Alpha-lipoic acid and alpha-lipoamide prevent oxidant-induced lysosomal rupture and apoptosis.

Alpha-lipoic acid (LA) and its corresponding derivative, alpha-lipoamide (LM), have been described as antioxidants, but the mechanisms of their putative antioxidant effects remain largely uncharacterised. The vicinal thiols present in the reduced forms of these compounds suggest that they might possess metal chelating properties. We have shown previously that cell death caused by oxidants may be initiated by lysosomal rupture and that this latter event may involve intralysosomal iron which catalyzes Fenton-type chemistry and resultant peroxidative damage to lysosomal membranes. Here, using cultured J774 cells as a model, we show that both LA and LM stabilize lysosomes against oxidative stress, probably by chelating intralysosomal iron and, consequently, preventing intralysosomal Fenton reactions. In preventing oxidant-mediated apoptosis, LM is significantly more effective than LA, as would be expected from their differing capacities to enter cells and concentrate within the acidic lysosomal compartment. As previously reported, the powerful iron-chelator, desferrioxamine (Des) (which also locates within the lysosomal compartment), also provides protection against oxidant-mediated cell death. Interestingly, although Des enhances the partial protection afforded by LA, it confers no additional protection when added with LM. Therefore, the antioxidant actions of LA and LM may arise from intralysosomal iron chelation, with LM being more effective in this regard.

Naloxone antagonizes GABA(A)/benzodiazepine receptor function in rat corticohippocampal synaptoneurosomes.

Several lines of behavioral and neurochemical evidence indicate GABA(A)-antagonistic properties of naloxone. Here, the effects of naloxone on rat brain GABA(A)/benzodiazepine receptor function in vitro were investigated. Naloxone, naltrexone and morphine (10-1,000 microM) reduced GABA-induced (10 microM) 36Cl- uptake in corticohippocampal synaptoneurosomes. Furthermore, the concentration-response curve for GABA-induced 36Cl- uptake (GABA 3-100 microM) was shifted to the right both by naloxone and morphine (1,000 microM). Naloxone also reduced the 36Cl- uptake induced by GABA + diazepam (3 microM + 1 microM) but not that induced by amobarbital (500 microM). The naloxone-induced (1,000 microM) reduction of GABA-mediated (10 microM) 36Cl- uptake was reversed by amobarbital (10-1,000 microM) but not by flumazenil (10-1,000 microM) or morphine (0.1-1,000 microM). These results indicate that naloxone, naltrexone and morphine are weak negative modulators of GABA(A)/benzodiazepine receptor function. The naloxone effect most likely does not involve opiate receptors or the benzodiazepine site on GABA(A) receptor complexes.

Gonadectomy enhances shock-induced behavioral inhibition in adult male rats: implications for impulsive behavior.

The effects of gonadectomy on shock-induced behavioral inhibition in a modified Vogel's drinking conflict model and on diazepam-induced disinhibition and sedation were investigated in adult male rats. Gonadectomy enhanced shock-induced behavioral inhibition when determined 9, 21, 45, and 65 days, but not 3 days, after operation, without affecting shock sensitivity or drinking motivation. Testosterone-substitution for 21 days following gonadectomy prevented this enhanced inhibition without significantly affecting the behavior in sham-operated rats. Diazepam produced behavioral disinhibition both in sham-operated and gonadectomized rats. However, after the highest dose (16 mg/kg, IP) the disinhibited behavior decreased only in sham-operated animals, most likely due to sedation. Moreover, whereas there was no difference in basal rotarod-performance between controls and gonadectomized rats, the latter animals were less sensitive to diazepam-induced disruption of rotarod walking ability. Sham-operated or gonadectomized animals did not differ with respect to serum diazepam levels at the postinjection times used in the behavioral tests. Taken together, gonadectomized rats were less sensitive towards diazepam-induced sedation, possibly due to a subsensitivity at or beyond GABA(A)/benzodiazepine receptors. Furthermore, the finding that lack of testosterone enhanced shock-induced inhibition could be interpreted to reflect increased impulse control and may involve an altered activation of GABA(A)/benzodiazepine receptors.

Disinhibitory behavior and GABA(A) receptor function in serotonin-depleted adult male rats are reduced by gonadectomy.

Impulsive and aggressive behaviors in, e.g., personality or substance abuse disorders in man and corresponding behaviors in rats may involve serotonin (5-HT), gamma-amino-butyric acid(A)/benzodiazepine receptor complexes (GABA(A)/BDZ-RC) and steroid hormones, e.g., testosterone. Here, we studied the effect of gonadectomy on disinhibitory behavior in individually housed 5-HT-depleted rats and on GABA(A)/BDZ-RC function in vitro, in corticohippocampal synaptoneurosomes prepared from the brain of these animals. 5-HT depletion by intracerebroventricular 5,7-dihydroxytryptamine (5,7-DHT)-induced disinhibitory behavior in a shock-induced behavioral inhibition model (punished conflict model) 14 days after operation. Gonadectomy in connection with the 5-HT depletion reduced the disinhibitory behavior and testosterone substitution prevented this effect. Shock threshold and drinking motivation were not affected by gonadectomy and/or 5-HT depletion. The relative epididymides weight was increased in 5-HT-depleted as compared to sham-operated rats. However, the serum concentrations of testosterone and the relative testes weights were not different in 5-HT-depleted rats as compared to controls. GABA-induced (30, 100, 300 microM) 36Cl(-)-uptake into synaptoneurosomes was lower in 5,7-DHT+gonadectomized rats compared to the control group. This effect was reversed by substitution with testosterone. These results demonstrate that gonadectomy reduces disinhibitory behavior in 5-HT-depleted rats and that GABA(A)/BDZ-RC may be involved in this effect.

Naloxone reverses disinhibitory/aggressive behavior in 5,7-DHT-lesioned rats; involvement of GABA(A) receptor blockade?

Effective medical treatment for impulsive aggression and several impulse control disorders is needed. Disinhibited, impulsive behavior of e.g. murderers, arsonists, suicidal patients, and patients suffering from antisocial personality or substance abuse disorders has been associated with signs of a deficiency in brain serotonin (5-HT) systems. Depletion of brain 5-HT consistently produces disinhibition and aggression also in experimental animals. The present series of experiments using a modified Vogel's conflict test indicates that the disinhibitory behavior of 5-HT-lesioned rats can be reversed by the commonly used opiate receptor antagonist naloxone at doses (0.1-5.0 mg/kg, s.c.) that do not significantly affect behavior in sham-lesioned controls. Moreover, this effect of naloxone, which resembles that previously observed after administration of negative modulators of gamma-aminobutyric acidA (GABA(A))/benzodiazepine receptor complexes, was reversed by a low inert dose (2.0 mg/kg, i.p.) of amobarbital. Furthermore, both naloxone (5.0 mg/kg, s.c.) and Ro 15-4513 (1.0 mg/kg, p.o.; a partial inverse agonist at benzodiazepine receptors) significantly decreased the number of attacks and the time spent in aggressive acts in 5,7-DHT-lesioned male residents. These results taken together with previous behavioral and neurochemical data suggest that the behavioral effects of naloxone observed here may involve an antagonistic action at brain gamma-aminobutyric acidA (GABA(A))/benzodiazepine receptor complexes. Thus, naloxone, its stable analogue naltrexone or other weak negative modulators of brain GABA(A)/benzodiazepine receptor complexes may represent a new pharmacological principle for the treatment of impulse control disorders.

Induction but not expression of behavioural sensitization to nicotine in the rat is dependent on glucocorticoids.

Behavioural sensitization has been implicated in the development of addictive behaviour, and several studies suggest that corticosteroids may be involved in this phenomenon. In the present study, the effects of adrenalectomy and steroid replacement treatments on the behavioural sensitization observed after daily injections of nicotine (0.4 mg/kg s.c.) were investigated in the rat. Adrenalectomy completely prevented sensitization to the locomotor stimulating effect of nicotine after repeated injections but did not influence the acute locomotor activating effect of the drug or an already established sensitization to nicotine. In adrenalectomized animals receiving replacement treatment with corticosterone or dexamethasone, but not aldosterone, repeated administration of nicotine produced behavioural sensitization. Repeated dexamethasone treatment per se failed, however, to sensitize rats to nicotine. Post mortem neurochemical studies showed that repeated administration of nicotine significantly increased homovanillic acid (HVA) levels, as well as the dihydroxyphenylacetic acid (DOPAC)/dopamine quotient, in the limbic forebrain. Adrenalectomy per se significantly increased HVA levels and tended to elevate the DOPAC/dopamine quotient. When repeatedly treated with nicotine, adrenalectomized rats displayed a higher DOPAC/dopamine quotient, but no significant difference in HVA levels, compared to nicotine-treated sham-operated controls. In the striatum and the cortex, no significant effects of nicotine treatment or adrenalectomy were observed on any of the neurochemical measures. The present results suggest that glucocorticoid (type II) receptor activation is required for induction of sensitization to the locomotor stimulatory effect of nicotine, whereas corticosteroids are not required for the expression of the behavioural sensitization once established. Provided that HVA levels and the DOPAC/dopamine quotient relatively well reflect the presynaptic dopamine activating effect of nicotine, it may be suggested that corticosteroid-related mechanisms associated with behavioural sensitization to nicotine are post- rather than presynaptically located in relation to mesolimbic dopamine neurons.