α₂-Adrenoceptor-ir neurons’ density changes after single dose of clonidine and yohimbine administration in the hippocampus of male rat

ABSTRACT

Objective: Despite the important role of α₂-adrenoceptors in pain modulation processes, the impact of administration of α₂-adrenoceptor agonist and antagonist on the density of hippocampal α₂-adrenoceptor-immunoreactive neurons has not been investigated. Therefore, we aimed to determine the effect of single doses of clonidine and yohimbine on the density of α₂-adrenoceptor-immunoreactive neurons in rat hippocampus.

Materials and Methods: Adult male Wistar rats received a single dose of clonidine (0.7 mg/kg) alone or 5 min after intraperitoneal (1 mg/kg) and/or intracerebroventricular (5 µg/kg) injection of yohimbine. After histological processing, neurons with α₂-adrenoceptor immunoreactivity were identified and counted through immunohistochemical analysis of hippocampal regions.

Results: Clonidine slightly increased the number of α₂-adrenoceptor-immunoreactive neurons in the hippocampal subregions compared with the normal saline group. Intraperitoneal injection of yohimbine followed by injection of clonidine significantly increased the number of α₂-adrenoceptor-immunoreactive neurons in subregions cornu ammonis 1 (CA1) and cornu ammonis 3 (CA3). Intracerebroventricular injection of yohimbine after injection of clonidine significantly reduced the number of α₂-adrenoceptor-immunoreactive neurons in all hippocampal subregions.

Conclusion: The present study demonstrates that intraperitoneal administration of α₂-adrenoceptor agonist clonidine increases the density of α₂-adrenoceptor-immunoreactive neurons in rat hippocampus, while intracerebroventricular injection of yohimbine decreases the density of these neurons.

KEYWORDS:

• Clonidine
• yohimbine
• α₂-adrenoceptor
• hippocampus

Acknowledgments

We would like to express our gratitude to the Neuroscience Research Center for performing the histological evaluations. This study has been supported by a grant from the Department of Research and Technology, Golestan University of Medical Sciences, Iran.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

Department of Research and Technology, Golestan University of Medical Sciences, Iran [grant number 1394.91].