Environmental enrichment decreases the afterhyperpolarization in senescent rats

Abstract

Previous research indicates that an age-related increase in the amplitude of the Ca 2+ -dependent, K + -mediated afterhyperpolarization (AHP) is related to cognitive decline. However, because the AHP is measured following completion of training, it is unclear whether the AHP amplitude is strictly dependent on biological aging or is modified by the training procedure. To address this distinction we examined the effect of environmental enrichment on the AHP amplitude. Young (5-8 months) and aged (22-24 months) male Fischer 344 rats were exposed to environmental enrichment conditions (EC) or maintained in individual cages (IC). Following 8-10 weeks of differential experience, sharp microelectrode current-clamp recordings were obtained in CA1 pyramidal neurons in hippocampal slices. Examination of the AHP demonstrated that the amplitude was significantly reduced in aged animals exposed to enriched conditions. The results indicate that the amplitude of the AHP in hippocampal pyramidal cells from aged animals is dependent on the history of experience and hippocampal activity.

Enhanced intrinsic excitability and EPSP-spike coupling accompany enriched environment-induced facilitation of LTP in hippocampal CA1 pyramidal neurons

“…This reduction in AP threshold was unlikely to be caused by a change in number or properties of voltagegated sodium channels, because we did not observe a change in peak dV/dt values. Finally, EE caused a decrease in AHP amplitude in CA1 neurons, which is in agreement with a similar finding on reduction of AHP in aged rats exposed to EE (Kumar and Foster 2007). These changes are likely to act together to enhance the capacity of EE cells to fire more spikes during TBS and thereby, support larger LTP.…”

Environmental enrichment modulates intrinsic cellular excitability of hippocampal CA1 pyramidal cells in a housing duration and anatomical location-dependent manner

“…For example, Duffy et al [9] did not find a difference in spike accommodation, which is tightly related to AHP currents, after 2 months of enrichment. Kumar and Foster [31] only saw an AHP difference in aged but not in adult rats after 8-10 weeks of enrichment. Although we did not find AHP reduction, we cannot rule out possibilities that AHP modulation occurred.…”

CREB overexpression in dorsal CA1 ameliorates long-term memory deficits in aged rats

“…This effect has been demonstrated before, where systemic application of L-type calcium channel blocker nimodipine (Deyo et al, 1989) or cholinesterase inhibitor galantamine (Weible et al, 2004) was beneficial for aged animals, but had no effect on young. Similarly, exposure to environmental enrichment, which can indirectly lead to increased CREB activation (Hu et al, 2013), reduced the AHP in neurons from aged animals, but not young (Kumar and Foster, 2007). For potential therapeutic purposes, this may be a desirable trait, so as to only affect those who have room for improvement.…”