeal nerve (n.sl) which is a vagal ramus terminating at the thyroid gland and adjacent muscles. The response to TRH, a tonic increase in the n.sl outflow, was dose dependent in the 0.005-5.0 micrograms/100 g B.W. range. In contrast to this, methionine-enkephalin (ENK), neurotensin (NT) and somatostatin (SRIF) (5 micrograms/100 g, i.c.v.) all caused a transient decrease in n.sl activity. SRIF showed the highest attenuating effect when injected alone and was capable of diminishing the increased activity produced by a prior injection of TRH. ENK and NT failed to affect the TRH-induced increased activity. When injected concomitantly with TRH, SRIF blocked the response to TRH while ENK and NT both failed to affect the response to TRH. Pretreatment with triiodothyronine for 5 days strongly inhibited the response of the n.sl outflow to TRH. On the other hand, pretreatment with atropine, haloperidol, propranolol, phenoxybenzamine and p-chlorophenylalanine failed to block the stimulating effect of TRH although the response was diminished by some antagonists. It therefore seemed that TRH transmission is involved in central stimulation and SRIF is antagonistic in this regulation of n.sl outflow to the thyroid gland.

Frontolateral hypothalamic knife cuts: interruption of paraventricular efferents to the thoracolumbar cord

Bilateral thoracolumbar cord injections of the fluorescent tracer bisbenzimide produced extensive retrograde labelling of cell bodies in the paraventricular nucleus of the hypothalamus. Unilateral retrochiasmatic knife cuts (1.5 mm radius) located anterolateral to the paraventricular nucleus dramatically reduced or eliminated the labelling of paraventricular neurons on the ipsilateral side following bilateral bisbenzimide injections into the thoracolumbar cord. Thus paraventricular efferents to the thoracolumbar cord must project in a lateral direction at the level of the nucleus prior to descending toward the spinal cord. Changes in endocrine function, reproductive and feeding behavior reported following similar hypothalamic knife cuts may be related to this efferent system.

Dye-marked paraventricular neuroendocrine cells in vivo in cat hypothalamus

In antidromically identified neurons in the cat hypothalamus we recorded and injected fluorescent dye-markers (Lucifer Yellow, LY; Procion Yellow, PY) intracellularly. The dye-filled neurons lay in the rostral portion of the magnocellular paraventricular nucleus of the hypothalamus. We observed two morphological cell types of similar size based on the intracellular injections of LY or PY: a bipolar cell type with fusiform perikaryon and a multipolar cell type with a polygonal perikaryon. These morphological cell types correspond to previous descriptions of immunocytochemically identified vasopressinergic and oxytocinergic magnocellular neurons in mammals. This study demonstrates the feasibility of in vivo intracellular dye-marking and electrophysiological recordings from mammalian hypothalamic neurons. We have here a basis for correlating morphological characteristics with the physiological traits of single magnocellular neuroendocrine cells.

Organization of some brain stem afferents to the paraventricular nucleus of the hypothalamus in the rat

Brain stem afferents to subnuclei of the paraventricular nucleus of the hypothalamus were studied by the anterograde autoradiographic technique in the rat. The parabrachial nuclei and locus coeruleus project to the posterior, periventricular, parvocellular and dorsal divisions. The ventral medulla projects to the posterior, medial, lateral, parvocellular and dorsal divisions. The A1 catecholamine cell group projects to the posterior, medial, lateral, parvocellular and dorsal divisions, and the nucleus of the solitary tract to the parvocellular and dorsal divisions. The A1 region and the ventral medulla also project to the supraoptic nucleus.