Antinociceptive effect of stimulating the occipital or retrosplenial cortex in rats.
A role for the occipital or retrosplenial cortex in nociceptive processing has not been demonstrated yet, but connections from these cortices to brain structures involved in descending pain-inhibitory mechanisms were already demonstrated. This study demonstrated that the electrical stimulation of the occipital or retrosplenial cortex produces antinociception in the rat tail-flick and formalin tests. Bilateral lesions of the dorsolateral funiculus abolished the effect of cortical stimulation in the tail-flick test. Injection of glutamate into the same targets was also antinociceptive in the tail-flick test. No rats stimulated in the occipital or retrosplenial cortex showed any change in motor performance on the Rota-rod test, or had epileptiform changes in the EEG recording during or up to 3 hours after stimulation. The antinociception induced by occipital cortex stimulation persisted after neural block of the retrosplenial cortex. The effect of retrosplenial cortex stimulation also persisted after neural block of the occipital cortex. We conclude that stimulation of the occipital or retrosplenial cortex in rats leads to antinociception activating distinct descending pain-inhibitory mechanisms, and this is unlikely to result from a reduced motor performance or a postictal phenomenon.


CONCLUSIONS
This study presents evidence that stimulation of the retrosplenial or occipital cortex produces antinociception in rat models of acute pain. These findings enhance our understanding of the role of the cerebral cortex in control of pain.
Reis
Glaucia Melo
GM
Department of Pharmacology, Faculty of Medicine of Ribeirão Preto, University of Sao Paulo, Ribeirão Preto, SP, Brazil.
Dias
Quintino Moura
QM
Silveira
João Walter S
JW
Del Vecchio
Flavio
F
Garcia-Cairasco
Norberto
N
Prado
Wiliam A
WA
D000700:Analgesics / Q000008:administration & dosage*; D000818:Animals; D004599:Electric Stimulation Therapy / Q000379:methods*; D000431:Ethanol / Q000008:administration & dosage / Q000031:analogs & derivatives; D018698:Glutamic Acid / Q000494:pharmacology; D006179:Gyrus Cinguli / Q000187:drug effects / Q000502:physiology; D008297:Male; D009043:Motor Activity / Q000187:drug effects / Q000502:physiology; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology; D009434:Neural Pathways / Q000187:drug effects / Q000502:physiology; D009778:Occipital Lobe / Q000187:drug effects / Q000502:physiology*; D010146:Pain / Q000175:diagnosis*; D010147:Pain Measurement / Q000379:methods; D017288:Pain Threshold / Q000187:drug effects / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar
D000700:Analgesics; C062527:tribromoethanol; D000431:Ethanol; D018698:Glutamic Acid