LORDOSIS BEHAVIOUR IN MALE RATS: EFFECT OF DEAFFERENTATION IN THE PREOPTIC AREA AND HYPOTHALAMUS K. YAMANOUCHI AND Y. ARAI Department of Anatomy, Juntendo University School of Medicine,
Hongo, Tokyo 113, Japan
(Received 18 October 1977) Differentiation of sexual behaviour patterns in male rats is dependent on the internal secretion of the testes during neonatal life. Removal of the testes at this time causes feminization and results in male rats which display female patterns of sexual behaviour (Gorski, 1971). Female patterns of behaviour are usually rare in normal male rats but recently we found that transection of the dorsal afferent neurones to the preoptic and anterior hypothalamic areas potentiated the display of lordosis in hormonally primed male rats (Yamanouchi & Arai, 1975). In the present study, further neuroanatomical analysis was carried out to clarify the localization of the afferent pathway involved in the regulation of lordosis behaviour. Anterior or posterior roof deafferentation (ARD or PRD) was performed by lowering an L-shaped Halasz knife (2-5 mm horizontal blade) to the level of the anterior commissure and then rotating it for 180° antero- or postero-horizontally. In some rats, the knife was removed without rotation (sham ARD). All operated male rats were castrated at the time of the operation and were then left undisturbed for 4 weeks. As a preliminary test which tends to facilitate behavioural responses, all rats were injected s.c. with 50 µg oestradiol benzoate for 2 successive days and then with 0-5 mg progesterone on the next day. In response to this treatment, seven out often rats with ARD displayed five or more lordosis responses and the lordosis quotient (LQ, ratio of number of lordosis responses : ten mounts 100) was 47-0 ± 11-1 (s.e.m.). In contrast, none of the seven rats with PRD showed lordosis and animals in the sham ARD and control groups were also less receptive (LQ 6-3 ± 3-8, 6-3 + 6-3 respectively). Two weeks later, the rats were treated with 2 µg oestradiol benzoate for 2 successive days and tested on day 4, 5-7 h after the injection of 0-5 mg progesterone. Table 1 shows that all rats with ARD displayed a high number of lordoses; the LQ was 89-0±4-8, which was comparable to that of similarly injected ovariectomized female rats. In addition, soliciting behaviour (ear-wiggling and hopping) was frequently observed in four out of ten rats with ARD. However, none of the rats with PRD responded with lordosis and few lordoses were observed in the sham ARD and control groups. Soliciting behaviour was also not seen in these groups. Two weeks later, the rats were injected with a further 2 µg oestradiol benzoate but without progesterone and in this case, rats with ARD still showed a high LQ (68-9 + 14-2) which was not signi¬ ficantly different from the value obtained in rats treated with oestradiol benzoate and progesterone. In the other groups, however, most of the rats did not display lordosis and no soliciting behaviour was observed. These results indicate that the dorsal neural inputs to the preoptic and anterior hypo¬ thalamic areas which pass only anterior to the anterior commissure exert an inhibitory influence on the mechanism which mediates oestrous behaviour. Since interruption of the fibre connections between the preoptic and anterior hypothalamic areas and other parts of the hypothalamus did not facilitate lordosis in male rats (K. Yamanouchi «fc Y. Arai, =
Table 1. Effect of anterior or posterior roof deafferentation (ARD or PRD) on lordosis behaviour (means ± s.e.m.) in male rats treated with oestradiol benzoate (2 µg) for 3 days with or without the addition of progesterone (0-5 mg) on the day of the test Oestradiol benzoate+
progesterone
Group
No. of
Incidence
rats
of lordosis
Control Sham ARD ARD PRD
1/8
2/8 10 7
10/lOf 0/7
Mean LQ* of group 5-0 ±5-0 20-0 ±13-2
89-0±4-8t 00 ±00
Oestradiol benzoate only Incidence of lordosis
1/8 2/8 9/10§ 0/7
Mean LQ of group 2-5 ±2-5 17-5 ±12-1 68-9 ± 14-211 00 ±00
*
LQ, lordosis quotient (ratio number of lordoses: ten mounts 100). t P
Hongo, Tokyo 113, Japan
(Received 18 October 1977) Differentiation of sexual behaviour patterns in male rats is dependent on the internal secretion of the testes during neonatal life. Removal of the testes at this time causes feminization and results in male rats which display female patterns of sexual behaviour (Gorski, 1971). Female patterns of behaviour are usually rare in normal male rats but recently we found that transection of the dorsal afferent neurones to the preoptic and anterior hypothalamic areas potentiated the display of lordosis in hormonally primed male rats (Yamanouchi & Arai, 1975). In the present study, further neuroanatomical analysis was carried out to clarify the localization of the afferent pathway involved in the regulation of lordosis behaviour. Anterior or posterior roof deafferentation (ARD or PRD) was performed by lowering an L-shaped Halasz knife (2-5 mm horizontal blade) to the level of the anterior commissure and then rotating it for 180° antero- or postero-horizontally. In some rats, the knife was removed without rotation (sham ARD). All operated male rats were castrated at the time of the operation and were then left undisturbed for 4 weeks. As a preliminary test which tends to facilitate behavioural responses, all rats were injected s.c. with 50 µg oestradiol benzoate for 2 successive days and then with 0-5 mg progesterone on the next day. In response to this treatment, seven out often rats with ARD displayed five or more lordosis responses and the lordosis quotient (LQ, ratio of number of lordosis responses : ten mounts 100) was 47-0 ± 11-1 (s.e.m.). In contrast, none of the seven rats with PRD showed lordosis and animals in the sham ARD and control groups were also less receptive (LQ 6-3 ± 3-8, 6-3 + 6-3 respectively). Two weeks later, the rats were treated with 2 µg oestradiol benzoate for 2 successive days and tested on day 4, 5-7 h after the injection of 0-5 mg progesterone. Table 1 shows that all rats with ARD displayed a high number of lordoses; the LQ was 89-0±4-8, which was comparable to that of similarly injected ovariectomized female rats. In addition, soliciting behaviour (ear-wiggling and hopping) was frequently observed in four out of ten rats with ARD. However, none of the rats with PRD responded with lordosis and few lordoses were observed in the sham ARD and control groups. Soliciting behaviour was also not seen in these groups. Two weeks later, the rats were injected with a further 2 µg oestradiol benzoate but without progesterone and in this case, rats with ARD still showed a high LQ (68-9 + 14-2) which was not signi¬ ficantly different from the value obtained in rats treated with oestradiol benzoate and progesterone. In the other groups, however, most of the rats did not display lordosis and no soliciting behaviour was observed. These results indicate that the dorsal neural inputs to the preoptic and anterior hypo¬ thalamic areas which pass only anterior to the anterior commissure exert an inhibitory influence on the mechanism which mediates oestrous behaviour. Since interruption of the fibre connections between the preoptic and anterior hypothalamic areas and other parts of the hypothalamus did not facilitate lordosis in male rats (K. Yamanouchi «fc Y. Arai, =
Table 1. Effect of anterior or posterior roof deafferentation (ARD or PRD) on lordosis behaviour (means ± s.e.m.) in male rats treated with oestradiol benzoate (2 µg) for 3 days with or without the addition of progesterone (0-5 mg) on the day of the test Oestradiol benzoate+
progesterone
Group
No. of
Incidence
rats
of lordosis
Control Sham ARD ARD PRD
1/8
2/8 10 7
10/lOf 0/7
Mean LQ* of group 5-0 ±5-0 20-0 ±13-2
89-0±4-8t 00 ±00
Oestradiol benzoate only Incidence of lordosis
1/8 2/8 9/10§ 0/7
Mean LQ of group 2-5 ±2-5 17-5 ±12-1 68-9 ± 14-211 00 ±00
*
LQ, lordosis quotient (ratio number of lordoses: ten mounts 100). t P
