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192-IgG Saporin lesions of the medial septum or nucleus basalis magnocellularis disrupt exploratory trip organization.

D.G. Wallace*, S.S. Winter, M.M. Martin, J.L. McMillinDept Psychology, Northern Illinois Univ., DeKalb, IL, USA

Long Evans female rats received injections of 192 IgG-Saporin into the medial septum (MS, n=5) or nucleus basalis magnocellularis (NB, n=4). Rats that received saline injected into either structure were collapsed into one group (Sham, n=7). Subsequent to recovery, rats were placed on a large circular table with access to a refuge under complete dark conditions (infrared cameras and goggles were used to visualize the rat). Rats were free to explore the table for 50 minutes. Rats were given five exploratory sessions. All exploratory trips (up to 25 trips) were digitized using the Peak Performance motion capture system.

Figure 2: Coronal sections stained for acetylcholinesterase are presented for a representative sham (A), medial septum (B), nucleus basalis magnicellularis (C). The graph (D) plots the average optical density for areas of the cortex and hippocampus. MS lesions produced selective hippocampal deafferentation. NB lesions failed to produce significant reductions in cortical acetylcholinesterase.

Previous work has demonstrated that rats use self-movement cues to organize their exploratory behavior. The hippocampus and several cortical areas have been implicated in processing self-movement cues. The current study investigated whether selective cholinergic deafferentation of the hippocampus or cortex differentially influenced the organization of exploratory behavior.

Acknowledgments: Bethany Barnes, Deirdre Clarke, Steve Wagner, Jenny

Raines, Patricia Wallace, Adam Sommerfeld, William Mcdermott

Correspondence: D.G. Wallace dwallace@niu.edu Web: www.niu.edu/user/tj0dgw1

Grant support: NINDS grant NS051218 to D.G. Wallace

Figure 4: Distance traveled on searching segments (blue bars) did not differ among groups. Each rat’s set of homeward segments (red bars) were divided into short and long segments. No group differences were observed in the distance traveled on short or long homeward segments.

Figure 1:Topographic and kinematic characteristics are plotted for three exploratory trips. Searching segments (blue lines) of exploratory trips are a sequence of progressions. Homeward segments (red lines) reflect the progression after the last stop. Note that homeward segment peak speed varies as a function of progression length.

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Figure 5: Searching segment (blue bars) path circuity did not differ among groups. Groups did not differ in homeward segment (red bars) path circuity. Long homeward segments were significantly more circuitous relative to short homeward segments.

Figure 6: Peak speeds observed on searching segments (blue bars) did not differ among groups. Both Sham and NB groups showed a significant increase in peak speeds across short and long homeward segments (red bars). The MS groups did not demonstrate a significant increase in peak speed across short and long homeward segments.

•MS lesions produced significant cholinergic deafferentation selective to the hippocampus.

•These lesions spared home base establishment and spared many characteristics of exploratory trip organization.•These lesions impaired modulation of peak speed observed across short and long homeward segments.

•NB lesions produced significant cholinergic deafferentation selective to the cortex.

•No impairments were observed in the organization of exploratory behavior.

•These results are consistent with previous work demonstrating a role for the medial septum in distance estimation derived from self-movement cues.

Abstract

Methods

Results

Conclusions

Figure 8: Groups did not differ in the error associated with the peak speed location on searching segments (blue bars). Although groups did not differ in error associated the peak speed location on homeward segments (red bars), larger errors were observed on long homeward segments relative to short homeward segments.

Figure 3: Quadrant preference (((T-B)+(T-C)+(T-D))/3) and total distance traveled were evaluated for the first exploratory session. Groups did not significantly differ in either of these general characteristics of exploratory behavior.

Figure 7: Groups did not differ in the standard deviation associated with the peak speed location on searching segments (blue bars). Although groups did not differ in standard deviations associated with the peak speed location on homeward segments (red bars), larger standard deviations were observed on long homeward segments relative to short homeward segments.

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