Reduced growth of intra- and infra-pyramidal mossy fibers is produced by continuous exposure to polychlorinated biphenyl.

Exposure to polychlorinated biphenyl (PCB) has been shown to produce cognitive deficits in both humans and laboratory animals. However, no study to date has identified long-term brain changes which could account for these problems. This study employed Timm's silver sulfide staining to visualize the hippocampal mossy fibers in Sprague-Dawley rats continuously exposed to either 125 ppm Aroclor 1254 or untreated control food beginning in utero. Reduced growth of hippocampal intra-and infra-pyramidal (II-P) mossy fibers were found in PCB treated rats compared to controls. Other measured hippocampal subdivisions remained relatively unaffected by PCB treatment, as did cortical thickness. The changes observed in hippocampal morphology in response to PCB exposure are the first to provide a potential explanation for at least part of the long-term PCB-induced cognitive deficits.

Dose- and age-dependent alterations in choline acetyltransferase (ChAT) activity, learning and memory, and thyroid hormones in 15- and 30-day old rats exposed to 1.25 or 12.5 PPM polychlorinated biphenyl (PCB) beginning at conception.

1. Polychlorinated biphenyls (PCB) were released into the environment through improper disposal for decades, causing widespread contamination. Slow biodegradation and lipophilic properties of PCB caused its persistence and concentration through food webs. Exposure to these environmental contaminants through maternal transfer during early development has been associated with neurological and endocrinological alterations in several different organisms. 2. The present study extended a preliminary investigation which suggested low level exposure to PCB altered acetylcholine biosynthesis enzyme, choline acetyltransferase (ChAT), activity in the hippocampus and basal forebrain and caused aberrations in thyroid hormone and behavior. 3. Dietary exposure of 15-day-old animals to 1.25 ppm of Aroclor 1254 (LPCB) during gestation and lactation significantly elevated ChAT activity in both areas of the brain. Animals exposed to 12.5 ppm of Aroclor 1254 (HPCB) until 15 days of age demonstrated significant elevations of ChAT activity in the basal forebrain. Thyroxine (T4) concentrations were slightly elevated in 15-day-old LPCB animals and significantly depressed in HPCB exposed pups; triiodothyronine (T3) concentrations were not altered. 4. At 30 days both LPCB and HPCB treatment groups displayed significantly depressed ChAT activity in both areas of the brain. T3 and T4 concentrations were subnormal, although T4 was not significantly depressed in LPCB animals. 5. In the Morris water maze all animals, when tested between 25 and 29 days of age, improved their latency time to the platform over 10 spatial learning trials. However, when combined means of trials 8-10 were compared, HPCB exposed animals had significantly increased latency time to the podium compared to control and LPCB animals.

Gender differences in the responses of serum insulin-like growth factor-1 and transthyretin (prealbumin) to trauma.

OBJECTIVE: To determine whether factors such as age, gender, and severity of injury should be considered when evaluating serum insulin-like growth factor (IGF)-1 and transthyretin concentrations as markers of nutritional status after trauma. A large, diverse group of patients was studied before the confounding effects of acute nutrient deprivation. DESIGN: Prospective, randomized, descriptive study. SETTING: Emergency room of a university hospital. PATIENTS: One hundred eight trauma patients. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: In this heterogeneous group of patients, Injury Severity Score ranged from 1 to 45 (11.5 +/- 10.3 [SD]), age ranged from 18 to 77 yrs (35 +/- 15.3 [SD]), and 68% were male and 32% were female. A venous blood sample was collected on admission and analyzed for serum IGF-1, transthyretin, albumin, and C-reactive protein concentrations. Relationships among variables were tested with multiple regression, Pearson's correlation coefficients, and analysis of variance. Gender, age, and severity of injury demonstrated strong and interactive effects on serum IGF-1 concentrations. IGF-1 concentrations were predicted with the following equations in women and men, respectively: y = 414 - 10.87(age) + 1.19(Injury Severity Score) + .09(age2); y = 454 - 10.87(age) - 2.57(Injury Severity Score) + .09(age2); (R2 = .35, p < .0001). The relationship between age and IGF-1 was curvilinear in both men and women. IGF-1 concentrations increased with age until approximately 57 yrs, and then decreased with increasing age. In women, IGF-1 concentrations increased with increasing severity of injury. In men, IGF-1 concentrations decreased with increasing Injury Severity Scores. This dissimilar response to injury between men and women was also seen in the significant interaction between gender and Injury Severity Score in predicting transthyretin concentrations (R2 = .32, p < .05). In men, transthyretin concentrations decreased significantly with severe injury; in women, transthyretin concentrations remained stable with severe injury. Albumin concentrations were predicted by injury severity and serum osmolality, but not gender. C-reactive protein, and time postinjury did not significantly influence the serum proteins (serum IGF-1, transthyretin, or albumin). Without consideration of age or severity of injury, mean concentrations of IGF-1, transthyretin, albumin, and C-reactive protein were not different between men and women, and were within normal expected ranges. CONCLUSIONS: Serum IGF-1 and transthyretin concentrations, measured without the confounding effects of acute nutrient deprivation, were influenced by the severity of the injury in patients suffering traumatic injury. Age was an important determinant of serum IGF-1 in men and women even in severe trauma. The present study indicated that men and women demonstrate different physiologic responses to trauma. Women responded to increasing severity of injury with increased serum IGF-1 and little change in transthyretin concentrations. In men, both IGF-1 and transthyretin concentrations decreased with severe injury. Interpretation of serum concentrations of IGF-1 and transthyretin as markers of nutritional status after trauma should include consideration of age, gender, and severity of injury.

Effects of exposure to polychlorinated biphenyl (PCB) from conception on growth, and development of endocrine, neurochemical, and cognitive measures in 60 day old rats.

Industrially employed PCB has caused wide-spread environmental contamination through improper disposal and has been associated with detrimental physiological states in exposed organisms, including depressed body weight, food consumption, and circulating levels of T4 and T3. Previously, the activity of choline acetyltransferase (ChAT) in the basal forebrain and hippocampus was shown to be depressed in young rats exposed to the PCB diet from the time of conception. The present study measured the neurochemical effects of similar PCB exposure in older (i.e., 60 day old) rats, and examined possible restoration of PCB-induced deficits by removing PCB at weaning (28 days). Possible PCB-induced impairment of memory was also evaluated with a radial arm maze. Findings included a significant depression of circulating levels of T4 in all treatment groups with the most profound depression seen in rats continuously fed PCB. Also, T3 levels and relative thyroid weights were not found to be severely depressed. The ChAT activity in both the basal forebrain and hippocampus was not different from control in all treatment groups. It appears that the effect of PCB on thyroxine is persistent, but its influence on ChAT activity is not. However, modest memory deficits were observed despite normal ChAT activity. Average number of working memory errors per test session in the maze increased in a dose-dependent manner across treatment groups.

Thyroxine normalizes polychlorinated biphenyl (PCB) dose-related depression of choline acetyltransferase (ChAT) activity in hippocampus and basal forebrain of 15-day-old rats.

Neonatal exposure to the toxic chemical polychlorinated biphenyl (PCB) induces hypothyroidism (depressed thyroid hormones). Neonatal rats made hypothyroid by other means (chemical or surgical) have subnormal activity of choline acetyltransferase (ChAT), which catalyzes synthesis of acetylcholine, in the hippocampus and basal forebrain. The present study examined whether neonatal rats with PCB-induced hypothyroidism had depressed ChAT activity in these two brain areas, and whether alterations in ChAT activity were secondary to hypothyroidism rather than/in addition to a direct effect of PCB. Neonatal rats were exposed to PCB by feeding pregnant female rats chow containing various concentrations of PCB (0, 62.5, 125 or 250 ppm) throughout pregnancy and lactation. During postnatal days 4-14, neonatal rats exposed to the highest concentration of PCB were injected with either saline, triiodothyronine (T3), or thyroxine (T4), or were not injected at all. Circulating thyroid hormone levels (T4 and T3) and brain ChAT activity were determined at 15 days of age. All concentrations of PCB depressed circulating T4 levels and ChAT activity in a dose-response manner, but did not modify T3 levels. Injections of T4, but not T3, elevated ChAT activity in PCB-exposed rats to near control levels. Thus, altered ChAT activity in PCB-exposed rats may partially result from the hypothyroidism accompanying PCB poisoning. The possible molecular mechanism(s) of action of PCB on brain ChAT activity remains unclear.

Effect of thiouracil-induced hypothyroidism on time course of adrenal response in 15 day old rats.

Previous investigations have supported the suggestion that perinatal induction of hypothyroidism, using the goitrogen thiouracil, completely prevents elevation of circulating corticosterone levels 15 min after ether stress in 15 day old rats. The present study used radioimmunoassay (RIA) to evaluate the effect of chemical hypothyroidism on response of circulating corticosterone to ether stress, or to exogenous corticotropin releasing factor (CRF), at 15, 30, or 45 min after stimulation. Fifteen day old hypothyroid rat pups responded to ether stress with a linear increase in circulating corticosterone over the time course of the study, and with the levels at 30 and 45 min significantly greater than unstimulated. However, the slope of the increase was markedly subnormal, as was corticosterone level at each time point after stress. On the other hand, CRF injection resulted in elevations of corticosterone along the time course that were similar for normal and thiouracil exposed rats. The results of this study do not support the previous conclusion that chemical hypothyroidism entirely abolishes adrenal axis response in 15 day old rats. Instead, thiouracil depresses the response at a number of post-stimulation time points, rather than causing a time-dependent delay in a normal corticosterone elevation. This is likely the result of thiouracil-induced functional deficits in all components of the neuroendocrine axis regulating corticosterone secretion, with particularly severe effects at the hypothalamus.

Characterization of a glucocorticoid-sensitive hippocampal protein.

Increased synthesis of a rat hippocampal protein with an apparent molecular weight (Mr) of 35,000 Da occurs in response to elevation of serum corticosterone levels. Subcellular fractionation has localized this protein in the cytosol. Two-dimensional gel electrophoresis indicated that this protein has an isoelectric point (IEP) of 6.6. A similar protein in liver has a slightly higher Mr and an IEP of 6.8. Increased synthesis of one additional hippocampal protein with an Mr of 46,000 Da and an IEP of 6.2 and of two other liver proteins, one with an Mr of 53,000 Da and an IEP of 6.2 and the other with an Mr of 45,000 Da and a range of IEPs from 8.7 to 7.8, was also seen after injection of corticosterone into rats. One possible identity of the 35,000 Da protein is glycerol 3-phosphate dehydrogenase (GPDH), based upon the reported Mr and IEP of this enzyme. The 35,000 Da hippocampal protein co-eluted from a gel filtration column with GPDH activity. No alteration of hippocampal GPDH activity was seen in intact rats 4 or 24 h after injection of either corticosterone or the type II receptor-specific agonist RU 28362. However, daily administration of corticosterone to rats beginning 10 days after adrenalectomy returned hippocampal GPDH activity to normal values after 2-3 days. In contrast, synthesis of the 35,000 Da protein was maximally increased 4 h after a single injection of steroid and not elevated at later times.

Modification of hypothalamic content of growth hormone regulatory peptides in maternally deprived neonatal rats.

The possibility that maternal deprivation (MD) modifies growth hormone releasing hormone (GHRH) and/or growth hormone release inhibiting hormone (GHRIH) in 10-day-old rat pups was investigated by quantifying the total hypothalamic content of these two hormones which regulate the release of growth hormone (GH), since MD has previously been shown to suppress circulating GH levels. At 10 days of age, rat pups were maternally deprived for either 1 or 6 hours (control pups remained with their mother while littermates were deprived). At the end of the time period, hypothalami were dissected free, homogenized, frozen, and then lyophilized. Reconstituted extracts were later subjected to radioimmunoassay for GHRH and GHRIH. Tests for differences in the brain content of the hormones were performed by analysis of variance; multiple comparison of the means was performed using Tukey's test. A significant increase in the GHRIH content was observed in the hypothalami of maternally deprived rats as compared to control animals (P = 0.026). Small differences in the mean GHRIH content between the different experimental groups suggested a trend toward elevation of GHRIH after either 1 or 6 hours of MD and a trend toward higher levels in males as compared to females (P = 0.0636). No differences in hypothalamic GHRH content were found between maternally deprived and control pups (175.8 pg/hypothalamus vs. 171.5 pg/hypothalamus). The modification of GHRIH hypothalamic content during MD of neonatal rats demonstrated in the present study may be related to the suppression of GH that is known to result from MD.

Hypothalamic CRF immunoreactivity in genetically hypothyroid (hyt/hyt) mice.

The induction of hypothyroidism in young rats by feeding thiouracil to their mothers during pregnancy has been shown to depress hypothalamic content of bioactive and immunoactive corticotropin-releasing factor (CRF). The present study was done to determine whether genetically hypothyroid young mice (hyt/hyt) born to euthyroid mothers (+/hyt) exhibited a similar depression in hypothalamic CRF immunoreactivity. Young euthyroid and hypothyroid littermate mice were examined by radioimmunoassay for hypothalamic CRF content at 15, 20, 25, or 30 days of age. Mean CRF content was depressed insignificantly (to about 80% of normal) by hypothyroidism, at 15-25 days of age. However, after weaning by the mother, 30-day-old hypothyroid pups demonstrated significantly depressed hypothalamic CRF levels (71%). It is suggested that maternal factors may be assisting in the maintenance of hypothalamic CRF until after weaning. Furthermore, genetic hypothyroidism does not appear to have nearly as marked an influence as thiouracil feeding on hypothalamic CRF levels.

Consequences of sequential induction of diabetes mellitus by streptozotocin and hypothyroidism by thiouracil in mice.

Both clinical diabetes and chemically-induced diabetes have been reported to alter control processes of the hypothalamic-pituitary-thyroid axis. One of the sites of alteration appears to be depression of thyrotrophin releasing hormone (TRH) stimulated thyrotrophin (TSH) release. The present study examined the influence of sequential administration of streptozotocin and the goitrogen thiouracil to male mice for 4 weeks in view of their possibly opposing effects on TSH release. The drugs produced the expected results when administered singly, with streptozotocin producing hyperglycemia and thiouracil causing hypothyroxinemia and goitrogenesis. Additionally, thiouracil administration produced hyperinsulinemia. Sequential administration of the drugs appeared to ameliorate the thyroid status and glycemic condition caused by individual exposure. Streptozotocin reduced the goitrogenic influence of thiouracil and thiouracil reduced the hyperglycemia of streptozotocin, but not to control levels. Thus, sequential administration resulted in mice with simultaneously elevated circulating glucose and insulin levels, and depressed thyroxine levels. Similar effects on glucose, insulin, and the thyroxine levels have been reported clinically in patients with non-insulin-dependent diabetes mellitus.

Depressed hypothalamic CRF immunoreactivity in 15 day old thiouracil-treated rats.

Depression of thyroid status with thiouracil has been shown to delay the response of the hypothalamus-pituitary-adrenal axis to stress in young rats. In vivo and in vitro bioassay studies have indicated that the hypothalamus is the main site of axis alteration in 15 day old animals. The present study has found a significantly depressed hypothalamic content of immunoassayable corticotropin-releasing factor (CRF) in thiouracil treated young rats.

Perinatal thiouracil exposure depresses corticotropin-releasing factor activity in 15 day old rats.

Although previous in vivo studies have shown thiouracil to delay maturation of the hypothalamus-pituitary-adrenal (HPA) axis response to stress, the nature of the developmental deficit was not determined. By in vitro methods we determined which HPA components are influenced by thiouracil-induced hypothyroidism in 15 day old rats. Our results indicate that adrenal response to ACTH stimulation and adenohypophysial ACTH content were not significantly modified by thiouracil exposure. On the other hand, the corticotropin-releasing factor-like activity of median eminence extracts was severely depressed by thiouracil-induced hypothyroidism. Thus, the delayed maturation of functional capacity of the central nervous system caused by hypothyroidism includes synthesis of biologically active corticotropin-releasing factor.

Altered growth patterns and depressed pituitary growth hormone content in young rats: effects of pre- and postnatal thiouracil administration.

The important influence of postnatal thyroid status on development is well recognized, while the effect of prenatal thyroid status on postnatal growth is less understood. The present study was undertaken to assess the effects of pre- and postnatal thiouracil administration on postnatal growth and pituitary grown hormone (GH) content in 25 day old rats. Pups were born to Sprague-Dawley rats fed lab chow mash containing 0.25% thiouracil according to the following schedules: a) during gestation only; b) during lactation only (25 days postpartum); and c) through gestation and lactation. Mothers of euthyroid controls were fed diet without thiouracil for the length of the experiment. Pups were weighed daily through day 21 and decapitated on day 25. Pituitary GH content was measured by densiometric comparison of disc gel column electrophoresed pituitary homogenates with similarly treated rat GH standard. Incorporation of thiouracil into the diet of pregnant and/or lactating rats significantly depressed the body weight and pituitary GH levels in their 25 day old pups. Furthermore, analysis of the daily mean body weight of each litter revealed four significantly different patterns of growth. While previous investigators have reported that prenatal thyroid restriction does not significantly alter the developmental processes of young rodents, the present study indicates that prenatal thyroid status is an important influence on normal postnatal growth.

Response of adrenal 3beta-hydroxy-delta5-steroid dehydrogenase to adrenocorticotropin treatment in thiouracil-fed male mice.

A number of parallels can be drawn between the reported endocrine status of thiouracil-fed young rodents and that of aged animals, particularly with regard to the hypothalamus-pituitary-adrenal axis. Since the activity of the adrenal steroidogenic enzyme 3beta-hydroxy-delta5-steroid dehydrogenase (3beta-HSD) has been shown to be depressed in aged rats and mice, the present study was done to determine whether exposure of young mice to thiouracil had a similar effect on adrenal 3beta-HSD activity. Feeding the goitrogen thiouracil at 0.25% (w/w) of the maternal diet from conception, and keeping it 0.25% of the offsprings' diet after weaning, significantly elevated activity of 3beta-HSD per gram of adrenal gland above control levels in 4-month-old mice, perhaps to compensate for depressed adrenal mass. Daily subcutaneous injections of physiological saline (0.9%) for 4 days was sufficient to increase 3beta-HSD activity per gram of adrenal tissue in euthyroid (P less than 0.05) but not in thiouracil-fed mice. Subcutaneous administration of ACTH (2 IU daily for 4 days) significantly increased adrenal 3beta-HSD activity to comparable levels in thiouracil-fed and euthyroid animals. Thus, thiouracil enhances the activity of 3beta-HSD per gram of adrenal tissue and does not prevent response of enzyme activity to exogenous ACTH.

Development of hypothalamic-pituitary-adrenal response to stress in rats made hypothyroid by exposure to thiouracil from conception.

The functional maturation of the hypothalamic-pituitary-adrenal (HPA) axis has been studied in rats of 20-35 days of age made hypothyroid by the administration of thiouracil from conception. Basal concentrations of corticosterone in serum were normal in hypothyroid animals. Ether stress led to an increase corticosterone content of the adrenal glands of hypothyroid and normal rats but not to a rise in serum corticosterone of hypothyroid rats until 30 days of age. Corticosterone secretion in response to ACTH administration was subnormal in hypothyroid rats. The hypothyroid state delays the development of the hypothalamic-pituitary-portion of the HPA axis until 30 days of age and causes a diminution in adrenal response to ACTH beyond this time.

Control of the hypothalamus-pituitary-adrenal axis in young and older rats injected with thyroxine.

Administration of T4 on alternate weeks for 30 weeks at a dosage which does not alter body weight depresses basal serum corticosterone levels in older rats (575 days), but not in young animals (260 days). Similar serum corticosterone response to HPA axis stimulation occurs regardless of age or T4 injection.