Kynurenate in the pontine reticular formation inhibits acoustic and trigeminal nucleus-evoked startle, but not vestibular nucleus-evoked startle.
The startle reflex is elicited by acoustic, trigeminal or vestibular stimulation, or by combinations of these stimuli. Acoustic startle is mediated largely by ibotenate-sensitive neurons in the ventrocaudal pontine reticular formation (PnC). In these studies we tested whether startle elicited by stimulation of different modalities is affected by infusion of the non-selective glutamate antagonist, kynurenate, into the PnC. In awake rats, startle responses evoked by either acoustic or spinal trigeminal nucleus stimulation were inhibited by kynurenate, but not saline, infusions, with the most effective placements nearest PnC. In chloral hydrate-anesthetized rats, kynurenate in the PnC reduced trigeminal nucleus-evoked hindlimb EMG responses, but not vestibular nucleus-evoked startle. Kynurenate in the vestibular nucleus had no effect on trigeminal nucleus-evoked startle. These results indicate that trigeminal nucleus stimulation evokes startle largely through glutamate receptors in the PnC, similarly to acoustic startle, but vestibular nucleus-evoked startle is mediated through other pathways, such as the vestibulospinal tract.
Steidl
S
S
Departments of Psychology and Zoology, University of Toronto, Toronto, Ontario, Canada M5S 3G3.
Faerman
P
P
Li
L
L
Yeomans
J S
JS
D000818:Animals; D004576:Electromyography; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology*; D007736:Kynurenic Acid / Q000494:pharmacology*; D008297:Male; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology; D011149:Pons / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D017470:Receptors, Glutamate / Q000502:physiology; D013216:Reflex, Startle / Q000187:drug effects* / Q000502:physiology; D012154:Reticular Formation / Q000187:drug effects / Q000502:physiology*; D014279:Trigeminal Nucleus, Spinal / Q000187:drug effects / Q000502:physiology*; D014726:Vestibular Nuclei / Q000187:drug effects / Q000502:physiology*
D018691:Excitatory Amino Acid Antagonists; D017470:Receptors, Glutamate; D007736:Kynurenic Acid