Circadian rhythms of prolactin secretion in neonatal female rabbits after acute separation from their mothers

Newborn rabbits (Oryctolagus cuniculus) are only nursed for 3–5 min every 24 h and show a circadian increase in activity in anticipation of nursing. The objective of this study was to determine, in neonatal female rabbits after acute separation from the doe for 48 h, the changes in 24-h rhythms of plasma prolactin and median eminence and anterior pituitary concentration of dopamine (DA) and serotonin (5HT). In addition, median eminence concentration of the excitatory amino acid transmitters glutamate (GLU) and aspartate (ASP) and of the inhibitory amino acid transmitters γ-aminobutyric acid (GABA) and taurine (TAU) was measured. A significant 21% increase of circulating prolactin occurred in isolated pups. In controls pups, plasma prolactin levels showed two peaks, during the first half of the light phase and at the beginning of the scotophase, respectively. In the isolated pups, a phase advance of about 4 h occurred for the two prolactin peaks. Hemicircadian changes of median eminence DA were found in controls, whereas a single daily peak (at 17:00 h) was found in the separated pups. Plasma prolactin and median eminence DA correlated significantly and inversely in the control group only. Pituitary DA content exhibited a single peak in controls and a hemicircadian pattern in isolated pups. Plasma prolactin and pituitary DA correlated significantly in isolated pups only 00000. Pup isolation decreased median eminence 5HT levels, augmented pituitary 5HT levels and disrupted their 24 h rhythmicity. Circulating prolactin correlated inversely with median eminence 5HT and directly with adenohypophysial 5HT only in controls. Isolation of pups generally modified the 24 h pattern of median eminence excitatory and inhibitory amino acid content by causing a prominent decrease at the beginning of the light phase. The results indicate that circadian rhythmicity of prolactin secretory mechanisms in female rabbit pups is significantly affected by pup’s isolation from the doe.