Twenty-Four Hour Pattern of Prolactin Levels in Female Rats Subjected to Transection of the Mesencephalic Raphe or Ablation of the Suprachiasmatic Nuclei

Abstract

The present study was undertaken to evaluate the 24-hour periodicity in serum prolactin levels subsequent to transecting the ascending serotonergic system or ablating the suprachiasmatic nuclei (SCN) of adult (185 g) female rats. The ascending serotonergic system was transected at the level of the rostral mesencephalon using a 1.5 mm wide knife and the SCN was ablated with a modified Halász-Pupp knife. The effect of raphe transection (RT) or SCN ablation on the circadian rhythm in nonstress serum prolactin levels was assessed 45 days after surgery by measuring with radioimmunoassay the serum prolactin concentration in serial blood samples obtained from the tail vein of lightly restrained rats. Serum prolactin concentration in control and RT animals showed circadian periodicity; peak levels occurred during the midafternoon, 4 h prior to the dark phase of the lighting regime (lights on at 4 a.m., off at 6 p.m.). The amplitude of the fluctuations of both groups varied markedly and were related to the estrous cycle. However, RT animals showed a reduced amplitude in the rhythm. In controls peak prolactin levels on days of proestrus and estrus were 15–20 times higher than on days of diestrus. In contrast, serum prolactin levels in SCN-ablated rats did not vary with a circadian periodicity but rather showed random, low amplitude fluctuations. Reproductive cyclicity was also abolished by SCN ablation, i.e., SCN-ablated rats presented persistent vaginal cornification. These data indicate that circadian periodicity in serum prolactin levels is not compromised by sectioning the ascending serotonergic fibers but is abolished after ablating the SCN.

A chronic technique for high frequency blood sampling/transfusion in the freely behaving rat which does not affect prolactin and corticosterone secretion

“…If the blood sampling procedure had been stressful the effect would have been consistent and much more pro¬ nounced. A circadian rhythm in prolactin secretion could not be established, but this rhythm is very weak, particularly on day 1 of dioestrus (authors, un¬ published results; Dunn, Johnson, Castro & Svenson, 1980). The pro-oestrous afternoon surge of prolactin secretion was not affected by the blood sampling pro¬ cedure (Fig.…”

Localization and developmental pattern of vasoactive intestinal polypeptide binding sites in the human hypothalamus

“…Moreover, the presence of high density of VIP binding sites and positive immunoreactive cells in the suprachiasmatic nucleus are in good agreement with the possible involvement of VIP in the neural regulation of many biological rhythms. For instance, experimental studies report the presence of nycthemeral variations of VIP in the rat suprachiasmatic nucleus (Alberts et al, 1987;Okamoto et al, 1991;Takahashi et al, 1989) underlying rhythmicity of hypothalamic pituitary hormone secretion such as prolactin (Dunn et al, 1980).…”

Effects of 5-hydroxytryptamine uptake blockers on the concentration in brain of 5-hydroxytryptamine and 5-hydroxyindoleacetic acid in male rats, pro-oestrous rats and ovariectomized rats treated with oestrogen and progesterone

“…The AH region contains the suprachiasmatic nuclei which are important for the control of the rhythmic release of LH and prolactin (Dunn, Johnson, Castro & Swenson, 1980;Héry, Dusticier & Calas, 1982), and whose activity is modulated by input from the raphe nuclei (Van de Kar & Lorens, 1979; Van de Kar & Bethea, 1982). The fact that there was no change in the 5-HIAA/5-HT ratio in the AH in any model after alaproclate at a time at which there were changes in both the PH and the raphe nuclei suggests that neu¬ rones in this area may respond differently or not at all to alaproclate.…”