In contrast, the exercising animals showed over time significantly less exploration behavior (walking and rearing). A remarkable observation was that during the second half of the novelty exposure these rats showed a progressive increase in lying and resting/sleeping behavior (Droste et al., 2007 and Collins et al., 2009). We concluded that exercising rats are substantially quicker in assessing a new environment regarding its potential dangers (and

opportunities) and after this assessment has been made these animals return to their normal behavior for this time of the day (early morning) which is resting and sleeping. This rapid assessment capability in the physically active animals is most likely the result of enhanced cognitive abilities in combination with a reduced state of anxiety. These U0126 observations underscore the benefit of regular physical activity for boosting resilience. To obtain insight into the molecular mechanisms underlying

the behavioral changes brought about by regular physical exercise we investigated the role of the signaling molecules pERK1/2 and pMSK1/2 and the IEG product c-Fos after forced swimming. As a detailed survey of pERK1/2 and pMSK1/2 had never been undertaken before, we assessed the immuno-reactivity of these molecules in many nuclei throughout the brain focusing on those brain regions known to SP600125 be involved in the stress response. In control (sedentary) rats at baseline, the number of pERK1/2-positive (pERK+) neurons was very low in the neocortex, except for the moderate numbers found in the piriform cortex (Collins A. & Reul J.M.H.M, unpublished). At 15 min after the start of forced swimming (15 min,

25 C water) the number of pERK+ neurons had moderately to strongly increased in the cingulate, somatosensory, motor, perirhinal, (-)-p-Bromotetramisole Oxalate prelimbic and infralimbic cortex but not in the piriform cortex. Moderate to strong increases were observed in the lateral septal nucleus, nucleus accumbens, locus coeruleus and dorsal raphe nucleus whereas no effects or small effects were observed in the magnocellular and parvocellular neurons of the hypothalamic PVN, central, medial and lateral nucleus of the amygdala, globus pallidus, caudate putamen, and median raphe nucleus. In the hippocampus, as shown before (Gutierrez-Mecinas et al., 2011), strong increases in pERK+ neurons were selectively found in the dorsal blade of the dentate gyrus (Fig. 2) whereas no or only small increments were found in the ventral blade of the dentate gyrus, CA1, CA2 and CA3 (Collins A. & Reul J.M.H.M, unpublished). In the neocortex of sedentary rats, the number of pMSK1/2-positive (pMSK+) neurons (presenting as nuclear staining) was low under baseline conditions except in the piriform cortex where numbers were already high under these conditions.