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 (CNTFRα) in the rat MNS. Robust immunoreactivity for CNTFRα 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 CNTFRα. Robust hybridization of an anti-sense [³⁵S]-cRNA probe to CNTFRα 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 CNTFRα mRNA by magnocellular neurons 7 days following unilateral transection of the hypothalamo-neurohypophysial tract. The level of CNTFRα 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 CNTFRα 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 S100β, 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.     

The efferent projections of the subfornical organ of the rat: A circumventricular organ within a neural network subserving water balance

The efferent projections of the subfornical organ (SFO) of rats were traced using the autoradiographic method of following anterograde transport of labelled proteins through axons.The efferents of the SFO go to two different areas. The first is the anteroventral third ventricular area of the preoptic region and the second is the hypothalamus particularly the neurosecretory, magnocellular nuclei. Specifically, the apparent terminal fields in the first area are in the nucleus medianus of the medial preoptic area (NM), the organum vasculosm of the lamina terminalis (OVLT), and the anterior periventricular area (PeV). Many efferent fibers to this area emerge from the rostral SFO, pass anteriorly over the anterior commissure in the midline and either descend along the anterior border of the NM or enter the PeV dorsally just beneath the anterior commissure. The apparent terminal fields within the hypothalamus are in the anterior and tuberal supraoptic nuclei (SON_a and SON_t), the paraventricular nucleus (PVN) including its rostral accessory cluster, the nucleus circularis (NC), the dorsal perifornical area (PFd), and in both the lateral preoptic area and lateral hypothalamus adjacent to the SON. Many efferent fibers to the hypothalamus emerge from the rostral SFO and enter the columns of the fornix, diverge with the ventral stria medullari to disperse medially and laterally over the columns of the fornix and along their dorsal border at the anterior dorsal level of the columns trajectory through the hypothalamus.These findings are discussed in terms of the SFO's role within a neural network mediating water balance behaviorally and physiologically.     

Ion transport peptide splice forms in central and peripheral neurons throughout postembryogenesis of Drosophila melanogaster

Ion transport peptides (ITPs) belong to a large arthropod neuropeptide family including crustacean hyperglycaemic hormones and are antidiuretic hormones in locusts. Because long and short ITP isoforms are generated by alternative splicing from a single gene in locusts and moths, we investigated whether similarly spliced gene products occur in the nervous system of Drosophila melanogaster throughout postembryogenesis. The itp gene CG13586 was reanalyzed, and we found three instead of the two previously annotated alternatively spliced mRNAs. These give rise to three different neuropeptides, two long C-terminally carboxylated isoforms (DrmITPL1 and DrmITPL2, both 87 amino acids) and one short amidated DrmITP (73 amino acids), which were partially identified biochemically. Immunocytochemistry and in situ hybridization reveal nine larval and 14 adult identified neurons: four pars lateralis neurosecretory neurons, three hindgut-innervating neurons in abdominal ganglia, and a stage-specific number of interneurons and peripheral bipolar neurons. The neurosecretory neurons persist throughout postembryogenesis, form release sites in corpora cardiaca, and invade corpora allata. One type of ITP-expressing interneuron exists only in the larval and prepupal subesophageal ganglia, whereas three types of interneurons in the adult brain arise in late pupae and invade circumscribed neuropils in superior median and lateral brain areas. One peripheral bipolar and putative sensory neuron type occurs in the larval, pupal, and adult preterminal abdominal segments. Although the neurosecretory neurons may release DrmITP and DrmITPL2 into the haemolymph, possible physiological roles of the hindgut-innervating and peripheral neurons as well as the interneurons are yet to be identified.     

Heterogeneity of neurons in the crustacean X-organ as revealed by intracellular recording and injection of horseradish peroxidase

The intracellular injection technique of HRP with simultaneous recordings of intracellular potential was applied to the crab X-organ-sinus gland peptidergic neurosecretory neurons. At least two classes of neurons were discriminated from the usual type of neurosecretory neurons morphologically as well as electrophysiologically. Possible roles of those neurons were suggested as the modulation and coordination of activities of the neurosecretory system.     

A case of Kabuki make-up syndrome with central diabetes insipidus and growth hormone neurosecretory dysfunction

A case of a 6 year old boy with Kabuki make-up syndrome with central diabetes insipidus and growth hormone neurosecretory dysfunction is reported. Magnetic resonance imaging revealed abnormal findings of the pituitary gland and stalk. Good catch-up growth was obtained by treatment with growth hormone. These findings suggest that hypothalamic-pituitary dysfunction might be involved in Kabuki make-up syndrome.     

Electron microscope immunohistochemical localization of neurophysin in the rat hypothalamus and pituitary

In order to identify the organelles associated with neurophysin in neurosecretory neurons and axons, an electron microscopic immunohistochemical localization of this protein has been performed in the rat hypothalamus and posterior pituitary gland. Rabbit antiserum to human neurophysin II (which shows a cross-reaction with rat neurophysin) was used as antibody and the complex peroxidase-rabbit antiperoxidase (PAP) as the marker with unlabelled antirabbit globulin. PAP molecules indicating the presence of neurophysin were detected in the secretory neurons of both supraoptic and paraventricular nuclei, in axons of the internal layer of the median eminence and in the nerve terminals of the posterior pituitary gland. The reaction product was observed only over the secretory granules, all other organelles being negative. In the positive cells and axons, all the secretory granules present were usually labelled. These results demonstrate for the first time that neurophysin is associated with neurosecretory granules which also contain presumably either vasopressin or oxytocin.     

Ultrastructural localization of inhibin β- and somatostatin-28-immunoreactivities in the paraventricular and supraoptic nuclei

Recent studies have supported the existence of projections to the paraventricular and supraoptic nuclei of the hypothalamus that arise from non-catecholaminergic neurons in the nucleus of the solitary tract, whose terminal distribution is suggestive of interactions with both parvocellular and magnocellular neurosecretory neurons. Pre-embedding immunolabeling methods were used to compare and characterize the termination patterns of axons immunoreactive for two putative markers for this projection system, inhibin β and somatostatin-28, at the ultrastructural level. Axon terminal profiles stained fro either peptide were found to form symmetric or asymmetric junctions predominantly with the shafts of unlabeled dendrites of varying caliber. A small percentage of peptidergic terminals was found in both hypothalamic nuclei to engage in so-called ‘shared synapses’, where a single terminal profile contacted two postsynaptic elements. Axo-somatic terminations were relatively rarely seen in the supraoptic nucleus, but were somewhat more abundant in the paraventricular nucleus. These comprised principally symmetric junctions onto the somatic membranes of an ostensibly mixed population of cells, some of which bore apparent neurosecretory specializations. Combined immunoperoxidase and immuno-autoradiographic staining methods were used to estimate the extent to which either terminal type interacts with oxytocin neurons. Oxytocin stained elements comprised a minority of the postsynaptic targets of both peptidergic terminal types in the paraventricular nucleus, and a scant majority of those in the supraoptic nucleus. These results support the view that peptidergic neurons in the caudal nucleus of the solitary tract interact synaptically with multiple cell types in the parvocellular division of the paraventricular nucleus, and preferentially with oxytocinergic elements in the magnocellular neurosecretory system.     

Terminal degeneration in supraoptic nucleus following subfornical organ lesions: ultrastructural observations in the rat

A projection from the subfornical organ (SFO) to the supraoptic nucleus, recently identified in light microscopic studies, was examined at the ultrastructural level following lesions in SFO. After 18–36 h, axon terminal degeneration was identified in axosomatic contacts with supraoptic neurosecretory neurons, and in axodendritic contacts within and around the supraoptic nucleus. These observations confirm a monosynaptic pathway from SFO to supraoptic neurosecretory neurons that may participate in the release of vasopressin following activation of angiotensin II receptors in SFO.     

Monoamines in the caudal neurosecretory complex: Biochemistry and immunohistochemistry

Monoaminergic inputs to the caudal neurosecretory complex (CNc) of Poecilia latipinna have been identified using histofluorescence and immunohistochemical techniques. The present study was undertaken to identify specific monoamines and determine the relative contribution of indolamines and catecholamines in supraspinal and intrinsic innervation of the nucleus. The CNc was deafferented by transecting the spinal cord rostral to the CNc. Ten days subsequently, CNc of spinal-transected and control fish were processed for either biochemical or immunohistochemical analysis. Norepinephrine and serotonin were detected in pooled samples of control CNc. Following deafferentation, the content of both monoamines was diminished. Using immunohistochemical labeling for serotonin or for the catecholamine-synthesizing enzymes, tyrosine hydroxylase (TH) or dopamine-beta-hydroxylase (DBH), the number of monoamine fibers was decreased in deafferented CNc compared to control. A substantial serotonergic innervation remains after deafferentation, as evidenced by serotonin-positive neurons and heavy, varicose fibers. Occasional TH/DBH-positive cells and fibers remain after deafferentation. These data suggest that both norepinephrine and serotonin are associated with descending supraspinal projections, while serotonin predominates as the intrinsic monoamine.