Postejaculatory Interval Research Articles

The development of olfactory conditioned ejaculatory preferences in the male rat: I. Nature of the unconditioned stimulus

We have demonstrated previously that repeated pairing of a neutral odor with copulation produces a subsequent conditioned ejaculatory preference (CEP) for a female bearing that odor. Here we examine the copulatory components that comprise the unconditioned stimulus (UCS). In Experiment 1, male Long–Evans rats were allowed to copulate with scented females for nine sessions in which they achieved two ejaculations, one ejaculation plus the first intromission following the postejaculatory interval (PEI), one ejaculation without a PEI, or five intromissions without ejaculation. Only the males that achieved two ejaculations or one ejaculation plus the PEI displayed significant CEP. In Experiment 2, males were allowed to remain in the presence of the scented female without access to her after different amounts of copulatory stimulation. Under these conditions, both one and two ejaculations, but not five intromissions, supported the development of CEPs. In Experiment 3, males were allowed to copulate to ejaculation with an unscented female followed by exposure without access to a scented female. This treatment also supported the development of CEP. These results indicate that ejaculation plus a PEI are necessary for the development of CEPs and that the female must be present during the PEI for this to occur. These findings indicate that events during the PEI are the critical components of the UCS for CEP development.

The critical window of brain development from susceptive to insusceptive: Effects of clomipramine neonatal treatment on sexual behavior

The immature brain is much more sensitive to abnormal experience, particularly sleep deprivation, drug exposure, and maternal separation. The critical time period during which features in the brain’s susceptibility to such experience change, however, has not yet been determined. In previous studies on rats, we found that neonatal treatment with clomipramine (CLI) during postnatal days 8–21 (P8–21) produced behavioral and physiological abnormalities in adult rats that resembled the abnormalities found in human endogenous depression. The objective of the present study is to determine (1) the critical (more specifically, the latest) time frame in which CLI treatment will produce adult depression and (2) the shortest treatment window during which CLI can induce adult depression. Male rats were neonatally treated with CLI (20 mg/kg, sc) twice daily or with an equivolume of saline. The treatment windows were P12–17, P14–20, P16–22, and P12–15. Six variables, including number of mounts, intromission, ejaculation, mount latency, ejaculation latency, and post-ejaculation interval, were measured visually between the ages of 4 and 5 months. Rats treated with CLI showed significant sexual impairment in treatment windows P12–17 and P14–20 and slight sexual deficiency in the short window P12–15. No significant sexual impairment was found in window P16–22. We concluded that P14–20 was the latest window during which CLI treatment produces adult sexual deficiency and that 6 days might be the shortest treatment window to produce significant behavior abnormalities.

Selectively bred male rat lines differ in naı̈ve and experienced sexual behavior

Ejaculatory behavior is facilitated by activating 5-hydroxytryptamine 1A (5-HT 1A) receptors. The present study examined male sexual behavior in rat lines that were selectively bred for their different hypothermic responses to 8-hydroxy-2-(di- n-propylamino)tetralin (8-OH-DPAT). Sexual behavior was examined in naı̈ve and experienced HDS (high 8-OH-DPAT sensitive), LDS (low 8-OH-DPAT sensitive), and RDS (randomly bred) rats lines. In addition, the effects of 8-OH-DPAT (0.05 mg/kg) and N-{2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl}- N-(2-pyridinyl)-cyclohexane-carboxamide (WAY 100,635; 1 mg/kg) were examined. Naı̈ve HDS animals had diminished ejaculatory behavior (as indicated by a decreased number of intromissions, mounts and ejaculations, increased ejaculation and intromission latency, and longer inter-copulatory interval), compared to the LDS and RDS groups. In addition, the post-ejaculatory interval (PEI) was longer in the HDS group. With experience, the HDS group improved its ejaculatory behavior. Experienced HDS animals had a lower number of intromissions and a longer PEI compared to the LDS group. 8-OH-DPAT facilitated ejaculatory behavior in both HDS and LDS groups. This effect was more pronounced in the LDS group. WAY 100,635 did not alter sexual behavior in either group. In summary, alteration in forebrain 5-HT 1A receptors in HDS animals may be involved in the ability of naı̈ve rats to achieve ejaculation. 5-HT 1A receptors are involved in the regulation of resumption of sexual behavior after ejaculation.

Masculine copulatory behavior is facilitated by intrathecally administered muscarine.

Behavioral experiments were conducted to examine the role of the cholinergic receptor-agonist muscarine or its antagonist homatropine on the mating behavior of sexually experienced male rats. Male copulatory behavior was recorded after intrathecally administered saline, muscarine (7.5 microg), or homatropine (25 microg). Changes in copulatory behavior were assessed by the following parameters: intromission latency, intromission frequency, intercopulatory interval, ejaculation latency, and postejaculatory interval. Intromission frequency, intercopulatory interval, and ejaculation latency were decreased significantly by muscarine. Intrathecal homatropine decreased the number of copulating animals (five out of 13). In the five animals that were able to ejaculate after homatropine, intromission latency, intercopulatory interval, and ejaculation latency increased significantly. The effects of both drugs on locomotion were also tested. Muscarine induced no significant changes in locomotion compared with saline. A significant increase in locomotion was found after homatropine treatment. These results suggest that acetylcholine, acting at spinal-cord muscarinic receptors, may be involved in ejaculation.

Chronic melanocortin 4 receptor blockage causes obesity without influencing sexual behavior in male rats.

We investigated the effects of continuous intracerebroventricular infusion of a melanocortin 4 receptor antagonist HS014 (cyclic [AcCys11, D-Nal14, Cys18, Asp-NH2(22)]beta-MSH-(11-22)) over 12 days and a subsequent 12-day recovery period on food intake, body weight and copulatory behavior in male rats. The results show that the food intake increased immediately after the start of the infusion of HS014 (0.16 nmol/h) and progressively increased thereafter. No tachyphylaxis was observed. When the infusion of HS014 was terminated, the food-intake levels dropped. The body weights of the rats had increased by 17% by the end of the study, compared with controls. During the recovery period, the body weight decreased towards the levels of the control rats. These results indicate that overeating and the subsequent increases in body weight caused by blockage of the melanocortin 4 (MC4) receptor are reversible when the blockage is ended. We also tested the copulatory behavior of vigorous male rats in the presence of female rats in estrous. We registered mount latency, the number of mounts, the intromission latency, the number of intromissions, the ejaculation latency and the post-ejaculatory interval three times during the study and also after acute administration of HS014 and alpha-MSH. The sexual behavior of the male rats was not affected. These results indicate that the MC receptors, in particular the MC4 receptor, may not be a major mediator of effects on copulatory behavior in male rats.

Female presence during postejaculatory interval facilitates penile erection and 22-kHz vocalization in male rats.

During the postejaculatory interval (PEI), male rats exhibit prolonged immobility, 22-kHz vocalization, and penile erections. To test whether females modulate these behaviors, females were removed after the first or second ejaculation or left in the test chamber. Female presence during the PEI delayed exploratory behavior and facilitated vocalization and erection. Female stimulation of vocalization is consistent with the hypothesis that vocalization has a communicative function, not just a thermoregulatory one. The timing of the effect of females on erection suggests that males are sexually arousable well before they resume copulation. Therefore, erection may be better than vocalization as an indicator of the male's sexual refractoriness. The findings also challenge the conventional view that the PEI comprises absolute and relative sexual refractory periods marked, respectively, by the presence and absence of 22-kHz vocalization.

Female presence during postejaculatory interval facilitates penile erection and 22-kHz vocalization in male rats.

Female presence during postejaculatory interval facilitates penile erection and 22-kHz vocalization in male rats.

Effects of Withdrawal from an Escalating Dose Schedule of d-Amphetamine on Sexual Behavior in the Male Rat

The present study sought to determine the effect of withdrawal from an escalating dose schedule of d-amphetamine on sexual behavior in male rats. Tests were conducted every 5 days until stable levels of sexual behavior were obtained. With repeated testing, male rats displayed an increase in their exploration of the testing chambers prior to the introduction of an estrous female. Half of the male rats were then subjected to a 4-day escalating dose schedule of d-amphetamine administration (1–12 mg/kg), while half received vehicle. Twelve hours after the final drug injection, subjects were tested for sexual behavior. Withdrawal from the drug was associated with decrements in several motivational components of sexual behavior, including decreased anticipatory locomotor and increased postejaculatory intervals, while consummatory measures remained largely unaffected. This pattern of sexual deficits resembles those seen in human depressive disorders, and therefore, provides additional support for the use of psychostimulant withdrawal as a rodent model of depression.

Lateral Hypothalamic Serotonin Inhibits Nucleus Accumbens Dopamine: Implications for Sexual Satiety

Dopamine (DA) is released in several brain areas, including the nucleus accumbens (NAcc), before and during copulation in male rats. DA agonists administered into this area facilitate, and DA antagonists inhibit, numerous motivated behaviors, including male sexual behavior. Serotonin (5-HT) is generally inhibitory to male sexual behavior. We reported previously that 5-HT is released in the anterior lateral hypothalamic area (LHA(A)) and that a selective serotonin reuptake inhibitor microinjected into that area delayed and slowed copulation. Our present results, using high temporal resolution microdialysis, (1) confirm previous electrochemical evidence that extracellular levels of DA increase in the NAcc during copulation and decrease during the postejaculatory interval (PEI) and (2) reveal that LHA(A) 5-HT can inhibit both basal and female-elicited DA release in the NAcc. These findings suggest that the neural circuit promoting sexual quiescence during the PEI includes serotonergic input to the LHA(A), which in turn inhibits DA release in the NAcc. These findings may also provide insights concerning the inhibitory control of other motivated behaviors activated by the NAcc and may have relevance for understanding the sexual side effects common to antidepressant medications.

Synergistic actions of the 5-HT 1A receptor antagonist WAY-100635 and citalopram on male rat ejaculatory behavior

The selective serotonin re-uptake inhibitor citalopram (0–40 mg kg −1, s.c., — 60 min) did not affect the male rat ejaculatory behavior, and there were no statistically significant effects of the 5-HT 1A receptor antagonist N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]- N-(2-pyridinyl) cyclohexane carboxamide 3HCl (WAY-100635) (0.04–0.08 mg kg −1, s.c., — 30 min). When combined, there was a marked, and statistically significant, prolongation of the ejaculation latency in comparison with saline treated controls, as well as in comparison with either drug by itself. This citalopram (10.0)/WAY-100635 (0.04)-induced effect was fully antagonized by the administration of the 5-HT 1B receptor antagonist isamoltane (4.0 mg kg −1). There were no consistent effects on other aspects of the male rat sexual behavior, i.e., number of mounts and intromissions preceding ejaculation and the post-ejaculatory interval. Finally, the intromission latency was also markedly enhanced in animals receiving both citalopram and WAY-100635, and at the higher dose of WAY-100635 (0.08 mg kg −1) 7 out of 18 animals failed to initiate copulation. It is suggested that blockade of inhibitory 5-HT 1A autoreceptors discloses inhibitory effects of the selective serotonin re-uptake inhibitor citalopram on male rat ejaculatory behavior mediated via stimulation of 5-HT 1B receptors.

Effects of a D 1 antagonist and of sexual experience on copulation-induced Fos-like immunoreactivity in the medial preoptic nucleus

The medial preoptic nucleus (MPN) of the medial preoptic area (MPOA) and the medial amygdala are two brain regions in which male rat sexual behavior increased Fos-like immunoreactivity (Fos-Li). Dopamine is released in the MPOA during male rat sexual behavior and facilitates copulation. Psychostimulants, which increase dopamine levels, induce Fos-Li in the striatum through D 1 receptors. We examined whether copulation-induced Fos-Li in the MPN was also mediated through D 1 receptors. In Experiment 1, sexually inexperienced male rats that received the D 1 antagonist Schering 39166 prior to their first sexual experience had fewer Fos-Li cells in the MPN than did those that received vehicle. In Experiment 2, no significant effect of the D 1 antagonist was observed on copulation-induced Fos-Li in male rats that had received repeated sexual experiences prior to the drug test day. Sexual experience increases copulatory efficiency; the mechanisms by which this improvement occurs are unclear. In Experiment 3, copulation by highly experienced male rats led to greater Fos-Li in the MPN than did copulation by sexually naive males. Although there were no differences between groups in amygdala Fos-Li in these studies, in several groups Fos-Li in the medial amygdala was positively correlated with the post-ejaculatory interval. These experiments indicate that (1) stimulation of D 1 receptors may contribute to the transient copulation-induced increase in Fos-Li in the MPN, and (2) repeated sexual experiences enhanced copulation-induced Fos-Li in the MPN, which may represent a marker of altered responsiveness of neurons in the MPN to sexual or conditioned stimuli.

Stimulating property of Turnera diffusa and Pfaffia paniculata extracts on the sexual-behavior of male rats.

Sexually potent and sexually sluggish/impotent male rats were treated orally with different amounts of Turnera diffusa and Pfaffia paniculata fluid extracts (0.25, 0.50, 1.0 ml/kg). While having no effect on the copulatory behavior of sexually potent rats, both plant extracts--singly or in combination--improved the copulatory performance of sexually sluggish/impotent rats. The highest dose of either extract (1 ml/kg) (as well as the combination of 0.5 ml/kg of each extract) increased the percentage of rats achieving ejaculation and significantly reduced mount, intromission and ejaculation latencies, post-ejaculatory interval and intercopulatory interval. Neither extract affected locomotor activity. These results seem to support the folk reputation of Turnera diffusa and Pfaffia paniculata as sexual stimulants.

Partial antagonism of 8-OH-DPAT'S effects on male rat sexual behavior with a D 2, but not a 5-HT 1A, antagonist

The serotonin agonist 8-hydroxy-di-propylaminotetralin (8-OH-DPAT), injected systemically or directly into the medial preoptic area (MPOA), reduces the ejaculatory threshold in male rats. While 8-OH-DPAT has been characterized as an agonist at the 5-HT 1A receptor, it also acts at other receptor sites including the dopamine D 2 receptor. The current experiments investigated whether 8-OH-DPAT injected into the MPOA facilitates male sexual behavior through stimulation of the 5-HT 1A receptor or the dopamine D 2 receptor. Experiment 1 co-administered 8-OH-DPAT (6 μg) with either the 5-HT 1A antagonist 4-iodo- N-[2-[4-(methoxyphenyl)-1-piperazinyl]ethyl]- N-2-pyridinyl-benzamide hydrochloride (MPPI) (10 μg) or the D 2 antagonist raclopride (10 μg). Raclopride blocked 8-OH-DPAT's facilitative effects on ejaculation frequency and latency, while the 5-HT 1A antagonist was ineffective. In Experiment 2, 8-OH-DPAT (500 μM), retrodialyzed into the MPOA through a microdialysis probe, enhanced male copulatory behavior similarly to the microinjection, increasing ejaculation frequency and decreasing ejaculation latency, postejaculatory interval and mount frequency. Retrodialyzing 8-OH-DPAT through a microdialysis probe in the MPOA had been previously shown to increase extracellular levels of dopamine and serotonin. The data from the present studies suggest that the effects of 8-OH-DPAT in the MPOA on male rat copulatory behavior may be mediated, at least in part, either directly through 8-OH-DPAT's activity at D 2 receptors or indirectly through 8-OH-DPAT's ability to increase extracellular dopamine.

A comparison of the effects of different serotonin reuptake blockers on sexual behaviour of the male rat

In human males, SSRIs differentially affect (premature) ejaculation; paroxetine and fluoxetine markedly and sertraline, moderately inhibited ejaculation latency, whereas fluvoxamine did not inhibit this parameter (Waldinger, M.D., Hengeveld, M.W., Zwinderman, A.H., Olivier, B., The effect of SSRI antidepressants on ejaculation: a double-blind, randomised, placebo-controlled study with fluoxetine, fluvoxamine, paroxetine and sertraline. J. Clin. Psychopharmacol. (in press)). The present studies tried to investigate, using sexual behaviour in male rats, whether such differences could also be found in animal paradigms of sexual behaviour. In a series of three experiments we compared various specific serotonin reuptake inhibitors (SSRIs) for their ability to suppress sexual behaviour in male rats. In the first experiment sexually experienced rats were tested 60 min after oral administration of clomipramine, fluvoxamine, fluoxetine (all in a range of 0, 3, 10 and 30 mg/kg p.o.), sertraline or paroxetine (both in a range of 0, 1, 3 and 10 mg/kg p.o.). Clomipramine, paroxetine and fluvoxamine did not significantly inhibit male sexual behaviour, although some trends were observed. Sertraline inhibited sexual behaviour at 3 and 10 mg/kg p.o., the effects being stronger at 3 mg/kg p.o. Fluoxetine (3 mg/kg p.o.) facilitated sexual behaviour, while at 30 mg/kg p.o. a modest increase in the postejaculatory interval was noted. In the second experiment, sexual behaviour of sexually naive male rats was slightly inhibited by paroxetine 10 mg/kg p.o., but sertraline (range 1–10 mg/kg p.o.), fluvoxamine and fluoxetine (both in a range of 3–30 mg/kg p.o.) were ineffective. In the last experiment the effects of paroxetine (0–10 mg/kg p.o.), fluvoxamine and fluoxetine (both 0–30 mg/kg p.o.) were studied during an exhaustion design in sexually experienced male rats. As rats get more `sluggish' when they have had multiple ejaculations, we hoped to see stronger inhibitory effects in the last cycle prior to exhaustion. None of the drugs dose-dependently inhibited the pattern of sexual behaviour during the first sexual cycle. In the last cycle the patterning of sexual behaviour differed, but only paroxetine (10 mg/kg p.o.) inhibited sexual behaviour significantly. The total number of ejaculations during the test was not reduced by any of the SSRIs tested. Contrary to human findings, we did not find major inhibitory effects of SSRIs on male rat sexual behaviour at non-sedative doses. The only differentiation that could be made is that paroxetine and sertraline had slightly stronger effects than the other 5-HT reuptake inhibitors. Masculine sexual behaviour in rats does not constitute a suitable model to investigate the differential mechanism of sexual inhibition of SSRIs that have been described in human males.

Effects of sexual behavioral manipulation on brain plasticity in adult rats

The purpose of the present study was to determine the effects of sexual behaviorial manipulation on brain plasticity in adult male rats. Adult male Sprague-Dawley rats that copulated during male sexual behavior testing were divided into four groups: control male; gonadectomized (Gdx) male; sexually active male; and sexually nonactive male. Female animals were used as an additional control group. At the end of a 12-week experimental period, the animals were again tested for male sexual behavior and tested for sexual motivation. Sexual behavior manipulations over the 12-week period resulted in significant differences in mount latency, mount frequency, intromission latency, intromission frequency, ejaculation latency, and the postejaculation interval. In the motivation test, significant differences in the number of approaches, contacts, and crossings of an electrified grid separating the test animal from a receptive female were also observed. Sexually dimorphic nucleus of the preoptic area (SDN-POA) volumes in sexually nonactive males were significantly smaller than in control males or sexually active males. Anteroventral periventricular nucleus (AVPV) volumes in the male groups were not significantly altered by sexual behavioral manipulations, however, the nonactive AVPV vol. was the only vol. not significantly different from the control female vol. These data demonstrate that in the adult rat, sexual behavioral manipulations resulted in significant alterations in behavior and in the vol. of the SDN-POA and that the effect of sexual behavior on the AVPV needs to be further investigated.

The Medial Amygdaloid Nucleus Modifies Social Behavior in Male Rats

STARK, C. P.; H. P. ALPERN; J. FUHRER; M. G. TROWBRIDGE; H. WIMBISH; AND T. SMOCK.The medial amygdaloid nucleus modifies social behavior in male rats.PHYSIOL BEHAV 63(2) 253–259, 1998.—Electrical stimulation of the medial amygdaloid nucleus (AME) produces a behavioral state in male rats that resembles the postejaculatory interval, but electrical recording from cells in the AME shows that they become active earlier in sexual behavior, around the time that the male first appears to become aware of estrus in the female. In an attempt to resolve which feature of sexual behavior was mediated by the AME, we stimulated the structure bilaterally in freely behaving males using voltage levels too low to produce the postejaculatory interval. We found that electrical activation of this kind facilitated sexual behavior when it would not otherwise occur (i.e., in the presence of a nonestrous female). However, the stimuli suppressed sexual behavior when it would normally occur (i.e., in the presence of a nonestrous female). We discuss alternative interpretations of the results in the context of a general model for the central organization of sexual behavior in males.

Extracellular Serotonin in the Lateral Hypothalamic Area Is Increased during the Postejaculatory Interval and Impairs Copulation in Male Rats

Serotonin (5-HT) is generally inhibitory to masculine sexual behavior. It has been suggested that 5-HT released after ejaculation may promote the sexual quiescence of the postejaculatory interval (PEI). The following experiments were conducted to test (1) whether extracellular 5-HT increases in either the anterior lateral hypothalamic area (LHAA) or the medial preoptic area (MPOA) of male rats after ejaculation; (2) whether increasing 5-HT in these sites, by microinjecting the selective serotonin reuptake inhibitor alaproclate, could inhibit copulatory abilities; and (3) whether copulation deficits produced by alaproclate were attributable to locomotor impairments. The effects of local application of alaproclate on extracellular 5-HT levels in the LHAA and the MPOA were also tested. Extracellular serotonin was measured in all experiments using in vivo microdialysis. Ejaculation was correlated with enhanced 5-HT release from the LHAA; no 5-HT increases were observed before ejaculation, and levels were decreased toward basal values during a subsequent copulatory series. Elevating 5-HT in the LHAA by microinjecting alaproclate inhibited copulation by increasing the latency to mount, intromit, and ejaculate. This inhibition did not result from nonspecific locomotor impairments. In the MPOA, 5-HT release remained stable throughout copulation, and microinjecting alaproclate into this site did not significantly alter sexual behavior. These data support the large body of evidence suggesting that 5-HT is inhibitory to masculine sexual behavior. Furthermore, the LHAA, but not the MPOA, may be one site responsible for serotonergic inhibition of copulation during the PEI.

Subcortical Multiple Unit Activity Changes During Rat Male Sexual Behavior

Hernandez-Gonzalez, M., M. A. Guevara, G. Morali and M. Cervantes. Subcortical multiple unit activity changes during rat male sexual behavior. Physiol Behav 61(2) 285–291, 1997.—Multiple unit activity (MUA) was recorded from the ventral tegmental area (VTA) and mesencephalic locomotor region (MLR) during copulatory behavior of freely moving male rats. Simultaneous accelerometric recordings of the copulatory pelvic thrusting performed by the male rat were taken to precisely correlate in time the changes in MUA with well defined elements of copulation. The baseline MUA firing rates recorded in the quiet-alert condition in the VTA and in the MLR were significantly increased during pursuit of the female by the male; significantly higher MUA firing rates were found in the VTA at the 500 ms periods before and during the execution of pelvic thrusting in mount, intromission, and ejaculation responses as compared to the baseline, and returned to this value when these responses ended. The maximum MUA firing rate in the MLR was obtained during the execution of pelvic thrusting in each copulatory response, and it remained significantly elevated, as compared to the baseline, after thrusting and at the postintromission and postejaculatory genital grooming, then decreasing to basal values at the initial part of the postejaculatory interval. The fact that the highest changes in MUA were related to pelvic thrusting suggests a major participation of both structures in the execution of motor copulatory responses.

8-OH-DPAT and Male Rat Sexual Behavior: Partial Blockade by Noradrenergic Lesion and Sexual Exhaustion

As previously shown, the 5-HT 1A agonist 8-OH-DPAT is a potent facilitator of male rat copulatory behavior in both sexually experienced and sexually exhausted male rats. The basis of this facilitation is still not clear. Therefore, the purpose of the present study was to determine whether 8-OH-DPAT-induced sexual-behavior facilitation could be counteracted by lesioning the NA system with the noradrenergic neurotoxin DS P 4. In NA-lesioned, sexually experienced, non-exhausted rats, the facilitatory effects of 8-OH-DPAT on the number of mounts and the postejaculatory interval were reduced, the effect on the intromission latency disappeared, while the percentage of copulating rats was not significantly altered. In sexually exhausted rats bearing a lesion of the NA system, the facilitatory effects of 8-OH-DPAT on the percentage of copulating rats was blocked. Data are discussed on the basis of the interactions between the noradrenergic and serotonergic systems in the mediation of the facilitatory effect of 8-OH-DPAT in sexually exhausted and non-exhausted rats.

Effect of Long-Term Ingestion of Chromium Compounds on Aggression, Sex Behavior and Fertility in Adult Male Rat

ABSTRACTThe effects of long-term ingestion of chromium chloride (trivalent compound) and potassium dichromate (hexavalent compound) was investigated on sexual bahavior, aggressive behavior and fertility in male rats. Adult male rats were exposed to chromium chloride and potassium dichromate in drinking water at a concentration of 1000 ppm for 12 weeks.The exposure of male rats to chromium chloride and potassium dichromate reduced the number of mounts. The exposure of male rats to potassium dichromate increased the time to ejaculation. On the other hand, the exposure of male rats to chromium chloride and potassium dichromate increased the post ejaculatory interval. The number of animals ejaculating were reduced in chromium chloride and potassium dichromate exposed male rats. The exposure of male rats to chromium chloride and potassium dichromate decreased lateralizations, boxing bouts and fights with stud male, The exposure of male rats to chromium chloride and potassium dichromate had no effect on fertility. Testes, seminal vesicle and preputial gland weights were significantly reduced in chromium chloride - and potassium dichromate - exposed males. In conclusion, the long-term ingestion of chromium chloride and potassium dichromate would have adverse effects on sexual behavior and territorial aggression in adult male rat.