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  • Title: Conditioning stimulation of the central amygdaloid nucleus inhibits the jaw-opening reflex in the cat.
    Author: Kowada K, Kawarada K, Matsumoto N.
    Journal: Jpn J Physiol; 1992; 42(3):443-58. PubMed ID: 1359177.
    Abstract:
    To elucidate a function of the central amygdaloid nucleus (ACE) in the trigeminal system, the ACE conditioning effect on the jaw-opening reflex (JOR) regarded as a nociceptive reflex was investigated in the cat anesthetized with pentobarbital sodium. The JOR to molar tooth pulp stimulation with an intensity 1.2-1.5 times the threshold was recorded in the ipsilateral digastric muscle. As conditioning stimulation, a train of 33 rectangular pulses (0.5 ms in duration) at 330 Hz with an intensity of 300 microA was applied to the ipsilateral ACE. The conditioning stimulation inhibited a JOR that had a latency of 7.90 +/- 0.88 ms (n = 36). The inhibition was maximum (83.1 +/- 11.2%) at a conditioning-test (C-T) interval of 110 ms and continued for C-T intervals of up to 1,000 ms. Likewise, microinjection of 0.5 M monosodium glutamate (10 microliters) into the ACE-inhibited the JOR for approximately 10 min. Additionally, the ACE conditioning stimulation inhibited the JOR induced by the stimulation of the sensory trigeminal nuclear complex in a similar manner, but not the jaw-opening response induced by the stimulation of the trigeminal motor nucleus (Mo V). Also, the conditioning stimulation influenced neither the evoked potentials induced by the tooth pulp stimulation at the main sensory and rostral nuclei nor the jaw-closing reflex induced by the stimulation of the mesencephalic trigeminal nucleus (Mes V). These results suggest that the excitation of the cell bodies in the ACE exerts an inhibitory modulation on the JOR with no effect on the non-nociceptive reflex such as the jaw-closing reflex at the level of Mo V.
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