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Impulse activity of lumbar interneurons was recorded extracellularly during fictious locomotion of thalamic cats. Neurons whose activity was modulated in the rhythm of fictitious locomotion were revealed in the lateral intermediate zone and in the lateral ventral born. 41.2% of these neurons were mainly activated at the phase of "flexion", 48.5%--at the phase of "extension" and 10.3%--at both phases. Neurons with tonically increasing or decreasing activity during rhythmic efferent discharges and neurons whose activity did not change during fictitious locomotion were also observed. All these types of neurons were similarly activated during late discharges in efferent nerves. But in this case the depth of modulation of neuronal activity was lower than during fictitious locomotion. Afferent inputs to the recorded interneurons were also investigated. The neuronal organization of the spinal locomotor generator is discussed on the basis of the obtained data.

The effect of intracellular cyclic adenosine monophosphate (cAMP) injection and extracellular theophylline application on calcium current were investigated in Helix RPa3 and LPa3 neurons. It was found that iontophoretic cAMP injection (current 10-35 nA, duration about 1 min) caused a decrease in the amplitude of calcium current which restored to the initial level following the cessation of injection. Its current-voltage characteristic was not displaced along the potential axis in the presence of cAMP injection indicating that the calcium current decrease was due to the fall of maximum calcium conductance. Extracellular theophylline application in concentration of 1 mM/1 caused a decrease in the calcium current amplitude by 50-75% from the initial level. The hypothesis is discussed about the participation of cytoplasmic factors in regulation of calcium current in mollusc neurons.

Impulse activity of lumbar interneurons was recorded extracellularly during the late long-lasting discharges in efferent nerves of immobilized thalamic animals. 70% of investigated neurons changed their activity during the late discharges. The activity of 35% of neurons increased, during late discharges in flexor nerves, while during activity in extensor nerves it was inhibited. 27% of neurons had the opposite reaction. Neurons, whose activity correspondingly increased (5%) or decreased (3%) during the late discharges both in flexor and extensor nerves were also observed. Most interneurons, changing their activity during late discharges, were located in the lateral parts of intermediate zone and in the lateral ventral horn at the depth of 2.8 mm. Certain dependence between the character of afferent inputs to the neuron and correlation of its activity with late efferent discharges was revealed. Neurons whose activity did not change during late discharges (40%) were mainly located somewhat dorsally, at the depth of about 2.0 mm. Possible role of described interneurons in generation of late discharges is discussed.