title: Morphine administration during low ovarian hormone stage results in transient over expression of fear memories in females.
abstract: Acute exposure to morphine after a traumatic event reduces trauma related symptoms in humans and conditioned fear expression in male rats. We aimed to determine whether acute administration of morphine alters consolidation of fear learning and extinction. Male and female rats in proestrus and metaestrus (high and low ovarian hormones respectively) underwent fear conditioning and received saline or morphine (2.5 mg/kg s.c.). The next day they underwent extinction. Results showed increased freezing during extinction only in the morphine metaestrus group while morphine did not affect males or proestrus females. Recall of extinction was similar on all groups. On a second experiment, a subset of rats conditioned during metaestrus was administered morphine prior to extinction producing no effects. We then measured mu opioid receptor (MOR) expression in the amygdala and periaqueductal gray (PAG) at the end of extinction (day 2). In males and proestrus females, morphine caused an increase in MOR in the amygdala but no in the PAG. In metaestrus females, morphine did not change MOR expression in either structure. These data suggests that ovarian hormones may interact with MORs in the amygdala to transiently alter memory consolidation. Morphine given after trauma to females with low ovarian hormones might increase the recall of fear responses, making recovery harder.
authors.affiliation: School of Behavioral and Brain Sciences, Ponce Health Sciences University - Ponce Research Institute Ponce, Puerto Rico.
authors.forename: Emily M
authors.initials: EM
authors.lastname: Perez-Torres
authors.affiliation: Department of Biology, Pontifical Catholic University of Puerto Rico Ponce, Puerto Rico.
authors.forename: Dinah L
authors.initials: DL
authors.lastname: Ramos-Ortolaza
authors.affiliation: Department of Counseling and Psychological Services, Institute of Translational Research in Behavioral Sciences, University of Puerto Rico at Ponce Ponce, Puerto Rico.
authors.forename: Roberto
authors.initials: R
authors.lastname: Morales
authors.affiliation: Department of Pharmaceutical Science, Palm Beach Atlantic University West Palm Beach, FL, USA.
authors.forename: Edwin
authors.initials: E
authors.lastname: Santini
authors.affiliation: School of Behavioral and Brain Sciences, Ponce Health Sciences University - Ponce Research Institute Ponce, Puerto Rico ; Department of Counseling and Psychological Services, Institute of Translational Research in Behavioral Sciences, University of Puerto Rico at Ponce Ponce, Puerto Rico.
authors.forename: Efrain J
authors.initials: EJ
authors.lastname: Rios-Ruiz
authors.affiliation: School of Behavioral and Brain Sciences, Ponce Health Sciences University - Ponce Research Institute Ponce, Puerto Rico ; Basic Sciences Division, Physiology, Ponce Health Sciences University - Ponce Research Institute Ponce, Puerto Rico.
authors.forename: Annelyn
authors.initials: A
authors.lastname: Torres-Reveron
keywords: estrous cycle; fear conditioning; fear extinction; morphine; sex-differences; trauma