Data were obtained from 104 injection sites in 73 rats, 47 males and 26 females. All animals exhibited some combination of complex behaviors in response to picrotoxin injections, and there was no site where the animal failed to show a behavioral response to the injection, As found by others (7), there was no behavioral effect of injecting saline into the hypothalamus instead of the picrotoxin.
Offense, in the form of bite-and-kick attack, was obtained at eight sites, all in the area of the anterior hypothalamus. Three sites were in females and five in males. These sites are shown as stars in Fig. 1, and they are all found at levels of 7.2 mm and 7.7 mm in the Paxinos and Watson atlas (22). Whereas bite-and-kick attack was obtained at 8 out of the 47 sites near the anterior hypothalamus, it was found at none of the other 57 sites in the hypothalamus, a difference which is statistically significant (Chi square = 8.7, p < 0.01).
Two other offense behaviors, offensive sideways posture and on-top posture, were obtained at 13 sites in the anterior hypothalamus, as well as at three sites outside of this area. All three of the offensive sideways postures noted on Fig. 1 were found in conjunction with bite-and-kick attack. While only 4 of the 15 on-top posture sites were in conjunction with bite-and-kick attack, most were in or adjacent to the anterior hypothalamus.
Mounting behavior was obtained in response to picrotoxin at 12 sites, all in the anterior hypothalamus and medial preoptic area, as shown in Fig. 2 by the filled triangles. Due to experimental design, in each case the test rat mounted an opponent of the same sex. Three females mounted female opponents. Nine males mounted male opponents, and when female opponents were alternated with the male opponents, the mounting continued with the same form and frequency. In two cases, the mounting behavior was obtained in conjunction with a bite-and-kick attack.
Mounting by the opponent was obtained at 10 sites, including two females being mounted by a female opponent. In three tests, there was mounting by the test animal and by the opponent in the same test. Mounting by the opponent was found in the anterior hypothalamus in all except one case, but unlike the mounting by the test animal it was found in the posterior portion of the anterior hypothalamus (Fig. 2, 7.2 mm) as well as in the anterior portion of the anterior hypothalamus (Fig. 2, 7.7 mm).
Persistent locomotion, often in the form of circling behavior (both ipsiversive and contraversive), was the most salient non-social behavior observed. It was found throughout the hypothalamus at 35 sites (Fig. 2, dark circles).
Other behaviors were found at various sites throughout the hypothalamus without any evident localization or association with offense or sexual behaviors. These behaviors included self-grooming, social grooming, upright posture and boxing, digging, pushing wood chips, leaping, and feeding.
The time courses of bite-and-kick attack, mounting, mounting by the opponent, and persistent locomotion in response to the picrotoxin injection are shown in Fig. 3. Mounting by the opponent began by the second minute after injection; however, bite-and-kick attack and mounting never occurred before the fifth minute after injection. Bite-and-kick attack peaked from minutes 5 to 20 and never occurred after 30 min. Mounting reached a peak frequency from minutes 13 to 28, and then dropped off, approaching zero again by the 36th min. Mounting by the opponent had a time course which peaked from minutes 5 to 24 and dropped to zero by minute 30. Locomotion peaked from minutes 5 to 24 and then gradually declined, but did not reach zero until after the 36th min.
Picrotoxin was also injected, using a similar procedure, into the ventromedial tegmentum in 26 rats. Most of the sites were near or immediately posterior to the lesion placements used previously to abolish offense (3, 13). Offense behavior was never observed in any of the rats. The most common behavior observed was circling locomotion (13 animals). Social grooming was observed in four cases, and upright posture and boxing in three cases.