Blocking the dopaminergic receptors in the hippocampal dentate gyrus reduced the stress-induced analgesia in persistent inflammatory pain in the rat

D2-like dopamine receptors blockade within the dentate gyrus shows a greater effect on stress-induced analgesia in the tail-flick test compared to D1-like dopamine receptors

“…Prior studies, however, showed that stress is often considered a prominent nociceptioninvolved player and exposure to particularly acute stress can be associated with decreased pain perception (al'Absi et al, 2021). Similarly, prior studies confirmed that exposure to acute FSS attenuated nociceptive response, either in acute thermal pain or inflammatory pain models (Merdasi et al, 2022;Noursadeghi et al, 2022), and it is in line with the present study results, which showed acute FSS for 6 min reduced nociceptive response in the thermal acute pain model as well as inflammatory pain, via dopamine receptors.…”

“…SCH23390 hydrochloride (C17H18ClNO.HCl) as a selective D1R antagonist and (RS)-(±)-sulpiride (C15H23N3O4S) as a D2R antagonist were purchased from Tocris Bioscience, Bristol, United Kingdom. Following the product datasheets, SCH23390 was dissolved in the doses of 0.25, 1, and 4 µg/0.5 µl normal saline (pH 6.9), and sulpiride was dissolved in the doses of 0.25, 1, and 4 µg/µl dimethyl sulfoxide (DMSO) 12% (pH 6.7) (Merdasi et al ., 2022; Noursadeghi et al ., 2022). Additionally, either normal saline or DMSO 12%, as vehicles of SCH 23390 or sulpiride, respectively, were used in the vehicle control groups.…”

“…In this regard, previously, it has been declared that D1R and D2R within the nucleus accumbens (NAc) (Faramarzi et al ., 2016, 2021) and hippocampal CA1 (Abdi Dezfouli et al ., 2022) modulate acute stress-induced analgesia (SIA) in persistent inflammatory pain. In continuation, a formalin test, as an algogenic substance-induced inflammatory pain, was performed, and it was indicated that DA receptors also within the hippocampal DG play the same modulatory role in SIA (Merdasi et al ., 2022). Various neurobiological types of pain, however, exist, and early researches suggest that noxious inputs can alter the nociceptive system neurochemistry.…”

The modulatory role of dopamine receptors within the hippocampal cornu ammonis area 1 in stress-induced analgesia in an animal model of persistent inflammatory pain

“…On the other hand, VTA dopaminergic neurons project to the amygdala, NAc, prefrontal cortex, and hippocampus [for review, see (Douma and de Kloet, 2020)]. Dopamine receptors in the NAc (Noursadeghi et al , 2022) and DG region of the hippocampus (Merdasi et al , 2022), nicotinic acetylcholine receptors of the ventral hippocampus (Ghasemzadeh and Rezayof, 2015), and the cannabinoid CB1 receptors in the basolateral amygdala (Connell et al , 2006) participate in the SIA.…”

“…Besides, it has been reported that intraventral hippocampal microinjection of nicotine mediates the SIA in mice via activating nicotinic acetylcholine receptors (Ghasemzadeh and Rezayof, 2015). Recently, it has been shown that blocking the dopaminergic receptors in the DG region of the hippocampus reduces the SIA in persistent inflammatory pain in rats (Merdasi et al , 2022). Since the mesolimbic dopamine system is involved in the SIA, and the hippocampus, as a significant part of the mesolimbic system, participates in pain modulation induced by stress via dopamine receptors, it seems that dopamine receptors of the CA1 region of the hippocampus might also have a role in the SIA.…”