One explanation for this seeming contradiction may be the involvement of short- term synaptic depression of the GP inhibitory synapses.
Nevertheless, the firing rate of GP neurons increases during various motor actions ( Georgopoulos et al., 1983 Mink and Thach, 1991 Gardiner and Kitai, 1992 Turner and Anderson, 1997). More than 80% of the inputs reaching the GP are inhibitory. The rat globus pallidus (GP), homologous of the primate and human Globus Pallidus external segment (GPe), is one of the nuclei of the basal ganglia and plays an important role in a variety of motor and cognitive processes ( Kita and Kitai, 1994 Kita, 2007 Sadek et al., 2007 Goldberg and Bergman, 2011). The computational model made additional predictions about GP activity during low and HFS that may further our understanding of the mechanisms underlying repetative stimulation of the GP. These finding suggest the existence of as yet unreported slower short-term dynamics in the GP. Reconstructions of experimental responses to HFS required adding slower forms of plasticity to the STN and GP collateral synapses, as well as adding metabotropic receptors to the STN-GP synapses. The simulations were qualitatively compared to a data set previously recorded in vitro in our lab. Mainly involved were fast forms of plasticity which have been found at these synapses. The in vitro recordings of responses to low frequency repetitive stimulation were highly reconstructed, including rate changes and locking to the stimulus. All synapses were implemented with a kinetic model of STP. To do this we constructed a model of a GP neuron connected to a small network of neurons from the three major input sources to GP neurons: striatum (Str), subthalamic nucleus (STN) and GP collaterals.
The current study used simplified single compartment modeling to explore the possible effect of STP on the activity of GP neurons during low and high frequency stimulation (HFS). In vitro and computational studies have suggested that short-term synaptic plasticity (STP) could be one of the underlying mechanisms. In vivo studies have shown that repetitive stimulation evokes complex modulations of GP activity. The rat globus pallidus (GP) is one of the nuclei of the basal ganglia and plays an important role in a variety of motor and cognitive processes. 2The Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat Gan, Israel.1The Leslie and Susan Gonda Multidisciplinary Brain Research Center, Bar-Ilan University, Ramat Gan, Israel.
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