Physiological interactions of the basic rest--activity cycle of the brain: pulsatile luteinizing hormone secretion as...

The hypothesis of the "basic rest--activity cycle" (BRAC) as an ultradian rhythm of CNS activity which integrates many somatic, visceral, and behavioral functions is supported by a variety of studies which demonstrate similar periodicities in the expression of a remarkable number of critical physiological systems. However, the existence of this BRAC has been supported primarily only by this similarity in cyclicity, and the argument in support of this potentially meaningful CNS oscillator is thus largely inferential. Since resolving consistent temporal relationships between a variety of these apparently otherwise unrelated rhythmic functions would strongly support the hypothesized existence of the BRAC, this article first presents methodology for reliable evaluation of these difficult to analyze interactions. Then, a relationship between rhythmic physical activity and pulsatile luteinizing hormone (LH) secretion is employed as a model interaction which allows analysis of the rhythmicity of the BRAC itself. This BRAC entrainment of pulsatile LH secretion is also utilized as a model to demonstrate how the BRAC may modulate the activity of various physiological functions via relatively direct mechanisms, secondary interactions, or entrainment of tissue with its own intrinsic pacemaker activity. The physiological function of the BRAC is discussed relative to this entrainment of pulsatile LH release.