In mammals, the increased secretion of arginine-vasopressin (AVP) (antidiuretic hormone) and oxytocin (natriuretic hormone) is a key physiological response to hyperosmotic stress. In this study, we examined whether chronic hyperosmotic stress weakens GABA A receptor-mediated synaptic inhibition in rat hypothalamic magnocellular neurosecretory cells (MNCs) secreting these hormones. Gramicidin-perforated recordings of MNCs in acute hypothalamic slices prepared from control rats and ones subjected to the chronic hyperosmotic stress revealed that this challenge not only attenuated the GABAergic inhibition but actually converted it into excitation. The hyperosmotic stress caused a profound depolarizing shift in the reversal potential of GABAergic response (E GABA ) in MNCs. This E GABA shift was associated with increased expression of NaϪ cotransporter 1 (NKCC1) in MNCs and was blocked by the NKCC inhibitor bumetanide as well as by decreasing NKCC activity through a reduction of extracellular sodium. Blocking central oxytocin receptors during the hyperosmotic stress prevented the switch to GABAergic excitation. Finally, intravenous injection of the GABA A receptor antagonist bicuculline lowered the plasma levels of AVP and oxytocin in rats under the chronic hyperosmotic stress. We conclude that the GABAergic responses of MNCs switch between inhibition and excitation in response to physiological needs through the regulation of transmembrane Cl Ϫ gradients.

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The ability to respond to environmental temperature variation is essential for survival in animals. Flies show robust temperature-preference behaviour (TPB) to find optimal temperatures. Recently, we have shown that Drosophila mushroom body (MB) functions as a center controlling TPB. However, neuromodulators that control the TPB in MB remain unknown. To identify the functions of dopamine in TPB, we have conducted various genetic studies in Drosophila. Inhibition of dopamine biosynthesis by genetic mutations or treatment with chemical inhibitors caused flies to prefer temperatures colder than normal. We also found that dopaminergic neurons are involved in TPB regulation, as the targeted inactivation of dopaminergic neurons by expression of a potassium channel (Kir2.1) induced flies with the loss of cold avoidance. Consistently, the mutant flies for dopamine receptor gene (DopR) also showed a cold temperature preference, which was rescued by MB–specific expression of DopR. Based on these results, we concluded that dopamine in MB is a key component in the homeostatic temperature control of Drosophila. The current findings will provide important bases to understand the logic of thermosensation and temperature preference decision in Drosophila.

Recent studies reporting trans‐differentiation of mononucleated cells derived from human umbilical cord blood into neuronal cells aroused interest among investigators for their clinical implication and significance in regenerative medicine. In the present study, purified populations of hematopoietic stem cells were isolated via magnetic bead sorting and fluorescence‐activated cell sorter (FACS) using a specific CD133 antibody, a cell type‐specific marker for hematopoietic stem cells, and grown in culture in the presence of retinoic acid (RA). CD133+ hematopoietic stem cells expressed neuronal and glial phenotypes after RA treatment. RT‐PCR analysis indicated that the RA treated CD133+ cells expressed mRNA transcripts for ATP‐binding cassettes transporter ABCG2 (a universal stem cell marker), nestin (a specific cell type marker for neural stem cells), Musashi1 (a specific marker for neural stem cells) and RA receptors (RAR) including RAR‐α, RAR‐β, and retinoid X receptor (RXR)‐γ. RA‐treated CD133+ cells expressed mRNA transcripts for neuron‐specific markers neurofilament proteins (NF‐L, ‐M, ‐H) and synaptophysin as determined by RT‐PCR, structural proteins characteristic of neurons including tubulin β III and neuron specific enolase (NSE) by Western blot, and neuron‐specific markers NeuN and microtubule‐associated protein‐2 (MAP2) by immunocytochemistry. RA‐treated CD133+ cells also expressed the astrocyte‐specific marker glial fibrillary acidic protein (GFAP), as demonstrated by RT‐PCR, Western blot, and immunocytochemistry. In addition, RA‐treated CD133+ cells expressed cell type‐specific markers for oligodendrocytes including myelin basic protein (MBP) as shown by RT‐PCR, proteolipid protein (PLP) by Western blot analysis, and cyclic nucleotide phosphodiesterase (CNPase) by immunostaining. Upregulated expression of several basic helix‐loop‐helix (bHLH) transcription factors important for early neurogenesis, including Otx2, Pax6, Wnt1, Olig2, Hash1 and NeuroD1, was also demonstrated in CD133+ cells after RA treatment. These results indicate that human cord blood‐derived CD133+ hematopoietic stem cells could trans‐differentiate into neural cell types of neuron‐like cells, astrocytes, and oligodendrocytes by RA treatment. © 2003 Wiley‐Liss, Inc.