Changes in behavior and ultrasonic vocalizations during antidepressant treatment in the maternally separated Wistar-Kyoto rat model of depression

Early-life stress affects drug abuse susceptibility in adolescent rat model independently of depression vulnerability

The development of substance abuse problems occurs due to a diverse combination of risk factors. Among these risks, studies have reported depression and early-life stress as of importance. These two factors often occur simultaneously, however, there is a lack of understanding of how their combined effect may impact vulnerability to drug abuse in adolescence. The present study used rats with different vulnerability to depression (Wistar and Wistar-Kyoto) to investigate the impact of maternal separation (MS) on emotional state and drug addiction vulnerability during the adolescence period. Mothers and their litters were subjected to MS (180 min/day) from postnatal day 2 to 14. The offspring emotional state was assessed by observing their exploratory behavior. Drug abuse vulnerability was assessed through conditioning to cocaine. MS impacted the emotional state in both strains. Wistar responded with increased exploration, while Wistar-Kyoto increased anxiety-like behaviours. Despite the different coping strategies displayed by the two strains when challenged with the behavioural tests, drug conditioning was equally impacted by MS in both strains. Early-life stress appears to affect drug abuse vulnerability in adolescence independently of a depression background, suggesting emotional state as the main driving risk factor.

Attention-Deficit/Hyperactivity Disorder Predominantly Inattentive Subtype/Presentation: Research Progress and Translational Studies

Research on the predominantly inattentive attention-deficit/hyperactivity disorder (ADHD-PI) subtype/presentation is important given its high prevalence, but paradoxically it is under-recognized and undertreated. The temporal stability of the inattention symptom could impact the high worldwide prevalence of ADHD-PI. Some evidence suggests differences in the nature of attentional deficit in ADHD-PI vs. that in other subtypes. Impairments in neuropsychological, neurocognitive, and social functioning are also evident in ADHD-PI, which could be specific to the subtype (e.g., processing speed, social perception, and skills), or differ from others in severity. Neuroimaging studies have also revealed ADHD-PI-specific neuropathological abnormalities and those that are shared with other subtypes. ADHD-PI is highly comorbid with learning and internalizing (e.g., anxiety and depression) disorders. There is no solid evidence for ADHD-PI-specific genetic etiologies and differential responses of subtypes to ADHD medications. Translational studies have used the Wistar Kyoto/NCrl substrain which requires further characterizations as an ADHD-PI model. Overall, ADHD-PI research has been conducted in the context of the Diagnostic and Statistical Manual, which arguably does not conform to the widely recognized "dimensional" view of ADHD. The Research Domain Criteria has been proposed to provide a novel framework for understanding the nature of neuropsychiatric illnesses and ultimately improve their diagnosis and treatment.

Female rats are resistant to developing the depressive phenotype induced by maternal separation stress

Many stress-related psychiatric disorders are more common in women than in men. We aimed to determine how female rats respond to maternal separation (MS; removal of the dam from the litter for 3 h/day from postnatal day (P) 2-14)). A subset of MS females were also exposed to chronic constant light for 3 weeks during adolescence (P42-63) to investigate whether the antidepressant effect of light treatment, previously observed in male rats, could be seen in female rats. Ultrasonic vocalizations (22 kHz) were recorded and the forced swim test was conducted immediately after light exposure (P65-67) and 33 days later (P98-99) to determine depressive-like behaviour. Key proteins in the MAPK signal transduction pathway (MKP-1, phospho-ERK, total ERK) and a synaptosomal marker (synaptophysin) were measured in the ventral hippocampus. We found that MS decreased the duration of 22 kHz vocalizations at P65 which was reversed by subsequent light. Light exposure increased time spent in the inner zone of the open field and the number of 22 kHz calls in response to novelty at P98. MS decreased the time females spent immobile and increased time actively swimming in the forced swim test at P67 but not at P99. MKP-1 and synaptophysin levels remained unchanged while MS decreased phospho-ERK levels in the ventral hippocampus. In contrast to clinical findings, the results suggest that female rats may be resistant to MS-induced depression-like behaviour. The behavioural effects of MS and light treatment in female rats may involve the MAPK/ERK signal transduction pathway.