Chronic electric stimulation of the midbrain ventral tegmental area increases spleen but not blood natural killer cell cytotoxicity in rats

Abstract

Previously we found that in conscious, freely behaving rats chronic electric stimulation of the lateral hypothalamus (LH) caused significant augmentation of natural killer cell cytotoxicity (NKCC) and a large granular lymphocyte (LGL) number more pronounced in the spleen than in the peripheral blood. The LH belongs to the so-called “brain reward system”, a collection of the central structures whose activation produce positive emotions. The midbrain ventral tegmental area (VTA) is another prominent reward-relevant structure. In the present work, chronic electric stimulation of VTA (constant current 0.1 ms duration cathodal pulses delivered at frequency 50 Hz during 60 min daily session for 14 consecutive days) caused in rats an increase in the spleen but not in the peripheral blood NKCC (chromium release assay) without simultaneous effect on the number of large granular lymphocytes (LGL) (morphological method) and plasma level of prolactin (PRL), growth hormone (GH), corticosterone (COR), and testosterone (TST). This effect was anatomically specific as no influence of analogous thalamic stimulation on immune and endocrine response was found. The results obtained indicate that both reward-related areas VTA and LH enhance the cell-mediated immune response, represented by natural killer cytotoxicity, especially in the spleen. However, the effect pronounced by VTA is weaker than that of LH, possibly due to additional connections of LH with the hormonal and/or autonomic control systems.