GABAA receptor modulation of temperature sensitive neurons in the diagonal band of Broca in vitro

The genetic risk of acute seizures in African children with falciparum malaria

Purpose

It is unclear why some children with falciparum malaria develop acute seizures and what determines the phenotype of seizures. We sought to determine if polymorphisms of malaria candidate genes are associated with acute seizures.

Methods

Logistic regression was used to investigate genetic associations with malaria-associated seizures (MAS) and complex MAS (repetitive, prolonged, or focal seizures) in four MalariaGEN African sites, namely: Blantyre, Malawi; Kilifi, Kenya; Kumasi, Ghana; and Muheza, Tanzania. The analysis was repeated for five inheritance models (dominant, heterozygous, recessive, additive, and general) and adjusted for potential confounders and multiple testing.

Key Findings

Complex phenotypes of seizures constituted 71% of all admissions with MAS across the sites. MAS were strongly associated with cluster of differentiation-ligand-rs3092945 in females in Kilifi (p = 0.00068) and interleukin (IL)-17 receptor E-rs708567 in the pooled analysis across the sites (p = 0.00709). Complex MAS were strongly associated with epidermal growth factor module-containing mucin-like hormone receptor (EMR)1-rs373533 in Kumasi (p = 0.00033), but none in the pooled analysis. Focal MAS were strongly associated with IL-20 receptor A-rs1555498 in Muheza (p = 0.00016), but none in the pooled analysis. Prolonged MAS were strongly associated with complement receptor 1-rs17047660 in Kilifi (p = 0.00121) and glucose-6-phosphate dehydrogenase-rs1050828 in females in the pooled analysis (p = 0.00155). Repetitive MAS were strongly associated with EMR1-rs373533 in Kumasi (p = 0.00003) and cystic fibrosis transmembrane conductance receptor-rs17140229 in the pooled analysis (p = 0.00543). MAS with coma/cerebral malaria were strongly associated with EMR1-rs373533 in Kumasi (p = 0.00019) and IL10-rs3024500 in the pooled analysis across the sites (p = 0.00064).

Significance

We have identified a number of genetic associations that may explain the risk of seizures in >2,000 cases admitted to hospitals with MAS across four sites in Africa. These associations differed according to phenotype of seizures and site.

Distinct α subunit variations of the hypothalamic GABAA receptor triplets (αβγ) are linked to hibernating state in hamsters

Background

The structural arrangement of the γ-aminobutyric acid type A receptor (GABA_AR) is known to be crucial for the maintenance of cerebral-dependent homeostatic mechanisms during the promotion of highly adaptive neurophysiological events of the permissive hibernating rodent, i.e the Syrian golden hamster. In this study, in vitro quantitative autoradiography and in situ hybridization were assessed in major hypothalamic nuclei. Reverse Transcription Reaction-Polymerase chain reaction (RT-PCR) tests were performed for specific GABA_AR receptor subunit gene primers synthases of non-hibernating (NHIB) and hibernating (HIB) hamsters. Attempts were made to identify the type of αβγ subunit combinations operating during the switching ON/OFF of neuronal activities in some hypothalamic nuclei of hibernators.

Results

Both autoradiography and molecular analysis supplied distinct expression patterns of all α subunits considered as shown by a strong (p < 0.01) prevalence of α₁ ratio (over total α subunits considered in the present study) in the medial preoptic area (MPOA) and arcuate nucleus (Arc) of NHIBs with respect to HIBs. At the same time α₂ subunit levels proved to be typical of periventricular nucleus (Pe) and Arc of HIB, while strong α₄ expression levels were detected during awakening state in the key circadian hypothalamic station, i.e. the suprachiasmatic nucleus (Sch; 60%). Regarding the other two subunits (β and γ), elevated β₃ and γ₃ mRNAs levels mostly characterized MPOA of HIBs, while prevalently elevated expression concentrations of the same subunits were also typical of Sch, even though this time during the awakening state. In the case of Arc, notably elevated levels were obtained for β₃ and γ₂ during hibernating conditions.

Conclusion

We conclude that different αβγ subunits are operating as major elements either at the onset of torpor or during induction of the arousal state in the Syrian golden hamster. The identification of a brain regional distribution pattern of distinct GABA_AR subunit combinations may prove to be very useful for highlighting GABAergic mechanisms functioning at least during the different physiological states of hibernators and this may have interesting therapeutic bearings on neurological sleeping disorders.

The importance of ‘awareness’ for understanding fetal pain

Our understanding of when the fetus can experience pain has been largely shaped by neuroanatomy. However, completion of the cortical nociceptive connections just after mid-gestation is only one part of the story. In addition to critically reviewing evidence for whether the fetus is ever awake or aware, and thus able to truly experience pain, we examine the role of endogenous neuro-inhibitors, such as adenosine and pregnanolone, produced within the feto-placental unit that contribute to fetal sleep states, and thus mediate suppression of fetal awareness. The uncritical view that the nature of presumed fetal pain perception can be assessed by reference to the prematurely born infant is challenged. Rigorously controlled studies of invasive procedures and analgesia in the fetus are required to clarify the impact of fetal nociception on postnatal pain sensitivity and neural development, and the potential benefits or harm of using analgesia in this unique setting.

GABA transporter deficiency causes tremor, ataxia, nervousness, and increased GABA-induced tonic conductance in cerebellum

GABA transporter subtype 1 (GAT1) knock-out (KO) mice display normal reproduction and life span but have reduced body weight (female, -10%; male, -20%) and higher body temperature fluctuations in the 0.2-1.5/h frequency range. Mouse GAT1 (mGAT1) KO mice exhibit motor disorders, including gait abnormality, constant 25-32 Hz tremor, which is aggravated by flunitrazepam, reduced rotarod performance, and reduced locomotor activity in the home cage. Open-field tests show delayed exploratory activity, reduced rearing, and reduced visits to the central area, with no change in the total distance traveled. The mGAT1 KO mice display no difference in acoustic startle response but exhibit a deficiency in prepulse inhibition. These open-field and prepulse inhibition results suggest that the mGAT1 KO mice display mild anxiety or nervousness. The compromised GABA uptake in mGAT1 KO mice results in an increased GABA(A) receptor-mediated tonic conductance in both cerebellar granule and Purkinje cells. The reduced rate of GABA clearance from the synaptic cleft is probably responsible for the slower decay of spontaneous IPSCs in cerebellar granule cells. There is little or no compensatory change in other proteins or structures related to GABA transmission in the mGAT1 KO mice, including GAT1-independent GABA uptake, number of GABAergic interneurons, and GABA(A)-, vesicular GABA transporter-, GAD65-, and GAT3-immunoreactive structures in cerebellum or hippocampus. Therefore, the excessive extracellular GABA present in mGAT1 KO mice results in behaviors that partially phenocopy the clinical side effects of tiagabine, suggesting that these side effects are inherent to a therapeutic strategy that targets the widely expressed GAT1 transporter system.

Two-photon imaging of spontaneous vesicular release in acute brain slices and its modulation by presynaptic GABAA receptors

Action potential-independent spontaneous vesicular release of gamma-aminobutyric acid (GABA) in the CNS mediates miniature inhibitory postsynaptic currents (mIPSCs) and exerts an important control on central excitability. Using dual-photon laser scan microscopy and hyperosmotic loading of the readily releasable vesicle pool with the fluorescent styryl dye FM1-43 in hippocampal slice, we demonstrate action potential-independent release of vesicles (fluorescence destaining) from proximal perisomatic, presumed GABAergic terminals and significant inhibition of this release by the specific GABA(A) receptor agonist muscimol in the presence of tetrodotoxin and glutamate receptor antagonists CNQX and AP5. These data agree with reduction of mIPSCs by muscimol in whole-cell recordings from CA3 pyramidal neurons. In contrast, rate of vesicle release from distal, presumably glutamatergic terminals, was significantly lower and not changed by muscimol. The effect of muscimol on mIPSCs was not blocked but rather enhanced in the absence of external calcium. Our data directly demonstrate a potent disinhibitory reduction of GABA release by GABA(A) receptor activation. Those novel methods should be well suited to study pathophysiological changes in inhibition in resections obtained from neurosurgical treatment of epilepsy patients.

Inhibition of GABA release by presynaptic ionotropic GABA receptors in hippocampal CA3

Vesicular transmitter release can be regulated by transmitter-gated ion channels at presynaptic axon terminals. The central inhibitory transmitter GABA acts on such presynaptic ionotropic receptors in various cells, including inhibitory interneurons. Here we report that GABA-mediated postsynaptic inhibitory currents in CA3 pyramidal cells of rat hippocampal slices are suppressed by agonists of GABAA receptors. The effect is present for both stimulus-induced and miniature IPSCs, indicating a reduction in the probability of vesicular release by presynaptic, action-potential-independent mechanisms. We conclude that the release of GABA from hippocampal CA3 interneurons is regulated by a negative feedback via presynaptic ionotropic GABA autoreceptors.

Brain structures and mechanisms involved in the generation of NREM sleep: focus on the preoptic hypothalamus

Four lines of research have greatly increased our understanding of the hypothalamic preoptic area (POA) sleep-promoting system. First, sleep-active neurons within the POA have been identified using both electrophysiological recording and immediate early gene protein (c-Fos) staining methods. Segregated sleep-active neurons were found in ventrolateral and median POA (VLPO and MnPN). Additional sleep-active neurons may be intermixed with non-sleep specific neurons in other POA regions and the adjacent basal forebrain. Second, the putative sleep factors, adenosine and prostaglandin D2, were found to excite sleep-active neurons. Other sleep factors may also modulate these sleep-active populations. Third, many sleep-active neurons are warm-sensitive neurons (WSNs). WSNs are identified by excitatory responses to small increases in local POA temperature. The same local POA thermal stimuli strongly modulate sleep propensity and EEG delta activity within sleep. Interactions between sleep regulation and thermoregulation are consistent with studies of circadian sleep propensity, prolonged sleep deprivation in rats, and species differences in sleep amounts. Fourth, sleep-active neurons were found to co-localize the inhibitory neurotransmitter, gamma-aminobutyric acid and to have projections to arousal-related neuronal subgroups in the posterior hypothalamus and midbrain. Sleep-active and arousal-related neurons exhibit reciprocal changes in discharge across the wake-NREM-REM cycle, and activation of WSNs suppresses the neuronal activity of some arousal-related neuronal groups. These studies establish mechanisms by which POA hypnogenic neurons can inhibit EEG and behavioral arousal. In addition, there is evidence that arousal-related neurotransmitters inhibit VLPO sleep-active neurons. Mutually inhibitory interactions between sleep-promoting and the arousal system provide a substrate for a <<<<sleep-wake switch>>>>. 2001 Harcourt Publishers Ltd

Discharge patterns of neurons in cholinergic regions of the basal forebrain during waking and sleep

A subset of neurons recorded in the magnocellular basal forebrain (mBF) of cats and rats exhibit elevated discharge rates during waking and REM sleep, and diminished discharge during sleep with cortical EEG synchrony (nonREM sleep). This pattern is observed in mBF neurons in cats with identified ascending projections, and in neurons located in cholinergic regions of the rat mBF. However, the cholinergic versus noncholinergic nature of recorded cells could not be determined with the extracellular recording method employed. During waking, discharge of mBF neurons is strongly movement-related. Peak discharge rates occur during a variety of head and limb movements. Discharge rates during waking immobility are reduced by >50% compared to rates during waking movement. The absence of movement accounts for more of the variance in discharge across the sleep-wake cycle than does the presence of cortical EEG synchronization. Several factors participate in the regulation of mBF neuronal activity across arousal states. Tonic inhibition mediated by adenosine appears to be present during both waking and sleep. In some mBF neurons, increased GABAergic inhibition contributes to nonREM sleep-related reductions in discharge rate. Fluctuations in mBF cell activity during waking behaviors may reflect changing excitatory input from neurons in the pontine and midbrain tegmentum.

More than a marker: interaction between the circadian regulation of temperature and sleep, age-related changes, and treatment possibilities

The neurobiological mechanisms of both sleep and circadian regulation have been unraveled partly in the last decades. A network of brain structures, rather than a single locus, is involved in arousal state regulation, whereas the suprachiasmatic nucleus (SCN) has been recognized as a key structure for the regulation of circadian rhythms. Although most models of sleep regulation include a circadian component, the actual mechanism by which the circadian timing system promotes--in addition to homeostatic pressure--transitions between sleep and wakefulness remains to be elucidated. Little more can be stated presently than a probable involvement of neuronal projections and neurohumoral factors originating in the SCN. This paper reviews the relation among body temperature, arousal state, and the circadian timing system and proposes that the circadian temperature rhythm provides an additional signaling pathway for the circadian modulation of sleep and wakefulness. A review of the literature shows that increased brain temperature is associated with a type of neuronal activation typical of sleep in some structures (hypothalamus, basal forebrain), but typical of wakefulness in others (midbrain reticular formation, thalamus). Not only local temperature, but also skin temperature are related to the activation type in these structures. Warming of the skin is associated with an activation type typical of sleep in the midbrain reticular formation, hypothalamus, and cerebral cortex (CC). The decreasing part of the circadian rhythm in core temperature is mainly determined by heat loss from the skin of the extremities, which is associated with strongly increased skin temperature. As such, alterations in core and skin temperature over the day could modulate the neuronal activation state or "preparedness for sleep" in arousal-related brain structures. Body temperature may thus provide a third signaling pathway, in addition to synaptic and neurohumoral pathways, for the circadian modulation of sleep. A proposed model for the effects of body temperature on sleep appears to fit the available data better than previous hypotheses on the relation between temperature and sleep. Moreover, when the effects of age-related thermoregulatory alterations are introduced into the model, it provides an adequate description of age-related changes in sleep, including shallow sleep and awakening closer to the nocturnal core temperature minimum. Finally, the model indicates that appropriately timed direct (passive heating) or indirect (bright light, melatonin, physical activity) manipulation of the nocturnal profile of skin and core temperature may be beneficial to disturbed sleep in the elderly. Although such procedures could be viewed by researchers as merely masking a marker for the endogenous rhythm, they may in fact be crucial for sleep improvement in elderly subjects.