We evoked changes in lower lip blood flow and systemic arterial blood pressure by electrically stimulating the central cut end of the lingual nerve in artificially ventilated, urethane-anesthetized, cervically vago-sympathectomized cats, rats, rabbits, and guinea pig. The systemic arterial blood pressure changes were species-dependent: increases in rat, consistent decreases in rabbit and guinea pig, and variable among individuals in cat. In cat and rabbit, lip blood flow increases, which occurred only ipsilaterally to the stimulated nerve and showed no statistically significant correlation with the systemic arterial blood pressure changes. In rat, the ipsilateral lip blood flow increase was markedly greater than the contralateral one, and although there was a significant correlation between each of them and the systemic arterial blood pressure changes, the ipsilateral increase presumably included an active vasodilatation. In guinea pig, lip blood flow decreased on both sides in proportion to the systemic arterial blood pressure reductions. Thus, species variability exists in the sympathetic-mediated systemic arterial blood pressure changes and parasympathetic-mediated lip blood flow responses themselves, and in the relationship between them.
Somatosensory evoked fields (SEFs) to electrical stimulation on the right and left sides of the lower lip were measured using magnetoencephalography and compared in the bilateral hemispheres of 31 healthy normal young and 29 healthy normal elderly subjects to evaluate age-related change in lip somatosensation. The initial peak of the response around 13 ms, designated as N13m, and the second peak of the response, designated as P21m, were investigated. The N13m response, which was detected in 22 of 62 hemispheres in young adults and 37 of 58 hemispheres in elderly adults, showed significantly prolonged latency and increased equivalent current dipole (ECD) moment in the elderly adults. The P21m response, which was detected in 56 of 62 hemispheres in young adults and in 52 of 58 hemispheres in elderly adults, showed longer peak latency in the elderly adults. No significant difference was found in the ECD moment for P21m, which suggests that aging affected the SEFs of the lip somatosensation, but the effects of aging on N13m and P21m differed. Prolonged latency and increased ECD moment of N13m might result from decreased peripheral conduction and increased cortical excitation system associated with aging. Therefore, the initial response component might be an objective parameter for investigating change in lip function with age.
To evaluate the localization of responses to stimulation of the periodontal mechanoreceptors in the primary somatosensory cortex, somatosensory evoked fields (SEFs) were measured for stimulation of the left mandibular canine and first molar using magnetoencephalography in 25 healthy subjects. Tactile stimulation used a handmade stimulus device which recorded the trigger at the moment of touching the teeth.SEFs for the canine and first molar were detected in 20 and 19 subjects, respectively. Both responses were detected in the bilateral hemispheres. The latency for the canine was 62.1 AE 12.9 ms in the ipsilateral hemisphere and 65.9 AE 14.8 ms in the contralateral hemisphere. The latency for the first molar was 47.4 AE 6.6 ms in the ipsilateral hemisphere and 47.8 AE 9.1 ms in the contralateral hemisphere. The latency for the first molar was significantly shorter than that for the canine. The equivalent current dipoles were estimated in the central sulcus and localized anteroinferiorly compared to the locations for the SEFs for the median nerve. No significant differences in three-dimensional coordinates were found between the canine and first molar. These findings demonstrate the precise location of the teeth within the orofacial representation area in the primary somatosensory cortex.
Elastic fibres are thought to be very important for the function of various organs including the temporomandibular joint (TMJ). The current study was designed to examine changes in the elastic fibres of the TMJ following discectomy. The TMJs of six rabbits were surgically exposed, and the disc removed with a scalpel. Three untreated and three sham-operated rabbits were used as controls. Complete TMJs were removed in three rabbits 1 month and in three rabbits 3 months after discectomy and processed for histochemical demonstration of elastic fibres. In the TMJ 1 month after discectomy, osteoarthritic changes and a significant increase in the numbers of elastic fibres were observed in the condyle and articular eminence. In the TMJs 3 months after discectomy, they tended to revert to the levels in the condyle and articular eminence of the control TMJs. Our results show that after experimental discectomy, elastic fibres very often appear initially in the condyle and articular eminence, but they are destined to disappear later. This information may improve our understanding of the consequences of removal of the disc in clinical practice.
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