Distribution of intrinsic cardiac neurons in whole-mount guinea pig atria identified by multiple neurochemical coding

Abstract

Functional data indicate that neurons in distinct regions of the heart exert preferential regional cardiac control. To date the regional distribution of specific types of neurons within the intrinsic cardiac nervous system remains unknown, as does their associations with distinct neurotransmitter and/or neuromodulatory profiles. This study was designed to ascertain: (1) the distribution of different classes of neurons within the intrinsic cardiac nervous system as determined by microscopic analysis; (2) the neurochemical profiles of neurons in differing atrial loci; (3) which neurochemicals are co-localized within specific populations of intrinsic cardiac neurons; and (4) the distribution of specific sub-populations of neurons expressing specific immunoreactivities. Taking advantage of confocal laser scanning microscopy and distinct immunoreactive fluorescent markers in various double-label combinations, several sub-populations of intrinsic cardiac neurons were identified. Of all identified neurons, 85-90% were located in ganglia (ganglionic neurons), the rest being isolated (individual neurons). The two general neuronal markers protein gene product 9.5 (PGP 9.5) and microtubule-associated protein (MAP-2) were associated with neurons clustered primarily in the interatrial septum and around the origins of the two vena cavae. Ganglia (group 1) contained three sub-populations of neurons: approx. 80% of ganglionic neurons were large (15-40 microm diameters; group 1a) and approx. 20% had smaller diameters (less than 15 microm; group 1b). All of these neurons were PGP-immunoreactive, exhibiting choline acetyltransferase (ChAT) immunoreactivity (IR), tyrosine hydroxylase (TH) IR, neuropeptide Y (NPY) IR, vasoactive peptide (VIP) IR and substance P (SP) IR. The remaining 5% of ganglionic neurons were small (group 1c; less than 20 microm). These displayed TH immunoreactivity but not MAP, PGP, CHAT, NPY or SP immunoreactivity. Ten to fifteen percent of all neurons loosely distributed outside of ganglia were small (10-25 microm) and located primarily around the origin of the superior vena cava. They displayed immunoreactivity to TH, ChAT, VIP, NPY and SP, but not to MAP-2 or PGP 9.5. These data provide anatomical and immunohistochemical evidence for specific localization of differing populations of intrinsic cardiac neurons with respect to their size, ganglionic distributions and capacity to express multiple neurotransmitters. Although the functional importance of such a regional distribution of differing populations of intrinsic cardiac neurons remains unknown, these anatomical data support the thesis that unique clustering of specific populations of neurons within this nervous system represents the anatomical substrate for complex local cardiac regulatory phenomena occurring at the level of the target organ.

Histopathology, ultrastructure and immunohistochemistry of Coregonus lavaretus hearts naturally infected with Ichthyocotylurus erraticus (Trematoda)

“…In vertebrates, the intrinsic cardiac nervous system exhibits a range of different morphological and immunohistochemical properties (Holmgren et al 1994, Horackova et al 1999, Kuncova et al 2003. Blood pressure and heart rate are regulated by circulating neuropeptides which involve the brain-cardiac axis (Xiang 1994, Matsumara et al 2003, Pedrazzini et al 2003 and by endogenous molecules synthesised by heart neurons (Lillywhite et al 1999).…”

Autonomic cardiac nerves: literature review

“…This is also confirmed by the results of a study by Hardwick et al [21], who found two types of neurons in the cardiac ganglia of guinea pigs: phasic, constituting about 95%, and tonic (the remaining 5%). Horackova et al [30] also found two morphological types of neurons: about 80% of large neurons, 15-40 µm in diameter, and about 20% of the so-called small neurons. Moreover, the authors demonstrated the presence of three cell subpopulations varying in neurochemical properties.…”

“…Immunohistochemical studies of Horackova et al [30] on the intracardiac ganglia of guinea pigs showed that ganglionic neurons can be divided into three subpopulations differentiated by size and the expression of various transmitters. About 80% of neurons located in ganglia had large diameters of up to 40 µm, and about 15% had small diameters below 15 µm.…”

“…In the Egyptian mouse, a plexoganglium on the dorsal side of the left ventricle, in the immediate vicinity of the interventricular groove, was found apart from atrial plexoganglia. Horackova et al [30] found cardiac ganglia in the guinea pig mostly in the atrial septum and around the openings of venae cavae to the right atrium; they contained 85-90% of neurons, while the rest were located individually. The results of studies by Singh et al [60] performed in the hearts of adult humans during autopsy or during transplantation procedures have shown that the largest populations of cardiac ganglia are near the sinoatrial and atrioventricular nodes.…”

“…There are reports of minimal numbers of adrenergic neurons in those ganglia [4,17,68]. Many authors suggest that ganglionic cardiac neurons are heterogeneous and include two main transmitter types: cholinergic and adrenergic [23,30,61,65].…”