Masahiro Ohta

Chaotic behavior in the Onchidium giant neuron under sinusoidal stimulation

Abstract The nonperiodic firing of the Onchidium giant neuron under sinusoidal stimulation is investigated. Attractors obtained stroboscopically show that state points on the attractor are mixed by the bakers transformation. The transition function with period three suggests that the nonperiodic oscillation is chaotic.

Amygdaloid and cortical facilitation or inhibition of trigeminal motoneurons in the rat

The effects of electrical stimulation of the rats contralateral frontal cortex as well as bilateral central amygdaloid nuclei were examined on the masseteric and mylohyoid-anterior digastric motoneurons which innervate a jaw closing muscle and jaw opening ones, respectively. Thirty-six percent of masseteric motoneurons were inhibited and 14% were facilitated by stimulation of the cortex and the central amygdaloid nucleus. Fifteen percent were inhibited or facilitated by either stimulation, although 36% were unaffected. No masseteric motoneuron was facilitated by one, stimulation and inhibited by the other. A majority of mylohyoid-digastric motoneurons were facilitated by stimulation of the cortex and the central amygdaloid nucleus although 17% were facilitated by either stimulation and 17% were unaffected. No mylohyoid-digastric motoneuron was inhibited. Therefore, the frontal cortex and the central amygdaloid nucleus have convergent control of jaw movements primarily in the opening direction.

C fiber generates a slow Na+ spike in the frog sciatic nerve

The present study was carried out to examine the properties of A and C fibers in the bullfrog sciatic nerves by applying several agents through perfusing solutions between stimulating and recording electrodes. The compound action potentials (CAPs) of A beta and A delta fibers were tetrodotoxin (TTX)-sensitive and were abolished in Na(+)-free solution. However, C fiber CAP was TTX-insensitive although CAP disappeared in Na(+)-free solution. Moreover, C fiber CAP was not blocked by Ca2+ channel blockers and its chronaxy (2 ms) and conduction velocity (0.70 m/s) indicate that the time constant of C fiber CAP is relatively large (2.88 ms). These suggest that a slow Na+ channel, which is TTX-resistant, contributes to C fiber action potentials.

Inhibitory pathway from the frontal cortex to the hypothalamic ventromedial nucleus in the rat

Stimulation of the dorsal frontal cortex (area 10, FCtx) evoked two negative waves with short latencies (N1 and N2) followed by a large, longlasting positive wave (P) in the ventromedial nucleus (VMH) as well as in the more dorsal structures in the hypothalamus and the ventral thalamus. Since the N1 followed high frequency stimulation, it was concluded to be due to antidromic activity. Double or triple pulse stimulation summated the P, and reduced the amplitude of the negative waves of the second and the third responses. VMH neuronal discharges were also decreased during the time course of the P. Therefore, the P was concluded to be composed of the IPSPs. VMH neuronal discharges were frequently superimposed on the N2, indicating the origin of this wave to be EPSPs. Strychnine reduced or blocked the inhibition of the VMH neurons caused by not only FCtx stimulation but also glycine application. The results indicate that the VMH receives both excitatory and inhibitory projections from the FCtx, and the inhibition may be transmitted by glycine.

Amygdaloid-induced jaw opening and facilitation or inhibition of the trigeminal motoneurons in the rat

1. Repetitive stimulation of the ratse central amygdaloid (CAm) nucleus induced rhythmic masticatory jaw movements or continuous jaw opening. Both types of jaw movements were accompanied by coincidental activities of the mylohyoid (Myl) nerve. 2. The effects of CAm stimulation were examined on activities of bilateral Myl and masseteric (Mass) nerves or their motoneurons (Myl-Dig and Mass, respectively). 3. CAm stimulation induced contralaterally dominant facilitation of the Myl nerve activity as well as Myl-Dig motoneurons. These facilitatory effects were caused by EPSPs seen in Myl-Dig motoneurons. 4. One third of the Mass motoneurons were inhibited or hyperpolarized by contralateral CAm stimulation, while a few were facilitated and the majority unaffected.

Amygdaloid or cortical facilitation of antidromic activity of trigeminal motoneurons in the rat.

1. Electrical stimulation of the rats contralateral central amygdaloid (CAm) nucleus or the contralateral frontal cortex markedly augmented the antidromic field potential evoked by stimulation of mylohyoid (Myl) nerve. 2. This facilitation was shown to be due to EPSPs of the mylohyoid-anterior digastric (Myl-Dig) motoneurons. 3. In a few motoneurons, cortical EPSPs had fixed short latencies following high-frequency double stimuli and this is believed to be due to a monosynaptic pathway. 4. The amygdaloid or cortically evoked EPSPs relieved IS-SD blockade in a few motoneurons and also facilitated antidromic discharge in others which did not show any IS or M spike response to the same subthreshold antidromic stimulation. The underlying mechanisms are discussed.

Cortical control of trigeminal motoneurons in the rat

Abstract 1. 1. Cortical influence on excitation of mylohyoid (Myl) and masseteric (Mass) nerves (Nn) and their motoneurons was studied in the rat. 2. 2. The frontal cortex excited a majority of the contralateral mylohyoid-digastric (c Myl-Dig) motoneurons, about a half of the ipsilateral (i) Myl-Dig motoneurons, about a third of c Mass motoneurons and the fewest i Mass motoneurons. 3. 3. A small number of c Mass motoneurons was considered to receive inhibitory influence since cortical stimulation inhibited antidromic activity and some of orthodromic activity. 4. 4. Stimulation of these motoneuron pool induced antidromic activity in the frontal cortex and a monosynaptic pathway is possible in the cortico-c Myl-Dig excitatory projection.

Evidence for the involvement of Na+-K+ pump and K+ conductance in the post-tetanic hyperpolarization of the tetrodotoxin-resistant C-fibers in the isolated bullfrog sciatic nerve

The post-tetanic hyperpolarizations (PTHPs) were recorded from the isolated bullfrog sciatic nerves using a modified vaseline gap method. Repetitive stimulation of tetrodotoxin-resistant (TTX-R) C-fibers produced frequency- and activity-dependent PTHPs. The ouabain solutions (0.1 mM), the solutions (0.1 mM ouabain + 2 mM tetraethylammonium (TEA)) and 5 mM TEA solutions reduced the PTHP amplitude to 56.2 +/- 10.7% (mean +/- SD, n = 9), to 37.0 +/- 12.3% (n = 8), to 76.0 +/- 10.9% (n = 5) of the control value, respectively. Each pair of the three solutions revealed a significant difference in their effects on the PTHP (P < 0.01). Furthermore, the Li-Ringer solutions and the solutions (Li-Ringer + 2 mM TEA) reduced the PTHP amplitude as well, thus resembling ouabain effects. These results strongly suggest that the repetitive stimulation of TTX-R C-fibers activates the membrane Na+-K+ pump resulting in a major part of the PTHP and induces TEA-sensitive K+ conductance composing a minor part of the PTHP, which might modulate repetitive firing of TTX-R C-fibers.

Tetrodotoxin-resistant Na+ spikes of C fibers have at least two subtypes in the isolated bullfrog sciatic nerve

The C fiber compound action potentials (C-CAPs) were studied for their properties with the vaseline gap method from the isolated bullfrog sciatic nerve. Two components (the fast and the slow C-CAPs) were found to be Na+ dependent and tetrodotoxin-resistant. The conduction velocities of the fast and the slow C-CAPs were 0.61 +/- 0.06 m/s (n = 13) and 0.42 +/- 0.05 m/s (n = 8), respectively; their time constants were 11.4 +/- 1.7 m/s and 16.3 +/- 1/7 ms, respectively, with both parameters being significantly different at P < 0.01. The slow C-CAP had about 1.3 times higher threshold than that of the fast C-CAP, with a significant difference (P < 0.01). They showed differential sensitivity to lidocaine and Cd2+. Capsaicin reduced the amplitudes of both fast and slow C-CAPs, but not abolished. These findings indicate that C fibers have at least two subtypes with different properties.

Haloperidol blocks an alpha adrenergic receptor in the reticulo-cortical inhibitory input.

Abstract The reticular inhibition of I waves of the pyramidal tract response was significantly reduced by haloperiodol, applied topically to the cortical surface, at a higher concentration than that used to block dopamine receptors preferentially. The blocking activity of haloperiodol was much weaker than that of alpha adrenergic blocker, phentolamine or phenoxybenzamine. The reticulo-cortical facilitation was unaffected by any of these agents. The results suggest that the reticulo-cortical inhibition may be mediated by noradrenaline and receptor sites are distributed in the cerebral cortex.