Adrenocortical Response to Novelty Stress in Rats with Dentate Gyrus Lesions

Abstract

Male rats exposed to a novel environment exhibited a marked rise of plasma corticosterone in response to the initial exposure. These animals showed a significant but not complete habituation of their adrenal response after 18 exposures. Following their first exposure to a novel environment, animals with bilateral lesions in the dentate gyrus of the hippocampus had plasma corticosterone concentrations which were significantly lower than those observed for the control animals. Whereas the control groups demonstrated a significant decrease in their adrenal response following 18 exposures (habituation), there was no decrease of the adrenocortical response to novelty stress within the dentate-lesioned group between trials 1 and 18. The effect of the dentate lesions appeared to be specific to the behavioral stress: dentate lesions failed to alter resting levels, or the animal’s adrenal responses to laparotomy stress and ether inhalation.

Tracelink: A model of consolidation and amnesia

“…The modulatory system may be activated through central states such as arousal and attention, and it can be identified with the basal forebrain, the amygdala, and other subcortical centres that control plasticity in the brain. A structure that certainly also plays a role in the modulatory system is the hippocampus, which many studies have implicated in novelty processing ( Johnson & Moberg, 1980;Knight & Nakada, 1998;Montag-Sallaz, Welzl, Kuhl, Montag, & Schachner, 1999;Mumby, Gaskin, Glenn, Schramek, & Lehmann, 2002). The hippocampus thus plays a double role in the TraceLink model: It is part of the link system, but it is also involved in regulating its own plasticity.…”

Hormones and the hippocampus

“…Handa et al 1994). Here, hippocampal lesions impair the glucocorticoid increase and the concentrations fail to acclimatise (Johnson & Moberg 1980). Glucocorticoid concentrations in rats also increase markedly in response to a previously learned aversive taste (but not with a neutral taste).…”

Mode shifting between storage and recall based on novelty detection in oscillating hippocampal circuits

“…Over the past decades, the hippocampus has been implicated in various functions, including episodic memory (Squire, 1992;Eichenbaum et al, 1999) and novelty detection of the contextual or spatial aspects of an experience (Johnson and Moberg, 1980;Kitchigina et al, 1997;Zhu et al, 1997;Knight and Nakada, 1998;Xiang and Brown, 1998;Montag-Sallaz et al, 1999;Lisman and Otmakhova, 2001;Mumby et al, 2002). From existing experimental studies, it is difficult to understand how these functions are interrelated, and whether they are subserved by the same processes or by different ones at the circuit level.…”

“…role in novelty detection (Johnson and Moberg, 1980;Lemaire et al, 1999). Notably, the orthogonalization between EC and dentate tends to drive the overlap between dentate representations toward all or nothing in retrieval mode.…”