Inhibiting Progesterone Metabolism in the Hippocampus of Rats in Behavioral Estrus Decreases Anxiolytic Behaviors and Enhances E
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Cognitive, Affective, & Behavioral Neuroscience 2001, 1 (3), 287-296 Inhibiting progesterone metabolism in the hippocampus of rats in behavioral estrus decreases anxiolytic behaviors and enhances exploratory and antinociceptive behaviors MADELINE E. RHODES and CHERYL A. FRYE State University of New York, Albany, New York Blocking progesterone’s metabolism to 5a -pregnan-3a -ol-20-one (3a ,5a -THP) with finasteride, a 5a -reductase inhibitor, and effects on anxiolytic, exploratory, and antinociceptive behaviors of rats in behavioral estrus were examined. Rats in behavioral estrus received finasteride systemically (SC), to the hippocampus, or to control implant sites, the nucleus accumbens (NA) or ventral tegmental area (VTA), and were tested in horizontal crossing, open-field, elevated plus-maze, emergence, holeboard, social interaction, tailflick, pawlick, and defensive freezing tasks. Finasteride, SC or intrahippocampally, reduced 3a ,5a -THP in the hippocampus relative to vehicle implants or finasteride to the NA or VTA. Systemic or intrahippocampal finasteride decreasedcentral entries in the open field and open-arm time on the elevated plus-maze and increasedfreezing in response to shock relative to vehicle. Finasteride to the hippocampus decreased emergence latencies and increased social interaction, pawlick, and tail- flick latencies relative to all other groups. Finasteride to the hippocampus of rats in behavioral estrous decreased anxiolysis and enhanced exploration and analgesia. In summary, these data demonstrate that decreasesin anxiolytic behavior of behavioral estrous rats can be produced by reductions in 3a ,5a - THP in the hippocampus, which suggest that elevations in 3a ,5a -THP in the hippocampus may give rise to anxiolysis seen during behavioral estrus. There are sex differences, as well as differences across Guasti et al., 1999; Fernandez-Guasti & Picazo, 1990; the ovarian cycle, in rodents on performance in anxiety Frye et al., 2000). tasks and responsiveness to noxious stimuli. Neonatally Evidence suggests that progestins modulate sex and feminized male and female rats spend more time on the ovarian cycle differences in anxiety behavior and respon- open arms of the elevated plus-maze and exhibitless con- siveness to noxious stimuli in rodents. Ovariectomy of ditioned defensive burying, as adults, than do neonatally rats makes the anxiety and reactivity behaviorof females androgenized female or male rats (Fernandez-Guasti, more male typical. Ovariectomy reduces open-arm time Martinez-Mota, Estrada-Camarena, Contreras, & Lopez- of females in the elevated plus-maze and produces conflict Rubalcava,1999; Fernandez-Guasti & Picazo, 1990, 1999; behavior that is comparable to that of males (Fernandez- Johnston& File, 1991; Zimmerberg & Farley, 1993). The Guasti & Picazo, 1990; Rodriguez-Sierra, Howard, Pol- anxiety behavior of proestrous females tends to be most lard, & Hendricks, 1984). Progesterone administration to different from that of males, whereas the performance of ovariectomizedfemales significantly increases open-arm diestrous females is more male typical.Proestrous females time in the elevated plus-maze relative to that seen fol- spend more time on the open arms of the elevated plus- lowing vehicle administration(Bitran, Shiekh, & McLeod, maze than do diestrous female or male rats (Fernandez- 1995), produces a decrease in conditioned defensive Guasti et al., 1999; Frye, Petralia, & Rhodes, 2000; Mora, behavior (Martinez-Mota, Estrada-Camarena, Lopez- Dussaubat, & Diaz-Veliz, 1996; Vinogradova, 1999). Pro- Rubalcava, Contreras, & Fernandez-Guasti,2000), and fa- estrous females have a longer latency to commence bury- cilitates lickingof an electrified water source in the Geller- ing an electrified prod and, once initiated,they bury it for Siefter conflict test (Rodriguez-Sierra, Hagley, & less time than do diestrous female or male rats (Fernandez- Hendricks, 1986; Rodriguez-Sierra et al., 1984). These data suggestthat progestinscan have salient activationalef- fects on anxiety behavior and reactivity to noxiousstimuli. This research was supported by Grant 96-10 from The Whitehall Over the estrous cycle, progestin levels vary concomi- Foundation and by Grants 95-14463 and 98-96263 from the National tant with the occurrence of physiological changes within Science Foundation.The technical assistance provided by Melissa Nu- the hippocampus. There is increased physiological activ- bruegge, Zoe Orecki, Erik Rist, and April Smith is greatly appreciated. Correspondenceshouldbe addressed to C. A. Frye, Department of Psy- ity (Kawakami, Terasawa, & Ibuki, 1970), enhancedplas- chology,University of Albany–SUNY,1400 WashingtonAve., Albany, ticity (Terasawa & Timiras, 1968),facilitatedlong-term po- NY 12222 (e-mail: [email protected]). tentiation(Korol et al., 1994; Warren, Humphreys, Juraska, 287 Copyright 2001 Psychonomic Society, Inc. 288 RHODES AND FRYE & Greenough, 1995), and greater synaptic density (Gould, AP = -3.8, ML = ±2.0, DV = -2.0), the nucleus accumbens (NA; n = Woolley, Frankfurt, & McEwen, 1990) observed in the 13; from bregma AP= +1.7, ML= ±1.5, DV= -6.0), or the ventral tegmental area (VTA; n = 9; from bregma AP= -5.3, ML= ±0.4, DV = hippocampus during proestrus when estradiol and pro- - gesterone levels are increased relative to other phases of 7.0). Cannulae consisted of 23-ga thin wall stainless steel guide tub- ing with 30-ga removable inserts, made to extend 3 mm beyond the the cycle. end of the guide cannulae. Prior to behavioral testing, control inserts Progestins may have effects in the hippocampus to either were tamped in cholesterol or were left empty. Inserts for the mediate anxiety and responsiveness to noxious stimuli experimental condition were tamped in finasteride. Immediately prior in rodents. First, there is evidence to suggest that the 5a- to application, we verified that the inserts contained a 1-mg implant of reduced progesterone metabolite 5a-pregnan-3a-ol-20- finasteride by checking the mass of the filled insert and/or confirm- one (3a,5a-THP) may mediate performance on some ing, with a dissecting microscope, that the end of the insert was filled. anxiety tasks. Systemic administration of 3a,5a-THP to Determination of Behavioral Estrous both males and females produces a reduction in condi- Daily screening was performed on all rats between 0700 and tioned defensive burying (Fernandez-Guasti & Picazo, 0800 h to determine whether the rats were in behavioral estrus. The 1999). Second, administrationof progestins to the hippo- rats were placed in an arena with a male that was allowed to mount campus, or areas connected to the hippocampus,appears once. If lordosis was exhibited, the female was considered in behav- to be sufficient to increase anxiolyticbehaviorin rodents. ioral estrus. (Note that behavioral estrus, rather than examination of Injections of pregnanalone, a prohormone for 3a,5a- vaginal epithelium, was used as an indicator of hormonal status of the rats in order to reduce vaginocervical stimulation, which occurs when THP, to the hippocampus increase the amount of time collecting vaginal cytology of rats and which might have had an ef- spent in the open arms of the elevated plus-maze and de- fect on performance in the behavioral measures examined.) Once a crease both the latency to burial of an electrified prod female exhibited a consistent pattern of behavioral estrus every 4–5 and the duration of burying behavior (Bitran, Dugan, days, it was tested on the subsequent occurrence of behavioral estrus. Renda, Ellis, & Foley, 1999). Infusions of 3a,5a-THP to Each rat was tested in the complete battery of tests, described below, the central nucleus of the amygdala increase open-arm during one test session, on the day that it was in behavioral estrus. time in the elevated plus-maze and punished responding Behavioral Testing in the Geller-Seifter conflict test (Akwa, Purdy, Koob, & There is no single measure of anxiolytic behavior in rodents; Britton, 1999). Third, progesterone and 3a,5a-THP lev- therefore, a battery of tests, each of which are considered an index of els are increased in the hippocampus coincident with anxiety behavior, are often used in conjunction to examine factors that anxiety reduction and decreased defensive responses in influence anxiety behavior (Johnston & File, 1991; Pellow, Chopin, proestrous rats relative to females in other phases of the File, & Briley, 1985). The order in which these tests were adminis- tered was not counterbalanced; hence, the effects of one or more of cycle or male rodents. Proestrous females spend more time these tasks may have influenced the rats’ behavior on subsequent on the open arms of the elevated plus-maze and spend tasks. All rats were exposed to the tests in the same order, so any order less time freezing in response to shock from an electri- effects of the tests would be expected to be uniform across groups. fied prod than do females in other phases of the estrous The rats in behavioral estrus that had not undergone surgery (n = cycle or male rats (Frye et al., 2000). Together, these data 40) were randomly assigned to receive systemic vehicle (sesame oil, are consistent with the notion that proestrous changes in 0.2 cc SC, n = 18) or systemic finasteride (50 mg/kg SC, n =22)2h prior to behavioral testing. The rats that had chronic guide cannulae some anxiety and defensive behaviors may be influenced and were in behavioral estrus were randomly assigned to receive ve- by 3a,5a-THP levels in the hippocampus.