An Antihyperkinetic Action by the Serotonin 1A–Receptor Agonist Osemozotan Co-administered With Psychostimulants or the Non-stimulant Atomoxetine in Mice

The Effects of 5-HTR1A Polymorphism on Cingulum Connectivity in Patients with Panic Disorder

OBJECTIVE

Serotonin-1A receptors (5-HTR1A) is suggested to be involved in the etiology of several psychiatric disorders including panic disorder (PD). A few imaging studies have suggested the alterations of the cingulum bundle in PD. The objective of this study is to examine the structural changes of cingulum related to the 5-HTR1A polymorphism rs6295 in the patients with PD.

METHODS

Thirty-two right-handed patients with PD [11 men, 21 women; 40.34±13.17 (mean±SD) age] who met the diagnostic criteria in Structured Clinical Interview for DSM-IV were examined by means of MRI at 3 Tesla. We divided the patients with PD into CC genotype group and non CC genotype group (GG/CG genotype group) of the 5-HTR1A rs6295 polymorphism to compare the cingulum white matter connectivity.

RESULTS

Tract-based spatial statistics showed significantly increased fractional anisotropy (FA) values in cingulate gyrus process of left cingulum in 5-HTR1A CC genotype compared to GG/CG genotype in PD. Significant positive correlations were shown between the Albany Panic and Phobia Questionnaire (APPQ) interoceptive fear subscale scores, the Anxiety Sensitivity Inventory-Revised fear of publicly observable anxiety reaction subscale scores and FA values of cingulate gyrus process of left cingulum in 5-HTR1A rs6295 GG/CG genotype group. In CC genotype group, APPQ total, APPQ agoraphobia subscale and APPQ social phobia subscale scores also showed significant positive correlations with FA values of hippocampal process of right cingulum.

CONCLUSION

This preliminary study suggests that 5-HTR1A polymorphism may be associated with the cingulum white matter connectivity in PD.

Cued and contextual fear conditioning in BTBR mice is improved with training or atomoxetine

The BTBR T+tf/J (BTBR) strain of mice is a model for autism spectrum disorders (ASDs). These mice display reduced social behavior, altered communication, and high levels of repetitive behavior. BTBR mice have shown a deficit in learning cued and contextual fear conditioning. In this study, experiments were conducted to determine if either changes in training or drug administration would improve learning in BTBR mice when compared to C57BL/6 (B6) mice in contextual and cued fear conditioning. The first experiment examined the effects of three conditioned stimulus-unconditioned stimulus (CS-US) training paradigms; a 1P (1 CS-US pairing), 4P (4 CS-US pairings), and 10P (10 CS-US pairings). Increasing the number of CS-US pairings to 10 caused an increase in freezing behavior by the BTBR mice in contextual and cued conditioning indicating that more training facilitated BTBR learning. B6 mice had a more complex reaction to the increased training; the mice increased freezing behavior in the cued fear conditioning but not contextual fear conditioning. The second experiment determined whether atomoxetine, a noradrenergic reuptake inhibitor that has been shown to improve attention and decrease hyperactivity, impulsivity, and social withdrawal, would enhance learning. There was a significant increase in freezing behavior in contextual fear conditioning following atomoxetine administration in BTBR mice but not in B6 mice. Our data demonstrates that contextual and cued learning in BTBR mice is facilitated by increased training. Furthermore, contextual learning is improved in BTBR mice with use of atomoxetine, which helps to improve attention. Both increased training and pharmacological intervention improved learning in the BTBR mice suggesting a role for the combination of the two.

The selective norepinephrine reuptake inhibitor atomoxetine counteracts behavioral impairments in trimethyltin-intoxicated rats

This study was carried out to assess the behavioral effects of the non-psychostimulant drug atomoxetine, in rats prenatally-exposed to the organic compound trimethyltin chloride (TMT) and in spontaneously hypertensive rat (SHR), two rodent models of Attention Deficit/Hyperactivity Disorder (ADHD). At birth, neonatal reflexes (righting, cliff aversion, forelimb placing, forelimb grasping, bar holding and startle) had an earlier onset (i.e. percent of appearance) and completion (maximum appearance, i.e. 100% of the brood exhibiting each reflex) in prenatally TMT-exposed and SHR pups as compared to control groups. Two months after birth, TMT-exposed and SHR rats showed impaired cognitive performances in both the step-through passive avoidance test and the shuttle box active avoidance test. Atomoxetine (1, 3 and 6 mg/kg, i.p.), already at the lowest dose tested, improved learning and memory capacity of prenatally TMT-exposed rats and SHR; while methylphenidate (1, 3 and 6 mg/kg, i.p.), used here as positive control, elicited a significant cognitive enhancing effect only at the higher doses. In the open field test, both TMT-exposed rats and SHR displayed enhanced locomotor activity. Methylphenidate further increased locomotor activity in all groups, whereas atomoxetine reduced the enhanced locomotor activity of TMT-exposed rats and SHR down to the level of controls. These results suggest that prenatal TMT-exposure could be considered as a putative experimental model of ADHD and further support the effectiveness of atomoxetine in the ADHD pharmacotherapy. Furthermore, despite the similar effect of the two drugs on cognitive tasks, they exhibit distinct profiles of activity on locomotion, in ADHD models.

Potential serotonin 5-HT(1A) and dopamine D(4) receptor modulation of the discriminative stimulus effects of amphetamine in rats

Activation of the dopaminergic system underlies the behavioral effects of (+)-amphetamine, and plays a major role in its discriminative stimulus properties. Although serotonin receptors modulate dopamine levels in the brain, and 5-HT(1A) and 5-HT(2) receptor agonists do not mimic (+)-amphetamine, pretreatment with 5-HT(2A/2C) agonists significantly potentiates the (+)-amphetamine cue. Further, 5-HT(2) antagonists do not modify the discriminative stimulus effect of (+)-amphetamine, but 5-HT(1A) antagonists have never been tested in (+)-amphetamine-trained rats. This study sought to characterize the effects of the 5-HT(1A) antagonist WAY 100635 on (+)-amphetamine-induced discriminative stimulus effects. Male Sprague-Dawley rats were trained in a two-lever, fixed ratio 50, food-reinforced task with (+)-amphetamine sulfate (1.0 mg/kg, i.p., 30 min pretreatment time) as the discriminative stimulus. Substitution and combination tests with WAY 100635 were then performed. WAY 100635 did not produce substitution in amphetamine-trained rats, but significantly increased behavioral disruption. In combination tests 0.4 and 5.4 mg/kg doses of WAY 100635 potentiated the amphetamine cue. We suggest that low doses of WAY 100635 potentiated the (+)-amphetamine cue by blockade of 5-HT(1A) receptors, but stimulation of the dopamine D(4) receptor by higher doses of WAY 100635 may be responsible for potentiation of amphetamine-induced behavioral sensitization. The high percentage of behavioral disruption in substitution tests might suggest that rats trained to discriminate (+)-amphetamine from saline show behavioral sensitization that is not detectable by the drug discrimination assay but may be expressed as hyperactivity and stereotypic behavior that disrupts operant behavior.