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

Sexually dimorphic expression of KCC2 and GABA function

GABA(A) receptors have an age-adapted function in the brain. During early development, they mediate depolarizing effects, which result in activation of calcium-sensitive signaling processes that are important for the differentiation of the brain. In more mature stages of development and in adults, GABA(A) receptors acquire their classical hyperpolarizing signaling. The switch from depolarizing to hyperpolarizing GABA(A)-ergic signaling is triggered through the developmental shift in the balance of chloride cotransporters that either increase (i.e. NKCC1) or decrease (i.e. KCC2) intracellular chloride. The maturation of GABA(A) signaling follows sex-specific patterns, which correlate with the developmental expression profiles of chloride cotransporters. This has first been demonstrated in the substantia nigra, where the switch occurs earlier in females than in males. As a result, there are sensitive periods during development when drugs or conditions that activate GABA(A) receptors mediate different transcriptional effects in males and females. Furthermore, neurons with depolarizing or hyperpolarizing GABA(A)-ergic signaling respond differently to neurotrophic factors like estrogens. Consequently, during sensitive developmental periods, GABA(A) receptors may act as broadcasters of sexually differentiating signals, promoting gender-appropriate brain development. This has particular implications in epilepsy, where both the pathophysiology and treatment of epileptic seizures involve GABA(A) receptor activation. It is important therefore to study separately the effects of these factors not only on the course of epilepsy but also design new treatments that may not necessarily disturb the gender-appropriate brain development.

Prenatal diazepam exposure alters respiratory control system and GABAA and adenosine receptor gene expression in newborn rats

In experimental animals, prenatal diazepam exposure has clearly been associated with behavioral disturbances. Its impact on newborn breathing has not been documented despite potential deleterious consequences for later brain development. We addressed this issue in neonatal rats (0-2 d) born from dams, which consumed 2 mg/kg/d diazepam via drinking fluid throughout gestation. In vivo, prenatal diazepam exposure significantly altered the normoxic-breathing pattern, lowering breathing frequency (105 vs. 125 breaths/min) and increasing tidal volume (16.2 vs. 12.7 mL/kg), and the ventilatory response to hypoxia, inducing an immediate and marked decrease in tidal volume (-30%) absent in controls. In vitro, prenatal diazepam exposure significantly increased the respiratory-like frequency produced by pontomedullary and medullary preparations (+38% and +19%, respectively) and altered the respiratory-like response to application of nonoxygenated superfusate. Both in vivo and in vitro, the recovery from oxygen deprivation challenges was delayed by prenatal diazepam exposure. Finally, real-time PCR showed that prenatal diazepam exposure affected mRNA levels of alpha1 and alpha2 GABAA receptor subunits and of A1 and A2A adenosine receptors in the brainstem. These mRNA changes, which are region-specific, suggest that prenatal diazepam exposure interferes with developmental events whose impact on the respiratory system maturation deserves further studies.

Long-lasting behavioral changes induced by pre- or neonatal exposure to diazepam in rats

Prenatal treatment with small doses of diazepam may counteract the effect of physical stress in rats, normalizing the time course of neonatal reflexes and the behavioral responses in adulthood. However, prenatal administration of diazepam in greater doses may induce desensitization of gamma-aminobutyric acid A (GABA(A)) receptors and induce hypersensitivity to convulsants. This study was designed to examine in rats the influence of prenatal or neonatal diazepam treatment on development of neonatal reflexes, as index of brain maturation, and susceptibility to pentylenetetrazol-induced convulsions in adulthood. Pregnant Wistar rats were injected with diazepam 2.5 mg/kg/day, intraperitoneally (i.p.) on days 14-21 of pregnancy. Offspring showed a delay in the appearing of neonatal reflexes (cliff aversion, forelimb placing, forelimb grasping and bar holding) except for righting and startle reflexes. At 50 days of age, male rats showed a greater sensitivity to pentylenetetrazol compared to controls. In contrast, females showed a decreased susceptibility to convulsions. The appearance of reflexes in pups exposed to diazepam during neonatal life appeared to be similar to that of controls. Only the appearance of cliff aversion and startle reflexes appeared to be delayed in animals exposed neonatally to diazepam as compared to controls. In adulthood, female rats exposed in early neonatal life to diazepam again showed a resistance to pentylenetetrazol-induced convulsions as compared to male animals. These data suggest that prenatal exposure to diazepam induces long-lasting behavioral changes, which may be influenced by sex-dependent factors.

Prolonged prenatal psychotropic medication exposure alters neonatal acute pain response

Selective serotonin reuptake inhibitors (SSRIs) and benzodiazepines are frequently used to treat maternal depression during pregnancy, however the effect of increased serotonin (5HT) and gamma-amino-butyric acid (GABA) agonists in the fetal human brain remains unknown. 5HT and GABA are active during fetal neurologic growth and play early roles in pain modulation, therefore, if prolonged prenatal exposure alters neurodevelopment this may become evident in altered neonatal pain responses. To examine biologic and behavioral effects of prenatal exposure, neonatal responses to acute pain (phenylketonuria heel lance) in infants with prolonged prenatal exposure were examined. Facial action (Neonatal Facial Coding System) and cardiac autonomic reactivity derived from the relationship between respiratory activity and short term variations of heart rate (HRV) were compared between 22 infants with SSRI exposure (SE) [fluoxetine (n = 7), paroxetine (n = 11), sertraline (n = 4)]; 16 infants exposed to SSRIs and clonazepam (SE+) [paroxetine (n = 14), fluoxetine (n = 2)]; and 23 nonexposed infants during baseline, lance, and recovery periods of a heel lance. Length of maternal SSRI use did not vary significantly between exposure groups-[mean (range)] SE:SE+ 183 (31-281):141 (54-282) d (p > 0.05). Infants exposed to SE and SE+ displayed significantly less facial activity to heel lance than control infants. Mean HR increased with lance, but was significantly lower in SE infants during recovery. Using measures of HRV and the transfer relationship between heart rate and respiration, SSRI infants had a greater return of parasympathetic cardiac modulation in the recovery period, whereas a sustained sympathetic response continued in the control group. Prolonged prenatal SSRI exposure appears to be associated with reduced behavioral pain responses and increased parasympathetic cardiac modulation in recovery following an acute neonatal noxious event. Possible 5HT-mediated pain inhibition, pharmacologic factors and the developmental course remain to be studied.

Prenatal stress induces body weight deficit and behavioural alterations in rats: the effect of diazepam

Prenatal stress may induce intrauterine growth retardation, but it is not known whether a treatment with the anxiolytic benzodiazepine, diazepam may interfere with this phenomenon. A daily physical stress consisting of a forced immersion for 15 min in cold water was applied to pregnant rats of the Wistar strain from gestational day 5 until parturition. Animals were treated either with physiological saline or with diazepam (0.1 or 1 mg/kg/day) injected intraperitoneally 1 h prior to stress application. Control animals received injections of physiological saline but were not subjected to physical stress. Newborn pups subjected to prenatal stress showed reduced body weight as compared to control animals. Offspring were also examined for the appearance day of the following reflexes: cliff aversion, startle, righting, forelimb placing, forelimb grasping and bar holding. Hair growth, and first day of ears and eyes opening was also scored. At 60 days of age, male rats from the three experimental groups were subjected to behavioural tests, i.e., constrained swim (despair test) and step-through passive avoidance response. Animals subjected to prenatal stress showed a delayed appearance of all neonatal reflexes and behavioural deficits in adulthood, namely increased immobility in the despair test and reduced retention of a passive avoidance task. The prenatal treatment with diazepam totally counteracted the effect of stress, normalizing the time-course of neonatal reflexes and the behavioural responses in adulthood. No difference was seen between the effects of the two drug doses. It is concluded that prenatal physical stress may induce body growth retardation and may be considered as a model for human intrauterine growth retardation. The treatment with an anxiolytic benzodiazepine, such as diazepam, may counteract the effects of prenatal stress interfering with the biological consequences of stress concerning probably cerebral neurotransmitters in both the unborn foetus and the pregnant rat.

An anxiolytic action of oxytocin is enhanced by estrogen in the mouse

The established role of oxytocin (OT) in facilitation of steroid-modulated reproductive and affiliative behaviors led to the speculation that it may have anxiolytic actions under certain hormonal conditions. NIH-Swiss mice were tested for responsiveness to OT in two behavioral tests of anxiety, the holeboard apparatus and elevated plus-maze. Dose-response assessment indicated that 3 mg/kg was the optimal dose for peripherally administered (IP) OT on the elevated plus-maze. There were no consistent effects at any dose on the holeboard apparatus. In ovariectomized mice pretreated with estradiol (E2), peripherally administered OT increased the number of entrances onto the open arms, as well as the amount of time on the open arms compared to other groups (ANOVA; p < 0.05). There was little to no effect of OT in ovariectomized animals not pretreated with E2. When OT was administered intracerebroventricularly (ICV), there was an increase in entrances and time on the open arms compared to that of females infused with arginine vasopressin (AVP). This increase was apparent in ovariectomized females, but was further enhanced in those pretreated with E2 (ANOVA; p < 0.05). In contrast, the combination of E2 pretreatment and ICV AVP decreased the number of entrances and time spent on the open arms of the elevated plus-maze compared to those receiving OT, suggesting an estrogen-modulated anxiogenic action of AVP. Analyses of [125]I-OVTA binding density indicated a significant increase in binding density in the lateral septum of E2-treated females compared to OIL-treated controls (ANOVA; p < 0.05). There was no effect of E2 treatment on [125]I-OVTA binding density in the amygdala or ventromedial nucleus of the hypothalamus. Taken together, these data indicate that OT exerts an anxiolytic action that is enhanced in the presence of circulating estrogen. This behavioral effect may be mediated by estrogen-induced increases in OT binding density in the lateral septum and may be important to the facilitation of social interactions.

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.