Effects of migratory status and habitat on the prevalence and intensity of infection by haemoparasites in passerines in eastern Spain

The Iberian peninsula is a suitable place to study the effects of migratory condition on the prevalence of blood parasites in avian communities as resident, local populations cohabit with migratory species and with abundant vector populations. In this study we examined the incidence of avian blood parasites in three localities in the Mediterranean region (east Spain), in relation to the migratory status of the species. We analyzed 333 blood smears from 11 avian species, and obtained an overall prevalence of 9.6 %. The prevalence of parasites varied among the different species studied, although intensity of infection did not. Our results are discussed in terms of population dynamics and abundance of Diptera vectors able to transmit blood parasites to other birds.

Pan-African polyspecific antivenom produced by caprylic acid purification of horse IgG: an alternative to the antivenom crisis in Africa

A polyspecific Pan-African antivenom has been produced from the plasma of horses immunized with a mixture of the venoms of Echis ocellatus, Bitis arietans and Naja nigricollis, the three most medically important snakes in sub-Saharan Africa. The antivenom is a whole IgG preparation, obtained by caprylic acid precipitation of non-IgG plasma proteins. The antivenom effectively neutralizes the most important toxic activities of the three venoms used in the immunization in standard assays involving preincubation of venom and antivenom before testing. This antivenom compares favourably with other antivenoms designed for use in Africa with respect to neutralization of the toxins present in the venom of E. ocellatus. Caprylic acid fractionation of horse hyperimmune plasma is a simple, convenient and cheap protocol for the manufacture of high quality whole IgG antivenoms. It constitutes a potentially valuable technology for the alleviation of the critical shortage of antivenom in Africa.

Primary neurotransmitters and regulatory substances onto vestibular nucleus neurons

This review article focused on the primary neurotransmitters involved in transmission from the otolith to the vestibular nucleus (VN), especially in relation to the neurotransmission to the VN neurons (gravity-sensitive neurons) activated by tilt stimulation. The medial vestibular nucleus (MVN) neurons were classified in 8 types (alpha-theta) according to the patterns in response to the clockwise and counterclockwise tilt-stimulations. The tilt-induced firing was inhibited by GDEE (a non-selective glutamate receptor antagonist) and/or atropine (a muscarinic receptor antagonist). Thus, glutamate and/or acetylcholine may serve as the primary neurotransmitters. This conclusion is supported by the previous findings that glutamate exists in the vestibular nerve and is released from the nerve besides the presence of glutamate receptor subtypes in the VN. In addition, acetylcholine induced atropine-reversible firing of MVN neurons, and the enzymes involved in acetylcholine synthesis/metabolism are also found in the VN. Furthermore, serotonin was found to inhibit the MVN neuronal activities via the 5-HT1A receptors. As such, the 5-HT1A agonist, tandospirone, may be effective in preventing and/or treating motion sickness and/or space sickness.

Inhibitory effects of tandospirone, a 5-HT1A agonist, on medial vestibular nucleus neurons responding to lateral roll tilt stimulation in rats

An electrophysiological study was performed using chloral hydrate-anesthetized rats to determine whether tandospirone, a 5-HT1A agonist, affects neuronal activities of the medial vestibular nucleus (MVN), since serotonergic innervation and 5-HT1A receptors are present in this nucleus. Tandospirone applied microiontophoretically at a current of 20-60 nA caused an inhibition of tilt-induced firing of alpha-type neurons, which showed increased and decreased firing with lateral tilt ipsilateral and contralateral to the recording site, respectively, along with that of beta-type neurons which exhibited the reverse responses to ipsilateral and contralateral tilt stimulation. The inhibition was antagonized during simultaneous, iontophoretic application of WAY-100635 (20-60 nA), a 5-HT1A receptor antagonist, although WAY-100635 alone rarely affected spontaneous or tilt-induced firing in either type of neurons. These results suggest that tandospirone acts on a 5-HT1A receptor to inhibit transmission of otolith information to alpha- and beta-type MVN neurons.

Enhanced Ca(2+) influx with mossy fiber stimulation in hippocampal CA3 neurons of spontaneously epileptic rats

This study was performed to determine whether the intracellular Ca(2+) concentration ([Ca(2+)](i)) is increased in hippocampal CA3 neurons of spontaneously epileptic rats (SER) which show both absence-like and convulsive seizures using hippocampal slices loaded with Calcium Green-1 when a weak single stimulation is given to the mossy fiber. [Ca(2+)](i) in the CA3 area was significantly increased after a single stimulus to mossy fibers in SER, while no changes were detected in normal Wistar rats. These findings suggest the existence of an abnormality in the Ca(2+) channel in the SER CA3 region and that this is probably responsible for epileptic seizures.

[Function of monoamine neurotransmitter transporters]

Monoamine transporters include plasma membrane and vesicular monoamine transporters(VMAT). The former selectively and Na+/Cl(-)-dependently transport dopamine, noradrenaline and serotonin into the cytoplasma, and the latter non-selectively carries monoamine into the vesicle. These transporters are composed of amino acid groups containing 12 folds more transmembrane components. Cytoplasmic transporters are a target site of certain drugs. Antiepileptic drugs such as SSRI and tricyclic antidepressants bind with serotonin transporter(SERT), noradrenaline transporter(NET) and/or dopamine transporters(DAT) to inhibit transport of monoamines into the cytoplasma, thereby increasing monoamine levels within the synaptic cleft. However, amphetamine, known to induce drug dependence, is transported by DAT and inhibit VMAT to induce reverse-transport of monoamines into the synaptic area, thereby producing psychiatric and behavioral alterations. Thus, monoamine transporters are target sites of drugs, and functional changes in the transporters may be involved in the pathogenesis of affective diseases, schizophrenia and/or personality disorders including neurogenerative diseases such as Parkinson's disease.

Excitation of rat striatal large neurons by dopamine and/or glutamate released from nerve terminals via presynaptic nicotinic receptor (A4beta2 type) stimulation

Previous in vivo experiments using rats anesthetized with chloral hydrate have revealed that nicotine applied iontophoretically increased firing of striatal neurons receiving excitatory dopaminergic input from the substantia nigra, and nicotine-induced firing was inhibited by domperidone, a dopamine D2 antagonist. The results suggest that nicotine increases release of dopamine from the terminals of dopaminergic neurons. Therefore, we performed the present patch clamp study using slice and acutely dissociated preparations of the rat striatum to elucidate the mechanisms underlying the nicotine-induced excitation of striatal neurons. Application of nicotine (100 microM) to large striatal neurons in slice preparations did not produce any effect on the resting membrane potential, but did increase the frequency of miniature postsynaptic potentials (mpps) and action potentials in all 15 neurons tested. The nicotine-induced increase in mpps and action potentials were inhibited during simultaneous application of domperidone; L-glutamic acid diethyl ester hydrochloride, a non-selective glutamate receptor antagonist; and/or dihydro-beta-erythroidine, a central nicotinic acetylcholine receptor (alpha4beta2 type) antagonist. Postsynaptic current was not induced by nicotine applied by U-tube in 96% of acutely dissociated striatal neurons. The present findings suggest that nicotine mainly acts on the presynaptic nicotinic receptors in the nerve terminals to release neurotransmitters such as dopamine and/or glutamate, thereby activating the striatal large neurons.

Potentiation of 5-HT(3) receptor functions in the hippocampal CA1 region of rats following repeated electroconvulsive shock treatments

Modulation of serotonin (5-HT)(3)-receptor function by repeated electroconvulsive shock (ECS) treatment was investigated to elucidate the mechanism underlying the effectiveness of electroconvulsive therapy (ECT) which is clinically used for drug-resistant depression. ECS (100 V, 1 s) was applied once a day for 14 days via an electrode placed on the ears of rats (ECS group). For controls, rats were handled similar to the ECS-treated group except for the stimulation. Hippocampal slices (thickness, 450 microm) were prepared 24 h after the final ECS treatment when rats were 5-6 weeks old. Intracellular recordings were made from the neurons in the CA1 pyramidal cell layer. Activation of 5-HT(3) receptors increased spontaneous postsynaptic potentials (sPSP). Increased sPSP was mainly mediated by GABA. The 5-HT(3) receptor mediated increase in sPSP was potentiated in the ECS group compared with the control group. These findings suggest that the 5-HT(3) receptor function is potentiated by repeated ECS.

Effect of JTH-601, a putative alpha(1L)-adrenoceptor antagonist, on guinea pig nasal mucosa vasculature

The existence of alpha(1)-adrenoceptors with low affinity for prazosin, an alpha(1L) subtype, has been proposed in addition to alpha(1)-adrenoceptor subtypes with high affinity for prazosin, i.e. the alpha(1H) group: alpha(1A), alpha(1B) and alpha(1D) subtypes. In the present study, we investigated the effect of JTH-601 (3-(N-[2-(4-hydroxy-2-isopropyl-5-methylphenoxy)ethyl]-N-methylaminomethyl)-4-methoxy-2,5,6-trimethylphenol hemifumarate), a putative alpha(1L)-adrenoceptor antagonist, on the isolated guinea pig nasal mucosa vasculature. JTH-601 (0.01-0.03 microM) competitively antagonized the noradrenaline-induced contraction of the tissue in a concentration-dependent manner. The pA(2) value for JTH-601 was 8.14 +/- 0.04 (means +/- SEM, n = 6). The data suggests that the alpha(1L)-subtype is involved in the noradrenaline-induced contraction of the guinea pig nasal mucosa vasculature.

Inhibition by L-3,4-dihydroxyphenylalanine of hippocampal CA1 neurons with facilitation of noradrenaline and gamma-aminobutyric acid release

Electrophysiological studies were performed to elucidate whether L-3,4-dihydroxyphenylalanine (L-DOPA) acted on hippocampal CA1 neurons, since this drug has been reported to act as a neurotransmitter in the hypothalamus and striatum. Hippocampal slices (450 microM thick) obtained from male Wistar rats (4-7 weeks of age) were placed in a bath (maintained at 30+/-1 degrees C) continuously perfused with artificial cerebrospinal fluid. The population spikes elicited by electrical stimuli applied to the Schaffer collateral/commissural fibers were recorded in the hippocampal CA1 region, using a glass micropipette filled with 3 M NaCl. Drugs were applied in the bath through a perfusion system. The population spikes were inhibited by L-DOPA (1 nM-10 microM) with a bell-shaped concentration-response curve (n=7-15). Maximum inhibitory effects were obtained at 100 nM. L-DOPA cyclohexyl ester, a putative L-DOPA recognition site antagonist, antagonized the L-DOPA-induced inhibition of population spike. However, the inhibition remained unaffected in the presence of 3-hydroxybenzylhydrazine, an aromatic amino acid decarboxylase inhibitor. Furthermore, bath application of either phentolamine, an alpha-adrenoceptor antagonist, or bicuculline, a GABA(A) receptor antagonist, antagonized the inhibitory effects of L-DOPA on population spikes. In addition, bicuculline (1 microM) antagonized the inhibition of population spike induced by 6-fluoronorepinephrine (10 microM), an alpha-adrenoceptor agonist, while phentolamine (10 microM) did not affect the muscimol (1 microM)-induced inhibition. These results suggested that L-DOPA itself acted on L-DOPA recognition sites to release noradrenaline, and that the latter facilitates gamma-aminobutyric acid (GABA) release via alpha-adrenoceptors located on the GABA-containing cells and/or their nerve terminals, thereby inhibiting the population spikes in the hippocampal CA1 field.

Enhanced calcium influx in hippocampal CA3 neurons of spontaneously epileptic rats

PURPOSE

The spontaneously epileptic rat (SER: tm/tm, zi/zi) shows both absence-like seizures and tonic convulsions. Our previous electrophysiologic studies have demonstrated that SER has abnormal excitability of hippocampal CA3 neurons, which shows a long-lasting depolarization shift by a single stimulation of mossy fibers, probably resulting from the Ca2+ channel abnorrmalities. The present study was performed to determine whether Ca2+ influx is actually enhanced in the CA3 area of SER.

METHODS

Hippocampal slices were prepared from normal Wistar rats and SER aged 11-16 weeks old, when the epileptic seizures had been observed, and loaded with fura-2AM. Intracellular Ca2+ concentration ([Ca2+]i) was monitored as the ratio of fluorescence intensities excited at wavelengths of 340 and 380 nm (RF340/F380) with photometric devices.

RESULTS

High K+ (10-60 mM) applied to the bath for 2 min increased [Ca2+]i in hippocampal CA1, CA3, and dentate gyrus (DG) areas of both the normal rats and SER in a concentration-dependent manner. However, the high K+-induced increase in [Ca2+]i was significantly more pronounced in the CA3 area of the SER than in that of the normal animals, whereas there were no significant differences in high K+-induced increases of [Ca2+]i in CA1 or DG between the SER and controls. The high K+-induced increases in [Ca2+]i of CA1, CA3, and DG were inhibited by nifedipine (1 to approximately 10 nM), a Ca2+ channel antagonist in both SER and controls. However, the inhibition of the high K+-induced increase in [Ca2+]i by nifedipine (1 nM) was significantly greater in the CA3 area of SER than that of controls.

CONCLUSIONS

These findings suggest that Ca2+ influx through the L-type Ca2+ channels is much greater in the CA3 area of SER than in that of normal animals and is involved in the epileptic seizures of the SER.

Detection of chromosomal aneusomy by fluorescence in situ hybridization in fine-needle aspirates from breast tumors: application to the preoperative diagnosis of breast carcinoma

BACKGROUND

The authors studied the clinical usefulness of fluorescence in situ hybridization (FISH) analysis of a numerical aberration of chromosomes (aneusomy) using fine-needle aspiration (FNA) samples from patients with breast tumors in the preoperative diagnosis of breast carcinoma.

METHODS

FNA samples were obtained from 176 breast tumors and were subjected to conventional cytology and FISH analysis using the centromere probes for chromosomes 1, 11, and 17. Patients with FNA samples that showed aneusomy in at least one of the three chromosomes were diagnosed as positive.

RESULTS

Histologic examination revealed 157 malignancies and 19 benign results (10 fibroadenomas, 6 intraductal papillomas, 1 intracystic papilloma, and 2 ADH). The sensitivity, specificity, and diagnostic accuracy were 85.4%, 94.7%, and 86.4%, respectively, for cytology and 90.4%, 100%, and 91.5%, respectively, for FISH. Of 15 breast malignancies that were diagnosed with indeterminate cytology, 13 were diagnosed as positive with FISH analysis (sensitivity, 86.7%).

CONCLUSIONS

The results demonstrate that the use of FISH in the diagnosis of FNA samples has a diagnostic accuracy comparable to conventional cytology and is useful in making a definitive diagnosis of malignancy (100% specificity) in patients with indeterminate cytologic results, suggesting that FISH diagnosis can be a good adjunct to conventional cytology.

Effect of hydrogen peroxide on guinea pig nasal mucosa vasculature

The effect of hydrogen peroxide (H2O2) on guinea pig nasal mucosa vasculature was studied by in vitro assay. H2O2 elicited relaxation of guinea pig nasal mucosa strips precontracted with phenylephrine in a concentration-dependent manner. The relaxant response to H2O2 was abolished in the presence of catalase. Preincubation of the strips with N(G)-nitro-L-arginine methyl ester or methylene blue significantly attenuated the relaxant responses elicited by H2O2. Fluorescence caused by DAF-2 DA, a fluorescence indicator for nitric oxide, was observed along the nasal mucosa vasculature in response to H2O2. These results suggest that H2O2 induced relaxation of the guinea pig nasal mucosa vasculature and that this relaxation is mediated by the NO/cGMP pathway.

Breast cancer screening by mammography in women aged under 50 years in Japan

BACKGROUND

The effectiveness of mammographic screening in women aged over 50 years has been confirmed in the United States and Europe, but its effectiveness in women aged from 40 to 49 years remains controversial. The optimum age for effective screening of subjects for breast cancer by mammography in Japan was studied based on the results of mammographic screening.

METHOD

The benefit of breast cancer screening in women was examined by stratifying the results of mammographic screening in a Tokushima trial on the basis of age: under 50 years and 50 years or older. The results of conventional screening by physical examination alone, which we performed in a Zentsuji trial, were used as the control.

RESULTS

The examinees numbered 13,982 and 18,619 in mammographic screening and screening by physical examination, respectively. Breast cancer was detected in 43 and 22 patients, respectively. The detection rate of breast cancer was 0.31% by mammographic screening, which is about 3 times higher than that (0.12%) by screening using physical examination. Mammographic screening thus showed significantly higher sensitivity (93.5% vs 73.3%, p = 0.015). The proportion of stage I cancer and the absence of nodal involvement were 67.4% and 79.1% by mammographic screening, compared with 31.8% and 59% by physical examination. Our results obtained with mammographic screening were equal to or higher than the results obtained in the United States and Europe. The clinical stage of the breast cancers detected by mammographic screening in the subjects aged under 50 years was stage 0 (DCIS) in one case and stage I in 10 cases, while the group aged 50 years or older showed stage 0 in 11 cases and stage I in 19 cases. There were three cases of false-negative; two false-negative cases were aged under 50 year, while one case was aged 50 years or older. The detection rates of cancer in the group under 50 years and that of 50 years or more were 0.19% and 0.39% by mammograpic screening and 0.09% and 0.15% by the physical examination. The sensitivities in the group under 50 years and that of 50 years or more were 84.6% and 97.0% by mammographic screening and 72.7% and 73.7% by physical examination, showing no significant difference. In the results of mammograms by Wolfe's classification with respect to the age groups, the proportion of DY (dense breast) pattern decreased significantly from 3.5% to 0.2% in women of 50 years or more and from 16.6% to 2.4% in those under 50 years when the values were compared between the period from 1992 to 1995 and the period from 1998 to 1999, respectively (p < 0.0001).

CONCLUSION

The above findings suggested the possible effectiveness of mammographic screening not only in women aged 50 years or more but also in those aged under 50 years, in Japan. Therefore, introduction of mammography should be considered at an early date, even for women aged from 40 to 49 years.

Activation by nicotine of striatal neurons receiving excitatory input from the substantia nigra via dopamine release

An electrophysiological study was performed to elucidate the role of nicotinic receptors in the striatal neurons in chloral hydrate-anesthetized rats. The effects of microiontophoretic application of nicotine and other drugs were examined on the caudate nucleus (CN) neurons activated monosynaptically by stimulation of the substantia nigra pars compacta (SN). Application of nicotine facilitated spontaneous firing. The nicotine-induced firing of the CN neurons was inhibited by concomitant application of domperidone or hexamethonium. These findings suggested that nicotine enhances dopamine release from the SN-derived dopaminergic nerve terminals by activating the neurons via D2 receptors.

Effects of sigma(1) receptor agonist SA4503 and neuroactive steroids on performance in a radial arm maze task in rats

This study examined the effects of sigma(1) receptor agonist SA4503 and neuroactive steroids dehydroepiandrosterone sulfate (DHEAS), pregnenolone sulfate (PREGS) and progesterone (PROG) on spatial working and reference memory in a radial arm maze task in rats. The insertion of a 6-min delay between the 2nd and 3rd choices caused a specific decline in working memory, but had no effect on reference memory. This decline in working memory was improved by SA4503, but not by DHEAS, PREGS or PROG. A non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist dizocilpine significantly impaired both working and reference memory in the presence or absence of a delay. The dizocilpine-induced impairments in the presence of a 6-min delay were ameliorated by SA4503, DHEAS and PREGS, whereas PROG had no effect. The beneficial effects of SA4503, DHEAS and PREGS were antagonized by treatment with sigma(1) receptor antagonist N, N-dipropyl-2-(4-methoxy-3-(2-phenylethoxy)phenyl)-ethylamine hydrochloride (NE-100). Furthermore, PROG attenuated the ameliorating effects of SA4503, DHEAS and PREGS on dizocilpine-induced memory deficits. These results suggest that sigma(1) receptors play a significant role in short-term working memory. Furthermore, it is suggested that DHEAS and PREGS ameliorate dizocilpine-induced memory impairments by acting as sigma(1) receptor agonists, while PROG antagonizes their effects by acting as a sigma(1) receptor antagonist.

Altered hippocampal expression of neuropeptide Y, somatostatin, and glutamate decarboxylase in Ihara's epileptic rats and spontaneously epileptic rats

By in situ hybridization and immunocytochemistry, expression of neuropeptide Y (NPY), somatostatin and glutamate decarboxylase 65 (GAD65) was studied in the hippocampus of two different epileptic mutant rats, Ihara's epileptic rat (IER) and the spontaneously epileptic rat (SER). GAD65 mRNA expression was enhanced in interneurons of the hippocampus in young IER, that had not yet developed generalized seizures. In older IER and older SER that both showed spontaneous seizures, marked increases of NPY mRNA in hippocampal granule cells and interneurons were found, as well as elevated GAD65 mRNA levels in interneurons. NPY immunoreactivity was enhanced in hilar interneurons and the dentate gyrus of older IER. In addition, some older IER stained heavily for NPY in mossy fibers. These findings suggest that up-regulation of NPY and GAD65 synthesis may be important in epileptogenesis.

Accumulation of N-acetyl-L-aspartate in the brain of the tremor rat, a mutant exhibiting absence-like seizure and spongiform degeneration in the central nervous system

The tremor rat is a mutant that exhibits absence-like seizure and spongiform degeneration in the CNS. By positional cloning, a genomic deletion was found within the critical region in which the aspartoacylase gene is located. Accordingly, no aspartoacylase expression was detected in any of the tissues examined, and abnormal accumulation of N-acetyl-L-aspartate (NAA) was shown in the mutant brain, in correlation with the severity of the vacuole formation. Therefore, the tremor rat may be regarded as a suitable animal model of human Canavan disease, characterized by spongy leukodystrophy that is caused by aspartoacylase deficiency. Interestingly, direct injection of NAA into normal rat cerebroventricle induced 4- to 10-Hz polyspikes or spikewave-like complexes in cortical and hippocampal EEG, concomitantly with behavior characterized by sudden immobility and staring. These results suggested that accumulated NAA in the CNS would induce neuroexcitation and neurodegeneration directly or indirectly.

Epileptic seizures induced by N-acetyl-L-aspartate in rats: in vivo and in vitro studies

Tremor rat (tm/tm), the parent strain of spontaneously epileptic rat (SER: zi/zi, tm/tm), exhibits absence-like seizures characterized by 5-7 Hz spike-wave-like complexes on cortical and hippocampal electroencephalograms (EEG) after 10 weeks of age, prior to development of convulsive seizures. Recently, this animal model has been demonstrated to display a genomic microdeletion within the critical region of tm, where aspartoacylase hydrolyzing N-acetyl-L aspartate (NAA) is located, besides showing the ability to accumulate NAA in the brain. Therefore, the present study was performed to determine the involvement of NAA in the induction of epileptic seizures. When NAA (4 micromol) was applied intracerebroventricularly (i.c.v.) to normal Wistar rats, 4-10 Hz polyspikes and/or spike-wave-like complexes followed by absence-like seizure before persistent 1-5 Hz waxing high-voltage after-discharges were observed on cortical and hippocampal EEG. At a higher dose (8 micromol), NAA induced convulsive seizures. The absence-like seizures with polyspikes and/or spike-wave-like complexes on the EEG were also observed with i.c.v. NAA in premature tremor rats without seizures. The NAA-induced seizures in normal rats were antagonized by i.c.v. glutamic acid diethyl ester, a non-selective glutamate receptor antagonist. In addition, NAA applied to the bath rapidly induced a long-lasting depolarization concomitantly with repetitive firings in hippocampal CA3 neurons of normal rat brain slice preparations. These findings suggest that NAA is involved in the induction of absence-like seizures and/or convulsion, probably via glutamate receptors.

Involvement of NMDA-receptor in kainate-induced neurotoxicity in cultured fetal retinal neurons

BACKGROUND

Both in vivo and in vitro studies suggest that excess stimulation of non-NMDA receptors can result in massive neuronal death in the retina. In particular, murine amacrine neurons have been known to show marked susceptibility to the toxic effects of kainate.

PURPOSE

This study was designed to examine and characterize the role of N-methyl-D-aspartate (NMDA) receptor vs non-NMDA receptor in glutamate-induced neurotoxicity in the retina.

METHODS

Primary cultures obtained from fetal rat retina (gestation day 16-19) were used for the experiment. The neurotoxicity was assessed quantitatively using the trypan blue exclusion method. Electrophysiological studies using patch-clamp techniques were performed to record whole-cell currents evoked by these excitatory amino acids.

RESULTS

Removal of extracellular Ca2+ from the medium or application of MK-801 reduced the extent of cell death induced by the brief exposure to glutamate, NMDA, and kainate. By contrast, cell death induced by a 60-min exposure to kainate was not affected by MK-801. The electrophysiological study demonstrated that MK-801 abolished the whole-cell currents evoked by NMDA but had no effect on those induced by kainate or AMPA.

CONCLUSION

These findings demonstrate that brief exposure to kainate induces cell death by way of activating NMDA receptors in cultured fetal retinal neurons and that NMDA receptors are the predominant route of fetal retinal neurotoxicity induced by brief glutamate exposure.

alpha(1)-adrenoceptor subtypes and effect of alpha(1A)-adrenoceptor agonist NS-49 on guinea pig nasal mucosa vasculature

It is now clear that alpha(1)-adrenoceptors comprise a heterogeneous family. In the present study, we characterized the alpha(1)-adrenoceptor subtype in the nasal mucosa vasculature of guinea pigs. A rectangular strip of guinea pig nasal mucosa was suspended in an organ bath containing Krebs' bicarbonate solution. Changes in tension were recorded isometrically. Concentration-response curves for agonists were obtained in a cumulative manner. Noradrenaline produced the greatest contraction of the nasal mucosa vasculature. NS-49 ((R)-(-)-3'-(2-amino-1-hydroxyethyl)-4'-fluoromethane sulfonanilide hydrochloride) and oxymetazoline worked as partial agonists. The intrinsic activities of NS-49 and oxymetazoline were 0.50+/-0.22 and 0.29+/-0.17, respectively, compared with noradrenaline (=1.00). Prazosin and the putative alpha(1A)-adrenoceptor antagonists WB-4101 (2-(2,6-dimethoxyphenoxyethyl)aminomethyl-1,4-benzodioxane) and 5-methylurapidil antagonized the response to noradrenaline competitively (pA(2) for prazosin<9.0). Conversely, putative alpha(1B) and alpha(1D)-adrenoceptor antagonists (spiperone and BMY7378 (8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4, 5]decane-7,9-dione), respectively) did not antagonize competitively. These results suggest that the alpha(1A)-subtype is predominant and that the alpha(1L) (or alpha(1N)) subtype may also be present in the guinea pig nasal mucosa vasculature. Furthermore, NS-49 might prove to be a nasal mucosa vasoconstrictor, which will improve nasal obstruction.

Human papillomavirus type 33 DNA in breast cancer in Chinese

BACKGROUND

The association between human papillomavirus (HPV) and anogenital tumors, especially cervical cancer, is well documented. However, it remains unclear whether there is also a correlation between HPV infection and human breast cancer.

METHODS

We used PCR and Southern blot hybridization to analyze HPV-related DNA specimens from 32 cases of invasive ductal carcinoma operated upon in the Shanghai region of China.

RESULTS

DNA derived from HPV33 was detected in 14 cases (43.8%). No HPV16 or HPV18 DNA was detected in any of the cases in this study. This is the first report demonstrating a correlation between HPV33 infection and breast cancer.

CONCLUSIONS

Our results suggest that HPV33 infection may be involved in the pathogenesis of breast cancer in Chinese.

[Detection of numerical aberrations in chromosomes by fluorescence in situ hybridization in fine needle aspirates in the preoperative diagnosis of cancer]

Fine needle aspiration (FNA) samples were obtained from 176 breast tumors suspected of malignancy, which were then subjected to conventional cytological and fluorescence in situ hybridization (FISH) analyses using the centromeric probes for chromosomes 1, 11, and 17. Histological examination revealed 157 breast cancers and 19 benign diseases (ten fibroadenomas, six intraductal papillomas, one intracystic papilloma, and two ADH). Sensitivity, specificity, and diagnostic accuracy were 85.4% 94.7%, and 86.4%, respectively, for cytology and 90.4%, 100%, and 91.5%, respectively, for FISH. These results demonstrate that FISH diagnosis of FNA samples has a diagnostic accuracy comparable to that of conventional cytology.

HPV33 DNA in premalignant and malignant breast lesions in Chinese and Japanese populations

The relationship between human papillomavirus (HPV) infection and breast cancer is controversial. In this study, paraffin-embedded tissue blocks prepared from 72 patients with benign, premalignant or malignant mammary lesions were randomly collected from the Shanghai region of China and Tokushima in Japan. DNA specimens extracted from all tissues were amplified by the polymerase chain reaction (PCR) using HPV16, 18 and 33 primers. Southern blot hybridization showed 19 cases to be positive for HPV33 DNA: The positive rate for HPV33 DNA in Chinese (41.7%) was significantly higher than in Japanese (11.1%) (P < 0.01): The positive rate for HPV33 DNA in invasive ductal carcinoma (34.1%) was higher than in benign or borderline mammary lesions (5%) (P < 0.02). There were no statistically significant difference among the relationship of the nuclear grade of breast cancers with HPV33 DNA-positivity. This is the first report of a positive correlation between HPV33 DNA and breast lesions in Chinese and Japanese populations. These results suggest that the infection by HPV33, but not HPV 16 or HPV 18, may be involved in breast hyperplastic lesions, especially breast cancer, in humans.

[Effects of OPC-24439, a sigma ligand, on neuronal activities in the hippocampus]

Sigma receptors in the central nervous system have been considered to play an important role in the modulation of mental diseases and memory/learning. However, the physiological function of sigma receptors still remains unknown. To elucidate physiological functions of the sigma receptors in modulation of neuronal activities, the effects of OPC-24439 (a sigma receptor ligand) on neuronal activities in hippocampal slices were studied with electrophysiological methods. Hippocampal slices (thickness ca. 450 microns) were prepared from male Wistar rats (4-7 weeks of age). In extracellular recording, population spikes in the CA1 region evoked by stimulation applied to the Schaffer collateral/commissural fibers were suppressed by OPC-24439 (1-100 microM) in a dose-dependent manner. This inhibition was antagonized by simultaneously applied haloperidol at 1 microM. In intracellular recording experiments, OPC-24439 (100 microM) did not affect the resting membrane potentials of neurons recorded. In addition, OPC-24439 had no effects on depolarization and firing induced by glutamate. These results indicate that sigma receptor activation caused suppression of neuronal activities in the hippocampus via the sigma receptors. This inhibition probably mediated via the suppression of ion channels that are not related to membrane potentials on post-synaptic neurons and/or sigma receptors on pre-synaptic neurons or interneurons.

Cholinergic and glutamatergic transmission in medial vestibular nucleus neurons responding to lateral roll tilt in rats

The responses of the medial vestibular nucleus (MVN) neurons to lateral tilt and the neurotransmitters mediating otolith information to MVN neurons were investigated using rats. A computer-operated goniometer was tilted 20 degrees clockwise and counterclockwise at an angular speed of 5 degrees /s and paused in the inclined positions for 10 s to record neuronal responses in the static phase. The 185 MVN neurons recorded were classified into eight types according to their responses to tilt (alpha, beta, gamma, delta, epsilon, zeta, eta and theta). A majority showed increased firing in response to ipsilateral tilting and decreased firing in response to contralateral tilting (alpha type: 31.4%) or exhibited the reverse pattern (beta type: 36.8%). Further, other groups of neurons increased (gamma type) or decreased (delta type) firing rates to either side tilting and increased (epsilon and zeta type) or decreased (eta and theta type) firing only on one side. Atropine or L-glutamic acid diethyl ester hydrochloride (GDEE) applied microiontophoretically antagonized tilt-induced firing of alpha type neurons in 58.8% or 60.0%, respectively, and of beta type neurons in 66.7% or 58.3%, respectively. When the effects of atropine and GDEE were examined in the same neurons, antagonizing effects of both drugs on tilt-induced firing were obtained in 28.6% and 40.0% of alpha and beta type neurons, respectively. These results suggest that both acetylcholine and glutamate act as neurotransmitters in the transmission of otolith information to most MVN neurons.

[Molecular mechanism underlying epileptic seizure: forwards development of novel drugs for untreatable epilepsy]

For the development of new drugs for hitherto untreatable epilepsy, it is necessary to clarify the basic pathophysiology involved in such epileptic seizures and find the target site. This review focused on molecular events related to the expression and expansion of the epileptic focus which are the target of novel antiepileptics. Immediate early genes such as c-fos followed by expression of nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) have been evidenced as initial important phenomena in the cascade of molecular systems that develop and complement the transient neuronal excitation to long-term neuronal plasticity. Non-receptor type tyrosine kinase Fyn in the Src family has been suggested to promote kindling development via tyrosine phosphorylation of the NMDA-receptor subunit, NR2B. The cause of abnormality in the inhibitory system is induced by lowering of glutamate-dependent GABA release in the epileptic focus within the hippocampus in human temporal epilepsy. This is probably attributed to a decrease in GABA transporters. Regarding abnormality of the excitatory system, there is an increase in glutamate release prior to convulsive seizures, an enhancement of NMDA receptor responsiveness and high levels of AMPA receptors related to convulsion after completion of kindling. In gene analysis of human familiar epilepsy, abnormalities and point mutations have recently been found in the following genes: KCNQ 2 and KCNQ3, coding for K+ channels; CHRNA4 of the nicotinic receptor subunit alpha 4; and the cystatin B gene. In epilepsy model mice, EL mice with several gene mutations known to be involved in the seizures, the El-1 gene contains an abnormality of the ceruloplasmin gene. SER (spontaneously epileptic rat: zi/zi, tm/tm), a double mutant, manifests a deletion of the region containing the aspartoacylase gene related to the tm gene. Since an increase in N-acetyl-L-aspartate (NAA) is observed in the SER brain, NAA may serve to evoke seizures.

Inhibition by aripiprazole of dopaminergic inputs to striatal neurons from substantia nigra

RATIONALE

Aripiprazole (OPC-14597) elicits both dopamine D(2) agonist and antagonist activities on dopaminergic neurons of the ventral tegmental area and nucleus accumbens neurons, respectively. However, the electrophysiological action of this drug on the striatal neurons is not clear.

OBJECTIVE

Therefore, the present electrophysiological study was performed to determine if aripiprazole modified the striatal neurons as a D(2) receptor agonist or antagonist.

METHODS

Spikes elicited by stimulation of pars compacta of the substantia nigra (SN) were extracellularly recorded from the striatal neurons with a glass microelectrode attached along a seven- barreled micropipette. Each barrel was filled with aripiprazole, quinpirole (D(2) receptor agonist), domperidone (D(2) receptor antagonist), glutamate or 2 M NaCl. The drugs were microiontophoretically applied on the neurons being recorded.

RESULTS

The effects of aripiprazole on SN stimulation-induced spikes of striatal neurons that were inhibited by domperidone were examined. Microiontophoretic application of aripiprazole inhibited spikes elicited by SN stimulation in all 18 neurons tested in a dose-dependent manner. In addition, quinpirole-induced firing was inhibited by aripiprazole in all ten neurons tested. However, glutamate-induced spontaneous firing was not affected by aripiprazole in any of the ten neurons tested.

CONCLUSIONS

These findings suggest that aripiprazole acts as a dopamine D(2) receptor antagonist on striatal neurons receiving excitatory inputs from the SN.

Attenuation by PACAP of glutamate-induced neurotoxicity in cultured retinal neurons

The effects of pituitary adenylate cyclase activating polypeptides (PACAPs: PACAP27, PACAP38) on glutamate-induced neurotoxicity were examined using cultured retinal neurons obtained from 3- to 5-day old Wistar rats. Cell viability was evaluated by double staining with fluorescein diacetate and propidium iodide. Effects of PACAPs on the increase in intracellular Ca(2+) concentration ([Ca(2+)](i)) in retinal neurons was investigated using the Ca(2+) image analyzing system with fura-2. The cAMP contents and the mitogen-activated protein (MAP) kinase activity in retinal cultures were measured by radioimmunoassay. Concomitant application of PACAPs (10 nM-1 microM) with glutamate (1 mM) for 10 min inhibited the delayed death of retinal neurons, which was observed 24 h after glutamate (1 mM) treatment in a dose-dependent manner. Protection by PACAPs (100 nM) against glutamate-induced neurotoxicity was antagonized by PACAP6-38 (1 microM), a PACAP antagonist, and H-89 (1 microM), a protein kinase A (PKA) inhibitor. However, PACAPs did not affect the glutamate-induced increase in [Ca(2+)](i), but PACAPs (1-100 nM) increased the cAMP levels in a dose-dependent manner. In addition, activation of MAP kinase by PACAP38 (1 microM) was inhibited by simultaneous application with H-89 (1 microM). These findings suggest that PACAPs attenuate glutamate-induced delayed neurotoxicity in cultured retinal neurons by activating MAP kinase through the activation of cAMP-stimulated PKA.

Two phases of behavioral plasticity in rats following unilateral excitotoxic lesion of the hippocampus

We investigated the effects of dizocilpine, a non-competitive N-methyl-D-aspartate receptor antagonist, on spatial reference and working memory in a radial arm maze task in rats with a unilateral hippocampal lesion. At a dose of 0.2 mg/kg to intact rats, dizocilpine significantly impaired both reference and working memory, and produced ataxia and impairment of food intake; at 0.1 mg/kg, dizocilpine had no effect on performance. Unilateral hippocampal lesion induced by quinolinic acid produced a marked working memory deficit concomitant with a slight but significant impairment of reference memory when mnemonic ability was examined one week after the lesion. The spatial memory deficits in the rats with a unilateral hippocampal lesion were ameliorated by repeated daily trainings over a 21-day period. Following recovery of the spatial memory deficits produced by the brain lesion (four weeks after the brain lesion), dizocilpine (0.1 mg/kg) significantly impaired both reference and working memory, without affecting general behavior or food intake in the brain-lesioned rats. An impairment of working memory, but not reference memory, by dizocilpine was observed six weeks after the brain lesion. However, the disrupting effect of dizocilpine at 0.1 mg/kg on spatial working memory had disappeared at eight weeks after the lesion. Ten weeks after the brain lesion, dizocilpine at 0.2 mg/kg was necessary to induce spatial memory impairment, which was accompanied by motor and food intake deficits, as in intact rats. In sham-operated rats, the dose-response effects of dizocilpine did not differ from those in intact rats at any time after the operation. These results suggest that two phases of behavioral plasticity take place, depending on demand, to compensate for brain dysfunction after the unilateral lesion of the hippocampus in rats.

Mechanism underlying the therapeutic effects of electroconvulsive therapy (ECT) on depression

Electroconvulsive therapy (ECT) is used to treat drug-resistant depressive disorders. The results of studies on the mechanism underlying the effectiveness of ECT on depression are still controversial. ECT stimulus is usually larger than the threshold of induction of seizures and activation of whole-brain is believed to be necessary to produce therapeutic effects. A single ECT session induces alterations of the electroencephalogram (EEG) including initial epileptic discharges, then slow waves, and finally flattened EEG. Repeated ECT results in an increasing number of slower waves in the EEG for as long as a month. ECT-induced changes in various neurotransmitter systems have also been reported. Serotonin (5-hydroxytryptamine, 5-HT) is one of the most important neurotransmitters involved in depressive illness, and ECT alters several 5-HT-receptor subtypes in the central nervous system. 5-HT1A receptors in post-synaptic neurons are sensitized by repeated ECT, but those in pre-synaptic neurons (auto-receptors) are not changed. In addition, our electrophysiological studies have shown that ECT increases sensitivity to 5-HT of 5-HT3 receptors in the hippocampus, resulting in an increase in release of neurotransmitters such as glutamate and gamma-aminobutyric acid. In contrast, ECT decreases the auto-receptor functions in noradrenergic and dopaminergic neurons in the locus coeruleus and substantia nigra, respectively, resulting in an increase in release of noradrenaline and dopamine. In conclusion, 5-HT1A-receptor sensitization may be important for explaining the effectiveness of ECT, as this change induces a decrease in the number of 5-HT2A receptors that are elevated in depressive patients. Facilitation of neurotransmitter releases due to 5-HT3-receptor sensitization by ECT may also play an important role in effective treatment of depressive patients refractory to therapeutic drugs.

[The function of sigma receptors--electrophysiological approach]

The functions of sigma (sigma) receptors were reviewed based on electrophysiological studies. Systemic administration of sigma ligands reportedly produces a variety of effects on dopamine (DA) neurons. In the mesolimbic DA system, (+)SKF-10,047 suppressed activities of the ventral tegmental area. In the substantia nigra, DTG also suppressed these activities, while BMY-14802 increased the activity of neurons. In the cerebellum, however, activities of Purkinje cells were suppressed by locally applied DTG, with probable involvement of the catecholaminergic system. This effect on Purkinje cells may explain the action of sigma ligands on the motor system. In the hippocampus, neuronal activities were inhibited by SR31742A in vivo (CA3 region) and by (+)SKF10,047 in vitro (CA1 region). DTG at high concentration (1 mM) completely suppressed population spikes (PS) in the CA1 region of hippocampal slice preparations. In our experiments, a novel sigma ligand, OPC-24439, suppressed PS in CA1 at concentrations of 1-100 microM. However, NMDA-induced neuronal firings in CA3 in vivo were augmented by low doses of DTG in a haloperidol-sensitive manner, but high doses were ineffective. In contrast, non-NMDA responses were not affected by DTG. In addition, several sigma ligands having no effect on the NMDA response have been reported. In addition, endogenous ligands, neuropeptide Y and dehydroepiandrosterone, augmented the NMDA-induced firing. In whole-cell patch clamp recording, NMDA-induced currents were suppressed by a relatively higher concentration of DTG in a concentration-dependent manner, while non-NMDA responses were only slightly suppressed. These findings suggest that effects of sigma ligands on NMDA receptor responses are biphasic, and sigma ligands may modulate memory and learning and suppress neuronal death by anoxia. In addition, sigma ligands are also reported to suppress Ca2+ channels in hippocampal culture neurons and induce current by closing K+ channels in NCB-20 cells. Thus, sigma receptors may be involved in the modulation of a variety of neurons that relate to psychiatric function and plasticity.

Rat retinal ganglion cells culture enriched with the magnetic cell sorter

The magnetic cell sorter (MACS) technique was applied to isolate retinal ganglion cells (RGCs) for culture. RGCs were labeled retrogradely with 1.1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (Dil). Subsequently retinal cell suspensions were incubated with biotinylated anti-rat Thy-1 antibody and MACS Streptavidin MicroBeads, and then applied onto the column in the magnetic fields. Cells attached on the column were flashed out without magnetism and plated on glass cover slips. RGCs were enriched to 31.0% of all cells with MACS from 0.55% before applying onto the magnetic column. Mean diameters of Dil-labeled cells were significantly larger than those of unlabeled cells. All cells with soma diameter over 11 microm were labeled. The number of viable RGCs were counted in the 10 fields of six cultures at a magnification of x200; the mean numbers on the 2nd, 7th and 14th culture-day were 53+/-3, 24+/-2 and 21+/-3, respectively (mean +/- SEM, n = 6). Thus, the MACS technique was confirmed to be useful for enrichment of RGCs and long-term study of cultured RGCs.

Effects of pramipexole on contraversive rotation and functional motor impairments in 1-methyl-4-phenyl1,2,3, 6-tetrahydropyridine-induced chronic hemiparkinsonian monkeys

Rotational and functional motor behavioral changes were studied in five MPTP lesioned chronic hemiparkinsonian Macaca nemestrina monkeys after i.m. pramipexole, a predominant D2 subfamily agonist. Pramipexole induced contraversive rotations in a dose-dependent manner with an optimal dose of 56 microg/kg for approximately 2 to 4 hr after injection. Three different rating scales were used to determine drug-induced functional improvement. They included a monkey parkinsonism rating scale, volitional responses to fruit presentations, and number of hand movements that appeared volitional. A dose of 56 microg/kg of pramipexole produced functional improvements on hand disability, and on a parkinsonian rating scale for monkeys in a dose-dependent manner from 32 to 100 microg/kg. These doses produced an increase in significant hand movements in the affected (contralateral) as well as in the normal (ipsilateral) hand to the side of the brain lesion compared with 5% dextrose in water vehicle control. With a dose of 100 microg/kg, the therapeutic effects of pramipexole on hand movements were less than with 56 microg/kg, due to side effects such as scratching.

Protective effects of vasoactive intestinal peptide against delayed glutamate neurotoxicity in cultured retina

The effects of vasoactive intestinal peptide (VIP) on glutamate-induced delayed death were examined using the primary cultures of rat retinal neurons. Effects of VIP on glutamate-induced neurotoxicity were evaluated by double staining with fluorescein diacetate and propidium iodide. Glutamate (1 mM) was applied to the culture for 10 min in the presence and absence of VIP, and visible cells enumerated 24 h after culture in normal medium. Effects of VIP on increase in the intracellular Ca2+ concentration and currents induced by glutamate in retinal neurons were investigated using the Ca2+ image analyzing system with fura-2 and whole-cell patch-clamp recording, respectively. The cAMP contents in retinal cultures were measured by radioimmunoassay. VIP (10 nM-1 microM) dose-dependently protected against glutamate-induced neurotoxicity in cultured retinal neurons. Protection by VIP (100 nM) against glutamate (1 mM)-induced neurotoxicity was antagonized by VIP6-28 (1 microM), a VIP antagonist, and H-89 (100 nM and 1 microM), a protein kinase A inhibitor. However, VIP had no effect on glutamate-induced inward currents nor glutamate-induced increase in the intracellular Ca2+ concentration. A 10-min exposure of VIP (100 nM) with glutamate (1 mM) resulted in an increase in the cAMP level to 446+/-58 from 22+/-1 pmol/mg protein. These findings suggest that VIP protects against the glutamate-induced neurotoxicity in retinal cultures by elevating the cAMP level via VIP receptors and thereby activating protein kinase A.

Radiation Complications Following Breast Conserving Therapy

BACKGROUND: Breast conserving therapy is being established as a standard therapeutic procedure for early breast cancer in Japan. However, the indications of radiotherapy and a standardized therapeutic procedure have not been established yet. In this study, complications following radiotherapy were evaluated in patients who had previously undergone breast conserving therapy at Tokushima University Hospital. METHODS From October 1989 to March 1996, 60 women with stage I or II breast cancer underwent radiation therapy after breast conserving surgery, and all patients were followed-up for a median of 27 months. Radiation morbidity scoring of the breast and adjacent organs was performed using the toxity criteria of the Radiation Therapy Oncology Group (RTOG) and European Organization for Research andTreatment of Cancer (EORTC). RESULTS: Only 1 patient developed local recurrence, and no distant metastasisor death was observed. The cause of recurrence in 1 case was considered to be due to extended intraductal component. Although transient dermal reaction was induced by irradiation of the breast, no side effects that may cause cosmetic problems were found. No serious radiation complications were found in the lungs, ribs, heart or other adjacent organs. CONCLUSION: The adverse reactions caused by irradiation does not reduce the merit of combined use of radiation therapy in breast conserving therapy, and therefore, are not the hesitation factor in application of radiotherapy.

Cold exposure enhances nitroxidergic nerve-mediated vasodilatation in canine nasal mucosa

We have previously reported that there is non-adrenergic, non-cholinergic (NANC) innervation in canine nasal mucosa and that the relaxation response to electrical stimulation of the NANC nerve is mainly mediated by nitric oxide (NO). In the present study, we examined the effect of cold exposure (24 degrees C) on nitroxidergic nerve-mediated vasodilatation in isolated canine nasal mucosa. Nasal mucosa strips, prepared from canine nasal septum and moderately precontracted with methoxamine in the presence of atropine and guanethidine, relaxed in response to transmural electrical stimulation (square pulses of 0.5-msec duration, at 5 Hz and 25 V). The degree of relaxation at 24 degrees C (55.4+/-13.2% of methoxamine-induced contraction, mean+/-S.D., n=6) was significantly greater than that at 34 degrees C (33.8+/-8.6%, n=6). This phenomenon was reversible. In contrast, the magnitude of relaxation responses to an NO donor (sodium nitroprusside of 0.1 and 1 microM) remained unchanged by cold exposure. These results suggest that the release of NO from the nitroxidergic nerve endings is augmented by cold exposure and, thus, vasodilatation of the nasal blood vessel is enhanced, thereby contributing to the swelling of the nasal mucosa in cold conditions.

Effects of talipexole on contraversive rotation and functional impairment in MPTP-induced chronic hemiparkinsonian monkeys

The effects of talipexole on functional motor improvement in comparison with contraversive circling were studied in five chronic (5-7 years post MPTP-lesioned) hemiparkinsonian Macaca nemestrina monkeys. Talipexole induced contraversive rotations in a dose of 32 microg/kg for about 1 hr after i.m. injection. Larger doses (56 and 100 microg/kg, i.m.) produced less effect due to sedation. Three different rating scales were used to assess functional improvement, including a clinical parkinsonism rating scale, volitional responses to fruit presentations, and number of significant hand movements. The optimal dose of talipexole was 32 microg/kg, i.m. Functional improvement by talipexole, including clinical parkinsonian rating scales and significant hand movements, as well as contraversive circling in hemiparkinsonian monkeys, confirm that this chronic animal model is useful in preclinical testing of drugs for the treatment of human parkinsonism.

Cytochemical and patch-clamp studies of calcium influx through voltage-dependent Ca2+ channels in vestibular supporting cells of guinea pigs

To clarify whether or not vestibular supporting cells have voltage-dependent Ca2+ channels, cytochemical and patch-clamp studies were performed using cells isolated from the ampullae of the semicircular canal of the guinea pig. Image analysis used fura-2 as a Ca(2+)-sensitive fluorescence dye and showed that the intracellular Ca2+ concentration ([Ca2+]i) increased with bath application of high (150 mM)K+, but was unaffected by 80 mM K+. The increase in [Ca2+]i induced by high K+ was completely blocked by 1 microM nifedipine as an L-type Ca2+ channel antagonist. In the patch-clamp whole-cell recording of the isolated supporting cells, the voltage-dependent inward current was induced by a depolarizing pulse lasting 2 s in a high (50 mM) Ca2+ and tetraethylammonium-containing external solution replaced by choline chloride and a Cs(+)-containing internal solution. The inward current was obtained when the membrane was depolarized to -50 mV and maximum current was observed at -10 to +10 mV. This inward current was completely blocked by 1 microM nifedipine. These findings strongly suggest that voltage-dependent Ca2+ channels exist in the vestibular supporting cells and regulate Ca2+ concentration in the vestibular endolymph.

Ethanol reduces spontaneous firing and potentiates GABA-induced currents in acutely dissociated rat medial vestibular nucleus neurons

Effects of ethanol on acutely dissociated medial vestibular nucleus (MVN) neurons were examined using whole-cell patch clamp technique to elucidate the mechanism underling the inhibitory effects of this drug on the neurons observed in in vivo studies. Dissociated MVN neurons obtained from male Wistar rats were superfused with extracellular solution continuously at a flow rate of 1-3 ml/min. Whole-cell patch clamp recording was performed according to standard procedures. GABA was applied by pressure from a pipette placed near the neuron recorded. Ethanol was applied via pipette by pressure or through bath perfusion. Acutely dissociated MVN neurons regularly showed spontaneous firing. Under current-clamp conditions, bath application of ethanol at 0.1% caused hyperpolarization and reduced spontaneous firing in MVN neurons, while 0.1% ethanol did not affect spontaneous firing. Pulse application of higher concentrations of ethanol (0.1-1%) caused similar hyperpolarization. Under voltage-clamp conditions at a holding potential of -30 mV, GABA induced outward currents in a concentration-dependent manner. GABA-induced currents were potentiated in the presence of 0.01% ethanol. These results indicate that high concentrations of ethanol (0.1-1%) directly induce inhibition of spontaneous firing and low concentrations (0.01%) enhance GABA-induced inhibition in the MVN neurons.

Suppression by topiramate of epileptiform burst discharges in hippocampal CA3 neurons of spontaneously epileptic rat in vitro

Topiramate, a novel antiepileptic drug, inhibits the seizures of spontaneously epileptic rat (SER), a double mutant (zi/zi, tm/tm) which exhibits both tonic convulsion and absence-like seizures from the age of 8-weeks. Hippocampal CA3 pyramidal neurons in SER show a long-lasting depolarization shift with accompanying repetitive firing when a single electrostimulation is delivered to the mossy fibers in vitro. The effects of topiramate on the excitability of CA3 pyramidal neurons in SER were examined to elucidate the mechanism underlying the antiepileptic action. Intracellular recordings were performed in 23 hippocampal slice preparations of 16 SER aged 8-17 weeks. Topiramate (10-100 microM) dose-dependently inhibited the depolarizing shifts with repetitive firing induced by mossy fiber stimulation without affecting the first spike and resting membrane potentials in hippocampal CA3 neurons of SER. Higher dose of topiramate (100 microM) sometimes inhibited the first spike, and decreased excitatory postsynaptic potentials in the SER CA3 neurons. However, topiramate up to 100 microM did not affect the single action potential elicited by the stimulation in the hippocampal CA3 neurons of age-matched Wistar rat devoid of the seizure. Application of topiramate (100 microM) did not significantly affect the firing induced by depolarizing pulse applied in the CA3 neurons of the SER. In addition, topiramate (100 microM) had no effects on the Ca2+ spike induced by intracellularly applied depolarizing pulse in the presence of tetrodotoxin and tetraethylammonium. In contrast, a dose-dependent inhibition of depolarization and repetitive firing induced by bath application of glutamate in CA3 pyramidal neurons was obtained with topiramate (10-100 microM). Furthermore, topiramate (100 microM) decreased the number of miniature postsynaptic potential of CA3 pyramidal neurons of SER. In patch clamp whole cell recording using acutely dissociated hippocampal CA3 neurons from SER aged 8-weeks and age-matched normal Wistar rats, there were no remarkable effects on voltage dependent Ca2+ current with topiramate up to 300 microM in either animal; the current was completely blocked by Cd2+ at a concentration of 1 mM. These findings suggest that topiramate inhibits release of glutamate from the nerve terminals and/or abnormal firing of the CA3 pyramidal neurons of SER by mainly blocking glutamate receptors in the neurons.