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Keywords:

  • suprachiasmatic;
  • circadian;
  • neuroendocrine;
  • transmitter;
  • light stimulation

ABSTRACT

Vasopressin (AVP) is both a neuroendocrine hormone located in magnocellular neurosecretory neurons of the hypothalamus of mammals but also a neurotransmitter/neuromodulator in the parvocellular suprachiasmatic nucleus (SCN). The SCN is the endogenous clock of the brain and exhibits a prominent circadian AVP rhythm. We have in this study of the brown 129sv mouse and the visual blind cone–rod homeobox gene knock out mouse (Crx−/−) with degeneration of the retinal rods and cones, but a preserved non-image forming optic system, studied the temporal Avp expression in both the neurosecretory magnocellular and parvocellular vasopressinergic systems in both genotypes. We here present a detailed mapping of all classical hypothalamopituitary and accessory magnocellular nuclei and neurons in the hypothalamus by use of immunohistochemistry and in situ hybridization in both genotypes. Semiquantitative in situ hybridization revealed a very high expression of Avp mRNA in all the magnocellular nuclei compared with a much lower level in the parvocellular suprachiasmatic nucleus. In a series of mice killed every 4 hours, the Avp mRNA expression in the SCN showed a significant daily rhythm with a zenith at late day time and nadir during the dark in both the Crx−/− and the wild type mouse. None of the magnocellular neurosecretory neurons exhibited a diurnal vasopressin expression. Light stimulation of both genotypes during the dark period did not change the Avp expression in the SCN. This shows that Avp expression in the mouse SCN is independent of Crx-regulated photoreceptor systems. J. Comp. Neurol. 521:4061–4074, 2013. © 2013 Wiley Periodicals, Inc.