The role of GABA-A and mitochondrial diazepam-binding inhibitor receptors on the effects of neurosteroids on food intake in mice

The present studies were undertaken to investigate the neuroactive steroidal modulation of feeding behavior and possible involvement of γ-aminobutyric acid type-A (GABA-A) and mitochondrial diazepam binding inhibitor (DBI) receptors (MDR) in food-deprived male mice. Allopregnanolone (0.5–2 mg/kg), a neurosteroid, progesterone (1–10 mg/kg), a neurosteroid precursor, and 4′-chlordiazepam (0.25–1  mg/kg), a specific high affinity MDR agonist, produced a dose-dependent hyperphagic effects. In contrast, neurosteroids pregnenolone sulfate (PS) (1–10 mg/kg) and dehydroepiandrosterone sulfate (DHEAS) (1–10 mg/ kg) produced a hypophagic effect, in a dose-dependent manner. The allopregnanolone-, progesterone- and 4′-chlordiazepam-induced hyperphagic effect was blocked by picrotoxin (1 mg/kg), a GABA-A chloride channel antagonist, but not by flumazenil (2 mg/kg), a benzodiazepine (BZD) antagonist. The 4′-chlordiazepam-induced hyperphagic effect was prevented by pretreatment with PK11195 (2 mg/kg), a selective partial MDR antagonist. The hypophagic effect of DHEAS (10 mg/kg) was reversed by dizocilpine (10 μg/kg), an NMDA receptor antagonist, but resistant to muscimol (0.1 mg/kg), a selective GABA-A receptor agonist. In contrast, the PS (10 mg/kg)-induced hypophagic response was resistant to dizocilpine, but sensitive to muscimol (0.1mg/kg). Both the sulfated neurosteroids PS and DHEAS also reversed the hyperphagic effect of allopregnanolone. In addition, the BZD agonist triazolam (0.05–0.25  mg/kg) also produced a flumazenil- and picrotoxin-sensitive hyperphagic effects, thereby suggesting the changes in feeding behavior by neurosteroids represent GABA-A receptor mediated hyperphagic action. Although the possible antistress or anxiolytic actions of neurosteroids may confound the hyperphagia, behavioral effects observed were specific to food because the mice were adopted to the test environment and diet, and of a possible variation between various neurosteroids in the extent to which antistress or anxiolytic effect produced at hyperphagic doses. The hyperphagic effects of progesterone and 4′-chlordiazepam resembled that of neurosteroid allopregnanolone. Therefore, the effect of progesterone may be imputed to its metabolism to allopregnanolone, while the 4′-chlordiazepam-induced hyperphagic response is related to its MDR-stimulated neurosteroidogenesis and subsequent modulation of GABA-A receptors. The hypophagic response following DHEAS may, at least partly, involve an NMDA receptor mechanism. However, PS-induced hypophagia may be mediated by GABA-A or other receptor systems. These data suggest a pivotal role for GABA-A and mitochondrial DBI receptors in the hyperphagic effects of neurosteroids and reinforces a role for endogenous neurosteroids in regulating feeding behavior. Future studies may lead to the development of neurosteroid-based anorectic/hyperphagic agents for therapeutic use. Received: 30 September 1997/Final version: 18 November 1997     

Neurosteroids may differentially affect the function of two native GABAA receptor subtypes in the rat brain

Hippocampal noradrenergic and cerebellar glutamatergic axon terminals are known to possess GABA_A receptors mediating, respectively, enhancement of noradrenaline (NA) and glutamate release. It has been recently found that the hippocampal receptor is benzodiazepine-sensitive, whereas the cerebellar receptor is insensitive to benzodiazepine agonists. We here tested the effects of neurosteroids on these two native GABA_A receptors using superfused rat hippocampal and cerebellar synaptosomes. Allopregnanolone (3α,5α-P), at nanomolar concentrations, potentiated the GABA-induced [³H]-NA release from superfused hippocampal synaptosomes; in the absence of GABA, the steroid was ineffective up to 10μM. The enhancement by GABA of the K⁺-evoked [³H]-D-aspartate release from cerebellar synaptosomes also was potentiated by nanomolar 3α,5α-P; in addition, at 1–10μM, the steroid increased [³H]-D-aspartate release in the absence of GABA. Both in hippocampus and cerebellum the potentiations of the GABA effects produced by nanomolar 3α,5α-P were abolished by dehydroepiandrosterone sulphate (DHEAS). Added up to 10μM, DHEAS could not inhibit the effects of GABA alone. The enhancement of [³H]-D-aspartate release elicited by 3μM 3α,5α-P in the absence of added GABA was antagonized completely by bicuculline and picrotoxin and halved by DHEAS. To conclude, 3α,5α-P, at nanomolar concentrations, behaves as a positive allosteric GABA modulator at both the GABA_A receptors under study. Low micromolar 3α,5α-P can directly activate the cerebellar receptor, whereas the hippocampal GABA_A receptor is insensitive to the neurosteroid alone. DHEAS appears to be a pure antagonist at the neurosteroid allosteric sites. Along with the previously observed differential sensitivity to benzodiazepines, the present data strengthen the idea that the two receptors investigated represent native subtypes of the GABA_A receptor having distinct pharmacology, neuronal localization and function. Received: 13 October 1997 / Accepted: 30 December 1997     

Effects of sigma(1) receptor agonist SA4503 and neuroactive steroids on performance in a radial arm maze task in rats

This study examined the effects of sigma(1) receptor agonist SA4503 and neuroactive steroids dehydroepiandrosterone sulfate (DHEAS), pregnenolone sulfate (PREGS) and progesterone (PROG) on spatial working and reference memory in a radial arm maze task in rats. The insertion of a 6-min delay between the 2nd and 3rd choices caused a specific decline in working memory, but had no effect on reference memory. This decline in working memory was improved by SA4503, but not by DHEAS, PREGS or PROG. A non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist dizocilpine significantly impaired both working and reference memory in the presence or absence of a delay. The dizocilpine-induced impairments in the presence of a 6-min delay were ameliorated by SA4503, DHEAS and PREGS, whereas PROG had no effect. The beneficial effects of SA4503, DHEAS and PREGS were antagonized by treatment with sigma(1) receptor antagonist N, N-dipropyl-2-(4-methoxy-3-(2-phenylethoxy)phenyl)-ethylamine hydrochloride (NE-100). Furthermore, PROG attenuated the ameliorating effects of SA4503, DHEAS and PREGS on dizocilpine-induced memory deficits. These results suggest that sigma(1) receptors play a significant role in short-term working memory. Furthermore, it is suggested that DHEAS and PREGS ameliorate dizocilpine-induced memory impairments by acting as sigma(1) receptor agonists, while PROG antagonizes their effects by acting as a sigma(1) receptor antagonist.     

酒精依赖和戒断时大鼠伏隔核、杏仁核区内神经甾体水平的变化

目的:采用♂大鼠酒精依赖模型,观察酒精依赖及戒断对大鼠伏隔核、杏仁核中不同神经甾体水平的影响。方法:通过大鼠自由饮含6%的乙醇溶液,连续42d使大鼠形成酒精依赖,并撤除酒精使其自然戒断。断头取脑分离取出伏隔核、杏仁核脑区。使用液液萃取和固相萃取两步法提取脑组织中的孕烯醇酮(PREG)、脱氢表雄酮(DHEA)、别孕烯醇酮(AP)、脱氢表雄酮硫酸酯(DHEAS)、孕烯醇酮硫酸酯(PREGS),以高效液相色谱-质谱联用法测定神经甾体含量。结果:与对照组相比,酒精依赖大鼠伏隔核DHEA,PREG,AP,DHEAS,PREGS的水平显著降低(P<0.05),杏仁核AP,PREGS的水平显著降低(P<0.05);酒精戒断6h大鼠伏隔核DHEA,DHEAS,PREGS的水平显著降低(P<0.05),杏仁核PREGS的水平显著降低(P<0.05);酒精戒断24h大鼠杏仁核DHEA的水平显著上升(P<0.05),伏隔核、杏仁核DHEAS、PREGS的水平显著下降(P<0.01)。结论:酒精依赖形成和戒断对伏隔核、杏仁核中的神经甾体水平有不同的影响,具有区域特异性。     

谷氨酸和γ-氨基丁酸对原代培养星形胶质细胞神经甾体合成释放的影响

目的研究氨基酸类神经递质对原代培养大鼠大脑皮质星形胶质细胞神经甾体合成释放的影响。方法采用原代培养的大鼠大脑皮质星形胶质细胞,分别加入不同浓度的谷氨酸和γ-氨基丁酸处理48h;采用固相萃取结合高效液相色谱质-谱联用分析方法提取分离和测定细胞培养液中游离型(脱氢表雄酮,DHEA;孕烯醇酮,PREG;别孕烯醇酮,AP)及结合型神经甾体(脱氢表雄酮硫酸酯,DHEAS;孕烯醇酮硫酸酯,PREGS)。结果与生理盐水对照组比较,谷氨酸处理使PREG和PREGS水平明显下降,DHEAS水平明显升高;γ-氨基丁酸处理使PREG水平明显降低,AP水平增加。结论谷氨酸和γ-氨基丁酸两种神经递质对原代培养的星形胶质细胞PREG合成释放均呈抑制作用;谷氨酸对DHE-AS、γ-氨基丁酸对AP的合成释放分别呈现明显促进作用;高剂量的谷氨酸还可以抑制PRGES的合成和释放。     

The sigma1 protein as a target for the non-genomic effects of neuro(active)steroids: molecular, physiological, and behavioral aspects

Steroids synthesized in the periphery or de novo in the brain, so called 'neurosteroids', exert both genomic and nongenomic actions on neurotransmission systems. Through rapid modulatory effects on neurotransmitter receptors, they influence inhibitory and excitatory neurotransmission. In particular, progesterone derivatives like 3alpha-hydroxy-5alpha-pregnan-20-one (allopregnanolone) are positive allosteric modulators of the gamma-aminobutyric acid type A (GABA(A)) receptor and therefore act as inhibitory steroids, while pregnenolone sulphate (PREGS) and dehydroepiandrosterone sulphate (DHEAS) are negative modulators of the GABA(A) receptor and positive modulators of the N-methyl-D-aspartate (NMDA) receptor, therefore acting as excitatory neurosteroids. Some steroids also interact with atypical proteins, the sigma (sigma) receptors. Recent studies particularly demonstrated that the sigma1 receptor contributes effectively to their pharmacological actions. The present article will review the data demonstrating that the sigma1 receptor binds neurosteroids in physiological conditions. The physiological relevance of this interaction will be analyzed and the impact on physiopathological outcomes in memory and drug addiction will be illustrated. We will particularly highlight, first, the importance of the sigma1-receptor activation by PREGS and DHEAS which may contribute to their modulatory effect on calcium homeostasis and, second, the importance of the steroid tonus in the pharmacological development of selective sigma1 drugs.     

Cholinergic Modulation of General Anesthesia

Acetylcholine in the brain promotes arousal and facilitates cognitive functions. Cholinergic neurons in the mesopontine brainstem and basal forebrain are important for activation of the cerebral cortex, which is characterized by the suppression of irregular slow waves, an increase in gamma (30-100 Hz) activity in the electroencephalogram, and the appearance of a hippocampal theta rhythm. During general anesthesia, a decrease in acetylcholine release and cholinergic functions contribute to the desired outcomes of general anesthesia, such as amnesia, loss of awareness and consciousness, and immobility. Animal experiments indicate that inactivation, lesion, or genetic ablation of cholinergic neurons in the basal forebrain potentiated the effects of inhalational and injectable anesthetics, including isoflurane, halothane, propofol, pentobarbital, and in some cases, ketamine. Increased behavioral sensitivity to general anesthesia, faster induction time, and delayed recovery of a loss of righting reflex have been observed in rodents with basal forebrain cholinergic deficits. Cholinergic stimulation in the prefrontal cortex, thalamus, and basal forebrain hastens recovery from general anesthesia. Anticholinesterase accelerates emergence from general anesthesia, but with mixed success, in part depending on the anesthetic used. Cholinergic deficits may contribute to cognitive impairments after anesthesia and operations, which are severe in aged subjects. We propose a cholinergic hypothesis for postoperative cognitive disorder, in line with the cholinergic deficits and cognitive decline in aging and Alzheimer’s disease. The current animal literature suggests that brain cholinergic neurons can regulate the immune and inflammatory response after surgical operation and anesthetic exposure, and anticholinesterase and α7-nicotinic cholinergic agonists can alleviate postoperative inflammatory response and cognitive deficits.     

Subunit-specific modulation of glycine receptors by neurosteroids

The effects of pregnene and androstane steroids were studied on recombinant human glycine receptors (GlyRs) by whole-cell voltage-clamp electrophysiology. The 3beta-sulphates of pregnenolone (PREGS) and dehydroepiandrosterone (DHEAS) inhibited GlyR currents with K(I) values of 2-20 microM for different (alpha(1), alpha(2), alpha(4) and beta) GlyR subunits. PREGS resulted in a parallel shift of the response curve of glycine for alpha(1) GlyRs. The inhibitory potencies of DHEAS relative to PREGS were decreased in transition from embryonic alpha(2) towards adult alpha(1)beta GlyRs. A decreased potency of DHEAS for alpha(4) versus alpha(2) GlyRs represents the first pharmacological difference reported between these subunits. A negative charge at C3 is required for GlyR antagonism but androsterone sulphate epimers at C3 inhibited without stereoselectivity. Some point mutations of alpha(1) GlyRs with characteristic functional consequences did not significantly affect the inhibitory potency of PREGS. Progesterone selectively inhibited alpha(2) GlyRs, while PREG and its acetic ester potentiated alpha(1) GlyRs. Coexpression of the alpha subunits with the beta subunit eliminated the enhancing effects of PREG and attenuated the inhibitory potencies of the neurosteroids. Based on these data we propose that neurosteroids might modulate perinatal GlyR activity and thereby influence neuronal development.     

Effects of morphine dependence and withdrawal on levels of neurosteroids in rat brain

AIM: To investigate the effects of morphine dependence and withdrawal on the concentrations of neurosteroids in rat brain. METHODS: A method of simultaneous quantification of neurosteroids by gas chromatography-mass spectrometry (GC-MS) had been established. RESULTS: The chronic morphine administration (ip) resulted in a marked decrease in the brain concentrations of pregnenolone (PREG), progesterone (PROG), and pregenenolone sulfate (PREGS) in rats killed 6 h after the last treatment. In contrast, there were no significant effects of morphine dependence on the brain concentrations of allopregnanolone (AP), dihydroepiandrosterone (DHEA), and dihydroepiandrosterone sulfate (DHEAS). Naloxone-induced withdrawal produced a significant increase in the concentrations of PREG, PROG, AP, DHEA, PREGS, and DHEAS as compared with the control group. CONCLUSION: Morphine dependence and withdrawal affected the concentrations of neurosteroids in rat brain, which suggests that endogenous neurosteroids in brain might be     

The neurosteroids dehydroepiandrosterone sulfate and pregnenolone sulfate inhibit the UNC-49 GABA receptor through a common set of residues

Neurosteroids are endogenous neuromodulators that bind and allosterically regulate GABA(A) receptors. Residues were recently identified in the first transmembrane domain (M1) of GABA(A) receptor subunits that are important for neurosteroid modulation. We are studying the inhibition of GABA(A) receptors by sulfated neurosteroids. One of these neurosteroid, pregnenolone sulfate (PS), depends on six identified M1 residues to inhibit the UNC-49 GABA receptor, a homomeric GABA receptor from Caenorhabditis elegans that is homologous to the mammalian GABA(A) receptor. Here, we investigate the inhibition of the UNC-49 GABA receptor by another sulfated neurosteroid, dehydroepiandrosterone sulfate (DHEAS). DHEAS is identical to PS except that it contains a carbonyl oxygen instead of an acetyl group at C17 on the steroid D ring. UNC-49 mutations that affect PS inhibition had broadly parallel effects on DHEAS, suggesting the two neurosteroids act through similar mechanisms. However, certain M1 mutations affected DHEAS differently than PS. Considering that first, the D ring contains the only structural difference between PS and DHEAS, and second, the strongest chemical and steric effects of a mutation are likely to be felt in the local environment of the altered residues, this result implies that the steroid D ring may contact M1 near the mutated residues. This possibility is interesting because current models of neurosteroid interactions with GABA(A) receptors, based on pregnane steroids, suggest that the steroid A ring binds M1, whereas the D ring binds M4. Our findings suggest that there may be considerable diversity in the way different classes of neurosteroids interact with GABA(A) receptors.     

Neurosteroids ameliorate conditioned fear stress: an association with sigma receptors.

Mice exhibited a marked suppression of motility (conditioned fear stress) when placed in an environment in which they had previously received an electric footshock. This conditioned fear stress response was dose-dependently attenuated by neurosteroids such as dehydroepiandrosterone sulfate (DHEAS; 25 and 50 mg/kg, s.c.) and pregnenolone sulfate (PREGS; 10-50 mg/kg, s.c.), and by a putative sigma(1) receptor agonist, (+)-N-allylnormetazocine ((+)-SKF-10,047; 3 and 6 mg/kg, s.c.). However, progesterone (PROG; 10-50 mg/kg, s.c. ) and allopregnanolone (5 and 20 mg/kg, s.c.) had no effect on this stress response. The attenuating effects of DHEAS (50 mg/kg, s.c.), PREGS (50 mg/kg, s.c.), and (+)-SKF-10,047 (6 mg/kg, s.c.) were reversed by NE-100 (5 mg/kg, i.p.), a sigma(1) receptor antagonist and PROG (5 or 10 mg/kg, i.p.). When DHEAS (25 mg/kg) was co-administered with (+)-SKF-10,047 (3 mg/kg) at doses that do not affect the conditioned fear stress response by themselves, motor suppression was significantly attenuated. In mice showing the conditioned fear stress response, the serum concentration of DHEAS was lower than that in non-shocked mice. These results suggest that the attenuating effects of DHEAS and PREGS on the conditioned fear stress response are mediated via sigma(1) receptors and that PROG has a sigma(1) receptor antagonistic property. Further, the endogenous DHEAS may be involved in the expression of conditioned fear stress response in mice.     

Pharmacological mechanisms and animal models of cognition

Requirements for an effective animal model of cognition are discussed with special reference to the cholinergic hypothesis of Alzheimer's disease. It is argued, with reference to research on vasopressin and ACE inhibitors, that many putative animal models of cognition lack predictive clinical validity because they either confound the effects of cognitive and arousal processes, or fail to model a specific component of cognitive functioning. A survey of recent research on the cholinergic hypothesis illustrates how these weaknesses can be overcome. Studies involving scopolamine and basal forebrain excitatory amino acid lesion models of the cholinergic deficit in Alzheimer's disease have employed a delayed-matching-to-position test in rodents which, unlike passive avoidance, allows the effects of memory and attentional variables to be distinguished. In combination with recent human studies, these experiments suggest that the cholinergic system has a major role in executive control of attentional resources, and lead to the recommendation of a 'top down' strategy in the investigation of neurochemical processes and pharmacological mechanisms underlying cognition.     

Pregnenolone sulfate and its enantiomer: Differential modulation of memory in a spatial discrimination task using forebrain NMDA receptor deficient mice

This study examined the role of forebrain n-methyl-d-aspartate receptors (NMDA-Rs) in the promnesiant effects of natural (+) pregnenolone sulfate (PREGS) and its synthetic (−) enantiomer ent-PREGS in young adult mice. Using the two-trial arm discrimination task in a Y-maze, PREGS and ent-PREGS administration to control mice increased memory performances. In mice with a knock-out of the NR1 subunit of NMDA-Rs in the forebrain, the promnesiant effect of ent-PREGS was maintained whereas the activity of PREGS was lost. Memory enhancement by PREGS involves the NMDA-R activity in the hippocampal CA1 area and possibly in some locations of the cortical layers, whereas ent-PREGS acts independently of NMDA-R function.     

Galanin: neurobiologic mechanisms and therapeutic potential for Alzheimer's disease

The neuropeptide galanin (GAL) is widely distributed in the mammalian CNS. Several lines of evidence suggest that GAL may play a critical role in cognitive processes such as memory and attention through an inhibitory modulation of cholinergic basal forebrain activity. Furthermore, GAL fibers hyperinnervate remaining cholinergic basal forebrain neurons in Alzheimer's disease (AD). This suggests that GAL activity impacts cholinergic dysfunction in advanced AD. Pharmacological and in vitro autoradiographic studies indicate the presence of heterogeneous populations of GAL receptor (GALR) sites in the basal forebrain which bind GAL with both high and low affinity. Interestingly, we have recently observed that GALR binding sites increase in the anterior basal forebrain in late-stage AD. Three G protein-coupled GALRs have been identified to date that signal through a diverse array of effector pathways in vitro, including adenylyl cyclase inhibition and phospholipase C activation. The repertoire and distribution of GALR expression in the basal forebrain remains unknown, as does the nature of GAL and GALR plasticity in the AD basal forebrain. Recently, GAL knockout and overexpressing transgenic mice have been generated to facilitate our understanding of GAL activity in basal forebrain function. GAL knockout mice result in fewer cholinergic basal forebrain neurons and memory deficits. On the other hand, mice overexpressing GAL display hyperinnervation of basal forebrain and memory deficits. These data highlight the need to explore further the putative mechanisms by which GAL signaling might be beneficial or deleterious for cholinergic cell survival and activity within basal forebrain. This information will be critical to understanding whether pharmacological manipulation of GALRs would be effective for the amelioration of cognitive deficits in AD.     

Sex differences in the acquisition of intravenously self-administered cocaine and heroin in rats

Endogenous pregnane steroids, such as allopregnanolone (3α-hydroxy-5α-pregnan-20-one; 3α, 5α-P) and pregnanolone (3α-hydroxy-5β-pregnan-20-one; 3α,5β-P), allosterically modulate GABA_A receptor function and exhibit behavioral effects similar to benzodiazepines, though acting at a distinct recognition site. Inasmuch as some positive allosteric modulators of GABA_A receptor function exhibit profound interactions with ethanol, the effects of 3α,5α-P and 3α,5β-P were compared to those of two benzodiazepines, triazolam and diazepam, on the motor function of mice and rats when administered either alone or in combination with ethanol. All four test compounds exhibited dose-related impairment of motor function in the horizontal wire task in mice and the rotorod task in rats. Ethanol caused a marked enhancement of triazolam- and diazepam-induced motor impairment. In contrast, ethanol enhanced to a lesser extent the motor impairment induced by both neurosteroids in mice and not at all in rats. All four compounds increased ethanol-induced behavioral sleep time in mice, although the benzodiazepines did so at a much smaller fraction of their ataxic doses as compared to the neurosteroids. As one of the undesired side-effects of therapeutic use of benzodiazepines is their interaction with ethanol, development of neuroactive steroids as drugs may offer therapeutic advantages. Received: 24 March 1998/Final version: 12 May 1988     

Relevance of endogenous 3α-reduced neurosteroids to depression and antidepressant action

The naturally occurring 3α-reduced neurosteroids allopregnanolone and its isomer pregnanolone are among the most potent positive allosteric modulators of γ-aminobutyric acid type A receptors. They play a critical role in the maintenance of physiological GABAergic tone and display a broad spectrum of neuropsychopharmacological properties. We have reviewed existing evidence implicating the relevance of endogenous 3α-reduced neuroactive steroids to depression and to the mechanism of action of antidepressants. A wide range of preclinical and clinical evidence suggesting the antidepressant potential of 3α-reduced neuroactive steroids and a possible involvement of a deficiency and a disequilibrium of neuroactive steroid levels in pathomechanisms underlying the etiology of major depressive disorder have emerged in recent years. Antidepressants elevate 3α-reduced neurosteroid levels in rodent brain, and clinically effective antidepressant pharmacotherapy is associated with normalization of plasma and cerebrospinal fluid (CSF) concentrations of endogenous neuroactive steroids in depressed patients, unveiling a possible contribution of neuroactive steroids to the mechanism of action of antidepressants. In contrast, recent studies using nonpharmacological antidepressant therapy suggest that changes in plasma neuroactive steroid levels may not be a general mandatory component of clinically effective antidepressant treatment per se, but may reflect distinct properties of pharmacotherapy only. While preclinical studies offer convincing evidence in support of an antidepressant-like effect of 3α-reduced neuroactive steroids in rodent models of depression, current clinical investigations are inconclusive of an involvement of neuroactive steroid deficiency in the pathophysiology of depression. Moreover, clinical evidence is merely suggestive of a role of neuroactive steroids in the mechanism of action of clinically effective antidepressant therapy. Additional clinical studies evaluating the impact of successful pharmacological and nonpharmacological antidepressant therapies on changes in neuroactive steroid levels in both plasma and CSF samples of the same patients are necessary in order to more accurately address the relevance of 3α-reduced neuroactive steroids to major depressive disorder. Finally, proof-of-concept studies with drugs that are known to selectively elevate brain neurosteroid levels may offer a direct assessment of an involvement of neurosteroids in the treatment of depressive symptomatology.     

Neurophysiology of Sleep and Wakefulness: Basic Science and Clinical Implications

Increased attention to the prevalence of excessive sleepiness has led to a clear need to treat this symptom, thus reinforcing the need for a greater understanding of the neurobiology of sleep and wakefulness. Although the physiological mechanisms of sleep and wakefulness are highly interrelated, recent research reveals that there are distinct differences in the active brain processing and the specific neurochemical systems involved in the two states. In this review, we will examine the specific neuronal pathways, transmitters, and receptors composing the ascending arousal system that flow from the brainstem through the thalamus, hypothalamus, and basal forebrain to the cerebral cortex. We will also discuss the mutually inhibitory interaction between the core neuronal components of this arousal system and the sleep-active neurons in the ventrolateral preoptic nucleus, which serves as a brainstem-switch, regulating the stability of the sleep-wake states. In addition, we will review the role of homeostatic and circadian processes in the sleep-wake cycle, including the influence of the suprachiasmatic nucleus on coordination of sleep-wake systems. Finally, we will summarize how the above processes are reflected in disorders of sleep and wakefulness, including insomnia, narcolepsy, disorders associated with fragmented sleep, circadian rhythm sleep disorders, and primary neurological disorders such as Parkinson’s and Alzheimer’s diseases.     

Chronic progesterone treatment augments while dehydroepiandrosterone sulphate prevents tolerance to ethanol anxiolysis and withdrawal anxiety in rats

We have recently shown that the neurosteroid allopregnanolone modulates anxiolytic effect of ethanol. In the present report, we attempted to examine whether neurosteroids progesterone and dehydroepiandrosterone sulphate (DHEAS), which modulate gamma-aminobutyric acid (GABA(A)) receptor function, affects development of tolerance to ethanol anxiolysis and withdrawal anxiety. Rats on ethanol (6% v/v in nutritionally balanced liquid diet) for prolong period (10 days) were injected twice daily either with vehicle, progesterone (a precursor of allopregnanolone, positive GABA(A) receptor modulator), finasteride (5alpha-reductase inhibitor) or DHEAS (negative GABA(A) receptor modulator). During this period, rats were acutely challenged periodically with ethanol (2 g/kg, i.p., 8% w/v) and subjected to the elevated plus maze test. For withdrawal studies, similar treatment protocols (except ethanol challenge) were employed and on day 11, rats were subjected to the elevated plus maze test at different time intervals post-ethanol withdrawal. While progesterone significantly advanced the development of tolerance to ethanol anxiolysis and enhanced withdrawal anxiety, DHEAS and finasteride prevented such behavioral alterations. These data highlight the important role played by GABAergic neurosteroids progesterone and DHEAS in the development of tolerance to ethanol anxiolysis and withdrawal anxiety in rats. Moreover, it points to the potential usefulness of specific neurosteroids as targets in the treatment of alcoholism.     

慢性低灌注对大鼠基底前脑胆碱能系统及认知功能的影响

目的探讨慢性低灌注状态对大鼠基底前脑胆碱能神经系统及认知功能的影响。方法永久结扎SD系大鼠双侧颈总动脉建立大鼠前脑慢性低灌注状态模型,于1、2及4个月时观察基底前脑组织病理学变化、应用免疫组织化学方法检测基底前脑胆碱乙酰转移酶(Cholineacetyltransferase,ChAT)的表达水平、应用改良的MG-2型“Y”型迷宫检测大鼠学习和记忆能力。结果与对照组相比,术后第1、2和4个月时,基底前脑神经元和胶质细胞结构紊乱、呈片状和灶性坏死,ChAT阳性神经元及纤维显著减少(P<0.01),并随时间延长逐渐加重;大鼠全天总反应时间(Totalreactiontime,TRT)明显延长(P<0.01);并且以上两者呈显著负相关(r=-0.83、P<0.01)。结论慢性低灌注状态时,大鼠基底前脑发生缺血性病理改变,导致基底前脑胆碱能神经系统损害,从而在整体水平出现学习记忆障碍。低灌注状态时,基底前脑胆碱能神经系统损伤是认知功能障碍形成的重要机制。     

3,4-Methylenedioxymethamphetamine enhances the release of acetylcholine in the prefrontal cortex and dorsal hippocampus of the rat

Rationale The neurochemical effects produced by acute administration of 3,4-methylenedioxymethamphetamine (MDMA) on the monoaminergic systems in the brain are well documented; however, there has been little consideration of the potential effects of MDMA on other neurotransmitter systems. Objective The present study was designed to investigate the acute effect of MDMA on cholinergic neurons by measuring acetylcholine (ACh) release in the medial prefrontal cortex (PFC) and dorsal hippocampus, terminal regions of cholinergic projection neurons originating in the basal forebrain. Methods In vivo microdialysis and high-performance liquid chromatography with electrochemical detection (HPLC-ED) were used to assess the effects of MDMA on the extracellular concentration of ACh in the PFC and dorsal hippocampus of the rat. Results The systemic administration of MDMA (3–20 mg/kg, i.p.) resulted in an increased extracellular concentration of ACh in the PFC and dorsal hippocampus. Reverse dialysis of MDMA (100 μM) into the PFC and hippocampus also increased ACh release in these brain regions. Treatment with parachlorophenylalanine and α-methyl-para-tyrosine, inhibitors of serotonin (5-HT) and dopamine (DA) synthesis, respectively, significantly attenuated the release of ACh stimulated by MDMA in the PFC, but not in the dorsal hippocampus. Conclusions MDMA exerts a stimulatory effect on the release of ACh in the PFC and dorsal hippocampus in vivo, possibly by mechanisms localized within these brain regions. In addition, these results suggest that the MDMA-induced release of ACh in the PFC involves both serotonergic and dopaminergic mechanisms.