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190 500 1000

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Cortex Hippocampus

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Methods

Results

Conclusions

Walking the plank: Role of the medial septum in distance estimation S.S. Winter; M.M. Martin; D.G. Wallace

Dept Psychology, Northern Illinois Univ., DeKalb, IL, USA

Figure 2: Histological analysis: (A) photographs in grayscale of coronal sections stained for AchE from representative animals in the MS SHAM (top) and MS SAP (bottom) groups. (B) optical density of photographs is plotted. Significant group differences were observed for the hippocampus but not the cortex

Correspondence:

S. Winter SWinter@niu.edu

D. Wallace DWallace@niu.edu

Web: www.niu.edu/user/tj0dgw1

Support Contributed By: NINDS grant NS051218

743.21

Introduction

Controversy surrounds the role of the septohippocampal system in spatial orientation. Recent work has demonstrated that selective cholinergic deafferentation of the hippocampus impairs use of self-movement cues while sparing environmental cue use (Martin, & Wallace, 2007). The deficit in self-movement cue use has been shown to be selective for distance estimates (Martin, Horn, Kusman, & Wallace, 2007). The current study examined the role of the septohippocampal cholinergic system in processing self-movement cues related to changes in position or distance estimation in a food carrying task.

Figure 3: Consumption time of each food item is plotted. Significant group differences were observed for all food items.

Figure 1: Photograph of each apparatus used; 240 cm plank (left) and elevated plus-maze (right).

Figure 4: Mean velocity of rats running to the food items (outward) and back to the refuge (homeward) during the last day of training is plotted. Significant main effects of group and direction, and interaction of group by direction were observed.

Figure 5: Probability to carry food items under dark conditions is plotted for each group. There were significant main effects of food and plank length. No significance was observed for the main effect of group, or any of the interactions.

A B

Figure 8: Percentage of time spent in open arms of the elevated plus-maze is plotted for each group. The MS SAP group spent significantly more time in the open arm.

References

Surgery: Female Long-Evans rats were used. The MS SAP group received two injections of 192 IgG-Saporin (0.5 μg/μL) into each hemisphere (AP: +0.3; ML: ±0.2; DV1: -7.5 [0.4 μL]; DV2: -6.5 [0.3 μL]). The MS SHAM group was given injections of phosphate buffered saline into the same coordinates. Lesions were assessed through optical density measures of brain slices stained for acetylcholine esterase (AchE).

Plank: The plank consisted of an elevated board (Short: 15 X 240; Long: 15 X 480 cm) with a refuge at one end. Rats were trained under dark conditions to retrieve food pellets from the end of the plank opposite the refuge. During testing, rats were given two food items of each size (190, 500, 1000 mg) in a random order. Rats were first tested on the 240 cm plank under dark conditions, followed by the 480 cm plank under dark conditions, then the 240 cm plank under light conditions, and finally the 480 cm plank under light conditions. Each testing condition lasted for five consecutive days. Probability to carry the item, time to eat each food item, and velocity traveled were assessed.

Plus-Maze: The elevated plus-maze consisted of two open arms (10 X 50 X 1.5 cm), two closed arms (10 X 50 X 50 cm), and a central platform (10 X 10 cm) connecting them. Testing was done under dark conditions. Rats were placed on the center platform facing one of the closed arms, and were allowed to freely explore for five minutes. Activity was monitored by tracking the rat using Noldus software to calculate the percent time, number of entries, and distance traveled in the open arms.

Martin, M.M., Horn, K.L., Kusman, K.J., & Wallace, D.G. (2007). Medial septum lesions disrupt exploratory trip organization: Evidence for septohippocampal involvement in dead reckoning. Physiology & Behavior, 90, 412-424.

Martin, M.M. & Wallace, D.G. (2007). Selective hippocampal cholinergic deafferentation impairs self-movement cue use during a food hoarding task. Behavioural Brain Research, 183, 78-86.

•Selective hippocampal cholinergic deafferentation influences food carrying by:

•Decreasing the time to consume food items.

•Increasing travel velocity.

•Increasing probability to carry food items.

•Selective hippocampal cholinergic deafferentation increases percent time spent in the open arms of the plus-maze, consistent with a decrease in anxiety.

•This observation demonstrates that an anxiety explanation is not sufficient to account for disruptions in food carrying behavior associated with medial septum lesions.

•The observed results on the plank are consistent with a role of hippocampal cholinergic function in accurate processing of distance estimates.

Experiment 1

Experiment 2

Figure 7: Percent change in probability to carry (between long and short planks) is plotted for each group across the different food items. Significant group differences were observed with the 1000 mg food item under both conditions. No difference was observed for the 190 or 500 mg food items.

Acknowledgements:

Shane Knapp

Michael DeMeyer

Figure 9: Number of entries in the open arms is plotted for each group. No significant differences were observed between groups.

Figure 10: Total distance traveled in the open arms is plotted for each group. No significant differences were observed between groups.

Figure 6: Probability to carry food items under light conditions is plotted for each group. There were significant main effects of group, food, and plank length, and an interaction of group by food by length. No other interactions were significant.