Modulation of exteroceptive suppression periods in human jaw-closing muscles by subanaesthetic dose of propofol.

Exteroceptive suppression (ES) periods in human jaw-closing muscles can be conditioned by a wide range of somatosensory stimuli and cognitive states. The aim of this study was to examine the effects of subanaesthetic doses of midazolam, ketamine and propofol on the short latency (ES1) and long latency (ES2) reflex in the jaw-closing muscles. First, we tried to evaluate the various methodological criteria for ES recording. We then examined the effect of subanaesthetic doses of midazolam (0·035 mg kg(-1)), ketamine (0·30 mg kg(-1)) and propofol (0·35 mg kg(-1)) on these reflexes of recording left masseter and temporalis muscle. ES duration did not differ greatly in the present study, recorded with the correct adjustment of stimulating and recording conditions. None of the subanaesthetic doses of the agents influenced ES1, and no significant effects on ES2 were observed with midazolam and ketamine. However, significant inhibitory change was observed in ES2 with propofol. ES2 is thought to be mediated by afferents, which descend in the spinal trigeminal tract and connect with a polysynaptic chain of excitatory interneurones located in the lateral reticular formation. Our observations indicate that propofol is uniquely effective not only through involvement of the gamma-aminobutyric acid type A receptor, but also through a range of other effects.

Optical imaging of excitation propagation evoked by stimulation to the trigeminal caudalis.

The present study reports on a characteristic spatio-temporal propagation of differential fluorescent images in the rat brain stem slice by a high-speed optical imaging technique. Coronal or sagittal slices were stained with a voltage-sensitive dye RH-414, and the superficial layer of the trigeminal caudalis (Vc) was then electrically stimulated. The marginal layer and substantia gelatinosa showed larger rostrocaudal excitation than coronal, despite a lack of tract stimulation expansion in either direction. A perfusion of 0.5 micromol/l TTX, not 10 micromol/l CNQX suppressed these propagations. These findings suggest that the superficial layer of Vc has spatial differences in neuronal excitation propagation, as evidenced by morphological observations that dendrites in the superficial layers extend in the rostrocaudal direction.

Temporal and spatial distribution of Fos protein in the lumbar spinal dorsal horn neurons in the rat with chronic constriction injury to the sciatic nerve.

The temporal and spatial expression pattern of Fos protein in spinal dorsal horn neurons was examined by immunohistochemistry in rats with chronic constriction injury (CCI) to the sciatic nerve. In normal animals, a few Fos-immunoreactive (-IR) neurons were detected in the dorsal horn of the lumbar spinal cord. Following induction of CCI, a very large number of Fos-IR neurons appeared in the spinal dorsal horn, but a significant number of Fos-IR neurons were also observed in the contralateral dorsal horn where primary afferents of the injured sciatic nerve rarely project. Sham-operated animals also had a significant number of Fos-IR neurons in the dorsal horn bilaterally. The number of Fos-IR neurons reached its maximal level 1 day following placement of the ligatures (PO 1d). The ratio of the number of Fos-IR neurons in the ipsilateral dorsal horn to the contralateral dorsal horn, however, had its peak level 3 days following CCI (3.1-fold increase compared to the contralateral dorsal horn). The number of Fos-IR neurons in the dorsal horn gradually decreased, but increased again around PO 15d. On PO 30d, the number of Fos-IR neurons decreased and became comparable to that in normal animals. The present results indicate that the induction of Fos-IR neurons in the dorsal horn caused by CCI is biphasic and reaches its maximal level on PO 3d, near the time of hyperalgesia onset.

Involvement of GABA(A) receptor in modulation of jaw muscle activity evoked by mustard oil application to the rat temporomandibular joint.

The effect of intrathecal administration of the GABA(A) receptor antagonist bicuculline methylbromide on jaw muscle electromyographic (EMG) activity evoked by mustard oil injection into the rat temporomandibular joint was studied. Bicuculline given prior to mustard oil augmented the EMG activity evoked by mustard oil, and "rekindling" of EMG activity was induced by bicuculline given 30 min after mustard oil. These results suggest that central GABA(A) receptors modulate reflex responses to noxious craniofacial stimuli.

Postnatal development of central nociceptive mechanisms modulating jaw muscle activity in the rat.

Postnatal changes in the electromyographic (EMG) activity of jaw muscles evoked by mustard oil (MO) application into the rat temporomandibular joint region and the recurrence of increased jaw muscle activities after intravenous injection of naloxone were compared among 4, 6 and 8-week-old rats. In all the groups, MO application increased EMG activity on the ipsilateral side, however, 4-week old rats showed only a small increase in EMG activity on the contralateral side. The EMG activity on the contralateral side increased in an age-dependent manner. The recurrence of increased jaw muscle activity was not induced in 4-week old rats. These results suggest that a neural circuit for generating contralateral responses and mechanisms for central excitation are not established until after 4 weeks postnatally.

Sevoflurane and isoflurane reduce oxygen saturation in infants.

Volatile anesthetics are generally known to exert several influences on the respiratory system, but their direct effect on oxygen saturation as measured by pulse oximetry (SpO2) in infants remains unknown. In this study, 70 infants under 2 years of age who received general anesthesia were examined to determine the effects of several volatile anesthetics and nitrous oxide on SpO2. After endotracheal intubation, the subjects were ventilated using a Jackson-Rees circuit with oxygen, nitrous oxide, and either sevoflurane, enflurane, or isoflurane adjusted to twice the adult minimum alveolar concentration (MAC) for the agents when used in combination with 67% nitrous oxide. In all cases, the end-tidal carbon dioxide tension (PetCO2) was maintained within the same range (28-35 mm Hg). Significantly lower SpO2 values (paired t test, P < .05) were observed when the subjects were ventilated with oxygen, 67% nitrous oxide, and sevoflurane or isoflurane--but not with oxygen, 67% nitrous oxide, and enflurane--than when they were administered oxygen, 50% nitrous oxide, and the original concentration of each volatile anesthetic. These results suggest that sevoflurane and isoflurane have different effects from enflurane on gas exchange systems.

Electromagnetic interference of an external temporary pacemaker during maxillofacial and neck surgery.

Indirect inhibition of an external temporary pacemaker by electrocautery is reported. Before induction of general anesthesia for a hemimaxillectomy and radical neck dissection, a temporary transvenous demand pacemaker was inserted into a patient with a first-degree atrioventricular block and complete left bundle-branch block. Although we provided common precautions to prevent electromagnetic interference by electrocautery, pacing failure still occurred. It was thought to be caused by current dispersing from the active electrocautery electrode. This case suggests that occipital placement of the electrocautery ground plate should be considered during neck surgery in a patient requiring a temporary pacemaker.

A case of sinus arrest caused by opening the mouth under general anesthesia.

We report a case in which transient sinus arrest was observed under general anesthesia. This was associated with opening the mouth and was thought to be caused by a trigeminovagal reflex. The reflex was interrupted by blocking bilaterally the third division of trigeminal nerve.

Effects of maxillomandibular fixation on respiration.

The effects of maxillomandibular fixation (MMF) on respiration were studied by measuring pulmonary function in 27 healthy volunteer subjects and in six post-operative patients who underwent MMF after sagittal split ramus osteotomies. In addition, airflow resistance of the mouth was measured in seven healthy subjects under MMF. In the healthy subjects, the ratio of forced expiratory volume in one second to forced vital capacity and peak expiratory flow rate were reduced by 22.9% and 52.1%, respectively, after application of MMF, indicating the presence of respiratory obstruction, whereas the ratio of forced vital capacity to predicted forced vital capacity, an indicator of restrictive respiratory defects, was not significantly affected. The obstructive type of respiratory defect was found to be the result of increased airflow resistance with MMF. The decrease of forced expiratory volume was greater in all postoperative patients than in the healthy subjects. The results indicate that careful preoperative and postoperative airway management is essential for the safety of patients undergoing MMF for the treatment of oral and maxillofacial conditions.