The contribution of the rostral ventromedial medulla to the antinociceptive effects of systemic morphine in restrained and unrestrained rats
| Autor: | D. Lowe, H.L. Fields, J.M. Mitchell |
|---|---|
| Rok vydání: | 1998 |
| Předmět: |
Male
Restraint Physical Tail medicine.medical_specialty Microinjections Central nervous system Neuropeptide Pain Rats Sprague-Dawley chemistry.chemical_compound Stress Physiological Internal medicine medicine Reaction Time Animals Cholecystokinin Pain Measurement Medulla Oblongata Morphine business.industry General Neuroscience Rats Analgesics Opioid Endocrinology medicine.anatomical_structure Nociception Muscimol chemistry Medulla oblongata Rostral ventromedial medulla business medicine.drug |
| Zdroj: | Neuroscience. 87(1) |
| ISSN: | 0306-4522 |
| Popis: | Although there are numerous opioid-sensitive structures in the central nervous system, the contribution of each to the analgesic effect of systemically administered morphine is controversial. One such structure is the rostral ventromedial medulla. In the present study, we tested the hypothesis that the rostral ventromedial medulla is necessary for the full expression of systemic morphine-induced antinociception. Additionally, we examined whether the modulatory effect of the rostral ventromedial medulla on tail-flick latency is dependent on the behavioral state of the animal. In unrestrained rats, inactivation of the rostral ventromedial medulla with either lidocaine (0.5 microl of 4%) or muscimol (50 ng) had no effect on tail-flick latency. In contrast, in restrained rats, inactivation of the rostral ventromedial medulla with either lidocaine (0.5 microl of 4%) or muscimol (50 ng) significantly decreased tail-flick latency. In both conditions, microinjection of morphine (5 microg) into this region significantly increased tail-flick latency. Additionally, in unrestrained rats, muscimol (50 ng) and cholecystokinin tetrapeptide (0.5 ng) infusion into the rostral ventromedial medulla completely reversed systemic morphine-induced analgesia, while lidocaine (0.5 microl of 4%) and cholecystokinin octapeptide (0.25 ng) infusion partially reversed systemic morphine-induced analgesia. These findings demonstrate that the rostral ventromedial medulla does not tonically modulate tail-flick latency in unrestrained rats, but does modulate tail-flick latency when animals are stressed via restraint. These findings also strongly support the hypothesis that the rostral ventromedial medulla is necessary for the full analgesic effects of systemically administered morphine. |
| Databáze: | OpenAIRE |
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