Aspects of the narcolepsy-cataplexy syndrome in O/E3-null mutant mice.

Orexins (hypocretins) are peptide neurotransmitters produced by a small group of neurons located exclusively in the lateral hypothalamus (LH). Orexins modulate arousal, and as a result, have profound effects on feeding behavior and the sleep-wake cycle. Loss of orexin producing neurons leads to a narcoleptic phenotype, characterized by sudden transitions from vigilance to rapid eye movement (REM) sleep (direct transition to REM, DREM) observed in electroencephalogram (EEG) and electromyogram (EMG) recordings. In this study, we demonstrate that mice lacking the basic helix-loop-helix transcription factor O/E3 (also known as ebf2) have a decrease in orexin-producing cells in the LH, in addition to a severely impaired orexinergic innervation of the pons. These changes in the orexinergic circuit of O/E3-null animals induce a narcoleptic phenotype, similar to the one arising in orexin-deficient and orexin-ataxin-3 mice. Taken together, our results suggest that O/E3 plays a central role during the establishment of a functional orexinergic circuit by controlling the expression of essential hypothalamic neurotransmitter and the correct development of the nerve fibers arising from the hypothalamus. This is the first report regarding the narcolepsy-cataplexy syndrome in O/E3-null mice, which adds the importance of transcription factors in the regulation of neural subpopulations that control the sleep-wake cycle.

Transforming growth factor-alpha induces neurogenesis and behavioral improvement in a chronic stroke model.

Transforming growth factor-alpha (TGFalpha) is a powerful endogenous mitogen and neurotrophic factor, which has previously been shown to induce a massive proliferative response in the brains of Parkinson's disease model rats injured by an acute neurotoxic lesion. We now show that TGFalpha can also produce a massive proliferative response in rat brains subjected to stroke caused by a middle cerebral artery occlusion (MCAO), even when the growth factor is administered as late as 4 weeks after injury. This combination of stimuli provokes DNA synthesis, shown by 5'-bromo-2-deoxyuridine incorporation, throughout the ependymal layer and subventricular zone (SVZ) of the forebrain during the 4 weeks of growth factor administration. The newly generated cells migrate preferentially along and ventral to the corpus callosum (CC) and external capsule to the site of the injury where many of them differentiate into several site-appropriate neuronal phenotypes in association with near complete (99%) behavioral recovery. We conclude that the injury response of endogenous neural stem cells as well as behavioral recovery can be significantly enhanced by application of TGFalpha, and that this approach represents a potential therapeutic strategy for chronic stroke and other neurological damage in human patients.

BDNF increases the early expression of TRH mRNA in fetal TrkB+ hypothalamic neurons in primary culture.

Known effects of neurotrophins in the developing central nervous system include induction or regulation of peptide expression. Hypothalamic postmitotic thyrotropin-releasing hormone (TRH)-producing neurons may require neurotrophins for survival and/or differentiation. This issue was investigated using primary cell cultures derived from 17-day-old fetal rat hypothalamus seeded in serum-free medium and analysed up to 4 days in vitro culture. Neurotrophin receptor (TrkB and TrkC) mRNA expression was detected by RT-PCR in fetal hypothalamus and throughout the culture period. Western blots confirmed the expression of the full-length proteins in vitro. Semi-quantitative RT-PCR showed that the addition of brain-derived neurotrophic factor (BDNF) increases TRH mRNA levels while the addition of neurotrophin-3 does not. TRH cell content was not modified. Studies on the effect of cell density or homologous conditioned medium demonstrated that endogenous factors probably contribute to determine TRH mRNA levels. One of these factors was BDNF because basal TRH mRNA levels were reduced by the addition of a Trk inhibitor or anti-BDNF. TrkB mRNA was expressed in 27% of cells and TRH mRNA in 2% of cells. The number of TRH+ cells was not affected by BDNF treatment. Forty-eight per cent of TRH neurons contained TrkB mRNA; these neurons had higher amounts of TRH mRNA than TrkB- neurons. Only TrkB+ cells responded to BDNF by increasing their TRH mRNA levels suggesting that BDNF may directly affect TRH biosynthesis. In conclusion, fetal hypothalamic TRH neurons are probably heterogeneous in regard to the neurotrophic factors enhancing peptide and mRNA levels. BDNF enhances TRH mRNA levels in a population of TrkB+ fetal hypothalamic TRHergic neurons in primary culture. However, additional influences may be necessary for the establishment of peptide phenotype in the TrkB+ neurons.