The effect of lactation on induced Fos-like immunoreactivity in the rat hypothalamic paraventricular nucleus.
Lactating rats display a period of blunted hypothalamo-pituitary-adrenal (HPA) response to a variety of stressors. This hyporesponsiveness is reported to be dependent upon continuous mother-pup interactions. In this study, computer-assisted densitometric methods were used to measure levels of induced Fos-like immunoreactivity (FLI) in the hypothalamic paraventricular nucleus (PVN) of lactating and non-lactating rats. Adrenalectomy (ADX) induces elevated levels of FLI in the PVN of non-lactating rats. We have observed that, between post-partum day (pd) 4 and pd 21, the level of ADX-induced FLI in the PVN of lactating rats follows a U-shaped distribution; that the persistence of this phenomenon is dependent upon continued mother-pup interaction and that sustained mother-pup interaction beyond the end of the normal suckling period (pd 21) does not extend the period of refractoriness. We have further determined that both the non-specific neural activator Metrazole, and the glutamate agonist N-methyl-D,L-aspartate (NMA), induced smaller increases in FLI in the PVN of lactating rats compared to non-lactating cohorts, and that the suppressing effect of lactation on Metrazole-induced FLI does not extend to all brain regions. These results suggest that mechanisms responsible for the onset and maintenance of the so-called lactational stress-hyporesponsive period (LSHRP) include altered function of glutamatergic pathways.
Wintrip
N
N
Department of Physiology and Biophysics, Dalhousie University, Faculty of Medicine, Halifax, Nova Scotia, Canada.
Nance
D M
DM
Wilkinson
M
M
D000315:Adrenalectomy; D000818:Animals; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D005260:Female; D007774:Lactation / Q000502:physiology*; D016202:N-Methylaspartate / Q000494:pharmacology; D010286:Paraventricular Hypothalamic Nucleus / Q000187:drug effects / Q000502:physiology*; D010433:Pentylenetetrazole / Q000494:pharmacology; D049590:Postpartum Period / Q000502:physiology*; D016760:Proto-Oncogene Proteins c-fos / Q000032:analysis / Q000096:biosynthesis*; D051381:Rats; D017207:Rats, Sprague-Dawley
D018690:Excitatory Amino Acid Agonists; D016760:Proto-Oncogene Proteins c-fos; D016202:N-Methylaspartate; D010433:Pentylenetetrazole