Microelectrophysiological Studies of the Ratio of Excitatory to Inhibitory Synaptic Processes in the Corticonigral Proje
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Microelectrophysiological Studies of the Ratio of Excitatory to Inhibitory Synaptic Processes in the Corticonigral Projection in a Model of Parkinson’s M. V. Poghosyan, L. M. Khachatryan, M. A. Danielyan, Z. A. Avetisyan, and J. S. Sarkissian
Translated from Rossiiskii Fiziologicheskii Zhurnal imeni I. M. Sechenova, Vol. 106, No. 3, pp. 301–314, March, 2020. Original article submitted October 21, 2019. Revised version received December 6, 2019. Accepted January 16, 2020. Experiments on 23 white male rats (250 g) analyzed the spike activity of individual neurons in the substantia nigra pars compacta (SNc, 242 neurons, n = 11) and substantia nigra pars reticulata (SNr, 289 neurons, n = 12) during high-frequency stimulation of the primary motor cortex (M1)in normal animals and in animals with a rotenone model of Parkinson’s disease (BP). SNc neurons in the model of PD showed a complete absence of depressor effects induced by stimulation, though tetanic potentiation was accompanied by posttetanic potentiation and depression at levels 1.65 and 2.02 times greater than in normal animals. In SNr neurons in normal animals, tetanic potentiation, accompanied by post-tetanic potentiation and depression, was 2.37 times greater than tetanic depression, while in the model of PD the levels of both depressor and excitatory activity induced by stimulation were below normal. Spike activity frequency in SNc and SNr neurons preceding and accompanying stimulation was significantly greater than normal in the model of PD. This is evidence for excitotoxicity accompanying neurodegenerative damage, which is completed by neuron apoptosis and death. In SNr neurons, both depressor and excitatory reactions accompanying stimulation were markedly dominant over those in SNc neurons, which is evidence for more extensive cortical projections to the SNr. Furthermore, SNc neurons demonstrated greater susceptibility to pathological changes due to poststimulus depressor effects than SNr neurons, with formation of more marked excitatory effects, which is evidence of a greater involvement of the SNc in PD. In the model of PD, lacking stimulation-induced depressor effects and more marked excitatory effects in SNc neurons, SNr neurons retained their depressor reactions and relatively decreased excitatory reactions, which is evidence of a lower level of susceptibility of SNr neurons to excitotoxicity, extreme increases in the excitability of surviving neurons compensating for the lack of excitation of dead cells. Keywords: substantia nigra compacta (SNc), substantia nigra reticulata (SNr), rotenone model of Parkinson’s disease (PD), primary motor cortex (M1), single-unit spike activity, programmed mathematical analysis.
The substantia nigra (SN) is an important neuronal structure responsible for mediating regulation of the activity of the basal ganglia (BG). The posteromedial part of the SN – the pars compacta (SNc) – among the dopaminergic (DA) nuclei of the brain [1], is mainly connected with the dorsal striatum [2]. The anterolateral zone of the SN – the
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