The role of the paratrigeminal nucleus in the pressor response to sciatic nerve stimulation in the rat.
The paratrigeminal nucleus (Pa5), an input site for spinal, trigeminal, vagus and glossopharyngeal afferents, is a recognized site for orofacial nociceptive sensory processing. It has efferent connections to brain structures associated with nociception and cardiorespiratory functions. This study aimed at determining the function of the Pa5 on the cardiovascular component of the somatosensory reflex (SSR) to sciatic nerve stimulation (SNS) in paralyzed and artificially-ventilated rats following Pa5 chemical lesions (ibotenic acid), synaptic transmission blockade (CoCl(2)), local anaesthetics (lidocaine) or desensitization of primary afferent fibers (capsaicin). The pressor response to sciatic nerve stimulation at 0.6 mA and 20 Hz (14+/-1 mm Hg) was strongly attenuated by contra- (-80%) or bilateral (-50%) paratrigeminal nucleus lesions. Ipsilateral Pa5 lesions only attenuated the response to 0.1 mA, 20 Hz SNS (-55%). Cobalt chloride or lidocaine injected in the contralateral paratrigeminal nucleus also attenuated the SSR. In capsaicin-treated animals, the pressor responses to 0.1 mA were abolished, whereas the responses to SNS at 0.6 mA were increased from 65 to 100% depending on the stimulus frequency. The paratrigeminal nucleus receives both, excitatory and inhibitory components; the later apparently involving capsaicin-sensitive fiber inputs mostly to the ipsilateral site whereas the capsaicin insensitive excitatory components that respond to high or low frequency stimulation, respectively, target the contralateral and ipsilateral sites. Thus, the paratrigeminal nucleus mediates excitatory and inhibitory components of the somatosensory reflex, representing a primary synapse site in the brain for nociceptive inputs from the sciatic innervation field.
Caous
Cristofer André
CA
Instituto Israelita de Ensino e Pesquisa Albert Einstein, São Paulo, SP, Brazil. ccaous@biofis.epm.br
Koepp
Janice
J
Couture
Réjean
R
Balan
Antonio Claudir
AC
Lindsey
Charles Julian
CJ
D000344:Afferent Pathways / Q000502:physiology*; D000818:Animals; D001794:Blood Pressure / Q000502:physiology*; D002211:Capsaicin / Q000494:pharmacology; D003714:Denervation; D004558:Electric Stimulation; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D007839:Functional Laterality / Q000502:physiology; D018836:Inflammation Mediators / Q000494:pharmacology; D008297:Male; D008526:Medulla Oblongata / Q000033:anatomy & histology / Q000502:physiology*; D009433:Neural Inhibition / Q000502:physiology; D009619:Nociceptors / Q000502:physiology*; D010146:Pain / Q000503:physiopathology; D017729:Presynaptic Terminals / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D012018:Reflex / Q000502:physiology; D012584:Sciatic Nerve / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology; D014279:Trigeminal Nucleus, Spinal / Q000033:anatomy & histology / Q000502:physiology*; D014661:Vasoconstriction / Q000502:physiology
D018836:Inflammation Mediators; D002211:Capsaicin