Although the dentate gyrus (DG) as a component of the hippocampal formation has been well known for its role in memory, various studies showed a diverse population of unique cell types and various inputs and outputs in this region. Besides, brain
dopamine is known for its roles in reward, motivation, pleasure, and being involved in the
pain process. Further, previous studies demonstrated the participation of DG dopaminergic receptors in antinociception induced by lateral hypothalamus stimulation. This study aimed to investigate the role of DG dopaminergic receptors (D1- and D2-like
dopamine receptors) in stress-induced
analgesia (SIA) using the
formalin test as a persistent inflammatory
pain model. One hundred two male Wistar rats were unilaterally implanted with a
cannula into the DG. Animals received an intra-DG infusion of
SCH23390 (0.25, 1, and 4 μg/rat), or
Sulpiride (0.25, 1, and 4 μg/rat) as D1- and D2-like
dopamine receptor antagonists, respectively, five min before exposure to forced swim stress (FSS). Ten minutes after FSS termination, 2.5%
formalin solution as an inflammatory agent was subcutaneously injected into the plantar surface of the hind paw, and the
pain score was quantified for one hour. The findings revealed that exposure to FSS produced SIA, though this FSS-induced
analgesia was attenuated in the early and late phase of the
formalin test by intra-DG microinjection of
SCH23390 or
Sulpiride. These results suggested that both D1- and D2-like
dopamine receptors in the DG have a considerable role in
analgesia induced by FSS.