Central Hypothalamic Pathways Mediating Stress Responsiveness Vary in Different Rat Strains

Abstract

Others have reported that the dorsomedial hypothalamus (DMH) mediates certain cardiovascular responses to behavioral stress. We sought to determine whether this variability is strain dependent and whether different stressors are similarly dependent on the DMH. We compared responses to cocaine (5 mg/kg, iv) with startle responses to 1 cm deep ice cold water (CWS) in Brown‐Norway (BN) and Dahl salt sensitive (DSS) rats. BN and DSS rats were instrumented for recording arterial pressure and for measuring blood flow changes in the abdominal aorta (hindquarters or Hq) and the superior mesenteric (Ms) artery using Doppler flowmetry. We calculated changes in vascular resistance (R) in animals. BN rats had greater increases in MsR (visceral) and HqR (skeletal muscle) to cocaine than DSS. In contrast, DSS rats had greater increases in MsR in response to CWS than BN rats. Microinjection of muscimol (80 pmol in 100 nl) in the DMH attenuated the increase in MsR in BN but not DSS rats in response to cocaine but not to CWS. DMH stimulation with kainate (10 pmol in 100 nl) elicited greater Ms vasoconstriction in BN compared to DSS rats. We conclude that there are unique strain‐dependent pathways mediating regional vascular resistance for specific stressors. The BN is more dependent on DMH in mediating cocaine‐induced visceral vasoconstriction. Supported by USPHS DA017371 and HL091440.