Circadian rhythms of heart rate variability have been widely studied in recent years. However, most previous reports described such rhythms in terms of normalized units of the low- and high-frequency (LF and HF) spectral components. In this study, we analyzed circadian rhythms of spectral components in absolute units and found unexpected results in normal subjects as well as coronary heart disease (CHD) and congestive heart failure (CHF) patient groups. The results indicate that the notion of sympathovagal balance needs to be re-evaluated.

Hypoglossal nerve rootlets in the transverse medullary slice prepared from neonatal rats exhibit a bursting‘respiratory’rhythm that increases in frequency with CO2, presumably due to activation of chemosensitive cells such as the central chemoreceptors. Carbonic anhydrase is associated with areas of central chemoreception and we propose a hypothesis for its involvement in the chemoreception process. We tested this hypothesis by blocking its activity with acetazolamide in six slice preparations. However, the addition of 1 mM acetazolamide dissolved in dimethyl sulphoxide to the superfusing bathing solution produced no alteration in the bursting frequency response of the slice to CO2. We concluded that the chemoreception process producing the CO2 response of the superfused, transverse medullary slice does not involve carbonic anhydrase.

In the transverse medullary slice prepared from neonatal rats the hypoglossal nerve rootlets exhibit a bursting 'respiratory' rhythm as do neurones in the pre-B

Inspiratory activity on the left and right sides must be coordinated to be effective. We used cross-correlation to examine the hypothesis that the coordination of left and right medullary inspiratory neurones is produced by excitation from common sources and by midline-crossing excitatory connections among these neurones. In adult rats, a total of 185 contralateral pairs of inspiratory neurones (n=370) were recorded extracellularly, and classified, according to their firing pattern, as augmenting (n=262), constant (n=82) or decrementing (n=26). Of the 262 augmenting inspiratory neurones, 98 were classified as phrenic premotor neurones by cross-correlation with phrenic nerve discharge. The 185 cross-correlograms showed little evidence of common activation, or midline-crossing excitatory connections. Of the 45 cross-correlograms for pairs of augmenting neurones, only 4 (≅9%) indicated a common activation, and only one a monosynaptic connection. Of the 45 for pairs of augmenting and phrenic premotor neurones, only 9 (20%) showed a common activation, and only 2 a monosynaptic excitatory connection. Of the 19 pairs of phrenic premotor neurones, 5 from the same rat showed high-frequency oscillations, and 1 a monosynaptic excitatory connection. Cross-correlograms for pair combinations of other types of neurones also exhibited few features. We suggest that, in the adult rat, although both common activation and excitatory cross-connections exexist as a means for coordinating left and right ventral group inspiratory neurones to the same respiratory rhythm, they are insufficient to account for it.

This study was to observe the changes of the neuronal and inducible nitric oxidesynthase(nNOS ＆ iNOS) as well as their mRNAs in the rostral ventrolateral mudulla(RVLM) of stress-induced hypertensive rats before and after acupuncture, and thereby to infer the curative mechanism of acupuncture on hypertension. The result indicated that the systolic blood pressure(SBP) of stress group rats was increased significantly(P＜0.01), it was accompanied that the expression of nNOS in the RVLM, including the immunoreactive neuron number(P＜0.05), the optical density(OD)(P＜0.01), and the mRNA(P＜0.01) were obviously elevated, while those of iNOS(P＜0.05, P＜0.01 and P＜0.01) were evidently lowered in the stress-induced hypertensive rats. Electroacupuncture(EA) points at "Zusanli" (St.36) and "Lanwei"(Extra 37) on the same hindlimb were stimulated by an EA apparatus(Type G6805-2) with dense sparse wave(4-20Hz) and 4mA intensity. EA application could return the SBP(P＜0.05), and the changes on the expression of both nNOS and iNOS(P＜0.05, P＜0.01 and P＜0.01). These results suggest that the curative mechanism of acupuncture on stress-induced hypertension is related to the changes of nNOS and iNOS in the RVLM of rats