Modulation of extracellular neurotransmitter levels in the nucleus accumbens by a taurine uptake inhibitor

Selective breeding for helplessness in rats alters the metabolic profile of the hippocampus and frontal cortex: a 1H-MRS study at 9.4 T

In humans metabolic changes, particularly in frontal areas of the brain, accompany depressive disorders, but few studies were conducted in animal models of depression. We used hydrogen-1 magnetic resonance spectroscopy at 9.4 T to measure the metabolic profiles of the hippocampus and frontal cortex in congenital learned helpless (cLH) and wild-type (WT) rats. The learned helplessness model of depression exposes animals to uncontrollable stress to induce changes in emotion, cognition and behaviour, but cLH rats were selectively bred to show changes in behaviour even without exposure to uncontrollable stress. Experimentally naive male 8- to 10-wk-old cLH (n = 10) and WT rats (n = 22) underwent spectroscopy and were exposed to uncontrollable stress 1 wk after the scan. We found that cLH compared to WT rats had lower levels of glutamate in the hippocampus and lower levels of choline-containing compounds in the hippocampus and frontal cortex, but higher levels of taurine and phosphocreatine in these regions, pointing to compensatory efforts of the brain to reduce excitotoxic potential and to increase neuroprotection and energy, possibly as a result of cellular stress and damage. The reduction in choline-containing phospholipids might represent a source or correlate of such stress. Overall, the results indicate that metabolic abnormalities are present in animals with a predisposition to helplessness even without exposure to explicit stress and may help identify non-invasive biomarkers in individuals who are prone to depression.

Intermittent high-dose ethanol exposures increase motivation for operant ethanol self-administration: possible neurochemical mechanism

We investigated the neurochemical mechanism of how high-dose ethanol exposure may increase motivation for ethanol consumption. First, we developed an animal model of increased motivation for ethanol using a progressive ratio (PR) schedule. Sprague-Dawley rats were trained to administer 10% ethanol-containing gelatin or plain gelatin (on alternate weeks) in daily 30-min sessions under different fixed ratio (FR) and PR schedules. During FR schedules, rats self-administered about 1 g/kg ethanol, which was decreased to 0.4+/-0.03 g/kg under PR10. Rats then received four pairs of either 3 g/kg ethanol or saline injections during the weeks when the reinforcer was plain gelatin. During subsequent ethanol gel sessions, breakpoints and ethanol consumption rose 40% in the high-dose ethanol group by the fourth set of injections with no change in plain gel responding. Alterations in amino acids in the ventral striatum (VS) during PR10 responding for 10% ethanol gelatin and plain gelatin were measured using microdialysis sampling coupled with capillary electrophoresis and laser-induced fluorescence detection. There was greater release of taurine, glycine and glutamate in the NAC of the high-dose ethanol rats during 10% ethanol-containing gelatin responding, compared to the control rats or during plain gel responding. An increase in the release of glycine in this same brain region has recently been shown to be involved with anticipation of a reward. Thus, it appears that intermittent high-dose ethanol exposure not only increases motivation for ethanol responding but may also change neurotransmitter release that mediates anticipation of reinforcement, which may play a key role in the development of alcoholism.

Suppression of heavy drinking and alcohol seeking by a selective ALDH-2 inhibitor

BACKGROUND

Inherited human aldehyde dehydrogenase 2 (ALDH-2) deficiency reduces the risk for alcoholism. Kudzu plants and extracts have been used for 1,000 years in traditional Chinese medicine to treat alcoholism. Kudzu contains daidzin, which inhibits ALDH-2 and suppresses heavy drinking in rodents. Decreased drinking due to ALDH-2 inhibition is attributed to aversive properties of acetaldehyde accumulated during alcohol consumption. However, daidzin can reduce drinking in some rodents without necessarily increasing acetaldehyde. Therefore, a selective ALDH-2 inhibitor might affect other metabolic factors involved in regulating drinking.

METHODS

Aldehyde dehydrogenase 2 inhibitors were synthesized based on the co-crystal structure of ALDH-2 and daidzin. We tested the efficacy of a highly selective reversible ALDH-2 inhibitor, CVT-10216, in models of moderate and high alcohol drinking rats. We studied 2-bottle choice and deprivation-induced drinking paradigms in Fawn Hooded (FH) rats, operant self-administration in Long Evans (LE), FH, and inbred P (iP) rats and in cue-induced reinstatement in iP rats. We also assayed blood acetaldehyde levels as well as dopamine (DA) release in the nucleus accumbens (NAc) and tested possible rewarding/aversive effects of the inhibitor in a conditioned place preference (CPP) paradigm.

RESULTS

CVT-10216 increases acetaldehyde after alcohol gavage and inhibits 2-bottle choice alcohol intake in heavy drinking rodents, including deprivation-induced drinking. Moreover, CVT-10216 also prevents operant self-administration and eliminates cue-induced reinstatement of alcohol seeking even when alcohol is not available (i.e., no acetaldehyde). Alcohol stimulates DA release in the NAc, which is thought to contribute to increased drinking and relapse in alcoholism. CVT-10216 prevents alcohol-induced increases in NAc DA without changing basal levels. CVT-10216 does not show rewarding or aversive properties in the CPP paradigm at therapeutic doses.

CONCLUSION

Our findings suggest that selective reversible ALDH-2 inhibitors may have therapeutic potential to reduce excessive drinking and to suppress relapse in abstinent alcoholics.

The selective A2A receptor antagonist SCH 58261 reduces striatal transmitter outflow, turning behavior and ischemic brain damage induced by permanent focal ischemia in the rat

Adenosine A(2A) receptor antagonists have been proved protective in different ischemia models. In this study we verified if the protective effect of the selective A(2A) antagonist, SCH 58261, could be attributed to the reduction of the excitatory amino acid outflow induced by cerebral focal ischemia. A vertical microdialysis probe was inserted into the striatum of male Wistar rats and, after 24 h, permanent right intraluminal middle cerebral artery occlusion (MCAo) was induced. Soon after waking, rats showed a definite contralateral turning behavior, which persisted up to 7 h after MCAo. During 4 h after MCAo, glutamate, aspartate, GABA, adenosine and taurine outflow increased. SCH 58261 (0.01 mg/kg, i.p.), administered 5 min after MCAo, suppressed turning behavior and significantly reduced the outflow of glutamate, aspartate, GABA and adenosine. At 24 h after MCAo, the rats showed severe sensorimotor deficit and damage in both the striatum and cortex. SCH 58261 significantly reduced cortical damage but did not protect against the sensorimotor deficit. The protective effect of SCH 58261 against turning behavior and increased outflow of excitatory amino acids in the first hours after MCAo suggests the potential utility of selective adenosine A(2A) antagonists when administered in the first hours after ischemia. Furthermore, this study, for the first time, proposes that turning behavior after permanent intraluminal MCAo, be used as a precocious index of neurological deficit and neuronal damage.