Localisation and morphology of cocaine- and amphetamine-regulated transcript (CART) peptide immunoreactive neurons in rat amygdala

Cocaine- and amphetamine-regulated transcript (CART) is a recently discovered mRNA in rat brain, upregulated in the nucleus accumbens after administration of cocaine and amphetamine. All data until now suggest a widespread distribution of this mRNA in the brain and endocrine tissues. The aim of this study was to precisely map and describe this mRNA product - CART peptide immunoreactive (IR) neurons in rat amygdala (AMY) by using immunohistochemical methods. Distribution and density of CART -IR neurons in AMY was very different The greatest density was in the lateral nucleus (La) and basolateral nucleus (BL) of AMY, and in Anterior Amygdaloid Area (AAA), moderate was in the central nucleus (Ce) and a small density was in the cortical posterior nucleus (CoP). By analysing the morphology of CART IR neurons in AMY, we found that the greatest number (43.75%) of these neurons has a bipolar shape. About 15% of investigated CART IR neurons are "bitufted" neurons, while an equal percentage is of multipolar (12.5%) and of ovoid neurons (12.5%). CART-IR neurons of pyramidal shape are present in about 9%, while the smallest number is of triangular neurons (6.25%). The largest CART-IR neurons are in La and, neurons with the smallest long diameter are present in BL AMY Even if there is not any morphologically distinct CART-IR neuron type in rat AMY, these neurons mainly are small and oval in most of AMY nuclei where they are usually present. This suggests the functional role of a majority of CART IR neurons in rat AMY, especially in BL, as small interneurons. The small number of large neurons could be projection neurons.