Roberto DeLucia

The prooxidant effect of 5-aminolevulinic acid in the brain tissue of rats: Implications in neuropsychiatric manifestations in porphyrias

5-Aminolevulinic acid (ALA), a heme precursor accumulated during the clinical expression of acute intermittent porphyria, lead poisoning, and tyrosinosis, has been hypothesized to act as an endogenous source of oxyradicals. We now report oxidative effects on brain tissue of rats submitted to ALA treatment. Upon acute treatment (40 mg/kg body weight) increased total nonheme iron in the cortex (20%) was observed. After prolonged ALA administration (40 mg/kg body weight on alternate days during 2 weeks), the following indicators of oxidative stress were found to be significantly increased: CuZnSOD activity (67%) in total brain homogenate, total iron (68%) and ferritin (71%) in the cortex, ferritin in striatum (44%), protein carbonyls in homogenate of cerebral cortex (threefold) and 45Ca2+ uptake by cortical synaptosomes (45%). In addition, synaptic membranes prepared from whole brain assayed with the radioligand 3H-muscimol, revealed increased Kd values (twofold) of the high-affinity GABAergic receptor binding and formation of protein carbonyl groups, thiobarbituric acid reactive products, and conjugated dienes. In vitro, ALA produced similar effects upon the high affinity 3H-muscimol binding. No apparent alteration of either dopaminergic or serotonergic [3H]-ligand binding was observed. These results argue in favor of ALA-triggered oxidative stress in brain accompanied by iron metabolism alterations and GABAergic receptor damage, which may be implicated in the neuropsychiatric manifestations of the aforementioned porphyrias.

Differential behavioral and neuroendocrine effects of repeated nicotine in adolescent and adult rats

Despite the high prevalence of tobacco abuse among adolescents, the neurobiology of nicotine addiction has been studied mainly in adult animals. Repeated administration of this drug to adult rats induces behavioral sensitization. Nicotine activates the HPA axis in adult rats as measured by drug-induced increases in ACTH and corticosterone. Both behavioral sensitization and corticosterone are implicated in drug addiction. We examined the expression of behavioral sensitization induced by nicotine as well as the changes in corticosterone levels after repeated injections of nicotine in adolescent and adult animals. Adolescent and adult rats received subcutaneous (s.c.) injections of saline or 0.4 mg/kg of nicotine once daily for 7 days. Three days after the last injection animals were challenged with saline or nicotine (0.4 mg/kg; s.c.). Nicotine-induced locomotion was recorded in an activity cage. Trunk blood samples were collected in a subset of adolescent and adult rats and plasma corticosterone levels were determined by radioimmunoassay. Adult, but not adolescent, rats expressed behavioral sensitization. Pretreatment with nicotine abolished corticosterone-activating effect of this drug only in adult animals, indicating the development of tolerance at this age. Our results provide evidence that adolescent rats exposed to repeated nicotine display behavioral and neuroendocrine adaptations distinct from that observed in adult animals.

Exposure to chronic stress increases the locomotor response to cocaine and the basal levels of corticosterone in adolescent rats

Repeated exposure to stress results in augmentation in the locomotor response to psychostimulant drugs. We investigated the locomotor response to a novel environment or cocaine [10 ? mg/kg, intraperitoneally (i.p.)] and basal corticosterone levels in male adolescent rats exposed to chronic restraint or variable stress. Animals in the chronic restraint group were restrained for 1 hour daily. The chronic variable stress protocol consisted of exposure to different stressors twice a day in random order. Chronic restraint and variable stress regimens began simultaneously on postnatal day (P) 25 and were applied for 10 days. During this period the control group was left undisturbed except for cleaning the cages. Three days after the last exposure to stress, cocaine‐ and novelty‐induced locomotion were recorded in an activity cage. Plasma corticosterone levels were determined in a subset of stress and control animals. Exposure to both chronic restraint and variable stress increased cocaine‐induced locomotion and basal corticosterone plasma levels, while no change was observed in the response to a novel environment. Moreover, rats exposed to variable stress displayed the greatest locomotor response following a challenge dose with cocaine when compared to control and chronic restraint stress groups. This observation indicates that the stress regimen is relevant to the degree of stress‐induced sensitization to cocaine.

Repeated predictable or unpredictable stress: effects on cocaine-induced locomotion and cyclic AMP-dependent protein kinase activity

Stressful experiences appear to have a strong influence on susceptibility to drug taking behavior. Cross-sensitization between stress and drug-induced locomotor response has been found. Locomotor response to novelty or cocaine (10 mg/kg, i.p.), cyclic AMP-dependent protein kinase (PKA) activity in the nucleus accumbens and basal corticosterone levels were evaluated in male adult rats exposed to acute and chronic predictable or unpredictable stress. Rats exposed to a 14-day predictable stress showed increased locomotor response to novelty and to cocaine, whereas rats exposed to chronic unpredictable stress demonstrated increased cyclic AMP-dependent PKA activity in the nucleus accumbens. Both predictable and unpredictable stress increased basal corticosterone plasma levels. These experiments demonstrated that stress-induced early cocaine sensitization depends on the stress regime and is apparently dissociated from stress-induced changes in cyclic AMP-dependent PKA activity and corticosterone levels.

Effects of chronic stress on nicotine-induced locomotor activity and corticosterone release in adult and adolescent rats

We examined nicotine‐induced locomotion and increase in corticosterone plasma levels in adolescent and adult animals exposed to chronic restraint stress. Adolescent [postnatal day (P) 28–37] and adult (P60–67) rats were restrained for 2 hours once daily for 7 days. Three days after the last exposure to stress, the animals were challenged with saline or nicotine (0.4 mg/kg subcutaneously). Nicotine‐induced locomotion was recorded in an activity cage. Trunk blood samples were collected in a subset of adolescent and adult rats and plasma corticosterone levels were determined by radioimmunoassay. Exposure to stress did not affect the nicotine‐induced locomotor‐ or corticosterone‐activating effects in both ages.

Amphetamine- and nicotine-induced cross-sensitization in adolescent rats persists until adulthood

Nicotine and psychostimulants are often abused in combination and drug abuse often begins during adolescence and can have long‐term consequences. Behavioral sensitization has been suggested as an animal model of neuroplasticity implicated in the development of drug addiction. We evaluated whether the pretreatment with nicotine (0.4 mg/kg; s.c.) or amphetamine (5.0 mg/kg; i.p.) in adolescent rats [from postnatal day (P) 28 to P34] could induce cross‐sensitization to nicotine and amphetamine when animals were challenged during both adolescence (P37) and adulthood (P70), in separate groups of animals. Adolescent animals pretreated with amphetamine displayed behavioral sensitization to nicotine, which persisted until adulthood. Moreover, adolescent animals pretreated with nicotine showed sensitized locomotor response to amphetamine in the adulthood. These data suggest that adolescents who abuse nicotine may be particularly susceptible to the effects of amphetamine and vice versa. Moreover, this increased vulnerability may persist through their development until adulthood.

Comparative biochemical and behavioural effects of fencamfamine and dl-amphetamine in rats.

Fencamfamine increased locomotion, rearing and sniffing behaviours at 10 mg/kg intraperitoneal doses in rats. Amphetamine increased rearing, sniffing and locomotion behaviours at respectively higher, same and lesser magnitudes than did fencamfamine at equimolar (5 mg/kg) intraperitoneal doses in rats. Forty-five minutes after fencamfamine (10 mg/kg), the levels of homovanillic acid in the tuberculum olfactorium, nucleus accumbens and striatum, and those of dihydroxyphenylacétic acid in accumbens were increased. Dihydroxyphenylacétic levels in tuberculum olfactorium and striatum were not changed. Forty-five minutes after amphetamine (5 mg/kg) the levels of homovanillic acid in tuberculum olfactorium, accumbens and striatum, and those of dihydroxyphenylacétic in accumbens were not changed; dihydroxyphenilacétic levels in tuberculum olfactorium and striatum were decreased. Fencamfamine-induced behavioural changes can be better correlated with neurochemical changes than those elicited by amphetamine.

Reinforcing properties of fencamfamine: involvement of dopamine and opioid receptors.

Fencamfamine (FCF) is a psychostimulant classified as an indirect dopamine agonist. The conditioning place preference (CPP) paradigm was used to investigate the reinforcing properties of FCF. After initial preferences had been determined, animals were conditioned with FCF (1.75, 3.5, or 7.0 mg/kg; IP). Only at the dose of 3.5 mg/kg FCF produced a significant place preference. Pretreatment with SCH23390 (0.05 mg/kg; SC) or naloxone (1.0 mg/kg; SC) 10 min before FCF (3.5 mg/kg, IP) blocked both FCF-induced hyperactivity and CPP. Pretreatment with metoclopramide (10.0 mg/kg; IP) or pimozide (1.0 mg/kg, IP), respectively, 30 min or 4 h before FCF (3.5 mg/kg; IP), which blocked the FCF-induced locomotor activity, failed to influence place conditioning produced by FCF. In conclusion, the present study suggests that dopamine D1 and opioid receptors are related to FCF reinforcing effect, while dopamine D2 subtype receptor was ineffective in modifying FCF-induced CPP.

On the mechanism of central stimulation action of fencamfamine

The stereotypy induced by fencamfamine (10 mg/kg i.p.) was compared in different groups of rats which had been pretreated with catecholaminergic drugs. Pretreatment with alpha-methyl-p-tyrosine (alpha-MpT) did not abolish the stereotypy, however the combination of alpha-MpT plus reserpine decreased, while reserpine alone increased this response. Pretreatment with haloperidol or metoclopramide reduced the intensity of stereotyped behaviour induced by fencamfamine, while phenoxybenzamine increased this behaviour. Fencamfamine showed low affinity for binding sites of [3H]haloperidol and [3H]dihydroergocriptine. These results support the view that fencamfamine is an indirectly acting drug of the non-amphetamine class, which releases both norepinephrine (NE) and dopamine (DA) from presynaptic terminals leading to stereotyped behaviour.

Involvement of dopamine receptors in diethylpropion-induced conditioning place preference

Diethylpropion (DEP) is an amphetamine-like agent used as an anorectic drug. Abuse of DEP has been reported and some restrictions of its use have been recently imposed. The conditioning place preference (CPP) paradigm was used to evaluate the reinforcing properties of DEP in adult male Wistar rats. After initial preferences were determined, animals weighing 250-300 g (N = 7 per group) were conditioned with DEP (10, 15 or 20 mg/kg). Only the dose of 15 mg/kg produced a significant place preference (358 +/- 39 vs 565 +/- 48 s). Pretreatment with the D1 antagonist SCH 23,390 (0.05 mg/kg, s.c.) 10 min before DEP (15 mg/kg, i.p.) blocked DEP-induced CPP (418 +/- 37 vs 389 +/- 31 s) while haloperidol (0.5 mg/kg, i.p.), a D2 antagonist, 15 min before DEP was ineffective in modifying place conditioning produced by DEP (385 +/- 36 vs 536 +/- 41 s). These results suggest that dopamine D1 receptors mediate the reinforcing effect of DEP.