Table 4.

Summary of statistically calculated VTA and LC neuronal responses for ED10 MPD compared with ED1 MPD

	ED10 MPD/ED1 MPD (Chronic)
MPD Dose, mg/kg	VTA				LC
n	↑	↓	≠	n	↑	↓	≠
Units recorded from all animals
Saline	36	0 (0%)	0 (0%)	36 (100%)	56	2 (3.6%)	3 (5.4%)	51 (91%)
0.6	115	39 (33.9%)	19 (16.5%)	57 (49.6%)	109	37 (33.9%)	20 (18.4%)	52 (47.7%)
2.5	135	59 (43.7%)	27 (20%)	49 (36.3%)	132	55 (41.7%)	35 (26.5%)	42 (31.8%)
10	117	64 (54.7%)	42 (35.9%)	11 (9.4%)	112	75 (67%)	29 (25.9%)	8 (7.1%)
Units recorded from sensitized animals
0.6	38	19 (50%)	3 (7.9%)	16 (42.1%)	47	23 (48.9%)	3 (6.4%)	21 (44.7%)
2.5	80	47 (58.8%)	15 (18.7%)	18 (22.5%)	61	35 (57.4%)	15 (24.6%)	11 (18%)
10	92	53 (57.6%)	32 (34.8%)	7 (7.6%)	81	63 (77.8%)	12 (14.8%)	6 (7.4%)
Units recorded from tolerant animals
0.6	77	20 (26%)	16 (20.8%)	41 (53.2%)	62	14 (22.6%)	17 (27.4%)	31 (50%)
2.5	55	12 (21.8%)	12 (21.8%)	31 (56.4%)	71	20 (28.2%)	20 (28.2%)	31 (43.6%)
10	25	11 (44%)	10 (40%)	4 (16%)	31	12 (38.7%)	17 (54.9%)	2 (6.4%)

Values are statistically calculated VTA and LC neuronal responses on ED10 following 0.6, 2.5, and 10 mg/kg MPD exposure compared with the neuronal responses following acute MPD exposure on ED1 (ED10 MPD/ED1 MPD); n = no. of units in each group. Up-arrow columns include the VTA and LC units that exhibited significant (P < 0.05) increases in neuronal unit activity after chronic MPD exposure. Down-arrow columns include the units that exhibited significant (P < 0.05) decreases in neuronal unit activity after chronic MPD exposure. Unequal-to columns include the units that exhibited no significant change after chronic MPD exposure. Data are shown for VTA and LC units recorded from all animals, for units recorded from animals that exhibited behavioral sensitization after chronic MPD exposure, and for units recorded from animals that exhibited behavioral tolerance after chronic MPD exposure.