INFLUENCE OF SEPARATE AND COMBINED SEPTAL AND AMYGDALA LESIONS ON MEMORY, ACOUSTIC STARTLE, ANXIETY, AND LOCOMOTOR-ACTIVITY IN RATS

The septohippocampal system and the amygdala have been implicated in c ognitive and emotional processes. A series of experiments was conducte d to examine the effects of separate and combined lesions of these are as on a variety of behaviors, including: startle responses to acoustic stimuli; sensory gating, using prepulse inhibition of acoustic startl e; anxiety, using the elevated plus-maze; locomotor activity in an ope n field; and memory, using both a spatial discrimination version of th e Morris water maze and the inhibitory (passive) avoidance test. Both septal and fimbria-fornix lesions markedly impaired the acquisition of spatial information in the water maze, had anxiolytic-like effects in the elevated plus-maze, increased reactivity to footshock, and had ma rginal effects on prepulse inhibition and baseline startle. Septal and fimbria-fornix lesions also increased locomotor activity in the later stages of a session of open field exploration, but only septal lesion s produced ''freezing'' during the early portion of this session and d uring inhibitory avoidance training. Amygdala lesions markedly impaire d prepulse inhibition of acoustic startle. Amygdala lesions also atten uated the effects of septal lesions on freezing in the open field and on footshock reactivity, but did not affect the anxiolytic-like effect s or hyperactivity associated with septal lesions. Amygdala lesions by themselves had no significant effect on water maze performance, but s ignificantly potentiated the effects of septal lesions. These results suggest that there are dissociations between the effects of septal and fimbria-fornix lesions and that the interactions between the amygdala and septum in cognitive and emotional processes are task dependent. ( C) 1995 Academic Press, Inc.