Stimulation of the nigrostriatal dopamine system inhibits both heat production and heat loss mechanisms in rats

[Dyskinesia-hyperpyrexia syndrome triggered by overdose of istradefylline: a case report]

We present a 71-year-old woman with an eight-year history of Parkinson's disease (PD). She began to experience wearing-off at the age of 66 and subsequently developed dyskinesia. She had worsened dyskinesias for three days, followed by a high fever, and she was subsequently hospitalized. On admission, severe dyskinesia, hyperpyrexia, and elevation of serum creatine kinase were observed. Severe dyskinesia without rigidity continued throughout the day and she was diagnosed with dyskinesia-hyperpyrexia syndrome (DHS). She was treated with standard medical care and anti-parkinsonian medications were reduced drastically. Dyskinesia started to wane three days after admission and almost disappeared on day twelve. Prior to admission, the patient reported she had been taking two to three times the dose prescribed of istradefylline, which was the suspected to be a trigger of DHS. Because DHS is a rare but potentially life-threatening complication, early recognition and diagnosis is vital. A proper treatment strategy for DHS may include standard medical care together with reduced anti-parkinsonian medications.

An Increase in Peripheral Temperature following Cocaine Administration Is Mediated through Activation of Dopamine D2 Receptor in Rats

Drug addiction has become a worldwide problem, affecting millions of people across the globe. While the majority of mechanistic studies on drug addiction have been focused on the central nervous system, including the mesolimbic dopamine system, the peripheral actions of drugs of abuse remain largely unknown. Our preliminary study found that the systemic injection of cocaine increased peripheral skin temperature. This led us to our present study, which investigated the mechanisms underlying the increase in peripheral temperature following cocaine injection. Male Sprague Dawley rats were anesthetized with pentobarbital sodium, and peripheral skin temperature measurements were taken using a thermocouple needle microprobe and an infrared thermal camera. Cocaine injection caused an acute rise in peripheral body temperature, but not core body temperature, about 10 min after injection, and the temperature increases were occluded by systemic injection of dopamine D2 receptor antagonist L741,626, but not D1 receptor antagonist SCH23390. In addition, systemic administration of bromocriptine, a dopamine D2 receptor agonist, significantly increased peripheral temperature. Infrared thermal imaging showed that the thermal increases following cocaine injection were predominantly in the distal areas of the forelimbs and hindlimbs, relative to core body temperature. Treatment with cocaine or bromocriptine decreased the size of skin blood vessels without affecting the expression of dopamine D2 receptors. These results suggest that increased peripheral temperature in skin following cocaine injection is associated with the activation of the dopamine D2 receptor.

The influence of preconditioning with low dose of LPS on paraquat-induced neurotoxicity, microglia activation and expression of α-synuclein and synphilin-1 in the dopaminergic system

Background

Prolonged inflammation, oxidative stress, and protein aggregation are important factors contributing to Parkinson’s disease (PD) pathology. A known ROS generator, pesticide paraquat (PQ), was indicated as an environmental substance potentially increasing the incidence of PD and is used to model this disease. We investigated if a combination of inflammation and oxidative stress in subthreshold doses would exacerbate the modelled neuropathology.

Methods

We examined the late effects of acute or repeated peripheral inflammation induced by low dose of LPS (10 μg/kg, ip) on PQ toxicity in the rat nigrostriatal dopaminergic pathway, microglial activation markers and expression of major Lewy bodies proteins, α-synuclein and synphilin-1.

Results

We observed that LPS increased, while PQ decreased body temperature and microglia CD11b expression in the SN. Single LPS pretreatment, 3 h before repeated weekly PQ injections (4×) slightly aggravated neuronal degeneration in the SN. Moreover, degeneration of dopaminergic neurons after weekly repeated inflammation itself (4×) was observed. Interestingly, repeated LPS administration combined with each PQ dose counteracted such effect. The expression of α-synuclein decreased after repeated LPS injections, while only combined, repeated LPS and PQ treatment lowered the levels of synphilin-1. Therefore, α-synuclein and synphilin-1 expression change was influenced by different mechanisms. Concomitantly, decreased levels of the two proteins correlated with decreased degeneration of dopaminergic neurons and with a normalized microglia activation marker.

Conclusions

Our results indicate that both oxidative insult triggered by PQ and inflammation caused by peripheral LPS injection can individually induce neurotoxicity. Those factors act through different mechanisms that are not additive and not selective towards dopaminergic neurons, probably implying microglia. Repeated, but small insults from oxidative stress and inflammation when administered in significant time intervals can counteract each other and even act protective as a preconditioning effect. The timing of such repetitive insults is also of essence.

Supplementary Information

The online version contains supplementary material available at 10.1007/s43440-021-00340-1.

Dyskinesia-hyperpyrexia syndrome in Parkinson's disease: a systematic review

PURPOSE

Dyskinesia-hyperpyrexia syndrome (DHS) is a rare but life-threatening disease. The clinical manifestations of this syndrome overlap substantially with Parkinson hyperpyrexia syndrome and serotonin syndrome and are often confused by clinicians. The purpose of this review was to enable clinicians to recognize this syndrome and thereby reach a correct diagnosis and provide optimal treatments to improve prognosis in clinical practice.

METHODS

Using the methodology described in the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement, we conducted a literature search of the PubMed, Embase, and MEDLINE databases using keywords in titles and abstracts of published literature. Quality assessment was performed using the modified Newcastle-Ottawa scale.

RESULTS

A total of 11 patients obtained from nine publications were included in this systematic review. All of the cases occurred in patients with advanced Parkinson's disease (PD) of long disease duration. High ambient temperature was the most common trigger of this syndrome. Hyperpyrexia and dyskinesias were present in all cases. The consciousness disturbances of this syndrome included confusion, hallucination, and lethargy or stupor. Autonomic dysfunction (except for hyperpyrexia) is uncommon in DHS, and only two patients presented with tachycardia. The treatment of this syndrome included supportive interventions (including rehydration, anti-pyretic and anti-infection treatments, and maintaining electrolyte balance), dopaminergic drug reduction and sedation. Two patients died due to DHS.

CONCLUSIONS

We summarized the triggers, clinical features, and treatments of all reported dyskinesia-hyperpyrexia syndrome cases, proposed guiding diagnostic criteria, and established a flow chart to guide diagnoses to quickly identify these three syndromes in clinical practice.

Task-Dependent Differences in Operant Behaviors of Rats With Acute Exposure to High Ambient Temperature: A Potential Role of Hippocampal Dopamine Reuptake Transporters

Behavioral or cognitive functions are known to be influenced by thermal stress from the change in ambient temperature (Ta). However, little is known about how increased Ta (i.e., when the weather becomes warm or hot) may affect operant conditioned behavior and the neural substrates involved. The present study thus investigated the effects of high Ta on operant behaviors maintained on a fixed-ratio 1 (FR1) and a differential reinforcement for low-rate responding 10 s (DRL 10-s) schedule of reinforcement. The rats were randomly assigned to three groups receiving acute exposure to Ta of 23°C, 28°C, and 35°C, respectively, for evaluating the effects of high Ta exposure on four behavioral tests. Behavioral responses in an elevated T-maze and locomotor activity were not affected by Ta treatment. Regarding operant tests, while the total responses of FR1 behavior were decreased only under 35°C when compared with the control group of 23°C, those of DRL 10-s behavior were significantly reduced in both groups of 28°C and 35°C. Distinct patterns of inter-response time (IRT) distribution of DRL behavior appeared among the three groups; between-group differences of behavioral changes produced by high Ta exposure were confirmed by quantitative analyses of IRT data. Western blot assays of dopamine (DA) D1 and D2 receptor, DA transporter (DAT) and brain-derived neurotrophic factor (BDNF) were conducted for the sample tissues collected in six brain areas from all the subjects after acute high Ta exposure. Significant Ta-related effects were only revealed in the dorsal hippocampus (dHIP). In which, the DAT levels were increased in a Ta-dependent fashion that was associated with operant behavior changes under high Ta exposure. And, there as an increased level of D1 receptors in the 28°C group. In summary, these data indicate that the performance of operant behavior affected by the present high Ta exposure is task-dependent, and these changes of operant behaviors cannot be attributed to gross motor function or anxiety being affected. The regulation of dHIP DAT may be involved in this operant behavioral change under high Ta exposure.

Hypothalamic or Extrahypothalamic Modulation and Targeted Temperature Management After Brain Injury

Targeted temperature management (TTM) has been recognized to protect tissue function and positively influence neurological outcomes after brain injury. While shivering during hypothermia nullifies the beneficial effect of TTM, traditionally, antishivering drugs or paralyzing agents have been used to reduce the shivering. The hypothalamic area of the brain helps in controlling cerebral temperature and body temperature through interactions between different brain areas. Thus, modulation of different brain areas either pharmacologically or by electrical stimulation may contribute in TTM; although, very few studies have shown that TTM might be achieved by activation and inhibition of neurons in the hypothalamic region. Recent studies have investigated potential pharmacological methods of inducing hypothermia for TTM by aiming to maintain the TTM and reduce the shivering effect without using antiparalytic drugs. Better survival and neurological outcome after brain injury have been reported after pharmacologically induced TTM. This review discusses the mechanisms and modulation of the hypothalamus with other brain areas that are involved in inducing hypothermia through which TTM may be achieved and provides therapeutic strategies for TTM after brain injury.

The hidden side of drug action: brain temperature changes induced by neuroactive drugs

RATIONALE

Most neuroactive drugs affect brain metabolism as well as systemic and cerebral blood flow, thus altering brain temperature. Although this aspect of drug action usually remains in the shadows, drug-induced alterations in brain temperature reflect their metabolic neural effects and affect neural activity and neural functions.

OBJECTIVES

Here, I review brain temperature changes induced by neuroactive drugs, which are used therapeutically (general anesthetics), as a research tool (dopamine agonists and antagonists), and self-administered to induce desired psychic effects (cocaine, methamphetamine, ecstasy). I consider the mechanisms underlying these temperature fluctuations and their influence on neural, physiological, and behavioral effects of these drugs.

RESULTS

By interacting with neural mechanisms regulating metabolic activity and heat exchange between the brain and the rest of the body, neuroactive drugs either increase or decrease brain temperatures both within (35-39 °C) and exceeding the range of physiological fluctuations. These temperature effects differ drastically depending upon the environmental conditions and activity state during drug administration. This state-dependence is especially important for drugs of abuse that are usually taken by humans during psycho-physiological activation and in environments that prevent proper heat dissipation from the brain. Under these conditions, amphetamine-like stimulants induce pathological brain hyperthermia (>40 °C) associated with leakage of the blood-brain barrier and structural abnormalities of brain cells.

CONCLUSIONS

The knowledge on brain temperature fluctuations induced by neuroactive drugs provides new information to understand how they influence metabolic neural activity, why their effects depend upon the behavioral context of administration, and the mechanisms underlying adverse drug effects including neurotoxicity.

The beta-lactam antibiotic, ceftriaxone, attenuates morphine-evoked hyperthermia in rats

BACKGROUND AND PURPOSE

Beta-lactam antibiotics are the first practical pharmaceuticals capable of increasing the expression and activity of the glutamate transporter, GLT-1, in the CNS. However, the functional impact of beta-lactam antibiotics on specific drugs which produce their pharmacological effects by increasing glutamatergic transmission is unknown. One such drug is morphine, which causes hyperthermia in rats, mediated by an increase in glutamatergic transmission. Since drugs (e.g. antibiotics) that enhance glutamate uptake also decrease glutamatergic transmission, we tested the hypothesis that ceftriaxone, a beta-lactam antibiotic, would block the glutamate-dependent portion of morphine-evoked hyperthermia.

EXPERIMENTAL APPROACH

A body temperature assay was used to determine if ceftriaxone decreased morphine-induced hyperthermia in rats by increasing glutamate uptake.

KEY RESULTS

Body temperatures of rats treated with ceftriaxone (200 mg kg(-1), i.p. x 7 days) did not differ from rats receiving saline. Morphine (1, 4, 8 and 15 mg kg(-1), s.c.) caused significant hyperthermia. Pre-treatment with ceftriaxone, as described above, decreased the hyperthermic response to these doses of morphine. The effects of ceftriaxone were prevented by TBOA (0.2 micromol, i.c.v.), an inhibitor of glutamate transport.

CONCLUSIONS AND IMPLICATIONS

Ceftriaxone attenuated the hyperthermia caused by morphine, an effect prevented by inhibiting glutamate transport. Thus this effect of ceftriaxone was most likely mediated by increased glutamate uptake. These data revealed a functional interaction between ceftriaxone and morphine and indicated that a beta-lactam antibiotic decreased the efficacy of morphine in conscious rats.

Relationships between locomotor activation and alterations in brain temperature during selective blockade and stimulation of dopamine transmission

It is well known that the dopamine (DA) system plays an essential role in the organization and regulation of brain activational processes. Various environmental stimuli that induce locomotor activation also increase DA transmission, while DA antagonists decrease spontaneous locomotion. Our previous work supports close relationships between locomotor activation and brain and body temperature increases induced by salient environmental challenges or occurring during motivated behavior. While this correlation was also true for psychomotor stimulant drugs such as methamphetamine and MDMA, more complex relationships or even inverted correlations were found for other drugs that are known to increase DA transmission (i.e. heroin and cocaine). In the present study we examined brain, muscle and skin temperatures together with conventional locomotion during selective interruption of DA transmission induced by a mixture of D1 and D2 antagonists (SCH-23390 and eticlopride at 0.2 mg/kg, s.c.) and its selective activation by apomorphine (APO; 0.05 and 0.25 mg/kg, i.v.) in rats. While full DA receptor blockade decreased spontaneous locomotion, it significantly increased brain, muscle and skin temperatures, suggesting metabolic brain activation under conditions of vasodilatation (or weakening of normal vascular tone). In contrast, APO strongly decreased skin temperature but tended to decrease brain and muscle temperatures despite strong hyperlocomotion and stereotypy. The brain temperature response to APO was strongly dependent on basal brain temperature, with hypothermia at high basal temperatures and weak hyperthermia at low temperatures. While supporting the role of DA in locomotor activation, these data suggest more complex relationships between drug-induced alterations in DA transmission, behavioral activation and metabolic brain activation.

Regulation of central dopamine-2 receptor sensitivity by a proportional control thermostat in humans

Central dopamine-2 (D2) receptors are importantly involved in the pathogenesis and treatment of schizophrenia. Central D2 receptors are also involved in thermoregulation. Recently, a type of central nervous system proportional control thermostat was described that governs the magnitude of several serotonin receptor-mediated core body thermoregulatory responses in proportion to both the amount of nocturnal melatonin secreted and the minimum level of nocturnal core body temperature (Tmin). The present study investigated whether the magnitude of D2 receptor-mediated hypothermia--a putative index of central D2 receptor sensitivity--is also regulated by this proportional control thermostat in humans. Twenty healthy subjects had their 02:00 h melatonin concentrations (MT2am) and Tmin measured during consecutive sleep episodes and their core body temperature responses (TAUC) measured the next two mornings after oral ingestion of either the D2 receptor agonist bromocriptine 3.125 mg or placebo. We found that the bromocriptine-induced TAUC was significantly and independently correlated with both Tmin and MT2am. In conclusion, D2 receptor-mediated hypothermia, an index of central D2 receptor sensitivity, is regulated by a proportional control thermostat in humans. The abnormal D2 receptor function in schizophrenia could be related to dysfunction of this thermostat.

NMDA receptors modulate morphine-induced hyperthermia

An accumulating body of evidence indicates that activation of NMDA receptor complexes modulates a number of morphine-induced responses. Because a single injection of morphine increases extracellular glutamate levels and downregulates NMDA receptors, acute morphine appears to increase glutamatergic transmission. On the basis of those data and the fact that morphine and glutamate induce hyperthermia, we investigated whether NMDA receptors modulate the hyperthermic effects of acute morphine in male Sprague-Dawley rats. Subcutaneous injection of morphine (0.1-15 mg/kg) evoked dose-dependent hyperthermia, which was rapid in onset and peaked 45-60 min post-injection. Pretreatment with LY 235959 (0.1-1 mg/kg, s.c.), a highly selective and competitive NMDA antagonist, or dextromethorphan (5-15 mg/kg, s.c.), a noncompetitive NMDA antagonist, attenuated the hyperthermic effect of morphine (4 mg/kg). In contrast, administration of LY 235959 (1 mg/kg) 15 min after morphine (4 mg/kg) did not reverse the hyperthermia. LY 235959 (1 mg/kg) depressed the hyperthermia caused by DAMGO (1 micro g/rat, i.c.v.), a selective mu agonist, confirming that NMDA receptor activation maximizes mu receptor-induced hyperthermia. Neither LY 2359595 nor dextromethorphan by itself significantly altered body temperature. These data indicate that NMDA receptors modulate morphine-induced hyperthermia and suggest that increases in glutamatergic transmission maximize the hyperthermia evoked by morphine.

Central serotonin level-dependent changes in body temperature following administration of tryptophan to pargyline- and harmaline-pretreated rats

1. The effect of tryptophan on body temperature was studied in rats pretreated with pargyline, an irreversible monoamine oxidase inhibitor (MAOI), and harmaline, a reversible MAOI. 2. Tryptophan (100 mg/kg IP) produced hypothermia followed by hyperthermia in pargyline-pretreated rats, and hypothermia in harmaline-pretreated rats, but tryptophan did not cause body temperature changes by itself. 3. The tryptophan-induced hypo- and hyperthermic effects, which peaked at about 1 and 6 hr after tryptophan administration, respectively, were accompanied by a significant increase in serotonin (5-HT) levels in the pargyline-pretreated rat brain (75%-138.7% and 207%-240.9% increase, respectively), and the 5-HT levels in the hyperthermic state were significantly higher than those in the hypothermic state. 4. In harmaline-pretreated rats, tryptophan also increased the central 5-HT levels (80.5%-95.5% increase) in the hypothermic state, and the effect peaked at about 1 hr after tryptophan administration. The central 5-HT levels in harmaline-pretreated rats slightly decreased at 6 hr after tryptophan administration and were significantly lower than those in the hyperthermic state in the pargyline-pretreated rats. 5. Tryptophan (100 mg/kg IP) administration decreased 5-hydroxy indole acetic acid (5-HIAA) levels, 5-HT turnover, and dopamine (DA) turnover in the brain of pargyline-pretreated rats, but these parameters were not significantly different between the hypothermic and hyperthermic states (i.e., at 1 and 6 hr after tryptophan administration, respectively). 6. These results suggest that the tryptophan-induced body temperature change depends on the different 5-HT levels in the brain and that the 5-HT level needed to induce hyperthermia is higher than that needed to induce hypothermia.

5-HT1A and 5-HT2 receptors mediate hypo- and hyperthermic effects of tryptophan in pargyline-pretreated rats

Mechanisms of tryptophan (a 5-HT precursor)-induced changes in body temperature were investigated in rats pretreated with pargyline, a monoamine oxidase inhibitor (MAO-I). Tryptophan (100 mg/kg, i.p.) did not affect the body temperature in rats, but it produced significant hypothermia followed by marked hyperthermia and higher mortality in the pargyline-pretreated rats. 5-HT depletion with p-chlorophenylalanine (p-CPA, 100 mg/kg/day for 3 days) significantly suppressed not only the body temperature change but also the mortality and 5-HT syndrome following tryptophan plus pargyline administration. Although propranolol (10 mg/kg, i.p.), a beta-adrenoceptor antagonist, did not alter the hypothermia caused by tryptophan in the pargyline-pretreated rats, pindolol (2 mg/kg, S.C.), a 5-HT1A receptor and beta-adrenoceptor antagonist, suppressed the hypothermia but not the hyperthermia or mortality caused by the same treatment. On the other hand, spiperone and ketanserin, 5-HT2 receptor antagonists, at doses of 3 mg/kg, potentiated the hypothermia and completely suppressed the hyperthermia and mortality caused by tryptophan in the pargyline-pretreated rats. These results suggest that tryptophan-induced hypo- and hyperthermia are mediated by 5-HT1A and 5-HT2 receptors, respectively, in the pargyline-pretreated pretreated rats.

Blunted oral body temperature response to MK-212 in cocaine addicts

Previous studies have suggested that chronic cocaine administration may affect serotonergic function and that serotonin (5-HT) may be of importance in cocaine craving. Ten male cocaine addicts and 28 male normal controls were challenged with MK-212 (6-chlor-2-[1-piperazinyl]-pyrazine) (20 mg), a direct acting 5-HT receptor agonist which has affinity for a variety of 5-HT receptor subtypes, and placebo, on separate days. The plasma cortisol and prolactin (PRL) concentrations and oral body temperature responses to MK-212 and placebo were compared between groups. The temperature response to MK-212 was significantly blunted in cocaine addicts compared to normal controls. However, the plasma cortisol and PRL responses to MK-212 did not differ between the two groups. These results suggest selective alteration of presynaptic 5-HT1A or postsynaptic 5-HT2A/2C function in cocaine addicts.

The interaction between locomotion, striatal dopamine and paramedian reticular nucleus in rats

Either intact rats, sham-operated rats, or rats with lesions of the paramedian reticular nucleus (PRN) were exposed to cold (2 degrees C) or heat (36 degrees C) stress and their locomotor activity responses and striatal dopamine (DA) release were compared. At room temperature (22 degrees C), results analyzed revealed significant effects in the PRN-lesioned rats: increases in locomotion (including both horizontal and vertical motion), direction of turnings (including both clockwise and anticlockwise) or striatal DA release. In both the intact rats and the sham-operated rats, either cold or heat stress increased the locomotion, the direction of turnings and the striatal DA release. The increases in both vertical motion and striatal DA release following cold or heat stress were attenuated by PRN lesions. The data suggest that a PRN-striatal DA link existing in rat's brain which affects both the spontaneous and the thermal stress induced locomotor activities.

Arterial baroreceptor information affects striatal dopamine release measured by voltammetry in rats

The effects of altering the arterial blood pressure on the extracellular levels of dopamine in the corpus striatum, measured using nafion-coated C fiber electrodes combined with differential pulse amperometry, were assessed in urethane-anesthetized rats. The striatal dopamine release was increased by increasing the carotid blood pressure with phenylephrine injection but decreased by decreasing the carotid blood pressure with bilateral carotid occlusion. The data indicate that baroreceptors inputs affect the striatal dopamine release in rats.

Antagonistic effects of lesions of paramedian reticular nucleus on amphetamine-induced locomotion and striatal dopamine release in rats

Systemic administration of amphetamine (1.25 mg/kg) produced increases of locomotion (including horizontal motion, vertical motion, and total distance travelled), elevations of turnings (including both clockwise and anticlockwise) and inhibition of postural freezing in freely moving rats. All the afore-mentioned activity measures induced by amphetamine were suppressed following electrolytic lesions of the paramedian reticular nucleus (PRN) in rat medulla. In addition, the spontaneous level of either the locomotor activity, the direction of turnings, or the postural freezing were slightly but significantly affected by the PRN lesions. In vivo voltammetric data revealed that amphetamine administration greatly enhanced the striatal dopamine release. Furthermore, the enhanced dopamine release in corpus striatum produced by amphetamine were greatly attenuated by PRN lesions. The results indicate that there exists a PRN-striatal dopamine link in rat brain which mediates the amphetamine-induced increases of locomotion and turnings, as well as decreases of postural freezing.