Pulsatile release of catecholamines in the hypothalamus of conscious rats

To investigate the patterns of catecholamine release in the brain, the hypothalamus of conscious, freely moving rats was superfused through a push-pull cannula with artificial cerebrospinal fluid and the catecholamines dopamine, noradrenaline and adrenaline were determined in the superfusate radioenzymatically. Superfusate was continuously collected in time periods of 20 min for at least 20 h. Dopamine, noradrenaline and adrenaline release rates fluctuated according to an ultradian rhythm with a frequency of 1 cycle/92 min (dopamine and noradrenaline) or 99 min (adrenaline). Additionally, the three catecholamines were released according to an ultradian rhythm with the following frequencies: noradrenaline and adrenaline 1 cycle/12 h, dopamine 1 cycle/8 h. The release rates of dopamine and adrenaline were similar during light and dark periods, while the release rate of noradrenaline in the dark period was slightly lower than that during the light period. It is concluded that in the hypothalamus of the conscious rat the release rates of dopamine, noradrenaline and adrenaline fluctuate according to two ultradian rhythms with different frequencies.