Long‐term Depression of Horizontal Connections in Rat Motor Cortex

The possibility for long‐term depression (LTD) of synaptic transmission in layer 11/11 I horizontal connections within motor cortex was investigated using field potentials and intracellular recordings in rat brain slices. The LTD was induced by low‐frequency stimulation at 2 Hz for 10 min in sites displaced horizontally by 0.5 mm from the stimulating electrode. Response amplitude measured 25‐30 min after 2 Hz stimulation ended was 79% of baseline values (n= 13) at half maximal stimulation and 59% when 2 Hz stimulus intensity was doubled (n= 10). In 13/15 tested cases LTD in horizontal connections was specific to the activated pathway. Intracellular recordings from six neurons confirmed synaptic character of response depression. Horizontal connections in which LTD was induced retained the capability of increasing synaptic strength. Long‐term potentiation could be induced in previously depressed pathways by simultaneous theta burst stimulation of two converging horizontal inputs combined with transient local application of GABAA receptor antagonist bicuculline methiodide (mean increase: 45 ± 8%, n = 6) or by simultaneous theta burst stimulation of converging horizontal and vertical inputs (mean change: 26 5 6%, n = 5). These data demonstrate that activity‐dependent mechanisms may regulate bidirectionally the effectiveness of horizontal synaptic coupling between cortical neurons, thus forming a potential mechanism for plasticity of cortical connections and the representation patterns they support.

[1]  J P Donoghue,et al.  Motor Areas of the Cerebral Cortex , 1994, Journal of clinical neurophysiology : official publication of the American Electroencephalographic Society.

[2]  J. Donoghue,et al.  N-methyl-d-aspartate receptor mediated component of field potentials evoked in horizontal pathways of rat motor cortex , 1994, Neuroscience.

[3]  M. Bear,et al.  Synaptic plasticity: LTP and LTD , 1994, Current Opinion in Neurobiology.

[4]  J. Donoghue,et al.  Long-term potentiation of horizontal connections provides a mechanism to reorganize cortical motor maps. , 1994, Journal of neurophysiology.

[5]  S. Siegelbaum,et al.  Postsynaptic induction and presynaptic expression of hippocampal long-term depression. , 1994, Science.

[6]  M. Bear,et al.  Homosynaptic long-term depression in the visual cortex , 1994, The Journal of neuroscience : the official journal of the Society for Neuroscience.

[7]  David A. Smith,et al.  Temporal covariance of pre- and postsynaptic activity regulates functional connectivity in the visual cortex. , 1994, Journal of neurophysiology.

[8]  M. Baudry,et al.  Blockade of long-term depression in neonatal hippocampal slices by a phospholipase A2 inhibitor. , 1994, Brain research. Developmental brain research.

[9]  D. Linden,et al.  Long-term synaptic depression in the mammalian brain , 1994, Neuron.

[10]  A Keller,et al.  The patterns and synaptic properties of horizontal intracortical connections in the rat motor cortex. , 1993, Journal of neurophysiology.

[11]  R. Malenka,et al.  An essential role for protein phosphatases in hippocampal long-term depression. , 1993, Science.

[12]  SM Dudek,et al.  Bidirectional long-term modification of synaptic effectiveness in the adult and immature hippocampus , 1993, The Journal of neuroscience : the official journal of the Society for Neuroscience.

[13]  M. Bear,et al.  Common forms of synaptic plasticity in the hippocampus and neocortex in vitro. , 1993, Science.

[14]  C. Gilbert,et al.  Long‐term changes in synaptic strength along specific intrinsic pathways in the cat visual cortex. , 1993, The Journal of physiology.

[15]  F. Crépel,et al.  Postsynaptic calcium is necessary for the induction of LTP and LTD of monosynaptic EPSPs in prefrontal neurons: An in vitro study in the rat , 1992, Synapse.

[16]  Y. Yoshimura,et al.  Input-specific induction of long-term depression in Ca(2+)-chelated visual cortex neurons. , 1991, Neuroreport.

[17]  KM Jacobs,et al.  Reshaping the cortical motor map by unmasking latent intracortical connections , 1991, Science.

[18]  W. Singer,et al.  Different voltage-dependent thresholds for inducing long-term depression and long-term potentiation in slices of rat visual cortex , 1990, Nature.

[19]  F. Crépel,et al.  Use‐dependent changes in synaptic efficacy in rat prefrontal neurons in vitro. , 1990, The Journal of physiology.

[20]  T. Sejnowski,et al.  Associative long-term depression in the hippocampus induced by hebbian covariance , 1989, Nature.

[21]  D. McCormick,et al.  Comparative electrophysiology of pyramidal and sparsely spiny stellate neurons of the neocortex. , 1985, Journal of neurophysiology.

[22]  W Singer,et al.  Intracellular injection of Ca2+ chelators blocks induction of long-term depression in rat visual cortex. , 1992, Proceedings of the National Academy of Sciences of the United States of America.

[23]  John P. Donoghue,et al.  Motor Cortex of Rodents , 1986 .