Expression and activity of cocaine- and amphetamine-regulated transcript peptide(1-39) in the rat

Cocaine- and amphetamine-regulated transcript (CART) peptide consists of a family of peptides. Expression of the peptide fragment CART(1-39) was explored in the rat using an antiserum directed against CART(1-39) of the short form of the human CART prohormone. CART(1-39)-immunoreactivity, herein referred to as irCART, was detected in the rat central and peripheral nervous tissues with a pattern similar to that labeled with the antiserum CART(55-102) or CART(79-102). For example, irCART cells were detected in the hypothalamus, pons, medulla oblongata, spinal cord, and adrenal medulla. In urethane-anesthetized rats, CART(1-39) (0.05 to 2 nmol) by intrathecal injection did not cause a significant change of blood pressure or heart rate, but potentiated the pressor effects of glutamate injected intrathecally. Lastly, the effect of CART(1-39) on intracellular calcium concentrations [Ca2+]i was assessed and compared to that caused by CART(55-102) in cultured rat cortical neurons using the microfluorimetric method. CART(1-39) (100 nM) induced two types of responses in a population of cortical neurons: 1) a slowly rising increase in [Ca2+]i superimposed with oscillations, and 2) a fast increase followed by a sustained increase of [Ca2+]i. CART(55-102) caused only a slowly rising increase in [Ca2+]i in cortical neurons. Our result shows that the expression pattern of irCART in the rat nervous system and the potentiating action of CART(1-39) on glutamate-induced pressor response is similar to that reported for CART(55-102); but the calcium mobilizing action of CART(1-39) differs from that of CART(55-102), suggesting the possible existence of multiple CART receptors coupled to different calcium signaling pathways.