Increasing copulatory behaviour in ageing male rats with an electrical stimulus.

In our laboratory, young male Holtzman rats have good libido but this decreases with age until some males will refuse to mate a receptive female. After accumulating data on a male's fertility and on his offspring, this lack of libido is a hindrance in certain types of experiments. One of the authors noted that when he pinched old males to wake them up or to make them more active, they frequently mated very quickly. In searching for a satisfactory stimulus for ageing males, it was noted that Barfield & Sachs (1968) augmented the sexual activity of male rats with electrical shock. The present report concerns the effect of electrical stimulation of ageing male rats on their frequency of copulation. Eighteen albino male Holtzman rats aged 14 to 18 months and weighing approximately 650 g, which had had good libido and were fertile but which now had a reduced interestin receptive females, were used. They were stimulated in the shaved dorso-lumbar region with an electrical shock of 10 to 15 V for 1 to 2 sec with an electroejaculation apparatus using electrodes 5 mm apart. The tests were made between 22.00 and 02.00 hours by placing an untreated female in oestrus in the cage where the male was housed. In the first experiment, ten males were tested as follows: 3 min with a re¬ ceptive female, then 3 min rest with no female present, then 3 min with a receptive female but stimulated electrically if no interest in the female was shown, and then 3 min rest. This was repeated three times in succession. In Exp. 2, eight 14to 16-month-old males were placed with receptive females for 30 min with intermittent electrical stimulation. On another day, they were placed with a receptive female but received no electrical stimulation. For four of the eight rats, the experimental period was first, and for the remaining four, the control period was first. The differences in the number ofmounts of the two groups was significant in Exp. 1 (P>0-05) (Table 1) and in Exp. 2 (P>0-005) (Table 2). In Exp. 2,