Comparative Effects of NO-Synthase Inhibitor and NMDA Antagonist on Generation of Nitric Oxide and Release of Amino Acids and Acetylcholine in the Rat Brain Elicited by Amphetamine Neurotoxicity

Brain dysfunctions and neurotoxicity induced by psychostimulants in experimental models and humans: an overview of recent findings

Preclinical and clinical studies indicate that psychostimulants, in addition to having abuse potential, may elicit brain dysfunctions and/or neurotoxic effects. Central toxicity induced by psychostimulants may pose serious health risks since the recreational use of these substances is on the rise among young people and adults. The present review provides an overview of recent research, conducted between 2018 and 2023, focusing on brain dysfunctions and neurotoxic effects elicited in experimental models and humans by amphetamine, cocaine, methamphetamine, 3,4-methylenedioxymethamphetamine, methylphenidate, caffeine, and nicotine. Detailed elucidation of factors and mechanisms that underlie psychostimulant-induced brain dysfunction and neurotoxicity is crucial for understanding the acute and enduring noxious brain effects that may occur in individuals who use psychostimulants for recreational and/or therapeutic purposes.

Neuropathologic Features in Chronic Methamphetamine Use

ABSTRACT

Methamphetamine is a psychostimulant that exerts its euphoric and stimulant effects by increasing cytosolic monoamine concentration at the nerve terminal. In addition to its known systemic cardiovascular effects, there is compelling evidence to suggest a direct neurotoxic effect of methamphetamine; however, the existing body of literature includes very few human tissue studies. This exploratory analysis used postmortem human brain specimens to examine histologic and immunohistochemical features associated with chronic methamphetamine use. This retrospective cohort study included 60 decedents who were autopsied at the University of Iowa Hospitals and Clinics between the years 2015 and 2021. Logistic regression models demonstrated no definite pathologic changes in the hippocampi of individuals with a history of chronic methamphetamine use. Decedents with a history of methamphetamine use had a marginally increased odds of basal ganglia arteriosclerosis, which did not reach statistical significance (odds ratio, 3.33; 95% confidence interval, 0.6-19.2; P = 0.17), which may be independent of the systemic hypertensive effects of methamphetamine. Future studies that include targeted examination of brain regions of interest, such as the basal ganglia and specifically the striatum, may prove revealing.

Possible mechanisms involved in the vasorelaxant effect produced by clobenzorex in aortic segments of rats

Clobenzorex is a metabolic precursor of amphetamine indicated for the treatment of obesity. Amphetamines have been involved with cardiovascular side effects such as hypertension and pulmonary arterial hypertension. The aim of the present study was to investigate whether the direct application of 10^–9–10^–5 M clobenzorex on isolated phenylephrine-precontracted rat aortic rings produces vascular effects, and if so, what mechanisms may be involved. Clobenzorex produced an immediate concentration-dependent vasorelaxant effect at the higher concentrations (10^–7.5–10^–5 M). The present outcome was not modified by 10^–6 M atropine (an antagonist of muscarinic acetylcholine receptors), 3.1×10^–7 M glibenclamide (an ATP-sensitive K⁺ channel blocker), 10^–3 M 4-aminopyridine (4-AP; a voltage-activated K⁺ channel blocker), 10^–5 M indomethacin (a prostaglandin synthesis inhibitor), 10^–5 M clotrimazole (a cytochrome P450 inhibitor) or 10^–5 M cycloheximide (a general protein synthesis inhibitor). Contrarily, the clobenzorex-induced vasorelaxation was significantly attenuated (P<0.05) by 10^–5 M L-NAME (a direct inhibitor of nitric oxide synthase), 10^–7 M ODQ (an inhibitor of nitric oxide-sensitive guanylyl cyclase), 10^–6 M KT 5823 (an inhibitor of protein kinase G), 10^–2 M TEA (a Ca²⁺-activated K⁺ channel blocker and non-specific voltage-activated K⁺ channel blocker) and 10^–7 M apamin plus 10^–7 M charybdotoxin (blockers of small- and large-conductance Ca²⁺-activated K⁺ channels, respectively), and was blocked by 8×10^–2 M potassium (a high concentration) and removal of the vascular endothelium. These results suggest that the direct vasorelaxant effect by clobenzorex on phenylephrine-precontracted rat aortic rings involved stimulation of the NO/cGMP/PKG/Ca²⁺-activated K⁺ channel pathway.

Nitric Oxide and Oxidative Stress in the Brain of Rats Exposed In Utero to Cocaine

The role of nitric oxide (NO) and lipid peroxidation (LPO) processes in the physiological deficits induced by in utero cocaine exposure was examined in rats. NO generation in the hippocampus and cortex was detected using the electron paramagnetic resonance and LPO products were measured as thiobarbituric acid reactive species (TBARS). Pregnant Sprague-Dawley rats received a daily intraperitoneal injection of 20 mg/kg cocaine (IUC) or saline solution for control dams (IUV) between E17-E20. NO level was lower in the brain of IUC rats at postnatal day 1 and 2, but not 4, as compared with IUV rats. TBARS content was increased at day 1-4. Animals were used for behavioral testing at 25 days of age. Both NO and TBARS were elevated in the hippocampus of IUC rats as compared with IUV rats. Juvenile IUC rats developed significant learning impairments in the water-maze, as revealed by probe test retrieval deficits. Behavioral sessions resulted in a significant increase of TBARS levels only in IUV animals. Therefore, IUC rats showed a significant oxidative stress in basal conditions that may be related to their impaired learning ability. We did not find direct correlation between the changes in NO generation and intensity of LPO processes. It may probably mean that changes in intensity of LPO processes observed during prenatal cocaine exposure are not directly linked to NO pathway activation.