Vincristine-induced peripheral neuropathic pain and expression of transient receptor potential vanilloid 1 in rat.

The clinical anti-cancer efficacy of vincristine is limited by the development of dose-dependent peripheral neuropathy. Up-regulation of transient receptor potential vanilloid 1 (TRPV1) is correlated with peripheral neuropathy following anti-cancer drug treatment. To analyze the contribution of TRPV1 to the development of vincristine-induced mechanical allodynia/hyperalgesia, TRPV1 expression in the rat dorsal root ganglion (DRG) was analyzed after vincristine treatment. Mechanical allodynia/hyperalgesia was tested with von Frey filaments 14 days after intraperitoneal administration of 0.1 mg/kg vincristine in rats. TRPV1 expression in DRGs following vincristine treatment was assessed with western blot analysis and in situ hybridization histochemistry. Vincristine-induced mechanical allodynia/hyperalgesia after day 14 was significantly inhibited by the TRP antagonist ruthenium red (3 mg/kg, s.c.) and the TRPV1 antagonist capsazepine (30 mg/kg, s.c.). Vincristine treatment increased the expression of TRPV1 protein in DRG neurons. In situ hybridization histochemistry revealed that most of the TRPV1 mRNA-labeled neurons in the DRG were small in size. Immunohistochemistry showed that isolectin B4-positive small DRG neurons co-expressed TRPV1 protein 14 days after treatment. These results suggest that vincristine treatment increases TRPV1 expression in small DRG neurons. TRPV1 expression may contribute to the development of vincristine-induced painful peripheral neuropathy.

Oxaliplatin administration increases expression of the voltage-dependent calcium channel α2δ-1 subunit in the rat spinal cord.

Oxaliplatin is a chemotherapeutic agent that is effective against various types of cancer including colorectal cancer. Acute cold hyperalgesia is a serious side effect of oxaliplatin treatment. Although the therapeutic drug pregabalin is beneficial for preventing peripheral neuropathic pain by targeting the voltage-dependent calcium channel α2δ-1 (Cavα2δ-1) subunit, the effect of oxaliplatin-induced acute cold hypersensitivity is uncertain. To analyze the contribution of the Cavα2δ-1 subunit to the development of oxaliplatin-induced acute cold hypersensitivity, Cavα2δ-1 subunit expression in the rat spinal cord was analyzed after oxaliplatin treatment. Behavioral assessment using the acetone spray test showed that 6 mg/kg oxaliplatin-induced cold hypersensitivity 2 and 4 days later. Oxaliplatin-induced acute cold hypersensitivity 4 days after treatment was significantly inhibited by pregabalin (50 mg/kg, p.o.). Oxaliplatin (6 mg/kg, i.p.) treatment increased the expression level of Cavα2δ-1 subunit mRNA and protein in the spinal cord 2 and 4 days after treatment. Immunohistochemistry showed that oxaliplatin increased Cavα2δ-1 subunit protein expression in superficial layers of the spinal dorsal horn 2 and 4 days after treatment. These results suggest that oxaliplatin treatment increases Cavα2δ-1 subunit expression in the superficial layers of the spinal cord and may contribute to functional peripheral acute cold hypersensitivity.

Paclitaxel-induced peripheral neuropathy increases substance P release in rat spinal cord.

Peripheral neuropathy is a common adverse effect of paclitaxel treatment. The major dose-limiting side effect of paclitaxel is peripheral sensory neuropathy, which is characterized by painful paresthesia of the hands and feet. To analyze the contribution of substance P to the development of paclitaxel-induced mechanical hyperalgesia, substance P expression in the superficial layers of the rat spinal dorsal horn was analyzed after paclitaxel treatment. Behavioral assessment using the von Frey test and the paw thermal test showed that intraperitoneal administration of 2 and 4mg/kg paclitaxel induced mechanical allodynia/hyperalgesia and thermal hyperalgesia 7 and 14 days after treatment. Immunohistochemistry showed that paclitaxel (4mg/kg) treatment significantly increased substance P expression (37.6±3.7% on day 7, 43.6±4.6% on day 14) in the superficial layers of the spinal dorsal horn, whereas calcitonin gene-related peptide (CGRP) expression was unchanged. Moreover, paclitaxel (2 and 4mg/kg) treatment significantly increased substance P release in the spinal cord on day 14. These results suggest that paclitaxel treatment increases release of substance P, but not CGRP in the superficial layers of the spinal dorsal horn and may contribute to paclitaxel-induced painful peripheral neuropathy.

Transient receptor potential ankyrin 1 that is induced in dorsal root ganglion neurons contributes to acute cold hypersensitivity after oxaliplatin administration.

BACKGROUND: Peripheral cold neuropathic pain is a serious side effect of oxaliplatin treatment. However, the mechanism of oxaliplatin-induced cold hyperalgesia is unknown. In the present study, we investigated the effects of oxaliplatin on transient receptor potential ankyrin 1 (TRPA1) in dorsal root ganglion (DRG) neurons of rats. RESULTS: Behavioral assessment using the acetone spray test showed that 3 and 6 mg/kg oxaliplatin (i.p.) induced acute cold hypersensitivity after 1, 2, 4, and 7 days. Real-time PCR showed that oxaliplatin (6 mg/kg) significantly increased TRPA1 mRNA expression in DRGs at days 1, 2, and 4. Western blotting revealed that oxaliplatin significantly increased TRPA1 protein expression in DRGs at days 2, 4, and 7. Moreover, in situ hybridization histochemistry revealed that most TRPA1 mRNA-labeled neurons in the DRGs were small in size. Oxaliplatin significantly increased co-localization of TRPA1 expression and isolectin B4 binding in DRG neurons. Oxaliplatin induced a significant increase in the percent of TRPA1 mRNA-positive small neurons in DRGs at days 1, 2, and 4. In addition, we found that intrathecal administration of TRPA1 antisense, but not TRPA1 mismatched oligodeoxynucleotides, knocked down TRPA1 expression and decreased oxaliplatin-induced cold hyperalgesia. Double labeling showed that p-p38 mitogen-activated protein kinase (MAPK) was co-expressed in TRPA1 mRNA-labeled neurons at day 2 after oxaliplatin administration. Intrathecal administration of the p38 MAPK inhibitor, SB203580, significantly decreased oxaliplatin-induced acute cold hypersensitivity. CONCLUSIONS: Together, these results demonstrate that TRPA1 expression via activation of p38 MAPK in DRG neurons, at least in part, contributes to the development of oxaliplatin-induced acute cold hyperalgesia.

Effect of psilocin on extracellular dopamine and serotonin levels in the mesoaccumbens and mesocortical pathway in awake rats.

Psilocin (3-[2-(dimethylamino)ethyl]-1H-indol-4-ol) is a hallucinogenic component of the Mexican mushroom Psilocybe mexicana and a skeletal serotonin (5-HT) analogue. Psilocin is the active metabolite of psilocybin (3-[2-(dimethylamino)ethyl]-1H-indol-4-yl dihydrogen phosphate). In the present study, we examined the effects of systemically administered psilocin on extracellular dopamine and 5-HT concentrations in the ventral tegmental area (VTA), nucleus accumbens, and medial prefrontal cortex of the dopaminergic pathway in awake rats using in vivo microdialysis. Intraperitoneal administration of psilocin (5, 10 mg/kg) significantly increased extracellular dopamine levels in the nucleus accumbens. Psilocin did not affect the extracellular 5-HT level in the nucleus accumbens. Conversely, systemic administration of psilocin (10 mg/kg) significantly increased extracellular 5-HT levels in the medial prefrontal cortex of rats, but dopamine was decreased in this region. However, neither extracellular dopamine nor 5-HT levels in the VTA were altered by administration of psilocin. Behaviorally, psilocin significantly increased the number of head twitches. Thus, psilocin affects the dopaminergic system in the nucleus accumbens. In the serotonergic system, psilocin contribute to a crucial effect in the medial prefrontal cortex. The present data suggest that psilocin increased both the extracellular dopamine and 5-HT concentrations in the mesoaccumbens and/or mesocortical pathway.

Effect of paclitaxel on transient receptor potential vanilloid 1 in rat dorsal root ganglion.

Peripheral neuropathy is a common adverse effect of paclitaxel treatment. To analyze the contribution of transient receptor potential vanilloid 1 (TRPV1) in the development of paclitaxel-induced thermal hyperalgesia, TRPV1 expression in the rat dorsal root ganglion (DRG) was analyzed after paclitaxel treatment. Behavioral assessment using the tail-flick test showed that intraperitoneal administration of 2 and 4 mg/kg paclitaxel induced thermal hyperalgesia after days 7, 14, and 21. Paclitaxel-induced thermal hyperalgesia after day 14 was significantly inhibited by the TRP antagonist ruthenium red (3 mg/kg, s.c.) and the TRPV1 antagonist capsazepine (30 mg/kg, s.c.). Paclitaxel (2 and 4 mg/kg) treatment increased the expression of TRPV1 mRNA and protein in DRG neurons. Immunohistochemistry showed that paclitaxel (4 mg/kg) treatment increased TRPV1 protein expression in small and medium DRG neurons 14 days after treatment. Antibody double labeling revealed that isolectin B4-positive small DRG neurons co-expressed TRPV1. TRPV1 immunostaining was up-regulated in paw skin day 14 after paclitaxel treatment. Moreover, in situ hybridization histochemistry revealed that most of the TRPV1 mRNA-labeled neurons in the DRG were small or medium in size. These results suggest that paclitaxel treatment increases TRPV1 expression in DRG neurons and may contribute to functional peripheral neuropathic pain.

IgG anti-Galnac-GD1a antibodies bind to neuromuscular junctions of rat hemidiaphragm.

INTRODUCTION: We investigated the localization of a ganglioside, N-acetylgalactosaminyl GD1a (GalNAc-GD1a), in peripheral nerves with an IgG anti-GalNAc-GD1a antibody, which was produced in rabbits immunized with GalNAc-GD1a. METHODS: Teased fibers from ventral and dorsal roots and hemidiaphragm sections of rats were assessed using fluorescent double- and triple-labeling methods. RESULTS: The nodal and paranodal regions of teased fibers from ventral roots were immunostained with IgG anti-GalNAc-GD1a antibodies. After collagenase treatment, no staining was seen with IgG anti-GalNAc-GD1a or anti-NF200 antibodies, whereas α-bungarotoxin selectively stained nerve terminals. In cross-sectional and longitudinal sections of rat hemidiaphragm, IgG anti-GalNAc-GD1a antibodies overlapped with α-BuTx and anti-NF200 antibodies, indicating that GalNAc-GD1a is localized to the nerve terminal. IgG anti-GalNAc-GD1a antibody staining also overlapped with that of AChR clusters and syntaxin-positive presynaptic nerve terminals. CONCLUSION: GalNAc-GD1 is localized in both pre- and postsynaptic nerve terminals of neuromuscular junctions.

Paclitaxel increases high voltage-dependent calcium channel current in dorsal root ganglion neurons of the rat.

Peripheral neuropathic pain is a serious side effect of paclitaxel treatment. However, the mechanism of this paclitaxel-induced neuropathic pain is unknown. In this study, we investigated the effects of paclitaxel on the voltage-dependent calcium channel (VDCC) current in rat dorsal root ganglion (DRG) neurons using the whole-cell patch clamp technique. Behavioral assessment using von Frey filament stimuli showed that 2 and 4 mg/kg paclitaxel treatment induced mechanical allodynia/hyperalgesia. Paclitaxel-induced mechanical hyperalgesia was significantly inhibited by gabapentin (100 mg/kg). Using the patch clamp method, we observed that paclitaxel (4 mg/kg) treatment significantly increased the VDCC current in small- and medium-diameter DRG neurons. Moreover, paclitaxel-induced increase in the VDCC current in medium-diameter DRG neurons was completely inhibited by 10 and 100 µM gabapentin. Similar effects in small-diameter DRG neurons were only seen with 100 µM gabapentin. Western blotting revealed that paclitaxel increased protein levels of the VDCC subunit α2δ-1 (Ca(v)α2δ-1) in DRG neurons. Immunohistochemistry showed that paclitaxel treatment increased Ca(v)α2δ-1 protein expression in DRG neurons. Thus, paclitaxel treatment increases the VDCC current in small- and medium-diameter DRG neurons and upregulates Ca(v)α2δ-1. The antihyperalgesic action of gabapentin may be due to inhibition of paclitaxel-induced increases in the VDCC current in DRG neurons.

Chronic administration of cardanol (ginkgol) extracted from ginkgo biloba leaves and cashew nutshell liquid improves working memory-related learning in rats.

Cardanol (ginkgol) extracted from Ginkgo biloba leaves and cashew nutshell liquid enhances the growth of NSC-34 immortalized motor neuron-like cells and, when chronically administered to young rats, improves working memory-related learning ability as assessed by eight-arm radial maze tasks. These findings suggest that cardanol is one of the components in Ginkgo biloba leaves that improves cognitive learning ability.

Identification of amino acids in the pore region of Kv1.2 potassium channel that regulate its glycosylation and cell surface expression.

The Kv1.4 potassium channel is reported to exhibit higher cell surface expression than the Kv1.1 potassium channel when expressed as a homomer in cell lines. Kv1.4 also shows highly efficient trans-Golgi glycosylation whereas Kv1.1 is not glycosylated. The surface expression and glycosylation of Kv1.2 is intermediate between those of Kv1.1 and Kv1.4. Amino acid determinants controlling the surface expression of Kv1 channels were localized to the highly conserved pore region and both positive and negative determinants of Kv1.1 and Kv1.4 trafficking have been reported. In this study, we analyzed the effect of substituting amino acids in the pore region of Kv1.2 with the corresponding amino acid present in Kv1.1 or Kv1.4 on glycosylation and trafficking of Kv1.2. Mutations in the outer pore region of Kv1.2 of Arg(354) to Pro (corresponding to Kv1.4) and to Ala (corresponding to Kv1.1) enhanced and reduced, respectively, cell surface expression of Kv1.2. Mutations in a different outer pore region of Val(381) to Lys (Kv1.4) and Tyr (Kv1.1) both reduced the cell surface expression. In contrast, mutation in the deep pore region of Ser(371) to Thr (Kv1.4) markedly enhanced cell surface expression. These results suggest that the cell surface expression of Kv1.2 is regulated by specific amino acids in the pore region in a similar manner to Kv1.1 and Kv1.4, and that the cell surface expression of Kv1.2, a channel intermediate between Kv1.1 and Kv1.4, can be attributed to these specific residues.

Effect of beta-phenylethylamine on extracellular concentrations of dopamine in the nucleus accumbens and prefrontal cortex.

It is known that psychostimulants stimulate dopamine transmission in the nucleus accumbens. In the present study, we examined the effects of systemically administered beta-phenylethylamine (beta-PEA), a psychomotor-stimulating trace amine, on dopamine concentrations in the nucleus accumbens and prefrontal cortex in freely moving rats, using an in vivo microdialysis technique. Intraperitoneal administration of beta-PEA (12.5 and 25 mg/kg) significantly increased extracellular dopamine levels in the nucleus accumbens shell. The observed increase in the dopamine concentration in nucleus accumbens shell dialysate after intraperitoneal administration of 25 mg/kg beta-PEA was inhibited by pre-treatment with a dopamine uptake inhibitor, GBR12909 (10 mg/kg, i.p.). In contrast, beta-PEA (25 mg/kg, i.p.) did not affect dopamine release in the nucleus accumbens core. Although a high dose of beta-PEA (50 mg/kg) significantly increased dopamine levels in the nucleus accumbens core, the dopamine increasing effect of beta-PEA was more potent in the nucleus accumbens shell. Systemic administration of 12.5 and 25 mg/kg beta-PEA also increased extracellular dopamine levels in the prefrontal cortex of rats. However, systemic 25 mg/kg beta-PEA-induced increases in extracellular dopamine levels were not blocked by GBR12909 within the prefrontal cortex. These results suggest that beta-PEA has a greater effect in the shell than in the core and low-dose beta-PEA stimulates dopamine release in the nucleus accumbens shell through uptake by a dopamine transporter. Similarly, beta-PEA increased extracellular dopamine levels in the prefrontal cortex. Thus, beta-PEA may increase extracellular dopamine concentrations in the mesocorticolimbic pathway.

IgM anti-GQ1b monoclonal antibody inhibits voltage-dependent calcium current in cerebellar granule cells.

Miller-Fisher syndrome (MFS), which is known to be associated with anti-GQ1b antibodies and to cause ataxia, is a variant of an acute inflammatory neuropathy. However, the pathogenic role of anti-GQ1b antibodies remains unclear. In this study, we investigated the effects of mouse IgM anti-GQ1b monoclonal antibody (IgM anti-GQ1b mAb) on the spontaneous muscle action potential of a rat spinal cord-muscle co-culture system and on the voltage-dependent calcium channel (VDCC) current in cerebellar granule cells and Purkinje cells using the whole-cell patch clamp technique. The frequency of spontaneous muscle action potential of the innervated muscle cells was transiently increased by IgM anti-GQ1b mAb and then was blocked completely, which was the same finding as reported previously. Moreover, the cerebellar granule cell VDCC current was decreased by 30.76+/-7.60% by 5 microg/mL IgM anti-GQ1b mAb, whereas IgM anti-GQ1b mAb did not affect the VDCC current in cerebellar Purkinje cells. In immunocytochemistry, IgM anti-GQ1b mAb stained the whole cell surface of cerebellar granule cells, but not that of Purkinje cells. Therefore, the clinical symptoms of Miller-Fisher syndrome, such as cerebellar-like ataxia, may be explained by the inhibitory effects of anti-GQ1b antibodies on VDCC current in cerebellar granule cells.

Cav2.1 voltage-dependent Ca2+ channel current is inhibited by serum from select patients with Guillain-Barré syndrome.

To investigate the pathophysiological mechanisms of immune-mediated peripheral neuropathies, we studied the effects of sera from patients with Guillain-Barré syndrome (GBS) on the Cav2.1 voltage-dependent calcium channel (VDCC) current in Purkinje cells. Using the whole-cell recording technique, Cav2.1 VDCC current was measured in cerebellar Purkinje cells in the presence of serum from GBS patients with acute motor axonal neuropathy (AMAN) or acute inflammatory demyelinating polyneuropathy (AIDP). The AMAN patient sera significantly inhibited the Cav2.1 VDCC current compared with healthy volunteer sera, and this inhibition was fully reversible by washing out the AMAN serum. Similarly, IgG purified from AMAN sera also inhibited the Cav2.1 VDCC current. However, the activation and inactivation kinetics of the Cav2.1 VDCC currents were not affected by serum from an AMAN patient. Moreover, the VDCC current of Purkinje cells was also inhibited by IgG anti-GM1 monoclonal antibody (anti-GM1 mAb). In an immunocytochemical study using double fluorescence staining, Purkinje cells were stained by monoclonal IgG anti-GM1 mAb. In contrast, AIDP patient and healthy volunteer sera did not affect the Cav2.1 VDCC current. These results suggest that in some case of GBS, particularly of AMAN patients with IgG anti-GM1 mAb, muscle weakness may be induced by dysfunction of Cav2.1 VDCC functioning at the motor nerve terminals.

Expression and localization of Kv1 potassium channels in rat dorsal and ventral spinal roots.

We investigated the expression and localization of Kv1 channels in dorsal spinal roots (DRs) and ventral spinal roots (VRs) in rats. Among Kv1.1-1.6 tested by RT-PCR, mRNAs of Kv1.1, 1.2, and 1.5 were moderately expressed, those of Kv1.3 and Kv1.6 were weakly expressed, and that of Kv1.4 was hardly expressed at all in both DRs and VRs, whereas all six mRNAs were detected in spinal cord. Western blotting revealed that the major immunoreactive proteins were Kv1.1 and Kv1.2 in both DRs and VRs. Quantitative analysis indicated that levels of Kv1.1 and Kv1.2 protein were significantly higher in DRs than VRs. Immunohistochemical examination showed that Kv1.1 and Kv1.2 were colocalized in juxtaparanodal regions of axons in both DRs and VRs. Finally, immunoprecipitation experiments revealed that Kv1.1 and Kv1.2 were coassembled. These findings indicate that Kv1 subtypes in DRs and VRs are somewhat different from those in spinal cord, and that the numbers of Kv1.1 and Kv1.2 channels are higher in DRs than VRs.

IgG anti-GalNAc-GD1a antibody inhibits the voltage-dependent calcium channel currents in PC12 pheochromocytoma cells.

We investigated the effects of IgG anti-GalNAc-GD1a antibodies, produced by immunizing rabbits with GalNAc-GD1a, on the voltage-dependent calcium channel (VDCCs) currents in nerve growth factor (NGF)-differentiated PC12 pheochromocytoma cells. VDCCs currents in NGF-differentiated PC12 cells were recorded using the whole-cell patch-clamp technique. Immunized rabbit serum that had a high titer of anti-GalNAc-GD1a antibodies inhibited the VDCCs currents in the NGF-differentiated PC12 cells (36.0+/-9.6% reduction). The inhibitory effect of this serum was reversed to some degree within 3-4 min by washing with bath solution. Similarly, application of purified IgG from rabbit serum immunized with GalNAc-GD1a significantly inhibited the VDCCs currents in PC12 cells (30.6+/-2.5% reduction), and this inhibition was recovered by washing with bath solution. Furthermore, the inhibitory effect was also observed in the GalNAc-GD1a affinity column binding fraction (reduction of 31.1+/-9.85%), while the GalNAc-GD1a affinity column pass-through fraction attenuated the inhibitory effect on VDCCs currents. Normal rabbit serum and normal rabbit IgG did not affect the VDCCs currents in the PC12 cells. In an immunocytochemical study using fluorescence staining, the PC12 cells were stained using GalNAc-GD1a binding fraction. These results indicate that anti-GalNAc-GD1a antibodies inhibit the VDCCs currents in NGF-differentiated PC12 cells.

Glycosylation and cell surface expression of Kv1.2 potassium channel are regulated by determinants in the pore region.

Voltage-gated K(+) channels contain six membrane spanning segments and a pore-forming domain. We used site-directed mutation to examine the role of specific amino acids in the extracellular region of the pore in Kv1.2. When expressed in CHO cells, a K(+) current was not observed for mutants S356A, S360A, T383A and T384A. However, coexpression of the Kvbeta2 subunit and the S360A mutant resulted in a robust peak current. Immunocytochemistry for Kv1.2 showed staining throughout the cytoplasm in cells coexpressing the beta2 and S360A, whereas only the perinuclear region was stained in cells expressing the S360A mutant. Western blotting revealed that the major immunoreactive protein in wild-type- and mutant-expressing cells is 60-kDa, but 87-kDa bands were also detected in cells expressing wild-type Kv1.2 and cells coexpressing beta2and S360A. These results suggest that amino acids in the pore region help regulate ion permeability or cellular trafficking by affecting glycosylation of Kv1.2.

GalNAc-GD1a is localized specifically in ventral spinal roots, but not in dorsal spinal roots.

We investigated the localization of GalNAc-GD1a biochemically in the human and bovine peripheral nervous system (PNS). The high-performance thin-layer chromatography (HPTLC)-overlay method with rabbit IgG polyclonal antibody against GalNAc-GD1a (anti-GalNAc-GD1a antibody) revealed expression of GalNAc-GD1a in the ventral spinal nerve roots (VRs) but not in the dorsal spinal nerve roots (DRs) of both species. The amount of GalNAc-GD1a in the human and bovine VRs was 2.22 +/- 0.35 microg/g wet tissue and 7.71 +/- 0.49 microg/g wet tissue, respectively. These results suggest that IgG anti-GalNAc-GD1a antibody may be involved in disturbance of peripheral motor nerves and in the pathogenesis of pure motor neuropathy.

Beta-phenylethylamine stimulates striatal acetylcholine release through activation of the AMPA glutamatergic pathway.

Using an in vivo intra-striatal microdialysis technique, we examined the effects of systemically administered beta-phenylethylamine (beta-PEA), a psychomotor stimulating trace amine, on striatal acetylcholine release in freely moving rats. Infusion of N-methyl-D-aspartic acid (NMDA; 10(-5) M) significantly increased acetylcholine release. In addition, locally applied amino-3-hydroxy-5-methylisozasole-4-propionic acid (AMPA; 10(-5) M) significantly increased acetylcholine release in the striatum. Intra-striatal application of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 10(-5) M), an AMPA-type glutamatergic receptor antagonist, had little effect on acetylcholine release, while application of MK-801 (10(-5) M, 10(-6) M), an NMDA-type glutamatergic receptor antagonist, significantly reduced acetylcholine release. Acetylcholine within striatal perfusate was significantly increased by intraperitoneal administration of beta-PEA in a dose-dependent manner. This increase in acetylcholine release was completely blocked by application of CNQX (10(-5) M) through the microdialysis probe into the striatum. However, increased acetylcholine response to systemic beta-PEA was unaltered by addition of MK-801 to the perfusion medium. These results suggest a regulatory function of beta-PEA, mediated by AMPA-type glutamatergic receptors, on the release of acetylcholine in the rat striatum.

Synthesis and neurotoxicity of tetrahydroisoquinoline derivatives for studying Parkinson's disease.

Parkinson's disease involves the progressive degeneration of dopaminergic neurons in the substantia nigra. However, the etiology of the disease remains to be elucidated. Endogenous amines, such as 1,2,3,4-tetrahydroisoquinoline (TIQ) derivatives present in the mammalian brain, are known to participate in the pathogenesis of Parkinson's disease. These endogenous neurotoxins have been extensively studied because of their structural resemblance to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), an agent widely used for generating animal models of Parkinson's disease-like symptoms. Investigations of the synthesis and pharmacological properties of TIQ derivatives are expected to contribute to the development of new therapeutic agents for treating Parkinson's disease. In the present study, we describe more efficient synthesis methods for TIQ derivatives via Pummerer-type cyclization of the substrate N-acyl sulfoxide. Furthermore, the modified Pummerer reaction provided a convenient and efficient method for synthesizing various TIQs. TIQ and its derivative, 1-benzyl-TIQ, can induce parkinsonism in primates and rodents. On the other hand, one TIQ derivative, 1-methyl-TIQ, has been shown to prevent MPTP, TIQ, and 1-benzyl-TIQ induced behavioral abnormalities. Therefore, TIQ derivatives are considered to play an important role in both the onset and prevention of Parkinson's disease. In this article, we focus on the synthesis and pharmacological aspects of 1,2,3,4-tetrahydroisoquinoline derivatives in Parkinson's disease.

Effects of beta-phenylethylamine on dopaminergic neurons of the ventral tegmental area in the rat: a combined electrophysiological and microdialysis study.

The effects of systemic administration of beta-phenylethylamine (beta-PEA) and microiontophoretically applied beta-PEA on the spontaneous discharge of dopamine (DA) neurons in the ventral tegmental area (VTA) of the anesthetized rat were examined. Intravenous administration of beta-PEA (1.0, 2.5, and 5.0 mg/kg) and microiontophoretic applications of beta-PEA caused inhibitory responses in DA neurons. Systemic administration and microiontophoretic applications of beta-PEA induced dose- or current-dependent responses. The systemic beta-PEA-induced inhibitory responses were reversed by pretreatment with the DA D(2) receptor antagonists haloperidol (0.5 mg/kg i.p.) and sulpiride (10 mg/kg i.p). Pretreatment with reserpine (5 mg/kg i.p. 24 h earlier) did not completely block the systemic administration of beta-PEA (2.5 mg/kg) inhibition. A microdialysis study of freely moving rats demonstrated that the extracellular DA level increased significantly in response to local application of beta-PEA (100 muM) in the VTA via a microdialysis probe, and local application of beta-PEA-stimulated somatodendritic DA release in the VTA. The beta-PEA-induced release of DA was calcium ion-independent and was enhanced by pretreatment with pertussis toxin. These findings indicate that beta-phenylethylamine inhibits DA neuron activity via DA D(2) autoreceptors in the rat VTA and that this inhibitory effect is mediated by the somatodendritic DA release.