Spexin is a central modulator of nociception. The aim of the present study was to investigate the effect of intra-hippocampal CA3 (IHCA3) injection of spexin and spexin-progesterone co-administration on pain sensitivity in ovariectomized rat. Thirty-five adult female rats were divided into five groups. Sham: the animals received injection of 0.5 μL ACSF by IHCA3. Experiments 1 and 2: the animals received injection of 0.5 μL of spexin bilaterally (10 and 30 nmol/rat respectively). Experiments 3 and 4: the animals received injection of 0.5 μL of spexin bilaterally (10 and 30 nmol/rat respectively) + subcutaneous (s.c.) injection of progesterone (5 mg/kg). Ovariectomy was performed in all groups to eliminate the effects of cyclic changes in the female rats. The formalin test (formalin 2.5%) was performed following the administration of spexin and progesterone. Results showed that bilateral injection of spexin in IHCA3 at both concentrations a significant (P < .05) decrease in the pain sensitivity in the two phases of formalin test. Similarly, the bilateral injection of spexin in IHCA3 at both concentrations following the s.c. injection of progesterone significantly (P < .05) decreases pain sensitivity in two phases of the formalin test. This pain attenuation due to the co-administration of spexin and progesterone was more potent than spexin-induced analgesia. According to the present results, spexin has a modulatory effect on pain sensitivity, which becomes more pronounced by progesterone administration.

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Background Work in humans has shown that impulsivity can be advantageous in certain settings. However, evidence for so-called functional impulsivity is lacking in experimental animals. Aims This study investigated the contexts in which high impulsive (HI) rats show an advantage in performance compared with mid- (MI) and low impulsive (LI) rats. We also assessed the effects of dopaminergic and noradrenergic agents to investigate underlying neurotransmitter mechanisms. Methods We tested rats on a variable inter-trial interval (ITI) version of the 5-choice serial reaction time task (5CSRTT). Rats received systemic injections of methylphenidate (MPH, 1 mg/kg and 3 mg/kg), atomoxetine (ATO, 0.3 mg/kg and 1 mg/kg), amphetamine (AMPH, 0.2 mg/kg), the alpha-2a adrenoceptor antagonist atipamezole (ATI, 0.3 mg/kg) and the alpha-1 adrenoceptor agonist phenylephrine (PHEN, 1 mg/kg) prior to behavioural testing. Results Unlike LI rats, HI rats exhibited superior performance, earning more reinforcers, on short ITI trials, when the task required rapid responding. MPH, AMPH and ATI improved performance on short ITI trials and increased impulsivity in long ITI trials, recapitulating the behavioural profile of HI. In contrast, ATO and PHEN impaired performance on short ITI trials and decreased impulsivity, thus mimicking the behavioural profile of LI rats. The effects of ATO were greater on MI rats and LI rats. Conclusions These findings indicate that impulsivity can be advantageous when rapid focusing and actions are required, an effect that may depend on increased dopamine neurotransmission. Conversely, activation of the noradrenergic system, with ATO and PHEN, led to a general inhibition of responding.

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