The effect of MK-801 on motor activity and c-Fos protein expression in the brain of adolescent Wistar rats

The influence of continuous prenatal exposure to valproic acid on physical, nociceptive, emotional and psychomotor responses during adolescence in mice: Dose-related effects within sexes

Clinical findings show that the use of valproic acid (VPA) during pregnancy increases the risk of birth defects and autism spectrum disorder in offspring. Although there is a consensus that monitoring of potential long-term outcomes of VPA exposure is needed, especially in undiagnosed individuals, preclinical studies addressing this issue are rare. The present study examined the effects of continuous intrauterine exposure to a wide dose range of VPA (50, 100, 200, and 400 mg/kg/day) on the physical and behavioral response in peripubertal mice as a rodent model of adolescence. Body weight and the hot plate test [on postnatal days (PND) 25 and 32], the elevated plus-maze test (on PND35), and the open field test (on PND40) served to examine physical growth, the supraspinal reflex response to a painful thermal stimulus and conditional learning, anxiety-like/risk-assessment behavior, as well as novelty-induced psychomotor activity, respectively. VPA exposure produced the following responses: (i) a negative effect on body weight, except for the dose of 100 mg/kg/day in both sexes; (ii) an increase in the percentage of animals that responded to the thermal stimulus above the defined cut-off time interval and the response latency in both sexes; (iii) dose-specific changes within sexes in behavior provoked by a novel anxiogenic environment, i.e., in females less anxiety-like/risk-assessment behavior in response to the lowest exposure dose, and in males more pronounced anxiety-like/risk-assessment behavior after exposure to the highest dose and 100 mg/kg/day; (iv) dose-specific changes within sexes in novelty-induced psychomotor activity, i.e., in females a decrease in stereotypy-like activity along with an increase in rearing, and in males a decrease in stereotypy-like activity only. These findings show that continuous intrauterine exposure to VPA produces maladaptive functioning in different behavioral domains in adolescence and that the consequences are delicate to assess as they are dose-related within sexes.

Use and abuse of dissociative and psychedelic drugs in adolescence

Adolescence is a period of profound developmental changes, which run the gamut from behavioral and neural to physiological and hormonal. It is also a time at which there is an increased propensity to engage in risk-taking and impulsive behaviors like drug use. This review examines the human and preclinical literature on adolescent drug use and its consequences, with a focus on dissociatives (PCP, ketamine, DXM), classic psychedelics (LSD, psilocybin), and MDMA. It is the case for all the substances reviewed here that very little is known about their effects in adolescent populations. An emerging aspect of the literature is that dissociatives and MDMA produce mixed reinforcing and aversive effects and that the balance between reinforcement and aversion may differ between adolescents and adults, with consequences for drug use and addiction. However, many studies have failed to directly compare adults and adolescents, which precludes definitive conclusions about these consequences. Other important areas that are largely unexplored are sex differences during adolescence and the long-term consequences of adolescent use of these substances. We provide suggestions for future work to address the gaps we identified in the literature. Given the widespread use of these drugs among adolescent users, and the potential for therapeutic use, this work will be crucial to understanding abuse potential and consequences of use in this developmental stage.

MK801-induced locomotor activity in preweanling and adolescent male and female rats: role of the dopamine and serotonin systems

RATIONALE

MK801, like other NMDA receptor open-channel blockers (e.g., ketamine and phencyclidine), increases the locomotor activity of rats and mice. Whether this behavioral effect ultimately relies on monoamine neurotransmission is of dispute.

OBJECTIVE

The purpose of this study was to determine whether these psychopharmacological effects and underlying neural mechanisms vary according to sex and age.

METHODS

Across four experiments, male and female preweanling and adolescent rats were pretreated with vehicle, the monoamine-depleting agent reserpine (1 or 5 mg/kg), the dopamine (DA) synthesis inhibitor ∝-methyl-_DL-p-tyrosine (AMPT), the serotonin (5-HT) synthesis inhibitor 4-chloro-_DL-phenylalanine methyl ester hydrochloride (PCPA), or both AMPT and PCPA. The locomotor activity of preweanling and adolescent rats was then measured after saline or MK801 (0.3 mg/kg) treatment.

RESULTS

As expected, MK801 increased the locomotor activity of all age groups and both sexes, but the stimulatory effects were significantly less pronounced in male adolescent rats. Preweanling rats and adolescent female rats were more sensitive to the effects of DA and 5-HT synthesis inhibitors, as AMPT and PCPA caused only small reductions in the MK801-induced locomotor activity of male adolescent rats. Co-administration of AMPT+PCPA or high-dose reserpine (5 mg/kg) treatment substantially reduced MK801-induced locomotor activity in both age groups and across both sexes.

CONCLUSIONS

These results, when combined with other recent studies, show that NMDA receptor open-channel blockers cause pronounced age-dependent behavioral effects that can vary according to sex. The neural changes underlying these sex and age differences appear to involve monoamine neurotransmission.

Investigation of the synergistic effects of haloperidol combined with Calculus Bovis Sativus in treating MK-801-induced schizophrenia in rats

Clinical studies that focused on treating schizophrenia showed that Calculus Bovis Sativus (CBS), a substitute of Calculus Bovis, when used in combination with haloperidol could significantly lower the dosage of haloperidol compared with treatment with haloperidol alone, whereas efficacy was maintained. The aim of this study was to investigate the synergetic anti-schizophrenia effects in rats using CBS in combination with haloperidol. An open field test was conducted to verify the pharmacodynamic effects of a combination treatment of CBS and haloperidol on MK-801-induced schizophrenic rats. Rat plasma concentrations of intragastric haloperidol and intravenous haloperidol were determined after oral administration of a single dose or 1-week of pretreatment with CBS (50 mg/kg). The pharmacodynamic data showed a significant decrease in locomotor activity and an increase in the percentage of the central distance when haloperidol was concomitantly administered with CBS compared with haloperidol administration alone. The AUC0-∞ and Cmax of haloperidol in the orally coadministered groups were significantly higher compared with the oral treatment with haloperidol alone. In conclusion, oral coadministration of CBS with haloperidol resulted in a synergistic effect in rats. The enhanced oral bioavailability of haloperidol when combined with CBS might be attributed to the interaction between them.

Differences between adolescents and adults in the acute effects of PCP and ketamine and in sensitization following intermittent administration

Adolescence is a phase of development during which many physiological and behavioral changes occur, including increased novelty seeking and risk taking. In humans, this is reflected in experimentation with drugs. Research demonstrates that drug use that begins during adolescence is more likely to lead to addiction than drug use that begins later in life. Despite this, relatively little is known of the effects of drugs in adolescence, and differences in response between adolescents and adults. PCP and ketamine are popular club drugs, both possessing rewarding properties that could lead to escalating use. Drug sensitization (or reverse tolerance), which refers to an increase in an effect of a drug following repeated use, has been linked with the development of drug cravings that is a hallmark of addiction. The current work investigated the acute response and the development of sensitization to PCP and ketamine in adolescent and adult rats. Periadolescent Sprague-Dawley rats (30days or 38days of age), and young adults (60days of age) received PCP (6mg/kg IP) or ketamine (20mg/kg IP) once every three days, for a total of five drug injections. Adolescents and adults showed a stimulant response to the first injection of either drug, however the response was considerably greater in the youngest adolescents and lowest in the adults. With repeated administration, adults showed a robust escalation in activity that was indicative of the development of sensitization. Adolescents showed a flatter trajectory, with similar high levels of activity following an acute treatment and after five drug treatments. The results demonstrate important distinctions between adolescents and adults in the acute and repeated effects of PCP and ketamine.

Puberty marks major changes in the hippocampal and cortical c-Fos activation pattern induced by NMDA receptor antagonists

Non-selective and subunit (GluN2B)-specific N-methyl-d-aspartate receptor (NMDAR) antagonists represent promising alternative antidepressant drugs with fast onset of the therapeutic action. The neuronal activation pattern induced by NMDAR antagonists is well characterized by c-Fos expression analysis only in the adult rodent brain. In contrast, there is little information available regarding their effects during postnatal development. Here we performed a systematic c-Fos brain mapping of the non-selective NMDAR antagonist MK-801 and the GluN2B-specific antagonist Ro 25-6981 from postnatal day 16 (P16) to P40. We found significant regional differences with gender-specificity in the activation pattern compared to the adult. Surprisingly, in the hippocampus, MK-801 triggered at pre-pubertal stages (especially at P24) very strong c-Fos expression, followed by low levels after P30, the approximate time point of puberty onset in mice. The cortical distribution of MK-801-triggered c-Fos expression before puberty differed also substantially from the adult brain, showing high levels only in deep cortical layers at pre-pubertal stages. In comparison, the cortical activation induced by Ro 25-6981 diminished from high pre-pubertal levels and was in comparison with that triggered by MK-801 low in the hippocampus. These results reveal highly dynamic changes in the c-Fos activation pattern induced by NMDAR antagonists during puberty. This article is part of the Special Issue entitled 'Ionotropic glutamate receptors'.

Dizocilpine (MK-801) impairs learning in the active place avoidance task but has no effect on the performance during task/context alternation

The prevention of engram interference, pattern separation, flexibility, cognitive coordination and spatial navigation are usually studied separately at the behavioral level. Impairment in executive functions is often observed in patients suffering from schizophrenia. We have designed a protocol for assessing these functions all together as behavioral separation. This protocol is based on alternated or sequential training in two tasks testing different hippocampal functions (the Morris water maze and active place avoidance), and alternated or sequential training in two similar environments of the active place avoidance task. In Experiment 1, we tested, in adult rats, whether the performance in two different spatial tasks was affected by their order in sequential learning, or by their day-to-day alternation. In Experiment 2, rats learned to solve the active place avoidance task in two environments either alternately or sequentially. We found that rats are able to acquire both tasks and to discriminate both similar contexts without obvious problems regardless of the order or the alternation. We used two groups of rats, controls and a rat model of psychosis induced by a subchronic intraperitoneal application of 0.08mg/kg of dizocilpine (MK-801), a non-competitive antagonist of NMDA receptors. Dizocilpine had no selective effect on parallel/sequential learning of tasks/contexts. However, it caused hyperlocomotion and a significant deficit in learning in the active place avoidance task regardless of the task alternation. Cognitive coordination tested by this task is probably more sensitive to dizocilpine than spatial orientation because no hyperactivity or learning impairment was observed in the Morris water maze.

Fos expression in the prefrontal cortex and ventral striatum after exposure to a free-operant timing schedule

It has been proposed that cortico-striato-thalamo-cortical circuits that incorporate the prefrontal cortex and corpus striatum regulate interval timing behaviour. In the present experiment regional Fos expression was compared between rats trained under an immediate timing schedule, the free-operant psychophysical procedure (FOPP), which entails temporally regulated switching between two operanda, and a yoked variable-interval (VI) schedule matched to the timing task for food deprivation level, reinforcement rate and overall response rate. The density of Fos-positive neurones (counts mm⁻²) in the orbital prefrontal cortex (OPFC) and the shell of the nucleus accumbens (AcbS) was greater in rats exposed to the FOPP than in rats exposed to the VI schedule, suggesting a greater activation of these areas during the performance of the former task. The enhancement of Fos expression in the OPFC is consistent with previous findings with both immediate and retrospective timing schedules. Enhanced Fos expression in the AcbS was previously found in retrospective timing schedules based on conditional discrimination tasks, but not in a single-operandum immediate timing schedule, the fixed-interval peak procedure. It is suggested that the ventral striatum may be engaged during performance on timing schedules that entail operant choice, irrespective of whether they belong to the immediate or retrospective categories.

Fos expression in the orbital prefrontal cortex after exposure to the fixed-interval peak procedure

It has been proposed that cortico-striato-thalamo-cortical circuits that incorporate the prefrontal cortex and dorsal striatum regulate interval timing behaviour. The present experiment examined whether performance on the fixed-interval peak procedure (FIPP), an immediate timing schedule, would induce neuronal activity in cortical and striatal areas, as revealed by enhanced expression of the Fos protein, a marker for neuronal activation. Regional Fos expression was compared between rats trained on the FIPP and rats trained on a variable-interval (VI) schedule matched to the FIPP for overall response rate and reinforcer delivery. Response rate in the peak trials of the FIPP conformed to a temporally differentiated pattern, which was well described by a modified Gaussian function; in agreement with previous findings, the peak time occurred close to the time at which the reinforcer was delivered in the fixed-interval trials, and the Weber fraction was within the range of values reported previously. The density of Fos-positive neurones (counts mm⁻²) in the orbital prefrontal cortex (OPFC) was greater in rats exposed to the FIPP than in rats exposed to the VI schedule, suggesting a greater activation of this area during the performance of the former task. This is consistent with the results of previous studies that have implicated the OPFC in interval timing behaviour. However, there was no significant difference between the levels of Fos expression in the dorsal or ventral striatum of the rats trained under the two schedules.

Persisting cognitive deficits induced by low-dose, subchronic treatment with MK-801 in adolescent rats

Cognitive impairments have been proposed as a core feature of schizophrenia. Studies have shown that chronic or subchronic treatment with N-methyl-d-aspartate (NMDA) antagonists could induce cognitive deficits that resemble the symptoms of schizophrenia, yet few studies have investigated the effects of repeated NMDA blockade during adolescence on cognition. In the current study, adolescent, male rats were treated with an intraperitoneal injection of MK-801 (0.05, 0.1, and 0.2mg/kg) once daily for 14days. They were then tested 24h and 14days after drug cessation, respectively, in a series of behavioural tasks, including the object recognition task, the object-in-context recognition task and the working memory task of the Morris water maze (MWM). Results showed that object-in-context recognition and spatial working memory in the MWM were significantly impaired by repeated MK-801 treatment when animals were tested 24h after drug cessation, but object recognition was left intact. In particular, such deficits were observed 14days after drug cessation in the 0.2mg/kg group. The cognition-impairing effect of MK-801 could not be attributed to malnutrition or alterations in motor functions. Taken together, this study may provide support for establishing an animal model of cognitive deficits of schizophrenia based on low-dose, repeated treatment of MK-801 during adolescence.