Reversible inactivation of the auditory thalamus disrupts HPA axis habituation to repeated loud noise stress exposures

A defining feature of adaptive behavior is our ability to change the way we interpret sensory stimuli depending on context. Rapid adaptation in behavior has been attributed to frontal cortical circuits, but it is not clear if sensory cortexes also play an essential role in such tasks. In this study we tested whether the auditory cortex was necessary for rapid adaptation in the interpretation of sounds. We used a two-alternative choice sound-categorization task for rats in which the boundary that separated two acoustic categories changed several times within a behavioral session. These shifts in the boundary resulted in changes in the rewarded action for a subset of stimuli. We found that extensive lesions of the auditory cortex did not impair the ability of rats to switch between categorization contingencies and sound discrimination performance was minimally impaired. Similar results were obtained after reversible inactivation of the auditory cortex with muscimol. In contrast, lesions of the auditory thalamus largely impaired discrimination performance and, as a result, the ability to modify behavior across contingencies. Thalamic lesions did not impair performance of a visual discrimination task, indicating that the effects were specific to audition and not to motor preparation or execution. These results suggest that subcortical outputs of the auditory thalamus can mediate rapid adaptation in the interpretation of sounds.

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Adaptive Changes in Basal and Stress-Induced HPA Activity in Lactating and Post-Lactating Female Rats

Endocrinology ◽

10.1210/en.2012-1779 ◽

2013 ◽

Vol 154 (2) ◽

pp. 749-761 ◽

Cited By ~ 24

Author(s):

Richard J. Windle ◽

Susan A. Wood ◽

Yvonne M. Kershaw ◽

Stafford L. Lightman ◽

Colin D. Ingram

Keyword(s):

Hpa Axis ◽

Mineralocorticoid Receptor ◽

Blood Sampling ◽

Female Rats ◽

Adaptive Changes ◽

Noise Stress ◽

Receptor Mrna ◽

Corticosterone Release ◽

Hpa Response ◽

Rise Phase

Lactation represents a period of marked adaptation of the hypothalamo–pituitary–adrenal HPA axis. We characterized basal and stress-induced HPA activity during lactation and experimental weaning using dynamic blood sampling in rats. Pulsatile and diurnal corticosterone release occurred at all reproductive stages studied (virgin; day 10 of lactation; 3 and 14 days after experimental weaning on day 10 of lactation). However, in lactating rats the diurnal peak was significantly reduced, resulting in a flattened rhythm, and three days after weaning, basal HPA activity was markedly suppressed: the number of pulses and underlying basal levels of corticosterone were reduced and the diurnal rise phase delayed. Marked changes in the HPA response to 10 min noise stress also occurred at these times: being completely absent in lactating animals, but restored and highly prolonged in early weaned animals. Injection of methylprednisolone (2 mg, iv) was used to determine whether changes in fast glucocorticoid suppression correlated with these adaptive changes. Methylprednisolone induced a rapid suppression of corticosterone in virgin animals, but this effect was markedly attenuated in lactating and early weaned animals and was accompanied by significant changes in relative expression of hippocampal glucocorticoid and mineralocorticoid receptor mRNA. All effects were reversed or partially reversed 14 days after experimental weaning. Thus, the presence of the pups has an important influence on regulation of the HPA axis, and while postpartum adaptations are reversible, acute weaning evokes marked reorganisation of basal and stress-induced HPA activity.

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