Characteristics of the pituitary-adrenal system in the syracuse high-and low-avoidance strains of rats (Rattus norvegicus)

Abstract

After many generations of selective breeding, rats of the high-avoidance strain (SHA) average 67% avoidance responses in a two-way shuttle box, whereas those of the low-avoidance strain (SLA) average 0%. Adrenal gland weights, both absolutely and relative to body weight, are 40-50% greater in adult SLA than SHA rats of both sexes. Females of both strains have larger adrenal glands than males. Morphometry revealed that the difference in adrenal size in adults is entirely in the three cortical zones. The strain difference occurs as early as 21 days of age, whereas the sex difference appears only after puberty. A 2-min exposure to either vapor induced an elevation in adrenal concentration of corticosterone which was significantly greater in SHA than SLA animals of both sexes at some time periods following the ether stress. Despite having smaller glands, older previously stressed SHA rats have higher basal adrenal concentrations of corticosterone than do SLA animals. The reduced steroidogenesis in the large adrenals of SLA rats suggests that there may be an enzymatic defect of genetic origin in those animals.

Hatano rats selectively bred for high- and low-avoidance learning: an overview

“…Furthermore, a higher neuroendocrine reactivity to stressors is observed in RLA rats than in RHA rats [6, 14, 17, 18, 43, 44]. Similar results have been obtained in Syracuse rats [9, 12].…”

Searching for Biological Markers of Personality: Are There Neuroendocrine Markers of Anxiety?

“…In accordance with their greater emotionality, SLA rats show a greater glucose response to an open-field [146]. However, SLA rats are characterized by modestly lower corticosterone response to ether stress, but much lower adrenal corticosterone content, as compared with SHA [147]. Similar results were observed after exogenous CRH administration [148].…”

Selective breeding for negative contrast in consummatory behavior.

“…This is of particular interest because previous studies have shown that the Brush Syracuse Low-Avoidance rats are more sensitive to chlordiazepoxide than the Syracuse High-Avoidance rats, and substantial evidence suggests that the Syracuse Low-Avoidance rats are more emotionally reactive than the Syracuse High-Avoidance rats in a variety of tasks including novelty stress, conditioned suppression, and active and passive avoidance learning (Brush et al, 1988;Flaherty & Rowan, 1989). Furthermore, the Syracuse Low-Avoidance rats have enlarged adrenal glands but have reduced corticosterone secretion compared with the Syracuse High-Avoidance rats (Brush, 1992;Brush, Isaacson, Pellegrino, Rykaszewski, & Shain, 1991;Del Paine & Brush, 1990). Thus, the previous finding from our laboratory that the Syracuse Low-Avoidance rats showed larger successive negative contrast effects than the Syracuse High-Avoidance rats, and that chlordiazepoxide was effective only in the Syracuse Low-Avoidance rats, suggested that more emotional rats show larger contrast effects and that the benzodiazepines are particularly effective in these rats.…”