Physiology and Behavior, Vol. 15, pp. 91--95. Brain Research Publications Inc., 1975. Printed in the U.S.A.
Variables Affecting "Spontaneous" Seminal Emission in Rats 1 F R A N K A. BEACH 2
University of California, Berkeley (Received 9 December 1974)
BEACH, F. A. Variables affecting "spontaneous" seminal emission in rats. PHYSIOL. BEHAV. 15(1) 91-95, 1975. The frequency of spontaneous seminal emission (SE) by isolated rats (X = 2.05 +- 0.64/day) was not increased when estrous females were housed in adjacent cages. Coital ejaculation during mating tests temporarily inhibited the production of SE, and inhibition was more marked after 5 than after 1 ejaculation with a female. Males experiencing only 1 coital ejaculation tended to resume production of SE somewhat sooner if they were exposed to stimuli from estrous females than if such stimuli were lacking. The possible functional significance of spontaneous and self-induced noncoital seminal emission which is common in a variety of mammals is discussed. Seminal Emission
Ejaculation
Sexual behavior
SUDDEN discharge of seminal fluid is a normal accompaniment of the ejaculatory reflex evoked by sexual stimulation in male mammals, but semen may be discharged under other conditions with or without ejaculatory contractions. Nocturnal emission is common in human males, occurring at least occasionally in 83 percent of American men according to Kinsey, e t al. [ 14]. " S p o n t a n e o u s " release of contents of the accessory sex glands is known to occur in males of other species including laboratory rats [16], hamsters [ 4 ] , cats [1], and chimpanzees [19]. The term spontaneous is set in quotation marks because of the possibility that ejaculation may be induced by manual masturbation in apes or by rubbing the penis against environmental objects in the case of other species. We have never observed such behavior on the part of rats or hamsters but its occurrence is not excluded. The present experiment was initiated to determine whether the frequency of spontaneous seminal emission (SSE) by physicially isolated male rats would be affected by exteroceptive stimuli derived from estrous females living in adjacent cages. Additional objectives were to investigate the consistency of individual differences in SSE frequency, possible relation o f size of the seminal vesicles to SSE production, and recovery of SSE after mating tests involving 1 or 5 coital ejaculations.
days of age. Until experimentation began at 100 days of age, and throughout the experiment, they were housed individually in metal cages (25.5 × 15 X 38 cm) with floors of 9 mm wire mesh which permitted fecal and seminal material to drop on the paper towelling underneath the cage. To prevent males from autogenital grooming and consumption of seminal products each rat wore one of the plastic corsets illustrated in Fig. 1. Pilot work showed that a week of corseting produced marked weight loss and therefore corsets were worn for 3 consecutive days during which the towelling beneath each cage was inspected daily at 1200 hr for the presence of seminal material. Corsets were then removed for 3 days, replaced for the next 3, and so on until the end of each phase of the experiment. Occasionally an animal worked free of his corset and in these instances the period of corseting was extended until the requisite number of collection days was reached. During 3 days of corseting the average weight loss was 6.38 g/day, and in the ensuing 3 day rest period the mean gain was 6.67 g/day. The lighting in the laboratory was natural. Nonfecal material recovered from the collecting paper included separate drops of seminal fluid containing sperm, fresh gelatinous plugs with large sperm masses, and hardened yellowish plugs with the consistency of dried wax. The latter sometimes were found intact and fully formed, but often only part of a plug could be identified. In daily records each fresh plug and each partial dried plug was scored as evidence of a separate emission. All plug material was preserved and weighed after thorough drying. Phase I o f the experiment lasted for 18 days comprising
METHOD Animals and Procedure
Twenty-two Long Evans male rats were obtained at 70
1This research was supported in part by U.S.P.H.S. grant 04000 from the National Institute of Mental Health. The assistance of J. J. Anisko and M. Buehler in collection of SE material and conduct of mating tests is acknowledged with thanks. 2Send reprint requests to: Dr. Frank A. Beach, Professor of Psychology, Department of Psychology, University of California, Berkeley, CA 94720. 91
92
BEACH
FIG. 1. Plastic corset worn during collection periods to prevent genital grooming and consumption of seminal material.
three day periods of corseting and collection alternating with three 3 day rest periods. During this phase no female rats were present in the building. At the beginning of the second phase ovariectomized females were introduced into individual living cages immediately adjacent to, or directly above or below, the cage of each experimental animal. For the first 3 days all males were corseted and checked for SSE. There followed 3 days of rest and then a second 3 day collection period. This was Phase IID (diestrus). Phase IIE followed immediately when all females were brought into estrus by injecting them with 10 /~g of estradiol benzoate SC every other day for a period of 7 days. Males were corseted and SSE counting began 3 days after the females received the first EB treatment. Three collection days were followed by 3 days of rest and then by 3 final days of corseting and SSE counting. Phase III began after at least 2 weeks of rest and consisted of mating tests in which each male was placed with a sexually receptive female and observed until he had ejaculated either 1 or 5 times. Groups assigned to the different ejaculation conditions were equated on the basis of SSE scores during Phase I. Phase IV began immediately after the mating test. Each male was corseted and returned to his home cage. Beginning 36 hr later and continuing for 7 days, with no intervening rests, records were kept of SSE production. During this post-test recovery period the 1 ejaculation (1E) and 5 ejaculation (5E) groups were subdivided. Members of approximately half of each group were placed in cages next to estrous females, and the other half were housed in a different building where no females were present.
Three months later all animals were corseted for 3 days, rested for 3 days, and recorseted for a final 3 days of SSE measurement, after which each rat was sacrificed and the seminal vesicles were removed and weighed after all secretory material had been removed. RESULTS Phases I, H and III Results obtained in Phases I, lID and IIE are summarized in Table 1. Noteworthy features of performance in the first phase were the average frequencies, and the range and day-to-day consistency of individual differences in SSE production. During Phase I the mean frequency of more than 2 emissions per 24 hours of corseting produced an average total of 36.6 mg of plug material for the entire period. Phase II results show clearly that simply exposing males to exteroceptive stimuli from diestrous or estrous females had no effect on SSE frequency. Mean total weights of dried seminal material were 36.0 mg and 39.l rag/rat/day for Phases lID and lIE respectively. When combined weights for I1D and IIE were correlated with total weight for Phase I the Rho value was +.72 (p
Variables Affecting "Spontaneous" Seminal Emission in Rats 1 F R A N K A. BEACH 2
University of California, Berkeley (Received 9 December 1974)
BEACH, F. A. Variables affecting "spontaneous" seminal emission in rats. PHYSIOL. BEHAV. 15(1) 91-95, 1975. The frequency of spontaneous seminal emission (SE) by isolated rats (X = 2.05 +- 0.64/day) was not increased when estrous females were housed in adjacent cages. Coital ejaculation during mating tests temporarily inhibited the production of SE, and inhibition was more marked after 5 than after 1 ejaculation with a female. Males experiencing only 1 coital ejaculation tended to resume production of SE somewhat sooner if they were exposed to stimuli from estrous females than if such stimuli were lacking. The possible functional significance of spontaneous and self-induced noncoital seminal emission which is common in a variety of mammals is discussed. Seminal Emission
Ejaculation
Sexual behavior
SUDDEN discharge of seminal fluid is a normal accompaniment of the ejaculatory reflex evoked by sexual stimulation in male mammals, but semen may be discharged under other conditions with or without ejaculatory contractions. Nocturnal emission is common in human males, occurring at least occasionally in 83 percent of American men according to Kinsey, e t al. [ 14]. " S p o n t a n e o u s " release of contents of the accessory sex glands is known to occur in males of other species including laboratory rats [16], hamsters [ 4 ] , cats [1], and chimpanzees [19]. The term spontaneous is set in quotation marks because of the possibility that ejaculation may be induced by manual masturbation in apes or by rubbing the penis against environmental objects in the case of other species. We have never observed such behavior on the part of rats or hamsters but its occurrence is not excluded. The present experiment was initiated to determine whether the frequency of spontaneous seminal emission (SSE) by physicially isolated male rats would be affected by exteroceptive stimuli derived from estrous females living in adjacent cages. Additional objectives were to investigate the consistency of individual differences in SSE frequency, possible relation o f size of the seminal vesicles to SSE production, and recovery of SSE after mating tests involving 1 or 5 coital ejaculations.
days of age. Until experimentation began at 100 days of age, and throughout the experiment, they were housed individually in metal cages (25.5 × 15 X 38 cm) with floors of 9 mm wire mesh which permitted fecal and seminal material to drop on the paper towelling underneath the cage. To prevent males from autogenital grooming and consumption of seminal products each rat wore one of the plastic corsets illustrated in Fig. 1. Pilot work showed that a week of corseting produced marked weight loss and therefore corsets were worn for 3 consecutive days during which the towelling beneath each cage was inspected daily at 1200 hr for the presence of seminal material. Corsets were then removed for 3 days, replaced for the next 3, and so on until the end of each phase of the experiment. Occasionally an animal worked free of his corset and in these instances the period of corseting was extended until the requisite number of collection days was reached. During 3 days of corseting the average weight loss was 6.38 g/day, and in the ensuing 3 day rest period the mean gain was 6.67 g/day. The lighting in the laboratory was natural. Nonfecal material recovered from the collecting paper included separate drops of seminal fluid containing sperm, fresh gelatinous plugs with large sperm masses, and hardened yellowish plugs with the consistency of dried wax. The latter sometimes were found intact and fully formed, but often only part of a plug could be identified. In daily records each fresh plug and each partial dried plug was scored as evidence of a separate emission. All plug material was preserved and weighed after thorough drying. Phase I o f the experiment lasted for 18 days comprising
METHOD Animals and Procedure
Twenty-two Long Evans male rats were obtained at 70
1This research was supported in part by U.S.P.H.S. grant 04000 from the National Institute of Mental Health. The assistance of J. J. Anisko and M. Buehler in collection of SE material and conduct of mating tests is acknowledged with thanks. 2Send reprint requests to: Dr. Frank A. Beach, Professor of Psychology, Department of Psychology, University of California, Berkeley, CA 94720. 91
92
BEACH
FIG. 1. Plastic corset worn during collection periods to prevent genital grooming and consumption of seminal material.
three day periods of corseting and collection alternating with three 3 day rest periods. During this phase no female rats were present in the building. At the beginning of the second phase ovariectomized females were introduced into individual living cages immediately adjacent to, or directly above or below, the cage of each experimental animal. For the first 3 days all males were corseted and checked for SSE. There followed 3 days of rest and then a second 3 day collection period. This was Phase IID (diestrus). Phase IIE followed immediately when all females were brought into estrus by injecting them with 10 /~g of estradiol benzoate SC every other day for a period of 7 days. Males were corseted and SSE counting began 3 days after the females received the first EB treatment. Three collection days were followed by 3 days of rest and then by 3 final days of corseting and SSE counting. Phase III began after at least 2 weeks of rest and consisted of mating tests in which each male was placed with a sexually receptive female and observed until he had ejaculated either 1 or 5 times. Groups assigned to the different ejaculation conditions were equated on the basis of SSE scores during Phase I. Phase IV began immediately after the mating test. Each male was corseted and returned to his home cage. Beginning 36 hr later and continuing for 7 days, with no intervening rests, records were kept of SSE production. During this post-test recovery period the 1 ejaculation (1E) and 5 ejaculation (5E) groups were subdivided. Members of approximately half of each group were placed in cages next to estrous females, and the other half were housed in a different building where no females were present.
Three months later all animals were corseted for 3 days, rested for 3 days, and recorseted for a final 3 days of SSE measurement, after which each rat was sacrificed and the seminal vesicles were removed and weighed after all secretory material had been removed. RESULTS Phases I, H and III Results obtained in Phases I, lID and IIE are summarized in Table 1. Noteworthy features of performance in the first phase were the average frequencies, and the range and day-to-day consistency of individual differences in SSE production. During Phase I the mean frequency of more than 2 emissions per 24 hours of corseting produced an average total of 36.6 mg of plug material for the entire period. Phase II results show clearly that simply exposing males to exteroceptive stimuli from diestrous or estrous females had no effect on SSE frequency. Mean total weights of dried seminal material were 36.0 mg and 39.l rag/rat/day for Phases lID and lIE respectively. When combined weights for I1D and IIE were correlated with total weight for Phase I the Rho value was +.72 (p
