HOMEODYNAMICS VERSUS HOMEOSTASIS - PERIODICITIES SUPERIMPOSED ON NONLINEAR DYNAMIC SYMPATHETIC TONE GENERATED IN VENTRAL MEDULLA

Homeodynamics based on theories of complexity and chaos and its impact on mechanisms generating sympathetic activity are presented. Activity in rats cervical, lumbar and renal sympathetic nerves was analyzed. I n time domain glutamate stimulation of neurons within medullary periam bigual area (PAA) disturbed temporal pattern of respiratory-sympatheti c synchronization. Divalent calcium antagonists, Co2+ and Mg2+, blocke rs of synaptic transmission, uncoupled respiratory oscillator and symp athetic activity. PAA neurons act as an interphase between different s ubsets of respiratory neurons and bulbospinal sympathoexcitatory neuro ns in rostral ventrolateral medulla (RVLM). In frequency domain sympat hetic activity analyzed by FFT algorithm and power density spectra (PD S) exhibited periodicities at the range from 0.4 Hz to 7.5 Hz. Blocker s of synaptic transmission microinjected bilaterally into RVLM reduced total power exhibited in PDS to low level of magnitude generated in s pinal cord and increased total, yet non-synchronized sympathetic activ ity and arterial blood pressure. A two component hybrid model of gener ation of sympathetic activity was proposed: a tone-generating system c onfined mainly to intrinsic activity of RVLM pacemaker neurons respons ible for chaos-like discharges and a second component -neuronal circui ts superimposed on tone-generating neurons and shaping the pattern of PDS. Contribution of spinal cord oscillatory mechanism to overall powe r of sympathetic periodicities was discussed.