Kiichi Takeuchi

Three-dimensional direction and interrelationship of prisms in cuspal and cervical enamel of dog tooth.

The three‐dimensional architecture of enamel prisms was examined in cuspal enamel and compared with that in cervical enamel by light and electron microscopy as well as computer‐assisted reconstruction using the developing enamel of several dog teeth.

Postnatal development of excitation propagation in the trigeminal subnucleus caudalis evoked by afferent stimulation in mice

The postnatal development of nociceptive afferent activity expansion and its modulation features were examined in mice using an optical imaging technique. Developing mice (1-2 weeks old (N1-2 w), 3-4 weeks old (N3-4 w), 5-6 weeks old (N5-6 w) and 7-8 weeks old (N7-8 w)) and neonatally capsaicin-treated mice were used. The propagation of neuronal excitation was measured by changes in fluorescent intensity in horizontal brain stem slices evoked by electrical stimulation to the trigeminal spinal tract. A single-pulse stimulation evoked excitation propagation in the trigeminal caudalis (Vc). The propagation area was larger in N1-2 w than in N7-8 w, and no differences were observed between capsaicin-treated and naive mice in the same age groups. Repetitive stimulation (100 Hz, 30 pulses) elicited long-lasting and widespread excitation propagation. The excitation propagation area was significantly larger in N7-8 w than in N1-2 w, N3-4 w and N5-6 w. This propagation was suppressed by 5 microM L-703.606, an NK1-receptor antagonist, suggesting that the repetitive stimulation-elicited excitation may require substance-P releases. Morphological observations demonstrated that the neural network in the Vc had grown by postnatal week 5. These results suggest that nociceptive afferent activity co-operatively matures with development of the network structure in the Vc, and that a mechanism for prolonged increase in central excitability is established during a later postnatal period.

Repetitive afferent stimulation propagates excitation in the trigeminal caudalis.

&NA; A high‐speed optical imaging technique was employed for visualizing neuronal excitation propagation elicited by afferent stimulation in the mouse trigeminal caudalis (Vc) to clarify the central nociceptive modulation mechanism. Membrane depolarization evoked by a single‐pulse stimulation to the spinal trigeminal tract (Tr) was propagated rostrally to the Vc, which was suppressed by CNQX. This is consistent with our morphological observation that axons expand from theTr into theVc. A trained‐pulse (tetanus) stimulation to theTr evoked a broad, persistent excitation in the Vc, while MK‐801 suppressed it. Neonatally capsaicin‐treated mice maintained a single‐pulse response but a lacked tetanus‐evoked one.These indicated that prolonged depolarization elicited by repetitive stimulation is a prerequisite to C‐fiber excitation for activating the NMDA receptors.

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 μmol/l TTX, not 10 μmol/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.