Periodically modulated inhibition and its postsynaptic consequences—I. General features. Influence of modulation frequency

• Published in: Neuroscience 1995-10, Vol.68 (3), p.657-692
• Main Authors: Segundo, J.P., Vibert, J.-F., Stiber, M., Hanneton, S.
• Format: Article
• Language: English
• Subjects: Action Potentials; Action Potentials - physiology; Animals; Astacoidea; Astacoidea - physiology; Biochemistry. Physiology. Immunology; Biological and medical sciences; Crustacea; Electrophysiology; Fundamental and applied biological sciences. Psychology; In Vitro; In Vitro Techniques; Invertebrates; Life Sciences; Mechanoreceptors; Mechanoreceptors - physiology; Membrane Potentials; Membrane Potentials - physiology; Models, Neurological; Nerve Fibers; Nerve Fibers - physiology; Neuronal Plasticity; Neuronal Plasticity - physiology; Neurons and Cognition; Periodicity; Physiology. Development; Procambarus; Research Support, Non-U.S. Gov't; Space life sciences; Synapses; Synapses - physiology
• ISSN: 0306-4522; 1873-7544
• DOI: 10.1016/0306-4522(95)00169-J

Our aim was to examine the relation, or “synaptic coding”, between spike trains across a synapse with inhibitory postsynaptic potentials when the presynaptic rate is modulated periodically and the postsynaptic cell is a pacemaker. Experiments were on the synapse in crayfish stretch receptor organs. Spike trains were considered point processes along time; the time series of corresponding pre- and postsynaptic intervals were extracted. Analyses used displays of intervals along time and order (“basic graphs”, and “rasters”, respectively), displays of differences between intervals along order (“recurrence plots”), cycle histograms (as such and as Lissajous diagrams with presynaptic and postsynaptic histograms on the abscissae and ordinate, respectively), and correlation histograms. Cycle histograms and correlation histograms demonstrated that all presynaptic modulation frequencies (1/60-10Hz) are reflected postsynaptically; novel frequencies may arise, not always relating simply to the pre- or postsynaptic ones. The transferred frequency domain is broad and physiologically meaningful. Indeed, vitally important functions have strong periodicities in all portions of the explored domain, and so do the discharges of participating neurons. Overall, pre- and postsynaptic discharges change oppositely, one accelerating while the other slows. Locally, however, pre- and postsynaptic discharges contrast clearly in other ways. The presynaptic evolution is everywhere smooth and orderly, half-cycles usually are symmetric, and there is a single kind of discharge, as expected because the presynaptic axon follows well the controlling stimuli. The postsynaptic cycle shows marked local distortions. These involve presynaptic domains called “congruent portions” where changes are in the same sense (e.g., joint accelerations), “saturated” domains where postsynaptic discharges are arrested, and asymmetric sensitivities to presynaptic change with hysteric loops in the Lissajous diagrams; the postsynaptic discharge is heterogeneous showing dissimilar forms in succession. Congruent portions are either “positive segments” with pre- to postsynaptic rate ratios practically 1:1, 2:1, 1:1, or parts of Lissajous loops. Different modulation frequencies have different postsynaptic consequences. Differences involve the width and number of positive segments, the proportion of the cycle with saturation, the sense, magnitude and lead-lag characteristics of the hysteretic loops, etc. Because their c