5-HT agonist-induced changes in peripheral immune cells in healthy volunteers: The impact of personality

The present study was conducted to investigate the relationship between the serotonergic neurotransmitter system and migration patterns of peripheral lymphocytes. Altogether 40 healthy male volunteers were given either a single dosage of the 5-HT 1 a -receptor agonist ipsapirone (10 mg) or a placebo ( n = 20 each) in a double-blind randomized trial. Blood samples were drawn 55, 90 and 110 min after drug intake (baseline) and were analyzed for the number of peripheral lymphocytes. Furthermore, saliva samples were obtained at 13 defined time points which were analyzed for cortisol concentrations. Personality traits impulsivity, psychoticism and boredom susceptibility) were measured by questionnaires to investigate personality related differences in levels of serotonergic responsiveness. Analyses of covariance indicated that ipsapirone leads to highly significant reductions of peripheral CD4+ cells (T-helper/inducer-cells). This was significantly correlated to the ipsapirone-induced release of cortisol in a time-dependent manner. Furthermore, subjects scoring high on impulsivity, psychoticism and boredom susceptibility could be identified as being more responsive to the 5-HT agonist, indicated by their larger reduction in T-helper cells and greater cortisol release. This was hypothesized to be either due to their subsensitivity of presynaptic or supersensitivity of postsynaptic 5-HT 1 a -receptors.