Functional-anatomical studies of neural control of heart rate in goldfish

Neural control of heart rate (HR) was investigated in goldfish, Carassius auratus, using electrical stimulation of the brain. Three types of HR response were evoked by stimulation: HR decreases during stimulation (type I); HR increases during stimulation (type II), and HR decreases during stimulation, followed by increased rates at the offset (type III). Type I bradycardias were evoked by stimulation of the preoptic area and diencephalon, specifically in the ventral thalamus-dorsal hypothalamus transitional area, and the region dorsal and medial to the nucleus glomerulosus. Additional sites were located above crossing tectobulbar fibers in the midbrain and in basolateral medullary reticular areas, motor nucleus of the vagus and caudalmost vagal roots. Type II tachycardias were evoked by stimulation of sites in the dorsal telencephalon, inferior lobes of the hypothalamus and dorsomedial region of the vagal lobes. Type III rebound tachycardias were evoked from sites dorsal and medial to the nucleus glomerulosus and in the inferior lobe of the hypothalamus. The location of cardioactive sites in the brain in goldfish is comparable to that in other vertebrates; however, these cardiac responses may be mediated by faciliatory or inhibitory pathways to the vagal motor nuclei rather than sympathetic cardiac nerves.