Regionally selective effects of GABA on hypothalamic GABAA receptor mRNA in vitro

Acute sleep deprivation preconditions the heart against ischemia/ reperfusion injury: the role of central GABA-A receptors

OBJECTIVES

Central γ-aminobutyric acid (GABA) neurotransmission modulates cardiovascular functions and sleep. Acute sleep deprivation (ASD) affects functions of various body organs via different mechanisms. Here, we evaluated the effect of ASD on cardiac ischemia/reperfusion injury (IRI), and studied the role of GABA-A receptor inhibition in central nucleus of amygdala (CeA) by assessing nitric oxide (NO) and oxidative stress.

MATERIALS AND METHODS

The CeA in sixty male Wistar rats was cannulated for saline or bicuculline (GABA-A receptor antagonist) administration. All animals underwent 30 min of coronary occlusion (ischemia), followed by 2 hr reperfusion (IR). The five experimental groups (n=12) included are as follows: IR: received saline; BIC+IR: received Bicuculline; MLP+IR: received saline, followed by the placement of animals in an aquarium with multiple large platforms; ASD+IR: underwent ASD in an aquarium with multiple small platforms; and BIC+ASD+IR: received bicuculline prior to ASD.

RESULTS

Bicuculline administration increased the malondialdehyde levels and infarct size, and decreased the NO metabolites levels and endothelial nitric oxide synthase (eNOS) gene expression in infarcted and non-infarcted areas in comparison to IR group. ASD reduced malondialdehyde levels and infarct size and increased NO metabolites, corticosterone levels and eNOS expression in infarcted and non-infarcted areas as compared to the IR group. Levels of malondialdehyde were increased while levels of NO metabolites, corticosterone and eNOS expression in infarcted and non-infarcted areas were reduced in the BIC+ASD+IR as compared to the ASD+IR group.

CONCLUSION

Blockade of GABA-A receptors in the CeA abolishes ASD-induced cardioprotection by suppressing oxidative stress and NO production.

GABAA receptor-mediated input change on orexin neurons following sleep deprivation in mice

Orexins are bioactive peptides, which have been shown to play a pivotal role in vigilance state transitions: the loss of orexin-producing neurons (orexin neurons) leads to narcolepsy with cataplexy in the human. However, the effect of the need for sleep (i.e., sleep pressure) on orexin neurons remains largely unknown. Here, we found that immunostaining intensities of the α1 subunit of the GABAA receptor and neuroligin 2, which is involved in inhibitory synapse specialization, on orexin neurons of mouse brain were significantly increased by 6-h sleep deprivation. In contrast, we noted that immunostaining intensities of the α2, γ2, and β2/3 subunits of the GABAA receptor and Huntingtin-associated protein 1, which is involved in GABAAR trafficking, were not changed by 6-h sleep deprivation. Using a slice patch recording, orexin neurons demonstrated increased sensitivity to a GABAA receptor agonist together with synaptic plasticity changes after sleep deprivation when compared with an ad lib sleep condition. In summary, the GABAergic input property of orexin neurons responds rapidly to sleep deprivation. This molecular response of orexin neurons may thus play a role in the changes that accompany the need for sleep following prolonged wakefulness, in particular the decreased probability of a transition to wakefulness once recovery sleep has begun.

Time- and behavioral state-dependent changes in posterior hypothalamic GABAA receptors contribute to the regulation of sleep

Sleep-wake behavior is regulated by a circadian rhythm, homeostatically and by additional mechanisms that determine the timing of slow-wave sleep and rapid eye movement sleep (REMS) episodes. The posterior hypothalamus coordinates the neural and humoral signals with the rest-activity cycle. It contains wake-active neurons, and is a site where stimulation of inhibitory GABA_A receptors promotes sleep, whereas their antagonism enhances wakefulness. We explored whether GABAergic mechanisms present in the posterior hypothalamus contribute to the homeostatic and other aspects of sleep-wake regulation. Using micropunches of tissue extracted from either the perifornical (PF) or dorsomedial (DM) regions of the posterior hypothalamus of rats, we determined that mRNA levels for selected subunits of GABA_A receptors (β1, β3 and ε) were higher at the end of the active period or following sleep deprivation, when the need for sleep is high, than after several hours of sleep, when sleep need is partially fulfilled. Such a pattern was present in the PF region only, and was consistent with changes in β1 subunit and GABA synthesizing enzyme (GAD) protein levels. In contrast, in the DM region, the levels of GABA_A receptor subunit mRNAs and proteins (α1, α2, β1) and GAD varied with circadian time, but were not responsive to sleep deprivation. Separate experiments with sleep-wake monitoring and local perfusion of the PF region with the GABA_A receptor antagonist bicuculline revealed that the antagonist had a weaker sleep-reducing effect when sleep need was enhanced by sleep deprivation and that the increased amount of REMS characteristic of the late sleep period was dependent on endogenous GABAergic inhibition. These results support the concept that a varying magnitude of GABAergic inhibition exerted within the PF region contributes to the homeostatic regulation of sleep and shapes its temporal pattern, whereas GABAergic mechanisms in the DM region contribute to circadian regulation.

Perinatal alcohol exposure leads to prolonged upregulation of hypothalamic GABA A receptors and increases behavioral sensitivity to gaboxadol

Prenatal alcohol exposure (AE) is associated with lasting abnormalities of sleep and motor development, but the underlying mechanisms are unknown. We hypothesized that AE alters development of GABAergic signaling in the hypothalamic regions important for the control of sleep and motor activity. Alcohol (5.25 g/(kg day)) was administered intragastrically to male rats on postnatal days (PD) 4-9, a period of brain development equivalent to the human third trimester (AE group). Control pups were sham-intubated (S group). Motor activity was monitored on PD27 and 28. On PD29 and 30, GABA A receptor subunit mRNA levels and alpha4 and delta subunit proteins were quantified by RT-PCR and immunoblotting, respectively, in the wake- and motor activity-promoting perifornical (PF) region of the posterior hypothalamus and the sleep-promoting ventrolateral preoptic (VLPO) region of the anterior hypothalamus. Then, in 47-52-day-old rats, motor activity was quantified following administration of GABA A receptor agonist, gaboxadol (5 mg/kg s.c.). In the PF region, mRNA and protein levels for the alpha4 and delta subunits were significantly higher and beta3 and gamma2 subunit mRNAs were also increased in the AE group. In the VLPO region, only the delta subunit mRNA was increased. Spontaneous motor activity was lower and suppressed more by gaboxadol in the AE than S group, and the latency to a transient total loss of activity after gaboxadol was shorter in the AE group. Thus, perinatal AE leads to GABA A receptor overexpression in the vigilance- and motor activity-promoting hypothalamic PF region, with the neurochemical and functional outcomes lasting long beyond the period of the insult.

Cyclopeptide alkaloid fraction from Zizyphi Spinosi Semen enhances pentobarbital-induced sleeping behaviors

This study aimed to investigate effects of cyclopeptide alkaloid fraction of ZSS (CAFZ) on pentobarbital-induced sleeping behaviors and to determine whether these effects were mediated by gamma-aminobutyric acid (GABA) receptors Cl(-) channel activation, using a Western blot technique and Cl(-) sensitive fluorescence probe. GABA receptors subunits expression and Cl(-) influx were investigated in cultured cerebellar granule cells. CAFZ shortened sleeping onset and prolonged sleeping time induced by pentobarbital (42 mg/kg). It also significantly increased the falling asleep rate and duration of sleeping time at a sub-hypnotic dosage of pentobarbital (28 mg/kg). In addition, CAFZ in combination with GABA A receptors agonist, muscimol, synergistically prolonged pentobarbital-induced sleeping time. Both of CAFZ and pentobarbital treatment decreased GABA A receptors alpha-subunit expression, but did not change beta- and gamma-subunit expression. However, we found CAFZ and pentobarbital increased Cl(-) influx, CAFZ showed similar effects with muscimol in potentiating Cl(-) influx inducing effects of low-dose pentobarbital. In conclusion, it is suggested that the enhancement of Cl(-) influx by CAFZ may play an important role in the potentiation of pentobarbital-induced sleeping behaviors.

Sex-dependent expression of CYP2C11 in spleen, thymus and bone marrow regulated by growth hormone

CYP2C11, the most commonly expressed isoform of cytochrome P450 in male rat liver, was measured in spleen, thymus and bone marrow by quantitative real-time PCR and enhanced Western blotting. CYP2C11 concentrations in the lymphoid tissues were a fraction of that observed in liver, but like the liver, were sexually dimorphic (M>F) with mRNA and protein levels in agreement. Although the response to hypophysectomy varied according to tissue and sex, expression levels of CYP2C11 in all measured tissues remained greater in males. Further differences in CYP2C11 expression between liver and lymphoid tissue were observed following restoration of the circulating masculine growth hormone profile in hypophysectomized rats. In contrast to the liver where the renaturalized growth hormone profile elevated CYP2C11 expression in both sexes, the response was opposite in spleen and thymus with isoform concentrations declining in both sexes. Lastly, the divergent response of CYP2C11 between the liver and immune system was examined in cultured splenocytes exposed to different mitogens. In contrast to the dramatic depletion of CYP2C11 reported in proliferating hepatocytes, mitogen-stimulation resulted in a significant elevation in splenocyte CYP2C11 expression. In summary, we report for the first time that thymus, spleen and bone marrow express, albeit nominal, sex-dependent levels of CYP2C11 (M>F) whose regulation appears to be under some hormonal control, but very different from that of the hepatic isoform.