Elsevier

Neuroscience

Volume 170, Issue 2, 13 October 2010, Pages 662-669
Neuroscience

Pain Mechanisms and Sensory Neuroscience
Research Paper
Environmental enrichment differentially modifies specific components of sensory-evoked activity in rat barrel cortex as revealed by simultaneous electrophysiological recordings and optical imaging in vivo

https://doi.org/10.1016/j.neuroscience.2010.07.029Get rights and content

Abstract

Environmental enrichment of laboratory animals leads to multi-faceted changes to physiology, health and disease prognosis. An important and under-appreciated factor in enhancing cognition through environmental manipulation may be improved basic sensory function. Previous studies have highlighted changes in cortical sensory map plasticity but have used techniques such as electrophysiology, which suffer from poor spatial resolution, or optical imaging of intrinsic signals, which suffers from low temporal resolution. The current study attempts to overcome these limitations by combining voltage-sensitive dye imaging with somatosensory-evoked potential (SEP) recordings: the specific aim was to investigate sensory function in barrel cortex using multi-frequency whisker stimulation under urethane anaesthesia. Three groups of rats were used that each experienced a different level of behavioural or environmental enrichment. We found that enrichment increased all SEP response components subsequent to the initial thalamocortical input, but only when evoked by single stimuli; the thalamocortical component remained unchanged across all animal groups. The optical signal exhibited no changes in amplitude or latency between groups, resembling the thalamocortical component of the SEP response. Permanent and extensive changes to housing conditions conferred no further enhancement to sensory function above that produced by the milder enrichment of regular handling and behavioural testing, a finding with implications for improvements in animal welfare through practical changes to animal husbandry.

Section snippets

Animals

Male Fischer-344 rats (F344/NHsd; n=31) were used and divided into three experimental groups: non-enriched (Non-E), minimally-enriched (Min-E) and maximally-enriched (Max-E). Animals in the Min-E and Max-E groups were supplied by Harlan (Bicester, UK) at 28-days of age (n=12 in each group) whereas animals in the Non-E group were supplied at 12 months of age (n=7) and only housed briefly before being used in the VSDI/SEP study. As many countries now standardise husbandry and housing conditions

Results

Optical signals evoked by whisker deflection exhibited rapid rise time and gradual decay in all experimental groups; Fig. 1 shows the average spread of activity in Non-E and Max-E groups in response to a single stimulus. Maximal activity in the stimulated barrel in response to the single stimulus was reached by 9.67±1.5 ms (±SD) in the Non-E group, similar to that in Min-E and Max-E groups: 9.67±1.5 ms and 10.0±1.3 ms. Latencies increased slightly with low- and high-frequency stimulation

Discussion

Environmental enrichment has long been known to influence the anatomy and function of sensory systems. The current study is the first to examine how individual components of sensory-evoked cortical responses, each of which relate to specific neural generators, are individually affected. The main finding of the current study was the differential effect of enrichment on specific SEP waveforms, mainly in response to single whisker deflections but not to trains of stimuli. We also report unexpected

Acknowledgments

This work was funded by grants from the Arete Initiative at the University of Chicago, the Mind Science Foundation and the James Martin 21st Century School.

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