Effects of a liquid diet on the response properties of temporomandibular joint nociceptive neurons in the trigeminal subnucleus caudalis of growing rats.

OBJECTIVE: To investigate whether low mechanical loading on the temporomandibular joint (TMJ) when ingesting a liquid diet affects the response properties of neurons in the trigeminal spinal tract subnucleus caudalis (Sp5C) in growing rats. MATERIALS AND METHODS: Shortly after weaning, 2-week-old male rats were fed chow pellets (control) or a liquid diet (experimental). Firing activities of single sensory units were recorded from the Sp5C at 4, 5, 7, and 9 weeks. Neurons were functionally classified by their responsiveness to TMJ stimuli. The responses of Class II and III neurons to TMJ stimuli were investigated. RESULTS: In both neuron classes, the firing threshold in the experimental group was significantly lower than in the control group at all time points, but remained static in the control group throughout the experimental period, whereas it peaked in the experimental group at 4 weeks, decreased at 5 weeks, and remained stable thereafter until 9 weeks. Similarly, the initial firing frequency was significantly higher in the experimental group than in the control group, but remained static in the control group throughout the experimental period, whereas in the experimental group, it was at its lowest at 4 weeks, increased at 5 weeks, and stayed stable thereafter until 9 weeks. CONCLUSION: Differences in TMJ loading arising from variable diet consistency during growth may affect the functional characteristics of Sp5C neurons.

Invertase production of common storage moulds in food and feed grains as a possibility for rapid detection of Aspergillus flavus group and Aspergillus fumigatus.

Invertase production of grain storage moulds was studied. Aspergillus spp. and Penicillium spp. were grown in a sucrose based liquid medium, at 37 degrees C. The A. flavus group (A. flavus, A. parasiticus, A. nomius, A. oryzae) and A. fumigatus showed a fast growth and intense invertase activity, while other Aspergillus spp. and Penicillium spp. grew slower and produced less invertase. The pattern of accumulated reducing sugar after 20 and 48 h of incubation was characteristic to the species studied. From inoculation studies the detection limit was calculated as: 1-10 conidia of A. flavus group and A. fumigatus, as compared to 10(3)-10(4) for the other species studied. The method may be recommended as a rapid test for the detection of A. flavus group and A. fumigatus in food and feed grains.

Increased occlusal vertical dimension induces cortical plasticity in the rat face primary motor cortex.

Previous studies have demonstrated that functional plasticity in the primary motor cortex (M1) is related to motor-skill learning and changes in the environment. Increased occlusal vertical dimension (iOVD) may modulate mastication, such as in the masticatory cycle, and the firing properties of jaw-muscle spindles. However, little is known about the changes in motor representation within the face primary motor cortex (face-M1) after iOVD. The purpose of the present study was to determine the effect of iOVD on the face-M1 using intracortical microstimulation (ICMS). In an iOVD group, the maxillary molars were built-up by 2mm with acrylic. The electromyographic (EMG) activities from the left (LAD) and right (RAD) anterior digastric (AD), masseter and genioglossus (GG) muscles elicited by ICMS within the right face-M1 were recorded 1, 2 and 8 weeks after iOVD. IOVD was associated with a significant increase in the number of sites within the face-M1 from which ICMS evoked LAD and/or GG EMG activities, as well as a lateral shift in the center of gravity of the RAD and LAD muscles at 1 and 2 weeks, but not at 8 weeks. These findings suggest that a time-dependent neuroplastic change within the rat face-M1 occurs in association with iOVD. This may be related to the animal's ability to adapt to a change in the oral environment.