Biomedical subjects

Z Ziakopoulos

Publications and source records attributed to Z Ziakopoulos.

2 recordsLinked to original sources

PubMed2000

GABAB receptors mediate frequency-dependent depression of excitatory potentials in rat perirhinal cortex in vitro.

Excitatory synaptic transmission in the perirhinal cortex exhibits marked homosynaptic paired pulse depression (PPD) at inter-pulse intervals between 100 and 1000 ms, being maximal at 200 ms. Additionally, there is greater PPD with stimulation of the pathway from the temporal cortex side than with stimulation of the pathway from the entorhinal cortex side. We establish that this frequency-dependent depression relies on the activation of GABAB (gamma-aminobutyric acid) receptors. PPD in both temporal and entorhinal pathways is abolished by either of the selective GABAB receptor antagonists, 3-N[1-(S)-(3, 4-dichlorophenyl)ethyl]amino-2-(S)-hydroxypropyl-p-benzyl-phosphinic acid (CGP55845A) or 3-amino-propyl(diethoxymethyl)phosphinic acid (CGP35348). Barium which blocks G-protein-coupled, inwardly rectifying potassium channels, does not block PPD. Heterosynaptic depression mediated by GABAB receptors was also observed. The depression of the entorhinal pathway by stimulation of the temporal pathway is greater than depression of the temporal pathway by stimulation of the entorhinal pathway. Moreover, PPD increases with stimulus strength and the depression is enhanced by short trains of stimuli, consistent with stronger stimulation resulting in more GABA reaching GABAB receptors on excitatory glutamatergic synapses. Synaptic activation of GABAB receptors may be important in regulating excitability in a frequency-dependent manner with maximal depression occurring at approximately 5 Hz, which approximates to the theta rhythm. That homosynaptic and heterosynaptic depression by stimulation of the temporal pathway is greater than by stimulation of the entorhinal pathway suggests that activation of temporal feedforward connections to the perirhinal cortex can dominate the GABAergic control of synaptic activity within the perirhinal cortex.

Animals↗

PubMed1999

Input-and layer-dependent synaptic plasticity in the rat perirhinal cortex in vitro.

The perirhinal cortex is crucially important in several forms of memory. Whilst it is important to understand the underlying mechanisms of this role in memory, little is known about the synaptic physiology or plasticity of this region of transitional cortex. In this study, we recorded evoked field potentials in superficial layers (approximately layer I) of the perirhinal cortex in vitro. One stimulating electrode was placed on the temporal side and the other on the entorhinal side of the rhinal sulcus in either the superficial or intermediate layers (approximately layers II/III). Paired stimuli resulted in depression of the second response. Paired-pulse depression was maximal at a 200-ms interpulse interval. Low-frequency stimulation resulted in synaptic depression, which returned to baseline within 60 min. The magnitude of both paired-pulse depression and low-frequency stimulation-induced depression was significantly greater at synapses activated from the temporal intermediate pathway than the other three pathways. Long-term potentiation, stable for at least 60 min, was induced by high-frequency stimulation of intermediate but not superficial pathways. Long-lasting depression (depotentiation) was induced by low-frequency stimulation following the induction of long-term potentiation. The induction of both long-term potentiation and depotentiation was N-methyl-D-aspartate receptor dependent. The group I/II metabotropic glutamate receptor antagonist (S)-alpha-methyl-4-carboxyphenylglycine was without effect on either of these forms of plasticity. Thus, both long- and short-lasting forms of synaptic plasticity exist at synapses in the perirhinal cortex, and these may mediate the changes in neuronal responses associated with visual recognition memory.

2-Amino-5-phosphonovalerate↗