title: Modest elevation of corticosterone in preweanling rats impairs subsequent trace eyeblink conditioning during the juvenile period.
abstract: The hippocampus is known to be especially sensitive to the deleterious effects of glucocorticoids. Previously, we administered exogenous corticosterone, the major stress-related glucocorticoid in rats, to young developing rats using subcutaneous pellets which produced high pharmacological levels of circulating corticosterone as well as a sex-specific learning deficit for males on a hippocampus-mediated associative learning task, trace eyeblink conditioning [1]. The present study evaluated the effects of corticosterone administered at a physiologically-relevant level by a more consistent release method, osmotic mini-pumps. Pumps were implanted subcutaneously in 15-day-old rats to deliver either corticosterone or the vehicle control (PEG) at a rate of 1 μl/h over 3 days. On Day 28, learning was assessed using trace eyeblink conditioning. The results of the present experiment revealed that a small elevation in corticosterone (11.77 μg/dl versus 6.02 μg/dl for controls) within the normal physiological range impaired learning as determined by a significantly lower percentage and amplitude of total conditioned responses (CRs) and lower amplitude of adaptive responses relative to the control group. There were no significant differences in response timing, although the corticosterone group tended to produce CRs which began and peaked a little later than controls. These findings indicate that even modest elevations of corticosterone for several days can produce later impairments on this hippocampally mediated learning task.
authors.affiliation: Department of Psychology, Wright State University, 335 Fawcett Hall, 3640 Colonel Glenn Hwy, Dayton, OH 45435, USA. Electronic address: dragana.claflin@wright.edu.
authors.forename: Dragana I
authors.initials: DI
authors.lastname: Claflin
authors.forename: Leslie R
authors.initials: LR
authors.lastname: Greenfield
authors.forename: Michael B
authors.initials: MB
authors.lastname: Hennessy
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D003215:Conditioning, Eyelid / Q000187:drug effects*; D003345:Corticosterone / Q000097:blood / Q000494:pharmacology*; D005260:Female; D006624:Hippocampus / Q000187:drug effects*; D008297:Male; D051381:Rats; D020318:Rats, Long-Evans
chemical_list: D003345:Corticosterone
keywords: CL; CML; CRA; Corticosterone; Development; EMG; Eyeblink; HPA; Hippocampus; Learning; PEG; PND; SEM; SHRP; SR; Trace conditioning; conditioned response amplitude; electromyography; hypothalamic–pituitary–adrenal axis; latency to maximum peak; polyethelyne glycol; postnatal day; response onset latency; standard error of the mean; startle response; stress hyporesponsive period