Iodine labelling of sea anemone toxin II,and binding to normal and denervated diaphragm

Summary Newborn rats were treated with 5,7-dihydroxytryptamine (5,7-HT; 2×100 mg/kg s.c., 24 h interval) after pretreatment with desipramine (20 mg/kg s.c.) for depletion of brain 5-hydroxytryptamine (5-HT) or with 6-hydroxydopamine (6-OHDA; 3×100 mg/kg s.c., 24 h interval) for selective reduction of brain noradrenaline (NA). The 5,7-HT treatment resulted in a 53% reduction in endogenous 5-HT in the cerebral cortex and a 60% increase in the ponsmedulla when determined in adult rats. The 5-HT content in the midbrain was not affected. Endogenous NA in the 6-OHDA treated animals was selectively reduced by 100% in the cerebral cortex, 35% in the midbrain and increased by 117% in the pons-medulla. No difference was found between the voluntary ethanol selection of these groups and that of the controls when measured at the age of 3 months. In a tilting-plane test, ethanol (2 g/kg i.p.) impaired the performance of the 6-OHDA treated rats significantly more than that of the controls. Moreover ethanol (4 g/kg i.p.) produced significantly longer narcosis in these rats. In contrast, the 5,7-HT treated rats were not affected significantly more than the controls in these tests. These results suggest that catecholamine neuronal systems interact with the expression of alcohol intoxication.     

Decreased intoxicating effect of ethanol in rats after 6-hydroxydopamine-induced degeneration of ascending dopamine pathways

Selective lesion of ascending dopamine pathways was made by injecting the neurotoxin 6-OHDA (8 μg/4 μl) bilaterally close to the nigro-striatal dopamine pathway of 18 male Long Evans rats. Similar injections of the vehicle were given to 10 control rats. Two months after the operation intoxication was measured in a tilting-plane test after an injection of ethanol (2 g/kg, IP). Ethanol impaired the performance of the 6-OHDA-treated rats significantly less than that of the controls. This finding suggests a role for the central dopamine neurons in the intoxicating effect of ethanol.     

Antidepressants attenuate both the enhanced ethanol intake and ethanol-induced anxiolytic effects in diazepam withdrawn rats.

We have recently shown that the abrupt discontinuation of chronic diazepam (DZM) administration facilitated ethanol consumption and enhanced the anxiolytic properties of ethanol. Tricyclic antidepressants such as desipramine and the selective serotonin reuptake inhibitor fluoxetine have been shown to reduce alcohol intake in rodent models of alcoholism and in alcoholics who are depressed. In the present study, we tested whether desipramine (1.25; 2.5 and 5 mg/kg, i.p.) and fluoxetine (5 mg/kg, i.p.) treatment affect both ethanol intake in a free-choice test and the anxiolytic effect induced by ethanol in DZM withdrawn rats. Adult male Wistar rats were submitted to a chronic DZM treatment (2 mg/kg per day) or vehicle (VEH) for 21 days. Twenty-four hours after the last DZM injection, rats were subjected to a free-choice paradigm between water and increasing ethanol concentrations with or without concurrent desipramine or fluoxetine administration (ethanol concentration (v/v) was increased every 4 days as follows: 2, 4, 6, 8 and 10% for the final 8 days). Chronic treatment with desipramine (24 days, twice a day, 2.5 and 5 mg/kg, i.p.) and fluoxetine (24 days, once a day; 5 mg/kg, i.p.) significantly reduced the amount of ethanol intake in DZM withdrawn rats. Furthermore, subchronic treatments with desipramine (4 days, twice a day, 2.5 and 5 mg/kg) and fluoxetine (4 days, once a day, 5 mg/kg, i.p.) blocked the anxiolytic-like behavior in the elevated plus maze induced by ethanol (1 g/kg; i.p.) in DZM withdrawn rats at day 5 of withdrawal. The present findings suggest that desipramine and fluoxetine could be effective pharmacological tools to prevent the subsequent development of ethanol dependence in rats previously exposed to DZM withdrawal.     

On the role of ascending dopamine systems in the control of voluntary ethanol intake and ethanol intoxication

Selective lesions of the ascending dopamine pathways were made by bilateral injection of the neurotoxin 6-OHDA (8 μg/4 μl). Catecholamine fluorescence histochemistry revealed a marked degeneration of the ascending mesostriatal and mesolimbic dopamine systems, while the hypothalamic dopamine and noradrenaline nerve terminals were unaffected. After recovery of feeding and drinking behaviors the voluntary ethanol intake was not different from that of the controls. The time of ethanol-induced narcosis and the extent of ethanol-induced hypothermia were not affected. In contrast, in a tilting-plane test conducted two months after the operation, ethanol impaired the performance of the 6-OHDA-treated rats significantly less than that of the controls. This finding suggests a role for the ascending dopamine neurons to the forebrain in the intoxicating effect of ethanol.     

Pharmacological evidence for dopaminergic pallido-striatal interaction

In rats the contents in dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) of neostriatum (nucleus caudatoputamen, NCP) and paleostriatum (globus pallidus, GP) were measured after transection of the capsula interna (CI) or after injection of 6-hydroxydopamine (6-OHDA; 20 μg/2 μl) into the GP of one side. The circling behaviour of the lesioned animals following apomorphine was also studied. 6-OHDA as well as transection decreased the contents in DA and DOPAC in NCP and GP significantly. Following both treatments DA levels in neostriatum were lowest. Nigro-neostriatal pathway lesioned animals (transected or injected with 6-OHDA 16 μg/2 μl into substantia nigra, SN) rotated towards the side of lesion after apomorphine (5 mg/kg IP), whereas GP lesioned animals rotated towards the intact side. In animals with both GP and SN lesions at one side turnings of similar intensity towards both sides were seen. In intact rats DA injections (200 μg/2 μl) into SN or NCP exhibited contralateral, injections into GP exhibited ipsilateral rotations. The results strengthen the hypothesis on the participation of GP in the regulation of neostriatal content of DA and shows the interaction of the hypothetical dopaminergic pallido-striatal pathway with nigro-neostriatal pathways.     

Stimulation of food intake in rats by the alpha 2-adrenoceptor agonists xylazine and detomidine

Effects of the alpha 2-adrenoceptor agonists xylazine and detomidine on food intake in freely feeding male rats were evaluated. Intraperitoneal (i.p.) injection of xylazine (0.25-3 mg/kg) and detomidine (25 and 50 micrograms/kg) significantly increased the 2 and 24 h food intake from control values. Treatment of rats with the alpha 2-adrenoceptor antagonist yohimbine (1 mg/kg, i.p.) 15 min before xylazine (0.5 mg/kg, i.p.) or detomidine (50 micrograms/kg, i.p.) significantly inhibited the increase in food intake. Yohimbine treatments alone at 0.5, 1 and 2 mg/kg, i.p. did not significantly change the 2 and 24 h food intake from control values. The results suggest that the alpha 2-agonists xylazine and detomidine enhance food intake in rats.     

"Priming" to dopamine agonist-induced contralateral turning as a model of non-associative sensitization to the expression of the post-synaptic dopamine message

In adult rats bearing unilateral 6-hydroxydopamine (6-OHDA) lesions of the ascending dopaminergic neurons, a single administration of a dopamine (DA) receptor agonist results in strong sensitization ("priming") of contralateral turning in response to D2 and particularly D1 receptor agonists. In order to investigate the role of distinct environmental cues associated with the effect of the agonist during exposure to the primer, rats bearing 15-day-old unilateral 6-OHDA lesions were primed in their home cage with L-dopa or with saline. L-Dopa but not saline induced medium to low but steady contralateral turning. Three days later, challenge with the D1 agonist SKF 38393 in the home cage also resulted in contralateral turning in the rats previously primed with L-dopa, but not in those primed with saline. In a second experiment rats lesioned with 6-OHDA were primed in two different contexts (hemispheres versus cylinders) with a single administration of the D2/D3 agonist quinpirole (LY 171555: 0.2mg/kg s.c.) or saline. Three days later the rats were placed in hemispheres and tested for contraversive turning in response to saline or to SKF 38393. SKF 38393 elicited high rate contraversive turning independently of the environment where priming with quinpirole took place; on the other hand no conditioned contraversive turning was observed after saline. In a third experiment, the possibility of priming SKF 38393-induced turning by stimulation of nigral or striatal DA receptors was investigated. Rats lesioned unilaterally with 6-OHDA were locally infused on the lesioned side in the substantia nigra with SKF 38393 or in the striatum with quinpirole. Both these treatments elicited contralateral turning, the intranigral injection of SKF 38393 eliciting a stronger and longer lasting contraversive turning than intrastriatal quinpirole. Challenge with SKF 38393 (3mg/kg s.c.) 3 days later induced contralateral turning only in rats previously primed with intrastriatal quinpirole. The results of these studies are consistent with the idea that "priming" is an example of non-associative sensitization induced by stimulation of denervated striatal DA receptors and expressed as an increased efficiency of post-synaptic dopaminergic transduction in the striatum.     

Administration of thyrotropin releasing hormone (TRH) to rats releases dopamine in n. accumbens but not n. caudatus.

Bilateral injection of thyrotropin releasing hormone (TRH; 10 μg) into the n. accumbens of rats produced a short-lasting increase in co-ordinated locomotor activity and behavioural changes similar to those produced by injection of dopamine at this site. These effects were potentiated and prolonged by pretreatment with tranylcypromine (5 mg/kg i.p.). Injection of haloperidol (2.5 μg bilaterally) into the n. accumbens blocked the behavioural changes produced by intra-accumbens injection of TRH (10 μg bilaterally. 30min after tranylcypromine 5 mg/kg i.p.). Destruction of the presynaptic dopamine terminals with 6-hydroxydopamine (8 μg bilaterally) abolished the effects of intra-accumbens injection of TRH (10 μg bilaterally) in either untreated or tranylcypromine pretreated rats. This inhibition was not due to non-specific damage to post-synaptic dopamine receptors since these rats showed a normal locomotor response to intra-accumbens injection of dopamine (5 μg bilaterally. 30min after tranylcypromine 5 mg/kg). These results suggest that TRH is acting by release of dopamine.Peripheral injection of TRH (20 mg/kg) produced behavioural changes similar to those observed after central administration of this drug. Although these effects were not enhanced by pretreatment with tranylcypromine (5 mg/kg. 30min before TRH), they were blocked by peripheral injection of haloperidol (1 mg/kg). Injection of thyroid stimulating hormone (TSH: 20 mg/kg i.p.) produced no behavioural changes suggesting that peripherally injected TRH is not acting by release of TSH.Injection of TRH (20 mg/kg i.p.) to unilateral nigro-striatal lesioned rats failed to induce circling. Furthermore pretreatment with TRH (2 mg/kg i.p.) did not enhance the turning produced by methamphetamine (0.5 mg/kg) 3 hr later in tranylcypromine-treated animals.This evidence suggests that in contrast to its effects in the n. accumbens TRH is unable to release dopamine in the n. caudatus.     

Resistance to ethanol sensitization is associated with increased NMDA receptor binding in specific brain areas

The purpose of the present study was to determine the acute effects of the anticraving compound acamprosate (calcium acetylhomotaurinate) and the closely related compound homotaurine on ethanol intake and ethanol-stimulated dopamine release in the nucleus accumbens. Male rats were treated with acamprosate (200 or 400 mg/kg intraperitoneally, i.p.) or homotaurine (10, 50, or 100 mg/kg i.p.) 15 min prior to access to 10% ethanol and water for 1 h in a two-bottle choice restricted access paradigm. A separate group of rats was implanted with microdialysis probes in the nucleus accumbens and given an acute injection of ethanol (1.5 g/kg i.p.) that was preceded by saline, acamprosate, or homotaurine. Acamprosate and homotaurine dose-dependently reduced ethanol intake and preference. These compounds also delayed or suppressed ethanol-stimulated increases in nucleus accumbens dopamine release, suggesting that acamprosate and homotaurine may reduce ethanol intake by interfering with the ability of ethanol to activate the mesolimbic dopamine reward system.     

Neuroprotective effects of caffeine in the model of 6-hydroxydopamine lesion in rats

The work shows the effects of caffeine after the intrastriatal injection of 6-OHDA in rats, considered as a model of Parkinson disease (PD). Two weeks after the 6-OHDA lesion, rats exhibit a characteristic rotation behavior as a response to the apomorphine challenge. Our results showed significant increases in the number of apomorphine-induced rotations in 6-OHDA-lesioned rats, as compared to sham-operated animals. A partial recovery was observed in 6-OHDA-lesioned rats, after caffeine (10 and 20 mg/kg, i.p., daily for 14 days) treatment. The stereotaxic injection of 6-OHDA produced loss of striatal neurons, as indicated by the decrease in monoamines levels, in the ipsilateral side (75-85%) when compared to the contralateral side. Significant decreases in noradrenaline levels were seen in the ipsilateral side of 6-OHDA group (62%), and this effect was not significantly reversed in caffeine-treated groups. While significant decreases in dopamine levels were seen in the ipsilateral side of 6-OHDA group (78%), in the caffeine-treated group (10 and 20 mg/kg, i.p.) the decreases were only 53 and 18%, indicating significant recoveries. In conclusion, our data demonstrated beneficial effects of caffeine in this model of PD, suggesting the potential use of A2A antagonists as a novel treatment for this neurodegenerative disease.     

Genetic differences in ethanol drinking of the rat following injection of 6-OHDA, 5,6-DHT or 5,7-DHT into the cerebral ventricles

The preference characteristics for ethanol of four different strains of rats were determined in a two-choice situation by offering water and ethanol in a concentration which was increased from 3 to 30% over a 12-day test sequence. Using stereotaxic procedures, 50 μg 5,6-dihydroxytryptamine (5,6-DHT), 200 μg 6-hydroxydopamine (6-OHDA) or 100 μg 5,7-dihydroxytryptamine (5,7-DHT) were then injected acutely into the lateral cerebral ventricle in a 20 μl volume. Rats of the Sprague-Dawley strain increased their ehthanol preference following the lesioning of the serotonergic system by 5,6-DHT, whereas similar destruction of catecholaminergic neurons by 6-OHDA markedly suppressed ethanol intake; Long-Evans rats displayed a similar trend in ethanol drinking patterns. However, animals of the Holtzman strain manifested the increased drinking after 5,6-DHT, but showed no suppression of drinking following 6-OHDA. The preference of rats of the Wistar strain was unaffected by 5,6-DHT but attenuated by 6-OHDA. 5,7-DHT had little or no effect on ethanol comsumption in any of these strains. These findings thus suggest that genetic factor are an important determinant in an animal's response to a drug that affects 5-HT or NE systems in the brain, particularly when ethanol selection is investigated.     

Extinction and recovery of cocaine self-administration following 6-hydroxydopamine lesions of the nucleus accumbens

The effect of 6-OHDA injections into the nucleus accumbens was examined on cocaine self-administration behaviour. Rats were given access to cocaine (0.75 mg/kg/inj.) for three hours/day on a continuous reinforcement schedule. After daily intake of cocaine had stabilized, rats were injected with 6-OHDA (8 μg/2 μl). When tested the day following the 6-OHDA injection most rats failed to self-administer cocaine, however this disruption did not resemble extinction. After several days self-administration recovered in many animals to near preoperative levels, and the rate of this recovery correlated (r = +0.75) with the levels of dopamine remaining in the nucleus accumbens. The animals with the greatest depletion of dopamine did not recover cocaine intake. In a separate experiment, animals were pretreated with desmethylimipramine and/or pargyline to achieve a more extensive and selective lesion. When tested five days after the lesion all animals in these 6-OHDA groups showed a significant decline in cocaine intake compared to vehicle injected control animals. Several 6-OHDA treated animals displayed a pattern of behaviour resembling extinction, where a high rate of lever pressing was followed by cessation of responding. Some animals were aalso tested for apomorphine self-administration and this was found not to be affected by the 6-OHDA treatment. These data support the hypothesis that non-striatal dopamine may subserve cocaine reward.     

The effect of di-isopropyl 1,3 dithiol-2-ylidenemalonate (malotilate) on the hepatic changes induced by ethanol administration in the rat

The sulphur-containing drug, di-isopropyl-1,3-dithiol-2-ylidenemalonate (Malotilate) protects against the increase in hepatic triglyceride concentration after acute ethanol administration (either 6 g/kg p.o. or 2 g/kg i.p.) in rats. The compound had no influence on the increased hepatic NADH:NAD ratio (measured as the lactate:pyruvate and 3-hydroxybutyrate:acetoacetate ratios) after acute ethanol dosing (2 g/kg i.p.), but was found to lower hepatic acetaldehyde concentrations and prevent some of the disturbances in lipid metabolism observed in liver slices from ethanol-treated animals (e.g. decreased oxidation of [1-14C]palmitate to 14CO2) after this ethanol dose. The drug did not inhibit ethanol metabolism in this acute experiment. Administration of Malotilate to Wistar rats (100 mg/kg/day orally) during chronic feeding of ethanol as 36% of the total calorie intake in a liquid diet, resulted in a lower intake of the alcohol-containing diet by ethanol-fed animals and reduced body weight gain in rats which received the drug, without blood ethanol levels or the ethanol intake (expressed in g/kg body weight/day) being affected. In ethanol-fed animals, Malotilate prevented the production of fatty liver and the adaptive increase in the ethanol elimination rate (EER) normally seen in ethanol-fed animals, although the drug actually caused a slight increase in EER in glucose pair-fed controls. Malotilate did not significantly decrease the degree of induction of microsomal cytochrome P-450 by ethanol, but the increase in aniline hydroxylation was much less marked in animals receiving ethanol and Malotilate, suggesting that the activity of the inducible microsomal ethanol oxidising system (MEOS) may be reduced by the compound. Determination of hepatic acetaldehyde concentrations during ethanol feeding, and during an acute ethanol challenge test following long-term ethanol treatment showed that the compound significantly lowered the level of this ethanol metabolite in the liver under both circumstances. This reduction of hepatic acetaldehyde concentrations, probably resulting in part from the reduced EER as well as increased low-Km aldehyde dehydrogenase activities and glutathione contents seen in the livers of Malotilate-treated rats, are possible mechanisms by which the drug protects against triglyceride accumulation after ethanol administration.     

Cyamemazine decreases ethanol intake in rats and convulsions during ethanol withdrawal syndrome in mice

The effect of cyamemazine a dopamine D₂ receptor antagonist on voluntary ethanol consumption in rats and on ethanol withdrawal in mice was examined. Male Sprague-Dawley rats were tested in a free choice (water and 10% ethanol) experiment and consumed 5 g/kg ethanol daily. Rats were treated daily IP with cyamemazine ( 0.5, 1, or 2 mg/kg) or acamprosate (100 mg/kg) during 2 weeks. Both acamprosate and 1 mg/kg cyamemazine significantly decreased ethanol intake by 45% without affecting either fluid or food intake. The lowest dose of cyamemazine had no effect on alcohol intake but increased food intake. The highest dose had no effect on any variables. During the post-treatment period, only 1 mg/kg cyamemazine decreased both ethanol and fluid intakes. Mice were made dependent on alcohol using a chocolate fluid diet containing increasing concentrations of alcohol and withdrawn after 9 days. Mice were treated with cyamemazine (1 or 0.5 mg/kg, respectively) or with the same doses of lorazepam acutely on the day of withdrawal or chronically (during alcohol treatment). Both chronic and acute cyamemazine and lorazepam treatments decreased convulsions during ethanol withdrawal. Both acute treatments decreased locomotor activity in control and alcohol dependent mice. Chronic treatment had no effect on locomotor activity. We suggest that cyamemazine could reduce alcohol consumption by antagonizing the activation of the dopaminergic pathways during the induction of alcohol dependence. The action of cyamemazine on 5-HT₃ receptors could also explain its effect on alcohol convulsions during withdrawal convulsions. Received: 19 October 1997/Final version: 6 April 1998     

Possible involvement of nigrostriatal dopamine system in the inhibition of thyrotropin secretion in the rat

The dopaminergic inhibition or cold-stimulated thyrotropin (TSH) secretion was studied in male rats. Serum TSH levels were decreased by apomorphine (1 mg/kg i.p.) but not by dopamine (DA. 0.2–5 mg/kg s.c.). This effect of apomorphine was abolished b haloperidol (1 mg/kg i.p.), meioclopramide and sulpiride (10 mg/kg i.p.) but not by domperidone (0.1–5 mg/kg i.p.) does not cross the blood-brain barrier while the other DA receptor antagonists do so. Higl doses of domperidone itself inhibited the cold-induced TSH secretion whereas the other DA antagonists did not. DA (1–10 μg/rat) into the medial basal hypothalamus (MBH) had no effect but 10–50 μg/rat into the 3rd ventricle inhibited the cold-stimulated TSH secretion. 6-Hydroxydopamine infusion after dcsipramine pretreatment (25 mg/kg i.p.) did not affect TSH secretion when given into the MBH (2 μg/rat), the 3rd ventricle (10 μg/rat) or unilaterally into the substantia nigra (SN. 6 μg/nucleus), but bilateral nigral infusions abolished the TSH cold The inhibitory effect of apomorphine (0.1 and 0.5 mg/kg i.p.) was amplified only in the rats whose SN was unilaterally destroyed. These results show that tuberoinfundibular DA neurons do not affect TSH secretion. Instead, the inhibition is mediated through the hypothalamic projections of the nigrostriatal DA system.     

14-methoxymetopon,a highly potent μ opioid agonist,biphasically affects ethanol intake in Sardinian alcohol-preferring rats

Rationale Increased opioidergic activity is thought to increase the propensity to consume ethanol. However, the dose monotonicity and receptor subtype for this effect remain uncertain. 14-methoxymetopon is a centrally acting, selective μ opioid receptor agonist with greater systemic antinociceptive potency than morphine and a putatively improved therapeutic index. Objective To determine whether 14-methoxymetopon influenced voluntary ethanol intake in Sardinian alcohol-preferring (sP) rats. Methods Male sP rats with continuous 2-bottle choice access to ethanol (10% v/v) or water were subjects. The effects of systemic 14-methoxymetopon administration (2, 5, 12.25, 30 μg/kg, s.c.) on 4-h ethanol intake were determined. The ability of naltrexone (50 μg/kg, s.c.), an opioid antagonist, to block actions of 14-methoxymetopon (12.25, 30 μg/kg, s.c.) was examined as were the effects of 14-methoxymetopon (12.25 μg/kg, s.c.) on self-administered blood alcohol levels (BALs) and clearance of a passive ethanol bolus (1 g/kg). Finally, the effects of central 14-methoxymetopon administration (0.0003–100 ng, i.c.v.) on 4-h ethanol intake were evaluated. Results Systemic 14-methoxymetopon very potently and dose-dependently suppressed ethanol and food intake for 30 min, followed by a greater, longer-lasting, and behaviorally specific increase in ethanol intake. The increased ethanol intake led to threefold higher BALs, was naltrexone-reversible, and not due to altered ethanol clearance. Intracerebroventricular 14-methoxymetopon administration rapidly altered ethanol intake per an inverted U-shaped dose-response function, increasing it at a 10 pg dose, while suppressing it at a 10,000-fold higher dose. Conclusions The novel μ analgesic increases ethanol intake, a potential therapeutic liability, and results suggest a non-monotonic influence of brain μ opioid receptor stimulation on ethanol intake. Valentina Sabino and Pietro Cottone contributed equally to this work.     

Depletion of catecholamines in the brain of rats differentially affects stimulation of locomotor activity by caffeine, D-amphetamine, and methylphenidate

The purpose of this study was to assess the role of catecholamines in brain, in the stimulation of locomotor activity, induced by caffeine, as compared to the psychomotor stimulants D-amphetamine and methylphenidate. Adult male rats were pretreated with either (1) 2.5 mg/kg (i.p.) reserpine, 24 hr prior to testing of locomotor activity, (2) 50 mg/kg (i.p.) alpha-methyl-para-tyrosine (AMPT) 6 hr and 2 hr prior to testing of locomotor activity, (3) 200 micrograms/rat (i.c.v.) 6-hydroxydopamine (6-OHDA), or 25 mg/kg (i.p.) desmethylimipramine (DMI) and 200 micrograms/rat 6-OHDA (i.c.v.), 6-8 weeks prior to testing. Each treatment group had a matched control group. Levels of catecholamines in the forebrain were determined in each of the treatment and corresponding control groups. All rats were tested with doses of caffeine, D-amphetamine and methylphenidate (excluding the 6-OHDA-treated animals), administered in random order intraperitoneally 35 min before locomotor activity was measured for 30 min. Pretreatment with either reserpine or AMPT attenuated the stimulation of locomotor activity induced by caffeine and D-amphetamine but not that induced by methylphenidate. The dose-response curve for amphetamine was shifted downward and to the right by reserpine but was flattened by AMPT. The dose-response curve for caffeine was displaced downward in a similar manner by both reserpine and AMPT. Treatment with 6-OHDA or DMI + 6-OHDA produced the expected changes in the content of catecholamines in brain, but failed to modify dose-response curves for caffeine or amphetamine.(ABSTRACT TRUNCATED AT 250 WORDS)     

Alcohol responsiveness, hyperreactivity, and motor restlessness in an animal model for attention-deficit hyperactivity disorder

Rationale: Attention-deficit hyperactivity disorder and related pervasive developmental disorders constitute risk factors for adult alcohol abuse and antisocial behaviours, including violent offending. Objectives: The present study assessed alcohol responsiveness and hyperemotionality in neonatally 6-OHDA-treated rats, which provides an animal model for attention-deficit hyperactivity disorder. Method: Male Wistar rats were given intracerebroventricular 6-OHDA (100 μg/5 μl) or vehicle (saline-ascorbic acid) on postnatal day 3. In adulthood, we measured motor activity, defensive behaviours and ethanol responsiveness. Results: 6-OHDA resulted in depletions of brain catecholamine levels. The experimental animals were markedly hyperactive, showed increases in active defensive behaviours (fleeing) and decreases in passive defensive responses (freezing) in response to an sudden auditory signal. In tests for reactivity to the experimenter (i.e. defensiveness to innocuous stimuli), 6-OHDA rats were hyperreactive in comparison to controls. With regard to home cage 6% ethanol and water consumption, there were no differences between experimental and control rats. However, 6-OHDA rats displayed a remarkable resistance to the motor-impairing effect of alcohol (0.5–1.0 g/kg, IP). A similar hyposensitivity to the motor-suppressive effect of diazepam (5.0 mg/kg, IP) was also found. Conclusions: The present results show that adult rats exposed to 6-OHDA as neonates are motorically restless, unusually prone to respond defensively to innocuous stimuli, and considerably less sensitive to the intoxicating effects of ethanol and diazepam. Received: 14 May 1998 / Final version: 19 March 1999     

Influence of age on effects induced by intermittent ethanol treatment on the ethanol drinking pattern and related neurochemical changes in the rat

Male rats were treated with one ethanol (2.0 g/kg i.p.) or saline injections once a week for 50 weeks. During this treatment period the rats had in addition access to ethanol (10% in drinking fluid) as a choice against water for 24 h prior to the injection. During the following evaluation period, animals had a continuous choice between ethanol and water and the concentration of the ethanol solution increased every 3rd week from 5 to 10, 15 and 25%, with 10% as a reference tested between the other concentrations. The animals were killed after an abstinence of 4 weeks, whereupon the concentrations of noradrenaline (NA), dopamine (DA), serotonin (5-HT) and 5-hydroxyindole acetic acid (5-HIAA) were determined in the frontal cortex. In the remaining cerebral cortex, activity of monoamine oxidase, reuptake of NA and stimulated inositol phospholipid (PI) breakdown was also determined. Muscarinic binding sites were determined in the striatum. During treatment, saline injected rats had a constant voluntary 24 h ethanol intake. There was a decrease in the corresponding intake in the animals given the ethanol injections. The diminishing of the intake was more marked in rats starting treatment at an age of 19.4 weeks when compared to rats starting at an age of 5.4 weeks. In the evaluation period the ethanol intake was fairly constant for all groups. However, the regressions between intake of the reference concentration when plotted against the different tested concentrations were most marked in the group where ethanol injections started at an early age. In the total material there were significant F-values when concentrations of NA, 5-HIAA, 5-HT/5-HIAA in the cortex and muscarinic binding sites in the striatum were tested. Age could not be excluded as a contributing factor, but for muscarinic binding sites in the striatum, concentrations of DA and 5-HIAA in the cortex, and potassium stimulated PI breakdown in the cortex significant regressions with voluntary ethanol intake as dependent variable could be established. Since these intakes are stable, a causal relation with dependence may be involved.     

Ontogenic homologous supersensitization of dopamine D1 receptors.

To determine whether prolonged supersensitization of dopamine D-1 receptors could be produced during ontogeny, rats were treated daily, from birth, for 33 consecutive days with the D-1 receptor agonist, SKF 38393 HCl (3.0 mg/kg per day i.p.). These rats were additionally treated at 3 days after birth with the neurotoxin, 6-hydroxydopamine HBr (6-OHDA; 200 micrograms i.c.v., half in each lateral ventricle) or its vehicle. At 6 to 7 weeks from birth a challenge dose of SKF 38393 HCl (3.0 mg/kg i.p.) increased stereotypy scores for a number of behaviors in 6-OHDA-lesioned rats that were treated repeatedly during ontogeny with SKF 38393. These accentuated behaviors included licking, grooming, taffy pulling, jumping, paw treading and locomotion. Although the findings demonstrate an increased sensitivity of D-1 receptors to an agonist, there was no change in the Bmax or Kd for D-1 receptors in the striatum. In rats that were treated during postnatal development with SKF 38393, but not lesioned with 6-OHDA, SKF 38393-induced stereotyped behaviors were not substantially different from control. The neonatally primed rat model may be useful for probing mechanisms of receptor supersensitivity.