INTRODUCTION Autonomic control of cardiac function is fundamental for the maintenance of circulatory homeostasis under changing environmental and behavioral conditions (Pardini et al., 1987). The intrinsic cardiac nervous system is principal in the maintenance of the adequate cardiac output, the power, the rate of contraction, and the volume of blood delivered to cardiac muscle thorough the coronary vasculatures (Armour and Ardell, 1994). For many years it has been thought that cardiac ganglia possess only cholinergic parasympathetic postganglionic neurons and serve as simple stations of transmission of inhibitory impulse to the heart (Mawe et al., 1996). However, recent morphological and physiological evidence indicates that the mammalian intrinsic cardiac nervous system contains afferent sensory (Ardell et al., 1991; Armour and Hopkins, 1990; Cheng et al., 1997), efferent sympathetic and parasympathetic postganglionic neurons (Horackova et al., 1996; Mawe et al., 1996; Randall et al., 1987), and a population of local circuit neurons that function to interconnect neurons within and between the separate aggregates of ganglia that form the various intrinsic cardiac ganglionated plexuses (Butler et al., 1990). These neurons might be unipolar, bipolar or multipolar in shape (Armour et al., 1997; Baptista and Kirby, 1997; Edwards et al., 1995; Xi et al., 1991) and possesses varied immunohistochemical properties (Singh et al., 1999). Functionally diverse cardiac ganglion neurons... [to full text]