Differential properties of GABAergic synaptic connections in rat hippocampal cell cultures

Abstract

Based on the effect of prolonged tetanic stimulation (30 Hz, 4 sec), we divided GABAergic synaptic connections in hippocampal cell cultures into two groups: connections facilitated ( approximately 45%) and connections depressed ( approximately 55%) by the tetanic stimulation. In order to reveal possible reasons for the differential effect of the tetanization, we compared several properties of the connections belonging to both groups. We found that, on average, evoked IPSCs in the connections facilitated by the tetanization have a smaller amplitude and larger coefficient of variation (CV) of IPSC amplitude compared to connections depressed by the tetanization. We also estimated quantal parameters for both groups of connections assuming that transmitter release is reasonably described by a binomial distribution. We found that a background release probability (P) is substantially lower in the connections facilitated by the tetanization (P approximately 0.5) than in the connections depressed by the tetanization (P approximately 0.9) and suggest that this difference may underlie the differential effect of the tetanization. We also found that the tetanization induces the opposite effect on connections made by distinct presynaptic neurons with the same postsynaptic cell (convergent connections) in a fraction of postsynaptic neurons studied (3 out of 9). These results support the idea that properties of the presynaptic neuron are of primary importance for the observed differential effect of the tetanization, but they do not exclude a role of the postsynaptic neuron in this effect.

An unexpected effect of capsaicin on spontaneous GABA-ergic IPSCS in hippocampal cell cultures

“…Cell cultures were prepared as described previously [6]. All cultures were kept at 36°C in humidified air with 5% CO 2 and were used for the experiments 14-22 days after plating.…”

Post-Tetanic and Depolarization-Induced Suppression of Inhibition in Hippocampal Cell Cultures: Are Similar Mechanisms Involved?

“…On the other hand, the same tetanic stimulation (30 sec -1 , 4 sec) of the presynaptic neuron also revealed the heterogeneity of GABA-ergic synaptic connections. About 45% of the connections were facilitated, while 55% were depressed [5,6]. In our present work, we demonstrate that depression is predominantly expressed in neuronal pairs susceptible to DSI, and that both phenomena have a very similar time course.…”

“…In particular, the heterogeneity of GABA-ergic synapses is manifested in terms of morphology [2], types of calcium channels involved in synaptic transmission [3], modulation by agonists of metabotropic glutamate receptors [4], and also by effects of paired stimulation [3]. We have found that the heterogeneity of GABA-ergic synaptic connections can also be revealed by tetanic stimulation [5,6]. In distinct synaptic connections, the same tetanic stimulation (30 sec -1 , 4 sec) elicited either posttetanic depression (PTD) or post-tetanic potentiation (PTP) of evoked GABA-ergic inhibitory postsynaptic currents (IPSCs).…”

Involvement of L-type calcium channels and mitochondria in post-tetanic potentiation: Is it a general rule for different types of synapses?

“…It should be noted that despite a clearly pronounced effect of dihydropyridines on PTP, control (pretetanic) postsynaptic potentials were not affected in the presence of these drugs. These results showed that L-type calcium channels are not involved in synaptic transmission per se.More recently, rather similar observations were reported regarding mammalian central inhibitory (GABA-ergic) synapses in a few preparations [3][4][5]. In particular, it was shown that both nifedipine [3,5] and isradipine [3] significantly reduced PTP in hippocampal cell cultures with no effect on synaptic potentials evoked by low-frequency stimulation.…”