Role of the spinal trigeminal nucleus in the rat autonomic reflex

Spectral Analysis of Heart Rate Variability During Trigger-Point Acupuncture of Various Muscles

Objective: The aim of this research was to clarify changes in cardiovascular autonomic nervous system function due to trigger-point (TP) acupuncture; the current author evaluated differences in responses among acupuncture at TPs of various muscles using spectral analysis of heart rate variability. Materials and Methods: Subjects were 48 healthy men. Before measurements began, subjects were assigned to a TP acupuncture or control group based on presence/absence of referred pain on applying pressure to a taut band within the right extensor digitorum muscle, tibialis anterior muscle, gluteus medius muscle, or masseter muscle. Measurements were conducted in a room with a temperature of 25°C, with subjects in a long sitting position after 10 minutes of rest. Acupuncture needles were retained for 10 minutes at 1 site on the right extensor digitorum muscle, tibialis anterior muscle, gluteus medius muscle, or masseter muscle. Electrocardiography was performed simultaneously with respiratory-cycle measurements. Based on the R-R interval on the electrocardiograms, frequency analysis was performed, low-frequency (LF) and high-frequency (HF) components were extracted, and the ratio of LF to HF components (LF/HF) was evaluated. Results: All subjects in the TP acupuncture group showed a transient increase in the HF component, but no significant changes in heart rate (HR) or LF/HF. In the control group, no significant changes were observed in HR, HF component, or LF/HF. Conclusions: These data suggest that acupuncture stimulation of TPs of the right extensor digitorum muscle, tibialis anterior muscle, gluteus medius muscle, and masseter muscle increases parasympathetic nerve activity transiently.

Spectral Analysis of Heart Rate Variability during Trigger Point Acupuncture

Objectives

To clarify changes in the cardiovascular autonomic nervous system function due to trigger point acupuncture, we evaluated differences in responses between acupuncture at trigger points and those at other sites using spectral analysis of heart rate variability.

Methods

Subjects were 35 healthy men. Before measurements began the subjects were assigned to a trigger point acupuncture or control group based on the presence/absence of referred pain on applying pressure to a taut band within the right tibialis anterior muscle. The measurements were conducted in a room with a temperature of 25°C, with subjects in a long sitting position after 10 min rest. Acupuncture needles were retained for 10 min at two sites on the right tibialis anterior muscle. ECG was performed simultaneously with measurements of blood pressure and the respiratory cycle. Based on the R–R interval on the ECG, frequency analysis was performed, low-frequency (LF) and high-frequency (HF) components were extracted and the ratio of LF to HF components (LF/HF) was evaluated.

Results

The trigger point acupuncture group showed a transient decrease in heart rate and an increase in the HF component but no significant changes in LF/HF. In the control group, no significant changes were observed in heart rate, the HF component or LF/HF. There were no consistent changes in systolic or diastolic blood pressure in either group.

Conclusions

These data suggest that acupuncture stimulation of trigger points of the tibialis anterior muscle transiently increases parasympathetic nerve activity.

Reflex arc of the teeth clenching-induced pressor response in rats

Although "teeth clenching" induces pressor response, the reflex tracts of the response are unknown. In this study, dantrolene administration inhibited teeth clenching generated by electrical stimulation of the masseter muscles and completely abolished the pressor response. In addition, trigeminal ganglion block or hexamethonium administration completely abolished the pressor response. Local anesthesia of molar regions significantly reduced the pressor response to 27 ± 10%. Gadolinium (mechanoreceptor blocker of group III muscle afferents) entrapment in masticatory muscles also significantly reduced the pressor response to 62 ± 7%. Although atropine methyl nitrate administration did not change the pressor response, a significant dose-dependent augmentation of heart rate was observed. These results indicate that both periodontal membrane and mechanoreceptors in masticatory muscles are the receptors for the pressor response, and that the afferent and efferent pathways of the pressor response pass through the trigeminal afferent nerves and sympathetic nerves, respectively.

Rats subjected to chronic-intermittent hypoxia have increased density of noradrenergic terminals in the trigeminal sensory and motor nuclei

Rodents subjected to chronic intermittent hypoxia (CIH) are used to investigate the mechanisms underlying the consequences of the obstructive sleep apnea (OSA) syndrome. Following CIH, rats have an increased density of noradrenergic terminals in the hypoglossal motor nucleus which innervates lingual muscles that protect the upper airway from collapse in OSA patients. Here, we investigated whether such an increase also occurs in other brainstem nuclei. Six pairs of male Sprague-Dawley rats were exposed to CIH or sham treatment for 10h/day for 35 days, with O(2) level oscillating between 24% and 7% every 3min. Brainstem sections were immunohistochemically processed for dopamine-β-hydroxylase, a marker for norepinephrine. Noradrenergic terminal varicosities were counted in the center of the trigeminal motor nucleus (Mo5) and the interpolar part of the spinal trigeminal sensory nucleus (Sp5). In the Mo5, noradrenergic varicosities tended to be 9% more numerous in CIH- than sham-treated rats, and in the Sp5 they were 18% more numerous in CIH rats (184±9 vs. 156±8 per 100×100μm counting box; p=0.03, n=18 section pairs).These data suggest that CIH elicits sprouting of noradrenergic terminals in multiple motor and sensory regions of the lower brainstem. This may alter motor and cardiorespiratory outputs and the transmission of cardiorespiratory and motor reflexes in CIH rats and, by implication, in OSA patients.