Activity of vasoactive intestinal peptide and serotonin in the paraventricular nucleus reflects the periodicity of the endogenous stimulatory rhythm regulating prolactin secretion.

PRL secretion in the female rat is regulated by an endogenous stimulatory rhythm (ESR) of prolactin-releasing factors of hypothalamic origin which has a bimodal periodicity with distinct nocturnal (N) and diurnal (D) phases. The N phase reaches peak magnitude by 0300 h and the D phase reaches peak magnitude by 1700 h. This rhythm was first unmasked in ovariectomized rats by correctly timed injection of a dopamine antagonist. OT, vasoactive intestinal peptide (VIP), and serotonin (5-HT) are differentially involved in generating the ESR. Pharmacological studies suggest that OT is the neurohormone and VIP and 5-HT are neuromodulators which act to stimulate OT release. Recently, we reported that activity of OTergic neurons in the paraventricular nucleus (PVN) and OT concentrations in the anterior pituitary mirror the periodicity of the ESR. The present experiments were conducted to determine if VIP and 5-HT activity in the hypothalamus also mirrors the periodicity of the ESR. Push-pull cannulae were surgically implanted in the PVN of ovariectomized female rats. Following recovery, push-pull perfusion was conducted from either 0600-1400 h, 1400-2200 h, or 2200-0600 h. VIP was measured in perfusates by RIA. There was no difference in VIP pulse frequency between rats perfused during the three periods studied. However, animals perfused from 2200-0600 h had significantly greater pulse amplitude as compared to rats at either 0600-1400 h or 1400-2200 h. Activity of 5-HTergic neurons in the hypothalamus was studied by estimating the turnover of 5-HT 10 min following the injection of pargyline. Hypothalamic nuclei were dissected using Palkovits' punch technique and 5-HT concentration assayed by HPLC in conjunction with electrochemical detection. Turnover of 5-HT was estimated by calculating the slope of the accumulation of 5-HT over 10 min at differing times of day using least squares regression analysis. There was a distinct diurnal rhythm of 5-HT accumulation in the PVN. Rats killed at 1700 h had significantly greater slopes of 5-HT accumulation in the PVN than rats killed at either 0300 or 1200 h. Similarly, there was a diurnal rhythm of 5-HT turnover in the suprachiasmatic nucleus. Rats sampled at either 1200 or 1700 h had significantly greater slopes of 5-HT accumulation in the suprachiasmatic nucleus than rats sampled at 0300 h. There was no diurnal rhythm of 5-HT turnover evident in either the median eminence or the supraoptic nucleus.(ABSTRACT TRUNCATED AT 400 WORDS)     

Androgen receptor YAC transgenic mice carrying CAG 45 alleles show trinucleotide repeat instability

X-linked spinal and bulbar muscular atrophy (SBMA) is caused by a CAG repeat expansion in the first exon of the androgen receptor (AR) gene. Disease-associated alleles (37-66 CAGs) change in length when transmitted from parents to offspring, with a significantly greater tendency to shift size when inherited paternally. As transgenic mice carrying human AR cDNAs with 45 and 66 CAG repeats do not display repeat instability, we attempted to model trinucleotide repeat instability by generating transgenic mice with yeast artificial chromosomes (YACs) carrying AR CAG repeat expansions in their genomic context. Studies of independent lines of AR YAC transgenic mice with CAG 45 alleles reveal intergenerational instability at an overall rate of approximately 10%. We also find that the 45 CAG repeat tracts are significantly more unstable with maternal transmission and as the transmitting mother ages. Of all the CAG/CTG repeat transgenic mice produced to date the AR YAC CAG 45 mice are unstable with the smallest trinucleotide repeat mutations, suggesting that the length threshold for repeat instability in the mouse may be lowered by including the appropriate flanking human DNA sequences. By sequence-tagged site content analysis and long range mapping we determined that one unstable transgenic line has integrated an approximately 70 kb segment of the AR locus due to fragmentation of the AR YAC. Identification of the cis - acting elements that permit CAG tract instability and the trans -acting factors that modulate repeat instability in the AR YAC CAG 45 mice may provide insights into the molecular basis of trinucleotide repeat instability in humans.      

Cryopreservation of human oocytes: a review of current problems and perspectives

It is well recognized that the ability to cryopreserve unfertilizedhuman oocytes would make a significant contribution to infertilitytreatment. However, despite considerable interest, very fewsuccessful pregnancies have arisen from cryopreserved oocytesafter thawing, insemination and transfer of the subsequent embryo.The reasons for this lack of progress may well result from adearth of information on how the various biophysical changesduring a cryopreservation regimen affect human oocyte function.Recently, fundamental studies on the effects of cooling, membranepermeability, cryoprotectant addition and ice formation havebeen performed on human oocytes by a number of groups, and theseform the basis of the current review. It is likely that successfulhuman oocyte cryopreservation will only follow once these factorsare fully understood, but the existing base of knowledge shouldprovide a platform for further improvements in the techniquescurrently employed.