Lateral geniculate neurons projecting to primary visual cortex show ocular dominance plasticity in adult mice.

Experience-dependent plasticity in the mature visual system is widely considered to be cortical. Using chronic two-photon Ca2+ imaging of thalamic afferents in layer 1 of binocular visual cortex, we provide evidence against this tenet: the respective dorsal lateral geniculate nucleus (dLGN) cells showed pronounced ocular dominance (OD) shifts after monocular deprivation in adult mice. Most (86%), but not all, of dLGN cell boutons were monocular during normal visual experience. Following deprivation, initially deprived-eye-dominated boutons reduced or lost their visual responsiveness to that eye and frequently became responsive to the non-deprived eye. This cannot be explained by eye-specific cortical changes propagating to dLGN via cortico-thalamic feedback because the shift in dLGN responses was largely resistant to cortical inactivation using the GABAA receptor agonist muscimol. Our data suggest that OD shifts observed in the binocular visual cortex of adult mice may at least partially reflect plasticity of eye-specific inputs onto dLGN neurons.

Pharmacological treatment of tardive dyskinesia: recent developments.

INTRODUCTION: Tardive dyskinesia (TD) occurs in patients receiving antipsychotic treatment with dopamine receptor antagonists. Despite the prevalence of TD and its negative impact on patients' lives, there has been a lack of approved treatments and limited evidence from controlled trials of pharmacological treatment. Areas covered: PubMed was searched for English-language papers published during 2007-2016 using terms 'tardive dyskinesia' or 'drug-induced movement disorder', and 'treatment'. Studies evaluating pharmacological agents for the treatment of TD were selected. A total of 26 studies (five meta-analyses, twelve randomized controlled trials, and nine open-label observational studies) are reviewed. Expert commentary: Treatment of TD necessitates a stepwise approach. Optimization of antipsychotic therapy should be considered before initiation of antidyskinetic therapies. Data from some recent studies indicate possible improvements in TD after switching antipsychotics or with the use of amantadine, levetiracetam, piracetam, zonisamide, propranolol, vitamin B6, or certain unregulated herbal medicines; although significance of these improvements is unclear and require further investigation in randomized controlled trials. By contrast, recent evidence from Phase III trials of novel vesicular monoamine transporter-2 inhibitors demonstrates they could have a significant effect on TD symptom severity and suggests these agents may have the potential to transform treatment of TD in coming years.

Development of a Robust Mammalian Cell-based Assay for Studying Recombinant α4 ß1/3 δ GABAA Receptor Subtypes.

δ-Containing GABAA receptors are located extrasynaptically and mediate tonic inhibition. Their involvement in brain physiology positions them as interesting drug targets. There is thus a continued interest in establishing reliable recombinant expression systems for δ-containing GABAA receptors. Inconveniently, the recombinant expression of especially α4 ß1/3 δ receptors has been found to be notoriously difficult, resulting in mixed receptor populations and/or stoichiometries and differential pharmacology depending on the expression system used. With the aim of developing a facile and robust 96-well format cell-based assay for extrasynaptic α4 ß1/3 δ receptors, we have engineered and validated a HEK293 Flp-In™ cell line stably expressing the human GABAA δ-subunit. Upon co-transfection of α4 and ß1/3 subunits, at optimized ratios, we have established a well-defined system for expressing α4 ß1/3 δ receptors and used the fluorescence-based FLIPR Membrane Potential (FMP) assay to evaluate their pharmacology. Using the known reference compounds GABA and THIP, ternary α4 ß1/3 δ and binary α4 ß1/3 receptors could be distinguished based on potency and kinetic profiles but not efficacy. As expected, DS2 was able to potentiate only δ-containing receptors, whereas Zn2+ had an inhibitory effect only at binary receptors. By contrast, the hitherto reported δ-selective compounds, AA29504 and 3-OH-2'MeO6MF, were non-selective. The expression system was further validated using patch clamp electrophysiology, in which the superagonism of THIP was confirmed. The established FMP assay set-up, based on transient expression of human α4 and ß1/3 subunits into a δ-subunit stable HEK293 Flp-In™ cell line, portrays a simple 96-well format assay as a useful supplement to electrophysiological recordings on δ-containing GABAA receptors.

Passiflora incarnata attenuation of neuropathic allodynia and vulvodynia apropos GABA-ergic and opioidergic antinociceptive and behavioural mechanisms.

BACKGROUND: Passiflora incarnata is widely used as an anxiolytic and sedative due to its putative GABAergic properties. Passiflora incarnata L. methanolic extract (PI-ME) was evaluated in an animal model of streptozotocin-induced diabetic neuropathic allodynia and vulvodynia in rats along with antinociceptive, anxiolytic and sedative activities in mice in order to examine possible underlying mechanisms. METHODS: PI-ME was tested preliminary for qualitative phytochemical analysis and then quantitatively by proximate and GC-MS analysis. The antinociceptive property was evaluated using the abdominal constriction assay and hot plate test. The anxiolytic activity was performed in a stair case model and sedative activity in an open field test. The antagonistic activities were evaluated using naloxone and/or pentylenetetrazole (PTZ). PI-ME was evaluated for prospective anti-allodynic and anti-vulvodynic properties in a rat model of streptozotocin induced neuropathic pain using the static and dynamic testing paradigms of mechanical allodynia and vulvodynia. RESULTS: GC-MS analysis revealed that PI-ME contained predominant quantities of oleamide (9-octadecenamide), palmitic acid (hexadecanoic acid) and 3-hydroxy-dodecanoic acid, among other active constituents. In the abdominal constriction assay and hot plate test, PI-ME produced dose dependant, naloxone and pentylenetetrazole reversible antinociception suggesting an involvement of opioidergic and GABAergic mechanisms. In the stair case test, PI-ME at 200 mg/kg increased the number of steps climbed while at 600 mg/kg a significant decrease was observed. The rearing incidence was diminished by PI-ME at all tested doses and in the open field test, PI-ME decreased locomotor activity to an extent that was analagous to diazepam. The effects of PI-ME were antagonized by PTZ in both the staircase and open field tests implicating GABAergic mechanisms in its anxiolytic and sedative activities. In the streptozotocin-induced neuropathic nociceptive model, PI-ME (200 and 300 mg/kg) exhibited static and dynamic anti-allodynic effects exemplified by an increase in paw withdrawal threshold and paw withdrawal latency. PI-ME relieved only the dynamic component of vulvodynia by increasing flinching response latency. CONCLUSIONS: These findings suggest that Passiflora incarnata might be useful for treating neuropathic pain. The antinociceptive and behavioural findings inferring that its activity may stem from underlying opioidergic and GABAergic mechanisms though a potential oleamide-sourced cannabimimetic involvement is also discussed.

Sex Differences in GABAA Signaling in the Periaqueductal Gray Induced by Persistent Inflammation.

The ventrolateral periaqueductal gray (vlPAG) is a key structure in the descending pain modulatory circuit. Activation of the circuit occurs via disinhibition of GABAergic inputs onto vlPAG output neurons. In these studies, we tested the hypothesis that GABAergic inhibition is increased during persistent inflammation, dampening activation of the descending circuit from the vlPAG. Our results indicate that persistent inflammation induced by Complete Freund's adjuvant (CFA) modulates GABA signaling differently in male and female rats. CFA treatment results in increased presynaptic GABA release but decreased high-affinity tonic GABAA currents in female vlPAG neurons. These effects are not observed in males. The tonic currents in the vlPAG are dependent on GABA transporter activity and are modulated by agonists that activate GABAA receptors containing the δ subunit. The GABAA δ agonist THIP (gaboxadol) induced similar amplitude currents in naive and CFA-treated rats. In addition, a positive allosteric modulator of the GABAA δ subunit, DS2 (4-chloro-N-[2-(2-thienyl)imidazo[1,2-a]pyridin-3-yl]benzamide), increased tonic currents. These results indicate that GABAA δ receptors remain on the cell surface but are less active in CFA-treated female rats. In vivo behavior studies showed that morphine induced greater antinociception in CFA-treated females that was reversed with microinjections of DS2 directly into the vlPAG. DS2 did not affect morphine antinociception in naive or CFA-treated male rats. Together, these data indicate that sex-specific adaptations in GABAA receptor signaling modulate opioid analgesia in persistent inflammation. Antagonists of GABAA δ receptors may be a viable strategy for reducing pain associated with persistent inflammation, particularly in females. SIGNIFICANCE STATEMENT: These studies demonstrate that GABA signaling is modulated in the ventrolateral periaqueductal gray by persistent inflammation differently in female and male rats. Our results indicate that antagonists or negative allosteric modulators of GABAA δ receptors may be an effective strategy to alleviate chronic inflammatory pain and promote opioid antinociception, especially in females.

GABAergic Agonists Modulate the Glutamate Release from Frontal Cortex Synaptosomes of Rats with Experimental Autoimmune Encephalomyelitis.

Experimental autoimmune encephalomyelitis (EAE) is an inflammatory demyelinating disease that mimics many of the clinical and pathological features of multiple sclerosis. We have previously described a significant diminution in the GABAergic regulation of glutamate release from synaptosomes of EAE rats isolated during the acute stage of the disease. In order to explore the possible metabolic pathways responsible for this alteration, in this work we evaluate the direct effect of different GABAergic agonists on the glutamate release and concomitant synapsin I phosphorylation in synaptosomes from the frontal cortex of control and EAE animals. The results show that GABA as well as the GABA receptor agonists Muscimol (GABAA agonist) and Baclofen (GABAB agonist) caused a decrease in glutamate release in control rats paralleled by a similar reduction in synapsin I phosphorylation. Meanwhile synaptosomes from EAE animals are responsive only to Baclofen with respect to nontreated EAE synaptosomes, since glutamate release from the synaptosomes treated with Muscimol was similar to that observed in EAE rat synaptosomes which was already reduced as consequence of the disease. In the case of the benzodiazepines Diazepam and Clonazepam (GABAA allosteric agonists), both of them induced a reduction in glutamate release in synaptosomes from the CFA rats, effect that was only observed in synaptosomes of EAE rats treated with Clonazepam. In all cases both benzodiazepines showed a higher effect on synapsin I phosphorylation than in glutamate release. These results indicate that the extent of GABAergic modulation of presynaptic terminals depends on the type of agonist employed and this regulation is altered in the frontal cortex during the acute phase of EAE with respect to control animals.

GABAergic neurons in cerebellar interposed nucleus modulate cellular and humoral immunity via hypothalamic and sympathetic pathways.

Our previous work has shown that cerebellar interposed nucleus (IN) modulates immune function. Herein, we reveal mechanism underlying the immunomodulation. Treatment of bilateral cerebellar IN of rats with 3-mercaptopropionic acid (3-MP), a glutamic acid decarboxylase antagonist that reduces γ-aminobutyric acid (GABA) synthesis, enhanced cellular and humoral immune responses to bovine serum albumin, whereas injection of vigabatrin, a GABA-transaminase inhibitor that inhibits GABA degradation, in bilateral cerebellar IN attenuated the immune responses. The 3-MP or vigabatrin administrations in the cerebellar IN decreased or increased hypothalamic GABA content and lymphoid tissues' norepinephrine content, respectively, but did not alter adrenocortical or thyroid hormone levels in serum. In addition, a direct GABAergic projection from cerebellar IN to hypothalamus was found. These findings suggest that GABAergic neurons in cerebellar IN regulate immune system via hypothalamic and sympathetic pathways.

Inhalation administration of the sesquiterpenoid aristolen-1(10)-en-9-ol from Nardostachys chinensis has a sedative effect via the GABAergic system.

Spikenard, the dried roots of Nardostachys chinensis, contains sesquiterpenoids and is widely used as an herbal tranquilizer. We previously demonstrated that spikenard vapor showed a sedative effect when administered by inhalation, and we identified hydrocarbon sesquiterpenoids as active components. Here we investigated the other components that contribute to the effects of spikenard. Six oxygenated sesquiterpenoids, including aristolane- and guaiane-types, were isolated from an acetone extract of spikenard. We evaluated the sedative activities of these oxygenated compounds using an inhalation administration method in a caffeine-treated excitatory mouse model. We identified aristolen-1(10)-en-9-ol and patchouli alcohol as highly effective sedative components. These compounds inhibited locomotion in mice by approximately 60% at a dose of 300 µg/cage. In addition, aristolen-1(10)-en-9-ol prolonged pentobarbital-induced sleep to the same extent as 1 mg/kg diazepam. This effect completely disappeared with the administration of the GABAA-benzodiazepine receptor antagonist flumazenil (3 mg/kg), suggesting that the sedative effect of aristolen-1(10)-en-9-ol is expressed via the GABAergic system. Furthermore, differently from diazepam, inhalation of aristolen-1(10)-en-9-ol for 1 h did not affect the motor coordination in the rota-rod test. In the present study, we identified active components and provided evidence supporting the traditional sedative use of spikenard. Our research suggests that aristolen-1(10)-en-9-ol may be an effective aromatherapy, providing mild sedation.

Alleviation of glutamate mediated neuronal insult by piroxicam in rodent model of focal cerebral ischemia: a possible mechanism of GABA agonism.

Neurotransmitter imbalance is an inevitable outcome in cerebral ischemia that leads to neuronal death. In the present study, we evaluated the effects of piroxicam, a nonsteroidal anti-inflammatory drug (NSAID), on extracellular brain glutamate and γ-aminobutyric acid (GABA) release, survival time, and neuronal cell death. Transient focal cerebral ischemia in male Charles Foster rat led to neuronal infarction and compromised intrinsic antioxidant status. Thirty-minute preadministration of piroxicam (10 mg/kg b.w.) showed a significant (P < 0.01) reduction in cerebral infarct volume and potentiation of the intrinsic antioxidant status. High-performance liquid chromatography of brain cortex and striatum revealed changes in extracellular concentrations of neurotransmitters which were found to be 0.519 ± 0.44 pmole/mg (GABA); 1.18 ± 0.28 pmole/mg (glutamate), and 0.63 ± 0.21 pmole/mg (serotonin), respectively. Hydroxyl radical (·OH) adduct of salicylate in the frontal cortex and striatum in control, untreated, and treated groups was found to be 0.261 ± 0.06, 0.68 ± 0.52, and 0.401 ± 0.68 pmole/mg, respectively. After stroke, the extracellular level of glutamate in rat brain increases continuously as compared to that of control group. However, piroxicam administration in stroke rat significantly reduced (P < 0.05) elevated extracellular cerebral glutamate. This indicates that piroxicam attenuates extracellular glutamate release and also reduces neuronal cell death due to reduction in oxidative stress in cerebral ischemia. Our results also indicate a consequent increase of extracellular GABA in brain regions administered with piroxicam, which hints that piroxicam alleviates glutamate excitotoxicity possibly by GABA agonism.

Souroubea sympetala (Marcgraviaceae): a medicinal plant that exerts anxiolysis through interaction with the GABAA benzodiazepine receptor.

The mode of action of the anxiolytic medicinal plant Souroubea sympetala was investigated to test the hypothesis that extracts and the active principle act at the pharmacologically important GABAA-benzodiazepine (GABAA-BZD) receptor. Leaf extracts prepared by ethyl acetate extraction or supercritical extraction, previously determined to have 5.54 mg/g and 6.78 mg/g of the active principle, betulinic acid, respectively, reduced behavioural parameters associated with anxiety in a rat model. When animals were pretreated with the GABAA-BZD receptor antagonist flumazenil, followed by the plant extracts, or a more soluble derivative of the active principle, the methyl ester of betulinic acid (MeBA), flumazenil eliminated the anxiety-reducing effect of plant extracts and MeBA, demonstrating that S. sympetala acts via an agonist action on the GABAA-BZD receptor. An in vitro GABAA-BZD competitive receptor binding assay also demonstrated that S. sympetala extracts have an affinity for the GABAA-BZD receptor, with an EC50 value of 123 µg/mL (EtOAc leaf extract) and 154 µg/mL (supercritical CO2 extract). These experiments indicate that S. sympetala acts at the GABAA-BZD receptor to elicit anxiolysis.

Astrocytes modulate a postsynaptic NMDA-GABAA-receptor crosstalk in hypothalamic neurosecretory neurons.

A dynamic balance between the excitatory and inhibitory neurotransmitters glutamate and GABA is critical for maintaining proper neuronal activity in the brain. This balance is partly achieved via presynaptic interactions between glutamatergic and GABA(A)ergic synapses converging into the same targets. Here, we show that in hypothalamic magnocellular neurosecretory neurons (MNCs), a direct crosstalk between postsynaptic NMDA receptors (NMDARs) and GABA(A) receptors (GABA(A)Rs) contributes to the excitatory/inhibitory balance in this system. We found that activation of NMDARs by endogenous glutamate levels controlled by astrocyte glutamate transporters, evokes a transient and reversible potentiation of postsynaptic GABA(A)Rs. This inter-receptor crosstalk is calcium-dependent and involves a kinase-dependent phosphorylation mechanism, but does not require nitric oxide as an intermediary signal. Finally, we found the NMDAR-GABA(A)R crosstalk to be blunted in rats with heart failure, a pathological condition in which the hypothalamic glutamate-GABA balance is tipped toward an excitatory predominance. Together, our findings support a novel form of glutamate-GABA interactions in MNCs, which involves crosstalk between NMDA and GABA(A) postsynaptic receptors, whose strength is controlled by the activity of local astrocytes. We propose this inter-receptor crosstalk to act as a compensatory, counterbalancing mechanism to dampen glutamate-mediated overexcitation. Finally, we propose that an uncoupling between NMDARs and GABA(A)Rs may contribute to exacerbated neuronal activity and, consequently, sympathohumoral activation in such disease conditions as heart failure.

The effects of elevated endogenous GABA levels on movement-related network oscillations.

The EEG/MEG signal is generated primarily by the summation of the post-synaptic potentials of cortical principal cells. At a microcircuit level, these glutamatergic principal cells are reciprocally connected to GABAergic interneurons and cortical oscillations are thought to be dependent on the balance of excitation and inhibition between these cell types. To investigate the dependence of movement-related cortical oscillations on excitation-inhibition balance, we pharmacologically manipulated the GABA system using tiagabine, which blocks GABA Transporter 1(GAT-1), the GABA uptake transporter and increases endogenous GABA activity. In a blinded, placebo-controlled, crossover design, in 15 healthy participants we administered either 15mg of tiagabine or a placebo. We recorded whole-head magnetoencephalograms, while the participants performed a movement task, prior to, one hour post, three hour post and five hour post tiagabine ingestion. Using time-frequency analysis of beamformer source reconstructions, we quantified the baseline level of beta activity (15-30Hz), the post-movement beta rebound (PMBR), beta event-related desynchronisation (beta-ERD) and movement-related gamma synchronisation (MRGS) (60-90Hz). Our results demonstrated that tiagabine, and hence elevated endogenous GABA levels causes, an elevation of baseline beta power, enhanced beta-ERD and reduced PMBR, but no modulation of MRGS. Comparing our results to recent literature (Hall et al., 2011) we suggest that beta-ERD may be a GABAA receptor mediated process while PMBR may be GABAB receptor mediated.

Use of electrophysiological methods in the study of recombinant and native neuronal ligand-gated ion channels.

Detailed in this unit are protocols for studying the effects of externally and internally applied agents on the behavior of ligand-gated ion channels (LGICs), specifically the GABA(A) receptor. These assays include a number of electrophysiological techniques applied to whole-cell and excised patch recordings of recombinant and native GABA(A) receptor subtypes used in the generation and analysis of a pharmacological data. Although applied to GABA(A) receptors, these techniques are equally applicable to other LGICs. The analysis is extended to incorporate consideration of post-synaptic inhibitory events. In addition, complementary descriptions of how tissues for such studies are prepared for studying recombinant and native receptors are included.

Biphasic effects of cannabinoids in anxiety responses: CB1 and GABA(B) receptors in the balance of GABAergic and glutamatergic neurotransmission.

Biphasic effects of cannabinoids have been shown in processes such as feeding behavior, motor activity, motivational processes and anxiety responses. Using two different tests for the characterization of anxiety-related behavior (elevated plus-maze and holeboard), we first identified in wild-type C57BL/6N mice, two doses of the synthetic CB1 cannabinoid receptor agonist CP-55,940 with anxiolytic (1 µg/kg) and anxiogenic properties (50 µg/kg), respectively. To clarify the role of CB1 receptors in this biphasic effect, both doses were applied to two different conditional CB1 receptor knockout (KO) mouse lines, GABA-CB1-KO (CB1 receptor inactivation in forebrain GABAergic neurons) and Glu-CB1-KO (CB1 receptor inactivation in cortical glutamatergic neurons). We found that the anxiolytic-like effects of the low dose of cannabinoids are mediated via the CB1 receptor on cortical glutamatergic terminals, because this anxiolytic-like response was abrogated only in Glu-CB1-KO mice. On the contrary, the CB1 receptor on the GABAergic terminals is required to induce an anxiogenic-like effect under a high-dose treatment because of the fact that this effect was abolished specifically in GABA-CB1-KO mice. These experiments were carried out in both sexes, and no differences occurred with the doses tested in the mutant mice. Interestingly, the positive allosteric modulation of GABA(B) receptor with GS-39783 was found to largely abrogate the anxiogenic-like effect of the high dose of CP-55,940. Our results shed new light in further understanding the biphasic effects of cannabinoids at the molecular level and, importantly, pave the way for the development of novel anxiolytic cannabinoid drugs, which may have favorable effect profiles targeting the CB1 receptor on glutamatergic terminals.

Updating memories: changing the involvement of the prelimbic cortex in the expression of an infant fear memory.

Recent work has found that infant rats (postnatal day (P) 18) do not require the prelimbic cortex (PL) to express learned fear, whereas older animals (adults and juveniles) do. In other words, there is a switch from a PL-independent fear expression system during infancy to a PL-dependent system later in life. The present study investigated whether the PL would be involved in fear expression in rats trained at P17 but tested at P23 (that is, as juveniles). The first two experiments showed that PL involvement in fear expression was determined by the age of the animal at the time of training rather than the animal's age at the time of test. More specifically, experiment 1 showed that expression of learned fear (measured by freezing, and elicited by a white noise previously paired with a shock) was PL-independent for memories that were acquired when the rat was P17 but then tested at P23. In experiment 2, rats trained at P23, when the PL is functionally mature, still required the PL to express fear when tested at P37. In the last experiment, using two different reactivation procedures, we showed that it is possible to update an infant memory and switch it from being PL-independent to being PL-dependent. Combined, these results have important implications for our understanding of the neural circuitry underlying fear expression across development and show that, at least in some cases, expression of fear responses learned early in life remain PL-independent even as the animal matures.

GABA(A) receptor modulators from Chinese herbal medicines traditionally applied against insomnia and anxiety.

Several Chinese herbal medicines (CHMs) are used in the treatment of insomnia, restlessness, or anxiety. However, mechanisms underlying this effect and scientific proof for their traditional use is scarce. In the present study CHMs were screened for their ability to modulate GABA-induced chloride currents (I(GABA)), and active principles were isolated thus providing scientific evidence for their use as sedative and/or anxiolytic agents in CM. Herbal drugs were extracted successively with petroleum ether, ethyl acetate, methanol and water and further fractionated according to their bioactivity. The obtained extracts, fractions and finally pure compounds were tested for their ability to potentiate I(GABA) using the two-microelectrode voltage clamp technique on recombinant α1ß2γ(2S) GABA(A) receptors expressed in Xenopus laevis oocytes. From all tested extracts the petroleum ether extract of Atractylodes macrocephala Koidz. rhizomes showed the strongest I(GABA) potentiation and was studied in more detail. This led to the isolation of the main components atractylenolide II and III, which seem to be responsible for the observed positive modulation of I(GABA) (166±12%, n=3 and 155±12%, n=3, respectively) in vitro. They were more active than the analogous compound atractylenolide I (96±3%, n=3) which differs in an additional double binding in position 9, 9a. Furthermore it could be shown that this effect is mediated independently of the benzodiazepine (BZ) binding site. In conclusion, A. macrocephala exerts its in vitro activity on recombinant GABA(A) receptors mainly through the two sesquiterpene lactones atractylenolide II and III (Fig. 1). This positive allosteric modulation of I(GABA) may partially be responsible for the traditional ethnopharmacological use of this herbal drug as a sedative.

20-OH-ecdysone prevents hot flushes in ovariectomized rats.

Hot flushes are due to the lack of estrogens and are the most characteristic climacteric complaints. Hormone replacement therapy was the standard treatment but now its use is limited because of side effects. Need therefore arises to search for non-estrogenic alternatives. The molting hormone 20-beta-hydroxyecdysone (Ecd) is produced by several plants including spinach and has no estrogenic or androgenic properties but enhances GABAergic effects in neurons. Since GABAergic compounds can ameliorate hot flushes, we investigated the effects of Ecd on subcutaneous body temperature of intact and ovariectomized (ovx) rats. The subcutaneous body temperature was recorded at 5-min intervals over a period of 3 hours. Rats were then ovx, and skin temperatures were recorded after an acute intravenous (5 mg) and during subchronic and chronic oral application of Ecd (73 mg/animal/day). For additional control purposes, a group of ovx rats received food containing estradiol-17 ß (E2). Skin temperature in individual ovx animals fluctuated largely with peaks (hot flushes) occurring every 20-40 minutes. Following the i.v. treatment with Ecd, skin temperature dropped by more than 1 °C, an effect much larger than in the controls. One and two weeks later, hot flushes were only seen in ovx controls but not in intact, E2-, or Ecd-treated animals. As a consequence, E2 and Ecd intake significantly (p < 0.05) reduced the mean temperature in ovx rats during the various time points of the study. These results suggest that Ecd is efficient to prevent hot flushes in ovx rats.

The effect of gabapentin on gap detection and forward masking in young and old gerbils.

OBJECTIVES: Auditory temporal processing frequently appears more affected in old subjects than would be predicted by the degree of peripheral hearing loss, pointing to an age-dependent central processing deficit. In parallel, an age-dependent decline of inhibitory function has been demonstrated in the auditory pathway, suggesting a causal relationship between temporal processing and inhibition. Gabapentin has been specifically synthesized as a potential gamma-amino-butyric-acid (GABA) mimetic with the capability to cross the blood-brain barrier. Gabapentin treatment ameliorated tinnitus in a rat model and improved tinnitus annoyance in humans with acoustic trauma. Consequently, the present study evaluated the effect of gabapentin on auditory temporal processing in the gerbil model. DESIGN: Psychometric functions were collected for different test paradigms. (A) "Gap detection": The detection of a gap in the middle of a 800 msec broadband noise pulse was determined either at 15 or at 30 dB SL. (B) "Forward masking": The detection of a 20 msec probe stimulus following 2.5 msec after a 400 msec 40 dB SPL masker was determined with masker and probe frequency at 2.85 kHz. The effect of gabapentin was evaluated by collecting gap detection and forward masking functions before, during, and after treating gerbils with gabapentin doses of 115 or 350 mg/kg/day administered via drinking water. Data under different experimental conditions were collected for groups of 3 to 5 young (<2 years) and 6 to 10 old (>2 years) gerbils. Two-way analyses of variance for the factors age groups and treatment groups with subsequent pairwise comparisons for significant effects were used for the statistical evaluation of the data. RESULTS: For gap detection, mean thresholds were significantly increased in the group of old as compared with the young gerbils at 30 dB SL (young 2.0 msec; old 3.2 msec) and at 15 dB SL (young 2.9 msec; old 9.1 msec). Gabapentin had no significant effect on gap detection, and there was no significant interaction between age group and gabapentin treatment. Mean thresholds in the forward masking paradigm were significantly elevated in old (45.5 dB SPL) as compared with young (35.0 dB SPL) gerbils. Overall, gabapentin had no significant effect on masked thresholds; however, there was a significant interaction between treatment and age. Subsequent pairwise comparisons revealed no significant effect on masked thresholds in old gerbils but showed significantly elevated thresholds of young gerbils during 350 mg/kg gabapentin (38.3 dB SPL) compared with thresholds obtained in young gerbils before (32.3 dB SPL) and after (33.5 dB SPL) treatment. CONCLUSIONS: Gabapentin did not exert a therapeutic effect on impaired gap detection and forward masking in old gerbils. The lack of an effect of gabapentin on impaired auditory temporal processing in old gerbils and the finding of elevated masked thresholds in young gerbils can be reconciled with reports of only moderate GABAergic effects compared with other drugs (e.g., comparing elevation of GABA levels in the brain by gabapentin and vigabatrin) and effects due to binding of gabapentin to alpha-2-delta units of voltage-gated calcium channels.

[Effect sites of anesthetics in the central nervous system network--looking into the mechanisms for natural sleep and anesthesia].

We showed the effect sites of anesthetics in the central nervous system (CNS) network. The thalamus is a key factor for loss of consciousness during natural sleep and anesthesia. Although the linkages among neurons within the CNS network in natural sleep are complicated, but sophisticated, the sleep mechanism has been gradually unraveled. Anesthesia disrupts the link-ages between cortical and thalamic neurons and among the cortical neurons, and thus it loses the integration of information derived from the arousal and sleep nuclei. It has been considered that anesthesia does not share the common pathway as natural sleep at the level of unconsciousness, because anesthetics have multiple effect sites within CNS network and may induce disintegration among neurons. Recent literatures have shown that the effects of anesthetics are specific rather than global in the brain. It is interesting to note that thalamic injection of anti-potassium channel materials restored consciousness during inhalation anesthesia, and that the sedative components of certain intravenous anesthesia may share the same pathway as natural sleep. To explore the sensitivity and susceptibility loci for anesthetics in the thalamocortical neurons as well as arousal and sleep nuclei within CNS network may be an important task for future study.

Involvement of GABAergic non-benzodiazepine sites in the anxiolytic-like and sedative effects of the flavonoid baicalein in mice.

Baicalein (BA), one of the main flavonoids obtained from the Chinese medicinal herb Scutellaria baicalensis, usually exerts several pharmacological effects. In the central nervous system (CNS), BA exerts a protective effect on neurons against several neuronal insults among other effects, but it is not clear if this effect is due to its metabolite, baicalin. The purpose of the present study was to assess the anxiolytic-like and related properties of BA following its central administration (i.c.v.) in mice. BA (0.02, 0.2pmol) exerted an anxiolytic-like effect at low doses, increasing the time spent in open arms and the head-dipping whereas reducing the stretched-attend postures in the elevated plus-maze. BA also increased the duration of ether-induced sleep without affecting the pentylenetetrazol (PTZ)-induced convulsions. In addition, pretreatment with flumazenil (FMZ), PTZ, dehydroepiandrosterone sulfate (DHEAS), and dl-p-chlorophenilalanine ethyl ester (PCPA) were conducted in order to investigate its mechanism of action. PTZ and DHEAS, but not FMZ or PCPA, antagonized the BA's anxiolytic-like effect. Taken together our results showed that BA, when directly injected into the CNS, promotes anxiolytic-like and sedative effects, pharmacological activities dependent on GABAergic non-benzodiazepine sites but not on the 5-HT system.