Male reproductive systems under chronic fluoxetine or trimipramine treatment

Physiology & Behavior, Vol. 59, No. 3,479-485, 1996 Copyright © 1996 Elsevier Science Inc. Printed in the USA. All rights reserved 0031-9384/96 $15.00 + .00

ELSEVIER

0031-9384(95)02088-D

Male Reproductive Systems Under Chronic Fluoxetine or Trimipramine Treatment G E O R G E T A Y L O R , *l M A R K BARDGETI',*]" JOHN C S E R N A N S K Y , t TERRY EARLY,:[: JOHN H A L L E R , t JEFF SCHERRER* A N D S H A R O N W O M A C K *

*Laboratory for Psychobiology, University of Missouri, St. Louis, MO 63121 USA, ~Department of Psychiatry, Washington University Medical School, St. Louis, MO 63110 USA, and JgDepartment of Psychiatry, University of Texas Medical School, Galveston, TX 77550 USA Received 2 January 1995 TAYLOR, G., M. BARDGETI', J. CSERNANSKY, T. EARLY, J. HALLER, J. SCHERRER AND S. WOMACK. Male reproductive systems under chronic fluoxetine or trimipramine treatment. PHYSIOL BEHAV 59(3) 479-485, 1996.--Adult male Long-Evans rats (n = 9 per group) received daily exposure for 4 weeks to fluoxetine (0.75 mg FLUOX/kg body weight) or trimipramine (1.6 mg TRIMI/kg body weight). Separate tests of copulation, sexual motivation, and intermale aggressive behaviors were used to evaluate functional changes during chronic exposure to either typical or atypical antidepressant drugs with more or less serotonin specificity. Circulating hormones, primary and secondary sex structures, and concentrations of dopamine (DA) and serotonin (5-HT) from mesolimbic tissue were assessed at necropsy. Results of tests with estrous females and untreated males revealed progressive disruption to sexual performance and aggressive responsiveness over time of treatment with TRIMI and, to a lesser extent, with FLUOX. By contrast, motivation, testosterone, and all measures of reproductive physiology were indistinguishable from controls. Ratios of transmitter metabolites relative to the parent compounds indicated similar reductions of 5-HT turnover with FLUOX and TRIMI. However, influences on DA turnover were significantly less with FLUOX than with TRIMI. Conclusions are that long-term intervention with antidepressant drugs may disrupt sociosexual exchanges without compromising male rats' interest in sexual contact or integrity of their reproductive physiology. Lessened disruption of sc¢iosexual behaviors with this regimen of chronic FLUOX treatment may be related to the greater selectivity on serotonin relative to dopamine turnover. Rat Copulation Dopamine Serotonin

Aggression Metabolism

Sexual

motivation

A FEATURE shared by medications used to treat depression is the specificity of their actions on neural pathways employing biogenic amine transmit~ers. Brain regions rich, particularly, in dopamine (DA) and serotonin (5-HT) also are intimately related to social behaviors (35,44), and it comes as no surprise that sexual dysfunction is a primary symptom of depression. Yet, chronic drug-induced modification of aminergic systems that gradually improves mood fails to improve sexual responsiveness (21,27). Indeed, laboratory evidence suggests prolonged exposure to antidepressant drugs suppresses copulation in previously sexually active animals (14,45). Extended drug treatment of depression is required because of the gradual onset of therapeutic effectiveness of the antidepres-

Steroids

Antidepressants

sants (24). The clear implication is for time-related neural changes that are translated slowly into functional changes during drug administration. Studies with animal models have confirmed markedly different initial and subsequent neural effects (4,32,34). Fluoxetine (FLUOX) is a premier representative of serotoninspecific reuptake inhibitor (SSRI) compounds (23). The more typical tricyclic antidepressants, of which trimipramine (TRIMI) is an example, promote a broader pattern of influence on monoamine transmitters (23,24). Results with drugs targeted at the serotonergic system have pointed to a special relation between rodent social behaviors and 5-HT (8). More accurately, the suggestion is of a subtle interaction between serotonergic and other aminergic systems (31) that

t Requests for reprints should be addressed to George T. Taylor, Ph.D., Professor, Laboratory for Psychobiology, University of Missouri-St. Louis, 8001 Natural Bridge Rd., S~E.Louis, MO 63121.

479

~0

TAYLOR ETAL.

underlies the special neurochemical relation with social behavior. The functional consequences of modifying this interaction may be revealed only during prolonged pharmacological manipulation. Changes in serotonergic transmission with long-term exposure to typical or atypical antidepressant agents are more uncertain than with acute administration (4,13). More important, perhaps, there is evidence of increasing interaction with dopamine (8,17,26). The suggestion is for a spreading of influence with extended intervention (12,18,30). Here, adult male rats injected daily for a month with FLUOX or TRIMI were employed to evaluate changes induced in social responding in relation to modification to serotonin and dopamine turnover in mesolimbic pathways. TRIMI was selected to represent the tricyclics because of its unique influence on serotonin with chronic exposure (20,32). Separate tests were used to assess copulatory performance, motivation to initiate sexual contact, and intermale aggressive responses over weeks of drug exposure. At necropsy structural (36) and endocrine contributions (5,43) to reproductive integrity were excised and analyzed, along with brain tissues from a primary projection area for the mesolimbic system, the olfactory tubercles (7). METHOD Animals and Housing The animals were sexually naive male rats (N = 27), 150-200 days old, of the Long-Evans strain housed individually in hanging wire cages, measuring 20 x 20 x 20 cm. In addition, females (n = 20) and another set of males (n = 20) of the same ages and strain as the experimental males were employed as "stimulus" animals in the behavior tests. Food and water were available ad lib throughout the experiment. Temperature (21 + I°C) and relative humidity (50%) were controlled automatically. Lighting was on a cycle of 12-h light and 12-h darkness, with lights off at 1400 h. Materials The metal and glass terrariums, each measuring 61.5 × 32.5 x 31 cm, used for behavioral observations have been described in detail previously (38). A single terrarium was used for testing aggression and sexual performance; the chamber for tests of motivation was two terrariums joined. End panels were removed to yield a double chamber with wire mesh floor under which sheets of filter paper (Fisher Scientific, St. Louis, MO) were placed for measuring urinary markings. Fluoxetine was donated generously by Eli Lilly & Co. (Indianapolis, IN), and trimipramine was purchased (Wyeth-Ayerst, Philadelphia, PA). Both substances were solubilized in 0.9% saline solution. Estrogen and progesterone (Sigma Chemical, St. Louis, MO) for inducing estrus in the ovariectomized females were suspended in oil.

days of each week during weeks 2-4. After a test session the apparatus was cleaned thoroughly with soap and water, and fresh bedding was added before the next pair was observed. Scheduling of sessions was counterbalanced within and between groups. Stimulus animals were, by necessity, paired with multiple subject males during the 3 weeks of behavior testing. However, care was taken that the same subject and stimulus animal were not paired more than once. Moreover, neither a subject male nor a stimulus animal was tested twice on the same day. Both injections and behavioral observations continued until the end of the study, and subject males were sacrificed 24 h after the final drug administration. A brief description for each method of data collection follows. Details can be found in the references cited for each method. Behavioral Measures Sexual performance was assessed (42) during pairings of a male with an OVX female induced to receptivity the day of a test session with SC injections of 100/xg estradiol benzoate and, 48 h later, 400 /zg progesterone 3 - 4 h prior to testing. A male was placed into the terrarium 5 min before the estrous female was introduced. Latencies to first intromission and frequencies of both intromissions and ejaculations were recorded during the 45-min sessions. We also measured the responses of the female to experimental and control males (1,39). Frequencies of female solicitations of the male and her rejections of his sexual approaches were tallied. Sexual motivation, or probability of actively searching and contacting a female, was evaluated apart from performance (1). Our test of sexual motivation uses a well-established paradigm (38) with estrous and nonestrous females in small wire cages at opposite ends of an apparatus. The male can move freely about the apparatus without the direct interactions with the females that confound assessment of the male's interest in making social contact. Motivation was quantified by relative time the male spent near the inaccessible estrous female and frequency of urinary markings in her proximity during a 20-min test session (1). Marks were quantified by counting squares (0.5 cm z) in which urine appeared on the filter sheets. Aggressive behavior was evaluated (40) in a terrarium during weekly 10-min sessions between a subject male and an untreated, unfamiliar male. The two animals were introduced into the terrarium simultaneously to avoid resident-intruder complexities (19). Frequencies of pushing, sideways kicking, aggressive grooming, aggressive posturing, and attack with biting (19) were totaled for a daily aggression score for each animal. As discussed earlier in detail (37), we prefer an aggressive score based on simple summation rather than assigning "weights" to the various aggression categories that requires speculating intentions of the rat.

Procedural Details Animals (n = 9 per group) received daily IP injections for 4 weeks of either fluoxetine (0.75 m g / k g body weight), trimipramine (1.6 mg/kg body weight), or only the vehicle (0.2 ml of 0.9% saline solution). These represent dosages at the lower end of ranges used in previous research (13,25), but they are within human therapeutic doses (6,33). Behavior tests began after a week of drug exposures. Separate settings were used to test sexual performance, sexual motivation, and intermale aggression with unfamiliar stimulus males and females. Observations were conducted Mondays through Fridays in experimental rooms away from the colony rooms. Every male was tested 60 min after an injection in three settings on separate

Physiological Measures Testosterone and corticosteroid were assayed from serum using methods previously published (38,40). At 24 h following the final injection, six males were selected at random from each group for physiological assessment. Animals were sacrificed by decapitation, and 2-3 ml trunk blood was collected, and serum was obtained from centrifugation of blood. Primary and secondary sex accessory organs representing targets of the steroids were examined at necropsy. Our interest was using multiple markers of the reproductive system to estimate drug influences on normal function (28) and to probe for indications of pathology (35). Structures were excised, and wet

5-HT AND MALE SOCIOSEXUAL FUNCTION

481

TABLE 1 MEANS + SEM OF SEXUAL PERFORMANCEPER SESSION OVER ALL WEEKS DURING TESTS OF ESTROUS FEMALES AND MALE RATS (n = 9 PER GROUP) WITH LONG-TERM ADMINISTRATION OF FLUOXETINE, TRIMIPRAMINE, OR VEHICLE ONLY Sexual Performance Group

Latency 1st Intromission*

Ejaculation Frequency*

1,2 ± 0.2 a

34.8 ± 2.2 a

12.2_+2.8 b 20.0 ± 4.2 c

11.0± 1.8b 5.6 ± 2.8 c

Controls

Fluoxetine Trimipramine

Sexual Motivation

lntromission Frequency*

Female Response

Proximity to Female (rain)

Urinary Marks

Solicitation of Male*

Aggressive Rejection*

3.2 ± 0.9 a

13.0±0.3

0.95:0.2 b 0.2 ± 0.1c

12.5±0.5 12.7 + 0.6

1 1 3 ± 17

64-1-3 a

5.4 ± 0.8 a

98± 14 112 ± 27

41 +3 b 30 ± 4c

1.6± 0.8 b 3.9 + 2.0ab

Presence or absence of an asterisk on each behavioral measure indicates results of the separate ANOVA for that measure. Superscript letters are used to indicate (read down columns) statistically reliable group differences (Tukey's HSD test, p < 0.05) for each measure achieving statistical significance.

weights were recorded for testes, epididymides, penis, seminal vesicles, bulbospongiosus muscles, and ventral prostate glands. Adrenal and pituitary glands also were examined and weighed. Concentrations of monoamines in olfactory tubercles were determined from HPLC methods already published (9). Olfactory tubercles represent a priimary projection area for the mesolimbic system (7) and, also, mz.y represent an unusually sensitive indicator of 5 - H T / D A interaction (35). Tissues were excised, frozen quickly in liquid nitro~en and maintained at - 7 0 ° C pending analyses. We used a Supelcosil LC-18-DB microbore column (particle size 5 /zM, 250 × 2.1 mm). The column was eluted at 0.5 ml per min, permitting neurochemicals to be separated and detected electrochemically at 0.40 V in a single run (9). Compounds detected included DA and its metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), and 5-HT and its metabolite, 5-hydroxyindoleacetic acid (5-HIAA).

Statistical Analyses Totals for behaviorall frequencies and latencies collapsed over all weeks were examined with one-way analyses of variance (ANOVA). Tukey's Honestly Significant Difference tests (HSD, p < 0.05) were used for post hoc, pairwise comparisons of mean group differences. Similar analyses were made of the physiological data obtained at necropsy. Wet weights of organs and glands were calculated as mg tissue per 100 g of body weight for the ANOVA. Circulating hormone titers were expressed as ng steroid/ml serum, and neurochemistry was c~dculated as ng per mg tissue weights. Ratios of each metabolite to its parent compounds were calculated by simple division. Behavioral data were examined, also, with 3 × 3 factorial ANOVA. Main factors were substance injected (TRIMI, FLUOX, or vehicle-only) and week of testing as

a repeated measure. Simple main effects were used to evaluate statistically significant ( p < 0.05) interactions. RESULTS TO provide a composite picture of the interactions of subject males with untreated stimulus males and estrous females, the initial data analyzed were the behavior totals. Summaries are reported in Tables 1 and 2 as group means _ SEM. Within-group analyses of the weekly behavior findings were used subsequently to assess behavioral shifts over the course of drug treatment. Results for sexual and intermale aggressive response frequencies are shown in Figs. 1 and 2. Results of the analyses of sociosexual behavior totals [range of F-values (2, 24) = 10.19-46.25, p < 0.05] revealed statistically reliable differences on all measures, with the notable exception of the measures of sexual motivation. Findings from the tests of sexual performance indicated that, compared to controls, animals in drug groups had longer latencies to first intromission and

.~4e| 30-

le

,...

....

TABLE 2 M E A N S ± SEM PER T E S T SESSION O F A G G R E S S I V E

RESPONSES OVER ALL WEEKS BY FLUOXETINE-, TRIMIPRAMINE-, OR VEHICLE-TREATED MALE RATS VS. UNTREATED MALE OPPONENTS lntermale Aggressiveness

it

Wk 2

Wk 3

leluoxetlne (/k) ~

Group

Subject Male*

Opponent Male*

Pair*

Controls Fluoxetine Trimipramine

25.9 + 0.7a 19.5 + 1.2b 19.5 + 0.9 b

23.9 + 0.7 a 17.2 + 1.4b 11.7 ± 0.9 ¢

49.8 + 1.2a 36.7 + 1.9t~ 31.2 ± 1.1c

Asterisks indicate statistical differences on a measure; superscript letters denote differences between groups on measures (read down columns) that achieved statistical significance (Tukey's HSD test, p < 0.05).

Wk 4

Week o f D r u g E x p o s u r e

Trtmpmmtne(A)

~

Coatrole0k)

" [] -- Fluoxetine (8) - • - TrJmpramine (S) - ~ -- Controls (S)

FIG. 1. Changes (means + SEM) in frequencies of aggressive (A) and sexual (S) responses beginning at week 2 and ending at week 4 of daily administration of fluoxetine (0.75 mg/kg b.wt.) or trimipramine (1.6 mg/kg b.wt.).

482

T A Y L O R E T AL.

75

o~

N

s~

I

Wk 2

I

Wk 3

Wk 4

Week of Drug Exposure

Jk

Control

~

Fluoxetlne ~

Trimipramine]

FIG. 2. Means+ SEM of sexual motivation, here as relative interest in a receptive vs. a nonreceptive female, over weeks 2 - 4 of fluoxetine or trimipramine treatments.

f e w e r i n t r o m i s s i o n s and e j a c u l a t i o n s . A n a l y s e s of i nt e rm ale hostility p o i n t e d to the s a m e c o n c l u s i o n . I n c i d e n c e s of a g g r e s s i v e r e s p o n s e s totals initiated by subjects t o w a r d their opponents, as w e l l as the s um of r e s p o n s e s by the pair, were reduced in e x p e r i m e n t a l groups. It is i n t e r e s t i n g to note, too, that s t i m u l u s a n i m a l s used in the b e h a v i o r a l tests r e s p o n d e d d i f f e r e n t l y to treated and control males. F e m a l e s w e re less s o l i c i t o u s of drug-t re a t e d m ales , and the m a l e o p p o n e n t s i ni t i a t e d f e w e r a g g r e s s i v e re s pons e s a g a i n s t e x p e r i m e n t a l than c ont rol m a l e s [ F ( 2 , 2 4 ) = 27.82 and 34.84, r e s p e c t i v e l y , bot h p < 0.05]. P o s t hoc c o m p a r i s o n s o f g r o u p m e a n s ( T u k e y ' s H S D test, p < 0.05) r e v e a l e d g r e a t e r b e h a v i o r a l d i s r u p t i o n by T R I M I than F L U O X . Thi s w a s i ndi c a t e d by m e a s u r e s of s e x u a l p e r f o r m a n c e and i n t e r m a l e a g g r e s s i o n , i n c l u d i n g r e s p o n s e s of the estrous f e m a l e s a nd unt re a t e d s t i m u l u s a n i m a l s to m a l e s from the tw o e x p e r i m e n t a l groups. The s i n g l e e x c e p t i o n w a s for the f e m a l e s ' a g g r e s s i v e re j e c t i ons of m a l e s . The T R I M I g r o u p did not differ from F L U O X nor from control groups. B y contrast, w e found no s t a t i s t i c a l l y re l i a bl e differences a m o n g the g r o u p s on s e x u a l m o t i v a t i o n . R e l a t i v e t i me and n u m bers o f uri na ry m a r k i n g n e a r the c a g e of an estrous f e m a l e vs. a

TABLE 3 MEANS 5: SEM OF PHYSIOLOGICAL MARKERS (mg TISSUE/ 100 g BODY WEIGHT) OF REPRODUCTIVE SYSTEM FUNCTION OF MALE RATS RECEIVING CHRONIC TREATMENT EITHER WITH FLUOXETINE, TRIMIPRAMINE, OR VEHICLE ONLY Group

Adrenals

Controls Fluoxetine Trimipramine

175:2 15±3 14 5:2

Pituitary* 2.8-1-0.4 a 1.6±0.1 b 1.2 ± 0.2 c

Epididymides

Testes

Penis

Seminal Vesicles

Bulbosp. Muscles

Ventral Prostate

3595:26 378:1:34 326 _+ 64

765+38 731±59 673 ± 64

26+2 31±1 29 ± 2

4485:19 4465:59 385 ± 35

4535: 9 513±12 480 ± 28

185:1 15± 1 16 ± 1

Asterisks indicate statistical differences on a measure; superscript letters denote differences between groups on measures (read down columns) that achieved statistical significance (Tukey's HSD test, p < 0.05).

TABLE 4 RESULTS OF HPLC ANALYSES OF OLFACTORY TUBERCLES FOR NEUROTRANSMI'VI~R AND METABOLITE CONCENTRATIONS (MEANS 5: SEM) OF MALE RATS TREATED FOR 4 WEEKS WITH FLUOXETINE OR TRIMIPRAMINE RELATIVE TO VEHICLE-INJECTED CONTROLS Concentration Group

Dopamine'~

DOPAC*

HVA

5-HT*

5-HIAA*

Controls Fluoxetine Trimipramine

100% 5: 3a 167%+ 15 b 111%5:4 b

100% 5:2 a 110% ± 6 b 93%_3 c

100% 5:3 a 113%__.7a 94%_+1 a

100% 5 : 3 a 149%+ l0 t' 100%± 10c

100% 5 : 6 a 80%5:13 b 80%+ 3 c

Asterisks indicate statistical differences on a measure; superscript letters denote differences between groups on measures (read down columns) that achieved statistical significance (Tukey's HSD test, p < 0.05).

TABLE 5 MEANS 5: SEM OF RATIOS OF METABOLITES RELATIVE TO THE PARENT TRANSMITTER COMPOUND AND ENDOCRINE VALUES AFTER CHRONIC EXPOSURE TO FLUOXETINE, TRIMIPRAMINE, OR VEHICLE ONLY Transminer/Metabolite Ratio Group Controls Fluoxetine Trimipramine

DA/DOPAC* 1.78 + 0.1 a 1.41 5: 0. Ib 1.18 5:0.1 c

CirculatingSteroids

DA/HVA*

5-HT/H1AA*

Testosterone

Conicosteroid*

5.26 5:0.2 a 4.20 5:0.2 b 3.57 ___0.1 c

1.67 + 0.1 a 1.13 5:0.2 b 0.91 5:0.1 b

1.72 5:0.1 1.55 5:0.1 1.39 5:0.2

44 5:6 a 84 + 9 b 58 5:6 c

Asterisks indicate statistical differences on a measure; superscript letters denote differences between groups on measures (read down columns) that achieved statistical significance (Tukey's HSD test, p < 0.05).

5-HT AND MALE SOCIOSEXUAL FUNCTION

nonestrous female indicated similar interest in the receptive female by drug-treated and control males. Conclusions for behavior totals were confirmed and extended by the within-groups findings from the repeated-measures factorial analyses. Results (Fig. 1) revealed significant differences for the groups × weeks interaction for intromission frequencies, F(4,48) ~ 8.62, p < 0.05, and for each of the three measures of aggressive behavior [range of F-values (4,48)~ 15.52-42.50, p < 0.05]. Only with drug treatments were there statistically reliable within group decreases from beginning to end of the study. The pattern emerges of increasing disruption to copulatory and aggressive responding with drug exposure that occurred earlier and more profoundly with TRIMI administration. Note that only the control males' data reflect the characteristic increasing copulatory effectiveness of a virgin male as he gains sexual experiences (35,41). The.re were no corresponding group differences over weeks of testing for sexual motivation (Fig. 2). No differences were,, detected in target structures of the steroidal axes. Although pituitary glands were significantly smaller, F(2,14) = 4.01, p < 0.05, all measures of primary and secondary sex glands and organs (Table 3) were unchanged with chronic drug exposure. As indicated in the endocrine findings included in Table 5, serum levels of testosterone were comparable for all groups. Analyses of corticosteroid titers, on the other hand, yielded a significant value, F(2,14) ~ 5.50, p < 0.05. FLUOX males had higher circulating corticosteroid than TRIMI or control groups. The suggestion is of modest to minimal effects by either drug treatment on endocrine and reproductive physiology. However, the differences that were obtained point to a pattem of broader functional influences by chronic administration of TRIMI than of FLUOX. Our neurochemical data suggest a similar conclusion. Results from the analyses of olfactory tubercles (Table 4) indicated statistically significant differences in absolute concentrations of dopamine and serotonin [F(2,15)~ 15.76 and l l.15, respectively, p < 0.05], and in each of their metabolites [range of F-values (2,15) ~ 4.45-8.14, p < 0.05]. Subsequent group comparisons indicated both drug groups had elevated DA compared to controls. Only FLUOX rats had higher concentrations of 5-HT than controls. Direct comparisons between drug groups indicated that FLUOX males had higher total concentrations than TRIMI males of every neurochemical measured except for levels of the metabolite of serotonin. There were similar reductions of 5-HIAA in both TRIMI and FLUOX animals compared with controls. Ratios of metaholites relative to the parent compounds were calculated as measures of transmitter turnover rates (Table 5). Results of the analyses revealed statistically reliable values for each ratio [range of F-values (2, 15) ~ 10.22-21.42, p < 0.05]. Post hoc findings for group differences suggested reduced turnover in drug groups. However, the findings indicated more widespread suppression of turnover by TRIMI than by FLUOX. Both treatments reduced 5-HT turnover similarly, but TRIMI reduced DA turnover to a significantly greater extent. Finally, histologic assessments for the presence or absence of gross pathology were made of peripheral structures removed at necropsy. There were no indications that chronic drug exposure induced pathologic changes in any of the tissues. DISCUSSION Results from the study can be summarized in three empirical statements. 1. Both the tricyclic compound, trimipramine, and the SSRI agent, fluoxetine, suppressed copulatory and aggressive re-

483

sponses of male rats. However, at the dosages employed, FLUOX treatment was less disruptive than TRIMI to these social interactions. 2. We uncovered no evidence that either drug compromised sexual motivation, circulating testosterone levels, or functional targets of the androgens in peripheral structures of the reproductive system. 3. Analyses of monoaminergic activity in olfactory tubercles obtained at necropsy suggested FLUOX promoted a distinctive pattern of interactions between dopamine and serotonin from TRIMI or control males. The conclusion is that more selective chronic inhibition of 5-HT uptake induced by FLUOX left a narrower band of influence than the tricyclic compound on neurotransmission and social responsiveness. As predicted by laboratory and clinical reports in the literature (27,32,44), chronic antidepressant treatments reduced all measures of copulatory performance. The literature on relations among antidepressants, hostility, and central monoaminergic function is more equivocal (16,29). Our findings support the conclusion that both typical and atypical compounds reduce intermale fighting (3,18). However, the results suggest that the selective 5-HT uptake inhibitor was notably less disruptive to sociosexual responding. FLUOX males were more likely than TRIMI males to complete successfully a copulatory bout with an estrous female. Social interchanges with another male also were more normal with FLUOX, in terms of aggression totals and latencies to initiate aggression. The same conclusion is indicated in the findings for the responses of untreated conspecifics to experimental animals. The social parmers of subject males showed parallel reductions of responsiveness to the drug-exposed males, particularly to TRIMI males. Estrous females were less solicitous, and stimulus males were less interactive, with experimental males than with control males. At the same time TRIMI and FLUOX were disrupting direct social interactions, sexual motivation was left undisturbed (14). There were no differences from beginning to end of the study in drug-exposed males' interest in initiating sociosexual contacts with an estrous vs. nonestrous female. Sexual dysfunction under sustained monoamine modification from antidepressant treatments appears to be specific to copulation (36,44). The nature of the separate tests of social behavior suggests a hypothesis about sociosexuality-monoamine relations. We observed behavioral decrements only in test settings, sexual performance, and aggression, in which treated males and their partners were in direct contact. There were no comparable decrements in our test of sexual motivation, a setting in which the animals were prevented from tactile contact by a wire-mesh screen. The suggestion is that it is the dyadic features of social behavior that are disturbed with drug exposure. Long-term drug administration appears to modify dynamics of a normal social exchange with an untreated conspecific (1,10). Neither FLUOX nor TRIMI interfered with peripheral reproductive systems. Systemic testosterone and primary and secondary sex structures were comparable in drug-treated and control males. The conclusion is that integrity of androgen-sensitive peripheral systems underlying reproduction (42) was not undermined. Sociosexual dysfunction observed with antidepressant therapies, it seems, is centrally mediated (36,43,45). The only statistically reliable differences from our various endocrine and physiology measures point to the hypothalamicpituitary-adrenal axis. Compared to the other groups FLUOX animals had elevated titers of circulating corticosterone, and hypophysial weights were reduced by both drugs. These data

484

TAYLOR ET AL.

suggest a sensitivity of the HPA axis to chronic intervention with central 5-HT reuptake (5,15). Nevertheless, the functional significance of this difference is not immediately obvious. Neurochemical data from olfactory tubercles served as markers of mesolimbic function. Tissues from olfactory tubercles were assayed for concentrations of dopamine, serotonin, and their metabolites. Compared to controls, total DA was elevated in both drug groups (26), whereas 5-HT was higher than controls only in the FLUOX group (11). Both drugs reduced 5-HIAA (4). Only in TRIMI animals were DOPAC and HVA lower than in controls. These results highlight the precariousness of simple generalizations on behavior-neurochemical concentration relations during chronic drug exposure (10). The bulk of the evidence suggests an inverse correlation of 5-HT, and a direct correlation of DA, with male sociosexual interactions (2). Yet, there are notable exceptions in the literature (27,44) and here. For example, our least sexual and aggressive group were the TRIMI animals with higher DA and similar 5-HT levels to controls. Comparisons of neurotransmitter metabolism and relations among the monoamines transmitter amounts may prove more helpful (3,22,31). Relative concentrations of metabolite to the parent compound serves as an index of transmitter release a n d / o r metabolic turnover (9). We calculated ratios for DA to DOPAC and HVA and for 5-HT to 5-HIAA to help explain behavioral differences between drug groups.

Findings of similarly reduced ratios of 5-HT turnover in drug groups turned our attention to the influence of TRIMI and FLUOX on dopaminergic activity (12,27). Reductions induced by TRIMI on DA turnover were markedly greater than FLUOX or controls (26). The conclusion is that a key to its lessened impact on normal sociosexual behaviors may lie in the capacity of long-term FLUOX treatment to maintain more normal dopamine transmission while reducing serotonin activity (23,45). In summary, chronic exposure to tricyclic and SSRI antidepressant drugs both disrupted dynamics of normal social exchanges of adult rats without affecting the male's interest in a receptive female or his peripheral reproductive physiology and endocrinology. The neurochemical findings indicated that fluoxetine and trimipramine, at least at the dosages we used, induced different patterns of changes in the interaction of serotonin and dopamine. Indeed, the attenuation of sociosexual behavior disruption relative to typical medications may be the capacity of selective 5-HT uptake inhibitors to promote a unique interaction between DA and 5-HT pathways. ACKNOWLEDGEMENTS The research was supported, in part, by grants from the UM-St. Louis Research Incentive Fund (G.T.), NIMH (T.E., J.H.) and Clinical Sciences NIMH Training Grant MUI4677 (M.B., J.C.).

REFERENCES 1. Barfield, R. J. Animal models of human sexual behaviour. In: Riley, A. J.; Peet, M.; Wilson, C. A., eds. Sexual pharmacology. Oxford: Oxford Medical Publications; 1993:73-86. 2. Bitran, D.; Hull, E. M. Pharmacological analysis of male rat sexual behavior. Neurosci. Biobehav. Rev. 11:365-389; 1987. 3. Brain, P. F.; Hang, M. Hormonal and neurochemical correlates of various forms of animal "aggression." Psychoneuroendocrinology 17:537-551; 1992. 4. Caccia, S.; Fracasso, C.; Garattini, S.; Guiso, G.; Sarati, S. Effects of short- and long-term administration of fluoxetine on the monoamine content of rat brain. Neuropharmacology 31:343-347; 1992. 5. Calogero, A.; Bagdy, G.; Moncada, M.; Dagata, R. Effect of selective serotonin agonists on basal, corticotrophin-releasing hormone induced and vasopressin-induced ACTH release invitro from rat pituitary ceils. J. Endocrinol. 136:381-388; 1993. 6. Cohn, J.; Wilcox, C.; Goodman, L. Antidepressant efficacy and cardiac safety of trimipramine in patients with mild heart disease. Clin. Ther. 15:114-126; 1993. 7. Cooper, J. R.; Bloom, F. E.; Roth, R. H. The biochemical basis of neuropharmacology. Cary, NC: Oxford University Press; 1991. 8. Corbett, R.; Hartman, H.; Kerman, L.; et al. Effects of atypical antipsychotic agents on social behavior in rodents. Pharmacol. Biochem. Behav. 45:9-18; 1993. 9. Csernansky, J. G.; Wrona, C.; Bardgett, M.; Early, T.; Newcomer, J. Subcortical dopamine and serotonin turnover during acute and subchronic administration of typical and atypical neuroleptics. Psychopharmacology (Berlin) 110:145-151; 1993. 10. Cutler, M. G. An ethological study of the effects of buspirone and the 5-HT3 receptor antagonist BRL 43694 (granisetron) on behaviour during social interactions in female and male mice. Neuropharmacology 30:299-306; 1991. 11. Delgado, P.; Price, L.; Heninger, G.; Chamey, D. Neurochemistry. In: Paykel, E. S., ed. Handbook of affective disorders. New York: Plenum Press; 1992:219-253. 12. De Montis, G. N.; Devoto, P.; Gessa, G.; et al. Central dopaminergic transmission is selectively increased in the limbic system of rats chronically exposed to antidepressants. Eur. J. Pharmacol. 180:31-35; 1990. 13. Dewar, K.; Grondin, L.; Nenanene, E.; Ohayon, M.; Reader, T. [3H]Paroxetine binding and serotonin content of rat brain: Absence

14.

15. 16.

17.

18. 19. 20. 21. 22. 23. 24. 25. 26.

of changes following antidepressant treatments. Eur. J. Pharmacol. 235:137-142; 1993. Foreman, M.; Doherty, P. Experimental approaches for the development of pharmacological therapies for erectile dysfunction. In: Riley, A. J.; Peet, M.; Wilson, C. A., eds. Sexual pharmacology. Oxford: Oxford Medical Publications; 1993:87-113. Fuller, R. W. The involvement of serotonin in regulation of pituitary- adrenocortical function. Front. Neuroendocrinol. 13:250-270; 1992. Gao, B.; Cutler, M. Effects of subchronic treatment with chlordiazepoxide, buspirone and the 5-HT-sub-3 receptor antagonist, BRL 46470, on the social behaviour of mice. Neuropharmacology 31:207213; 1992. Gardier, A.; Lepoul, E.; Trouvin, J.; Chanut, E.; Dessalles, M.; Jacquot, C. Changes in dopamine metabolism in rat forebrain regions after cessation of long-term fluoxetine treatment: Relationship with brain concentrations of fluoxetine and norfluoxetine. Life Sci. 54: 51-56; 1994. Garmendia, L.; Sanchez, J.; Azpiroz, A.; Brain, P.; Simon, V. Clozapine: Strong antiaggressive effects with minimal motor impairment. Physiol. Behav. 51:51-54; 1992. Grant, E. C.; Mackintosh, J. H. A comparison of the social postures of some common laboratory rodents. Behaviour 21:246-259; 1963. Gross, G.; Xin, X.; Gastpar, M. Trimipramine: Pharmacological reevaluation and comparison with clozapine. Neuropharmacology 30:1159-1166; 1991. Herman, J. B.; Brotman, A. W.; Pollack, M. H.; Falk, W. E.; Biederman, J.; Rosenbaum, J. F. Fluoxetine-induced sexual dysfunction. J. Clin. Psychiatry 51:25-27; 1990. Hoffman, N.; Gerall, A.; Kalivas, P. Sexual refractoriness and locomotion effects on brain monoamines in the male rat. Physiol. Behav. 41:563-569; 1987. Hollister, L. E.; Claghorn, J. L. New antidepressants. Annu. Rev. Pharmacol. Toxicol. 33:165-177; 1993. Hollister, L. E.; Csemansky, J. G. Clinical pharmacology of psychotherapeutic drugs. New York: Churchill Livingstone; 1990. Holtzman, S.; Steinfels, G. Monoamine systems in the discriminative effects of spiradoline, a kappa-opioid agonist. Pharmacol. Biochem. Behav. 47:575-578; 1994. Juorio, A. V.; Li, X. M.; Boulton, A. A. The effects of chronic

5-HT A N D M A L E S O C I O S E X U A L F U N C T I O N

27.

28.

29.

30.

31. 32.

33.

34.

35.

36.

trimipramine treatment on biogenic amine metabolism and on dopamine D 2, 5-HT 2 and tryptamine binding sites in rat brain. Gen. Pharmacol. 21:759-762; 1990. Kellet, J. The nature of human sexual desire and its modification by drags. In: Riley, A. J.; Peet, M.; Wilson, C. A., eds. Sexual pharmacology. Oxford: Oxford Medical Publications; 1993:130-145. Komitowski, D.; Muto, S.; Weiss, J.; Schmitt, B.; Taylor, G. T. Structural changes in nuclear chromatin in rat pituitary after chronic stress of low intensity. Anat. Rec. 220:125-131; 1988. Marazziti, D.; Rotondo, A.; Presta, S.; Pancioli-Guadagnucci, M.; Palego, L.; Conti, L. Role of serotonin in human aggressive behaviour. Aggress. Behav. 19:347-354; 1993. Massicotte, G.; Bernard, J.; Ohayon, M. Chronic effects of trimipramine, an antidepre~sant, on hippocampal synaptic plasticity. Behav. Neural Biol. 59:100-106; 1993. Meltzer, H. Y. The mechanism of action of novel antipsychotic drugs. Schiz. Bull. 17:263-287; 1991. Mitchell, P. J.; Redfern, P. H. Acute and chronic antidepressant drug treatment induce opposite effects in the social behaviour of rats. J. Psychopharmacol. 6:1-- 11; 1992. Orsulak, P.; Kenney, J.; Debus, J.; Crowley, g.; Wittman, P. Determination of the antidepressant fluoxetine and its metabolite norfluoxetine in serum by reversed-phase HPLC with ultraviolet detection. Clin. Chem. 34:1875-1878; 1988. Perry, K. W.; Fuller, R. W. Effect of fluoxetine on serotonin and dopamine concentration in microdialysis fluid from rat striatum. Life Sci. 50:1683-1690; 1992. Sachs, B. D.; Meisel, R. L. The physiology of male reproductive behavior. In: Knobil, E.; Neill, J., eds. The physiology of reproduction, vol. 2. New York: Raven Press, Inc.; 1994:3-106. Seagraves, R. T. Effec'Is of pychotropic drugs on human erection and ejaculation. Arch. Gen. Psychiatry 46:275-284; 1989.

485

37. Taylor, G. T. Affiliation in highly aggressive domesticated rats. J. Comp. Physiol. Psychol. 91:1128-1135; 1977. 38. Taylor, G. T.; Bardgett, M.; Farr, S.; Womack, S.; Komitowski, D.; Weiss, J. Steroidal interactions in the ageing endocrine system: Absence of suppression and pathology in reproductive systems of old males from a mixed-sex, socially stressful rat colony. J. Endocrinol. 137:115-122; 1993. 39. Taylor, G. T.; Bardgett, M. E.; Griffin, M. G.; Weiss, J. Reproductive behavior and physiology of nulliparous female rats after sexual experience. Behav. Proc. 19:31-46; 1989. 4('. Taylor, G. T.; Hailer, J.; Rupich, R.; Weiss, J. Testicular hormones and intermale aggressive behaviour in the presence of a female rat. J. Endocrinol. 100:315-321; 1984. 41. Taylor, G. T.; Komitowski, D.; Muto, S.; Weiss, J. Behavioral endocrinology of male rats with periodic sexual contacts with exclusive or varied females. Proc. Soc. Exp. Biol. Med. 192:236-241; 1989. 42. Taylor, G. T.; Scherrer, J.; Weiss, J.; Pitha, J. Endocrine interactions: Adrenal steroids and precursors. Am. J. Physiol. 266:E676-681; 1994. 43. Vitale, M.; Chiocchio, S. Serotonin, a neurotransmitter involved in the regulation of luteinizing hormone release. Endocr. Rev. 14:480499; 1993. 44. Wilson, C. A. Pharmacological targets for the control of male and female sexual behaviour. In: Riley, A. J.; Peet, M.; Wilson, C. A., eds. Sexual pharmacology. Oxford: Oxford Medical Publications; 1993:1-58. 45. Yells, D~; Prendergast, M.; Hendricks, S.; Nakamura, M. Fluoxetineinduced inhibition of male rat copulatory behavior: Modification by lesions of the nucleus paragigantocellularis. Pharmacol. Biochem. Behav. 49:121-127; 1994.