Inverse relationship of hippocampal serotonin to avoidance behavior, serotonergic activation by emotional stress differentiated by estrous cycle and surgical stress

• Published in: Behavioural brain research 2002-01, Vol.128 (1), p.41-52
• Main Authors: Sfikakis, Anastasia, Papadopoulou-Daifotis, Zeta, Bikas, Nicholas
• Format: Article
• Language: English
• Subjects: Adrenal Glands - physiology; Animals; Arthritis, Experimental - physiopathology; Avoidance behavior; Avoidance Learning - physiology; Biological and medical sciences; Emotional reactivity; Estrous cycle; Estrous Cycle - physiology; Female; Hippocampal serotonin; Hippocampus - metabolism; Hippocampus - physiology; Hydroxyindoleacetic Acid - metabolism; Hypothalamus - metabolism; Organ Size - physiology; Preoptic Area - metabolism; Rats; Rats, Wistar; Serotonin - metabolism; Serotonin - physiology; Species Specificity; Stress, Physiological - physiopathology; Stress, Psychological - metabolism; Surgical Procedures, Operative; Surgical stress
• ISSN: 0166-4328; 1872-7549
• DOI: 10.1016/S0166-4328(01)00267-4

The hippocampus is involved in learning, affect, and the neurobiology of stress. After recording individual emotional reactivity (ER) during handling for vaginal smear screening (VSS), serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA), in the hypothalamus-preoptic area (HY-PA) and hippocampus were studied in two rat lines with different susceptibility to Freund's adjuvant arthritis (FAA), in relation to active avoidance behavior (AB), and under basal conditions in the FAA susceptible strain, in relation to ER, cycle stage and 20 h prior surgical stress. FAA susceptible rats compared to non-susceptible under equally low ER, showed higher AB, but lower 5-HIAA and 5-HIAA/5-HT ratio, under basal conditions, and upon termination of avoidance assay, only in hippocampus. In rats with different ER after prolonged VSS, high ER paralleled on diestrus-2 (DE-2), increased 5-HIAA and 5-HIAA/5-HT in the hippocampus and HY-PA, and adrenal weight, but decreased thymus and hippocampal weight. Under equal ER 5-HIAA and 5-HIAA/5-HT in the hippocampus and 5-HIAA/5-HT in the HY-PA were diminished on proestrus vs DE-2 but not estrus. Under equal distribution of proestrus and estrus higher ER paralleled higher hippocampal 5-HIAA. After equally high ER, combined with 20 h prior surgical stress, diminished hippocampal 5-HIAA/5-HT ratio, paralleled pronounced increase in adrenal weight compared to controls. Results suggest: negative association of hippocampal 5-HT to avoidance learning, a positive one to ER, modulated by cycle stage, and a role of differentiated 5-HT in homeostasis of HPA system.