164 DEPRESSIVE-LIKE BEHAVIOUR IN NEUROPATHIC PAIN IS ASSOCIATED WITH DECREASED GLIAL AND NEURONAL CELLS IN THE PREFRONTAL CORTEX OF THE RAT

Abstract

Depression is commonly observed in patients with chronic pain. Pain can be divided into a sensitive and emotional component processed by different neural circuitries; the emotional component is largely modulated by the structures within the limbic system. The consolidation of pain-related aversive behaviours is attributed to the anterior cingulated cortex, where it has been showed that decreased glial cell density is associated with the development of depressive-like behaviour in stressed animals. Our aim was to investigate the possibility of an association between alterations in cell density in the prefrontal cortex (PFC) and depressive-like behaviour in neuropathic rats. One and two months after inducing spared nerve injury (SNI), neuropathic animals were tested for the presence of depressive-like behaviour (forced-swimming test) and evaluation of locomotor activity (open field test). Stereological analysis of the PFC considered three major areas, the cingulated I (CgI), the pre-limbic (PrL) and the infralimbic (IL) cortices, which were subdivided in three cortical areas, for quantification. The development of depressive-like behaviour was paralleled by a decrease in the number of glial cells in layer II (external granular layer) of the CgI, PrL and IL. Moreover there was a specific decrease in neurone numbers in IL layer II. These data indicate that alterations of glial and neuronal cell content in the PFC contribute to the development of depressive-like behaviour.