Synaptic control of rat magnocellular neurosecretory cells by warm-sensing neurons in the organum vasculosum lamina terminalis

Increases in core body temperature cause secretion of vasopressin (vasopressin, antidiuretic hormone) to promote water reabsorption and blunt water losses incurred through homeostatic evaporative cooling. Subtypes of transient receptor potential vanilloid (Trpv) channels have been shown to contribute to the intrinsic regulation of vasopressin-releasing magnocellular neurosecretory cells (MNCs) in the supraoptic nucleus (SON) and paraventricular nucleus (PVN). However, MNCs in vivo can also be excited by local heating of the adjacent preoptic area, indicating they receive thermosensory information from other areas. Here, we investigated whether neurons in the organum vasculosum lamina terminalis (OVLT) contribute to this process using in vitro electrophysiological approaches in male rats. We found that the majority of OVLT neurons are thermosensitive in the physiological range (36-39°C) and that this property is retained under conditions blocking synaptic transmission. A subset of these neurons could be antidromically activated by electrical stimulation in the SON. Whole cell recordings from SON MNCs revealed that heating significantly increases the rate of spontaneous excitatory postsynaptic currents (sEPCSs), and that this response is abolished by lesions targeting the OVLT, but not by bilateral lesions placed in the adjacent preoptic area. Finally, local heating of the OVLT caused a significant excitation of MNCs in the absence of temperature changes in the SON, and this effect was blocked by inhibitors of ionotropic glutamate receptors. These findings indicate that the OVLT serves as an important thermosensory nucleus and contributes to the activation of MNCs during physiological heating.

Long-range axonal projections of transplanted mouse embryonic stem cell-derived hypothalamic neurons into adult mouse brain

The hypothalamus is comprised of heterogenous cell populations and includes highly complex neural circuits that regulate the autonomic nerve system. Its dysfunction therefore results in severe endocrine disorders. Although recent experiments have been conducted for in vitro organogenesis of hypothalamic neurons from embryonic stem (ES) or induced pluripotent stem (iPS) cells, whether these stem cell-derived hypothalamic neurons can be useful for regenerative medicine remains unclear. We therefore performed orthotopic transplantation of mouse ES cell (mESC)-derived hypothalamic neurons into adult mouse brains. We generated electrophysiologically functional hypothalamic neurons from mESCs and transplanted them into the supraoptic nucleus of mice. Grafts extended their axons along hypothalamic nerve bundles in host brain, and some of them even projected into the posterior pituitary (PPit), which consists of distal axons of the magnocellular neurons located in hypothalamic supraoptic and paraventricular nuclei. The axonal projections to the PPit were not observed when the mESC-derived hypothalamic neurons were ectopically transplanted into the substantia nigra reticular part. These findings suggest that our stem cell-based orthotopic transplantation approach might contribute to the establishment of regenerative medicine for hypothalamic and pituitary disorders.

Maternal deprivation during early infancy in rats increases oxytocin immunoreactivity in females and corticosterone reactivity to a social test in both sexes without changing emotional behaviour

Impairment of social behaviour is a hallmark of emotional disorders, with increased avoidance of social contact. In rats, the 24 h maternal deprivation (DEP) paradigm is used to understand the impact of extreme neglect on neurodevelopment. Due to the distinct immediate effects of DEP on postnatal days (PND) 3 (DEP3) or 11 (DEP11), in the present study we investigated the long-term effects of DEP at these ages on anxiety-like behaviour, by recording the visits and time spent in the centre part of the open-field, social investigation of a confined, same-sex, unfamiliar animal, basal and post-social test corticosterone plasma levels and the immunoreactivity to oxytocin in the paraventricular (PVN) and supraoptic nuclei of the hypothalamus (SON). Whole litters were distributed into control (CTL), DEP3 or DEP11 groups and behavioural tests and biological samples were collected between PNDs 40 and 45 in males and females. There were no differences in the exploration of the central part of the open field or on the time investigating the unfamiliar rat. However, the percent increase in post-test corticosterone secretion from baseline was greater for both DEP3 male and female subgroups than their CTL and DEP11 counterparts. DEP3 females showed more oxytocin staining than DEP11 counterparts in magnocellular neurons of the SON and PVN. These results suggest that DEP at the ages chosen does not alter social investigation, although it results in distinct neurobiological outcomes, depending on the developmental phase when it is imposed.

The supraoptic and paraventricular nuclei in healthy aging and neurodegeneration

The supraoptic (SON) and paraventricular (PVN) nuclei of the hypothalamus undergo structural and functional changes over the course of healthy aging. These nuclei and their connections are also heterogeneously affected by several different neurodegenerative diseases. This chapter reviews the involvement of the SON and PVN, the hypothalamic-pituitary axes, and the peptide hormones produced in both nuclei in healthy aging and in neurodegeneration, with a focus on Alzheimer's disease (AD), frontotemporal dementia (FTD), amyotrophic lateral sclerosis, progressive supranuclear palsy, Parkinson's disease (PD), dementia with Lewy bodies (DLB), multiple system atrophy, and Huntington's disease. Although age-related changes occur in several regions of the hypothalamus, the SON and PVN are relatively preserved during aging and in many neurodegenerative disorders. With aging, these nuclei do undergo some sexually dimorphic changes including changes in size and levels of vasopressin and corticotropin-releasing hormone, likely due to age-related changes in sex hormones. In contrast, oxytocinergic cells and circulating levels of thyrotropin-releasing hormone remain stable. A relative resistance to many forms of neurodegenerative pathology is also observed, in comparison to other hypothalamic and brain regions. Mirroring the pattern observed in aging, pathologic hallmarks of AD, and some subtypes of FTD are observed in the PVN, though to a milder degree than are observed in other brain regions, while the SON is relatively spared. In contrast, the SON appears more vulnerable to alpha-synuclein pathology of DLB and PD. The consequences of these alterations may help to inform several of the physiologic changes observed in aging and neurodegenerative disease.

[Time course study of growth hormone releasing peptide-6-induced c-fos expression in neurons of feeding-related nuclei of hypothalamus]

The present study was aimed to explore the effects of intraperitoneal injection of growth hormone releasing peptide-6 (GHRP-6), a ghrelin receptor agonist, on food intake and neuronal activity of feeding-related nuclei in the hypothalamus of NMRI mice. Accumulated amount of food intake was measured, and total number of c-fos immunoreactive neurons in arcuate nucleus (ARC), paraventricular nucleus (PVN) and supraoptic nucleus (SON) was counted by immunohistochemistry at 1, 3 and 6 h after the GHRP-6 injection. The results showed that GHRP-6 significantly increased the amount of food intake with a peak at 3 h after the GHRP-6 injection. Meanwhile, GHRP-6 could promote c-fos expression in the ARC and PVN independent of food intake, and the total number of c-fos immunoreactive neurons was peaked at 1 h after injection and then decreased gradually. These results suggest that GHRP-6 may increase food intake in time-dependent manner, which is associated with up-regulations of c-fos protein expression in the ARC and PVN.

Acute hypernatremia exerts an inhibitory oxytocinergic tone that is associated with anxiolytic mood in male rats

Anxiety disorders are the most common psychiatric illnesses and are associated with heightened stress responsiveness. The neuropeptide oxytocin (OT) has garnered significant attention for its potential as a treatment for anxiety disorders; however, the mechanism mediating its effects on stress responses and anxiety is not well understood. Here we used acute hypernatremia, a stimulus that elevates brain levels of OT, to discern the central oxytocinergic pathways mediating stress responsiveness and anxiety-like behavior. Rats were rendered hypernatremic by acute administration of 2.0 M NaCl and had increased plasma sodium concentration, plasma osmolality, and Fos induction in OT-containing neurons relative to 0.15 M NaCl-treated controls. Acute hypernatremia decreased restraint-induced elevations in corticosterone and created an inhibitory oxytocinergic tone on parvocellular neurosecretory neurons within the paraventricular nucleus of the hypothalamus. In contrast, evaluation of Fos immunohistochemistry determined that acute hypernatremia followed by restraint increased neuronal activation in brain regions receiving OT afferents that are also implicated in the expression of anxiety-like behavior. To determine whether these effects were predictive of altered anxiety-like behavior, rats were subjected to acute hypernatremia and then tested in the elevated plus maze. Relative to controls given 0.15 M NaCl, rats given 2.0 M NaCl spent more time in the open arms of the elevated plus maze, suggesting that acute hypernatremia is anxiolytic. Collectively the results suggest that acute elevations in plasma sodium concentration increase central levels of OT, which decreases anxiety by altering neuronal activity in hypothalamic and limbic nuclei.

Central injections of capsaicin cause antidiuresis mediated through neurokinin-1 receptors in rat hypothalamus and vasopressin release

Intracerebroventricular injections of capsaicin at 100-500 nmol elicited dose-dependent decreases in urine outflow volume in anesthetized, hydrated rats. The capsaicin (500 nmol)-induced antidiuresis was inhibited by pretreatment with CP96345 (30 nmol, a neurokinin-1-receptor antagonist), but not by that with phenoxybenzamine (20 nmol, an alpha-adrenoceptor antagonist), timolol (100 nmol, a beta-adrenoceptor antagonist) or atropine (300 nmol, a muscarinic antagonist) into the hypothalamic supraoptic nucleus (SON). Intravenous injections of d(CH2)5-D-Tyr(Et)VAVP (50 microg/kg, a vasopressin-receptor antagonist) completely blocked the antidiuresis. In intra-SON microdialysis experiments, acetylcholine concentration in the perfusate of the capsaicin-injected rats was not different from that of the vehicle-injected rats. These findings suggested that capsaicin stimulated substance P release in the SON and caused the antidiuresis as a result of the increased release of vasopressin into the circulation from the neurohypophysis mediated through neurokinin-1 receptors in the SON.

Up-regulation of calretinin in the supraoptic nucleus of the rat after chronic salt loading

We immunocytochemically examined the effect of chronic salt loading on the content of calretinin, a calcium-binding protein, in both the supraoptic nucleus and the magnocellular parts of the hypothalamic paraventricular nucleus. In control rats that were given water for drinking, the supraoptic nucleus contained a cluster of calretinin-stained cells. Drinking 2% sodium chloride solution for 7 days resulted in an increase of the staining intensity of calretinin in cells of the suprasoptic nucleus. In both the control and salt-loaded rats, the magnocellular parts of the paraventricular nucleus were almost devoid of calretinin-labeled cells. It is suggested that expression of calretinin in cells of the supraoptic nucleus is up regulated by chronic salt loading.

Single-step isolation and sequencing of vasopressin and oxytocin precursors

The pre- and post-Golgi processing of preprovasopressin and prepro-oxytocin was evaluated by microsequencing for incorporated radiolabel. 35S-Cysteine and 3H-fucose were microinjected into rat supraoptic nuclei (SON), and proteins and peptides related to the biosynthesis of vasopressin (VP) and oxytocin (OT) were isolated at various times from the supraoptic nuclei and neural lobe by employing a one-step procedure of high performance liquid chromatography (HPLC). These proteins and peptides were recognized through their binding to specific antibodies against VP, OT, and rat neurophysins (RNPs), and by their binding to ConA-Sepharose. Two immunoreactive glycoproteins related to VP biosynthesis were recovered from the SON and both contained fucose and had a 35S-cysteine placement consistent with the location of the hormone sequence at the N-terminus. SDS-electrophoresis revealed the major protein form to be 21,000 daltons and the minor protein form to be 19,000 daltons. One nonglycosylated protein of 16,000 daltons related to oxytocin biosynthesis was recovered from the SON, and this protein also had a 35S-cysteine placement consistent with an N-terminal OT sequence. These data provide the first sequential evidence that prior to, or shortly after, packaging in the Golgi the preprohormones of VP and OT have lost their entire leader-peptide structures.

The supraoptic and paraventricular nuclei of the human hypothalamus in relation to sex, age and Alzheimer's disease

Volume and total cell number were determined in the supraoptic (SON) and paraventricular (PVN) nuclei of 14 male and 16 female subjects ranging in age from 10 to 93 years. In addition, 4 male and 6 female subjects suffering from Alzheimer's disease (AD) and ranging in age from 46 to 97 years were studied. Subjects were divided into two age groups, viz., "young" for subjects up to 60 years, and "old" for subjects older than 60. No sex differences in volume and in total cell number were observed in the SON and PVN in either age group. In addition, no significant correlation was found between total cell number in the SON and PVN and brain weight. No significant differences in volume and total cell number were found in either the SON or PVN between young and old control subjects or between AD cases and controls, indicating that these nuclei are spared from degenerative changes in senescence and AD. Determination of neuron numbers in the SON supported this view. In contrast, volume and total cell counts in the suprachiasmatic decreased in senescence and were dramatically reduced in AD. The present results indicate the occurrence of differential patterns of cell loss within the human hypothalamus with aging and in AD, which are proposed to be related to functional differences between the hypothalamic nuclei.

Effects of fentanyl, injected into the hypothalamic supraoptic and paraventricular nuclei, in a water-loaded and ethanol-anesthetized rat

The analgesic fentanyl, having a predominantly mu-opioid agonist activity, when injected into the supraoptic or paraventricular nucleus of the hypothalamus in a water-loaded and ethanol-anesthetized rat, induced a potent antidiuretic effect in a time- and dose-dependent manner. The outflow of urine decreased to a minimal level of approximately 5% of the initial control, at 20-40 min and recovered to approximately 80% at 90 min after injection of fentanyl (30 nmol). The median effective dose (ED50) for the antidiuretic effect of fentanyl was approximately 13 nmol, when injected into the supraoptic or paraventricular nucleus, being nearly equipotent with morphine. The osmotic pressure of urine increased up to approximately 200% of control, at the minimal rate of outflow of urine when fentanyl (30 nmol) was injected into the supraoptic or paraventricular nucleus. Transient but significant decreases in mean blood pressure and in rate of respiration were observed when fentanyl (30 nmol) was injected into the supraoptic or paraventricular nucleus. The antidiuretic and the autonomic effects (transient decreases in mean blood pressure and rate of respiration) were inhibited by the previous injection of an opioid receptor antagonist, naloxone (300 or 600 nmol) into the nuclei. The results suggest that the effects of fentanyl were induced through opioid receptors in the nuclei.

A technique for controlling the membrane potential of neurons during unit recording

While extracellular unit recordings are technically easier to perform than intracellular recordings, the latter permits control of neuron excitability by changing the membrane potential with steady current passed across the recording micropipette. Utilizing an intracellular amplifier with bridge circuit for the passage of low current (1-10 nA), we show that an extracellular recording micropipette of high resistance (5-20 M omega) can be used in a similar fashion while monitoring single unit activity in the rat brain. This procedure allows fine control of two neuronal mechanisms which are voltage-sensitive: action potential discharge and regenerative bursting. Control of a neuron's membrane potential expands the capabilities of unit recording in the study of evoked synaptic input and bursting behaviour. It can also facilitate classification of neurons based on their firing characteristics.

Correction of genetic diabetes insipidus by adult hypothalamic grafts

Brattleboro rats manifest chronic diabetes insipidus as a result of the genetic deficiency of hypothalamic vasopressin. When basal hypothalamic tissue derived from adult F344 rats was implanted as cell suspensions or tissue blocks in the supraoptic regions of these animals, concentration of urine together with reduced urine output and water intake was observed in some animals. Histologic examination of the grafted brains from the responding animals revealed neuronal cells at the implant sites and vasopressin-staining fibers in the median eminence. This study demonstrates the feasibility of the grafting of adult cerebral tissues to correct a genetic hormonal deficiency.

Antidiuretic effects of oxotremorine microinjected into the hypothalamic supraoptic and paraventricular nuclei in a water-loaded and ethanol-anesthetized rat

The effect of oxotremorine, a muscarinic agonist, on urine outflow compared with the effects of other cholinergic agonists and inhibitory effects of cholinergic antagonists upon the cholinergic actions were studied by microinjecting drugs stereotaxically, unilaterally into the supraoptic (SON) or paraventricular nuclei (PVN) in the hypothalamus of the rat which was loaded with water and anesthetized with ethanol. Oxotremorine decreased the urine outflow in dose- and time-dependent manners when microinjected into these nuclei. The median effective doses (ED50) were approx. 0.3 and 0.2 nmol in SON an PVN, respectively, being much less than ED50 values for nicotine. The time course of the antidiuretic effects was relatively slow, with the minimal urine outflow at approx. 30 min and the duration of one or longer hours. The antidiuretic effects of oxotremorine in these nuclei as well as the effects of acetylcholine and nicotine were completely blocked by pretreatment with atropine. The pretreatment with hexamethonium inhibited partially the effects of nicotine, but was unable to inhibit the effects of oxotremorine and acetylcholine. The data suggest that the antidiuretic effects of cholinergic agonists in SON and PVN are predominantly mediated through a muscarinic type of acetylcholine receptor. A possible mechanism for the antidiuretic effects is discussed.

Experimental diabetes insipidus in a marsupial, Macropus eugenii (Desmarest)

A new method is described for placing lesions in the supraoptico-neurohypophysial tract to produce diabetes insipidus. The method is particularly useful with species such as Macropus eugenii in which different individuals show a large variation in relative skull measurements. The development of the diabetes insipidus syndrome in the tammar wallaby (Macropus eugenii) is shown to have essentially the same triphasic pattern of urine production as in eutherians. Increased values of adrenal corticosteroids (less than 16 mug/100 ml plasma) were observed in the oliguric interphase. This has not been previously reported and we suggest that these increased values are most probably due to potentiation of corticotrophic releasing factor by the uncontrolled release of vasopressin during this phase.

ULTRASTRUCTURE OF NEUROSECRETORY CELLS IN THE SUPRAOPTIC NUCLEUS OF THE DOG AND RAT

The hypothalamo-neurohypophysial systems of the dog and rat have been investigated with the electron microscope. The best preparations were obtained from anaesthetized animals cooled to about 7°.

Neuronal cell bodies in the supraoptic nuclei of the dog were characterized both by their size, by their occasional proximity to the capillary basement membranes, and by their content of electron-dense, membrane-bound inclusions measuring between 750 and 3000 å in diameter. Similar inclusions, measuring between 800 and 2400 å in diameter, characterized nerve terminals in the infundibular process. These inclusions are the same size as those found to be associated with high antidiuretic activity in samples taken from the posterior pituitary and from the hypothalamus of the dog, and could therefore be the vehicles of antidiuretic hormone. It has been calculated that in the dog these inclusions, if they contain antidiuretic hormone, are numerous enough in the neuronal cell body for the latter to constitute the only site of hormone synthesis.

Similar secretory neurones were found in the supraoptic nucleus of the rat. They were more difficult to identify than in the dog, for they contained fewer inclusions of the size which filled nerve terminals in the infundibular process.

Reactions of neurons in or near the supraoptic nuclei

The reactions of neurons within or near the supraoptic nuclei of the hypothalamus to a variety of "stimuli" were studied. A few neurons were found to be excited by stimulation of muscle afferents. Other neurons were inhibited by stimulation of gastrocnemius and tibialis nerve fibers. Stimulation of the vagus nerve activated some neurons and inhibited a few but, as in the case of muscle nerve stimulation, the vast majority of neurons were unaffected. Stimulation of midbrain and pontine reticular formation inhibited some neurons and activated others. Intracarotid injections of isotonic saline had no effect on neuron discharge but low concentrations of glucose augmented neuron firing as did hypertonic NaCl. Distilled water reduced neuron activity. Epinephrine, norepinephrine, and acetylcholine accelerated neuron firing; atropine was without effect in concentrations employed. Responses to injected materials developed more slowly and lasted longer than did effects of nerve stimulations. Some neurons were affected by several of the stimuli employed but the majority of neurons were unresponsive during the periods of recording which could be maintained.

The effects of nicotine, hexamethonium and ethanol on the secretion of the antidiuretic and oxytocic hormones of the rat

The actions of nicotine, hexamethonium, and ethanol on the hypothalamo-hypophysial system have been investigated in the rat. The antidiuretic action of nicotine was not inhibited by ethanol, nor by doses of hexamethonium which were sufficient to block both its pressor and convulsant actions. Hexamethonium itself had an antidiuretic action the mechanism of which has been investigated. Nicotine caused a release of oxytocin into the blood which was not blocked by ethanol nor significantly reduced by hexamethonium. The results suggest that any synapse which exists at the supraoptic nuclei is dissimilar in its pharmacological properties to synapses at autonomic ganglia.