Jm Koolhaas

A single social stress-experience alters glutamate receptor-binding in rat hippocampal CA3 area

The distribution of glutamate receptors in the rat hippocampus was investigated 24 h after the social stress of confrontation with a dominant opponent. AMPA-type glutamate receptors were labeled with the antagonist [3H]CNQX, and NMDA-type receptors were labeled with the competitive antagonist [3H]CGP39653. Increased [3H]CGP39653 labeling was exclusively found in the CA3 stratum radiatum and a decreased [3H]CNQX labeling was found in several hippocampal areas. Consequently, the ratio NMDA/AMPA binding was significantly increased in CA3 stratum oriens and CA3 stratum radiatum. These results suggest that a single unescapable social stress of defeat alters the impact of the excitatory neurotransmitter glutamate, which is restricted to hippocampal CA3 neurons. Possible consequences of the present findings are discussed.

Chicks from a high and low feather pecking line of laying hens differ in apomorphine sensitivity

Proactive rodents show a larger behavioral response to apomorphine (APO) than reactive copers, suggesting a more sensitive DA system in proactive individuals. Previously, chicks from a high feather pecking (HFP) and low feather pecking line (LFP) have been suggested to display a proactive and reactive coping strategy, respectively. Therefore, at approximately 4 weeks of age, the behavior of 48 LFP and 48 HFP chicks in response to an APO injection was studied using an open field. Another objective of the present study was to determine whether behavioral variation (in an open field) between HFP and LFP birds, after APO injection, is also reflected by variation of D(1) and D(2) receptor densities in the brain. Receptor binding capacities were assessed by measuring specific binding of tritiated D(1) and D(2) receptor ligands in different regions of the brain of control HFP and LFP chicks. In the present study, it is shown that indeed HFP chicks display a more enhanced behavioral response to acute APO treatment (0.5 mg/kg BW) than LFP birds in an open field. This difference was not reflected by variation of D(1) and D(2) receptor densities in the brain between both lines.

VASOPRESSIN PROLONGS BEHAVIORAL AND CARDIAC RESPONSES TO MILD STRESS IN YOUNG BUT NOT IN AGED RATS

In young male Wistar rats sudden silence superimposed on low intensity background noise evokes a relative decrease in heart rate. This bradycardia is accompanied by immobility behavior. In the present study, involving young (3 month), late-adult (14 month), aged (20 month), and senescent (25 month) rats the magnitude of the stress-induced bradycardia shows an age-related reduction while the behavioral immobility response remained unchanged during the process of aging. Arginine-8-vasopressin (AVP, 6 micrograms/kg SC) administered 60 min prior to the experiment led to a prolonged behavioral and cardiac stress response in young and late-adult rats, but not in aged and senescent animals. The peripheral and central mechanisms possibly involved in the failure of systemically applied AVP to improve bradycardiac stress responses in aged rats are discussed.