The mechanic-opto-electronic system COGITAT (Version 5, Cognitron GmbH, Göttingen, Germany) records activities of rodents by a set of infrared beams which are situated at different levels in transparent tubes mounted within the holes of a board. The board with 25 deep holes containing the transparent tubes is framed by transparent walls and has a special entrance for the rats. Eight of the holes are baited with small hidden food pellets (40 mg) distributed in a distinct pattern not visible to the animals while walking. The animals learn during exploration in several daily sessions the pattern using their individual strategy. Spatial learning, working and reference memory were tested. Before entering the hole-board, the animal remains in its home cage for adaptation to the laboratory for one hour. A trial on the board is finished either when a fixed time is over or as soon as the animal has collected and eaten of the 8 pellets. Animals with a good knowledge of the pattern are able to collect all pellets within an average time of 20 s.

The software is running on Windows 95 or Windows NT. The operator uses a comfortable graphical interface to analyze and to display information about inspected holes on the surface of the plate, the number of visits deep in the holes, the number of collected and eaten pellets in a given time, inspections and/or visits of baited or unbaited holes (reference learning), reinspections and/or revisits of previously baited or unbaited holes (working memory errors). The data allow recognition of the searching strategies, the learning and memory capacities and the orientation capacities within the space using distal cues. The system is useful for investigations of rats, mice, and transgenic or knock-out mice. For demonstration here we used an animal model with rats that were affected by predamaged brains, with/without focal lesions in two different brain structures.

The model

Both oligemic episodes and increased iron concentrations in discrete brain regions have been reported to occur with age, and are thought to be associated with neurodegenerative diseases [1, 2]. Following bilateral clamping of carotid arteries (BCCA) in normotensive adult male rats for 60 min under pentobarbital anesthesia, animals subsequently received bilaterally 30ng FeCl₃ dissolved in 0.25ml buffer into the substantia nigra pars compacta [BCCA+FeCl₃SN], or 1.5mg FeCl₃ in 2ml unilaterally into the ventrolateral striatum [BCCA+FeCl₃Strvl]. BCCA does not result in delayed neuronal death [3]. Three months post surgery the animals learnt to find all hidden pellets during 10 sessions (one per day) of 3 min, during 12 sessions of 1 min, and 12 sessions of 30 s.

Results

Using COGITAT, progressive changes in learning and memory were analyzed in time. BCCA rats found and ate fewer pellets than BCCA+FeCl₃SN rats during the learning period of 3min during 9 subsequent days. The opposite was found in BCCA+FeCl₃Strvl rats. The time to find all 8 pellets was shorter in the BCCA+FeCl₃SN rats than in the BCCA+FeCl₃Strvl rats. BCCA+FeCl₃SN rats showed most visits of unbaited holes on the 3rd day, but the rats learnt very fast to prevent the wrong searching strategy. BCCA+FeCl₃Strvl rats, however, showed an increasing number of reference memory errors during 8 days, and reached a plateau until day 10, whereas BCCA rats without additional iron in the striatum showed the same increased amount of reference memory errors as BCCA+FeCl₃SN rats, but learnt very fast to correct the unsuccessful searching strategy. BCCA+FeCl₃SN rats showed the most working memory errors.

Summary

The system COGITAT provides data from which specific deficiencies in different pathological situations can be recognized. The computerized and automatic analysis of the complete behavioral parameters with the statistic and graphic presentation offers an objective characterization of the system analyzed.

References

1. Heim, C.; Zhang, J.; Lan, J.; Sleklucka, M.; Kurz, T.; Sontag, T.; Arzberger, T.; Riederer, P.; Gerlach, M.; Sontag, K.H. (1998). Transient cerebral oligemia triggers late congnitive deficiencies - consequences of free radical formation? Submitted.
2. Connor, J.R. (1992). Proteins of iron regulation in the brain in Alzheimer’s disease. In: Iron and Human Disease (R.D. Lauffer, ed.), 365-393. Boca Raton: CRC Press.
3. Melzacka, M.; Weiner, N.; Helm, C.; Schmidt-Kastner, R.; Rieklucka, M.; Sontag, K.H.; Wesemann, W. (1994). Effect of transient reduction of cerebral blood flow on membrane anisotropy and lipid peroxidation in different rat brain areas. Neurochem. Int., 25, 161-168.
4. Heim, C.; Sontag, K.H. (1994). Reference memory is affected by transient bilateral clamping of the carotid arteries in rats (BCCA). J. Neural Transm. [PDSect], 7, 47-59.