Reticular thalamic responses to nociceptive inputs in anesthetized rats.
The present study compares nociceptive responses of neurons in the reticular thalamic nucleus (RT) to those of the ventroposterior lateral nucleus (VPL). Extracellular single-unit activities of cells in the RT and VPL were recorded in anesthetized rats. Only units with identified tactile receptive fields in the forepaw or hindpaw were studied. In the first series of experiments, RT and VPL responses to pinching with a small artery clamp were tested with the rats under pentobarbital, urethane, ketamine, or halothane anesthesia. Under all types of anesthesia, many RT units were inhibited. Second, the specificity of the nociceptive response was tested by pinching and noxious heating of the unit's tactile receptive field. Of the 39 VPL units tested, 20 were excited by both types of noxious stimuli. In sharp contrast, of the 30 RT units tested, none were excited and 17 were inhibited. In a third series of experiments, low-intensity and beam-diffused CO(2) laser irradiation was used to activate peripheral nociceptive afferents. Wide-dynamic-range VPL units responded with short- and long-latency excitations. In contrast, RT units had short-latency excitation followed by long-latency inhibition. Nociceptive input inhibited RT units in less than 500 ms. We conclude that a significant portion of RT neurons were polysynaptically inhibited by nociceptive inputs. Since all the cells tested were excited by light tactile inputs, the somatosensory RT may serve in the role of a modality gate, which modifies (i.e. inhibits) tactile inputs while letting noxious inputs pass.
Yen
Chen-Tung
CT
Department of Zoology, National Taiwan University, #1, Sect. 4, Roosevelt Road, Taipei, 106 Taiwan, ROC. ctyen@ntu.edu.tw
Shaw
Fu-Zen
FZ
D000200:Action Potentials / Q000502:physiology; D000344:Afferent Pathways / Q000502:physiology; D000758:Anesthesia; D000778:Anesthetics, Dissociative / Q000494:pharmacology; D018685:Anesthetics, Inhalation / Q000494:pharmacology; D018686:Anesthetics, Intravenous / Q000494:pharmacology; D000818:Animals; D005552:Forelimb / Q000294:innervation; D006221:Halothane / Q000494:pharmacology; D006358:Hot Temperature / Q000009:adverse effects; D006993:Hypnotics and Sedatives / Q000494:pharmacology; D007266:Inhibition, Psychological; D020646:Intralaminar Thalamic Nuclei / Q000502:physiology*; D007649:Ketamine / Q000494:pharmacology; D028022:Low-Level Light Therapy / Q000009:adverse effects; D009474:Neurons / Q000502:physiology*; D009619:Nociceptors / Q000502:physiology*; D010146:Pain / Q000503:physiopathology; D010424:Pentobarbital / Q000494:pharmacology; D010812:Physical Stimulation; D051381:Rats; D011930:Reaction Time; D014520:Urethane / Q000494:pharmacology; D020651:Ventral Thalamic Nuclei / Q000502:physiology
D000778:Anesthetics, Dissociative; D018685:Anesthetics, Inhalation; D018686:Anesthetics, Intravenous; D006993:Hypnotics and Sedatives; D014520:Urethane; D007649:Ketamine; D010424:Pentobarbital; D006221:Halothane