Efferent connections from the lateral hypothalamic region and the lateral preoptic area to the hypothalamic paraventricular nucleus of the rat

The lateral preoptic and lateral hypothalamic regions contain the majority of the cell groups embedded in the fibre trajectories of the medial forebrain bundle on its course through the hypothalamus. Recent studies have extended considerably the parcellation of the lateral hypothalamic region, and, therefore, the need to emphasize new insights into the anatomical organisation of projections from the neurons of the lateral hypothalamic region. In the present study we describe the anatomical organisation of efferent projections from the lateral preoptic and lateral hypothalamic regions to the hypothalamic paraventricular nucleus (PVN) on the basis of retrograde- and anterograde-tracing techniques. Iontophoretic injections of the retrograde tracer, cholera toxin subunit B, into the PVN revealed that most hypothalamic nuclei project to the PVN. Within the lateral hypothalamic region, retrogradely labelled cells were concentrated in the intermediate hypothalamic area, the lateral hypothalamic area, and the perifornical nucleus, whereas fewer retrogradely labelled cells were found in the lateral preoptic area. To determine the distribution of terminating fibres in subnuclei of the heterogeneous PVN, iontophoretic injections of the anterograde tracer Phaseolus vulgaris-leucoagglutinin were delivered into distinct areas of the lateral hypothalamic region. Neurons of the intermediate hypothalamic area projected mainly to the PVN subnuclei, which contained parvicellular neuroendocrine cells. In contrast, neurons of the rostral and tuberal parts of the lateral hypothalamic area and the perifornical nucleus projected to the PVN subnuclei, which contained parvicellular neurons that send descending projections to preganglionic cell groups in the medulla and spinal cord. The perifornical nucleus was the only area within the lateral hypothalamic region that consistently innervated magnocellular perikarya of the PVN. Finally, all areas of the lateral hypothalamic region contributed substantially to fibres terminating in the perinuclear shell of the PVN. These results demonstrate that anatomically distinct areas of the lateral hypothalamic region have distinct projections to subnuclei of the PVN and further substantiate the view that the lateral hypothalamic region as well as the PVN constitute anatomically and functionally heterogeneous structures. © 1994 Wiley-Liss, Inc.     

Trophic effects of basic fibroblast growth factor on fetal rat hypothalamic cells: interactions with insulin-like growth factor I

The existence of different growth factors within a single brain region suggests that developing brain cells are exposed to a variety of trophic factors throughout neurogenesis. Cooperative interactions between growth factors are known to orchestrate growth and differentiation of various cell types. We explored the possibility that two growth factors may interact in promoting in vitro growth in fetal hypothalamic cells. We found that basic fibroblast growth factor (b-FGF) exerts trophic effects on primary mixed hypothalamic cell cultures, on enriched hypothalamic neuronal cultures, and on hypothalamic glial cultures. In addition, b-FGF increased the growth rate of two virally transformed hypothalamic cell lines. Since insulin-like growth factor I (IGF-I) also promotes growth of rat hypothalamic cells in vitro, we examined the combined effects of b-FGF and IGF-I on hypothalamic cells. Significantly higher numbers of neurite-bearing cells were present in primary mixed hypothalamic cultures when b-FGF and IGF-I were added together than were added separately. The effect was additive. These results establish b-FGF as a putative hypothalamic neurotrophic factor and demonstrate potential coordinate interactions between IGF-I and b-FGF in stimulating the growth or survival of developing hypothalamic cells.     

Serial lateral hypothalamic destruction: Infancy and adulthood

Male and female albino rats sustained unilateral destruction of the lateral hypothalamic area as infants (10 days of age) or as adults (150 days of age). Also, rats receiving unilateral destruction of the lateral hypothalamic area as infants had their contralateral (intact) lateral hypothalamic area destroyed at 150 days of age, i.e., two-stage serial lateral hypothalamic area destruction separated by 140 days, thereby producing bilateral destruction. The animals were tested for homeostatic regulatory capacity. Loss of one lateral hypothalamic area during adulthood produced greater regulatory deficits than were produced by the loss of one during infancy. These results suggest that the intact lateral hypothalamic area of infant rats has greater capacity to maintain function than does the same intact area of adults.The regulatory deficits produced with two-stage lateral hypothalamic area destruction (one lateral hypothalamic area destroyed during infancy followed by destruction of the contralateral area during adulthood) were nearly identical to the deficits produced with one-stage bilateral destruction, i.e., the regulatory deficits were persistent and severe in spite of the fact that 140 days separated the two lesions.Thus, infant rats can maintain approximately normal regulatory capacity with one intact lateral hypothalamic area. This “sparing of function” was due to the intact lateral hypothalamic area, as its subsequent destruction produced more profound regulatory deficits than were produced with unilateral destruction of the lateral hypothalamic area sustained during adulthood. These results suggest that the “plasticity” of the infant lateral hypothalamic area is greater than that of the adult and that infantile “plasticity” is manifest by the capacity of the intact lateral hypothalamic area to subsume the function of the damaged contralateral area.     

Estradiol promotes cell shape changes and glial fibrillary acidic protein redistribution in hypothalamic astrocytes in vitro: a neuronal-mediated effect.

We have previously shown that in hypothalamic mixed neuronal-glial cultures both astrocytic shape and distribution of glial fibrillary acidic protein (GFAP) are modified by estradiol. In the present study, we have investigated whether or not the presence of neurons is necessary for these hormonal effects. In mixed neuronal-glial hypothalamic cultures the proportion of process-bearing GFAP-immunoreactive cells was significantly increased after treatment for 30 min with 10(-12) M 17 beta estradiol. This effect was present for at least 1 day and was reverted by incubating the cells in estradiol-free medium. Estradiol incubation resulted in a progressive differentiation of GFAP-immunoreactive cells from a flattened epithelioid morphology to bipolar, radial, and stellate shapes. This effect was not observed in pure hypothalamic glial cultures. Furthermore, incubation of hypothalamic glial cells with medium conditioned by estradiol-treated mixed hypothalamic cultures did not affect the shape of GFAP-immunoreactive astrocytes. In contrast, addition of hypothalamic neurons, but not cerebellar neurons or fibroblasts, to established hypothalamic glial cultures affected the development of estradiol sensitivity in astrocytes. These results indicate that estradiol induction of shape changes in hypothalamic astrocytes is not only dependent on the presence of hypothalamic neurons, but that physical contact between astrocytes and neurons is necessary for the manifestation of the effect of this hormone.     

Collateral axonal projections from hypothalamic hypocretin neurons to cardiovascular sites in nucleus ambiguus and nucleus tractus solitarius

Hypocretin-1 (hcrt-1)-containing axons have been shown to have an extensive distribution within the central nervous system, although the total number of hypothalamic hcrt-1 neurons has been shown to be small. This suggests that hcrt-1 neurons may innervate central structures with similar function through collateral axonal projections. Retrograde tract-tracing techniques combined with immunohistochemistry were used in this study to investigate whether hypothalamic hcrt-1-containing neurons send collateral axonal projections to cardiovascular sites in the nucleus of the solitary tract (NTS) and in the nucleus ambiguus (Amb) in the rat. Fluorogold- (FG) and/or rhodamine (Rd)-labeled latex microspheres were microinjected into either the NTS or Amb at sites that elicited bardycardia responses (L-glutamate; 0.25 M; 10 nl). After a survival period of 10-15 days, the rats were sacrificed and tissue sections of the hypothalamus were processed immunohistochemically for the identification of hcrt-1-containing cell bodies. After injection of the tract-tracers into the NTS or Amb, retrogradely labeled neurons were observed within several hypothalamic regions; the paraventricular hypothalamic nucleus, lateral hypothalamic area, perifornical hypothalamic area, and posterior hypothalamus, bilaterally, but with an ipsilateral predominance. In addition, after NTS injections, retrogradely labeled neurons were found within the ipsilateral caudal arcuate nucleus. Of the total number (1107+/-97) of hcrt-1-immunoreactive neurons found bilaterally within the lateral and perifornical hypothalamic nuclei, 7.9+/-1.4% were found to be retrogradely labeled from the NTS, 16.4+/-1.8% from the Amb, and 3.1+/-0.5% from both medullary sites. Hcrt-1 neurons projecting to the NTS were found mainly in and around the perifornical hypothalamic region, with a smaller number in the caudal lateral hypothalamic area. On the other hand, those innervating the Amb were primarily observed within the caudal lateral hypothalamic area, with a smaller number in the perifornical hypothalamic area. Neurons with collateral axonal projections to NTS and Amb were observed within two specific hypothalamic areas: one group of neurons was found in the perifornical hypothalamic area, and the other was observed in the lateral hypothalamic region just dorsal to the retrochiasmatic component of the supraoptic nucleus. These data indicate that axons from hcrt-1 neurons bifurcate to innervate functionally similar cardiovascular-responsive sites in the NTS and Amb. Although the function of these hcrt-1-containing hypothalamic-medullary pathways is not known, they likely represent the anatomical substrate by which the lateral hypothalamic hcrt-1 neurons simultaneously coordinate autonomic-cardiovascular responses to different behaviors.     

Coexistence of substance P- and enkephalin-like peptides in single neurons of the rat hypothalamus

The distribution of substance P- and enkephalin-like immunoreactivity in single cells were examined by the double immunofluorescence method. Substance P- and leucine-enkephalin-like compounds coexisted within individual neurons of some hypothalamic areas such as the medial preoptic area, anterior hypothalamic area, perifornical area, lateral hypothalamic area, premammillary nuclei and posterior hypothalamic nucleus, although they did not coexist in the majority of immunoreactive cells.     

Corticotropin-releasing hormone and dexamethasone do not alter secretion of immunoreactive beta-endorphin from dissociated fetal hypothalamic cell cultures

Corticotropin-releasing hormone (CRH) and glucocorticoids are major regulators of the hypothalamic-pituitary-adrenal (HPA) axis controlling secretion of beta-endorphin and other pro-opiomelanocortin (POMC)-derived peptides from pituitary. Although previous work has shown that CRH stimulates secretion of beta-endorphin from adult hypothalamic explants, and that glucocorticoids can inhibit basal and stimulated secretion of POMC-derived peptides from pituitary, the role of glucocorticoids on hypothalamic beta-endorphin secretion is not known. Studies were performed to assess the effects of CRH and dexamethasone, a potent glucocorticoid, on secretion of immunoreactive (IR) beta-endorphin from dissociated fetal hypothalamic cell cultures. CRH (10(-9)-10(-6) M) did not stimulate secretion of IR-beta-endorphin from hypothalamic cells which did release IR-beta-endorphin upon potassium-induced depolarization. However, CRH did stimulate IR-beta-endorphin secretion from fetal hypothalamic explants which were similar to hypothalamic tissue from which dissociated hypothalamic cell cultures were derived. Exposure of cells to dexamethasone (10(-6) M) did not inhibit basal or potassium-stimulated release of IR-beta-endorphin. These results indicate that: (1) dissociated fetal hypothalamic cells in culture do not exhibit a functional CRH receptor coupled to stimulation of IR-beta-endorphin secretion; (2) exposure of hypothalamic cells to dexamethasone does not inhibit basal nor depolarization-induced release of IR-beta-endorphin; and (3) dissociated fetal hypothalamic cells may have limited utility in elucidating specific regulatory relationships because of in vitro conditions and/or cytoarchitectural relationships.     

Cerebellar connections: hypothalamus

Morphological studies have described reciprocal cerebello-hypothalamic projections in various species. These connections provide evidence for the key role of the cerebellum and hypothalamus in physiological regulatory processes such as autonomic and endocrine homeostasis. Our recent study using horseradish peroxidase (HRP) retrograde axonal transport technique showed cerebellar connections with the posterior and the dorsomedial hypothalamic nuclei. Further, we have demonstrated regional differences of the connections of the dorsomedial hypothalamic nucleus in rat. The results of HRP labelling showed that afferent pathways originating from the anterior and posterior parts of dorsomedial hypothalamic nucleus indicate a number of differences in the projections. The posterior part of the dorsomedial hypothalamic nucleus and the posterior hypothalamic nucleus receives direct distinct projections from the cerebellum, whereas the anterior part of the dorsomedial hypothalamic nucleus does not. Moreover, the posterior part of the dorsomedial nucleus of the hypothalamus when compared to the posterior hypothalamic nucleus has more intense connections with the cerebellum. These observations bring a new perspective on the question of how the cerebellum is involved in the regulation visceromotor functions.     

Octreotide-induced suppression of the hyperglycemic response to neostigmine or bombesin: relationship to hypothalamic noradrenergic drive

Neostigmine (cholinesterase inhibitor) or bombesin, when injected into the third cerebral ventricle of awake rat, dose-dependently increased serum glucose with the simultaneous rise in hypothalamic noradrenergic neuronal activity (NAA). Co-administration of octreotide with neostigmine or bombesin suppressed the hypothalamic NNA response with the simultaneous inhibition of the hyperglycemic response. There was a close relationship between hypothalamic NNA and serum glucose in these studies. On the basis of the concept that hypothalamic noradrenergic drive plays an important role in mediating the hyperglycemic response to stressful stimuli, the present findings suggest that the hyperglycemic response to neostigmine or bombesin is mediated via the interaction with hypothalamic noradrenergic neurons.     

The effect of hypothalamic lesions on the immune response in rats

The nervous and immune systems are thought to have important roles in the host defence mechanism. Recent reports have suggested that presence of common antigens between the nervous and immune systems. It would be of interest to know the possibility of mutual relations between both systems. For the purpose of examining the relations, the author investigated peripheral blood lymphocyte blastogenesis, growth curves of inoculated subcutaneous tumor and serum levels of catecholamine and corticosterone, 2 weeks after the bilateral stereotaxic destruction of WKA rat medial hypothalamic nuclei. As a result of hypothalamic destruction, lower stimulation indices to PHA of the lymphocytes in the peripheral blood were obtained in rats with anterior hypothalamic lesions, premamillary lesions and mamillary lesions, and higher stimulation indices in those with dorsomedial hypothalamic lesions. On the other hand, lower stimulation indices to PWM were obtained in rats with dorsomedial hypothalamic lesions and higher ones in those with mamillary lesions. These results may suggest the existence of reciprocal function between the dorsomedial hypothalamic nucleus and mamillary nucleus. To examine the effect of hypothalamic lesions on tumor immunity, subcutaneous tumor inoculation and its growth curves were studied. As the tumor cells of KMT-17 are allogeneic in WKA rats, inoculated subcutaneous tumors grew temporarily and disappeared within 15 days. The peak of the growth curves was raised in rats with anterior hypothalamic lesions. Rats with other hypothalamic lesions and controls showed almost the same growth curves. From the results, it is suggested that the anterior hypothalamic nucleus may have some effect on tumor immunity.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of hypothalamic lesion on pancreatic autonomic nerve activity in the rat

The effects of hypothalamic lesions and intravenous glucose infusion on the efferent activity of vagal and splanchnic nerves to the pancreas were studied in anesthetized rats. Lesions of the ventromedial hypothalamic (VMH), the dorsomedial hypothalamic (DMH) and the paraventricular (PVN) nuclei increased vagal and reduced splanchnic nerve activity. Lesion of the lateral hypothalamic area (LHA) decreased pancreatic vagal nerve activity, and produced either increased or decreased activity of pancreatic splanchnic nerve. Intravenous glucose infusion increased activity of the vagal nerve and reduced that of the splanchnic nerve. These glucose responses were influenced by hypothalamic lesions only slightly or not at all. The findings suggest that hypothalamic modulation of pancreatic hormone secretion involves both the parasympathetic and sympathetic nervous systems, and provide evidence that not only the VMH and the LHA but also the DMH and the PVN are involved in this mechanism.     

Adrenocorticotropin and growth hormone secretions after intracerebroventricular administration of neostigmine in rats: their relationships to hypothalamic monoaminergic neuronal activities

Serum adrenocorticotropic hormone (ACTH) and growth hormone (GH) concentrations were assessed simultaneously with hypothalamic neuronal activities of norepinephrine (NE), dopamine (DA), and serotonin (5-HT) 60 min after the third cerebroventricular administration of neostigmine (a cholinesterase inhibitor) in awake rats. Serum ACTH and GH concentrations were significantly increased and decreased, respectively. Neostigmine caused significant increases in hypothalamic NE and DA activities and a significant decrease in hypothalamic 5-HT activity. The reciprocal changes of serum ACTH and GH cencentrations were similar to those of hypothalamic NE and 5-HT activities. Multiple regression analyses with stepwise procedure revealed that hypothalamic NE and 5-HT activities were respectively significant determinants of serum ACTH and GH concentrations. Apart from the direct influence of neostigmine on ACTH and GH secretions, it is suggested that the changes in hypothalamic monoaminergic activities play an important role in modulating ACTH and GH secretions following the administration of neostigmine.     

Orbitomedial prefrontal cortical projections to hypothalamus in the rat

A previous study in the rat revealed that distinct orbital and medial prefrontal cortical (OMPFC) areas projected to specific columns of the midbrain periaqueductal gray region (PAG). This study used anterograde tracing techniques to define projections to the hypothalamus arising from the same OMPFC regions. In addition, injections of anterograde and retrograde tracers were made into different PAG columns to examine connections between hypothalamic regions and PAG columns projected upon by the same OMPFC regions. The most extensive patterns of hypothalamic termination were seen after injection of anterograde tracer in prelimbic and infralimbic (PL/IL) and the ventral and medial orbital (VO/MO) cortices. Projections from rostral PL/IL and VO/MO targeted the rostrocaudal extent of the lateral hypothalamus, as well as lateral perifornical, and dorsal and posterior hypothalamic areas. Projections arising from caudal PL/IL terminated within the dorsal hypothalamus, including the dorsomedial nucleus and dorsal and posterior hypothalamic areas. There were also projections to medial perifornical and lateral hypothalamic areas. In contrast, it was found that anterior cingulate (AC), dorsolateral orbital (DLO), and agranular insular (AId) cortices projected to distinct and restricted hypothalamic regions. Projections arising from AC terminated within dorsal and posterior hypothalamic areas, whereas DLO and AId projected to the lateral hypothalamus. The same OMPFC regions also projected indirectly, by means of specific PAG columns, to many of the same hypothalamic fields. In the context of our previous findings, these data indicate that, in both rat and macaque, parallel but distinct circuits interconnect OMPFC areas with specific hypothalamic regions, as well as PAG columns.     

Carbon monoxide-prostaglandin E2 interaction in the hypothalamic circulation

The heme oxygenase (HO)-carbon monoxide pathway was earlier shown to increase hypothalamic blood flow after inhibition of nitric oxide synthesis in rats. We hypothesized that this effect is mediated by prostaglandin E2 (PGE2). Inhibition of constitutive HO activity decreased cerebral PGE2 production and simultaneously increased hypothalamic nitric oxide synthase (NOS) activity without changing hypothalamic blood flow. Furthermore, HO blockade induced cyclooxygenase-dependent decrease and NOS-mediated increase of the hypothalamic blood flow after inhibition of NOS and cyclooxygenase, respectively. Therefore, constitutive carbon monoxide release seems to have two indirect effects on the hypothalamic circulation: vasodilation mediated by PGE2 and vasoconstriction as a result of NOS inhibition.     

Developmental changes in the hypothalamic mRNA expression levels of brain-derived neurotrophic factor and serum leptin levels: Their responses to fasting in male and female rats

The actions and responses of hypothalamic appetite regulatory factors change markedly during the neonatal to pre-pubertal period in order to maintain appropriate metabolic and nutritional conditions. In this study, we examined the developmental changes in the hypothalamic mRNA levels of brain-derived neurotrophic factor (BDNF), which is a potent anorectic factor and the changes in the sensitivity of the hypothalamic expression of this factor to fasting during the neonatal to pre-pubertal period. Under fed conditions, hypothalamic BDNF mRNA expression decreased during development in both male and female rats. Similarly, the serum levels of leptin, which is a positive regulator of hypothalamic BDNF expression, also tended to fall during the developmental period. The serum leptin level and the hypothalamic BDNF mRNA level were found to be positively correlated in both sexes under the fed conditions. Hypothalamic BDNF mRNA expression was decreased by 24 h fasting (separating the rats from their mothers) in the early neonatal period (postnatal day 10) in both males and females, but no such changes were seen at postnatal day 20. Twenty-four hours’ fasting (food deprivation) did not affect hypothalamic BDNF mRNA expression in the pre-pubertal period (postnatal day 30). On the other hand, the rats’ serum leptin levels were decreased by 24 h fasting (separating the rats from their mothers at postnatal day 10 and 20, and food deprivation at postnatal day 30) throughout the early neonatal to pre-pubertal period. The correlation between serum leptin and hypothalamic BDNF mRNA levels was not significant under the fasted conditions. It can be speculated that leptin partially regulates hypothalamic BDNF mRNA levels, but only in fed conditions. Such changes in hypothalamic BDNF expression might play a role in maintaining appropriate metabolic and nutritional conditions and promoting normal physical development. In addition, because maternal separation induces a negative energy balance and short- and long-term stress responses, it is also possible that reductions in hypothalamic BDNF mRNA levels in the early neonatal period (postnatal day 10) may be partially induced by stress responses of the maternal deprivation.     

Hypothalamic attack area-mediated activation of the forebrain in aggression

It is believed that aggressive attacks are activated by a downward stimulatory stream that includes the medial amygdala, hypothalamic attack area, and periaqueductal grey. However, the hypothalamic attack area (from which attacks can be induced by electrical stimulation) sends projections to the forebrain, the significance of which is unknown. Here we report that the unilateral stimulation of the hypothalamic attack area per se induced an unilateral c-Fos activation of most brain nuclei involved in attack, and that attacks occurred only when cortical regions were also activated, and the activation of the medial amygdala and hypothalamic attack area were bilateral. This suggests that the hypothalamic attack area not only transmits information to lower brain structures but also activates forebrain structures involved in attack.     

The effect of rewarding hypothalamic stimulation on behavioral and neural hippocampal responses during trace eyeblink conditioning in rabbit (Oryctolagus cuniculus)

Rabbits were trace-conditioned with a tone as a conditioned stimulus and an airpuff as an unconditioned stimulus. Electrical stimulation to the medial forebrain bundle in the lateral hypothalamus was delivered either before or after the tone-airpuff pair. The purpose of the present study was to test whether the effect of post-trial hypothalamic stimulation differed from the effect of pre-trial hypothalamic stimulation on trace conditioning in the same subjects. Additionally, hippocampal responses were measured during sessions to see if hypothalamic stimulation activated dopaminergic fibres and affected hippocampal cell functioning and thus learning. The results showed that behavioral nictitating membrane conditioned responses were acquired quickly and hippocampal multiple unit activity increased with post-trial hypothalamic stimulation in comparison to almost non-existent conditioned responses and activity changes in the pre-trial hypothalamic stimulation sessions. The results suggest that hypothalamic stimulation affects trace conditioning differently depending on its time of delivery during conditioning.     

Androgens stimulate the morphological maturation of embryonic hypothalamic aromatase-immunoreactive neurons in the mouse

Gonadal steroids play an important role as developmental factors for the rodent brain and are implicated in the sexual differentiation of neural structures. Estrogens have been linked to survival and plasticity of central neurons, thereby regulating the development of hypothalamic and limbic structures associated with reproductive functions. Besides estrogens, androgens also contribute actively to CNS maturation. We have shown recently that androgens stimulate the receptor-mediated functional differentiation of cultured hypothalamic aromatase-immunoreactive (Arom-IR) neurons by stimulating the expression of Arom, the key enzyme in estrogen formation. In the present study, we investigated whether androgens are capable of influencing morphological differentiation of hypothalamic Arom-IR neurons. Androgen treatment, unlike estrogen, stimulated the morphological differentiation of cultured embryonic hypothalamic Arom-IR cells by increasing neurite outgrowth and branching, soma size, and the number of stem processes. This effect was brain region- and transmitter phenotype-specific; neither cortical Arom-IR neurons nor hypothalamic GABAergic neurons responded to androgens. Moreover, morphogenetic effects depended on androgen receptor (AR) activation, since morphological changes were completely inhibited by flutamide. Double-labeling of hypothalamic Arom-IR neurons revealed a considerable number of cells coexpressing AR, whereas cortical Arom-IR cells did not label for AR. Our data demonstrate that androgens function as morphogenetic signals for developing hypothalamic Arom-IR cells, thus being potentially effective in influencing plasticity and synaptic connectivity of hypothalamic Arom-systems.