A comparison of two immediate-early genes, c-fos and NGFI-B, as markers for functional activation in stress-related neuroendocrine circuitry.
The promoter regions of the rat corticotropin-releasing factor (CRF), oxytocin (OT), and vasopressin (AVP) genes contain sequences similar to the cis-acting response element identified for NGFI-B, an immediate-early gene structurally related to the steroid hormone receptor superfamily. Combined immuno- and hybridization histochemical approaches were used to determine whether challenges that influence the synthesis and secretion of CRF, OT, and/or AVP result in altered expression in neurosecretory neurons of NGFI-B and another immediate-early gene, c-fos, which is widely used as a marker for functionally activated neurons. NGFI-B mRNA was found to be expressed at constitutively high levels in the telencephalon, but not in the endocrine hypothalamus, of unperturbed controls; basal levels of c-fos expression were uniformly low throughout the CNS. NGFI-B and c-fos mRNAs, and Fos protein, were induced with a similar time course and in similar neuroendocrine cell types in response to acute hypotensive hemorrhage (15% reduction in blood volume), intravenous injection of interleukin-1 beta (IL-1 beta; 1.87 micrograms/kg), chronic salt loading (7 d maintenance on 2% saline), and acute bilateral adrenalectomy. c-fos mRNA and Fos protein were readily demonstrable in afferent pathways that have been implicated as mediating the neuroendocrine responses in the three stress paradigms; these include medullary catecholaminergic cell groups in response to IL-1 beta and hemorrhage, and cell groups lining the lamina terminalis in response to salt loading. Challenge-specific induction of NGFI-B expression was detectable in these extrahypothalamic cell groups, though with a lesser sensitivity than that required to reveal NGFI-B induction in the hypothalamus, or c-fos expression in these related afferents. These results establish NGFI-B as a useful adjunct to c-fos, for revealing synaptic and/or transcriptional activation in the magno- and parvocellular neurosecretory systems. Differences in the sensitivity of the two markers in revealing functionally related activation in extrahypothalamic regions speak to general issues concerning the use of immediate-early genes in mapping functional circuitry in the CNS.
Chan
R K
RK
Laboratory of Neuronal Structure and Function, Salk Institute, San Diego, California 92186-5800.
Brown
E R
ER
Ericsson
A
A
Kovács
K J
KJ
Sawchenko
P E
PE
D000315:Adrenalectomy; D000818:Animals; D001127:Arginine Vasopressin / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D003346:Corticotropin-Releasing Hormone / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism*; D015870:Gene Expression; D006470:Hemorrhage / Q000378:metabolism; D008297:Male; D008969:Molecular Sequence Data; D009490:Neurosecretory Systems / Q000378:metabolism*; D057105:Nuclear Receptor Subfamily 4, Group A, Member 1; D010121:Oxytocin / Q000235:genetics / Q000378:metabolism; D010286:Paraventricular Hypothalamic Nucleus / Q000378:metabolism / Q000502:physiology; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics* / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D018160:Receptors, Cytoplasmic and Nuclear; D011987:Receptors, Steroid; D012965:Sodium Chloride / Q000494:pharmacology; D013312:Stress, Physiological / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism*
D004268:DNA-Binding Proteins; C539820:Nr4a1 protein, rat; D057105:Nuclear Receptor Subfamily 4, Group A, Member 1; D016760:Proto-Oncogene Proteins c-fos; D012333:RNA, Messenger; D018160:Receptors, Cytoplasmic and Nuclear; D011987:Receptors, Steroid; D014157:Transcription Factors; D001127:Arginine Vasopressin; D012965:Sodium Chloride; D010121:Oxytocin; D003346:Corticotropin-Releasing Hormone