Intravenous (+)-methamphetamine causes complex dose-dependent physiologic changes in awake rats

Activation of mGluR5 and NMDA Receptor Pathways in the Rostral Ventrolateral Medulla as a Central Mechanism for Methamphetamine-Induced Pressor Effect in Rats

Acute hypertension produced by methamphetamine (MA) is well known, mainly by the enhancement of catecholamine release from sympathetic terminals. However, the central pressor mechanism of the blood-brain-barrier-penetrating molecule remains unclear. We used radio-telemetry and femoral artery cannulation to monitor the mean arterial pressure (MAP) in conscious free-moving and urethane-anesthetized rats, respectively. Expression of Fos protein (Fos) and phosphorylation of N-methyl-D-aspartate receptor subunit GluN1 in the rostral ventrolateral medulla (RVLM) were detected using Western blot analysis. ELISA was carried out for detection of protein kinase C (PKC) activity in the RVLM. MA-induced glutamate release in the RVLM was assayed using in vivo microdialysis and HPLC. Systemic or intracerebroventricular (i.c.v.) administration of MA augments the MAP and increases Fos expression, PKC activity, and phosphorylated GluN1-ser 896 (pGluN1-ser 896) in the RVLM. However, direct microinjection of MA into the RVLM did not change the MAP. Unilateral microinjection of a PKC inhibitor or a metabotropic glutamate receptor 5 (mGluR5) antagonist into the RVLM dose-dependently attenuated the i.c.v. MA-induced increase in MAP and pGluN1-ser 896. Our data suggested that MA may give rise to glutamate release in the RVLM further to the activation of mGluR5-PKC pathways, which would serve as a central mechanism for the MA-induced pressor effect.

Effects of acute and chronic systemic methamphetamine on respiratory, cardiovascular and metabolic function, and cardiorespiratory reflexes

KEY POINTS

Methamphetamine (METH) abuse is escalating worldwide, with the most common cause of death resulting from cardiovascular failure and hyperthermia; however, the underlying physiological mechanisms are poorly understood. Systemic administration of METH in anaesthetised rats reduced the effectiveness of some protective cardiorespiratory reflexes, increased central respiratory activity independently of metabolic function, and increased heart rate, metabolism and respiration in a pattern indicating that non-shivering thermogenesis contributes to the well-described hyperthermia. In animals that showed METH-induced behavioural sensitisation following chronic METH treatment, no changes were evident in baseline cardiovascular, respiratory and metabolic measures and the METH-evoked effects in these parameters were similar to those seen in saline-treated or drug naïve animals. Physiological effects evoked by METH were retained but were neither facilitated nor depressed following chronic treatment with METH. These data highlight and identify potential mechanisms for targeted intervention in patients vulnerable to METH overdose. Methamphetamine (METH) is known to promote cardiovascular failure or life-threatening hyperthermia; however, there is still limited understanding of the mechanisms responsible for evoking the physiological changes. In this study, we systematically determined the effects on both autonomic and respiratory outflows, as well as reflex function, following acute and repeated administration of METH, which enhances behavioural responses. Arterial pressure, heart rate, phrenic nerve discharge amplitude and frequency, lumbar and splanchnic sympathetic nerve discharge, interscapular brown adipose tissue and core temperatures, and expired CO2 were measured in urethane-anaesthetised male Sprague-Dawley rats. Novel findings include potent increases in central inspiratory drive and frequency that are not dependent on METH-evoked increases in expired CO2 levels. Increases in non-shivering thermogenesis correlate with well-described increases in body temperature and heart rate. Unexpectedly, METH evoked minor effects on both sympathetic outflows and mean arterial pressure. METH modified cardiorespiratory reflex function in response to hypoxia, hypercapnia and baroreceptor unloading. Chronically METH-treated rats failed to exhibit changes in baseline sympathetic, cardiovascular, respiratory and metabolic parameters. The tonic and reflex cardiovascular, respiratory and metabolic responses to METH challenge were similar to those seen in saline-treated and drug naive animals. Overall, these findings describe independent and compound associations between physiological systems evoked by METH and serve to highlight that a single dose of METH can significantly impact basic homeostatic systems and protective functions. These effects of METH persist even following chronic METH treatment.

Comparison of noradrenaline, dopamine and serotonin in mediating the tachycardic and thermogenic effects of methamphetamine in the ventral medial prefrontal cortex

Methamphetamine (METH) is a psychostimulant that disrupts monoaminergic neurotransmission to evoke profound behavioral and physiological effects. Rapidly distributing to forebrain regions to increase synaptic concentrations of three monoamines (dopamine (DA), serotonin (5-HT) and noradrenaline (NA)), the medial prefrontal cortex (mPFC) is important in METH-altered behavioral and psychological profiles. Activation of the ventral mPFC can modify physiological variables, however, METH-evoked autonomic changes from this region are unknown. Therefore, the aim of this study was to characterize the respiratory, metabolic and cardiovascular effects of microinjection of METH, DA, 5-HT and NA into the ventral mPFC in urethane-anesthetized Sprague-Dawley rats. METH and NA microinjection evoked dose-related increases in heart rate, interscapular brown adipose tissue temperature and expired CO2, a pattern of response characteristic of non-shivering thermogenesis. NA and 5-HT microinjection elicited pressor and depressor responses, respectively, with matching baroreflex adjustments in sympathetic nerve activity while METH and DA evoked no change in vasomotor outflow. Low doses of METH and DA may evoke respiratory depression. These data suggest that METH's actions in the ventral mPFC, likely via adrenergic receptors, evoke non-shivering thermogenesis which may contribute to the increased body temperature and tachycardia seen in those that abuse METH.

The orexin-1 receptor antagonist SB-334867 decreases sympathetic responses to a moderate dose of methamphetamine and stress

We recently discovered that inhibiting neurons in the dorsomedial hypothalamus (DMH) attenuated hyperthermia, tachycardia, hypertension, and hyperactivity evoked by the substituted amphetamine 3, 4-methylenedioxymethamphetamine (MDMA). Neurons that synthesize orexin are also found in the region of the DMH. As orexin and its receptors are involved in the regulation of heart rate and temperature, they would seem to be logical candidates as mediators of the effects evoked by amphetamines. The goal of this study was to determine if blockade of orexin-1 receptors in conscious rats would suppress cardiovascular and thermogenic responses evoked by a range of methamphetamine (METH) doses. Male Sprague-Dawley rats (n=6 per group) were implanted with telemetric transmitters measuring body temperature, heart rate, and mean arterial pressure. Animals were randomized to receive pretreatment with either the orexin-1 receptor antagonist SB-334867 (10mg/kg) or an equal volume of vehicle. Thirty minutes later animals were given intraperitoneal (i.p.) injections of either saline, a low (1mg/kg), moderate (5mg/kg) or high (10mg/kg) dose of METH. Pretreatment with SB-334867 significantly attenuated increases in body temperature and mean arterial pressure evoked by the moderate but not the low or high dose of METH. Furthermore, animals treated with SB-334867, compared to vehicle, had lower temperature and heart rate increases after the stress of an i.p. injection. In conclusion, temperature and cardiovascular responses to a moderate dose of METH and to stress appear to involve orexin-1 receptors. The failure to affect a low and a high dose of METH suggests a complex pharmacology dependent on dose. A better understanding of this may lead to the knowledge of how monoamines influence the orexin system and vice versa.

Brain edema and breakdown of the blood-brain barrier during methamphetamine intoxication: critical role of brain hyperthermia

To clarify the role of brain temperature in permeability of the blood-brain barrier (BBB), rats were injected with methamphetamine (METH 9 mg/kg) at normal (23 degrees C) and warm (29 degrees C) environmental conditions and internal temperatures were monitored both centrally (nucleus accumbens, NAcc) and peripherally (skin and nonlocomotor muscle). Once NAcc temperatures peaked or reached 41.5 degrees C (a level suggesting possible lethality), animals were administered Evans blue dye (protein tracer that does not normally cross the BBB), rapidly anaesthetized, perfused and had their brains removed. All METH-treated animals showed brain and body hyperthermia associated with relative skin hypothermia, suggesting metabolic activation coupled with peripheral vasoconstriction. While METH-induced NAcc temperature elevation varied from 37.60 to 42.46 degrees C (or 1.2-5.1 degrees C above baseline), it was stronger at 29 degrees C (+4.13 degrees C) than 23 degrees C (+2.31 degrees C). Relative to control, METH-treated animals had significantly higher brain levels of water, Na(+), K(+) and Cl(-), suggesting brain edema, and intense immunostaining for albumin, indicating breakdown of the BBB. METH-treated animals also showed strong immunoreactivity for glial fibrillary acidic protein (GFAP), possibly suggesting acute abnormality or damage of astrocytes. METH-induced changes in brain water, albumin and GFAP correlated linearly with NAcc temperature (r = 0.93, 0.98 and 0.98, respectively), suggesting a key role of brain hyperthermia in BBB permeability, development of brain edema and subsequent functional and structural neural abnormalities. Therefore, along with a direct destructive action on neural cells and functions, brain hyperthermia, via breakdown of the BBB, may be crucial for both decompensation of brain functions and cell injury following acute METH intoxication, possibly contributing to neurodegeneration resulting from chronic drug use.

Methamphetamine and cardiovascular pathology: a review of the evidence

AIMS

To examine the literature pertaining to the cardiovascular effects of methamphetamine and discuss the implications for methamphetamine users.

METHODS

Relevant literature was identified through comprehensive MEDLINE and EMBASE searches.

FINDINGS AND CONCLUSIONS

There is sufficient clinical and experimental evidence to suggest that methamphetamine can have adverse and potentially fatal effects on the cardiovascular system. The existing literature suggests that: (1) methamphetamine users are at elevated risk of cardiac pathology; (2) risk is not likely to be limited to the duration of their methamphetamine use, because of the chronic pathology associated with methamphetamine use; (3) the risk of cardiac pathology is greatest among chronic methamphetamine users; (4) pre-existing cardiac pathology, due to methamphetamine use or other factors, increases the risk of an acute cardiac event; and (5) methamphetamine use is likely to exacerbate the risk of cardiac pathology from other causes, and may therefore lead to premature mortality.

Safety and efficiency of an anti-(+)-methamphetamine monoclonal antibody in the protection against cardiovascular and central nervous system effects of (+)-methamphetamine in rats

The purpose of these studies was to determine if a high-affinity, anti-(+)-methamphetamine (METH) monoclonal antibody (mAb6H4; KD=11 nM) protects against METH-induced central nervous and cardiovascular system effects in rats. Rats (n=5 per group) received one of three anti-METH mAb6H4 doses, equal to 0.32, 0.56 or 1 times the mole equivalent (mol-eq) amount of METH in the body following a 1 mg/kg i.v. METH dose. Each rat was challenged with METH (1 mg/kg, i.v.) 1 and 4 days after the anti-METH mAb dose. The 1 mol-eq anti-METH mAb dose significantly reduced the duration of METH-induced locomotor activity (horizontal locomotion and rearing events), heart rate and blood pressure effects from 2 to 3 h to about an hour. This resulted in a significant reduction in total locomotor activity and the area under the hemodynamic effect vs. time curve for heart rate and blood pressure. In addition, the time to peak locomotor activity was decreased after the 1 mol-eq mAb dose vs. the lower doses. These changes were limited to the first METH challenge. The responses to the second METH challenge were not different from baseline. The peak hemodynamic and locomotor activity values were unchanged after both challenges. These results indicate anti-METH mAb6H4 can safely reduce the hemodynamic and locomotor effects of METH given one day after anti-METH IgG, and that the mAb is safe when administered in the absence of METH. These results are important because they indicate these antibody medications have simultaneous beneficial effects in multiple organ systems.

Methamphetamine and amphetamine pharmacokinetics in oral fluid and plasma after controlled oral methamphetamine administration to human volunteers

BACKGROUND

Methamphetamine (METH) and amphetamine (AMP) concentrations in 200 plasma and 590 oral fluid specimens were used to evaluate METH pharmacokinetics and pharmacodynamics after oral administration of sustained-release METH.

METHODS

Eight participants received four oral 10-mg S-(+)-METH hydrochloride sustained-release tablets within 7 days. Three weeks later, five participants received four oral 20-mg doses. Blood samples were collected for up to 24 h and oral fluid for up to 72 h after drug administration.

RESULTS

After the first oral dose, initial plasma METH detection was within 0.25-2 h; c(max) was 14.5-33.8 micro g/L (10 mg) and 26.2-44.3 micro g/L (20 mg) within 2-12 h. In oral fluid, METH was detected as early as 0.08-2 h; c(max) was 24.7-312.2 micro g/L (10 mg) and 75.3-321.7 micro g/L (20 mg) and occurred at 2-12 h. The median oral fluid-plasma METH concentration ratio was 2.0 across 24 h and was highly variable. Neutral cotton swab collection yielded significantly higher METH and AMP concentrations than citric acid candy-stimulated expectoration. Mean (SD) areas under the curve for AMP were 21% +/- 25% and 24% +/- 11% of those observed for METH in plasma and oral fluid, respectively. After a single low or high dose, plasma METH was >2.5 micro g/L for up to 24 h in 9 of 12 individuals (mean, 7.3 +/- 5.5 micro g/L at 24 h); in oral fluid the detection window was at least 24 h (mean, 18.8 +/- 18.0 micro g/L at 24 h). The plasma and oral fluid 24-h METH detection rates were 54% and 60%, respectively. After four administrations, METH was measurable for 36-72 h (mean, 58.3 +/- 14.5 h).

CONCLUSIONS

Perceived advantages of oral fluid for verifying METH exposure compared with urine include simpler specimen collection and reduced potential for adulteration, but urine offers higher analyte concentrations and a greater window of detection.