Fig. 1. Effect of the nNOS inhibitor 7-nitroindazole (7-NI) on the acute response to amphetamine analogs, and the induction and maintenance of psychomotor sensitization. Swiss–Webster mice were administered saline or 7-NI (25 mg/kg) 30 min before administration of saline (control), MPD (10 mg/kg), cocaine (15 mg/kg), METH (0.5 mg/kg), MDMA (10 mg/kg), and PCA (5 mg/kg). (A) Following the first exposure to the amphetamines, the hyperlocomotion response to MPD, cocaine, and METH was blocked by 7-NI pretreatment. MDMA- and PCA-induced hyperlocomotion was not attenuated by 7-NI. (B) Following repeated daily administration of MPD (5 days), cocaine (5 days), METH (5 days), MDMA (6 days), and PCA (6 days), saline pretreated mice developed psychomotor sensitization as the response on days 5–6 was greater than on day 1. Sensitization to MPD, cocaine, and METH was attenuated in groups pretreated with 7-NI; however, sensitization to MDMA and PCA was not suppressed in groups pretreated with 7-NI. The findings suggest that 7-NI blocked the induction of sensitization to MPD, cocaine, and MET, but not MDMA and PCA. (C) Mice were challenged with drug injections 10 days after drug treatments were stopped. The responses to all drug challenges of the groups pretreated with 7-NI were significantly lower than the responses of groups pretreated with saline. The findings suggest that 7-NI pretreatment inhibited the maintenance of sensitization to all 5 drugs tested. Note that because the time course of hyperlocomotion induced by each drug is different, the time frame of ambulatory counts (recorded by infrared beam interrupts) for each drug tested is different. MPD counts represent 120 min, cocaine counts 30 min, METH, MDMA, and PCA counts 60 min each, and saline counts 60 min. *p < 0.05 for comparison between saline and 7-NI pretreated mice. Data from Itzhak, 1997, Itzhak & Martin, 2002a, Anderson & Itzhak, 2003.

Fig. 2. Effect of repeated administration of METH and MDMA to WT and nNOS KO mice. Animals received daily injections of METH (1 mg/kg) or MDMA (10 mg/kg) (following 60 min habituation period) for 5 days and locomotor activity was recorded for 60 min. A challenge drug injection was given after a 40-day drug free period. (A) METH induced progressive increase in ambulatory activity of WT mice during the 5-day drug treatment and remained sensitized on day 45; KO mice did not develop sensitized response to METH. (B) MDMA induced progressive increase in ambulatory activity of WT and KO mice during the 5-day drug treatment. Following a 40-day withdrawal period, WT but not KO mice remained sensitized to challenge MDMA. *p < 0.05 comparison between WT and KO mice. Data from Itzhak et al., 2004a.

Fig. 3. Schematic presentation of the effects of METH on dopaminergic, glutamatergic, and nitrergic systems. METH causes reverse transport of DA and increases extracellular level of DA. High doses of METH causes depletion of DA. Changes in extracellular DA may signal the release of glutamate (GLU). Activation of NMDA type of glutamate receptors increases calcium influx and binding of calcium to calmodulin stimulates nNOS to release NO. NO may function as an interneuronal messenger to increase release of DA and glutamate. DA, glutamate, and NO participate in synaptic plasticity including long-term potentiation (LTP) and depression (LTD), which underlie the development of persistent psychomotor sensitization. NO may also interact with H₂O₂ and to produce ONOO⁻, which is considered a major neurotoxicant. As recent evidence suggests direct DA/NO interaction (left portion of the scheme), the extent of which glutamate is involved in METH-induced increase in NO production is unclear.

Levels of DA, DAT, 5-HT, and 5-HTT in 4 brain regions of WT and nNOS KO mice following administration of METH, MDMA, PCA, and FEN

WT and KO mice were treated with saline (control), METH (5 mg/kg × 3; 1 day), MDMA (15 mg/kg × 2; 3 days), PCA (15 mg/kg × 2; 1 day), and FEN (25 mg/kg × 2; 2 days). Animals were sacrificed 3 days after the last treatment and brain regions were dissected for determination of DA, 5-HT, and their corresponding transporter bindings sites. Data modified from Itzhak et al., 1998b, Itzhak et al., 2003a and Itzhak et al., 2004a. N/D, not detected.