Daily injections alter spine density in rat medial prefrontal cortex

Apical dendrites of pyramidal neurons in medial prefrontal cortex are reorganized after chronic corticosterone treatment. In this study, we assessed the effects of chronic corticosterone administration on dendritic spines. Adult male rats received sc injections of either corticosterone or vehicle daily for 3 weeks or were left untreated. Layer II-III neurons in medial prefrontal cortex were stained using a Golgi-Cox procedure and spines were counted on the portions of apical dendrites where maximal corticosterone-induced dendritic changes occur. In vehicle- and corticosterone-treated rats, spine density proximal to the soma was increased relative to untreated rats, while spine density in the distal portion of the apical arbor was unchanged, suggesting that daily handling alone altered spine density. This stress-induced change in spine density likely reflects important functional changes in excitatory synaptic inputs in prefrontal cortex.