Effect of prenatal exposure to diazepam on brain GABA(A) receptor mRNA levels in rats examined at late fetal or adult ages

This study tested the hypotheses that in utero exposure to diazepam (DZ): (1) exerts long-lasting effects on GABA(A) receptor function by altering GABA(A) receptor subunit mRNA levels in specific brain regions of adult animals and/or (2) alters GABA(A) subunit mRNA expression in exposed fetuses. We assayed levels of mRNAs encoding several of the most predominant GABA(A) receptor subunits as well as cyclophilin mRNA. Analysis of mRNA levels in the cortex in adults showed that only gamma2S mRNA levels varied significantly with prenatal drug exposure, an effect unrelated to DZ action to the GABA(A) receptor. Analysis in fetuses indicated that mRNA levels varied as a function of both fetal sex and fetal drug environment. Irrespective of sex, DZ exposure increased both alpha1 and cyclophilin mRNAs in fetal brainstem whereas the mRNA levels of gamma2S were increased and decreased, respectively, in the telencephalon and hypothalamus of DZ-exposed fetuses.

Sex-specific effects of in utero manipulation of GABA(A) receptors on pre- and postnatal expression of BDNF in rats

Exposure to diazepam (DZ) during the last week of in utero development in rats induces neurobehavioral effects that do not become apparent in exposed animals until young adult ages. Some of the effects are sex specific. This study evaluated the hypothesis that late gestational exposure to DZ, a positive modulator of GABA(A) receptors, affects the developmental appearance of brain-derived neurotrophic factor (BDNF), an effect that could be linked to the later consequences of the exposure. Pregnant Long-Evans rats were injected with DZ (2.5 mg/kg) over gestation days 14-20, and their male and female offspring were evaluated for levels of BDNF mRNA and protein in the cerebral cortex and hypothalamus at fetal day 20 and at postnatal ages spanning birth to young adulthood. The effects of the exposure were sex and region specific. At fetal day 20 the expression of BDNF was reduced by about 20% in the hypothalamus of males only. The early exposure affected postnatal expression of BDNF in the hypothalamus only modestly, influencing the age-related profile in both sexes. Postnatal development of BDNF in the cerebral cortex was significantly affected by the in utero exposure in males only with mRNA levels lower in the exposed group and protein levels higher during juvenile ages. At adulthood, both levels were lower in DZ-exposed males. GABA serves a role as a trophic factor during early development, and these results suggest that manipulation of GABA(A) receptors during early development could interact with the developmental action of other trophic factors thereby leading to altered neural organization and later neurobehavioral dysfunction.

Synchronous postnatal increase in alpha1 and gamma2L GABA(A) receptor mRNAs and high affinity zolpidem binding across three regions of rat brain

The objective of this study was to correlate postnatal changes in levels of mRNAs encoding predominant GABA(A) receptor subunits with a functional index of receptor development. This study is the first to quantify the temporal relationship between postnatal changes in predominant GABA(A) receptor mRNAs and zolpidem-sensitive GABA(A) receptor subtypes. In Experiment 1, we measured zolpidem displacement of 3H-flunitrazepam from rat cerebral cortex, hippocampus, and cerebellum at 0, 6, 14, 21, 29, and 90 postnatal days. Three independent 3H-flunitrazepam sites with high (K(i)=2. 7+/-0.6 nM), low (K(i)=67+/-4.8 nM), and very low (K(i)=4.1+/-0.9 mM) affinities for zolpidem varied in regional and developmental expression. In Experiment 2, we used RNAse protection assays to quantify levels of alpha1, alpha2, beta1, beta2, gamma2S and gamma2L mRNAs in the above regions at the same postnatal ages. Although there was a high degree of regional variation in the developmental expression of zolpidem-sensitive GABA(A) receptors and subunit mRNAs, a dramatic increase in high affinity zolpidem binding sites and alpha1 mRNA levels occurred within all three regions during the second postnatal week. Furthermore, a temporal overlap was observed between the rise in alpha1 mRNA and high affinity zolpidem binding and a more prolonged increase in gamma2L in each region. These results point to the inclusion of the alpha1 and gamma2L subunits in a GABA(A) receptor subtype with a high zolpidem affinity and suggest that a global signal may influence the emergence of this subtype in early postnatal life.

Sex differences in long-term consequences of prenatal diazepam exposure: possible underlying mechanisms

Prenatal exposure to diazepam, a benzodiazepine (BZD) compound, leads to pronounced effects on responses to stressors in exposed animals when they reach adulthood. Many of the responses are sex specific. The mechanisms mediating the effects of the exposure on the organism have not been elucidated; however, the time course for the appearance of altered function following in utero drug exposure indicates that the exposure interfered with neural organization of mechanisms mediating responses to stressors. The article discusses possible mechanisms that relate to sites of action of the drug in the developing brain: the GABA(A) receptor, and the mitochondrial BZD receptor. The mechanisms mediating the sex-specific impact of diazepam on the developing brain appear to be complex and interactive.

Reduced progesterone metabolites are not critical for plus-maze performance of lactating female rats

Lactation has been associated with anxiolysis in several tests of anxiety. These observations, considered together with observations that progesterone and its 5alpha-reduced metabolites are anxiolytic in cycling, nonlactating females, raised the question of whether the changes in anxiety-related behaviors that accompany lactation are driven by reduced progesterone metabolites. Lactating female rats were tested on the plus-maze on postpartum days 2 or 7, and demonstrated enhanced open-arm performance relative to cycling, nonlactating females. Hormonal analysis indicated that while serum levels of both progesterone and its 3alpha,5alpha-reduced metabolite were increased in lactating females, the turnover of progesterone to the metabolite was markedly reduced during lactation. Furthermore, treatment with a 5alpha-reductase inhibitor for 3 days prior to testing potentiated the open-arm performance in lactating females, implying that enhanced open-arm performance was not mediated by the reduction of progesterone or other steroids. Additionally, analysis of GABA(A) receptor function indicated that parturition and lactation did not alter the sensitivity of the receptor to GABA or to modulation by reduced steroids. The mechanisms driving enhanced plus-maze behavior in lactating females appear to differ from mechanisms identified in nonlactating females.

Endogenous levels of 5 alpha-reduced progestins and androgens in fetal vs. adult rat brains

5 Alpha-reduced metabolites of certain steroids have been shown to have important functions in adult brains and may play a role in brain development. To assess which 5 alpha-reduced steroid metabolites may have an impact during development, endogenous levels of 5 alpha-reduced androgens and progestins and their parent hormones were measured in male and female fetal brains over the last 5 days of gestation. These levels were compared to levels measured in adult male and female brains (evaluated at different stages of the estrous cycle). Neither the brain levels of parent hormones nor of their 5 alpha-reduced metabolites varied as a function of fetal sex or of gestational age. Therefore, the data from the two sexes were combined. In fetal brains, the levels of the progesterone reduced metabolites were 20-fold higher than levels of progesterone itself whereas levels of testosterone reduced metabolites were 10-fold lower than testosterone levels. In contrast to fetal brain, conversion of progesterone to reduced metabolites was much lower in adult brain, but the level of 5 alpha-reduced androgens was 3-10-fold higher than the level of testosterone in all adult tissue, indicating more conversion of androgen to 5 alpha-reduced metabolites in adult than in fetal brains. These results imply that the reduction of progesterone to reduced metabolites may play a critical role in brain development.

Brain androgen-inducible aromatase is critical for adolescent organization of environment-specific social interaction in male rats

Previous observations have indicated that specific behavioral responses to anxiogenic stimuli emerge over adolescent development in male rats and that gonadal androgens during puberty are essential for this emergence. The objective of the current study was to evaluate mechanisms via which androgens might be organizing the brain during adolescence for appropriate mature adaptive responses. Male rats were exposed to fadrozole (an aromatase inhibitor, 5 mg/kg), flutamide (an androgen receptor antagonist, 10 mg/kg), or MK-434 (a 5 alpha-reductase inhibitor, 10 mg/kg) from day 29 to 60 and tested for environment-specific social interaction (SI) at 60 days of age. The emergence of adult-typical SI was impaired by exposure to the aromatase inhibitor and to the antiandrogen, whereas exposure to the 5 alpha-reductase inhibitor was without effect. Peripheral indices of drug effects indicated that the respective mechanisms had been altered by the different compounds. These results suggest that testosterone induction of aromatase is critical for the organization of mature SI behavior in male rats over adolescent development.

Early developmental modulation of GABAA receptor function. Influence on adaptive responses

If GABA is serving a trophic role during early brain development, before taking on its function as a neurotransmitter, interference with the function of GABA during this period should have a profound influence on neural organization. We have addressed this hypothesis by evaluating the effects of exposing rat fetuses to diazepam (DZ), a positive modulator of GABA at the GABAA receptor, over gestation days 14 to 20. Studies have shown that adult rats exposed in utero to DZ over this developmental period make inappropriate behavioral responses and have altered neural and hormonal responses to environmental stimuli that threaten the organism's stability and homeostasis. Thus, the early exposure led to altered adaptive responses. These effects of the early exposure did not become apparent until late in adolescent development. Furthermore, specific behavioral and neural responses to environmental challenges normally emerge over adolescent development. Other studies have shown that the GABAA receptor in adult brains is responsive to environmental challenges. Thus, we hypothesize that early modulation of the action of GABA mediated via the GABAA receptor interfered with the neural organization of adaptive responses.

Neurosteroid action at the GABAA receptor in fetal rat forebrain

In utero exposure to diazepam (DZ), a positive modulator of the GABAA (gamma-aminobutyric acid type A) receptor exerts profound effects on the offspring that become most apparent after the maturation of the brain during puberty and that are often sex specific, suggesting that the early exposure might have interfered with organizing actions of sex steroids. In addition to genomic actions, many reduced steroids interact directly with membrane receptors, including the GABAA receptor. In the present study, the effect of in vitro exposure to neurosteroids on GABA-stimulated 36chloride uptake in synaptoneurosomes from adult cerebral cortex or fetal forebrain (gestation day 20) was examined. The initial study examined the effects of incubation with DZ (10 microM) and the neuroactive steroid, 3 alpha,5 beta-THP (500 nM), alone and in combination. In adult tissue, the presence of either drug alone decreased the EC50 for GABA stimulation, and incubation with both drugs had an additive effect. In fetal tissue, while both compounds decreased the EC50, an additive effect was apparent only when comparing the combined exposure to 3 alpha,5 beta-THP alone. DZ alone reduced the EC50 as much as both drugs together. In the second study, the effect of in vitro exposure to androsterone (2.5 microM) was evaluated in male and female fetal tissue separately as well as in the adult. Androsterone enhanced the sensitivity to GABA in all groups but also reduced the efficacy of GABA in fetal tissue, irrespective of gender. While neurosteroids and DZ elicited similar responses in fetal and adult tissue, the study identified a greater vulnerability of fetal GABAA receptors to modulatory compounds.

Adolescent development alters stressor-induced Fos immunoreactivity in rat brain

Adult-typical behavioural responses to environmental challenges as well as the stressor responsiveness of several neural systems emerge over adolescent development. The present study was undertaken to determine whether stressors might activate different neural populations in adult vs juvenile male rats. Fos-immunoreactivity was determined in various forebrain nuclei following 15 min or 2 h of restraint in 28- and 60-day-old male rats (representing late juvenile and young adult ages, respectively) and compared to non-restrained control animals at each age. Few Fos-positive cells were identified in unrestrained controls at either age. Restraint, however, induced the production of Fos in several areas. Fos immunoreactivity was marked in parvocellular regions of the paraventricular nucleus of the hypothalamus following both restraint periods and at both ages, an observation consistent with previous observations that restraint increases plasma corticosterone at both ages. And at both ages, Fos immunoreactivity was evident in magnocellular regions of the hypothalamus only following the longer restraint period. Fos immunoreactivity, however, clearly varied as a function of adolescent age in several regions. Moderate to intense Fos immunoreactivity was observed in adults in all divisions of the anterior olfactory nucleus, cortical and medial amygdaloid nuclei, pyriform cortex and tenia tecta. In contrast to the adult, only a few Fos positive cells were observed in any of these regions in juveniles. Exposure to the same stressor induced Fos in a broader spectrum of neurons in young adult than in juvenile male rats. The lack of Fos-positive cells in specific areas of juveniles may relate to maturation in specific amygdaloid nuclei, which project to many of the other regions that showed age-related differences in Fos production. The emergence over adolescence of Fos-positive cells in specific areas in response to stressors may underlie the emergence of adult-typical behavioural and neural stressor-responsiveness.

Neonatal exposure to cocaine enhances the reward-potentiating properties of the drug in young adult animals

Either cocaine (20 mg/kg) or saline vehicle was administered to rat pups once daily on postnatal days 1-8. The enhancement of brain stimulation reward (BSR) by acute administration of cocaine (2.5, 5, and 10 mg/kg i.p.) was assessed in adult offspring (70-90 days of age) using a rate-frequency curve-shift paradigm. Acute administration of cocaine produced orderly dose-related shifts of the rate-frequency function toward lower frequencies in all groups indicating a reward-enhancing effect of the drug on BSR. However, offspring neonatally exposed to cocaine displayed a greater drug-induced potentiation of BSR. Of particular note, the small but significant enhancement of the reward-potentiating properties of cocaine was more pronounced in female offspring neonatally exposed to the drug. These findings indicate that the rewarding properties of cocaine were altered by neonatal exposure to the drug in a sexually dimorphic fashion.

Control of endogenous norepinephrine release in the hypothalamus of male rats changes over adolescent development

In order to evaluate mechanisms that could contribute to the effect of adolescent development on the in vivo utilization of norepinephrine (NE) in the hypothalamus, the depolarized release of endogenous norepinephrine (using 50 mM potassium) was measured in vitro in hypothalamic explants from male rats over late juvenile (28 days) to young adult (70 days) ages. Depolarized release, expressed as a percent of the total endogenous pool, was significantly greater in juveniles than in either adolescents (42 days) or young adults. Incubation in the presence of idazoxan, an alpha 2-adrenoceptor antagonists, increased the depolarized fractional NE release in adolescent and young adult rats; however, the same drug decreased depolarized release in juveniles. Inhibition of norepinephrine reuptake by incubation in the presence of nisoxetine (1 microM) significantly increased depolarized release (fractional and absolute) in young adults only. A higher concentration of nisoxetine (5 microM) significantly increased depolarized release in juveniles, but significantly reduced release in adults. Nisoxetine did not influence release in adolescents at either concentration. The possibilities that adolescents development brings about a change in alpha 2-adrenoceptor subtype and that juveniles may have a greater NE reuptake capacity than adults are discussed. Hypothalamic NE projections are important to several regulatory functions, and changes that take place in this system over adolescence may be important for the emergence of adult-typical responses as well as render adolescents vulnerable to specific dysfunctions.

Neonatal exposure to cocaine enhances the reward-potentiating properties of the drug in young adult animals

Either cocaine (20 mg/kg) or saline vehicle was administered to rat pups once daily on postnatal days 1-8. The enhancement of brain stimulation reward (BSR) by acute administration of cocaine (2.5, 5, and 10 mg/kg i.p.) was assessed in adult offspring (70-90 days of age) using a rate-frequency curve-shift paradigm. Acute administration of cocaine produced orderly dose-related shifts of the rate-frequency function toward lower frequencies in all groups indicating a reward-enhancing effect of the drug on BSR. However, offspring neonatally exposed to cocaine displayed a greater drug-induced potentiation of BSR. Of particular note, the small but significant enhancement of the reward-potentiating properties of cocaine was more pronounced in female offspring neonatally exposed to the drug. These findings indicate that the rewarding properties of cocaine were altered by neonatal exposure to the drug in a sexually dimorphic fashion.

Adolescent development influences functional responsiveness of noradrenergic projections to the hypothalamus in male rats

Hypothalamic noradrenergic utilization in vivo and the in vitro depolarized release of norepinephrine (NE) were measured at 28, 42, and 70 days of age in male rats to determine the impact of adolescent development on the functional responsiveness of this transmitter system. At each age, function was determined in control rats and rats challenged by restraint. NE utilization in vivo was estimated by measuring the decrease in NE levels following administration of a synthesis inhibitor, alpha-methyl-p-tyrosine methyl ester (alpha-MT, 250 mg/kg). The half-life of approach to a new steady-state was determined. To measure depolarized release of NE, the hypothalamus was incubated in vitro in a high potassium (50 mM) medium and the percent of endogenous NE released into the medium was determined. The in vivo results indicated that hypothalamic NE utilization in control animals decreases as animals mature. Additionally, the in vitro results indicated that the percent NE released upon depolarization also decreased with maturation in control animals. Restraint shifted the NE decay curve measured in vivo to the right at all ages. Overall, however, restraint tended to increase NE utilization at 70 days, have little effect at 42 days, and retard utilization at 28 days. Furthermore, restraint markedly reduced the depolarized release of NE at 28 days, had no effect at 42 days and slightly, but significantly, increased release at 70 days. Restraint significantly increased plasma corticosterone at all ages. Hypothalamic NE projections are important to an organism's regulatory responses, and changes that take place over adolescence in this system may be important for the emergence of adult-typical responses as well as render adolescents vulnerable to specific dysfunctions.

Hypothalamic GABAA receptor blockade modulates cerebral cortical systems sensitive to acute stressors

Pharmacologic blockade of GABA binding sites in the hypothalamus elicits a pattern of physiological and behavioral arousal. The latter outcome implicates a perturbation in the neural functioning of higher brain centers. The effect that hypothalamic GABAA receptor modulation has on the function of cerebral cortical neural substrates linked with responses to stressors was assessed using microinfusion of bicuculline methiodide (BMI) into the medial hypothalamus of freely moving, handling habituated rats. BMI led to rapid increases in frontal cortical dopamine (DA) utilization (calculated from the sum of the levels of the DA metabolites, homovanilic and dihydroxyphenylacetic acids, divided by DA levels) resembling that identified following restraint-induced stress. Also, cortical GABAA receptor function [using chloride (Cl-) enhancement of 3H-flunitrazepam (Flu) binding as an index] was disrupted; i.e. there was a loss of typical Cl- enhancement of 3H-Flu binding in animals after BMI infusions. However, placing animals in restraint after BMI infusion reversed the effects of BMI, with both DA utilization and Cl- facilitated 3H-Flu binding similar to control basal values. Muscimol infusions in separately prepared animals did not alter either frontal cortical DA utilization or GABAA receptor function. The present results implicate GABA in the hypothalamus as "gating" activity of cortical systems involved in sensation of and/or responses to stressors. These findings may have important implications for effects of autonomic arousal on neural substrates involved in mediating stress responses.

Immunohistochemical and neurochemical evidence for GABAA receptor heterogeneity between the hypothalamus and cortex

This study examined both the function of the GABAA receptor complex and the expression of its alpha 1, alpha 2 and alpha 3 subunits within the hypothalamus as compared to that of the cerebral cortex. A large number of different GABAA receptor subunit combinations potentially exist in various brain regions which, presumably, would intimate differing receptor structure and function. Here, we present evidence that the average functional characteristics of GABAA receptors within the rat hypothalamus are considerably different from those of the cerebral cortex. We assessed two neurochemical measures of GABAA receptor function: namely, chloride-facilitation of [3H]flunitrazepam binding and GABA-mediated 36chloride uptake. [3H]Flunitrazepam binding in the rat cortex was facilitated by increasing concentrations (12.5-500 mM) of chloride, and this facilitation was responsive to 15 min restraint. Yet, hypothalamic [3H]flunitrazepam binding was not responsive to increasing chloride-concentration in either the basal or restraint conditions. Also, maximal facilitation of GABA-mediated 36chloride uptake was significantly blunted in the hypothalamus relative to cortex (7.4 +/- 0.9 versus 35.8 +/- 1.5 nmoles/mg protein, respectively). While in vitro addition of 10 microM diazepam shifted GABA-mediated 36chloride uptake curves of the cortex to the left, diazepam addition appeared to be without effect in the hypothalamus. However, the blunted maximal facilitation of GABA on hypothalamic 36chloride uptake made accurate determination of the EC50 for the diazepam-potentiation difficult. In addition to these functional disparities between the regions, differences in subunit expression were also apparent. Distributions of alpha 1, alpha 2 and alpha 3 subunit immunoreactivities within cingulate, parietal and temporal cortices and 8 major hypothalamic regions were assessed. Staining of the alpha 1 subunit was prevalent throughout the hypothalamus and cortex, and dense in both regions. However, the alpha 2 and alpha 3 subunits, while of intermediate density in cortex, were of low density or absent (alpha 3) in the hypothalamus. The alpha 2-immunoreactivity was restricted to cell bodies of the arcuate nucleus, dorsomedial nucleus and overlying dorsal area and to neuropil staining of the median eminence. Thus, functional responsiveness of the GABAA receptor differs in the hypothalamus relative to the cortex and this would seem related to the presence of different receptor alpha subunits in homogenate preparations of the two regions.

Alterations in behavioral responses to stressors following excitotoxin lesions of dorsomedial hypothalamic regions

The dorsomedial hypothalamus is important for regulation of cardiovascular responses associated with emotional arousal. This region has also been identified as a component of neural circuitry involved in fear/anxiety, yet clear evidence as to the effects of lesioning on stress-related behaviors is missing. In this study, we lesioned the dorsomedial hypothalamic region with the neurotoxin, ibotenic acid (IBO; 2.0 micrograms in 0.2 microliter), and studied the impact on spontaneous and unlearned behavioral responses to stressors. In the open field test, we observed non-generalized increases in motility parameters in the IBO rats with the differences occurring in the latter two-thirds of the test. In the elevated plus-maze, the IBO rats displayed a classic anxiolytic response with a greater proportion of entries into (and greater time spent in) the open arms of the maze. In the environment-specific social interaction (SI) test, the IBO rats showed a normal familiar/unfamiliar environment discrimination with respect to Total SI; however, the composition of the behaviors ('curiosity' vs. physical contact) by the IBO rats was markedly altered, with there being a 2-fold increase in non-violent physical interactions. Additionally, the differences in these traditional indices of anxiety were associated with lesioned animals exhibiting greater acoustic startle responsiveness than controls as a function of prepulse intensity. Overall, the results following IBO lesions indicate an altered responsiveness to sudden stressors, particularly as relates to novelty or exploration-oriented behaviors. The hypothalamic lesion may, therefore, have resulted in a disinhibition of normally suppressed responding to innate fear or challenging stimuli. This study contributes to those that have begun to define neural interactions that are essential for integrated stress responses.

Treatment with an anabolic-androgenic steroid affects anxiety-related behavior and alters the sensitivity of cortical GABAA receptors in the rat

The putative psychotropic effect of the anabolic-androgenic steroid, testosterone propionate (TP), was determined in intact adult male rats after 1 or 2 weeks of continued exposure via subcutaneously implanted capsules. Behavior was assessed in a novel open-field arena and in the elevated plus-maze. In addition, gamma-aminobutyric acid (GABA)-stimulated 36chloride (Cl-) influx was determined in cerebral cortical synaptoneurosomes as a function of TP exposure. The weight of the prostate gland was taken and blood serum level of total testosterone (T) was assayed. One week of TP exposure (approximately 3.5-5.0 mg/kg per day) resulted in anxiolytic behavior, as evidenced by an increase in the exploration of the open arms of the elevated plus-maze. The behavioral effect in the elevated plus-maze was not observed in animals exposed to TP for a 2-week period. Ambulation scores in the novel open field did not change as a function of TP exposure. Blood T levels were increased 7-fold by 1 week of exposure, and increased 10-fold in animals with implants for a 2-week period. After 1 week of TP exposure, the concentration of GABA that elicited 50% of the maximal Cl- influx in cortical synaptoneurosomes (i.e., EC50) was significantly decreased; this effect was not seen in animals exposed to TP for 2 weeks. The maximal efficacy of the GABAA receptor-gated Cl- influx was not affected after 1 or 2 weeks of TP treatment. Thus, 1 week of treatment with TP resulted in anxiolytic behavior that was accompanied by an increase in the sensitivity of cortical GABAA receptors. However, the behavioral and neurochemical changes were no longer present after 2 weeks of TP exposure. These results are discussed in terms of the agonist effects of reduced androgen metabolites at the GABAA receptor and the possible development of tolerance to these effects.

Anxiolytic effect of progesterone is associated with increases in cortical allopregnanolone and GABAA receptor function

The effects of a SC injection of progesterone (0, 1, or 4 mg) on locomotor behavior and exploration of an elevated plus-maze were examined in ovariectomized rats. At the completion of the behavioral tests, blood serum and cerebral cortical level of the 3 alpha-hydroxy ring-A metabolite of progesterone, 3 alpha-hydroxy-5 alpha-pregnan-20-one (allopregnanolone), was also assessed. GABA-stimulated 36Cl- influx was studied in cortical synaptoneurosomes from a subgroup of ovariectomized females treated with vehicle or 4 mg progesterone. Whereas progesterone treatment did not affect ambulation in a novel arena, significant anxiolytic behavior was detected in the plus-maze 4 h after administration of 1 or 4 mg progesterone. A dose-dependent increase in allopregnanolone level was found in serum and cortical homogenates. Studies of GABA-stimulated Cl- influx demonstrated that progesterone treatment increased the sensitivity of cortical synaptoneurosomes to GABA (i.e., decreased the EC50) and increased the maximal efficacy with which GABA stimulated Cl- transport (i.e., increased the Emax). Together, these data support the hypothesis that the psychotropic effects observed after progesterone administration are due to the bioconversion of progesterone to allopregnanolone, which subsequently augments GABAA receptor-mediated function.

Importance of hypothalamic function to stressor-induced responsiveness of the GABAA receptor in the cerebral cortex: a non-corticosterone influence

Catecholamine terminals in the paraventricular nucleus (PVN) of the hypothalamus of 60-day-old rats were destroyed by the stereotaxic injection of 6-hydroxydopamine into the PVN (6-OHDA; 9 micrograms/1.5 microliters bilaterally), and the rats were tested 2 weeks later. Lesions led to a 70% reduction of norepinephrine in the hypothalamus and a loss of dopamine-beta-hydroxylase immunoreactivity in the PVN. Furthermore, 6-OHDA lesions in the hypothalamus disrupted stressor-induced (15 min of restraint) changes in GABAA receptor function in the cerebral cortex (assessed by measuring chloride-facilitated benzodiazepine binding) but did not alter stressor-induced increases in plasma corticosterone levels. Additionally, the lesion did not change the responsiveness of the GABAA receptor to the corticosterone metabolite, allotetrahydrodeoxycorticosterone. These results indicate that stressor-induced changes in cortical GABAA receptor function are not driven by the stressor-induced release of corticosterone. A separate group of animals were tested for behavioral responses to challenge, and while 6-OHDA-induced lesions did not alter total scores in the test of environment-specific social interaction, the lesions did induce a change in composition of the behavior. Lesioned animals demonstrated increased physical (vigorous contact) interactions, similar to behavior previously observed in younger rats. The results of the behavioral study support a role for the GABAA receptor in the cerebral cortex in mediating appropriate behavioral responses to challenge in the adult rat. Thus, a hypothalamic lesion that prevented challenge-induced changes in GABAA receptor function in the cortex (with no change in the corticosterone response to the stressor) also led to altered behavioral responses to challenge.

Altered stressor-induced changes in GABAA receptor function in the cerebral cortex of adult rats exposed in utero to diazepam

Prenatal administration of the anxiolytic drug diazepam (DZP), 2.5 mg/kg) to the pregnant rat over gestational days 14-20 altered function and stressor-induced responsiveness of the GABAA receptor in the cerebral cortex of exposed animals as adults. In Experiment 1, the impact of 15 min of restraint on chloride-facilitated benzodiazepine binding was evaluated in male and female rats at 70-90 days of age. Early exposure to DZP led to an enhanced potency of chloride on binding in both males and females. In Experiment 2, GABA stimulation of 36chloride uptake was measured in male rats at 35 or 70 days of age following 10 min of forced swimming at ambient temperature. In control animals, stressor-induced changes in receptor function were not evident until 70 days, and in DZP-exposed rats the stressor had no effect on receptor function at either age. These changes in GABAA receptor responsiveness induced by early exposure to DZP may underlie the disrupted behavioral responses to environmental challenge that have been previously reported.

Selective effects on CRF neurons and catecholamine terminals in two stress-responsive regions of adult rat brain after prenatal exposure to diazepam

Earlier work demonstrated that prenatal exposure to diazepam (DZ) selectively affected the noradrenergic (NE) terminals in the hypothalamus, leading to decreased basal NE levels, turnover rate, and release in adult offspring as well as altered responses to stressors in these NE projections. The exposure also affected plasma hormonal responses to stressors. In the present work, we used immunocytochemistry to study the effects of prenatal DZ exposure on NE terminals and on corticotropin-releasing factor (CRF)-containing neurons in the paraventricular nucleus (PVN) of the hypothalamus. DZ exposure (2.5 or 10 mg/kg over gestational days 14-20) led to a decrease in dopamine-beta-hydroxylase (DBH)-immunoreactivity (-ir) and a decrease in CRF-ir containing cells within the PVN of adult rats. The exposure also decreased DBH-ir in the ventral portion of the bed nucleus of the stria terminalis (BNST) but did not affect CRF-ir in the oval nucleus of BNST. Therefore, this study provides anatomic evidence that targeting benzodiazepine binding sites prenatally affects two neurotransmitter systems involved in responses to stressors.

Development of fibroblast-type-II cell communications in fetal rabbit lung organ culture

The development of the fetal lung is regulated by fibroblast-type-II cell communications which involve fibroblast pneumonocyte factor (FPF). FPF production is positively regulated by glucocorticoids and negatively regulated by dihydrotestosterone (DHT) and transforming growth-factor beta (TGF-beta). We studied whether DHT or TGF-beta affected other steps in the process of lung maturation, by studying how the developing lung in organ culture would respond to exogenously supplied FPF after DHT or TGF-beta exposure. Fetal rabbit (day 19 of gestation) lung organ cultures were prepared and cultured in the presence of cortisol, DHT or TGF-beta. After seven days, the media were replaced with serum-free medium containing either cortisol or FPF conditioned medium. The incorporation of [14C]glycerol into surfactant lamellar body DSPC was studied over 24 h as the index of surfactant synthesis. Results were compared to simultaneous control cultures. Treatment had no significant effect on tissue protein concentration or on the efficiency of lamellar body recovery. Cortisol stimulated baseline incorporation of glycerol into DSPC. This was inhibited by DHT, such that DHT plus cortisol treatment was no different from untreated controls. FPF stimulated the incorporation of glycerol into DSPC, and did so even after culture treatment with DHT. Cultures treated with TGF-beta exhibited glycerol incorporation similar to untreated controls. After TGF-beta exposure, FPF did not stimulate glycerol incorporation into DSPC. We conclude that DHT interferes with progression of lung development by delaying the appearance of FPF production by the fibroblast. TGF-beta, on the other hand, inhibits other elements of lung maturation besides FPF production. We speculate that TGF-beta interferes with type-II cell development such that the cell cannot respond to FPF.

Norepinephrine utilization in the hypothalamus of the male rat during adolescent development

This study examined the influence of adolescent development and pubertal changes in gonadal function on the development of norepinephrine (NE) turnover in the hypothalamus and cerebral cortex of rats from late juvenile to young adult ages. In one study, NE utilization was estimated in intact male rats and in male rats castrated at 14 days of age. NE levels were measured 15, 30, 45, 60, 120, and 240 min after inhibition of catecholamine synthesis at 28, 42, and 70 days of age. In a second study, male rats were made precocious by chronic testosterone exposure over days 14-28 and on the 28th day NE utilization was measured in both the hypothalamus and cerebral cortex. Turnover rates were calculated based on steady-state kinetics. The results indicate that in vivo NE levels and turnover rates in both the hypothalamus and cortex significantly increase from a late juvenile age to adulthood. However, when NE levels measured after synthesis inhibition were expressed as a percentage of the mean basal values, there was a significant effect of age only in the hypothalamus. Hence, the age-related increases in hypothalamic NE turnover appear to reflect age-related changes in NE utilization, whereas the increases in cortical turnover rates reflect the increasing basal levels and not age-related changes in NE utilization. During mid-puberty (42 days), NE utilization in the hypothalamus was markedly different from that observed in this region at either 28 or 70 days. At 28 and 70 days, NE levels decreased to 50% of basal levels by 4 h following synthesis inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)

Neonatal caffeine exposure alters developmental sensitivity to adenosine receptor ligands

Studies were done to determine whether the apparent changes in behavioral sensitivity to adenosine receptor ligands that occur with age and with neonatal caffeine exposure were due to a change in sensitivity of the receptor for the ligand or to a more fundamental change in the receptor. Using an animal model that mimics the brain developmental period and level of caffeine exposure in human premature neonates treated with caffeine for apnea of prematurity, behavioral and neurochemical investigations were undertaken. The locomotor responses to acute challenge with caffeine (15, 30 and 60 mg/kg) and with D-phenylisopropyladenosine (D-PIA) (0.038 and 0.38 mg/kg), an adenosine receptor agonist, were measured in control and neonatally caffeine-exposed rats at 12, 15, 18, and 28 days of age. The dissociation constants (Kd) and maximal binding densities (Bmax) for agonist binding at the adenosine A1 receptor site were determined over a similar time period. Caffeine displacement of an adenosine A1 agonist was also measured to examine in vitro sensitivity to caffeine as a function of age and neonatal caffeine exposure. Our studies demonstrated that the differential responses to adenosine receptor ligands seen as a function of both age and neonatal caffeine exposure could not be overcome by merely increasing the doses of ligand administered. In addition, the results of the binding studies indicated that changes in the adenosine receptor are occurring as a function of age in different regions of the brain of control animals and that this development is influenced by neonatal caffeine exposure.

Gonadal status and pubertal age influence the responsiveness of the benzodiazepine/GABA receptor complex to environmental challenge in male rats

Pubertal age and gonadal status in male rats influenced the functional response of the benzodiazepine (BZD)/GABA receptor chloride channel complex to an environmental challenge, i.e., encountering a stranger in familiar versus an unfamiliar environment. Chloride (Cl-) enhancement of [3H]flunitrazepam [( 3H]Flu) binding was facilitated by exposure to an unfamiliar environment relative to that measured in response to a familiar environment in gonadally intact adult rats but not in prepubertal rats (28 days). Enhancement of [3H]Flu by Cl- at 28 days was not differentially affected by the two environments and did not differ from that measured in non-handled control rats at this age. While a differential effect of the two environments on Cl- enhancement of [3H]Flu binding was also present in adult rats castrated as juveniles (at 19 days), the relationship of environmental challenge to Cl- facilitation was the reverse of that measured in intact adult rats. In addition. GABA-mediated 36Cl- uptake was facilitated in intact adult rats tested in either the familiar or unfamiliar environment relative to non-handled intact adult rats. This change in GABA-gated chloride channel function in response to environmental challenge, however, was not present in adult rats castrated as juveniles nor in 28-day-old rats. Therefore, both pubertal age and gonadal status influenced the responsiveness of the BZD/GABA receptor complex to environmental challenge. These findings suggest that pubertal development and adult hormonal status are important determinants of the functional responsiveness of the BZD/GABA receptor complex to environmental challenge.

Anxiolytic effects of 3 alpha-hydroxy-5 alpha[beta]-pregnan-20-one: endogenous metabolites of progesterone that are active at the GABAA receptor

The effects of intracerebroventricular administration of reduced metabolites of progesterone on locomotor activity and on exploration in the elevated plus-maze were assessed in adult female rats. Allopregnanolone (3 alpha-hydroxy-5 alpha-pregnan-20-one; 1.25, 5.0, and 10 micrograms) and pregnanolone (3 alpha-hydroxy-5 beta-pregnan-20-one; 2.5, 5.0, and 10 micrograms) elicited anxiolytic effects and, at the highest dose tested, allopregnanolone resulted in sedation. In contrast, the 3 beta-hydroxy-epimer of allopregnanolone was without effect in either behavioral paradigm. The anxiolytic response to pregnanolone was blocked by picrotoxin (0.75 mg/kg, i.p.), a dose that by itself did not affect behavior in the plus-maze. These data suggest that the anxiolytic effect of 3 alpha-hydroxy metabolites of progesterone is mediated by brain GABAA receptors in a stereospecific manner, and are in good agreement with the well-documented in vitro effects of these steroids as potent modulators of the GABAA receptor.

Ovarian endocrine status modulates the anxiolytic potency of diazepam and the efficacy of gamma-aminobutyric acid-benzodiazepine receptor-mediated chloride ion transport

The effect of ovarian steroid hormones on the behavioral and neurochemical sensitivity of the gamma-aminobutyric acid (GABA)-benzodiazepine (BZD) receptor chloride ion channel complex was studied. Locomotor activity and behavior in the elevated plus maze were examined in female rats of various ovarian states as was the efficacy and potency of GABA-stimulated chloride uptake in cortical synaptoneurosomes from proestrous and ovariectomized rats. A significant increase in the exploration of the open arms of the plus maze was observed in lactating females, in relation to diestrous, proestrous, ovariectomized, and pregnant females. The anxiolytic effect of diazepam (DZ) was decreased in ovariectomized females, in relation to proestrus females. Although 1.0 mg/kg DZ in proestrous females resulted in significant anxiolytic activity, this dose was ineffective in ovariectomized females but was reinstated by injection of estradiol benzoate and progesterone. A reduced efficacy of GABA-stimulated chloride ion transport in cortical synaptoneurosomes from ovariectomized females, in relation to that from proestrous females, was observed. Furthermore, the facilitative effect of DZ on the potency of GABA-stimulated chloride ion influx that was observed in cortical synaptoneurosomes from proestrous females was absent in synaptoneurosomes from ovariectomized females. These results are discussed in terms of the effect of ovarian steroids and reduced metabolites on GABA-BZD receptor-mediated functions.

Gestational exposure to diazepam increases sensitivity to convulsants that act at the GABA/benzodiazepine receptor complex

Experiments examining seizure sensitivity were conducted on adult male offspring exposed to diazepam at 1.0 or 2.5 mg/kg per day in utero over gestational days 14-20. Threshold dosages to facial clonus, myoclonic jerk, clonic seizure, and extensor tonus were determined via i.v. infusion of bicuculline, methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM), picrotoxin, pentylenetetrazol, caffeine and strychnine. Relative to uninjected and vehicle-exposed adult male offspring, prenatal diazepam administration reduced the threshold for bicuculline- and DMCM-induced facial clonus and myoclonic jerk by 40-50%. The threshold dosages to facial clonus, myoclonic jerk and clonic seizure from picrotoxin infusion were similarly reduced in animals exposed to diazepam in utero. In contrast, seizure thresholds to pentylenetetrazol, caffeine and strychnine were not affected by early developmental exposure to diazepam. In parallel biochemical studies, an increased sensitivity to the antagonistic effects of bicuculline methiodide on gamma-aminobutyrate (GABA)-stimulated chloride influx was observed in cortical synaptoneurosomes from adult male progeny of diazepam-treated dams. The results are interpreted to reflect a long-lasting alteration in the function of the GABA/benzodiazepine receptor complex by prenatal diazepam exposure that is manifest at the behavioral and neurochemical level in a pharmacologic specific manner.

Experience influences environmental modulation of function at the benzodiazepine (BZD)/GABA receptor chloride channel complex

Function of the benzodiazepine (BZD)/GABA receptor chloride channel complex was selectively altered by specific aspects of an environmental challenge, i.e. encountering a stranger in a familiar versus an unfamiliar environment. Chloride (Cl-) enhancement of [3H]flunitrazepam [( 3H]flu) binding was facilitated in rats tested in an unfamiliar environment relative to that in rats tested in a familiar environment. Basal [3H]flu binding (binding in the absence of NaCl) also was greater in rats tested in the unfamiliar environment than in rats tested in the familiar environment, and Scatchard analysis of [3H]flu binding indicated that increased [3H]flu binding in the unfamiliar environment reflected an increase in both binding affinity and maximal binding capacity. In addition, both the sensitivity of [3H]flu binding to Cl- and the affinity of BZD recognition sites were decreased in handled control rats relative to non-handled control rats as well as to environmentally-challenged (prehandled) rats, suggesting that the experience of daily handling as well as familiarization with the environment modulates function at the BZD/GABA receptor complex. GABA-mediated 36Cl- uptake was facilitated by testing in either the familiar or unfamiliar environment relative to that measured in non-handled control rats. Thus, changes in GABA-gated chloride channel function may reflect a more fundamental response of this complex to challenging situations. These findings suggest that components of the BZD/GABA receptor complex are differentially influenced by specific aspects of an environmental challenge. Furthermore, function at the BZD recognition site/chloride channel component of this receptor complex is influenced by both repeated and single exposure to specific environments.

Sexually dimorphic influence of prenatal exposure to diazepam on behavioral responses to environmental challenge and on gamma-aminobutyric acid (GABA)-stimulated chloride uptake in the brain

Early developmental exposure to diazepam (DZ) via administration of the drug to the pregnant rat (1.0 or 2.5 mg/kg) over gestational days 14 to 20 altered both behavior of adult progeny on two tests of anxiety and function of the benzodiazepine/gamma-aminobutyric acid (GABA) receptor complex (a neural substrate of anxiety-related behavior) in a sexually dimorphic manner. Adult male rats (60-90 days) exposed in utero to DZ spent significantly more time on the open arm of the elevated plus-maze than male rats exposed to vehicle, whereas plus-maze performance in female rats was unaffected by the early drug exposure. Similarly, early exposure to DZ markedly altered environment-specific social interaction in male rats, leading to increased social interaction in the unfamiliar environment and decreased social interaction in the familiar environment. Social interaction in adult female rats is not normally environment-specific; however, female rats exposed in utero to DZ at 2.5 mg/kg demonstrated a significant effect of the novel environment on social interaction, thus responding like unmanipulated male rats. The sensitivity of GABA-mediated 36chloride uptake to GABA was enhanced in synaptoneurosomes from male rats exposed in utero to DZ at 2.5 mg/kg and early exposure to either dose of DZ prevented the facilitative effect of DZ added in vitro on GABA-mediated chloride uptake. Function of the receptor complex was not altered in female rats by early DZ exposure. Thus, perinatal insults at the molecular level may underlie gender-related behavioral disorders in the young adult.

Modulation of noise-potentiated acoustic startle via the benzodiazepine-!g-aminobutyric acid receptor complex

Diazepam (DZ), an anxiolytic benzodiazepine (BZD) compound, attenuated the facilitation of the acoustic startle response by background noise. In Experiment 1, using a cumulative dosing paradigm, the effect of DZ on noise potentiation was found to be dose related. In Experiment 2, using a between-animals exposure design, the effect of DZ on noise potentiation was attenuated by coexposure to the central-type BZD receptor antagonist RO 15-1788, which itself was without effect. Using a cumulative dosing design in Experiment 3, RO 15-1788 was found to reverse the effect of DZ, whereas the peripheral-type BZD receptor ligand RO 54864 was without effect. The differences in the effect of cumulative exposure versus single dose exposure to RO 15-1788 were interpreted as indicative of either an intrinsic effect of the antagonist after repeated exposure or an influence of background noise itself on the BZD-gamma-aminobutyric acid receptor complex.

Ovarian endocrine status modulates the anxiolytic potency of diazepam and the efficacy of !g-aminobutyric acid-benzodiazepine receptor-mediated chloride ion transport

The effect of ovarian steroid hormones on the behavioral and neurochemical sensitivity of the gamma-aminobutyric acid (GABA)-benzodiazepine (BZD) receptor chloride ion channel complex was studied. Locomotor activity and behavior in the elevated plus maze were examined in female rats of various ovarian states as was the efficacy and potency of GABA-stimulated chloride uptake in cortical synaptoneurosomes from proestrous and ovariectomized rats. A significant increase in the exploration of the open arms of the plus maze was observed in lactating females, in relation to diestrous, proestrous, ovariectomized, and pregnant females. The anxiolytic effect of diazepam (DZ) was decreased in ovariectomized females, in relation to proestrus females. Although 1.0 mg/kg DZ in proestrous females resulted in significant anxiolytic activity, this dose was ineffective in ovariectomized females but was reinstated by injection of estradiol benzoate and progesterone. A reduced efficacy of GABA-stimulated chloride ion transport in cortical synaptoneurosomes from ovariectomized females, in relation to that from proestrous females, was observed. Furthermore, the facilitative effect of DZ on the potency of GABA-stimulated chloride ion influx that was observed in cortical synaptoneurosomes from proestrous females was absent in synaptoneurosomes from ovariectomized females. These results are discussed in terms of the effect of ovarian steroids and reduced metabolites on GABA-BZD receptor-mediated functions.

Gonadal hormones during puberty organize environment-related social interaction in the male rat

This study examined the role of gonadal androgens during puberty on the development of environment-related social interaction (SI) in male rats. SI in an unfamiliar environment versus SI in a familiar environment was evaluated in young adult rats as a function of sex and gonadal status. Intact male rats at 60 days of age exhibited a differential response to the two environments, whereas SI in intact female rats at 60 days was equivalent in the two environments. Furthermore, male rats castrated as juveniles and tested for SI at 60 days displayed a pattern of environment-related SI similar to SI in intact adult female rats. This effect of juvenile castration on SI in male rats was prevented by chronic exposure to testosterone propionate (TP) over Days 30 through 60. SI in male rats castrated in adulthood, on the other hand, was not altered either 2 or 4 weeks postcastration. The results from this study indicate that pubertal secretions of gonadal androgen(s) are necessary for the development of environment-related SI in male rats. In contrast, secretions of gonadal androgens in adulthood do not appear to be critical for the continued expression of environment-related SI, as suggested by the observation that environment-related SI in male rats remains unchanged by castration in adulthood.

Aging-related changes in brain metabolism are altered by early developmental exposure to diazepam

To study the long-term effects of prenatal diazepam (DZ) exposure, 31P NMR (nuclear magnetic resonance) spectra and levels of thiobarbituric acid (TBA)-reactive material were measured in the brains of rats from 3 to 26 months of age. In control rats, there were aging-related increases in levels of TBA-reactive material, decreases in intracellular pH (pHi) and alterations in phosphocreatine (PCr) utilization. Prenatal (late gestational) DZ exposure induced lasting, dose-related and age-related alterations in levels of TBA-reactive material and pHi. The results indicate that the prenatal chemical environment can influence cellular metabolism throughout the lifetime of the organism, and that the process of aging can in turn interact with the consequences of prenatal drug exposure.

Early developmental exposure to benzodiazepine ligands alters brain levels of thiobarbituric acid-reactive products in young adult rats

Levels of thiobarbituric acid (TBA)-reactive material were measured in brain regions of 3-4 month-old rats following prenatal exposure to several benzodiazepine (BDZ) receptor ligands over gestational days 14-20. Prenatal exposure to diazepam (DZ) at 1.0 mg/kg/day markedly elevated levels of brain TBA-reactive material while exposure to a higher dose (2.5 mg/kg) induced a significant increase only in the hippocampus. Early exposure to the central-type BDZ agonist clonazepam as well as to the central-type antagonist Ro 15-1788 also increased brain levels of TBA-reactive material. Concurrent exposure to the higher dose of DZ partially attenuated the effect of Ro 15-1788. Prenatal exposure to the peripheral-type BDZ ligand PK11195 produced a profound increase in TBA-reactive products in all regions, and concurrent DZ exposure did not attenuate this effect, except in the basal ganglia. Measurement of TBA-reactive material from birth to 3 months indicated that the effect of prenatal exposure to DZ was not apparent until after 8 weeks of age. Acute in vitro exposure of adult and fetal tissue to DZ had no effect on TBA-reactive material. The results suggest an interference in the organization of cellular metabolism in the brain by developmental exposure to BDZ ligands.

Pubertal-related changes influence the development of environment-related social interaction in the male rat

The influence of pubertal age on the differential effect of a familiar versus an unfamiliar environment on social interaction (SI) in pairs of male rats was evaluated. The decrease in SI induced by the unfamiliar environment in adult rats is considered an anxiety-related response. Intact male rats and male rats castrated at 19 days were tested for SI at 28, 35, and 60 days of age. The results revealed that in the intact rats, decreased SI in an unfamiliar environment was evident at 35 and 60 days but not at 28 days. The behavioral composition of the environment-induced response at 35 days was different from that measured at 60 days. Prepubertal castration prevented the decrease in SI in the unfamiliar environment at both 35 and 60 days. This study demonstrated the emergence with the onset of puberty of a specific behavioral response to an anxiogenic condition. Furthermore, the development of this environment-related behavioral response was influenced by gonadal secretion(s), suggesting the importance of gonadal function to the emergence of this response.

GABA-stimulated chloride uptake and enhancement by diazepam in synaptoneurosomes from rat brain during prenatal and postnatal development

The present study was undertaken to evaluate the ability of diazepam (DZ) to elicit a response in the brains of developing animals. gamma-Aminobutyric acid (GABA)-stimulated 36Cl- uptake in the presence and absence of DZ was measured in synaptoneurosomal preparations from whole brain of fetal rats at 20 and 21 days gestation and from cerebral cortex of rats at 7, 14, 21, 28 and 60-90 days postnatal age. The ability of GABA to stimulate 36Cl- uptake in a concentration-dependent manner was evident from gestational day 20. The EC50 for GABA stimulation but not the maximum stimulation increased significantly from day 20 to day 21 of gestation. Postnatally, only moderate changes in the EC50 were evident, but the maximum 36Cl- transported increased significantly from 7 to 14 days and remained stable thereafter. DZ enhanced GABA-mediated 36Cl- influx from 20 days gestation, and this enhancement was seen as a decrease in the EC50 for GABA stimulation. However, DZ also significantly increased maximum GABA-stimulated 36Cl- transport in synaptoneurosomal preparations at 21 days gestation and at 7 days postnatal age, a response to DZ not seen at older ages. DZ had a less robust effect on GABA-mediated 36Cl- transport at 28 days postnatal age than at any other age, a result consistent with functional observations of decreased responsivity to DZ in late juvenile, early adolescent rats. The benzodiazepine antagonist Ro 15-1788 prevented the effect of DA on GABA-stimulated 36Cl- uptake in tissue from 21-day fetuses and from 60- to 90-day-old adults.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthetic-induced corneal lesions in developmentally sensitive rats

Developmental critical periods for the induction of abnormalities by exposure to exogenous substances need not be confined to the early embryonic stage of organogenesis. The combination of ketamine hydrochloride and xylazine, two commonly used anesthetic agents, resulted in a corneal epithelial calcium deposition in 84% of rat pups whose exposure was limited to a single injection during the third postnatal week only. Concurrent exposure to ketamine hydrochloride, xylazine, and yohimbine, an alpha 2 adrenergic receptor antagonist, resulted in corneal lesions in only 6% of rat pups so exposed. The etiology is presently not understood but may involve interference with neurally directed corneal development. Corneal desiccation may also play a role. Altered drug metabolism, and toxic interactions resulting from a changing oxygen or light milieu are less likely etiologic mechanisms. Aspects of corneal development and mechanisms by which drugs can interact with and disturb normal maturational sequences can now be approached.

Release of [3H]norepinephrine: alteration by early developmental exposure to diazepam

The effect of prenatal exposure to diazepam (over gestational days 13-20) on the release of tritiated norepinephrine [( 3H]NE) from selected brain regions was analyzed to determine mechanisms whereby such exposure could disrupt functioning in specific NE neurons, as previously observed. Pregnant rats were administered diazepam (DZ) once daily at doses of 1.0, 2.5 or 10.0 mg/kg and the offspring studied as adults at 70-90 days of age and during development at 14, 21, 35 and 56 days of age. Release of [3H]NE was measured during in vitro incubation using 25 mM potassium as the depolarizing stimulus. As noted previously, prenatal exposure to DZ induced an effect only on NE neurons innervating the hypothalamus, sparing the NE innervation to the hippocampus and cerebellum. Prenatal exposure to DZ had no effect on the depolarized release of [3H]NE in the hypothalamus until after 35 days of age, a developmental pattern previously observed with respect to endogenous NE levels. In adult rat offspring, however, the depolarization-induced release of [3H]NE from the hypothalamus decreased 28%, 32% and 64% (relative to uninjected control values) in animals prenatally exposed to DZ at 1.0, 2.5 or 10 mg/kg/day respectively. Concurrent exposure of the pregnant dam to benzodiazepine antagonists (Ro 15-1788 or ethyl-beta-carboline-3-carboxylate) prevented the effects of DZ (2.5 mg/kg/day) on [3H]NE release, demonstrating again the importance of the benzodiazepine binding site to the effects induced by the early DZ exposure. The initial accumulation of the [3H]NE was not altered by the prenatal exposure.(ABSTRACT TRUNCATED AT 250 WORDS)

Prenatal diazepam exposure in rats: long-lasting functional changes in the offspring

Adult (90-100 day-old) rats exposed prenatally (13-20 days of gestation) to diazepam (DZ) at 1.0, 2.5, or 10 mg/kg/day, were examined for functional deficits. Tests were designed to (1) correlate with known neural alterations induced by the prenatal exposure, or (2) to address the problem of developing tests of functional teratology in animals which have relevance to complex human functions. The careful selection of functional tests has disclosed several effects of prenatal DZ exposure on adult rat progeny. The dose-effect relationship was found to vary with the different tests, indicating that a thorough evaluation of the consequences of prenatal drug exposure necessitates utilization of several functional approaches. The results of these studies on the effects of prenatal exposure to DZ support the hypothesis that in utero exposure to drugs targeted for action on the central nervous system can induce long-lasting alterations on the neural substrates of behavior on the offspring with resulting functional consequences.

Prenatal exposure to diazepam alters central and peripheral responses to stress in adult rat offspring

Central and peripheral responses to restraint stress were evaluated in 90-day-old rats exposed prenatally to diazepam (1.0, 2.5, or 10.0 mg/kg/day) over gestational days 13-20. As a measure of a central response to stress, the utilization of norepinephrine (NE) by hypothalamic NE neurons was assessed by determining the effect of stress on the loss of NE after synthesis inhibition. The stress-induced changes in plasma corticosterone and prolactin levels were evaluated as a physiologic index of stress. While stress increased the loss of NE after synthesis inhibition in the non-exposed control animals, it totally prevented any loss of NE after synthesis inhibition in offspring prenatally exposed to DZ. Additionally, the stress-induced change in plasma corticosterone was attenuated in a dose-related manner by prenatal exposure to DZ. The stress-induced change in plasma prolactin was also altered in a dose-related manner by the prenatal exposure. Both the altered response to stress within hypothalamic NE neurons and the attenuated change in plasma corticosterone induced by prenatal exposure to DZ (2.5 mg/kg) were prevented by concurrent administration of the centrally acting benzodiazepine antagonist Ro15-1788 to the pregnant dam, indicating that the effects of DZ were mediated via binding of the drug to central sites during gestation. These results indicate that activation of specific binding sites during early development can induce neural alterations in the adult offspring which can be reflected in functional changes which may compromise the organism.

Prenatal diazepam exposure in rats: long-lasting, receptor-mediated effects on hypothalamic norepinephrine-containing neurons

The concentration and turnover of catecholamines (CAs) were measured in the cortex, hippocampus, and hypothalamus of rats exposed in utero to diazepam (DZ, 1.0, 2.5, or 10.0 mg/kg/day) over gestational days 13-20. Prenatal DZ induced a regionally specific, dose-related decrease in the level of norepinephrine (NE) (maximum decrease, 65%) and turnover rate of NE (maximum decrease, 85%) in the hypothalamus of 90-day-old adult rats. Dopamine levels were not altered in this region and neither of the CAs were altered in the other regions. Dividing the prenatal exposure period into two shorter periods revealed that late gestation (days 17-20) was the period when factors influencing NE function in the hypothalamus were most sensitive to DZ. Analysis of the development of the CA in the hypothalamus demonstrated that the effect of the prenatal exposure on NE levels did not become apparent until after 28 days of age. However, at 28 days, there was a dose-related increase in turnover rate of NE (maximum increase, 52%). Concurrent administration of the specific benzodiazepine (BZ) antagonist RO15-1788 with DZ (2.5 mg/kg) to pregnant rats effectively reversed the effects of DZ in the hypothalamus of the adult offspring, suggesting that the effects were mediated via the BZ receptor. These data have provided insight into the intricate processes of neuronal development; in particular the importance of target cell-nerve terminal interactions and the role of early developing receptors.

Prenatal diazepam: distribution and metabolism in perinatal rats

Previous investigations have revealed that prenatal exposure to diazepam (DZ) alters brain development and behavior in the offspring of rats and mice. In order to understand how DZ may affect the developing nervous system it is necessary to examine its metabolic fate in the neonate. It is therefore the aim of this study to investigate the disposition, metabolism, and persistence of DZ in the neonate. Dams were injected s.c. with 2.5 mg/kg of 14C DZ (10 muCi/day) on days 13-20 of gestation and their litters were fostered at birth. Dams killed within 24 hours postpartum and neonates killed at postnatal days 0, 10, and 20 were analyzed for 14C activity. Brain levels (pmoles DZ and metabolites/100 mg tissue SE) were 3.4 +/- 0.3 in the dam and in the neonates were 3.2 +/- 0.3 (day 0), 3.4 +/- 0.3 (day 10), and undetectable at day 20. Neonatal peripheral tissue 14C activity was undetectable by day 10. Brain regional analysis indicates 14C is highest in the colliculi at day 0, but not at day 10. Brain levels of DZ, oxazepam (OXA), N-desmethyldiazepam (NDZ), and the glucuronide (GLU) determined by high-performance liquid chromatography (HPLC), were GLU (49%), DZ (28%), and NDZ (24%) in the dam; GLU (52%), DZ (24%), and NDZ (25%) in the day 0 neonate; and GLU (32%), DZ (12%), NDZ (39%), and OXA (19%) at day 10. The distribution and metabolism of 14C DZ that persists in the neonate following prenatal exposure differs from that which occurs in the dam.(ABSTRACT TRUNCATED AT 250 WORDS)

Neonatal lead exposure: effects on development of behavior and striatal dopamine neurons

Rats treated directly with water or lead acetate (25 or 75 mg/kg) on postnatal days 2 through 14 were tested for the development of spontaneous activity and for locomotor responses to d-amphetamine as weanlings. The development of striatal dopamine (DA) levels, uptake, release, and the disappearance of DA after synthesis inhibition were also examined. Blood and brain levels were markedly increased at 15 days in exposed animals; by 35 days blood lead levels had decreased 90% while lead level in neostriatum decreased only 55-60%. The effects of the early lead exposure fell into two classes. Shortly after cessation of lead treatment, changes were observed in exposed animals in the development of motor activity, as well as in the disappearance of DA after synthesis inhibition, accumulation of labelled DA, and endogenous DA levels. As brain lead decreased from 15 to 35 days many of the behavioral and neurochemical abnormalities also dissipated. However, at 35 days, striatal DA levels remained decreased in animals given the higher lead dose with a resultant decrease in turnover rate and alterations were noted in activity responses to d-amphetamine in lead-treated animals.