The cone field: a spatial discrimination task for the automatic and simultaneous assessment of working and reference memory in rats.

A cone field apparatus was developed in which spatial working memory (WM) and reference memory (RM) can be assessed automatically and simultaneously. The cone field is a large open field with 16 cones in it. A configuration of four cones was baited with a food pellet. In the holeboard, the predecessor of the cone field, no clear criteria exist to distinguish between accidental and directed orientations toward the target (hole). In the cone field the visit to the target (cone) is unambiguously defined. We found that senescent rats were impaired on both the WM and the RM. The development of a fixed pattern of visiting the baited cones was effectively prevented by starting the rats randomly from four different positions. When only one start position was used, rats developed a fixed pattern of visiting the baited cones. This pattern was more pronounced in the young than in the senescent animals. In the last experiment we explored whether the task might be suited for the assessment of WM and RM performance in longitudinal studies. Rats performed like naive animals on both memory components when re-acquisitions were separated by 4-month intervals without training.

Excessive grooming induced by somatostatin or its analog SMS 201-995.

Intracerebroventricular (i.c.v.) administration of somatostatin or SMS 201-995 induces excessive grooming behavior in rats. The grooming inducing effect of somatostatin is rather weak, as doses of 300 ng or less did not result in increased total grooming scores. In contrast a dose of 10 ng SMS 201-995 already significantly increased the total grooming scores. However, doses of 100 ng and more did not further increase the total grooming scores reached with a 50 ng dose of this peptide. Systemic administration of SMS 201-995 in doses up to 900 micrograms did not result in excessive grooming behavior. The patterns of excessive grooming induced by i.c.v. SMS 201-995 and somatostatin were characterized by a predominant display of scratching. Since peptide-induced scratching is mainly due to activation of opiate receptor systems it is suggested that opiate receptors are involved in the behavioral response to SMS 201-995 and somatostatin administration. This suggestion is further supported by the suppressive effect of naloxone on excessive grooming induced by these peptides. Haloperidol and neurotensin also suppress the excessive grooming induced by somatostatin but not that induced by SMS 201-995. Finally, tolerance developed to the grooming-inducing effect of SMS 201-995 and somatostatin. In addition there was cross tolerance between somatostatin and SMS 201-995.