The crown dimensions were compared between dp4 and M1 on the maxilla in Tupaia glis. Although the dp4 resembled the MI in pattern, the structure of the dp4 was more primitive than that of the Ml. The dp4 was 86.707% of the Ml in the module. The mean values of the crown dimensions were larger in the MI than in the dp4 and these differences were significant statistically except for the distal buccolingual diameter (DBL). The DBL was slightly larger in the dp4 than in the Ml, but the difference was not significant. More pronounced differences between these two teeth were found in the lingual mesiodistal diameter (LMD) and the mesial buccolingual diameter (MBL). This result could be explained by the differences in the development of the hypocone and the mesiobuccal stylar shelf.
The crown dimensions of the dp4 and the M1 on the mandible in Tupaia glis were measured. The dp4 resembled the M1 in pattern, although they were by no means identical. The dp4 was approximately 60 to 85 % of Ml in size, and it was more compressed in the buccolingual than in the mesiodistal direction. The relative size of the talonid was larger for the dp4 than for the Ml. This result may be correlated with an occlusal function.
The inhibitory effects of electrical stimulation of large myelinated afferents on spinal dorsal horn neurons were investigated. In rats anesthetized with thiamylal sodium, responses of 153 dorsal horn neurons to noxious heating or innocuous mechanical stimulation (light brushing) of the tail were recorded from the sacral and coccygeal levels of the spinal cord by extracellular microelectrodes. Of these neurons, 45 were low-threshold mechanoreceptive (LTM), 47 were nociceptive-specific (NS), and 61 were wide-dynamic-range (WDR) neurons. In 22.2% of the LTM neurons, responses to innocuous mechanical stimulation were inhibited by electrical stimulation of large myelinated afferents applied to the ipsilateral hindlimb for 5 min. This conditioning stimulation (large myelinated afferent stimulation, LMAS) also inhibited noxious heat responses in 19.2% of the NS neurons. The inhibitory effect of LMAS on WDR neurons was nonselective in that both responses to light brushing and noxious heating were inhibited. Of the WDR neurons, 27.3 % were inhibited by LMAS. These results indicate that inhibition produced by LMAS is exerted on all 3 classes of spinal dorsal horn neurons.