RAPID COMMUNICATION Bidirectional Associative Plasticity of Unitary CA3-CA1 EPSPs in the Rat Hippocampus In Vitro

Debanne, Dominique, Beat H. Gähwiler, and Scott M. from 5to 7-day-old rat pups were dissected at 400 mm and attached to glass coverslips in clotted chicken plasma. The Thompson . Bidirectional associative plasticity of unitary CA3CA1 EPSPs in the rat hippocampus in vitro. J. Neurophysiol. coverslips were placed in individual sealed test tubes containing semisynthetic medium and maintained on a roller drum 77: 2851–2855, 1997. Associative long-term potentiation (LTP) and depression of compound and unitary CA3-CA1 excitin an incubator for 2 – 4 wk. For electrophysiological recordings, cultures were transferred to a recording chamber atory postsynaptic potentials (EPSPs) were investigated in rat hippocampal slice cultures. The induction of LTP with synchromounted on an inverted microscope and continuously superfused with a warmed ( 327C ) saline containing ( in mM ) : 149 nous pairing of synaptic activation and postsynaptic depolarization resulted in an increase in the amplitude of EPSPs to the Na , 149 Cl , 2.7 K , 2.8 Ca 2/ , 2.0 Mg 2/ , 11.6 HCO3 , 0.4 same absolute level, regardless of whether the input was naive H2PO4 , 5.6 glucose, and also 10 mg / l phenol red, at pH Å 7.4. or had been previously depressed by asynchronous pairing of Pyramidal neurons were impaled by using sharp microelecpreand postsynaptic activity. Saturated LTP of compound and trodes filled with 1 M potassium methylsulphate. EPSPs were unitary EPSPs was reversed by asynchronous pairing and could recorded from postsynaptic CA1 cells. Compound EPSPs were be reinduced by synchronous pairing. The likelihood that an evoked by field stimulation within area CA3; unitary EPSPs action potential in a presynaptic CA3 cell failed to trigger an were evoked by generation of single presynaptic action potenunitary EPSP in a postsynaptic CA1 cell decreased after inductials in intracellularly impaled CA3 pyramidal cells. The monotion of associative potentiation and increased after induction of synaptic nature of unitary EPSPs was assessed as described associative depotentiation. These changes in the rate of transmispreviously ( Debanne et al. 1995 ) . sion failures were accompanied by large changes in the ampliThe naive amplitude is the EPSP amplitude before induction of tude of nonfailure EPSPs. We conclude that the same CA3-CA1 either LTP or LTD in a given culture. Values of potentiation and synapses can alternatively undergo associative potentiation and depression were derived from averages of EPSPs over 2–3-min depression, perhaps through opposite changes in a single expresperiods, taken 10 min after the pairing procedure unless otherwise sion mechanism. noted (Debanne et al. 1994). The Mann-Whitney U-test was used for all statistical comparisons.