EFFECTS OF ARTIFICIAL HYPOINSULINEMIA ON SYNAPTIC ACTIVITY AND PLASTICITY OF GLUTAMATERGIC NEUROTRANSMISSION IN CULTURE OF HIPPOCAMPAL NEURONS
M.S. Shypshyna, K.I. Kuznetsov, S.A. Fedulova, M.S. Veselovsky
O.O. Bogomoletz Institute of Physiology, NAS of Ukraine, Kyiv, Ukraine
DOI: https://doi.org/10.15407/fz67.04.003

Abstract
We investigated the effect of chronic hypoinsulinemia on
the level of synaptic activity and short-term plasticity in cultured hippocampal neurons. Hypoinsulinemia was induced
by culturing mature (16-20 days in vitro) rat’s hippocampal neurons without insulin for 1, 2, and 4 days. The control insulin concentration was 100 nM. Spontaneous and evoked
glutamatergic excitatory postsynaptic currents (sEPSC and
eEPSC, respectively) in these neurons were analyzed using
the whole-cell patch-clamp method and the method of local
electrical stimulation of individual axon. Hypoinsulinemia
during the 1st, 2nd and 4th days led to significantly reduction
of the mean sEPSC’s frequency to 49.9 ± 15.8% (n = 6), 8.5 ±
7.7% (n = 6) and 16.6 ± 5.2% (n = 8) respectively, relative
to control. Also, there was a decrease of the average sEPSC’s
amplitudes to 52.6 ± 5.5% (n = 6), 36.6 ± 5.8% (n = 6) and
43.9 ± 8.4% (n = 8), respectively, relative to control. Quantal
analysis of the sEPSC’s amplitudes showed a decrease of
multivesicular glutamate release at the synapses under such
conditions. Hypoinsulinemia caused a shift in the direction of short-term plasticity in glutamatergic hippocampal
synapses from potentiation to depression. The paired-pulse
ratio decreased from 1.83 ± 0.25 in the control to 0.59 ± 0.07,
0.77 ± 0.07, and 0.80 ± 0.06 after the 1st, 2nd, and 4th days
under cultivation without insulin. Accordingly, the ratio of
the coefficients of variation of eEPSC’s amplitudes (CV2/
CV1) increased from 0.82 ± 0.07 to 1.30 ± 0.28, 1.52 ± 0.27,
and 1.61 ± 0.24. The presented results indicate a significant
reduction of synaptic activity and decrease in the probability of
multivesicular release of glutamate at the synapses of cultured
hippocampal neurons under hypoinsulinemia.
Keywords:
hypoinsulinemia; hippocampus; glutamatergic neurotransmission; postsynaptic currents; short-term plasticity
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