Low wnt/β-catenin signaling determines leaky vessels in the subfornical organ and affects water homeostasis in mice

The circumventricular organs (CVOs) in the central nervous system (CNS) lack a vascular blood-brain barrier (BBB), creating communication sites for sensory or secretory neurons, involved in body homeostasis. Wnt/β-catenin signaling is essential for BBB development and maintenance in endothelial cells (ECs) in most CNS vessels. Here we show that in mouse development, as well as in adult mouse and zebrafish, CVO ECs rendered Wnt-reporter negative, suggesting low level pathway activity. Characterization of the subfornical organ (SFO) vasculature revealed heterogenous claudin-5 (Cldn5) and Plvap/Meca32 expression indicative for tight and leaky vessels, respectively. Dominant, EC-specific β-catenin transcription in mice, converted phenotypically leaky into BBB-like vessels, by augmenting Cldn5+vessels, stabilizing junctions and by reducing Plvap/Meca32+ and fenestrated vessels, resulting in decreased tracer permeability. Endothelial tightening augmented neuronal activity in the SFO of water restricted mice. Hence, regulating the SFO vessel barrier may influence neuronal function in the context of water homeostasis.

Glutamate and GABA Activate Different Receptors and Cl− Conductances in Crab Peptide-Secretory Neurons

Responses to rapid application of glutamic acid (Glu) and γ-aminobutyric acid (GABA), 0.01–3 mM, were recorded by whole-cell patch clamp of cultured crab ( Cardisoma carnifex) X-organ neurons. Responses peaked within 200 ms. Both Glu and GABA currents had reversal potentials that followed the Nernst Cl− potential when [Cl−]i was varied. A Boltzmann fit to the normalized, averaged dose-response curve for Glu indicated an EC50 of 0.15 mM and a Hill coefficient of 1.05. Rapid ( t 1/2 ∼ 1 s) desensitization occurred during Glu but not GABA application that required >2 min for recovery. Desensitization was unaffected by concanavalin A or cyclothiazide. N-methyl-D-aspartate, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid, quisqualate, and kainate (to 1 mM) were ineffective, nor were Glu responses influenced by glycine (1 μM) or Mg2+ (0–26 mM). Glu effects were imitated by ibotenic acid (0.1 mM). The following support the conclusion that Glu and GABA act on different receptors: 1) responses sum; 2) desensitization to Glu or ibotenic acid did not diminish GABA responses; 3) the Cl−-channel blockers picrotoxin and niflumic acid (0.5 mM) inhibited Glu responses by ∼90 and 80% but GABA responses by ∼50 and 20%; and 4) polyvinylpyrrolydone-25 (2 mM in normal crab saline) eliminated Glu responses but left GABA responses unaltered. Thus crab secretory neurons have separate receptors responsive to Glu and to GABA, both probably ionotropic, and mediating Cl− conductance increases. In its responses and pharmacology, this crustacean Glu receptor resembles Cl−-permeable Glu receptors previously described in invertebrates and differs from cation-permeable Glu receptors of vertebrates and invertebrates.

Selective Inhibition of Transient K+ Current by La3+ in Crab Peptide-Secretory Neurons

Selective inhibition of transient K+ current by La3+ in crab peptide-secretory neurons. Although divalent cations and lanthides are well-known inhibitors of voltage-dependent Ca2+ currents ( I Ca), their ability to selectively inhibit a voltage-gated K+ current is less widely documented. We report that La3+ inhibits the transient K+current ( I A) of crab ( Cardisoma carnifex) neurosecretory cells at ED50 ∼5 μM, similar to that blocking I Ca, without effecting the delayed rectifier K+ current ( I K). Neurons were dissociated from the major crustacean neuroendocrine system, the X-organ-sinus gland, plated in defined medium, and recorded by whole cell patch clamp after 1–2 days in culture. The bath saline included 0.5 μM TTX and 0.5 mM CdCl2 to eliminate inward currents. Responses to depolarizing steps from a holding potential of −40 mV represented primarily I K. They were unchanged by La3+ up to 500 μM. Currents from −80 mV in the presence of 20 mM TEA were shown to represent primarily I A. La3+ (with TEA) reduced I A and maximum conductance ( G A) by ∼10% for 1 μM and another 10% each in 10 and 100 μM La3+. Normalized G A- V curves were well fit with a single Boltzmann function, with V 1/2 +4 mV and slope 15 mV in control; V 1/2 was successively ∼15 mV depolarized and slope increased ∼2 mV for each of these La3+ concentrations. Cd2+ (1 mM), Zn2+ (200 μM), and Pb2+ (100 μM) or removal of saline Mg2+ (26 mM) had little or no effect on I A. Steady-state inactivation showed similar right shifts (from V 1/2 −39 mV) and slope increases (from 2.5 mV) in 10 and 100 μM La3+. Time to peak I A was slowed in 10 and 100 μM La3+, whereas curves of normalized time constants of initial decay from peak I A versus V c were right-shifted successively ∼15 mV for the three La3+ concentrations. The observations were fitted by a Woodhull-type model postulating a La3+-selective site that lies 0.26–0.34 of the distance across the membrane electric field, and both block of K+ movement and interaction with voltage-gating mechanisms; block can be relieved by depolarization and/or outward current. The observation of selective inhibition of I A by micromolar La3+ raises concerns about its use in studies of I Ca to evaluate contamination by outward current.

Regulatory Influences on Crustacean Neurosecretory Cells

During the last decade, new evidence has been produced on the subtle mechanisms by which invertebrate neurosecretory cell activity is regulated. Multiple synaptic and humoral mechanisms regulate the endogenous activity of secretory neurons. Specific cellular interactions and ionic mechanisms have been disclosed, and new insights are now available on the integrative features of invertebrate neurosecretory systems.

Association of pituitary adenoma with neuronal christoma: A TEM study

The association of a pituitary adenoma with nervous tissue consisting of neuron-like cells and neuropil is a rare abnormality. In the majority of cases, the pituitary tumor is a chromophobic adenoma, accompanied by acromegaly. Histology reveals widely variable proportions of endocrine and nervous tissue in alternating or intermingled patterns. The lesion is perceived as a composite one consisting of two histogenetically distinct parts. It has been suggested that the neuronal component, morphologically similar to secretory neurons of the hypothalamus, may initiate adenoma formation by releasing stimulatory substances. Immunoreactivity for growth hormone releasing hormone (GRH) in the neuronal component of some cases supported this view, whereas other findings such as consistent lack of growth hormone (GH) cell hyperplasia in the lesions called for alternative explanation.Fifteen tumors consisting of a pituitary adenoma and a neuronal component have been collected over a 20 yr. period. Acromegaly was present in 11 patients, was equivocal in one, and absent in 3.