Tyrosine hydroxylase immunochemistry and quantitative light microscopic studies of the mesolimbic dopamine system in rat brain: effects of chronic methamphetamine administration

Nanowired Delivery of Mesenchymal Stem Cells with Antioxidant Compound H-290/51 Reduces Exacerbation of Methamphetamine Neurotoxicity in Hot Environment

Military personnel are often exposed to hot environments either for combat operations or peacekeeping missions. Hot environment is a severe stressful situation leading to profound hyperthermia, fatigue and neurological impairments. To avoid stressful environment, some people frequently use methamphetamine (METH) or other psychostimulants to feel comfortable under adverse situations. Our studies show that heat stress alone induces breakdown of the blood-brain barrier (BBB) and edema formation associated with reduced cerebral blood flow (CBF). On the other hand, METH alone induces hyperthermia and neurotoxicity. These effects of METH are exacerbated at high ambient temperatures as seen with greater breakdown of the BBB and brain pathology. Thus, a combination of METH use at hot environment may further enhance the brain damage-associated behavioral dysfunctions. METH is well known to induce severe oxidative stress leading to brain pathology. In this investigation, METH intoxication at hot environment was examined on brain pathology and to explore suitable strategies to induce neuroprotection. Accordingly, TiO₂-nanowired delivery of H-290/51 (150 mg/kg, i.p.), a potent chain-breaking antioxidant in combination with mesenchymal stem cells (MSCs), is investigated in attenuating METH-induced brain damage at hot environment in model experiments. Our results show that nanodelivery of H-290/51 with MSCs significantly enhanced CBF and reduced BBB breakdown, edema formation and brain pathology following METH exposure at hot environment. These observations are the first to point out that METH exacerbated brain pathology at hot environment probably due to enhanced oxidative stress, and MSCs attenuate these adverse effects, not reported earlier.

Effects of adolescent methamphetamine and nicotine exposure on behavioral performance and MAP-2 immunoreactivity in the nucleus accumbens of adolescent mice

The neurotoxic effects of methamphetamine (MA) exposure in the developing and adult brain can lead to behavioral alterations and cognitive deficits in adults. Previous increases in the rates of adolescent MA use necessitate that we understand the behavioral and cognitive effects of MA exposure during adolescence on the adolescent brain. Adolescents using MA exhibit high rates of nicotine (NIC) use, but the effects of concurrent MA and NIC in the adolescent brain have not been examined, and it is unknown if NIC mediates any of the effects of MA in the adolescent. In this study, the long-term effects of a neurotoxic dose of MA with or without NIC exposure during early adolescence (postnatal day 30-31) were examined later in adolescence (postnatal day 41-50) in male C57BL/6J mice. Effects on behavioral performance in the open field, Porsolt forced swim test, and conditioned place preference test, and cognitive performance in the novel object recognition test and Morris water maze were assessed. Additionally, the effects of MA and/or NIC on levels of microtubule associated-2 (MAP-2) protein in the nucleus accumbens and plasma corticosterone were examined. MA and NIC exposure during early adolescence separately decreased anxiety-like behavior in the open field test, which was not seen following co-administration of MA/NIC. There was no significant effect of early adolescent MA and/or NIC exposure on the intensity of MAP-2 immunoreactivity in the nucleus accumbens or on plasma corticosterone levels. These results show that early adolescent MA and NIC exposure separately decrease anxiety-like behavior in the open field, and that concurrent MA and NIC exposure does not induce the same behavioral change as either drug alone.

Methamphetamine alters microglial immune function through P2X7R signaling

Background

Purinoceptors have emerged as mediators of chronic inflammation and neurodegenerative processes. The ionotropic purinoceptor P2X7 (P2X7R) is known to modulate proinflammatory signaling and integrate neuronal-glial circuits. Evidence of P2X7R involvement in neurodegeneration, chronic pain, and chronic inflammation suggests that purinergic signaling plays a major role in microglial activation during neuroinflammation. In this study, we investigated the effects of methamphetamine (METH) on microglial P2X7R.

Methods

ESdMs were used to evaluate changes in METH-induced P2X7R gene expression via Taqman PCR and protein expression via western blot analysis. Migration and phagocytosis assays were used to evaluate functional changes in ESdMs in response to METH treatment. METH-induced proinflammatory cytokine production following siRNA silencing of P2X7R in ESdMs measured P2X7R-dependent functional changes. In vivo expression of P2X7R and tyrosine hydroxylase (TH) was visualized in an escalating METH dose mouse model via immunohistochemical analysis.

Results

Stimulation of ESdMs with METH for 48 h significantly increased P2X7R mRNA (*p < 0.0336) and protein expression (*p < 0.022). Further analysis of P2X7R protein in cellular fractionations revealed increases in membrane P2X7R (*p < 0.05) but decreased cytoplasmic expression after 48 h METH treatment, suggesting protein mobilization from the cytoplasm to the membrane which occurs upon microglial stimulation with METH. Forty-eight hour METH treatment increased microglial migration towards Fractalkine (CX3CL1) compared to control (****p < 0.0001). Migration toward CX3CL1 was confirmed to be P2X7R-dependent through the use of A 438079, a P2X7R-competitive antagonist, which reversed the METH effects (****p < 0.0001). Similarly, 48 h METH treatment increased microglial phagocytosis compared to control (****p < 0.0001), and pretreatment of P2X7R antagonist reduced METH-induced phagocytosis (****p < 0.0001). Silencing the microglial P2X7R decreased TNF-α (*p < 0.0363) and IL-10 production after 48 h of METH treatment. Additionally, our studies demonstrate increased P2X7R and decreased TH expression in the striata of escalating dose METH animal model compared to controls.

Conclusions

This study sheds new light on the functional role of P2X7R in the regulation of microglial effector functions during substance abuse. Our findings suggest that P2X7R plays an important role in METH-induced microglial activation responses. P2X7R antagonists may thus constitute a novel target of therapeutic utility in neuroinflammatory conditions by regulating pathologically activated glial cells in stimulant abuse.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0553-3) contains supplementary material, which is available to authorized users.

Social affiliation relates to tyrosine hydroxylase immunolabeling in male and female zebra finches (Taeniopygia guttata)

The catecholamines dopamine and norepinephrine are implicated in affiliative behaviors, yet few studies have addressed the extent to which affiliative behaviors within distinct social settings rely upon similar or distinct catecholaminergic mechanisms. To explore the role of catecholamines in affiliative behavior within distinct long-term social contexts, we examined the density of the catecholamine synthetic enzyme tyrosine hydroxylase (TH) in brain regions within both the mesolimbic dopaminergic system and "social behavior network" in male and female zebra finches (Taeniopygia guttata) paired for 21 days with either a same- or opposite-sex conspecific. On days 16-21 after pairing, members of both same- and mixed-sex pairs produced similar rates of affiliative behaviors. Measures of affiliation related to TH labeling in the ventral tegmental area (VTA), nucleus accumbens (Ac), medial preoptic nucleus (POM), and ventromedial nucleus of the hypothalamus (VMH). Relationships between TH labeling density and specific measures of affiliative behavior differed in rostral compared to caudal subregions of Ac and VTA, suggesting distinct roles for these subregions in the regulation of affiliative behavior. Finally, TH labeling density in the VMH and rostral VTA were positively related to the amount of courtship received from the partner and TH labeling in Ac was denser in opposite-sex pairs compared to same-sex pairs, indicative of socially induced brain plasticity. Overall, results highlight a complex region- and behavior-specific role for catecholamines in vertebrate affiliation.

Neurochemical consequences of dysphoric state during amphetamine withdrawal in animal models: a review

Chronic abuse of amphetamines, such as d-amphetamine (AMPH) and d-methamphetamine, results in psychological dependence, a condition in which the drug produces a feeling of satisfaction and a drive that requires periodic or continuous administration of the drug to produce overwhelming pleasure or to avoid discomfort such as dysphoria. The dysphoric state of AMPH withdrawal has been recognized as depressive syndromes, such as anhedonia, depression, anxiety, and social inhibition, in early drug abstinence. Medication for treatment of the dysphoric state is important for AMPH abusers to avoid impulsive self-injurious behavior or acts that are committed with unconscious or uncontrolled suicidal ideation. However, successful treatments for AMPH withdrawal remain elusive, since the exact molecular basis of the expression of dysphoria has not been fully elucidated. This review focuses on the molecular aspects of AMPH withdrawal as indexed by neurochemical parameters under a variety of injection regimens (for example, levels of brain monoamines and their metabolites, and gamma-aminobutyric acid, expression of genes and proteins involved in neuronal activity, and monoamine metabolism and availability) in rodent models which exhibit significant phenotypic features relevant to the syndromes of AMPH withdrawal in humans.

Effects of neonatal exposure to methamphetamine: catecholamine levels in brain areas of the developing rat

Neonatal exposure to moderate doses of methamphetamine during the first month of life in the rat affects tyrosine hydroxylase gene expression in the substantia nigra and nigrostriatal tyrosine hydroxylase activity. The main goal of this work was to evaluate the ontogeny of the neurochemical effects of repeated exposure to moderate doses of methamphetamine during the first month of life in the rat. Norepinephrine, dopamine, and dihydroxyphenylacetic acid levels were measured in target areas of methamphetamine: the substantia nigra, ventral tegmental area, caudate-putamen, nucleus accumbens, and medial prefrontal cortex. On postnatal day 1 (PND1), Wistar rat litters, culled to eight pups, sex balanced, were randomly attributed to either methamphetamine or control groups. Methamphetamine groups were administered 10 mg of (+/-)-methamphetamine/kg body weight/day, subcutaneously, from PND1 until the day prior to sacrifice; control groups received isovolumetric saline. Groups were sacrificed on PND7, PND14, and PND30. Neonatal methamphetamine exposure increased norepinephrine levels in the substantia nigra of PND30 rats; on PND14, this variation was evident only in male pups. In the substantia nigra, the dihydroxyphenylacetic/dopamine ratio was also affected in PND30 males. In the ventral tegmental area, catecholamine levels were not affected by methamphetamine. Norepinephrine levels were also increased in the caudate-putamen of PND7 male and PND14 female methamphetamine-exposed pups and in the nucleus accumbens of PND14 female and PND30 male and female pups. Catecholamine levels in the medial prefrontal cortex were not affected by neonatal methamphetamine administration.

Neurotoxic morphological changes induced in the medial prefrontal cortex of rats behaviorally sensitized to methamphetamine

The present study examined whether the development in rats of behavioral sensitization to methamphetamine (MAP) is related to the development of neurotoxic morphological changes presumably induced in the medial prefrontal cortex (MFC). Male rats were intraperitonieally injected with MAP (5 mg/kg) once a day for 12 days (day 1-day 12), and then the drug was withdrawn for 7-42 days (WD7-WD42). The MAP- treatment caused hypersensitivity of a successive head-movement stereotypy, which reached a basic plateau level on day 4, and rose successively to a higher level by day 12. Morphological changes were histochemically and morphometrically examined in the MFC. In the strata covering layers II and III, the densities of tyrosine hydroxylase (TH)-immunoreactive axons decreased on a daily basis to 50% of the control on day 4 and then to 40% on days 6 and 12. The densities of dopamine-,beta-hydroxylase (DBH)-immunoreactive axons did not change during the injection period. A few TUNEL-positive cells were observed in a unit area (0.25 mm2) covering layers II-V on day 6 and they increased to 19 and 16 on day 12 and WD7, respectively. These observations demonstrate a role for the neurotoxic changes in the MFC in the processes of behavioral sensitization of a stereotypy to a low dose of MAP.

Parvalbumin neuron circuits and microglia in three dopamine-poor cortical regions remain sensitive to amphetamine exposure in the absence of hyperthermia, seizure and stroke

The dopamine-releasing and depleting substance amphetamine (AMPH) can make cortical neurons susceptible to damage, and the prevention of hyperthermia, seizures and stroke is thought to block these effects. Here we report a 2-day AMPH treatment paradigm which affected only interneurons in three cortical regions with average or below-average dopamine input. AMPH (six escalating doses/day ranging from 5 to 30 mg/kg for 2 days) was given at 17-18 degrees C ambient temperature (T) to adult male rats. During the 2-day AMPH treatment, peak body T stayed below 38.9 degrees C in 40% of the AMPH treated rats. In 60% of the rats, deliberate cooling suppressed (<39.5 degrees C) or minimized (<40.0 degrees C) hyperthermia. Escalation of stereotypes to seizure-like behaviors was rare and post-mortem morphological signs of stroke were absent. Neurons labeled with the anionic, neurodegeneration-marker dye Fluoro-Jade (F-J) were seen 1 day after dosing, peaked 3 days later, but were barely detectable 14 days after dosing. Only nonpyramidal neurons in layer IV of the somatosensory barrel cortex and in layer II of the piriform cortex and posterolateral cortical amygdaloid nucleus were labeled with Fluoro-Jade. Isolectin B-labeled activated microglia were only detected in their neighborhood. F-J labeled neurons were extremely rare in cortical regions rich in dopamine (e.g. cingulate cortex), and were absent in cortical regions with no dopamine (e.g. visual cortex). Parvalbumin was seen in some Fluoro-Jade-labeled neurons and parvalbumin immunostaining in local axon plexuses intensified. This AMPH paradigm affected fewer cortical regions, and caused smaller reduction in striatal tyrosine hydroxylase (TH) immunoreactivity than previous 1-day AMPH regimens generating seizures or severe (above 40 degrees C) hyperthermia. Correlation between peak or mean body T and the extent of neurodegeneration or microgliosis was below statistical significance. Astrogliosis (elevated levels of the astroglia-marker, glial fibrillary acidic protein (GFAP)) was detected in many brain regions. In the striatum and midbrain, F-J labeled neurons and activated microglia were absent, but astrogliosis, decreased TH immunolabel, and swollen TH fibers were detected. In sum, after this AMPH treatment, cortical pyramidal neurons were spared, but astrogliosis was brain-wide and some interneurons and microglia in three cortical regions with average or below-average dopamine input remained sensitive to AMPH exposure.

Neonatal methamphetamine in the rat: evidence for gender-specific differences upon tyrosine hydroxylase enzyme in the dopaminergic nigrostriatal system

Methamphetamine (Meth) neurotoxicity upon the mesencephalic dopaminergic systems was demonstrated in the adult, both in humans and in experimental models. In the rat, the development and maturation of the dopaminergic systems is accomplished during the first month of postnatal life, a period of particular vulnerability to environmental influences. In this study, the effect of Meth exposure during the first month of life was assessed in the nigrostriatal dopaminergic system of the rat. For this purpose, Wistar rat litters were culled to 8 pups, retaining preferentially 4 males and 4 females, which, in the day following birth (postnatal day 1, PND1), were randomly attributed to either the Meth or control group. Meth-groups were administered 10 mg of (+)-methamphetamine hydrochloride/kg body weight/day, subcutaneously, twice daily, from PND1 until PND29; control groups received isovolumetric doses of saline. Animals were sacrificed at PND30. Males exposed to Meth during the first month of life had increased tyrosine hydroxylase (TH) activity both in the caudate-putamen and substantia nigra. Males also had increased nigral TH mRNA levels, as assessed by in situ hybridization. These effects did not exist in females. These results support the evidence that Meth exposure during the first month of life in the rat has a gender-specific stimulatory effect upon the maturation of TH, the key enzyme for dopamine biosynthesis in the nigrostriatal dopaminergic system.

Chronic methamphetamine exposure decreases high affinity uptake function in norepinephrine afferents in the cerebellar cortex: an electrophysiological and electrochemical study

It has been reported that chronic methamphetamine (MA) treatment decreases monoamine release in different brain regions. However, the clearance of norepinephrine (NE) after chronic MA intake is not clear. In the present study, we administered MA to Sprague-Dawley rats for 1 month. The animals were later anesthetized with urethane for electrophysiological recording. Previous studies have indicated that gamma-aminobutyric acid (GABA)-induced electrophysiological responses are enhanced by norepinephrine (NE) acting via postsynaptic beta-adrenergic receptors. We found that local application of the NE high affinity uptake inhibitor desmethylimipramine (DMI) significantly potentiated GABA-induced electrophysiological depressions in cerebellar Purkinje neurons in control rats. In contrast, DMI did not augment GABA responses in rats chronically treated with MA for 1 month, or in rats withdrawn from MA for 7-14 days after a 1-month MA treatment. To further examine if DMI-induced GABA modulation is altered by post- or pre-synaptic mechanisms in chronic MA-treated rats, we examined the electrophysiological interaction of GABA and isoproterenol (ISO), a postsynaptic beta-adrenergic receptor agonist, in Purkinje neurons. We found that GABA-induced inhibition is potentiated by local application of ISO in both control and chronic MA rats, suggesting that the reduction in DMI/GABA interactions is probably not mediated through post-synaptic noradrenergic mechanisms. Presynaptic NE clearance was further examined using in vivo chronoamperometric methods. Extracellular NE levels in the cerebellar cortex were measured using Nafion-coated carbon fiber sensors. We found that local application of DMI inhibited NE clearance in control rats, but not in chronic MA animals, suggesting that presynaptic NE clearance is reduced after chronic MA treatment. In addition, NE levels in cerebellar tissue were measured using HPLC-ECD. The NE concentration was significantly decreased in chronic MA rats. Taken together, our data suggest that regulation of uptake by DMI at central noradrenergic nerve terminals is abnormal after chronic MA exposure.

A single dose model of methamphetamine-induced neurotoxicity in rats: effects on neostriatal monoamines and glial fibrillary acidic protein

The neurotoxic effects of a single administration of methamphetamine (MA) were studied under conditions conducive to MA-induced hyperthermia. After a single dose of MA (10, 20, 30, or 40 mg/kg, s. c.) or saline (3 ml/kg) to Sprague-Dawley CD rats, rectal temperatures were monitored for 9 h in a room with an ambient temperature of 22.0+/-0.5 degrees C. MA induced significant dose-dependent hyperthermia, however, no significant increase in mortality occurred. Neostriatal DA, 5-HT, TH, and GFAP were assayed 3 days following treatment. MA induced dose-dependent reductions of DA, 5-HT and TH, and increased GFAP. For DA, at doses of 20, 30, or 40 mg/kg the reductions were to 71%, 49%, and 29%, and for 5-HT were to 73%, 44%, and 19% of control values. No reductions were seen after the 10 mg/kg dose. Semiquantitative analysis Western blots of TH and GFAP demonstrated that TH was reduced to 52%, 75%, and 28%, and GFAP was increased to 125%, 134%, and 149% of control values at MA doses of 20, 30, or 40 mg/kg, respectively. No significant changes in TH or GFAP were seen at the 10 mg/kg MA dose. These results demonstrate that a single-dose of MA can be as effective as the widely used four-dose every 2 h regimen. Moreover, mortality can be minimized by monitoring core body temperature and preventing MA-induced hyperthermia from exceeding 41.5 degrees C.

alpha-Phenyl-N-tert-butyl nitrone attenuates methamphetamine-induced depletion of striatal dopamine without altering hyperthermia

Methamphetamine (MA) administration to adult rats (4 x 10 mg/kg s.c.) induces neurotoxicity predominately characterized by a persistent reduction of neostriatal dopamine (DA) content. Hyperthermia following MA administration potentiates the resulting DA depletion. DA-derived free radicals are postulated to be a mechanism through which MA-induced neurotoxicity is produced. The spin trapping agent PBN reacts with free radicals to form nitroxyl adducts, thereby preventing damaging free radical reactions with cellular substrates. MA with saline pretreatment (Sal-MA) reduced neostriatal DA by 55% (P < 0.01 vs. Sal-Sal). MA with PBN pretreatment (PBN-MA) at 36 or 60 mg/kg reduced neostriatal DA by 36 and 22%, respectively (P < 0.05 and P < 0.01 vs Sal-MA) indicating partial protection. PBN pretreatment did not alter MA-induced hyperthermia. Thus, PBN does not attenuate MA-induced neurotoxicity by reducing MA-induced hyperthermia. These results support a role for free radicals in the generation of MA-induced dopaminergic neurotoxicity.

Neonatal methamphetamine-induced long-term acoustic startle facilitation in rats as a function of prepulse stimulus intensity

Neonatal exposure to methamphetamine (MA) has previously been shown to induce acoustic startle facilitation when the animals were tested as adults. The present experiment sought to replicate and extend this effect using a lower dose of MA and to determine if the effect varied as a function of prepulse stimulus intensity. Sprague-Dawley CD rat offspring were culled on the day after birth to eight (preferentially retaining females). On days 1-10, progeny were injected SC with either 20 mg/kg of d-MA twice per day (doses spaced at least 8 h apart) or distilled water. On postnatal day 50, offspring were administered 51 acoustic startle trials followed by 36 prepulse trials. Prepulse intensities were 0, 70, 75, 80, 85, or 90 dB. MA progeny showed augmented startle response amplitudes on both paradigms but the effect was most pronounced on the prepulse trials. Prepulse intensity interacted with MA treatment in that significant facilitation in the MA animals occurred on 0 and 70 dB prepulse trials but was only a trend (p < 0.10) on 75, 80, 85, and 90 dB trials. This implies that the effect of MA is most likely upon the basic startle reflex and not upon inhibitory pathways that modify startle reactivity.

Protective effects of MK-801 on methamphetamine-induced depletion of dopaminergic and serotonergic terminals and striatal astrocytic response: an immunohistochemical study

It has been shown previously that methamphetamine induces dopaminergic nerve terminal degeneration, serotonin depletion and striatal reactive astrogliosis, and that the noncompetitive N-methyl-D-aspartate (NMDA) antagonist MK-801 can block methamphetamine (MA)-induced depletion of dopamine and serotonin and reduction in activity of their synthetic enzymes. In this study, immunohistochemistry was used to evaluate the effect of MK-801 on methamphetamine-induced neuropathological alterations of dopaminergic and serotonergic terminals and striatal astrocytic responses. Adult male rats were treated with methamphetamine (4 injections of 10 mg/kg at 2 hour intervals) in conjunction with MK-801 which was administered 15 min before each methamphetamine administration at doses of 1 mg/kg or 2 mg/kg. Brains were examined three days following treatment. MK-801 administration prevented methamphetamine-induced depletion of 5-hydroxytryptophan (5-HT) terminals in the forebrain and depletion of tyrosine hydroxylase-positive dopaminergic terminals and astrocytic response in the neostriatum in most animals. These results support the concept that excitatory amino acids acting through an NMDA receptor are involved in methamphetamine-induced neuronal damage on dopaminergic and serotonergic terminal fields. A minor depletion of TH-positive terminals and astrogliosis in the neostriatum was seen in three of nine MA-MK-801-treated animals. This indicates that the protective effects of MK-801 on MA-induced dopaminergic terminal degeneration varies among animals with complete protection in most animals and partial protection in the others using the present doses and dosing regimen.

Dopamine-glutamate interactions in methamphetamine-induced neurotoxicity

Repeated administration of methamphetamine (m-AMPH) to rats induces dopamine (DA) terminal damage, and coadministration of antagonists of the N-methyl-D-aspartate (NMDA) or dopamine D1 or D2 receptors are protective. Striatal microdialysis of rats given a neurotoxic regimen of 4 x m-AMPH (4 mg/kg, s.c.) treatments revealed a dramatic and prolonged elevation of extracellular DA after the final m-AMPH administration. Neuroprotective regimens of MK-801, SCH 23390, or eticlopride greatly attenuated the overflow of DA resulting from the fourth m-AMPH treatment. By itself, MK-801 had no significant influence on striatal DA overflow, whereas either DA antagonist given alone elevated dialysate DA concentrations. A significant correlation was found between the magnitude of the m-AMPH-induced DA overflow of individual microdialyzed rats and their striatal DA content at sacrifice one week later. We conclude that the ability of non-competitive NMDA antagonists and of the D1 or D2 antagonists to protect against m-AMPH-induced striatal DA terminal injury can be accounted for by their attenuation of m-AMPH-evoked DA overflow. These findings underscore the important role played by elevated extracellular DA concentrations to the injurious effects of this stimulant drug.

Differing neurotoxic potencies of methamphetamine, mazindol, and cocaine in mesencephalic cultures

The potent reinforcing effects of methamphetamine and cocaine are thought to be mediated by their interactions with CNS dopamine neurons. Both stimulants share the ability to block dopamine uptake potently, and methamphetamine can release cytoplasmic dopamine as well. There is also abundant evidence demonstrating the neurotoxic effects of methamphetamine. There are, however, limited studies that attempt to discern the neurotoxic mechanisms of these agents. The purpose of the present study was to characterize and compare the chronic in vitro effects of methamphetamine, cocaine, and the dopamine uptake blocker, mazindol, on cultured fetal mesencephalic dopamine neurons. Our studies examined biochemical mechanisms to evaluate the contribution of reuptake blockade versus release of dopamine. Using a dispersed cell preparation of fetal mesencephalon, cultures were treated for 5 days with the three uptake blockers. Dopamine function was assessed by measuring high-affinity [3H]dopamine uptake and by examining cultures for the presence of tyrosine hydroxylase-immunopositive neurons. Nonspecific neurotoxicity was assessed by staining for neuron-specific enolase and measuring lactate dehydrogenase activity. The results indicate that repeated administration of high concentrations of methamphetamine (10(-4) and 10(-3) M) caused a generalized neurotoxicity whereas the effects of 10(-5) M methamphetamine appeared to be specific to dopamine cells. Likewise, treatment of the cultures with mazindol (10(-6) M) resulted in reduced dopamine uptake while not significantly affecting neuron-specific enolase or tyrosine hydroxylase immunostaining. On the other hand, repeated exposure to cocaine (10(-5) and 10(-4) M) did not alter dopaminergic function in these cultures. The different mechanisms of action of these stimulants may explain the differences in neurotoxic potency of these compounds.(ABSTRACT TRUNCATED AT 250 WORDS)

Stimulant-induced alterations in dopaminergic and serotonergic function in fetal raphe neurons

Methamphetamine and its structural analogues have been demonstrated to be neurotoxic to CNS dopamine (DA) and serotonin (5-HT) neurons both in vivo and in vitro. Our laboratory has been actively characterizing mesencephalic cultures and the effects of methamphetamine exposure on neurochemical and immunochemical indices. The purpose of the present studies was to extend our findings with mesencephalic cultures and compare them with methamphetamine-induced alterations in fetal raphe cultures that contain both DA and 5-HT cells. Methamphetamine (10 and 100 microM) was added to the cultures 24 h after plating and fresh daily thereafter. The effects of chronic methamphetamine exposure on [3H]-DA and [3H]-5-HT uptake were determined after 5 days of drug treatment. Additional cultures were immunochemically analyzed for the presence of DA- and 5-HT-containing cells and total neuronal density. Results indicate that repeated methamphetamine exposure decreased DA and 5-HT uptake. Furthermore, repeated exposure to the higher concentration of methamphetamine (100 microM) caused a significant reduction in the number of DA and 5-HT cells as well as reducing the total neuronal density. This would suggest that this higher concentration of methamphetamine results in generalized neurotoxicity. Exposure to 10 microM methamphetamine resulted in more specific effects on dopaminergic function. These findings indicate that repeated methamphetamine administration can induce similar alterations in both dopaminergic and serotonergic neurons in raphe cultures.

Survival of developing dopaminergic neurons in reaggregate tissue culture following treatment with methamphetamine

Developing central dopamine (DA)-containing neurons in rotation-mediated reaggregate tissue culture exposed to 10(-4) M methamphetamine for 1 week (at a time corresponding to the 2nd week of postnatal development) exhibit decreased DA levels. DA neurons were visualized either by a histofluorescent method after 'loading' with exogenous DA, or by tyrosine hydroxylase (TH) immunocytochemistry. An apparent loss of histofluorescent DA cell bodies was observed due to a methamphetamine-induced reduction in exogenous DA accumulation. No decrease in the number of TH-immunoreactive neurons was observed. Thus, developing DA neurons when visualized by TH immunocytochemistry survive despite methamphetamine-induced reductions in DA levels.

Age-related toxicity in prefrontal cortex and caudate-putamen complex of gerbils (Meriones unguiculatus) after a single dose of methamphetamine

Single, intermediate to large doses (6-60 mg/kg) of methamphetamine were applied to study the acute neurotoxic effects in developing male gerbils (up to 24 months). A sensitive silver-staining method was used to analyze the toxicity of methamphetamine by light and electron-microscopy. It was shown that treatment with the drug degraded synaptic components, as well as a small population of neurones in the caudate-putamen complex accompanied by accumulation of lysosomes in fibers and axon terminals. In juveniles, methamphetamine in doses of 25-60 mg/kg, resulted in accumulation of lysosomes, selectively in the prefrontal cortex. In young adults, only about half of these doses were sufficient to produce consistent and/or additional effects in the caudate-putamen complex. When the gerbils grew older than 8 months, treatment with drug led to accumulation of lysosomes, exclusively in the caudate-putamen, with acute doses ranging from 6 to 12 mg/kg. Acute neurotoxicity with methamphetamine has thus been induced by doses, which hitherto have been claimed to produce behavioural sensitization. Since dopamine (DA) seems the most likely transmitter to be affected, age-related differences in methamphetamine-induced neurotoxicity are discussed in relation to the background of developing DA-response systems, which are still changing in pattern during ageing.

Single doses of methamphetamine cause changes in the density of dendritic spines in the prefrontal cortex of gerbils (Meriones unguiculatus)

Single doses of methamphetamine (25 mg/kg) were administered to adult gerbils. All detectable spines were counted along defined segments of basal, apical and lateral dendrites of Golgi-impregnated pyramidal cells in the medial prefrontal cortex (layers III and V) and the parietal cortex (layer V). These two areas were selected because previous investigations had shown methamphetamine-induced neurotoxicity in prefrontal cortex but not in parietal cortex. The frequencies of dendritic spines in methamphetamine-treated gerbils were found to be significantly increased in the prefrontal cortex, while no significant change was found in the parietal cortex.

Contrasting tissue factors predict heterogeneous striatal dopamine neurotoxicity after MPTP or methamphetamine treatment

Treatment of mice with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) or (+)-methamphetamine (METH) results in regionally heterogeneous patterns of dopaminergic depletion. The magnitude of the MPTP-induced dopamine (DA) depletion corresponds directly to the density of [3H]mazindol binding to DA transport sites, but not the DA concentration, in intact mouse striatal regions. In contrast, the extent of METH-induced DA depletion corresponds to the intact dopamine concentration, not the [3H]mazindol binding, in the same striatal regions. The findings provide a rationale for testing different hypotheses regarding the neurobiological substrates of mesostriatal injury in idiopathic Parkinson's disease (PD).

Effects of high-dose methamphetamine administration on serotonin uptake sites in rat brain measured using [3H]cyanoimipramine autoradiography

Repeated administration of high doses of methamphetamine (15 mg/kg given for 5 doses over 24 h) resulted in long-term decreases in the binding of [3H]cyanoimipramine ([3H]CN-IMI) to serotonin uptake sites measured using quantitative autoradiography. Seven days after termination of drug administration decreases were seen in 23 of 28 regions examined. This is consistent with previous studies indicating that methamphetamine and related amphetamines are neurotoxic to serotonin neurons. Significant decreases were still present in many brain areas on the same dosage schedule 30 days after drug administration. However, the number of areas affected was considerably less, consistent with some regrowth of serotonin neurons. At a lower dosage (7.5 mg/kg on the same schedule) no effects on [3H]CN-IMI binding were seen. The results of this study provide support for the serotonergic neurotoxicity of repeated methamphetamine administration in rats. They also show that the neurotoxicity is highly regional and dose dependent.