Generation of locomotor activity in fin motoneurons of the lamprey during "fictive locomotion"

The river lamprey (Lampetra fluviatilis) possesses two different types of muscles responsible for swimming. For propulsion of the animal during undulatory movement the lateral, in the trunk of the lamprey located, myotomal musculature is responsible, that is antiphasically active. These muscles are controlled by myotomal motoneurons. For controlling of the horizontal position of the lamprey, the fin of the lamprey is used, controlled by fin motoneurons. Both types of motoneurons are located in the spinal cord. Intracellular recordings of myotomal and fin motoneurons showed during swimming that the latter ones are antiphasic activated compared to myotomal motoneurons. The main aim of this thesis was to find the answer of the question how this antiphasic activation is controlled. Therefore all experiments were performed on the �fictive swimming� animal. First it was tried to characterize fin motoneurons morphologically and electrophysiologically. Then it was resolved by current injection to the recorded fin motoneurons if they get a phasic inhibitory or excitatory drive from other neurons. Lesion experiments were used to identify whether fin motoneurons receive contralateral or ipsilateral synaptic input and whether this input was inhibitory or excitatory. It could be shown that there are at least two morphological distinct types of fin motoneurons in the spinal cord of the lamprey, both characterized by a probably specialized shape of membrane potential oscillation. After classification of the different shapes of the membrane potential oscillations of all recorded fin motoneurons using �hierarchical clustering� it could be shown that there is a third different membrane potential pattern, besides the two mentioned before. This third shape could not be allocated to the morphological fin motoneurons so far. The results show that there are at least three different patterns of membrane potential oscillations in the fin motoneurons of "Lampetra fluviatilis" and therefore this could be a hint that there are also three different types of cells located in the lamprey spinal cord. After injection of negative current to these three different types of fin motoneurons it could be shown for two types of them that they receive phasic inhibitory and excitatory input during membrane potential oscillations. The data for the third type are not enough yet to confirm this result. After sagittal and transversal lesions performed on the spinal cord of Lampetra fluviatilis showed that the shape of the membrane potential oscillation of fin motoneurons still persisted, but that the peak-to-peak amplitude was affected. It could be shown that after performing a sagittal lesion the peak-to-peak amplitude decreased significantly whereas a transversal lesion (rostral or caudal to the recorded cell) showed a significant increase of the peak-to-peak amplitude. This means that fin motoneurons receive excitatory drive from the contralateral hemisegment and that they receive inhibitory drive from ipsilateral located segments. According to all the collected results and based on known literature a possible model was developed to show which neurons, located in the spinal cord, could be involved for coordinating and controlling fin motoneurons and their antiphasic activation compared to myotomal motoneurons