Ciliary neurotrophic factor increases the survival of magnocellular vasopressin and oxytocin neurons in rat supraoptic nucleus in organotypic cultures

Arginine vasopressin-Venus reporter mice as a tool for studying magnocellular arginine vasopressin neurons

Arginine vasopressin (AVP) synthesized in the magnocellular neurons of the hypothalamus is transported through their axons and released from the posterior pituitary into the systemic circulation to act as an antidiuretic hormone. AVP synthesis and release are precisely regulated by changes in plasma osmolality. Magnocellular AVP neurons receive innervation from osmosensory and sodium-sensing neurons, but previous studies showed that AVP neurons per se are osmosensitive as well. In the current study, we made AVP-Venus reporter mice and showed that Venus was expressed exclusively in AVP neurons and was upregulated under water deprivation. In hypothalamic organotypic cultures from the AVP-Venus mice, Venus-labeled AVP neurons in the supraoptic and paraventricular nuclei survived for 1 month, and Venus expression was upregulated by forskolin. Furthermore, in dissociated Venus-labeled magnocellular neurons, treatment with NaCl, but not with mannitol, decreased Venus fluorescence in the soma of the AVP neurons. Thus, Venus expression in AVP-Venus transgenic mice, as well as in primary cultures, faithfully showed the properties of intrinsic AVP expression. These findings indicate that AVP-Venus mice as well as the primary hypothalamic cultures could be useful for studying magnocellular AVP neurons.

Age-dependent increase in Thy-1 protein in the rat supraoptic nucleus

Mature mammalian CNS neurons often do not recover successfully following injury. To this point, unilateral lesion of the hypothalamo-neurohypophysial tract results in collateral sprouting from uninjured axons of the supraoptic nucleus (SON) in 35-day-old but not in 125-day-old rats. Thus, it appears that there are age-related changes within the SON that preclude the older rat from recovering following axotomy. We hypothesize that the intrinsic capacity for axon reorganization may depend, in part, on age-related alterations in cell adhesion molecules that allow normal astrocyte-neuron interactions in the SON. In support of our hypothesis, numerous reports have shown that Thy-1 is increased in neurons at the cessation of axon outgrowth. Therefore, we compared protein levels of Thy-1 and the Thy-1 interacting integrin subunits, alpha-v (α_v), beta-3 (ß₃), and beta-5 (ß₅), in 35- and 125-day-old SON using western blot analysis. Our results demonstrated that there was significantly more Thy-1 protein in the 125-day-old SON compared to 35-day-old SON, but no change in the protein levels of the integrin subunits. Furthermore, we localized Thy-1-, α_v integrin-, ß₃ integrin-, and ß₅ integrin-immunoreactivity to both neurons and astrocytes in the SON. Altogether, our results suggest that the observed increase in Thy-1 protein levels in the SON with age may contribute to an environment that prevents collateral axonal sprouting in the SON of the 125-day-old rat.

Absence of axonal sprouting following unilateral lesion in 125-day-old rat supraoptic nucleus may be due to age-dependent decrease in protein levels of ciliary neurotrophic factor receptor alpha

Within the supraoptic nucleus (SON) of a 35-day-old rat, we previously demonstrated a collateral sprouting response that reinnervates the partially denervated neural lobe (NL) after unilateral lesion of the hypothalamo-neurohypophysial tract. Others have shown a decreased propensity for axonal sprouting in an aged brain; therefore, to see if the SON exhibits a decreased propensity for axonal sprouting as the animal ages, we performed a unilateral lesion in the 125-day-old rat SON. Ultrastructural analysis of axon profiles in the NL of the 125-day-old rat demonstrated an absence of axonal sprouting following injury. We previously demonstrated that ciliary neurotrophic factor (CNTF) promotes process outgrowth from injured magnocellular neuron axons in vitro. Thus, we hypothesized that the lack of axonal sprouting in the 125-day-old rat SON may be due to a reduction in CNTF or the CNTF receptor components. To this point, we found that as the rat ages there is significantly less CNTF receptor alpha (CNTFRα) protein in the uninjured, 125-day-old rat compared to the uninjured, 35-day-old rat. We also observed that protein levels of CNTF and the CNTF receptor components were increased in the SON and NL following injury in the 35-day-old rat, but there was no difference in the protein levels in the 125-day-old rat. Altogether, the results presented herein demonstrate that the plasticity within the SON is highly dependent on the age of the rat, and that a decrease in CNTFRα protein levels in the 125-day-old rat may contribute to the loss of axonal sprouting following axotomy.

The MAPK and PI3K pathways mediate CNTF-induced neuronal survival and process outgrowth in hypothalamic organotypic cultures

While collateral sprouting has been shown to occur in a variety of neuronal populations, the factor or factors responsible for mediating the sprouting response remain largely un-defined. There is evidence indicating that ciliary neurotrophic factor (CNTF) may play an important role in promoting neuronal survival and process outgrowth in neuronal phenotypes tested to date. We previously demonstrated that the astrocytic Jak-STAT pathway is necessary to mediate CNTF-induced oxytocinergic (OT) neuronal survival; however, the mechanism (s) of CNTF-mediated process outgrowth remain unknown. Our working hypothesis is that CNTF mediates differential neuroprotective responses via different intracellular signal transduction pathways. In order to test this hypothesis, we utilized stationary hypothalamic organotypic cultures to assess the contribution of the MAPK-ERK and PI3-AKT pathways to OT neuron survival and process outgrowth. Our results demonstrate that the MAPK-ERK½ pathway mediates CNTF-induced neuronal survival. Moreover, we show that inhibition of the p38-, JNK-MAPK, and mTOR pathways prevents loss OT neurons following axotomy. We also provide quantitative evidence indicating that CNTF promotes process outgrowth of OT neurons via the PI3K-AKT pathway. Together, these data indicate that distinct intracellular signaling pathways mediate diverse neuroprotective processes in response to CNTF.

Inhibition of the Jak-STAT pathway prevents CNTF-mediated survival of axotomized oxytocinergic magnocellular neurons in organotypic cultures of the rat supraoptic nucleus

Previous studies have demonstrated that ciliary neurotrophic factor (CNTF) enhances survival and process outgrowth from magnocellular neurons in the paraventricular (PVN) and the supraoptic (SON) nuclei. However, the mechanisms by which CNTF facilitates these processes remain to be determined. Therefore, the aim of this study was to identify the immediate signal transduction events that occur within the rat SON following administration of exogenous rat recombinant CNTF (rrCNTF) and to determine the contribution of those intracellular signaling pathway(s) to neuronal survival and process outgrowth, respectively. Immunohistochemical and Western blot analyses demonstrated that axonal injury and acute unilateral pressure injection of 100 ng/μl of rrCNTF directly over the rat SON resulted in a rapid and transient increase in phosphorylated-STAT3 (pSTAT3) in astrocytes but not neurons in the SON in vivo. Utilizing rat hypothalamic organotypic explant cultures, we then demonstrated that administration of 25 ng/ml rrCNTF for 14days significantly increased the survival and process outgrowth of OT magnocellular neurons. In addition, pharmacological inhibition of the Jak-STAT pathway via AG490 and cucurbitacin I significantly reduced the survival of OT magnocellular neurons in the SON and PVN; however, the contribution of the Jak-STAT pathway to CNTF-mediated process outgrowth remains to be determined. Together, these data indicate that CNTF-induced survival of OT magnocellular neurons is mediated indirectly through astrocytes via the Jak-STAT signaling pathway.

Neuronal activity and axonal sprouting differentially regulate CNTF and CNTF receptor complex in the rat supraoptic nucleus

We demonstrated previously that the hypothalamic supraoptic nucleus (SON) undergoes a robust axonal sprouting response following unilateral transection of the hypothalamo-neurohypophysial tract. Concomitant with this response is an increase in ciliary neurotrophic factor (CNTF) and CNTF receptor alpha (CNTFRα) expression in the contralateral non-uninjured SON from which the axonal outgrowth occurs. While these findings suggest that CNTF may act as a growth factor in support of neuronal plasticity in the SON, it remained to be determined if the observed increase in neurotrophin expression was related to the sprouting response per se or more generally to the increased neurosecretory activity associated with the post-lesion response. Therefore we used immunocytochemistry and Western blot analysis to examine the expression of CNTF and the components of the CNTF receptor complex in sprouting versus osmotically-stimulated SON. Western blot analysis revealed a significant increase in CNTF, CNTFRα, and gp130, but not LIFRß, protein levels in the sprouting SON at 10days post lesion in the absence of neuronal loss. In contrast, osmotic stimulation of neurosecretory activity in the absence of injury resulted in a significant decrease in CNTF protein levels with no change in CNTFRα, gp130, or LIFRß protein levels. Immunocytochemical analysis further demonstrated gp130 localization on magnocellular neurons and astrocytes while the LIFRß receptor was found only on astrocytes in the SON. These results are consistent with the hypothesis that increased CNTF and CNTFR complex in the sprouting, metabolically active SON are related directly to the sprouting response and not the increase in neurosecretory activity.

In vitro functionality of isolated embryonic hypothalamic vasopressinergic and oxytocinergic neurons: modulatory effects of brain-derived neurotrophic factor and angiotensin II

There are only a few studies on the ontogeny and differentiation process of the hypothalamic supraoptic-paraventriculo-neurohypophysial neurosecretory system. In vitro neuron survival improves if cells are of embryonic origin; however, surviving hypothalamic neurons in culture were found to express small and minimal amounts of arginine-vasopressin (AVP) and oxytocin (OT), respectively. The aim of this study was to develop a primary neuronal culture design applicable to the study of magnocellular hypothalamic system functionality. For this purpose, a primary neuronal culture was set up after mechanical dissociation of sterile hypothalamic blocks from 17-day-old Sprague-Dawley rat embryos (E17) of both sexes. Isolated hypothalamic cells were cultured with supplemented (B27)-NeuroBasal medium containing an agent inhibiting non-neuron cell proliferation. The neurosecretory process was characterized by detecting AVP and OT secreted into the medium on different days of culture. Data indicate that spontaneous AVP and OT release occurred in a culture day-dependent fashion, being maximal on day 13 for AVP, and on day 10 for OT. Interestingly, brain-derived neurotrophic factor (BDNF) and Angiotensin II (A II) were able to positively modulate neuropeptide output. Furthermore, on day 17 of culture, non-specific (high-KCl) and specific (Angiotensin II) stimuli were able to significantly (P < 0.05) enhance the secretion of both neuropeptides over respective baselines. This study suggests that our experimental design is useful for the study of AVP- and OT-ergic neuron functionality and that BDNF and A II are positive modulators of embryonic hypothalamic cell development.

Peripheral osmotic stimulation inhibits the brain's innate immune response to microdialysis of acidic perfusion fluid adjacent to supraoptic nucleus

During the brain's innate immune response microglia, astroglia and ependymal cells resolve/repair damaged tissue and control infection. Released interleukin-1beta (IL-1beta) reaching cerebroventricles stimulates circumventricular organs (CVOs; subfornical organ, SFO; organum vasculosum lamina terminalis, OVLT), the median preoptic nucleus (MePO), and magnocellular and parvocellular neurons in the supraoptic (SON) and paraventricular (PVN) nuclei. Hypertonic saline (HS) also activates these osmosensory CVOs and neuroendocrine systems, but, in contrast to IL-1beta, inhibits the peripheral immune response. To examine whether the brain's innate immune response is attenuated by osmotic stimulation, sterile acidic perfusion fluid was microdialyzed (2 microl/min) in the SON area of conscious rats for 6 h with sterile HS (1.5 M NaCl) injected subcutaneously (15 ml/kg) at 5 h. Immunohistochemistry identified cytokine sources (IL-1beta(+); OX-42(+) microglia) and targets (IL-1R(+); inducible cyclooxygenase, COX-2(+); c-Fos(+)) near the probe, in CVOs, MePO, ependymal cells, periventricular hypothalamus, SON, and PVN. Inserting the probe stimulated magnocellular neurons (c-Fos(+); SON; PVN) via the MePO (c-Fos(+)), a response enhanced by HS. Microdialysis activated microglia (OX-42(+); amoeboid/hypertrophied; IL-1beta(+)) in the adjacent SON and bilaterally in perivascular areas of the PVN, periventricular hypothalamus and ependyma, coincident with c-Fos expression in ependymal cells and COX-2 in the vasculature. These microglial responses were attenuated by HS, coincident with activating parvocellular and magnocellular neuroendocrine systems and elevating circulating IL-1beta, oxytocin, and vasopressin. Acidosis-induced cellular injury from microdialysis activated the brain's innate immune response by a mechanism inhibited by peripheral osmotic stimulation.

Effects of ciliary neurotrophic factor and leukemia inhibiting factor on oxytocin and vasopressin magnocellular neuron survival in rat and mouse hypothalamic organotypic cultures

Organotypic cultures of mouse and rat magnocellular neurons (MCNs) in the hypothalamo-neurohypophysial system (HNS) have served as important experimental models for the molecular and physiological study of this neuronal phenotype. However, it has been difficult to maintain significant numbers of the MCNs, particularly vasopressin MCNs, in these cultures for long periods. In this paper, we describe the use of the neurotrophic factors, leukemia inhibiting factor (LIF) and ciliary neurotrophic factor (CNTF) to rescue rat vasopressin (Avp)- and oxytocin (Oxt)-MCNs from axotomy-induced, programmed cell death in vitro. Quantitative data are presented for the efficacy of the LIF family of neurotrophic factors on the survival of MCNs in three nuclei, the paraventricular (PVN), supraoptic (SON), and accessory (ACC) nuclei in the mouse and rat hypothalamus.

CNTF receptor alpha is expressed by magnocellular neurons and expression is upregulated in the rat supraoptic nucleus during axonal sprouting

Ciliary neurotrophic factor (CNTF) is expressed by glial cells at multiple levels of the magnocellular neurosecretory system (MNS). CNTF is present in astrocytes in the hypothalamic supraoptic nucleus (SON) as well as in perivascular cells in the neurohypophysis, and a several fold increase in CNTF immunoreactivity occurs in the SON following either axotomy of magnocellular neurons or during axonal sprouting by intact magnocellular neurons. CNTF also promotes survival and stimulates process outgrowth from magnocellular neurons in vitro. While these findings suggest that CNTF may act as a growth factor in support of neuronal plasticity in the MNS, little is known regarding possible expression of receptors for CNTF in the MNS. We have therefore used immunocytochemistry and in situ hybridization to examine the expression of CNTF receptor alpha (CNTFRalpha) in the rat MNS. Robust immunoreactivity for CNTFRalpha was observed associated with oxytocinergic and vasopressinergic neurons distributed throughout the SON. Astrocytes located within the ventral glial lamina (VGL) of the SON were also immunoreactive for CNTFRalpha. Robust hybridization of an anti-sense [(35)S]-cRNA probe to CNTFRalpha mRNA was observed throughout the SON, while binding of a control sense probe was much lower. Grains were found clustered predominantly over neuronal somata, indicative of expression by magnocellular neurons within the SON. We next examined changes in expression of CNTFRalpha mRNA by magnocellular neurons 7 days following unilateral transection of the hypothalamo-neurohypophysial tract. The level of CNTFRalpha mRNA was increased 32% (compared to age-matched intact controls; p<0.05) in magnocellular neurons in the SON contralateral to the lesion, which are undergoing extensive collateral axonal sprouting, but was unchanged in axotomized magnocellular neurons in the SON ipsilateral to the lesion. These findings suggest that CNTF produced by MNS glia and acting via CNTFRalpha may exert neurotrophic effects on magnocellular neurons.

Perivascular cells increase expression of ciliary neurotrophic factor following partial denervation of the rat neurohypophysis

The expression of ciliary neurotrophic factor (CNTF) was investigated immunocytochemically during the axonal degeneration and collateral axonal sprouting response that follows partial denervation of the rat neurohypophysis. A significant increase in the number of CNTF-immunoreactive (CNTF-ir) cells was observed in the neurohypophysis of partially denervated animals compared to age-matched sham-operated controls by 5 days post-denervation, remaining elevated throughout the 30 day post-denervation period. Stereometric assessment of the numbers of CNTF-ir cells within the partially denervated neurohypophysis demonstrated a 36% increase by 3 days following denervation reaching 130% of control values by 10 days post-lesion. The cell numbers remained elevated throughout the 30 day post-lesion period suggesting that CNTF may play a role in the neurosecretory axonal sprouting process known to occur between 10 and 30 days post-denervation. Subsequent preparations pairing anti-CNTF with antibodies against ED1, CR3, p75 low affinity neurotrophin receptor (p75(LNGFR)), and S100beta, demonstrated that CNTF was exclusively localized in a phenotypically-distinct population of perivascular cells. The association of perivascular cells with phagocytic activity was confirmed by dual-label fluorescence microscopy showing the colocalization of P75(LNGFR)-ir and OX-42-ir in cells expressing the ED-1 antigen. No increase in CNTF-ir was observed in non-injured animals in which heightened levels of neurosecretory activity were induced physiologically. These results suggest that increased CNTF-ir occurs in response to conditions which induce high levels of phagocytic activity by perivascular cells in the axotomized neurohypophysis which is sustained throughout a period in which axonal sprouting is known to occur in the partially denervated neurohypophysis.

Apoptosis of supraoptic AVP neurons is involved in the development of central diabetes insipidus after hypophysectomy in rats

Background

It has been reported that various types of axonal injury of hypothalamo-neurohypophyseal tract can result in degeneration of the magnocellular neurons (MCNs) in hypothalamus and development of central diabetes insipidus (CDI). However, the mechanism of the degeneration and death of MCNs after hypophysectomy in vivo is still unclear. This present study was aimed to disclose it and to figure out the dynamic change of central diabetes insipidus after hypophysectomy.

Results

The analysis on the dynamic change of daily water consumption (DWC), daily urine volume(DUV), specific gravity of urine(USG) and plasma vasopressin concentration showed that the change pattern of them was triphasic and neuron counting showed that the degeneration of vasopressin neurons began at 10 d, aggravated at 20 d and then stabilized at 30 d after hypophysectomy. There was marked upregulation of cleaved Caspase-3 expression of vasopressin neurons in hypophysectomy rats. A "ladder" pattern of migration of DNA internucleosomal fragments was detected and apoptotic ultrastructure was found in these neurons. There was time correlation among the occurrence of diabetes insipidus, the changes of plasma vasopressin concentration and the degeneration of vasopressin neurons after hypophysectomy.

Conclusion

This study firstly demonstrated that apoptosis was involved in degeneration of supraoptic vasopressin neurons after hypophysectomy in vivo and development of CDI. Our study on time course and correlations among water metabolism, degeneration and apoptosis of vasopressin neurons suggested that there should be an efficient therapeutic window in which irreversible CDI might be prevented by anti-apoptosis.

Bcl-xL and caspase inhibition increase the survival of rat oxytocin and vasopressin magnocellular neurons in organotypic culture

Hypothalamic magnocellular neurons (MCNs) are highly vulnerable to axotomy-induced cell death in vivo and in vitro. In this study, we determined whether the anti-apoptotic agent Bcl-xL, a member of the Bcl-2 family which prevents programmed cell death in the central nervous system, can rescue oxytocin (OT) and vasopressin (VP) MCNs in the supraoptic nucleus (SON) in organotypic culture. We found that the novel, membrane permeant form of Bcl-xL that we employed in these studies protected both OT and VP MCNs from degeneration as long as the Bcl-xL was present in the medium. In contrast, z-VAD-fmk, an inhibitor of caspases that are involved in apoptosis, was less effective in that it significantly rescued OT MCNs (P < 0.01) but not VP MCNs (P > 0.09). Unlike the Bcl-xL, Z-VAD-fmk's effectiveness in reducing MCN cell death was not sustained for the full 15 days in vitro.

Ciliary neurotrophic factor is expressed in the magnocellular neurosecretory system of the rat in vivo: evidence for injury- and activity-induced upregulation

Although ciliary neurotrophic factor (CNTF) has been shown to promote the survival of magnocellular neurons when applied exogenously to explants of the paraventricular and supraoptic nuclei (SON) in vitro, little is known regarding its expression or regulation in the adult magnocellular neurosecretory system (MNS) following injury in vivo. Therefore, we utilized in situ hybridization and immunocytochemical analysis in conjunction with quantitative optical densitometric analysis to identify the cellular source of CNTF and examine the temporal pattern of its expression, following unilateral transection of the hypothalamo-neurohypophysial tract in the adult rat. In intact rats, CNTF immunoreactivity (CNTF-ir) was predominantly localized within identified astrocytes within the ventral glial limitans subjacent to the SON. Quantitative optical densitometric analysis of CNTF-ir levels in the axotomized SON demonstrated that the proportional area of CNTF-ir was significantly elevated between 3 and 30 days following injury. A significant but more limited increase was also observed in the non-injured contralateral SON. In situ hybridization confirmed the expression and upregulation of CNTF in the axotomized SON. These results demonstrate the expression of CNTF in the adult rodent MNS in vivo and provide evidence that levels of CNTF are upregulated in response to both direct injury, and heightened metabolic activity, within the lesioned and sprouting SON, respectively.

Differential effects of forskolin on tyrosine hydroxylase gene transcription in identified brainstem catecholaminergic neuronal subtypes in organotypic culture

The regulation of gene expression of tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine synthesis, was studied in brainstem noradrenergic nuclei, locus coeruleus (LC), A2 and A1, in vitro. Several novel experimental approaches employed in this study included: (i) the development of a slice-explant model in which these brainstem nuclei maintained a high survival of the noradrenergic neurons, an organotypic topology and the coexpression of two identifying markers in addition to TH, i.e. norepinephrine transporter (NET) and vesicular monoamine transporter 2 (VMAT2); (ii) quantitative analysis of TH transcription in these nuclei was made using a labelled intronic probe to measure TH heteronuclear RNA (hnRNA) and (iii) the use of tetrodotoxin in the media to eliminate spontaneous neural activity in these nuclei, thereby providing a basal state as the starting point for the study of TH transcription under various pharmacological perturbations. In the presence of TTX, the adenylcyclase stimulator, forskolin, produced a 155% increase in LC, a 130% increase in A1, and a 220% increase in A2 in TH hnRNA as compared to control nuclei. This effect of forskolin was abolished in the LC and A1 by the PKA inhibitor, H89 (5 microm), but not by the MAP kinase pathway (MEK) inhibitor, PD98059 (75 microm). In contrast, the robust increase in TH transcription produced by forskolin in A2 neurons, was completely inhibited by PD98059, and only partially inhibited by H89, showing that induced TH transcription is mediated by different kinase pathways in specific central noradrenergic neuronal subtypes.

Development of the mouse hypothalamo-neurohypophysial system in the munc18-1 null mutant that lacks regulated secretion

The hypothalamo-neurohypophysial system (HNS) is composed of hypothalamic magnocellular neurons and neural lobe pituicytes that accommodate the nerve terminals. Here we have investigated if the communication of the peptidergic neurons of the HNS with neighbouring cells plays a role in the development and assembly of the HNS. We employed munc18-1-deficient mice, which completely lack neurotransmitter secretion. Morphological and immunohistological analysis of the HNS in these mutant embryos during brain development showed that this peptidergic system was formed normally during early embryogenesis. However, the development arrested at embryonal day 14.5, the stage when terminal differentiation has to take place. The peptidergic neurons targeted axons in the correct direction, but few arrived at their final location and the neurons were not maintained in later stages. The pituicytes in the neural lobe of the pituitary were generated, but failed to organize normally. Our results indicate that peptide gene expression, axon outgrowth and migration are intrinsic developmental events in these peptidergic neurons, that are initiated in the munc18-1 null mutant. The further expansion and the integration of outgrowing axon terminals with neural lobe pituicytes requires munc18-1-dependent processes, probably exocytosis, at multiple levels. Firstly, to maintain and propagate neuronal outgrowth and guidance, and secondly, to control the cellular organization of the pituicytes. Thus, the communication between the outgrowing neurons and the pituicytes could serve to integrate these two cell types to constitute a functional peptidergic system.

Neural activity protects hypothalamic magnocellular neurons against axotomy-induced programmed cell death

Axotomy typically leads to retrograde neuronal degeneration in the CNS. Studies in the hypothalamo-neurohypophysial system (HNS) have suggested that neural activity is supportive of magnocellular neuronal (MCN) survival after axotomy. In this study, we directly test this hypothesis by inhibiting neural activity in the HNS, both in vivo and in vitro, by the use of tetrodotoxin (TTX). After median eminence compression to produce axonal injury, unilateral superfusion of 3 microM TTX into the rat supraoptic nucleus (SON), delivered with the use of a miniature osmotic pump for 2 weeks in vivo, produced a decrease in the number of surviving MCNs in the TTX-treated SON, compared with the contralateral untreated side of the SON. In vitro application of 2.5 microM TTX for 2 weeks to the SON in organotypic culture produced a 73% decrease in the surviving MCNs, compared with untreated control cultures. Raising the extracellular KCl in the culture medium to 25 mM rescued the MCNs from the axotomy- and TTX-induced cell death. These data support the proposal that after axotomy, neural activity is neuroprotective in the HNS.

Specific localization of signal transducer and activator of transcription 1 immunoreactivity in oxytocin neurons of the rat hypothalamus

The transcription factor STAT1 participates in signaling pathways and cellular responses triggered by several cytokines, growth factors and hormones. The present work demonstrates for the first time the immunohistochemical distribution of STAT1 in the rat hypothalamus. STAT1 immunoreactivity was observed in somas, dendrites and axons of neurons throughout the supraoptic and paraventricular nuclei and co-localized specifically with oxytocin. These findings indicate that STAT1 is positioned to participate in specific neuroendocrine regulation in the nonpathological rat brain.

Transgenesis and the study of expression, cellular targeting and function of oxytocin, vasopressin and their receptors

The neuropeptides oxytocin and vasopressin and the neurons in the hypothalamus that synthesize them have been a rich source for the exploration and understanding of both the brain and the endocrine system. Because of their large size and compact nuclear organization the magnocellular neurons of the hypothalamoneurohypophysial system have traditionally attracted scientists using state-of-the-art techniques, including the subject of this review, transgenesis. We discuss the role of transgenics in deciphering gene elements necessary for the appropriate expression of oxytocin and vasopressin and to deliver exogenous genes, such as green fluorescent protein, selectively to secretory granules in the neurons in the hypothalamoneurohypophysial system. Finally, we review the studies of mice whose genes for oxytocin and, most recently, for the oxytocin and vasopressin receptors have been knocked out through homologous recombination.

Long-term effects of ciliary neurotrophic factor on the survival of vasopressin magnocellular neurones in the rat supraoptic nucleus in vitro

The use of hypothalamic organotypic cultures for the long-term study of mechanisms in magnocellular neurones (MCNs) of the hypothalamic-neurohypophysial system has been limited by the relatively poor maintenance of the vasopressin MCNs in vitro. Recent studies have shown that addition of ciliary neurotrophic factor (CNTF) to the media significantly reduced the apoptosis of both oxytocin and vasopressin MCNs. Here, we studied various temporal factors in the CNTF treatment that can influence the efficacy of MCN survival. Immunohistochemistry was used to identify and count surviving vasopressin and oxytocin MCNs in the supraoptic nucleus (SON) in hypothalamic slices cultured in the presence of CNTF (10 ng/ml media) for various time intervals, and in situ hybridization for vasopressin mRNA was used to evaluate the vasopressin mRNA gene expression in the SON under the same conditions. The presence of CNTF in the medium for 10 days produced a maximal increase in the survival of vasopressin MCNs (by 11-fold) and in the survival of oxytocin-MCNs (by approximately four-fold) over controls. These effects persisted for an additional 7-10 days even in the absence of CNTF. The ability of CNTF to increase survival of the MCNs or increase vasopressin mRNA levels in the SON required that the CNTF be present during the initial 7-10 days of culture. CNTF failed to rescue vasopressin or oxytocin MCNs when added to the media only for the last 7 days of a total of 14 days in vitro. Similar results were observed when SON vasopressin mRNA levels were measured. These results indicate that the presence of CNTF is required at the outset to rescue the vasopressin and oxytocin MCN from axotomy induced apoptosis, and that, after 10 days in CNTF, the MCNs no longer require the CNTF for survival.

Regulatory domains in the intergenic region of the oxytocin and vasopressin genes that control their hypothalamus-specific expression in vitro

Previous studies of oxytocin (OT) and vasopressin (VP) cell-specific gene expression in the hypothalamus using transgenic mouse and rat models focused attention on the intergenic region (IGR) as the site of critical enhancer elements. In this study, we used organotypic slice-explant cultures of rat hypothalamus as in vitro models, and particle-mediated gene transfer (biolistics) transfection methods to identify critical DNA sequences in the IGR between the OT and VP genes responsible for hypothalamic-specific gene expression. Reducing the 5' flanking region in the mouse VP gene from 3.5 kbp to 288 bp did not alter the efficacy of its expression in hypothalamic slices. All subsequent VP constructs were based on this 288 bp VP gene construct with changes made only to the IGR. These studies, which used various constructs with OT and VP promoters driving enhanced green fluorescent protein reporter gene expression, demonstrated that the IGR is necessary for OT and VP gene expression in hypothalamic slices in vitro. The DNA sequences in the IGR responsible for both OT and VP gene expression were located in a 178 bp domain immediately downstream of exon 3 of the VP gene. In addition, another domain in the IGR, 430 bp immediately downstream of exon 3 of the OT gene, contained a positive regulatory element for OT gene expression in the hypothalamus. Alignment of the DNA sequences in the 178 and 430 bp domains reveals four common sequences (motifs) that may be candidates for the putative enhancers in the IGR that regulate OT and VP gene hypothalamic-specific expression.

GABAergic control of neuropeptide gene expression in parvocellular neurons of the hypothalamic paraventricular nucleus

To assess the functional impact of local inhibitory gamma-aminobutyric acid (GABA)ergic interneuron population on the cellular and transcriptional activity of parvocellular neurosecretory neurons in the hypothalamic paraventricular nucleus (PVH), we followed the expression of corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP) genes along with the activation marker c-fos in response to the blockade of GABA-A receptors. First, we analysed the effect of the GABA-A receptor antagonist bicuculline methiodide (BMI) in organotypic cultures of hypothalamic slices. These preparations preserve the cytoarchitecture of CRH-synthesizing cell populations and elements of local interneuronal networks, while remote connections originating from limbic- and brainstem areas are missing. In vitro, BMI resulted in a selective induction of c-Fos immunoreactivity that was localized exclusively to the PVH and upregulated both CRH mRNA and AVP hnRNA levels. Local microinjection of BMI into the paraventricular region of freely moving rats increased the adrenocorticotropin secretion and activated PVH neurons ipsilateral to the injection. c-Fos immunoreactivity was distributed within the PVH and in the perinuclear region, where it appeared in GABAergic and also in non-GABAergic profiles. This treatment induced AVP hnRNA expression in the parvocellular compartment without any reliable stimulation of CRH transcription in the parvocellular- and AVP hnRNA levels in the magnocellular neurons. These results reveal an intrinsic GABAergic mechanism in the PVH microenvironment that by itself, without limbic contribution, impinges a tonic inhibitory influence on the parvocellular CRH neurons in vitro. In vivo, remote inputs are superimposed on the local circuit, allowing differential transcriptional regulation of CRH and AVP genes in the hypophysiotropic neurons.

Removal of PSA from NCAM affects the survival of magnocellular vasopressin- and oxytocin-producing neurons in organotypic cultures of the paraventricular nucleus

The expression of the polysialic acid neural cell adhesion molecule (PSA-NCAM) in the hypothalamo-neurohypophyseal system has been correlated with morphofunctional plasticity. In this study, we investigated the role of PSA-NCAM in the survival of oxytocin (OT)- and vasopressin (VP)-producing magnocellular cells of this system. We used a recently developed organotypic slice culture model of the rat hypothalamic paraventricular nucleus (PVN) in which ciliary neurotrophic factor (CNTF) and leukemia inhibitory factor (LIF) are potent survival factors for magnocellular neurons. We demonstrate by means of confocal microscopy that cultured magnocellular VP and OT neurons express strong immunoreactivity for PSA-NCAM. Removal of PSA from NCAM by the enzyme Endo N leads to a significant loss of both VP and OT neurons in the presence of low concentrations of CNTF. Endo N treatment did not change cell survival in the presence of LIF. These results suggest that, in addition to its role in neuro-glial plasticity, PSA-NCAM might also influence the trophic factor responsiveness of hypothalamic VP and OT neurosecretory cells.

The magnocellular neuronal phenotype: cell-specific gene expression in the hypothalamo-neurohypophysial system

The magnocellular oxytocin (OT) and vasopressin (VP) neurons of the hypothalamo-neurohypophysial system are exceptional cell biological models to study mechanisms of cell-specific gene expression and neurosecretion of neuropeptides in the central nervous system. Single cell differential gene expression experiments have further defined these phenotypes by identifying novel and distinct regulatory molecules in these neurons. Transgenic mouse studies have led to the intergenic region (IGR) hypothesis, which states that the DNA sequences between the OT- and VP-genes contain critical enhancer sites for their cell-specific expression. The recent cloning and sequencing of the human IGR, and its comparison with the mouse IGR sequence has identified conserved sequences as putative, cell-specific enhancer sites which are now being evaluated by biolistic transfections of organotypic hypothalamic cultures. With these data, it is possible to target the gene expression of specific molecules to magnocellular neurons both in vivo and in vitro, in order to perturb and/or visualize neurosecretory and other processes.