Acid Sensing Ion Channels (ASICs) are a group of sodium-selective ion channels that are activated by low extracellular pH. The role of ASIC in disease states remains unclear partly due to the lack of ...selective pharmacological agents. In this report, we describe the effects of A-317567, a novel non-amiloride blocker, on three distinct types of native ASIC currents evoked in acutely dissociated adult rat dorsal root ganglion (DRG) neurons. A-317567 produced concentration-dependent inhibition of all pH 4.5-evoked ASIC currents with an IC50 ranging between 2 and 30muM, depending upon the type of ASIC current activated. Unlike amiloride, A-317567 equipotently blocked the sustained phase of ASIC3-like current, a biphasic current akin to cloned ASIC3, which is predominant in DRG. When evaluated in the rat Complete Freud's Adjuvant (CFA)-induced inflammatory thermal hyperalgesia model, A-317567 was fully efficacious at a dose 10-fold lower than amiloride. A-317567 was also potent and fully efficacious when tested in the skin incision model of post-operative pain. A-317567 was entirely devoid of any diuresis or natriuresis activity and showed minimal brain penetration. In summary, A-317567 is the first reported small molecule non-amiloride blocker of ASIC that is peripherally active and is more potent than amiloride in vitro and in vivo pain models. The discovery of A-317567 will greatly help to enhance our understanding of the physiological and pathophysiological role of ASICs.
This report of the proceedings of a symposium presented at the 2004 Research Society on Alcoholism Meeting provides evidence linking stress during sobriety to craving that increases the risk for ...relapse. The initial presentation by Rajita Sinha summarized clinical evidence for the hypothesis that there is an increased sensitivity to stress‐induced craving in alcoholics. During early abstinence, alcoholics who were confronted with stressful circumstances showed increased susceptibility for relapse. George Breese presented data demonstrating that stress could substitute for repeated withdrawals from chronic ethanol to induce anxiety‐like behavior. This persistent adaptive change induced by multiple withdrawals allowed stress to induce an anxiety‐like response that was absent in animals that were not previously exposed to chronic ethanol. Subsequently, Amanda Roberts reviewed evidence that increased drinking induced by stress was dependent on corticotropin‐releasing factor (CRF). In addition, rats that were stressed during protracted abstinence exhibited anxiety‐like behavior that was also dependent on CRF. Christopher Dayas indicated that stress increases the reinstatement of an alcohol‐related cue. Moreover, this effect was enhanced by previous alcohol dependence. These interactive effects between stress and alcohol‐related environmental stimuli depended on concurrent activation of endogenous opioid and CRF systems. A.D. Lê covered information that indicated that stress facilitated reinstatement to alcohol responding and summarized the influence of multiple deprivations on this interaction. David Overstreet provided evidence that restraint stress during repeated alcohol deprivations increases voluntary drinking in alcohol‐preferring (P) rats that results in withdrawal‐induced anxiety that is not observed in the absence of stress. Testing of drugs on the stress‐induced voluntary drinking implicated serotonin and CRF involvement in the sensitized response. Collectively, the presentations provided convincing support for an involvement of stress in the cause of relapse and continuing alcohol abuse and suggested novel pharmacological approaches for treating relapse induced by stress.
Basis of the Gabamimetic Profile of Ethanol Breese, G. R.; Criswell, H. E.; Carta, M. ...
Alcoholism, clinical and experimental research,
April 2006, Volume:
30, Issue:
4
Journal Article
Peer reviewed
Open access
This article summarizes the proceedings of a symposium held at the 2005 Research Society on Alcoholism meeting. The initial presentation by Dr. Wallner provided evidence that selected GABAA receptors ...containing the δ subunit display sensitivity to low intoxicating ethanol concentrations and this sensitivity is further increased by a mutation in the cerebellar α6 subunit, found in alcohol‐hypersensitive rats. Dr. Mameli reported that ethanol affects γ‐aminobutyric acid (GABA) function by affecting neural circuits that influence GABA release. Dr. Parsons presented data from electrophysiological and microdialysis investigations that ethanol is capable of releasing GABA from presynaptic terminals. Dr. Morrow demonstrated that systemic ethanol increases neuroactive steroids in brain, the absence of which alters various functional responses to ethanol. Dr. Criswell presented evidence that the ability of ethanol to increase GABA was apparent in some, but not all, brain regions indicative of regional specificity. Further, Dr. Criswell demonstrated that neurosteroids alone and when synthesized locally by ethanol act postsynaptically to enhance the effect of GABA released by ethanol in a region specific manner. Collectively, this series of reports support the GABAmimetic profile of acutely administered ethanol being dependent on several specific mechanisms distinct from a direct effect on the major synaptic isoforms of GABAA receptors.
Smoking and mental illness Leonard, S.; Adler, L.E.; Benhammou, K. ...
Pharmacology, biochemistry and behavior,
12/2001, Volume:
70, Issue:
4
Journal Article
Peer reviewed
Patients with mental illness have a higher incidence of smoking than the general population and are the major consumers of tobacco products. This population includes subjects with schizophrenia, ...manic depression, depression, posttraumatic stress disorder (PTSD), attention-deficit disorder (ADD), and several other less common diseases. Smoking cessation treatment in this group of patients is difficult, often leading to profound depression. Several recent findings suggest that increased smoking in the mentally ill may have an underlying biological etiology. The mental illness schizophrenia has been most thoroughly studied in this regard. Nicotine administration normalizes several sensory-processing deficits seen in this disease. Animal models of sensory deficits have been used to identify specific nicotinic receptor subunits that are involved in these brain pathways, indicating that the α7 nicotinic receptor subunit may play a role. Genetic linkage in schizophrenic families also supports a role for the α7 subunit with linkage at the α7 locus on chromosome 15. Bipolar disorder has some phenotypes in common with schizophrenia and also exhibits genetic linkage to the α7 locus, suggesting that these two disorders may share a gene defect. The α7 receptor is decreased in expression in schizophrenia.
3H-Nicotine binding studies in postmortem brain indicate that high-affinity nicotinic receptors may also be affected in schizophrenia.
Safe, long-term gene expression is a primary criteria for effective gene therapy in the brain, so studies were initiated to evaluate adeno-associated virus (AAV) vector transfer of a reporter gene ...into specific sites of the rat brain. In the 4 day old rat, site infusions of AAV-CMV-
lacZ (1 μ1; 5 × 10
4 particles) produced neuronal β-galactosidase gene expression 3 weeks later in the hippocampus and inferior colliculus, but not in the cerebral cortex. Seven days after infusion of AAV-CMV-
lacZ viral vectors (1 μ1) in the adult rat, β-galactosidase gene expression was found in the olfactory tubercle, caudate, hippocampus, piriform cortex and inferior colliculus, primarily in multipolar neurons close to the infusion site. Three months after vector microinfusion, similar levels of gene expression remained in the olfactory tubercle and the inferior colliculus, with some reduction found in the caudate, but substantial reductions in β-galactosidase gene expression occurred in the hippocampus and piriform cortex. In no case were obvious signs of toxicity noted. Therefore, AAV vectors can transfer foreign genes into the adult and neonatal CNS, but the pattern and longevity of gene expression depends upon the area of brain being studied.
Anxiety-like behaviors are integral features of withdrawal from chronic ethanol exposure. In the experiments in the current study, we tested the hypothesis that anxiety can be regulated independently ...of other withdrawal signs and thus may be responsive to selective pharmacological agents. For 17 days, rats were fed ethanol (8–12 g/kg/day) in a liquid diet. Between 5 and 6 h after cessation of ethanol treatment, rats were tested in either the social interaction or plus-maze test of anxiety-like behavior after treatment with drugs hypothesized to have anxiolytic action. SB242084, flumazenil, and CRA1000—antagonists for 5-hydroxytryptamine (serotonin) (5-HT) 2C (5-HT
2C), benzodiazepine, and corticotropin-releasing factor type 1 (CRF
1) receptors, respectively—attenuated decreased social interaction without concomitant effects on activity measures. In contrast, ifenprodil, MDL 72222, and zolpidem—antagonists for
N-methyl-
d-aspartate (NMDA) and 5-HT
3 receptors, and agonist for benzodiazepine type 1 receptors, respectively—did not share this effect. Results for SB242084, flumazenil, and ifenprodil in the elevated plus-maze test were comparable to those in the social interaction test. These results support the suggestion that multiple neuronal systems (CRF
1, 5-HT
2C, and benzodiazepine receptors) contribute to the ethanol withdrawal sign of decreased social interaction. Furthermore, the selective effects of pharmacological agents on social interaction seem to indicate that this behavior can be dissociated from other signs. Because anxiety may be a complicating factor in alcohol withdrawal and relapse, future studies of this type are needed to provide focus for the effort to define selective and novel antianxiety agents for these disorders.
The rationale for proposing the "kindling"/stress hypothesis is to provide a conceptual basis for the insidious development and maintenance of alcohol abuse.
An objective of the hypothesis is to ...emphasize how continued alcohol abuse is linked to progressive neural adaptation. Work has shown that repeated withdrawals from chronic low levels of alcohol sensitize ("kindle") anxiety-like behavior ("anxiety") in rats, a finding consistent with multiple withdrawal kindling of seizure activity. Additionally, stress substitutes for initial cycles of the multiple withdrawal protocol to sensitize withdrawal-induced anxiety, which is indicative that stress is capable of facilitating neuroadaptive processes related to withdrawal. The persistence of adaptation caused by stress and multiple withdrawals is revealed by the appearance of withdrawal-induced anxiety following a future re-exposure to a single 5-day period of alcohol. This persisting adaptation also permits stress to induce anxiety during a period of abstinence--a response not observed in animals without previous exposure to alcohol. Furthermore, stress interacts with repeated withdrawals to enhance voluntary alcohol drinking. Results of other preclinical and clinical studies reported in the literature are integrated with these investigations in support of the proposed hypothesis.
The "kindling"/stress hypothesis is based on the premise that repeated withdrawals from cycles of chronic alcohol exposure contribute to a progressive development of persisting adaptive change that sensitizes withdrawal-induced anxiety and allows stress to evoke symptoms associated with negative affect during abstinence. Thus, these consequences of repeated withdrawals account for the evolution of major characteristics of alcoholism, which include worsened acute withdrawal symptoms and increased stress-induced negative affect during abstinence, both of which enhance the likelihood of relapse--and with relapse an inability to limit an abusive pattern of alcohol intake. The "kindling"/stress hypothesis provides a clear strategy for future studies to explore the advancing neural adaptation proposed to contribute to the pathogenesis of alcoholism.
Previous research indicated that male rats exhibited anxiety-like behavior following withdrawal from chronic ethanol exposure. This behavior, as well as other symptoms of withdrawal such as seizure ...susceptibility, may be sensitized in male rats repeatedly withdrawn from chronic ethanol exposure. Because there are sex differences in some alcohol effects, the present study explored whether male and female rats would respond differently to a course of repeated ethanol withdrawals. Similarly aged male and female rats were exposed to a control liquid diet or a diet containing ethanol (7% w/v). Ethanol-exposed rats had only one 5-day cycle of exposure or three cycles, with 2 days of control diet (CD) between cycles. At 5 h after the final ethanol was removed, the rats were placed as same-sexed pairs in the social interaction test; approximately half of the rats were tested later in the elevated plus maze. Rats withdrawn from ethanol after three cycles exhibited reduced the time spent in social interaction and general activity in the social interaction test and reduced the open and closed arm entries in the elevated plus maze. There were no sex differences in these effects. However, male rats exhibited a small anxiety-like response after one cycle of 5 days' exposure to ethanol and female rats did not. Thus, there are no sex differences in the three-cycle multiple-withdrawal paradigm, but there may be differences after briefer exposures.
Subanesthetic doses of ketamine have been shown to exacerbate symptoms in schizophrenia and to induce positive, negative, and cognitive schizophrenic-like symptoms in normal subjects. The present ...investigation sought to define brain regions affected by subanesthetic doses of ketamine, using high resolution autoradiographic analysis of
14C-2-deoxyglucose (2-DG) uptake and immunocytochemical staining for Fos-like immunoreactivity (Fos-LI). Both functional mapping approaches were used because distinct and complementary information is often obtained with these two mapping methods. Ketamine, at a subanesthetic dose of 35 mg/kg, substantially increased 2-DG uptake in certain limbic cortical regions, including medial prefrontal, ventrolateral orbital, cingulate, and retrosplenial cortices. In the hippocampal formation, the subanesthetic dose of ketamine induced prominent increases in 2-DG uptake in the dentate gyrus, CA-3 stratum radiatum, stratum lacunosum moleculare, and presubiculum. Increased 2-DG uptake in response to 35 mg/kg ketamine was also observed in select thalamic nuclei and basolateral amygdala. Ketamine induced Fos-LI in the same limbic cortical regions that exhibited increased 2-DG uptake in response to the subanesthetic dose of the drug. However, no Fos was induced in some brain regions that showed increased 2-DG uptake, such as the hippocampal formation, anterioventral thalamic nucleus, and basolateral amygdala. Conversely, ketamine induced Fos in the paraventricular nucleus of the hypothalamus and central amygdala, although no effect of the drug on 2-DG uptake was apparent in these regions. In contrast to the increase in 2-DG uptake observed in select brain regions after the subanesthetic dose, an anesthetic dose of ketamine (100 mg/kg) produced a global suppression of 2-DG uptake. By contrast, a robust induction of Fos-LI was observed after the anesthetic dose of ketamine that was neuroanatomically identical to that produced by the subanesthetic dose. Results of the present investigation show that anesthetic and subanesthetic doses of ketamine have pronounced effects on regional brain 2-DG uptake and induction of Fos-LI. The alterations in regional brain metabolism induced by the subanesthetic dose may be relevant to effects of ketamine to induce schizophrenic-like symptoms.
The prenatal and postnatal ontogeny of D1A and D2 dopamine receptors was assessed by in situ hybridization of messenger RNAs encoding the receptors and by radioligand binding autoradiography. On ...gestational day 14, signals for D1A and D2 dopamine receptor messages were observed in selected regions in ventricular and subventricular zones which contain dividing neuroblasts, and in intermediate zones that contain maturing and migrating neurons. Specifically, D1A and D2 dopamine receptor message was observed in the developing caudate-putamen, olfactory tubercle, and frontal, cingulate, parietal and insular cortices. Additionally, D1A dopamine receptor messenger RNA was found in the developing epithalamus, thalamus, hypothalamus, pons, spinal cord and neural retina; D2 dopamine receptor messenger RNA was also observed in the mesencephalic dopaminergic nuclear complex. Gene expression of D1A and D2 dopamine receptor subtypes in specific cells as they differentiate precedes dopamine innervation and implies that receptor expression is an intrinsic property of these neurons. The early expression of dopamine receptor messenger RNA suggests a regulatory role for these receptors in brain development. While the signal for both messages increased in the intermediate zones on gestational day 16, it decreased in the ventricular and subventricular zones, and was no longer apparent in these zones by gestational day 18. By gestational day 18, abundant D1A or D2 dopamine receptor messenger RNA was observed in cell groups similar in location to those observed in the adult brain. On gestational day 18, D1A dopamine receptor message was noted in the neural retina, anterior olfactory nucleus, the insular, prefrontal, frontal, cingulate, parietal and retrosplenial cortices, the olfactory tubercle, caudate-putamen, lateral habenula, dorsolateral geniculate nucleus, ventrolateral and mediolateral thalamic nuclei, and the suprachiasmatic and ventromedial nuclei of the hypothalamus. D2 dopamine receptor message was observed on gestational day 18 in the insular, prefrontal, frontal and cingulate cortices, the olfactory tubercle, caudate-putamen, ventral tegmental area, substantia nigra, and the intermediate lobe of the pituitary. At birth, expression of messenger RNA for both dopamine receptor subtypes in the striatum approximated that seen in mature rats. In contrast, D1A and D2 receptor binding, measured with 3HSCH-23390 and 3Hraclopride, respectively, was low at birth and progressively increased to reach adult levels between days 14 and 21. The in situ hybridization data showing early prenatal expression of messenger RNA for the D1A and D2 dopamine receptors are consistent with the hypothesis that these receptors have a regulatory role in neuronal development.
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