Monoaminergic innervation of the carotid sinus in mammals: a histochemical study.

The bifurcations of the common carotid arteries in the rabbit, cat, pig, rat and guinea pig were examined for the comparative structure and adrenergic innervation of the carotid sinus. The carotid sinus was poorly innervated in the cat, pig and guinea pig but densely innervated in the rabbit. No adrenergic innervation could be detected in the carotid arteries or carotid sinus of the rat. The relationship of adrenergic innervation to the tunica media also varies between species, penetration being pronounced in the pig, occasional in the cat and rabbit and very slight in the guinea pig. The arrangement of adrenergic nerve fibres is circular in the cat and pig, circular and plexiform in the guinea pig and spiral in the rabbit where an additional longitudinal plexus is present. The functional implications of species variations in innervation of the carotid sinus region in relation to cardiovascular control is discussed.