Original Paper Veterinarni Medicina, 53, 2008 (8): 434–444 434 A comparison of the distribution and morphology of ChAT-, VAChT-immunoreactive and AChE-positive neurons in the thoracolumbar and sacral spinal cord of the pig J. Calka 1 , M. Zalecki 1 , K. Wasowicz 1 , M.B. Arciszewski 2 , M. Lakomy 1 1 Faculty of Veterinary Medicine, University of Warmia and Mazury, Olsztyn, Poland 2 Faculty of Veterinary Medicine, University of Life Sciences, Lublin, Poland ABSTRACT: Present knowledge concerning the organization of cholinergic structures of the spinal cord has been derived primarily from studies on small laboratory animals, while there is a complete lack of information concerning its structure in the pig. In the present study we employed choline acetyltransferase (ChAT) and vesicular acetylcho- line transporter (VAChT) immunocytochemistry and acetylcholinesterase (AChE) histochemistry to identify the cholinergic neuronal population in the thoracolumbar and sacral spinal cord of the pig. The distribution of ChAT-, VAChT- and AChE-positive cells was found to be similar. Distinct groups of cholinergic neurons were observed in the gray matter of the ventral horn, intermediolateral nucleus, intermediomedial nucleus as well as individual stained cells were found in the area around the central canal and in the base of the dorsal horn. Double staining confirmed complete colocalization of ChAT with AChE in the ventral horn and intermediolateral nucleus although in the intermediomedial nucleus only 64% of the AChE-positive neurons expressed ChAT-immunoreactivity, indi- cating unique, region restricted, diversity of ChAT and AChE staining. Our results revealed details concerning spatial distribution and morphological features of the cholinergic neurons in the thoracolumbar and sacral spinal cord of the pig. We also found that the pattern of distribution of cholinergic neurons in the porcine spinal cord shows great similarity to the organization of the cholinergic system in other mammalian species studied. Keywords: porcine; cholinergic system; choline acetyltransferase; vesicular acetylcholine transporter; acetylcho- linesterase; central nervous system Distribution of acetylcholinesterase (AChE), the degradative enzyme for acetylcholine, has prima- rily enabled to describe the cholinergic neuronal network in the spinal cord of a number of spe- cies (Galabov, 1976; Galabov and Davidoff, 1976; Malatova, 1983; Satoh and Fibiger, 1985). Later de- velopment of immunocytochemistry for choline acetyltransferase (ChAT), the enzyme catalyzing the formation of acetylcholine, provided a commonly accepted specific marker of cholinergic structures within the nervous tissue (Fonnum, 1973). Recently, vesicular acetylcholine transporter (VAChT), an additional specific marker for cholinergic neurons, allowed the immunocytochemical identification of acetylcholine-containing neurons in the nervous system (Arvidsson et al., 1997). An immunocytochemical analysis revealed cy- toarchitectonics of the cholinergic system in spinal cords of several species: rat (Borges and Iversen, 1986; Ichikawa et al., 1997), mouse (Chan-Palay et al., 1982), guinea pig (Davidoff et al., 1989), rabbit (Kan et al., 1978), cat (Kimura et al., 1981) and humans (Muroishi et al., 2000; Oda and Nakanishi, 2000). Renewed interest in the structure and function of the spinal cholinergic neuronal system has been increased in recent years by the study associated with impairment of cholinergic functions. Indeed, a reduced activity of cholinergic motoneurons (Oda,