Pattern of catecholamine release in the nucleus tractus solitarii of the cat

The release of endogenous dopamine, noradrenaline and adrenaline was studied in the nucleus tractus solitarii (subnucleus medialis) of anaesthetized cats. Two push-pull cannulae were inserted into the right and left nuclei tractus solitarii which were simultaneously superfused with artificial cerebrospinal fluid. The release of the neurotransmitters was determined in the superfusates which were continuously collected in 10 min or 2.5 min time periods for 6 h or 2 h, respectively. Collection of the superfusates in time periods of 10 min showed that the release rates of endogenous dopamine, noradrenaline and adrenaline varied rhythmically according to an ultradian rhythm, the time interval between 2 adjacent phases of high release rate being approximately 1 h. Some of the phases of high release rates of the three endogenous catecholamines timely coincided with each other. Collection of the perfusates in time periods of 2.5 min revealed the existence of additional oscillations with a frequency of about 1 cycle/10 min for dopamine, noradrenaline and adrenaline. The findings suggest that catecholamines are released in the nucleus tractus solitarii according to an ultradian rhythm with low (1 cycle per h) and high (1 cycle per 10 min) frequencies, which might reflect the activity of catecholaminergic neurons in this brain structure.