Dopamine D-2 receptors regulate unconditioned fear in deep layers of the superior colliculus and dorsal periaqueductal gray

Author(s)

Muthuraju, Sangu ^{[1, 2]} ; Talbot, Teddy ^{[2, 3]} ; Brandao, Marcus Lira ^{[1, 2]}

Affiliation

^[1] Univ Sao Paulo, FFCLRP, Lab Neuropsychopharmacol, BR-14049901 Ribeirao Preto, SP - Brazil

^[2] Inst Neurociencias & Comportamento, BR-14050000 Sao Paulo - Brazil

^[3] Univ Sao Paulo, Ribeirao Preto Sch Med, Dept Neurosci & Behav, BR-14049901 Ribeirao Preto, SP - Brazil

• Document type: Journal article
• Source: Behavioural Brain Research; v. 297, p. 116-123, JAN 15 2016.
• Web of Science Citations: 7

Abstract

Rationale: Electrical and chemical stimulation of the dorsal periaqueductal gray (dPAG), deep layers of the superior colliculus (dISC), and inferior colliculus (IC) causes freezing and escape behavior in rodents. Systemic injections of the selective dopamine D-2 receptor antagonist sulpiride increased the number of switch-off responses (SORs) to light and auditory evoked potentials in response to loud sounds. Dopamine D-2 receptor inhibition in the IC was shown to enhance unconditioned fear. Nevertheless, the role of dopamine receptors in the dISC and dPAG in the mediation of unconditioned fear has not yet been demonstrated. Objectives: The purpose of the present study was to characterize the effects of sulpiride injections (4 and 8 mu g/0.2 mu l) in the dISC and dPAG in rats that were subjected to unconditioned fear paradigms. Methods: Switch-off responses to light and exploratory behavior in the elevated plus maze were used to evaluate unconditioned fear in rats. Results: Intra-d1SC microinjections of sulpiride increased the number of SORs to light. Intra-d1SC and intra-dPAG injections of sulpiride reduced the number of entries into and time spent on the open arms and decreased end-arm exploration and head dipping in the elevated plus maze. Conclusion: These findings suggest that dopamine, through D-2 receptors in the dISC and dPAG, is involved in defense reactions that are organized in the midbrain tectum. (C) 2015 Elsevier B.V. All rights reserved. (AU)

• FAPESP's process: 11/00041-3 - Neurobiology of stress: the sensorimotor gating
• Grantee: Marcus Lira Brandão
• Support type: Research Projects - Thematic Grants
• FAPESP's process: 14/02000-0 - Characterization of the dopamine role in the mediation of distinct kinds of fear
• Grantee: Sangu Muthuraju
• Support type: Scholarships in Brazil - Post-Doctorate