Elsevier

Physiology & Behavior

Volume 62, Issue 6, December 1997, Pages 1265-1271
Physiology & Behavior

Article
Kindling of the Dorsal and the Ventral Hippocampus: Effects on Learning Performance in Rats

https://doi.org/10.1016/S0031-9384(97)00303-XGet rights and content

Abstract

BECKER, A., K. LETZEL, U. LETZEL AND G. GRECKSCH.

Kindling of the dorsal and the ventral hippocampus: Effects on learning performance in rats.

PHYSIOL BEHAV 62(6) 1265–1271, 1997.—The hippocampus represents a heterogeneous structure which has been associated with different functions. It has been suggested that it plays an important role in both learning and memory and epileptogenesis. Thus, it is not surprising that seizure activity generated in the hippocampal formation interferes with memory storage. Little is known about the functional differentiation between the dorsal (DH) and ventral hippocampus (VH). To study this functional differentiation, we kindled Wistar rats either in the DH or in the VH by electrical stimulation. Afterwards, learning performance of these rats was tested in three different models, i.e., response to change (short-term memory), shuttle box (two-way active avoidance), and Y-chamber (brightness discrimination reaction). It was found that VH-kindled rats reached higher seizure scores than DH-kindled rats, but there was no difference in seizure duration. Kindling induced in the VH significantly impaired shuttle box learning, whereas DH-kindled rats showed a dramatically worsened acquisition in the brightness discrimination task. Different anatomical projections probably account, in part, for these differences.

Section snippets

Materials and Methods

For all procedures followed, ethical approval was sought prior to the experiments according to the requirements of the National Act on the Use of Experimental Animals (Germany).

Results

Repeated stimulation to both hippocampal structures resulted in constantly increasing seizure severity and seizure duration (Fig. 2). Regarding seizure severity, significant differences between the experimental groups were found (F(1, 50) = 18.02, p < 0.001). In the course of kindling development, seizure duration increased considerably (Fig. 2). However, there were no differences in seizure duration in rats after kindling of the ventral or the dorsal hippocampus (F(1, 50) = 0.68, p = 0.405).

Discussion

The results of this study indicate a functional differentiation of two regions in the hippocampal formation with regard to the induction of electrical kindling and subsequent learning impairments.

We found stimulation of the hippocampal formation resulted in kindling characterized by constantly increasing seizure severity (Fig. 2). Interestingly, there were striking differences in the initial phase of kindling. VH-kindled rats reached higher seizure scores, but following stimulation 10, the

Acknowledgements

We thank Mr. A. Toms (U.K.) for his help in improving the English.

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