Mother-offspring interaction begins before birth. The foetus is particularly vulnerable to environmental insults and stress. The body responds by releasing excess of the stress hormone cortisol, which acts on glucocorticoid receptors. Hippocampus in the brain is rich in glucocorticoid receptors and therefore susceptible to stress. The stress effects are reduced when the animals are placed under a model wooden pyramid. The present study was to first explore the effects of prenatal restraint-stress on the plasma corticosterone levels and the dendritic arborisation of CA3 pyramidal neurons in the hippocampus of the offspring. Further, to test whether the pyramid environment would alter these effects, as housing under a pyramid is known to reduce the stress effects, pregnant Sprague Dawley rats were restrained for 9 h per day from gestation day 7 until parturition in a wire-mesh restrainer. Plasma corticosterone levels were found to be significantly increased. In addition, there was a significant reduction in the apical and the basal total dendritic branching points and intersections of the CA3 hippocampal pyramidal neurons. The results thus suggest that, housing in the pyramid dramatically reduces prenatal stress effects in rats.
Changes in gut microbiota composition have been linked to anxiety behavior in rodents. However, the underlying neural circuitry linking microbiota and their metabolites to anxiety behavior remains unknown. Using male C57BL/6J germ-free (GF) mice, not exposed to live microbes, increased anxiety-related behavior was observed correlating with a significant increase in the immediate early c-Fos gene in the basolateral amygdala (BLA). This phenomenon coincided with increased intrinsic excitability and spontaneous synaptic activity of BLA pyramidal neurons associated with reduced small conductance calcium-activated potassium (SK) channel currents. Importantly, colonizing GF mice to live microbes or the microbial-derived metabolite indoles reverted SK channel activities in BLA pyramidal neurons and reduced the anxiety behavioral phenotype. These results are consistent with a molecular mechanism by which microbes and or microbial-derived indoles, regulate functional changes in the BLA neurons. Moreover, this microbe metabolite regulation of anxiety links these results to ancient evolutionarily conserved defense mechanisms associated with anxiety-related behaviors in mammals.