Neuroadaptations Involved in Long-Term Exposure to ADHD Pharmacotherapies: Alterations That Support Dependence Liability of These Medications

Experimentally altered male mating behaviour affects offspring exploratory behaviour via nongenetic paternal effects

Evidence is emerging that fathers can have nongenetic effects on the phenotypes of their offspring. Most studies have focused on the role that nongenetic modifications to sperm can have on offspring phenotype; however, fathers can also have nongenetic effects on offspring through their interactions with females, called female-mediated paternal effects. These effects can occur in situations where male phenotype, e.g. behaviour or morphology, affects female stress and/or provisioning of offspring. These effects are potentially widespread, but few studies have explicitly investigated the role of female-mediated paternal effects on offspring phenotype. Here, we asked if male mating interactions can affect offspring via female mediated paternal effects in the Trinidadian guppy, Poecilia reticulata. To do this, we manipulated mating behaviour by: (i) administering a drug known to affect the neurotransmitter dopamine, and (ii) varying the familiarity of potential mates, which affects attractiveness in this species. With these treatments, we successfully manipulated the mating behaviour of male guppies and female preference for those males. Further, we found significant effects of sire mating behaviour, sire drug treatment, and parental familiarity status on behavioural measures of offspring anxiety in response to a novel object. Because Control offspring of 'familiar' and 'unfamiliar' pairs differed in their behaviour, our results cannot be solely attributed to potential nongenetic modifications to sperm caused by the drug. These results emphasize the importance of female-mediated paternal effects, including those caused by altered male mating behaviour, in shaping offspring phenotype.

Methylphenidate treatment in the spontaneously hypertensive rat: influence on methylphenidate self-administration and reinstatement in comparison with Wistar rats

RATIONALE

Methylphenidate is a psychostimulant given for extended periods of time as a treatment of attention-deficit/hyperactivity disorder (ADHD). The long-term effects of the drug are not yet known, and it is speculated that repeated exposure may produce drug dependence.

OBJECTIVE

To investigate the effects of repeated methylphenidate treatment on methylphenidate self-administration and reinstatement in the most validated animal model of ADHD, the spontaneously hypertensive rat (SHR), and Wistar rat, strain representing the "normal" heterogeneous population.

METHODS

Rats were administered intraperitoneally with saline or methylphenidate (2 mg/kg) for 14 days, prior to experiments. Thereafter, responses for intravenous methylphenidate under the fixed ratio (FR1 and FR3) and progressive ratio (PR) schedules were assessed. Extinction experiments followed, as well as tests to determine the ability of intraperitoneal administration of methylphenidate (2 and 5 mg/kg) to reinstate extinguished drug-seeking behaviors in rats.

RESULTS

Previous exposure to methylphenidate enhanced methylphenidate self-administration in Wistar rats but not in SHR (FR3). Methylphenidate pretreatment reduced responding for methylphenidate in SHR but did not affect self-administration behaviors of Wistar rats (PR). Methylphenidate pre-exposure robustly reinstated drug-seeking behaviors in Wistar rats, but not in SHR.

CONCLUSION

The contrasting effects of repeated methylphenidate treatment in methylphenidate self-administration and reinstatement in Wistar and SHR, and the increased susceptibility of the Wistar rat strain to the reinforcing effects of methylphenidate indicate that "normal" individuals are more likely to develop psychological dependence to the drug and experience relapse. Meanwhile, the clinical use of methylphenidate may not produce drug dependence or relapse in ADHD patients.

Conditioned place preference studies with atomoxetine in an animal model of ADHD: effects of previous atomoxetine treatment

To investigate the putative rewarding effects of atomoxetine, a non-stimulant medication for Attention-deficit/hyperactivity disorder (ADHD), we conducted conditioned place preference (CPP) tests in an animal model of ADHD, the spontaneously hypertensive rat (SHR). The effects of drug pre-exposure were also evaluated, thus, parallel experiments were done in rats which have undergone 14 days of atomoxetine treatment. The responses of SHR were compared with the rat strain representing the "normal" heterogeneous population, the Wistar rats. Neither rat strain showed significant CPP to atomoxetine. However, previous atomoxetine treatment produced place preference responses in rats, more profoundly in Wistar rats conditioned with the low and moderate atomoxetine doses. In conclusion, acute exposure to atomoxetine does not have any rewarding effect, however, drug pretreatment produces responses characteristic of reward or psychological dependence, more specifically in the "normal" vs. the ADHD animal model. The present findings call for more studies with atomoxetine, especially those that investigate the effects of long-term or chronic drug treatment.