Table 1.

Impulse activity of VTA and SNc DA cells when the cells were divided into burst-firing cells (cells that in addition to several two-spike bursts also displayed at least two triplets during 500 consecutive spikes) versus nonburst-firing cells

Cells	VTA LR	VTA HR	SNc LR	SNc HR
Burst-firing cells
n	45	50	39	43
% of total population	88.24%	90.91%	66.10%	79.63%
Firing rate (Hz)	4.25  ± 0.22	5.39  ± 0.251-168	4.43  ± 0.29	4.94  ± 0.25
Bursting activity	35.54  ± 3.39%	50.11  ± 3.31%1-165	30.31  ± 3.43%	35.15  ± 2.73%
Burst events/10 sec	5.51  ± 0.58	8.28  ± 0.621-160	5.07  ± 0.68	6.41  ± 0.57
Burst size	2.82  ± 0.08	3.28  ± 0.14*	2.56  ± 0.08	2.74  ± 0.13
Nonburst-firing cells
n	6	5	20	11
% of total population	11.76%	9.09%	33.90%	20.37%
Firing rate (Hz)	1.86  ± 0.15	2.25  ± 0.50	2.64  ± 0.25	3.13  ± 0.45
Bursting activity	10.25  ± 5.51%	4.58  ± 0.76%	5.67  ± 0.82%	8.10  ± 0.02%
Burst events/10 sec	0.96  ± 0.54	0.45  ± 0.07	0.67  ± 0.08	1.54  ± 0.68
Burst size	2.01  ± 0.01	2.04  ± 0.03	2.04  ± 0.01	2.03  ± 0.01

For both the VTA and the SNc, the proportion of burst-firing cells versus nonburst-firing cells was greater in both HRs and LRs. In burst-firing cells of the VTA, HRs showed a similar percentage of burst-firing cells (t₉₃ = −0.43;p > 0.67) but increased firing rate, bursting activity, burst events, and burst size compared with LRs (t₉₃ = −3.39,t₉₃ = −3.07,t₉₃ = −3.23,t₉₃ = −2.66;

F1-168: p < 0.001,

F1-165: p < 0.003,

F1-160: p < 0.002,

^*p < 0.01, respectively). It is difficult to determine whether there were any HR or LR differences in nonburst-firing cells of the VTA, because the number of cells in this cell population was very low for both groups of rats (t₉ = 0.14,t₉ = −0.8, t₉= 0.92, t₉ = 0.85,t₉ = −1.10; p > 0.14,p > 0.44, p > 0.38, p > 0.41,p > 0.29, for the percentage of nonburst-firing cells, firing rate, bursting activity, burst events, and burst size, respectively). In the SNc, there were no differences between HRs and LRs either in the burst-firing or the nonburst-firing cell population for each of the variables studied (burst-firing cells,t₈₀ = −1.38,t₈₀ = −1.35,t₈₀ = −1.11,t₈₀ = −1.51,t₈₀ = −1.14; p > 0.17,p > 0.18, p > 0.26, p > 0.13,p > 0.25; nonburst-firing cells,t₂₉ = 0.79, t₂₉= −1.04, t₂₉ = −1.19,t₂₉ = −1.71,t₂₉ = 0.71; p > 0.43,p > 0.31, p > 0.24, p > 0.10,p > 0.45, for percent of cells, firing rate, bursting activity, burst events, and burst size, respectively).