No abstract

The present study was undertaken to investigate whether the relatively selective neuronal nitric oxide synthase (NOS) inhibitor, 7‐nitroindazole (7‐NI), protects against methamphetamine (METH)‐induced neurotoxicity. Male Swiss Webster mice received the following treatments (i.p.; q 3 h × 3): (a) vehicle/saline, (b) 7‐NI (25 mg/kg)/saline, (c) vehicle/METH (5 mg/kg), and (d) 7‐NI (25 mg/kg)/METH (5 mg/kg). On the second day, groups (a) and (b) received two vehicle injections, and groups (c) and (d) received two 7‐NI injections (25 mg/kg, each). Administration of vehicle/METH resulted in 68, 44, and 55% decreases in the concentration of dopamine, 3,4‐dihydroxyphenylacetic acid, and homovanillic acid, respectively, and a 48% decrease in the number of [3H]mazindol binding sites in the striatum compared with control values. Treatment with 7‐NI (group d) provided full protection against the depletion of dopamine and its metabolites and the loss of dopamine transporter binding sites. Administration of 7‐NI/saline (group b) affected neither the tissue concentration of dopamine and its metabolites nor the binding parameters of [3H]mazindol compared with control values. 7‐NI had no significant effect on animals' body temperature, and it did not affect METH‐induced hyperthermia. These findings indicate a role for nitric oxide in methamphetamine‐induced neurotoxicity and also suggest that blockade of NOS may be beneficial for the management of Parkinson's disease.

Oxidative stress, reactive oxygen (ROS), and nitrogen (RNS) species have been known to be involved in a multitude of neurodegenerative disorders such as Parkinson's disease (PD), Alzheimer's disease (AD), and amyotrophic lateral sclerosis (ALS). Both ROS and RNS have very short half‐lives, thereby making their identification very difficult as a specific cause of neurodegeneration. Recently, we have developed a high performance liquid chromatography/electrochemical detection (HPLC/EC) method to identify 3‐nitrotyrosine (3‐NT), an in vitro and in vivo biomarker of peroxynitrite production, in cell cultures and brain to evaluate if an agent‐driven neurotoxicity is produced by the generation of peroxynitrite. We show that a single or multiple injections of methamphetamine (METH) produced a significant increase in the formation of 3‐NT in the striatum. This formation of 3‐NT correlated with the striatal dopamine depletion caused by METH administration. We also show that PC12 cells treated with METH has significantly increased formation of 3‐NT and dopamine depletion. Furthermore, we report that pretreatment with antioxidants such as selenium and melatonin can completely protect against the formation of 3‐NT and depletion of striatal dopamine. We also report that pretreatment with peroxynitrite decomposition catalysts such as 5, 10,15,20‐tetrakis(N‐methyl‐4′‐pyridyl)porphyrinato iron III (FeTMPyP) and 5, 10, 15, 20‐tetrakis (2,4,6‐trimethyl‐3,5‐sulfonatophenyl) porphinato iron III (FETPPS) significantly protect against METH‐induced 3‐NT formation and striatal dopamine depletion. We used two different approaches, pharmacological manipulation and transgenic animal models, in order to further investigate the role of peroxynitrite. We show that a selective neuronal nitric oxide synthase (nNOS) inhibitor, 7‐nitroindazole (7‐NI), significantly protect against the formation of 3‐NT as well as striatal dopamine depletion. Similar results were observed with nNOS knockout and copper zinc superoxide dismutase (CuZnSOD)‐overexpressed transgenic mice models. Finally, using the protein data bank crystal structure of tyrosine hydroxylase, we postulate the possible nitration of specific tyrosine moiety in the enzyme that can be responsible for dopaminergic neurotoxicity. Together, these data clearly support the hypothesis that the reactive nitrogen species, peroxynitrite, plays a major role in METH‐induced dopaminergic neurotoxicity and that selective antioxidants and peroxynitrite decomposition catalysts can protect against METH‐induced neurotoxicity. These antioxidants and decomposition catalysts may have therapeutic potential in the treatment of psychostimulant addictions.

In brain, nitric oxide (NO) is considered as a retrograde messenger involved in synaptic plasticity. The present study was undertaken to investigate whether mice lacking the neuronal nitric oxide synthase (nNOS) gene are protected from cocaine-induced behavioral sensitization. Mice were administered, IP. either saline or cocaine (15 mg/kg) for 5 days. Sensitization was determined as an increase in cocaine-induced locomotor activity on day 5 compared with day 1 and an amplified response of cocaine-experienced mice to a challenge cocaine injection given after a 10-day drug free period (e.g., on day 15). To investigate the development of a context-dependent locomotion (conditioning), the responses of cocaine- and saline-experienced mice to a saline injection were determined on day 17. Male homozygote nNOS(-/-) mice were sensitive to the acute effect of cocaine (15 mg/kg) on day 1; however, they developed neither a sensitized response to cocaine (on day 5 and 15) nor a conditioned locomotion. Female homozygote nNOS(-/-) mice neither were responsive to 15 mg/kg cocaine on day 1,5 and 15, nor did they develop a conditioned locomotion. In contrast, the same cocaine regimen delivered to male and female heterozygote nNOS(+/-) mice, and wild type mice (B6 J/sv129, C57BL/6 and sv129) resulted in sensitization to cocaine-induced locomotor activity and context-dependent locomotion. Investigation of [3H]cocaine disposition in the striatum and frontal cortex of the mice revealed neither gender nor strain differences in the drug disposition. Also, no major difference in striatal dopaminergic markers between homozygote nNOS(-/-) and wild type mice was observed. The most significant distinction, however, was the finding that nNOS(-/-) mice are completely deficient in striatal nNOS binding sites. Taken together, our results suggest that the resistance of homozygote nNOS(-/-) mice to cocaine-induced behavioral sensitization is primarily due to the deletion of the nNOS gene. Considering the role of NO in synaptic plasticity, it is conceivable that reduced brain NOS activity blunts the processes that underlie the development of sensitization to cocaine.

Long-term memory of cocaine-associated context was established by conditioned place preference learning. After 1 week, exposure to context in the absence of cocaine (memory retrieval) was paired with one of the following treatments: saline, scopolamine (muscarinic acetylcholine receptor antagonist), dizocilpine (MK-801; noncompetitive N-methyl-D-aspartate antagonist) or D-cycloserine (partial N-methyl-D-aspartate agonist). In subsequent conditioned place preference tests, place preference was suppressed in the drug-treated groups but not saline-treated groups. Results suggest that the amnesic agents, scopolamine and MK-801, disrupted reconsolidation of cocaine-associated contextual memory. In contrast, the mnemonic agent D-cycloserine might have facilitated extinction learning during context exposure in the absence of cocaine. Challenge administration of cocaine reinstated place preference in all groups except the MK-801 group, suggesting that suppression of conditioned response may or may not suppress memory evoked by drug-context reexposure.