Differential Startle Amplitude and Corticosterone Response in Rats

Abstract

Different rat strains exhibit large differences in hypothalamic pituitary-adrenal activity that have been used to determine the role of the neuroendocrine system in susceptibility to autoimmune disease. To further characterize potential behavioral correlates of these differences, the amplitude of the acoustic (ASR) and tactile (TSR) startle response and the corticosterone response to acoustic startle stimuli were compared between two histocompatible strains, Lewis (LEW/N) and Fischer (F344/N) rats, as well as outbred Harlan Sprague-Dawley (SD) rats. Startle stimuli elicited larger ASR and TSR in LEW/N rats than in F344/N rats, with SD rats exhibiting an intermediate response. The ASR habituated at a similar rate in LEW/N and F344 rats, while the ASR did not habituate in SD rats. After handling and placement in the startle chambers, the three strains did not differ in control levels of corticosterone. In contrast, exposure to acoustic startle stimuli increased corticosterone 5-fold in F344/N rats and 2-fold in SD rats, but had no effect on corticosterone in LEW/N rats. These findings suggested an inverse relationship between the amplitude of the ASR and hypothalamic-pituitary-adrenal activation across strains. This relationship was further supported by a high negative correlation between corticosterone level and ASR amplitude within the F344/N group.

Differential Neuroendocrine and Behavioral Responses to Cocaine in Lewis and Fischer Rats

“…In accordance with pre vious reports showing an enhanced corticosterone re sponse to stressors in F344 rats [22,34], plasma CS fol lowing saline injections was greater in F344 compared to LEW rats. The hormonal response to cocaine exposure is also consistent with earlier studies.…”

“…CRF con tent was significantly greater in F344 rats compared with LEW rats, perhaps explaining the greater HPA reactivity of this strain. Furthermore, the decreases in hypothalamic CRF content suggest enhanced CRF release following cocaine injections in F344 rats, supporting previous stud ies which demonstrated a hyperresponsive HPA axis in these rats to several types of stimuli [22,34,35], The decrease in hypothalamic CRF in both LEW and F344 rats following acute cocaine is in agreement with a similar study which demonstrated decreased CRF within several brain regions of Sprague-Dawley rats in response to intraperitoneal cocaine injection [15].…”

Strain differences in response to escapable and inescapable novel environments and their ability to predict amphetamine-induced locomotor activity

“…Although F1 rats show more variable responses, their grooming and defection responses are more F344-like again supporting genetic bases to these effects. Previous studies report similar strain differences in grooming (Glowa et al 1992a;Sternberg et al 1992;Chaouloff et al 1995;Haile et al 2001b) and in fecal boli response (Sternberg et al 1992;Rex et al 1996;Stohr et al 1998). In the present study, grooming was assessed during the period of object exploration and contacts in the playground maze.…”

Genetic variation in vulnerability to the behavioral effects of neonatal hippocampal damage in rats.

“…For instance, three strains of rats-Sprague-Dawley (SD), Lewis, and Fischer 344 (F344)-differ substantially in a number of respects, including responsiveness to stress, predisposition to inflammatory diseases, and preference for drugs of abuse (1)(2)(3)(4)(5). Moreover, it has been suggested that these differences are associated with differential responsiveness of the hypothalamic-pituitary-adrenal (HPA) axis to stressful or inflammatory stimuli (3,6,7), differential interactions between neurotransmitter systems and the HPA axis (8), and the functional state of the mesolimbic dopamine (DA) system (9)(10)(11)(12). F344 and Lewis rats appear to represent two ends of a spectrum of stress responsivity; F344 rats are hyperresponsive to stress whereas Lewis rats are hyporesponsive to stress as assessed by behavioral and neuroendocrine responses to an open field, swim test, restraint, etc.…”