Depletion of brain noradrenaline and dopamine by 6‐hydroxydopamine

Summary 10 After intracisternal administration, 6-hydroxydopamine had a greater effect on brain noradrenaline than on dopamine. 2) Administration of two doses of 6-hydroxydopamine increased the depletion of noradrenaline but not of dopamine. 3) Small doses of 6‐hydroxydopamine decreased the concentration of noradrenaline with little or no effect on dopamine. Tyrosine hydroxylase activity was not reduced with these treatments. 4) While pargyline pretreatment offered no advantage in the depletion of brain noradrenaline after 6-hydroxydopamine, depletion of brain dopamine was greatly potentiated by this treatment. The reduction of striatal tyrosine hydroxylase activity observed after 6-hydroxydopamine was also potentiated by pargyline pretreatment. 5) The amounts of labelled noradrenaline and dopamine formed from 3H-tyrosine were greatly reduced by 6-hydroxydopamine treatment. After 3H-DOPA, formation of noradrenaline was greatly reduced while formation of labelled dopamine was only moderately reduced suggesting that decarboxylation of DOPA can occur in other than catecholamine containing neurones. 6) Desmethylimipramine and imipramine inhibited depletion of noradrenaline produced by 6-hydroxydopamine but did not alter depletion of dopamine. Reserpine did not inhibit depletion of catecholamines produced by 6-hydroxydopamine. 7) Administration of 6-hydroxydopamine to developing rats lowered both noradrenaline and dopamine concentrations as well as the tyrosine hydroxylase activity in the brains of these animals

Effect of 6-hydroxydopamine on brain norepinephrine and dopamine evidence for selective degeneration of catecholamine neurons.

After the intracisternal administration of 6-hydroxydopamine, brain levels of norepinephrine were reduced significantly with or without pargyline pretreatment. Depletion of dopamine in the central nervous system was found to be enhanced markedly by pargyline administration at higher dose levels of 6-hydroxydopamine. Brain serotonin concentrations were not altered. The effects of 6-hydroxydopamine were long-lasting with the depletion of brain amines persisting at 78 days. After norepinephrine-H3 intracisternally to animals treated with 6-hydroxydopamine, labeled norepinephrine uptake was diminished with a corresponding reduction of deaminated catechols and a marked increased in methylated amines. Tyrosine hydroxylase activity was found to be reduced in brainstem, caudate nucleus and whole brain in 6-hydroxydopamine-treated animals. Conversion of tyrosine-H3 to labeled norepinephrine and dopamine was also markedly diminished. The results support the view that 6-hydroxydopamine produces a "central sympathectomy" when introduced into cerebrospinal fluid

GABAergic Modulation of Ethanol-Induced Motor Impairment

Direct or indirect pharmacological manipulation of γ-aminobutyric acid (GABA) receptor activity was examined in relation to the motor incoordinating actions of ethanol in the rat. Ethanol (1.13–3.0 g/kg i.p.) caused a dose-dependent increase in the height of aerial righting. This motor impairment was increased selectively by intracisternal injection of the GABA agonists muscimol (0.10 μg), 4,5,6,7-tetrahydroisoxazole(5,4-c) pyridin(3-ol) (1.0 μg) and GABA (1000 μg). The GABA antagonist, bicuculline (1.0 and 5.0 μg intracisternally), reduced impairment. Thus, direct manipulation of GABA receptor activity modulated motor incoordination caused by ethanol. In addition, indirect-acting GABA-mimetics, such as γ-acetylenic GABA (100 mg/kg i.p.), aminooxyacetic acid (50 mg/kg i.p.), ethanolamine-O-sulfate (250 mg/kg i.p.) and L-2,4-diaminobutyric acid (600 mg/kg i.p.) all potentiated the increase in the height of aerial righting caused by ethanol treatment. Failure of ethanol to modify the binding of [3H]muscimol to cerebral cortical membranes in vitro suggested there was no direct competition for GABA binding sites or facilitation of the binding of GABA to these sites by ethanol. Also, no simple relationship was observed between the degree of motor impairment caused by either ethanol or γ-acetylenic GABA and changes in GABA concentration in three brain areas. Although GABAergic neurons may be involved in the mechanism underlying ethanol-induced depression of motor coordination, the interaction does not involve a direct activation of GABA receptors by ethanol

SCH-23390 antagonism of a D-2 dopamine agonist depends upon catecholaminergic neurons

SCH-23390, a selective D-1 dopamine antagonist, was found to antagonize the locomotor stimulation induced by LY-171555, an action similar to that for haloperidol in control animals. However, this action of SCH-23390 was prevented in rats treated with 6-hydroxydopamine (6-OHDA) or with reserpine plus α-methyl-tyrosine pretreatment. These results indicate that the action of SCH-23390 to antagonize D-2 dopamine receptor actions is dependent upon functional catecholamine-containing neurons. In contrast to the lack of action of SCH-23390 to antagonize LY-171555 in 6-OHDA-treated rats, SCH-23390 blocked the locomotor stimulation induced by SKF-39393, a D-1 dopamine agonist, after this treatment. Thus, D-1 dopamine receptors are distinct from D-2 receptor sites and can exhibit a behavior similar to that observed when D-2 receptors are stimulated. These data suggest that D-1 receptor sites modulate D-2 dopamine receptor function through a mechanism dependent upon functionally intact catecholamine-containing neurons

Electrophysiological Evidence that Ethanol Alters Function of Medial Septal Area Without Affecting Lateral Septal Function

Evidence is provided in this manuscript that ethanol acts directly on neurons in the medial septal area (MSA). Initially, the electrophysiological characteristics of MSA neurons in freely moving rats were characterized and found similar to that observed in rats anesthetized with urethane, but not chloral hydrate. Therefore, urethane was used to evaluate the effects of ethanol in anesthetized rats. The conclusion that ethanol influences neural function in the MSA is based on electrophysiological data that ethanol (0.75–3.0 g/kg i.p.) suppresses neural firing of medial septal cells in urethane-anesthetized as well as in unanesthetized rats in a dose-related fashion. Concurrent with the suppression of firing rate, the rhythmic bursting pattern of activity of MSA neurons is disrupted by ethanol. The changes observed in the MSA could not be attributed to an indirect action of ethanol on afferents from the lateral septum to the MSA, because ethanol did not alter neural activity of cells in the lateral septum. These data indicate that ethanol does not have a common action on all neurons. Neural activity in the MSA recovered from the acute action of ethanol at a time when blood ethanol levels were near maximal, indicating an acute tolerance to this effect of ethanol. The time course of change in neural activity in the MSA was highly correlated with the time course of a measure of behavioral sedation, but not the hypothermia produced by ethanol. Thus, the work in this manuscript supports the view that ethanol has selective actions on MSA neurons in the rat septal area and that these actions may influence the behavioral sedation induced by ethanol

Site-Specific Enhancement of γ-Aminobutyric Acid-Mediated Inhibition of Neural Activity by Ethanol in the Rat Medial Septal Area

Because of uncertainty concerning the interaction of ethanol with γ-aminobutyric acid (GABA) receptor-mediated events, the present work was designed to investigate the effect of ethanol on GABA transmission in the rat septal area using behavioral and electrophysiological techniques. Microinjection of the GABAA agonist muscimol into the medial septal area (MSA) enhanced, and bicuculline administration antagonized, ethanol-induced impairment of the aerial righting reflex. Microinjection of these drugs into the lateral septum (LSi) did not influence this measure of ethanol-induced sedation. Furthermore, intraseptal injections of muscimol or bicuculline in saline-treated rats had no effect on the aerial righting reflex. These data suggest that the MSA plays a critical modulatory role in the sedative actions of ethanol. To assess the effect of ethanol on muscimol responses in the MSA and LSi at the cellular level, GABA was applied by iontophoresis to rhythmically bursting neurons of the MSA and to cells in the LSi. The magnitude of the resultant inhibition by GABA on these cells was assessed before and after systemic administration of ethanol. Ethanol enhanced GABA-mediated inhibition of MSA neural activity, but did not alter GABA-mediated inhibition of cellular activity in the LSi. In contrast, the inhibition of cellular activity in the MSA, caused by a maximally effective concentration of the benzodiazepine flurazepam, was not altered by ethanol. Other work in the MSA demonstrated that electrical stimulation of the fimbria caused an inhibition of ongoing single unit activity that was reduced by concurrent application of bicuculline. The duration of this electrically elicited inhibition in the MSA was enhanced after ethanol injection and then recovered to base-line levels. In addition, ethanol (1.5 mg/kg) caused an enhancement of the inhibition induced by nipecotic acid, a GABA uptake inhibitor. These findings demonstrate that GABA-mediated neural inhibition is enhanced by ethanol in the MSA but not the LSi, indicating that the actions of ethanol on GABA-induced inhibition can be site specific. It is proposed that the cellular action of ethanol may depend upon a specific molecular composition of the GABA receptor complex which may vary at selected sites in the brain

Mechanistic and Functional Divergence Between Thyrotropin-releasing Hormone and RO 15-4513 Interactions with Ethanol

Both thyrotropin-releasing hormone (TRH) and RO 15-4513 antagonize ethanol-induced depression, but this common property does not infer that both compounds share similar mechanisms of action. In the present studies, both TRH (30 mg/kg, i.p.) and RO 15-4513 (10 mg/kg, i.p.) reversed ethanol-induced depression of locomotor activity, in accord with previous reports. However, the benzodiazepine antagonist, RO 15-1788, blocked this action of RO 15-4513, while exerting no effect on the analeptic action of TRH. Using a model of seizure activity electrically elicited from the inferior colliculus, ethanol exerted a dose-related attenuation of seizure activity. This anticonvulsant action of ethanol was not altered by TRH (30 mg/kg, i.p.), but RO 15-4513 (3 mg/kg) reversed the effect of the 0.5, but not the 1.0 g/kg, dose of ethanol. In addition, pretreatment with RO 15-4513 (1 or 3 mg/kg, i.p.), but not TRH (30 mg/kg, i.p.), caused seizure generalization into the forebrain following inferior collicular stimulation, further verifying the proconvulsant properties of RO 15-4513. In conclusion, the analeptic action of TRH appears independent of benzodiazepine activity, and in contrast to RO 15-4513, TRH does not exhibit proconvulsant properties. Furthermore, because TRH did not antagonize both depressant actions of ethanol studied, it appears unlikely that TRH directly interacts with the molecular basis of ethanol action

Persistent adaptation by chronic alcohol is facilitated by neuroimmune activation linked to stress and CRF

This review updates the conceptual basis for the association of alcohol abuse with an insidious adaptation that facilitates negative affect during withdrawal from chronic intermittent alcohol (CIA) exposure – a change that later supports sensitization of stress-induced anxiety following alcohol abstinence. The finding that a CRF1-receptor antagonist (CRF1RA) minimized CIA withdrawal-induced negative affect supported an association of alcohol withdrawal with a stress mechanism. The finding that repeated stresses or multiple CRF injections into selected brain sites prior to a single 5-day chronic alcohol (CA) exposure induced anxiety during withdrawal provided critical support for a linkage of CIA withdrawal with stress. The determination that CRF1RA injection into positive CRF-sensitive brain sites prevented CIA withdrawal-induced anxiety provided support that neural path integration maintains the persistent CIA adaptation. Based upon reports that stress increases neuroimmune function, an effort was undertaken to test whether cytokines would support the adaptation induced by stress/CA exposure. Twenty-four hours after withdrawal from CIA, cytokine mRNAs were found to be increased in cortex as well as other sites in brain. Further, repeated cytokine injections into previously identified brain sites substituted for stress and CRF induction of anxiety during CA withdrawal. Discovery that a CRF1RA prevented the brain cytokine mRNA increase induced by CA withdrawal provided critical evidence for CRF involvement in this neuroimmune induction after CA withdrawal. However, the CRF1RA did not block the stress increase in cytokine mRNA increases in controls. The latter data supported the hypothesis that distinct mechanisms linked to stress and CA withdrawal can support common neuroimmune functions within a brain site. As evidence evolves concerning neural involvement in brain neuroimmune function, a better understanding of the progressive adaptation associated with CIA exposure will advance new knowledge that could possibly lead to strategies to combat alcohol abuse

Age related differences in anxiety-like behavior and amygdalar CCL2 responsiveness to stress following alcohol withdrawal

Behavioral and neuroimmune vulnerability to withdrawal from chronic alcohol varies with age. The relation of anxiety-like behavior to amygdalar CCL2 responses following stress after withdrawal from chronic intermittent alcohol (CIA) was investigated in adolescent and adult rats

Chronic alcohol neuroadaptation and stress contribute to susceptibility for alcohol craving and relapse

Alcoholism is a chronic relapsing disorder. Major characteristics observed in alcoholics during an initial period of alcohol abstinence are altered physiological functions and a negative emotional state. Evidence suggests that a persistent, cumulative adaptation involving a kindling/allostasis-like process occurs during the course of repeated chronic alcohol exposures that is critical for the negative symptoms observed during alcohol withdrawal. Basic studies have provided evidence for specific neurotransmitters within identified brain sites being responsible for the negative emotion induced by the persistent cumulative adaptation following intermittent-alcohol exposures. After an extended period of abstinence, the cumulative alcohol adaptation increases susceptibility to stress- and alcohol cue-induced negative symptoms and alcohol seeking, both of which can facilitate excessive ingestion of alcohol. In the alcoholic, stressful imagery and alcohol cues alter physiological responses, enhance negative emotion, and induce craving. Brain fMRI imaging following stress and alcohol cues has documented neural changes in specific brain regions of alcoholics not observed in social drinkers. Such altered activity in brain of abstinent alcoholics to stress and alcohol cues is consistent with a continuing ethanol adaptation being responsible. Therapies in alcoholics found to block responses to stress and alcohol cues would presumably be potential treatments by which susceptibility for continued alcohol abuse can be reduced. By continuing to define the neurobiological basis of the sustained alcohol adaptation critical for the increased susceptibility of alcoholics to stress and alcohol cues that facilitate craving, a new era is expected to evolve in which the high rate of relapse in alcoholism is minimized. 25