Involvement of pre- and post-synaptic serotonergic receptors of dorsal raphe nucleus neural network in the control of the sweet-substance-induced analgesia in adult Rattus norvegicus (Rodentia, Muridae).
In order to investigate the effects of monoaminergic mechanisms of the dorsal raphe nucleus on the elaboration and control of sweet-substance-induced antinociception, male albino Wistar rats weighing 180-200 g received sucrose solution (250 g/L) for 14 days as their only source of liquid. After the chronic consumption of sucrose solution, each animal was pretreated with unilateral microinjection of methiothepin mesylate (5.0 microg/0.2 microL), or methysergide maleate (5.0 microg/0.2 microL) in the dorsal raphe nucleus. Each rat consumed an average of 15.6g sucrose/day. Their tail withdrawal latencies in the tail-flick test were measured immediately before and after this treatment. An analgesia index was calculated from the withdrawal latencies before and after the pharmacological treatment. The blockade of serotonergic receptor in the dorsal raphe nucleus with methysergide after the chronic intake of sucrose decreased the sweet-induced antinociception. However, microinjections of methiothepin in the dorsal raphe nucleus did not cause a similar effect on the tail-flick latencies after the chronic intake of sucrose solution, increasing the sweet-substance-induced analgesia. These results indicate the involvement of serotonin as a neurotransmitter in the sucrose-produced antinociception. Considering that the blockade of pre-synaptic serotonergic receptors of the neural networks of the dorsal raphe nucleus with methiothepin did not decrease the sweet-substance-induced antinociception, and the central blockade of post-synaptic serotonergic receptors decreased the sucrose-induced analgesia, the modulation of the release of serotonin in the neural substrate of the dorsal raphe nucleus seems to be crucial for the organization of this interesting antinociceptive process.
Miyase
Cátia Isumi
CI
Laboratório de Neuroanatomia e Neuropsicobiologia, Departamento de Farmacologia, Faculdade de Medicina de Ribeirão Preto da Universidade de São Paulo (FMRP-USP), Avenida dos Bandeirantes 3900, Ribeirão Preto (SP) 14049-900, Brazil.
Kishi
Renato
R
de Freitas
Renato Leonardo
RL
Paz
Denise Amorim
DA
Coimbra
Norberto Cysne
NC
D000698:Analgesia; D000818:Animals; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D008297:Male; D008719:Methiothepin / Q000494:pharmacology; D008784:Methysergide / Q000494:pharmacology; D008845:Microinjections / Q000379:methods; D009415:Nerve Net / Q000187:drug effects / Q000502:physiology*; D017288:Pain Threshold / Q000187:drug effects; D011903:Raphe Nuclei / Q000187:drug effects*; D051381:Rats; D017208:Rats, Wistar; D011985:Receptors, Serotonin / Q000187:drug effects / Q000502:physiology*; D012702:Serotonin Antagonists / Q000494:pharmacology; D013395:Sucrose / Q000494:pharmacology*; D013569:Synapses / Q000187:drug effects* / Q000502:physiology; D013997:Time Factors
D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D008719:Methiothepin; D013395:Sucrose; D008784:Methysergide