Nocturnal light pulses selectively induce Egr-1/NGFI-A protein in periventricular hypophysiotrophic somatostatinergic neurons.
Recent reports showing that circadian light cues may induce gene-specific patterns of expression in periventricular hypothalamic neurons has extended the functional correlates of light-pulse stimuli, which are conventionally restricted to circadian phase-setting actions within the suprachiasmatic nucleus (ScN). The aims of the present study were, first, to broaden these observations to the protein level using an Egr-1/NGFI-A antibody, and second to investigate the cell-type specificity of induction with respect to associated hypophysiotrophic neurons. In order to co-localize Egr-1 with neuroendocrine peptides, a same-species, double immunofluorescence protocol has been used. The Egr-1 antibody used for immunohistochemistry was first characterized by Western analysis, and we have shown that the C19 antisera detects a single 75 kDa protein species, which has a primarily nuclear subcellular localization. Immunohistochemical analysis has shown that Egr-1 protein is markedly induced by a 1 h nocturnal light pulse both in the body of the suprachiasmatic nucleus and in a dorsal ScN zone, which extends up into the periventricular nucleus (PeN). In contrast, induction of Egr-1 was not observed within the arcuate region of the hypothalamus. Double immunofluorescence histochemistry has shown that Egr-1 is extensively, although not exclusively, co-localized with somatostatin in PeN neurons. The selective induction of the 75 kDa protein product of the egr-1 gene in PeN somatostatinergic neurons, as contrasted with hypophysiotrophic (somatostatin and growth hormone-releasing hormone [GH-RH]) neurons of the arcuate nucleus is indicative of a cell- and stimulus-specific neuroendocrine paradigm, which may be used to address temporal characteristics of somatostatin function that determine pulsatile growth-hormone secretion.
Slade
J P
JP
School of Biosciences, Cardiff University, UK.
Knight
C
C
Carter
D
D
D000818:Animals; D001111:Arcuate Nucleus of Hypothalamus / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D051766:Early Growth Response Protein 1; D005786:Gene Expression Regulation; D007031:Hypothalamus / Q000378:metabolism*; D017874:Immediate-Early Proteins / Q000378:metabolism*; D015151:Immunoblotting; D007150:Immunohistochemistry; D008297:Male; D008856:Microscopy, Fluorescence; D009474:Neurons / Q000378:metabolism; D010775:Photic Stimulation; D010902:Pituitary Gland / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013004:Somatostatin / Q000378:metabolism*; D013493:Suprachiasmatic Nucleus / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism*
D004268:DNA-Binding Proteins; D051766:Early Growth Response Protein 1; C486110:Egr1 protein, rat; D017874:Immediate-Early Proteins; D014157:Transcription Factors; D013004:Somatostatin