Abstract
Chronic stress is a key factor in psychiatric and neurological disorders often worsening disease symptoms. In this study, a unique animal model, the dopamine transporter knockout (DAT-KO) rat exhibiting behavioral signs resembling those occurring in mania, schizophrenia, attention deficit hyperactivity disorder, and obsessive-compulsive disorder was used. We have tested the hypothesis that the hyperdopaminergic state in DAT-KO rats (i) modulates behavioral response to the NMDA antagonist MK-801 (dizocilpine) and (ii) leads to abnormal endocrine and immune activation under subchronic stress induced by an immune challenge. Glutamatergic modulation with MK-801 induced a different behavioral pattern. While the WT rats responded to MK-801 injection with a robust rise in their locomotor activity, the hyperactive DAT-KO rats exhibited reduced locomotion. Signs of chronic stress including increased basal corticosterone and aldosterone but blunted anxiety were demonstrated in rats lacking the DAT. Repeated injections of increasing doses of lipopolysaccharide (LPS, 5 days) did not modify plasma prolactin concentrations which were however significantly lower in DAT-KO than in WT rats. Concentrations of plasma high mobility group box 1 (HMGB1) protein were significantly higher in LPS-treated DAT-KO than in WT rats. The gene expression of interleukin-6 in the anterior pituitary increased under the stress induced by the immune challenge in the WT but not the DAT-KO rats. The most evident differences between the genotypes were revealed in the spleen. The splenic gene expression of interleukin-1β, interleukin-6, and HMGB1 was lower and that of ferritin was higher in DAT-KO compared to WT rats. Obtained results emphasize the functional interaction of the endocrine and immune systems with monoamine and glutamatergic neurotransmission in the mechanisms leading to behavioral alterations and psychiatric disorders associated with dopamine dysfunction.
