Fig. 1

Cranial irradiation induces alterations in the firing pattern of dopamine neurons in the ventral tegmental area (VTA) without affecting their firing rate. In vivo, VTA dopamine neurons display spontaneous activity, generating both single spikes and bursts. Extracellular recordings from VTA dopamine neurons [(A) spikes train and (B) single action potential)] were obtained to assess (C) firing rates, (D) bursting levels, and (E) the coefficient of variation of interspike intervals at 1, 3, 7, and 28 days after the last of 5 treatment fractions of cranial irradiation to a total dose of 20 Gy. Although no significant changes were observed in VTA dopamine neuron firing rates (sham control: 3.56 ± 0.14 Hz, n = 149 from 20 rats; day 1: 3.38 ± 0.32 Hz, n = 43 from 5 rats; day 3: 3.50 ± 0.32 Hz, n = 44 from 5 rats; day 7: 3.19 ± 0.34 Hz, n = 39 from 5 rats; day 28: 3.51 ± 0.29 Hz, n = 39 from 5 rats; one-way ANOVA F_{(4, 309)} = 0.318, P = 0.866), both bursting levels and coefficient of variation initially increased (Bursting: day 3: 23.09 ± 3.84, n = 44 from 5 rats; vs. sham control: 12.37 ± 1.48, n = 149 from 20 rats; one-way ANOVA, F_{(4, 309)} = 4.727, P = 0.001; CV: day 3: 66.80 ± 3.88, n = 44 from 5 rats; vs. sham control: 52.57 ± 1.82, n = 149 from 20 rats; one-way ANOVA, F_{(4, 309)} = 4.153, P = 0.003) and then returned to control levels (Bursting: day 28: 10.27 ± 3.33, n = 44 from 5 rats; vs. sham control: 12.37 ± 1.48, n = 149 from 20 rats; one-way ANOVA, F_{(4, 309)} = 4.727, P = 0.95; CV: day 28: 48.92 ± 4.47, n = 44 from 5 rats; vs. sham control: 52.57 ± 1.82, n = 149 from 20 rats; one-way ANOVA, F_{(4, 309)} = 4.153, P = 0.93). *P < 0.05; **P < 0.01