Depolarization of trigeminal afferents induced by stimulation of brain-stem and peripheral nerves.

Abstract

1. In nembutalized cats the excitability of supraorbital (SO) and infraorbital (IO) primary afferents was tested by microelectrode stimulation within the trigeminal nuclei. SO excitability increased after conditioning stimulation of IO nerve, brain-stem throughout its extent and ipsi- and contralateral fore- and hindlimb nerves. The conditioning curves did not change in decerebrate preparations. 2. In decerebrate cats a negative slow potential (trigeminal dorsal root potential, TDRP) was recorded from the isolated sensory trigeminal root following stimulation of contralateral SO nerve, homolateral common radial trunk and brain-stem. 3. In nembutalized as in decerebrate cats, a single IO impulse induced in the trigeminal complex a focal synaptic potential (N1-N2-waves) followed by a prolonged (200 msec) slow potential (P-wave). P-waves were also produced by high frequency stimulation of the brain-stem reticular regions. They were positive laterally to the trigeminal nucleus and inverted along a line between nucleus and tract. The N-wave had maximal amplitude in the trigeminal nucleus and became positive at the level of its medial boundary. 4. Unit discharges in the trigeminal nucleus responding to IO volley and lemniscal potentials evoked by the same stimulus were depressed by reticular activation following a time course of over 100 msec. 5. The results suggest a process of primary afferent depolarization (PAD), of trigeminal fibers induced by stimulations of brain-stem, fore- and hind-limbs nerves and other trigeminal afferents in absence of forebrain and cortical structures.