NMDA-GABA interactions in an animal model of behaviour: a gating mechanism from motivation toward psychotic-like symptoms

Single and chronic L-serine treatments exert antidepressant-like effects in rats possibly by different means

In the present study, the effects of both single (6 mmol L-serine/10 ml/kg orally administrated) and chronic (2% L-serine solution freely given for 28 days) treatments on depression-like behavior were evaluated in Wistar rats, representing the control, and Wistar Kyoto rats, representing an animal model of depression. Both single and chronic L-serine treatments decreased the duration of immobility, which is an index of a depressive-like state, in the forced swimming test in both strains. However, the decreases in the duration of immobility appear to be regulated differently by the different mechanisms involved in single and chronic L-serine treatments. In the prefrontal cortex and hippocampus, single L-serine treatment increased the concentrations of L-serine, but not D-serine, while chronic L-serine treatment increased those of D-serine, but not L-serine. These data suggest that the antidepressant-like effects of single and chronic L-serine treatments may have been induced by the increased L-serine and D-serine concentrations, respectively, in the brain. In addition, chronic L-serine treatment increased cystathionine concentrations in the hippocampus and prefrontal cortex in Wistar rats, but not in Wistar Kyoto rats, suggesting that Wistar Kyoto rats have an abnormality in the serine-cystathionine metabolic pathway. In conclusion, single and chronic L-serine treatments may induce antidepressant-like effects via the different mechanisms related to serine metabolism in the brain.

Kindling epileptogenesis in immature rats leads to persistent depressive behavior

Depression is a frequent comorbidity in epilepsy patients. A variety of biological factors may underlie epilepsy-associated depression. We examined whether kindling-induced chronic increase in seizure susceptibility is accompanied by behavioral symptoms of depression. Three-week-old Wistar rats underwent rapid kindling: 84 initially subconvulsant electrical stimulations of ventral hippocampus delivered every 5 minutes, followed by depression-specific behavioral tests performed 2 and 4 weeks later. Kindled animals exhibited a sustained increase in immobility time in the forced swim test and the loss of taste preference toward calorie-free saccharin, as compared with controls. Initial loss of preference toward the intake of calorie-containing sucrose was followed by the increased consumption at 4 weeks. At both time points, animals exhibited enhanced seizure susceptibility on test stimulations of the hippocampus. We conclude that neuronal plastic changes associated with the kindling state are accompanied by the development of depressive behavior.

Agastache mexicana may produce anxiogenic-like actions in the male rat

Behavioral effects of a water-soluble extract of Agastache mexicana, a plant with purported anxiolytic actions, were studied in male Wistar rats. In the elevated plus-maze test, various doses of the plant extract (3.0 mg/kg body wt.; 9.0 mg/kg body wt.; 12.0 mg/kg body wt.) administered intraperitoneally (i.p.) decreased the exploration of open arms, showing an anxiogenic-like effect. Agastache mexicana (12 mg/kg body wt.; i.p.) did not change immobility in the forced swimming test (i.e., had no anti-depressant effect) but increased the anti-immobility action of 32.0 mg/kg body wt. (i.p.) of desipramine (i.e., increased the antidepressant-like effect of desipramine). A. mexicana had no effect on exploratory activity in an open field test, indicating that it had no sedative effect at the doses used. It is concluded that effects of the water extract of A. mexicana are more consistent with an anxiogenic-like property than an anxiolytic-like one.

Dopamine receptor D4 is not associated with antidepressant activity of sleep deprivation

Total sleep deprivation (TSD) is an effective treatment for mood disorders which is thought to act through an enhancement in several neurotransmitter pathways including dopaminergic transmission. However, not all patients respond to TSD and genetic factors are likely to play a major role in determining TSD response. The aim of this study is to investigate the influence of dopamine receptor D4 exon 3 (DRD4) variants on TSD antidepressant efficacy in bipolar disorder. One hundred and twenty-four depressed inpatients affected by bipolar disorder (DSM-IV) were treated with repeated cycles of TSD and were typed for DRD4 variants at the third exon using polymerase chain reaction (PCR) techniques. DRD4 variants were not associated with TSD outcome. Consideration of possible stratification effects such as gender, age at onset and duration of illness did not reveal any association either. DRD4 exon 3 variants are not a main factor influencing TSD outcome in bipolar disorder.

Neuropsychology of selective attention and magnetic cortical stimulation

Informed volunteers were asked to perform different neuropsychological tests involving selective attention under control conditions and during transcranial magnetic cortical stimulation. The tests chosen involved the recognition of a specific letter among different letters (verbal test) and the search for three different spatial orientations of an appendage to a square (visuo-spatial test). For each test the total time taken and the error rate were calculated. Results showed that cortical stimulation did not cause a worsening in performance. Moreover, magnetic stimulation of the temporal lobe neither modified completion time in both verbal and visuo-spatial tests nor changed error rate. In contrast, magnetic stimulation of the pre-frontal area induced a significant reduction in the performance time of both the verbal and visuo-spatial tests always without an increase in the number of errors. The experimental findings underline the importance of the pre-frontal area in performing tasks requiring a high level of controlled attention and suggest the need to adopt an interdisciplinary approach towards the study of neurone/mind interface mechanisms.