Thyroid Feeding From Conception and Hypo-thalamo Pituitary-Adrenal Axis Response in 30-Day-Old Rats

Author Institution: Department of Biological Sciences, Bowling Green State UniversityElevation of thyroid status in pre- and postnatal rats has been previously shown to accelerate the development of the neuroendocrine axis controlling adrenal response to stress. The present study determined the influence of feeding desiccated thyroid powder (0.03%) in the maternal diet from conception until young were 30 d old. Circulating corticosterone levels were compared in control and thyroid-fed young before stimulation, after a general stress (one min exposure to ether fumes), direct adrenal stimulation (subcutaneous adrenocorticotropin (ACTH) injection) or control injection (physiological saline subcutaneously). Corticosterone levels were measured by both fluorometric assay and radioimmunoassay (RIA). These comparisons revealed that thyroid feeding did not significantly influence basal corticosterone levels, or response to general stress or saline injection. However, injected ACTH stimulated a significantly greater adrenal response in controls than thyroid-fed rats. Since responses relying on endogenous ACTH were not altered by thyroid feeding, it is suggested that absorption of subcutaneously injected ACTH was subnormal in the experimental animals. Results were similar for both assay techniques, indicating that the advantages of precision and specificity given by RIA over fluorometric assay were not critical in this study

Influence of Pre- and Postnatal Thiouracil Administration on Pituitary Growth Hormone Content in Mice

Author Institution: Department of Biological Sciences, Bowling Green State UniversityWe examined the influence of thiouraeil-induecd hypothyroidism imposed at various stages of development upon pituitary growth hormone (OH) concentration. Balb/e-derived mice were mated and fed thionracil, 0.25% in Purina Lab Chow, from the first day of pregnancy until 25 days postpartum, or for shorter periods of time (last % of pregnancy and postpartum, last j/$ of pregnancy and postpartum, or postpartum only). Using disc gel eleetrophoresis, pituitary Gil concentration of 25 day old pups exposed to thiouracil was compared with that of unexposed animals. Concentration of pituitary GH was depressed significantly in animals whose mothers were first given thiouracil at the initiation of pregnancy or \% of the way through pregnancy. Young of mothers first given thiouracil % of the way through gestation or on the first day postpartum did not have significantly lower pituitary GH concentrations than controls. The factor determining the presence or absence of thiouracil-induced depression of pituitary GH concentration may be the initiation of fetal thyroid function that occurs between days 15-17, approximately % of the way through gestation

Kainic Acid Induced Seizures and the GABA System in the Substantia Nigra

Author Institution: Department of Biological Sciences, Bowling Green State UniversityGamma-aminobutyric acid (GABA) is an inhibitory neurotransmitter implicated in the control of generalized seizures induced by various convulsants. A specific anatomical site of action, the substantia nigra (SN), has been shown to be involved in the GABA mediation of seizures. It was the objective of this study to investigate the GABA system in the SN and its response to seizures induced by the neuroexcitant kainic acid (KA). Since there have been conflicting reports of the effects of convulsants on GABA-related measures in some brain regions, with some reporting increases and others showing decreases, one purpose of this investigation was to examine the directionality of changes in GABA content of the SN, along with the magnitude of the effects of KA and the time course over which these effects were manifested. Rats were injected intraperitoneally with either 12.5 mg/kg KA or saline. GABA and protein contents of the SN were measured at 2, 16, 24 and 48 hrs subsequent to injection. The levels of GABA in the SN were found to increase in KA-injected animals over control levels for all time intervals except the 16 hr condition. These results are generally in conflict with those obtained by many researchers using the activity of the GABA synthetic enzyme glutamic acid decarboxylase (GAD) as a measure of GABA levels. It is suggested that GABA levels may actually increase in response to convulsants and serve to negatively feed back to its synthetic enzyme. Therefore, a decrease in GAD activity would not necessarily reflect a decrease in GABA levels. Future research directions include enzyme studies of both GAD and GABA transaminase and their regulation by products and substrates

Determining the Critical Window of Influence of PCB Perinatally on Behavioral and Hormonal Development in Sprague-Dawley Rat Pups

Polychlorinated biphenyls (PCB) had widespread use in the United States in commercial manufacturing in the United States until the late 1970s. Even though they were banned, measurable amounts can still be found in the environment and food sources. PCB has known effects on altering hormone development and behavior in the species Rattus norvegicus. To determine the most crucial developmental time of exposure to PCB in Sprague-Dawley rat pups, rat pups were exposed to PCB at differing weeks of either gestation period or the first postnatal week. Behavioral tests were performed for the different rat pups, as well as blood serum was analyzed for the concentration of thyroid hormone. This paper presents data for PCB exposed pups that were tested for play behavior on PND 22. Statistical tests were used to determine the week of PCB exposure with the greatest effects on the rat pups. The results are that exposure of PCB led to a significant increase in the play behavior of the pups. The dorsal contact play behavior was significantly altered by PCB, while the pin behavior was not significantly altered. The critical window for PCB exposure was not identified, but it can be seen that PCB alters dorsal contact behavior in exposed rat pups