Hypothalamic neurons in dissociated cell culture

Gene regulation in the magnocellular hypothalamo-neurohypophysial system

The hypothalamo-neurohypophysial system (HNS) is the major peptidergic neurosecretory system through which the brain controls peripheral physiology. The hormones vasopressin and oxytocin released from the HNS at the neurohypophysis serve homeostatic functions of water balance and reproduction. From a physiological viewpoint, the core question on the HNS has always been, "How is the rate of hormone production controlled?" Despite a clear description of the physiology, anatomy, cell biology, and biochemistry of the HNS gained over the last 100 years, this question has remained largely unanswered. However, recently, significant progress has been made through studies of gene identity and gene expression in the magnocellular neurons (MCNs) that constitute the HNS. These are keys to mechanisms and events that exist in the HNS. This review is an inventory of what we know about genes expressed in the HNS, about the regulation of their expression in response to physiological stimuli, and about their function. Genes relevant to the central question include receptors and signal transduction components that receive and process the message that the organism is in demand of a neurohypophysial hormone. The key players in gene regulatory events, the transcription factors, deserve special attention. They do not only control rates of hormone production at the level of the gene, but also determine the molecular make-up of the cell essential for appropriate development and physiological functioning. Finally, the HNS neurons are equipped with a machinery to produce and secrete hormones in a regulated manner. With the availability of several gene transfer approaches applicable to the HNS, it is anticipated that new insights will be obtained on how the HNS is able to respond to the physiological demands for its hormones.

Effects of osmotic pressure and brain-derived neurotrophic factor on the survival of postnatal hypothalamic oxytocinergic and vasopressinergic neurons in dissociated cell culture

Neurons from hypothalamic paraventricular nuclei (PVN) and supraoptic nuclei (SON) from postnatal day 6-8 rats were enzymatically dissociated and separately maintained in monolayer cultures for 14 days. The osmotic pressure of the culture medium, based on Neurobasal medium (Life Technologies), was varied (255, 300 and 330 mOsm/l) by adjustment using mannitol. The survival of oxytocin (OT), vasopressin (VP) and oxytocin-vasopressin (OT/VP) coexpressing neurons were studied under these varied conditions, and the identification of the cell phenotypes in the cultures was carried out by using double-label immunofluorescence. Under control osmolar conditions (300 mOsm/l) equivalent numbers of OT and VP neurons were found in the SON (P = 0.8398) and PVN (P = 0.4721) cultures. The OT neurons' survival did not change in 255 or 330 mOsm media in the SON cultures, but the VP neurons in the SON cultures were significantly increased in 255 mOsm/l medium as compared to control (300 mOsm/l) medium (P = 0.0088). No significant changes were found in VP neuron survival in SON cultures between the 300-330 mOsm/l media (P = 0.2372). Similar data were obtained for the VP neurons in PVN-derived cultures, but the OT neurons in these cultures survived significantly better at 300 mOs/l than at 255 mOsm/l (P<0.0001), but were not significantly different at 330 mOsm/l (P = 0.1208). In general, the VP neurons were more vulnerable than OT neurons to increases of culture medium osmolarity with respect to their survival. The number of OT/VP coexpressing neurons was greater in SON-derived cell cultures as compared to PVN-derived cell cultures, and their numbers were higher in the lower osmolarity media. The effects of adding brain-derived neurotrophic factor (BDNF) to the culture medium on survival were determined. BDNF significantly increased the numbers of all three types of neurons in both PVN and SON cell cultures (P = 0.0001-0.0060). The phenotypically identified cells, cultured in the 300 mOsm/l medium, responded by depolarization or hyperpolarization when transferred to hypertonic or hypotonic perfusion salines, respectively.

Dispersion and culture of magnocellular neurons from the supraoptic nucleus of the adult rat

A simple and efficient procedure for the dispersion and culture of magnocellular neurons of the adult rat hypothalamus was developed. The enzymatically and mechanically dispersed cells were highly viable and showed neurite outgrowth after 3 days of culture. The neurons could be maintained for more than 4 weeks without any sign of deterioration. Light-optic immunocytochemistry of the cultured cells revealed the presence of many oxytocin- and vasopressin-immunoreactive neurons. The results indicate that the method may be suitable for many experimental purposes.

High-affinity uptake of noradrenaline in postsynaptic neurones

1. Neurotransmitters released from nerve endings are inactivated by re-uptake into the presynaptic nerve terminals and possibly into neighbouring glial cells. While analysing the functional properties of alpha 1-adrenoceptors in the hypothalamus, we observed a high-affinity uptake process for noradrenaline in postsynaptic peptidergic neurones. 2. In primary hypothalamic cell cultures and in a hypothalamic neuronal cell line, [3H]-prazosin bound with high affinity and was displaced by unlabelled prazosin in concentrations of 10(-10) to 10(-7) M. However, at concentrations of unlabelled prazosin above 10(-7) M, there was a paradoxical increase in apparent [3H]-prazosin binding. 3. Methoxamine, an alpha 1-adrenoceptor ligand that is not subject to significant neuronal uptake, displaced [3H]-prazosin but did not cause the paradoxical increase in the apparent binding of [3H]-prazosin. Cooling the cells to 4 degrees C reduced the total amount of prazosin associated with the cells; under these conditions, methoxamine almost completely inhibited [3H]-prazosin binding to the cells. 4. In the presence of desipramine (DMI), unlabelled prazosin displaced [3H]-prazosin as before, but no paradoxical increase in apparent binding was seen above 10(-7) M. 5. The paradoxical increase of [3H]-prazosin binding was not observed in membrane preparations of hypothalamic neurones. These findings indicated that the paradoxical increase in apparent [3H]-prazosin binding was due to a cellular uptake process that becomes evident at high concentrations of the ligand. 6. DMI (10(-5) M) had no effect on the specific binding of [3H]-prazosin. The presence of alpha1-adrenoceptors was confirmed by binding of [125]-HEAT, but [3H]-idazoxan (an alpha2- ligand) did not bind to the cells.7. The uptake of prazosin obeyed the Michaelis-Menten model, with similar Km and Vmax values in both types of cultures.8. Noradrenaline was taken up with high affinity by both types of cultures. (+/-)-[3H]-noradrenaline uptake was reduced by DMI and by excluding sodium from the medium, indicating that this process has some of the properties of uptake 1. (+/-)-[3H]-noradrenaline uptake in the cell line was unaffected by testosterone.9. The measured uptake of (-)-noradrenaline in the cell line was considerably increased by blockade of catechol-omicron-methyl-transferase and monoamine oxidase, suggesting that (-)-noradrenaline is metabolized to lipophilic products that escape across the plasma membrane.10. Studies in rats, in which the noradrenaline isomer 6-hydroxydopamine was used, suggested that the post synaptic uptake process is operative in hypothalamic CRH and vasopressin neurones in vivo.11. The Km for (-)-noradrenaline was within the range for the high affinity uptake, process in noradrenergic neurones. Uptake takes place in concentrations at which noradrenaline activates alpha1-adrenoceptors.Removal of noradrenaline from the vicinity of the receptors may prevent desensitization,thus maintaining the responsiveness of postsynaptic neurones to the actions of the neurotransmitter.

Cell types and cell-substrate interactions in serum-free dissociated cultures of rat hypothalamus

We have developed a system for the long-term cultivation of hypothalamic neurons at low density in defined serum-free medium, and have identified the major classes of cells in these cultures. Cells prepared from the dissociation of embryonic rat hypothalami are plated, in serum-free medium, onto monolayers of cortical astrocytes. Neurons adhere and begin to extend neurites soon after plating, and survive for up to several weeks in culture. Cell-type-specific immunological markers were utilized to identify neurons and the major classes of glial cells in these cultures. The culture of hypothalamic neurons in serum-free conditions provides a valuable system for the study of the cellular basis of hypothalamic neuronal heterogeneity and functional diversity.

Primary explants as a model of the hypothalamus in situ

Anatomical and electrophysiological studies with neurotensin and somatostatin were performed to assess the integrity of primary explants of the preoptic anterior hypothalamus (POAH) maintained in organ culture as a model to study peptidergic neurons in vitro. POAH neurons maintained in vitro were found to be morphologically similar to those visualized histologically in situ. Somatostatin- and neurotensin-immunoreactive neurons were also present in both preparations. Additionally, electrophysiological responses of neurons in vitro to neurotensin and somatostatin were qualitatively similar to neuronal responses in situ. The striking morphological and pharmacological similarity between POAH neurons in vitro and in situ suggests that primary explants of the POAH are organotypic.

Cells in neonatal rat hypothalamus primary culture--an immunofluorescence study

Hypothalami from 1 day neonatal rats were dissociated and cultured for 4-16 days. Using immunofluorescence and antisera against neurofilament (NF) peptides, glial fibrillary acidic protein (GFAP), galactocerebroside and fibronectin we have distinguished neurons, astrocytes, oligodendrocytes and fibroblast-like cells in culture. Astrocytes initially grew as islets of 15-30 cells which dispersed as the culture aged. These cells, together with fibronectin-reactive flat cells, formed a monolayer upon which ovoid and process-bearing cells grew after 4 days in culture. Neurofilament-positive neurons constituted 5-10% of the total cell population. In maturing cultures the number of neurons decreased and fibroblasts increased. Oligodendrocytes represented less than 1% of total cell population. These studies emphasize the necessity of using the complementary techniques of morphology and immunocytochemistry for the characterization of hypothalamic neural cells in vitro.

Sympathetic ganglion neurons from aged humans grown in monolayer culture

Sympathetic ganglia were dissected from aged patients during surgical operation done for a therapeutic purpose in the University Hospital. Nerve cells were isolated from the ganglia by trituration after incubation with collagenase, and were grown on collagen-coated plastic dishes with a growth medium. These nerve cells regenerated their axons and survived in the tissue culture for more than 3 weeks. The nerve cells tended to reduce the size in an early stage of the in vitro growth.

Cultured neurones from the mature bovine mediobasal hypothalamus contain LHRH but not catecholamine

The in vitro culture of mature neurones from bovine mediobasal hypothalamus (MBH) is reported, providing a model for studies of mammalian neurosecretion at the cellular level. Explant tissue cultures of mature bovine MBH containing the arcuate nucleus were examined for LHRH, ACTH and catecholamines with a view to investigating the control of prolactin and gonadotropin secretion. LHRH immunoreactivity was found in both neuronal and non-neuronal cells in the outgrowth monolayer region of the explant. Neurones in this region appeared able to attach to a substrate and regenerate, in monolayer culture, well developed neurites characterized by beaded swellings as observed in vivo. Neither ACTH immunoreactivity nor catecholamine fluorescence was detected. Cultured neurones and astrocytes were labelled by tetanus toxin and anti-GFAP, respectively. Double labelling of cultures with tetanus toxin and anti-LHRH demonstrated the neuronal nature of many LHRH-immunoreactive cells. Radio-immunoassay data confirmed the presence of LHRH in the cultures but application of 60 mM KC1 failed to evoke hormone release. These studies have confirmed the view of previous workers that hypothalamic control of prolactin secretion in the bovine may be very different from that thought to occur in non-ruminants such as the rat and guinea pig. Finally, this work demonstrates that a cultured system from the mature bovine may prove a good model for study of neuronal regulation of gonadotropin secretion by the bovine mediobasal hypothalamus.

In vitro development of chick hypothalamic neurosecretory cells

The in vitro maturation of chick hypothalamic neurosecretory cells has been studied by the Golgi method and electron microscopy. Rotary cultures prepared from chick embryos aged 6, 8 and 10 days of development fail to assemble histotypic cultures; however, cultures prepared from older embryos, i.e. 12, 14 and 16 days of development, progressively exhibited more neurosecretory characteristics. It is interesting to point out that cultures prepared from 12-, 14- and 16-day-old chick embryos form complex surfaces composed of patches of glioepithelial cells alternating with zones containing neurosecretory nerve endings partially surrounded by glial processes. This particular distribution of the nerve endings seems to indicate that cytotypic hypothalamic neurons in rotary cultures deliver their products to the incubation medium; this interpretation is further reinforced by the observed exocytosis of the neurosecretory material within the external neuropile of histotypic cultures. Details of the neurosecretory cell maturation are given in the text.

Hypothalamic neurons in dissociated cell culture: the mechanism of increased survival times in the presence of non-neuronal cells

Rat hypothalamic neurons were cultured in the presence of fluorodeoxyuridine to inhibit nonneuronal cell proliferation. Under these conditions, neuronal cell survival was dependent on contact with homologous nonneuronal cells. This phenomenon did not seem to be due to the release of diffusable trophic factors, since neither growth on polylysine in the close proximity of nonneuronal cells nor the use of preconditioned medium significantly increased neuronal survival. However, metabolically active cell layers were required, since growth on heat-killed or fixed homologous nonneuronal cells did not increase neuronal survival. The increased survival of neurons seen here in the presence of homologous nonneuronal cells therefore appears to be due to metabolic co-operation mediated by specific, direct cell-cell contact.

Adult mouse dorsal root ganglia neurons in cell culture

A method has been developed for the long-term culture of dissociated adult mouse dorsal root ganglia (DRG). Of critical importance to the success of this technique was a three-hour incubation in collagenase which softened the DRG and permitted gentle dissociation. The morphological and electrophysiological features of the dissociated adult DRG were similar to those observed in previous studies of immature (i.e., embryonic and newborn) DRG in culture and also to those of adult DRG in situ. With regard to electrophysiological work, the adult DRG neurons are superior to embryonic and newborn neurons because of their larger size and greatly increased survival in culture (no degeneration for first six days, and thereafter a relatively slow decrease). The adult neurons regenerated nerve fibers to an extent comparable to that of immature neurons. Therefore, the adult DRG cultures might be useful to study factors influencing regeneration in the adult mammalian nervous system. The adult cultures might also be useful to investigated factors influencing the aging process.

Identification of catecholamine and luteinizing hormone-releasing hormone (LHRH)-containing neurons in primary cultures of dispersed cells of the basal hypothalamus

Primary cultures of dispersed cells were prepared from 3-5 mg pieces of basal hypothalami of 10-12-day-old rats. The tissue included median eminence, arcuate nucleus and variable amounts of adjacent hypothalamus and preoptic area. The dispersion procedure consisted basically of tissue trypsinization and mechanical dissociation of cells. They were cultured in a modified L-15 medium in an air atmosphere. Neurons survived approximately 3 months. On the basis of morphological characteristics, two basic cell types could be distinguished. One was a larger (50 mum diameter) multipolar cell; microspectrofluorometric analysis revealed that a small percentage of these neurons contained a catecholamine. A second type was smaller, fusiform or ovoid and generally bipolar; a significant number of these were immunoreactive for the releasing hormone LHRH.