Norepinephrine dialysate levels in the hypothalamic paraventricular nucleus: influence on photoperiod-driven prolactin levels in the female siberian hamster.
Basal prolactin (PRL) levels in Siberian hamsters are modulated by ambient photoperiod via the nocturnal melatonin signal. Recent evidence from our laboratory has demonstrated that norepinephrine (NE), a putative neurochemical regulator of PRL secretion shows photoperiod-dependent fluctuations in the hypothalamic paraventricular nucleus (PVN) that are independent of the pineal melatonin signal. NE content in the PVN is elevated under a short-day photoperiod with a time course that follows the short-day-induced decline in PRL. NE could thus modulate the release of a prolactin-releasing factor that subsequently drives PRL synthesis and release rates. In order to determine whether NE release in the PVN correlates with basal PRL levels, this study evaluated the relationship between extracellular NE levels in the PVN and basal PRL under long- and short-day photoperiod conditions. In addition, the profile of NE during the proestrous surge of PRL was investigated. Female Siberian hamsters were housed either in long-day or short-day photoperiods for 8 weeks. After 6 weeks of photoperiod exposure, the animals were implanted with a stainless steel guide cannula aimed at the PVN. Two weeks later, the animals were fitted with a jugular cannula for serial blood sampling and implanted with an indwelling microdialysis probe. Dialysis samples were collected every 20 min for 5 h (12.00-17.00 h) from short-day-exposed animals and from long-day-exposed animals classified as being either in diestrus or proestrus. Blood samples were collected every hour and analyzed for PRL levels by radioimmunoassay. NE and methoxy-4-hydrophenylglycol (MHPG) levels were significantly higher in short-day-exposed animals, correlating with the suppressed basal secretion of PRL. Both long-day groups had lower NE and MHPG levels, and higher PRL, than the short-day group. However, long-day animals showed a significant decline in NE in proestrus just prior to the onset of the afternoon surge of PRL. These data suggest that NE released within the PVN participates in the regulation of photoperiod effects upon PRL secretion, as well as that of the afternoon surge of PRL on proestrus.
Behavioral Neuroscience Division, Psychology Department, SUNY at Buffalo, Buffalo, NY, USA.
J C
JC
Dodge
L L
LL
Badura
D000818:Animals; D002851:Chromatography, High Pressure Liquid; D006224:Cricetinae; D004031:Diestrus; D004971:Estrus; D005110:Extracellular Space / Q000737:chemistry; D005260:Female; D007986:Luteinizing Hormone / Q000097:blood; D008734:Methoxyhydroxyphenylglycol / Q000032:analysis; D017551:Microdialysis; D009638:Norepinephrine / Q000032:analysis* / Q000378:metabolism; D009929:Organ Size; D010286:Paraventricular Hypothalamic Nucleus / Q000737:chemistry* / Q000378:metabolism; D017111:Phodopus; D017440:Photoperiod; D011359:Proestrus; D011863:Radioimmunoassay; D014599:Uterus / Q000033:anatomy & histology
D008734:Methoxyhydroxyphenylglycol; D007986:Luteinizing Hormone; D009638:Norepinephrine