Alpha 1-adrenergic receptor-mediated excitation from the locus coeruleus of the sacral parasympathetic preganglionic neuron

Electrophysiological studies using alpha-chloralose anesthetized cats were performed to elucidate whether or not noradrenaline derived from the locus coeruleus (LC) activates sacral intermediolateral (IML) cell column neurons, from which the sacral parasympathetic neurons originate. LC stimulation induced a spike in the sacral IML cell column neurons (parasympathetic interneurons), which were not antidromically activated by stimulation of the pelvic nerve, with a mean latency of 65.4 +/- 4.64 msec (mean +/- S.E., n = 12). In the sacral IML cell column neurons (parasympathetic preganglionic neurons), which were antidromically activated by pelvic nerve stimulation with a mean latency of 5.32 +/- 1.23 msec, LC stimulation also elicited a spike with the mean latency of 67.9 +/- 4.53 msec (n = 7). Iontophoretic application of prazosin, an alpha 1-adrenergic blocking agent, inhibited spikes elicited by LC stimulation in 8 of 12 sacral parasympathetic interneurons tested, but no alterations of LC stimulation-induced spikes were seen during iontophoretic application of sotalol, a beta-blocking agent. In contrast, spikes elicited by LC stimulation in the sacral parasympathetic preganglionic neurons tested were not affected by iontophoretic application of either prazosin or sotalol. These results suggests that noradrenaline derived from the LC activities the parasympathetic interneurons in the sacral IML cell column through alpha 1-adrenergic receptors, thereby inducing excitation of the sacral parasympathetic neurons receiving impulses from the interneuron.

Muscarinic regulation of spontaneously active medial vestibular neurons in vitro

We examined the effects of cholinergic agonists and antagonists on spontaneously occurring action potentials extracellularly recorded from medial vestibular nucleus (MVN) neurons in rat brainstem slice preparation to elucidate the cholinergic mechanism involved in excitation. Addition of carbachol (10(-6)-10(-5) M) and muscarine (10(-6)-10(-5) M) into the bath dose-dependently increased the spontaneous firing rate, while nicotine (10(-5)-10(-4) M) had no effects. Acetylcholine (10(-6)-10(-5) M) in the presence of physostigmine (10(-7) M) also increased the firing rate in a dose-dependent manner. Conversely, atropine (10(-8)-3 x 10(-7) M) slightly decreased the firing and dose-dependently inhibited the carbachol-induced increase in the firing rate. These results suggest that the firing rate of spontaneously active MVN neurons are regulated by acetylcholine via muscarinic receptors.

Ventral tegmental area-mediated inhibition of neurons of the nucleus accumbens receiving input from the parafascicular nucleus of the thalamus is mediated by dopamine D1 receptors

Microiontophoretic experiments were performed to determine whether inhibition mediated by the ventral tegmental area neurons of the nucleus accumbens, receiving input from the parafascicular nucleus of thalamus, is mediated by dopamine D1 or D2 receptors, using rats anesthetized with chloral hydrate. Spikes, elicited by test stimuli applied to the parafascicular nucleus were inhibited by conditioning stimuli to the ventral tegmental area, given 30 msec before the test stimuli. This inhibition was antagonized by iontophoretic application of SCH 23390, a D1 antagonist, in 18 of 25 neurons of the nucleus accumbens, but in only 3 of 22 neurons of the nucleus accumbens during application of domperidone, a D2 antagonist. The reduction by conditioning stimulation of the ventral tegmental area of the mean number of spikes of the 25 neurons upon stimulation of the parafascicular nucleus, was abolished by SCH 23390. In contrast, domperidone did not affect the mean number of spikes of the 22 neurons upon stimulation of the parafascicular nucleus in the presence of conditioning stimulation of the ventral tegmental area. In addition, spikes elicited by stimulation of the parafascicular nucleus were dose-dependently inhibited by iontophoretic application of both SKF 38393, a D1 agonist and bromocriptine, a D2 agonist. These results suggest that inhibition by dopamine, derived from the ventral tegmental area of neurons of the nucleus accumbens, receiving input from the parafascicular nucleus, is mediated mainly by dopamine D1 receptors, although both D1 and D2 receptors are expressed on the same neuron of the nucleus accumbens, which is also inhibited by exogenously applied D2 agonists.

The role of extraocular proprioception in vestibulo-ocular reflex of rabbits

This study was undertaken to elucidate the role of extraocular proprioception in the vestibulo-ocular reflex, using pigmented rabbits. The presence of extraocular afferent projections in the ophthalmic branch (OB) of the trigeminal nerve was confirmed by retrograde transport of horseradish peroxidase. The OB of the left trigeminal nerve was transected at its junction with the trigeminal ganglion. Vestibular nystagmus was produced by rotating the animal clockwise and counter-clockwise in the horizontal plane in a dark room. The number and direction of the quick phase of nystagmus induced by rotation in the eye on the operated side were not different from those in the eye on the unoperated side or from those before the transection. However, the eye on the operated side moved slowly and unstably without directional preponderance during and after rotation at an angular velocity of 30 degrees/sec. In the sham-operated and unoperated groups, when the angular velocity was increased to over 90 degrees/sec, the eyes deviated in the anticompensatory direction to the head movement (the same direction as the head movement) during and immediately after the rotation. At an angular velocity of over 30 degrees/sec, however, the eye on the operated side exhibited anticompensatory response more frequently and markedly than that on the unoperated side. These results suggest that extraocular proprioception is important for fixation of the eye position in spacial relation to the head, and that loss of the sensation readily induces anticompensatory oculomotor response to head movement.

Ethanol inhibits vestibular and caloric nystagmus without affecting optokinetic nystagmus in rabbits

Effects of ethanol on optokinetic, vestibular and caloric nystagmus were investigated in pigmented rabbits to determine whether or not it affects a specific site involved in the induction of various nystagmus. Optokinetic nystagmus was produced by rotation of the drum with vertical stripes at an angular velocity of 0.85 degrees/sec. Vestibular nystagmus was induced by horizontal rotation at an angular velocity of 30 degrees/sec and caloric nystagmus by infusion of cold water into the external meatus. Cumulative injection of ethanol into the auricular vein to doses of 0.1, 0.2, 0.4 and 0.8 g/kg inhibited both vestibular and caloric nystagmus dose-dependently, but did not affect the optokinetic nystagmus. These results suggest that relatively low doses of ethanol mainly act on the peripheral vestibular organ and impair the vestibular function without affecting the optokinetic system.

Ethanol potentiates the effect of gamma-aminobutyric acid on medial vestibular nucleus neurons responding to horizontal rotation

Electrophysiological studies were performed to determine whether or not ethanol potentiates the inhibitory effects of gamma-aminobutyric acid (GABA) on medial vestibular nucleus (MVN) neurons responding to horizontal sinusoidal rotation using alpha-chloralose anesthetized cats. The MVN neurons were classified into types I, II, III and IV neurons according to the responses to the horizontal rotation of the animal placed on the turntable in directions ipsilateral and contralateral to the recording site. In addition, the effects of ethanol and GABA on type I neurons were also examined. Micro-osmotic application of ethanol up to 100 nA did not affect the spontaneous firing or the rotation-induced increase in firing of type I neurons. However, the inhibitory effects of GABA up to 50 nA on the rotation-induced increase in firing were potentiated during simultaneous application of ethanol up to 100 nA. This potentiated inhibition was blocked by iontophoretic application of bicuculline (25-150 nA) and picrotoxin (45-150 nA). These results suggest that ethanol potentiates the inhibitory effects of GABA on MVN type I neurons by acting on the GABA receptor and/or receptor-coupled chloride ion channel.

Inhibitory effects of L-threo-DOPS, an L-noradrenaline precursor, on locus coeruleus-originating neurons in the caudate nucleus

Electrophysiological studies using reserpine-treated cats were carried out to elucidate the effects of L-threo-3,4-dihydroxyphenylserine (L-threo-DOPS) on the noradrenergic pathway from the locus coeruleus (LC) to the caudate nucleus (CN) neurons, which were activated by iontophoretically applied bromocriptine, a dopamine D-2 receptor agonist. In the CN neurons, glutamate-induced firing was inhibited by iontophoretic application of noradrenaline, but not by repetitive stimulation of the LC or iontophoretically applied L-threo-DOPS. After intraventricular administration of L-threo-DOPS, however, LC stimulation inhibited the glutamate-induced firing. These results suggest that L-noradrenaline that was produced from the conversion of L-threo-DOPS inhibited the CN neurons which possess dopamine D-2 receptors.

Electrophysiological evidence for cholinoceptive neurons in the medial vestibular nucleus: studies on rat brain stem in vitro

Electrophysiological studies were performed to determine whether or not cholinoceptive neurons are present in the rat medial vestibular nucleus (MVN) using brainstem slice preparations. Fifty-three MVN neurons, whose activities were extracellularly recorded, fired spikes spontaneously and regularly with an interspike interval of 180 +/- 27 ms (mean +/- S.E.M.) and a coefficient of variation of 0.11 +/- 0.02. Intracellularly recorded neurons also exhibited similar spontaneous and regular generation of action potentials. Carbachol dose-dependently increased the spontaneous firing, although the firing rate was decreased in a few neurons. The addition of atropine reduced the firing rate, and dose-dependently attenuated the carbachol-induced excitation of the neurons. In a low Ca2+ and high Mg2+ medium, carbachol also increased the firing rate. These results indicate that the MVN contains neurons with spontaneous and regular firing, and that the excitability of these neurons is regulated by a cholinergic muscarinic mechanism.

Muscarinic inhibition as a dominant role in cholinergic regulation of transmission in the caudate nucleus

The effects of cholinergic agonists and antagonists were investigated using slice preparations of the rat caudate nucleus (CN) to elucidate the role of the cholinergic system in the CN. Either carbachol (10(-7) to 10(-5) M) or muscarine (10(-7) to 10(-5) M) dose-dependently inhibited extracellular action potentials orthodromically elicited by local stimulation in the CN. A combination of acetylcholine (10(-6) to 10(-4) M) with physostigmine (10(-6) M) also inhibited the orthodromic response of CN neuron, but nicotine (10(-6) to 10(-3) M) had no effects on the neuronal activity. Atropine (10(-8) to 10(-6) M) antagonized the carbachol-induced inhibition of CN neuron with pA2 of 7.58. Carbachol (10(-5) M) or muscarine (10(-5) M) decreased the amplitude of excitatory postsynaptic potential (EPSP) without altering the resting membrane potential or input impedance of the CN neuron, whereas nicotine (10(-5) M) did not affect either the resting membrane potential or amplitude of EPSP. When carbachol (10(-5) M) was added to the bath, the number of action potentials elicited by applying a depolarizing current into the cell was increased, whereas action potentials transsynaptically elicited by local stimulation were inhibited conversely. The excitatory effects of carbachol on the postsynaptic site of the neuron were also blocked by atropine (3 x 10(-7) M). Carbachol (10(-5) M) did not affect the time courses of the rise and decay phases of EPSP induced by the local stimulation, but did reduce the amplitude of the EPSP.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of antiepileptic drugs on absence-like and tonic seizures in the spontaneously epileptic rat, a double mutant rat

Electroencephalographic (EEG) studies were performed to examine the effects of several antiepileptic drugs (AEDS) on absence-like and tonic seizures in the spontaneously epileptic rat (SER: zi(zi), tm/tm,), a double mutant rat, which was obtained by mating the tremor heterozygous animals (tm/ +) with the zitter homozygous animals (zi/zi), and to determine whether the seizures in the SER correspond to human absence and tonic seizures. Spontaneous EEG was continuously recorded from the frontal cortex and hippocampus using implanted electrodes. The SER showed paroxysmal and synchronized 5-7-Hz spike-wave-like complexes in both cortical and hippocampal EEG during the absence-like state, which was characterized by immobility and staring. The animal also exhibited tonic convulsion without external stimulation concomitant with low-voltage fast waves on cortical and hippocampal EEG. In some animals, sporadic low-amplitude spikes appeared in the low-voltage fast waves during tonic convulsion. the absence-like seizures were inhibited by trimethadione (100 mg/kg intraperitoneally, i.p.) and ethosuximide 100 mg/kg i.p.), whereas the tonic convulsion was not affected by these drugs. In contrast, phenytoin (20 mg/kg i.p.) inhibited the tonic seizures without affecting the absence-like seizures. Phenobarbital (10 mg/kg i.p.) and valproate (200 mg/kg i.p.) inhibited both seizures to a similar degree. These results suggest that the SER, with both absence-like and tonic seizures, is a useful model for evaluation of AEDS.

Muscarinic receptor-mediated inhibition of dopaminergic excitatory input to caudate neurons from the substantia nigra

Microiontophoretic studies using rats anesthetized with chloral hydrate were performed to elucidate the relationship between the striatal cholinergic system and nigrostriatal dopaminergic system. Iontophoretic application of carbachol inhibited the spikes elicited by substantia nigra (SN) stimulation in 21 of 24 caudate neurons in which the spikes induced by SN stimulation were inhibited by microiontophoretically applied domperidone, a dopamine D-2 receptor antagonist. This inhibitory effect was completely blocked by atropine, although the spike generation induced by SN stimulation remained unaffected by the drug. However, carbachol did not affect the glutamate-induced firing of the caudate neurons of which the spikes induced by SN stimulation were inhibited by application of both domperidone and carbachol. Furthermore, carbachol had inhibitory effects on the spikes induced by SN stimulation even after the systemic application of bicuculline. In contrast, in 17 of 24 caudate neurons in which the spikes induced by SN stimulation were not affected by domperidone, carbachol did not inhibit the spikes induced by SN stimulation. These results suggest that the muscarinic receptors located on the SN-derived dopaminergic nerve terminals mainly play a role in inhibiting inputs from the SN to the caudate neurons, probably by reducing the release of dopamine from the nerve terminals.

Different sensitivity to hypoxia in neuronal activities of lateral vestibular and spinal trigeminal nuclei

Electrophysiologic studies were performed to examine the effects of hypoxia on neuronal activities of the lateral vestibular and spinal trigeminal nuclei using rats anesthetized with chloral hydrate. The rats inhaled a gas mixture of 5% oxygen and 95% nitrogen for 3.5 minutes to induce hypoxia, followed by room air. Under these conditions, mean PaO2 was decreased from 85 to 22 mm Hg 3 minutes after the start of the inhalation concomitant with a decrease in blood pressure from 108 to 55 mm Hg. There were no significant differences in these variables between rats used for vestibular nucleus experiments and rats used for trigeminal nucleus experiments. In the lateral vestibular nucleus, hypoxia inhibited postsynaptic components of the evoked field potential, spike generation of monosynaptic neurons on vestibular nerve stimulation, and firing induced by iontophoretic application of glutamate. In the spinal trigeminal nucleus, however, there were no alterations of the field potential or spike generation of the neurons on trigeminal nerve stimulation. These results indicate that the lateral vestibular nucleus neurons are much more sensitive to hypoxia than the spinal trigeminal nucleus neurons. The failure of transmission in the monosynaptic neurons of the lateral vestibular nucleus is suggested to be due to the inhibition of excitability of the postsynaptic membrane.

Contraction of urinary bladder by central norepinephrine originating in the locus coeruleus

Studies were performed to elucidate the role of the locus coeruleus, which is rich in norepinephrine-containing cell bodies, in vesical function using alpha-chloralose anesthetized cats. Stimulation of the locus coeruleus caused contraction of the urinary bladder, which was not affected by transection of the bilateral hypogastric nerves, but blocked by intravenous administration of hexamethonium, a ganglion blocking agent. In animals with transected hypogastric nerves, the locus coeruleus-induced contraction was inhibited by intrathecal administration of phentolamine (alpha-blocker) and prazosin (alpha 1-blocker), but not affected by intrathecal sotalol (beta-blocker) or yohimbine (alpha 2-blocker). In animals treated with reserpine, the locus coeruleus-induced contraction was enhanced by intravenous application of L-dopa, a precursor of norepinephrine. These results suggest that norepinephrine derived from the locus coeruleus activated preganglionic neurons in the sacral intermediolateral nuclei via alpha 1-receptors, thereby producing urinary bladder contraction.

Presynaptic inhibition of excitatory input from the substantia nigra to caudate nucleus neurons by a substituted quinolinone derivative, 7-[3-(4-(2,3-dimethylphenyl)piperazinyl)propoxy]-2(1H)-quinolinone (OPC-4392)

The effects of a newly synthesized quinolinone derivative, 7-[3-(4-(2,3-dimethylphenyl)piperazinyl) propoxy]-2(1H)-quinolinone (OPC-4392) on neuronal activities of the caudate nucleus (CN) were investigated in cats anesthetized with alpha-chloralose using a microiontophoretic method. In the CN neurons of which spikes elicited by stimulation of the pars compacta of substantia nigra (SN) were suppressed by iontophoretically applied domperidone, a dopamine D-2 receptor antagonist, application of OPC-4392 (100-200 nA) inhibited the spike generation induced by SN stimulation. Conversely, the CN neurons insensitive to domperidone were unaffected by OPC-4392. Iontophoretic application of CPC-4392 up to 200 nA did not affect glutamate-induced firing of the CN neurons, of which the firing was blocked by dopamine less than 100 nA. In addition, OPC-4392 did not inhibit firing induced by bromocriptine, a dopamine D-2 agonist; while domperidone suppressed the bromocriptine-induced firing without affecting the glutamate-induced firing. These results suggest that OPC-4392 acts on the dopaminergic nerve terminals and inhibits excitatory transmission from the SN to the CN.

Effects of L-threo-DOPS, an L-noradrenaline precursor, on locus coeruleus-originating neurons in spinal trigeminal nucleus

Electrophysiological studies using reserpinized cats were performed to examine the effects of L-threo-3,4-dihydroxyphenylserine (L-threo-DOPS) on the noradrenergic pathway from the locus coeruleus (LC) to the spinal trigeminal nucleus (STN). The spike generation of STN relay neurons induced by trigeminal nerve stimulation was not affected by LC conditioning stimulation nor iontophoretic application of L-threo-DOPS. After intraventricular administration of L-threo-DOPS, the inhibition of the spike generation was seen with LC conditioning stimulation and blocked by iontophoretically applied sotalol, suggesting that L-noradrenaline converted from L-threo-DOPS inhibits transmission of STN relay neurons.

Inhibitory effects of thyrotropin-releasing hormone on neuronal activity in the nucleus accumbens

The effects of thyrotropin-releasing hormone (TRH) were examined on neuronal activity in the nucleus accumbens, receiving an input from the parafascicular nucleus of the thalamus or the hippocampus, in chloral hydrate-anesthetized rats, using a microiontophoretic technique. The spikes produced by stimulation of the parafascicular nucleus were predominantly and dose-dependently inhibited during iontophoretic application of TRH. When the effects of TRH and dopamine were tested on the same neurons of the nucleus accumbens, inhibition of the generation of spikes by both drugs was observed in most neurons. In contrast, spikes elicited by stimulation of the hippocampus in most neurons of the nucleus accumbens were not affected by TRH or dopamine. Both TRH- and dopamine-induced inhibition of the spikes induced by stimulation of the parafascicular nucleus was antagonized by simultaneous application of haloperidol. In animals treated with reserpine, inhibition of the generation of spikes upon stimulation of the parafascicular nucleus did not occur in any neurons in the nucleus accumbens during application of TRH, whereas the dopamine-induced inhibition was still observed. These results suggest that inhibitory effects of TRH on the neurons of the nucleus accumbens receiving an input from the parafascicular nucleus are mediated by dopamine released from the dopaminergic nerve terminals located in the nucleus accumbens.

Excitatory and inhibitory effects of dopamine on neuronal activity of the caudate nucleus neurons in vitro

Effects of dopamine on the rat caudate nucleus neurons were examined in a slice preparation using an intracellular recording technique. Perfusion of the bath with a low concentration (1 microM) of dopamine produced a depolarization concomitant with an increase in the spontaneous firing and the number of action potentials evoked by a depolarizing pulse applied into the cells. In contrast, higher concentrations (100-500 microM) of dopamine inhibited the spontaneous and current-induced firings without apparent effects on the resting membrane potential. In addition, during application of a high concentration (100 microM) of dopamine there was a marked elevation of the threshold potential of the action potential elicited by a higher depolarizing current. Simultaneous application of haloperidol (0.5-5 microM) antagonized both excitatory and inhibitory effects induced by the low and high concentrations of dopamine, respectively. In addition, the excitatory effect induced by a low concentration (1 microM) of dopamine was antagonized by domperidone (0.5 microM), a selective D2 receptor antagonist, while the inhibitory effect by a high concentration (100 microM) was blocked by SCH 23390, a selective D1 receptor antagonist. These results strongly suggest that the postsynaptic sites of caudate nucleus neurons have at least two subtypes of dopamine receptors (D1 and D2 receptors) that mediate inhibitory and excitatory responses of the neuron to dopamine, respectively.

Opioid-mediated inhibition from the subnucleus caudalis of spinal trigeminal nucleus to the neurons in the subnucleus oralis

The influence of enkephalin-containing neurons in the subnucleus caudalis of the spinal trigeminal nucleus (STN caudalis) on the subnucleus oralis of the STN (STN oralis) was examined using chloral hydrate-anesthetized rats. In the STN oralis, conditioning stimuli applied to the STN caudalis 10-50 ms preceding the test stimulus inhibited spikes produced by tooth pulp stimulation in type B interneuron, which was activated by orthodromic stimulation but not by thalamic stimulation, without affecting those of the relay neuron. When the type B interneurons were further classified into type B1 and type B2 neurons, which were characterized by the occurrence of the STN caudalis-induced inhibition with long and short latencies, respectively, microiontophoretically applied naloxone reduced the STN caudalis-induced inhibition of th orthodromic spikes of type B1 interneurons with little effects on type B2 interneuron. Furthermore, naloxone-reversible inhibition of tooth pulp-induced spikes of the type B1 interneurons were also observed during iontophoretic application of enkephalin. These results suggest that the type B1 interneurons in the STN oralis are inhibited by opioid peptides-containing neurons in the STN caudalis.

[Effects of 1-[2-[bis(fluorophenyl)methoxy]ethyl]-4-(3-phenylpropyl) piperazine dihydrochloride (I-893) on turnover of dopamine and norepinephrine in the brain]

Studies were performed to elucidate the effects of 1-[2-[bis (fluorophenyl) methoxy]ethyl]-4-(3-phenylpropyl) piperazine dihydrochloride (I-893), a newly synthesized aryl-1,4-dialkyl-piperazine derivative, on turnover of dopamine and norepinephrine in the rat brain. The contents of both monoamines were not affected by I-893 at an oral dose of 10 mg/kg. The oral administration of 50-250 mg/kg produced a transient increase in dopamine content of the caudate nucleus and hypothalamus, and thereafter, the content dose-dependently decreased. Norepinephrine levels in the hypothalamus and frontal cortex were slightly decreased by I-893. I-893 potentiated the rate of alpha-methyl-p-tyrosine-induced depletion of dopamine and norepinephrine. The 3-methoxytyramine content in animals treated with pargyline was increased by I-893 in the caudate nucleus and olfactory tubercle. NSD-1015-induced accumulation of DOPA was suppressed by larger doses of I-893. Oral administration of I-893 (10-50 mg/kg/day) for 14 days slightly attenuated the inhibitory effects of the drug on the norepinephrine level, while it did not affect the inhibitory effect on the dopamine level. These results suggest that I-893 facilitates the release of dopamine and norepinephrine and/or inhibits the uptake of the monoamines in the presynaptic nerve terminals.

Inhibition of vestibular nerve activity by efferent fibres in the cat

Electrophysiological studies were performed in anesthetized cats to examine the role of the parvocellular reticular nucleus (PCRN) in vestibular afferent fibers originating in the horizontal semicircular canal. When the primary afferent fibres intra-axonally recorded in the brainstem were classified into regular, intermediate, and irregular types, repetitive stimuli over 100 Hz applied to the PCRN inhibited spontaneous firing and the increase in firing during horizontal rotation in irregular and intermediate type units, whereas in regular type units PCRN stimulation affected neither the spontaneous firing nor rotation-induced responses. These results strongly suggest that the PCRN stimulation inhibits the primary afferent terminals of irregular type units receiving impulses from type I hair cells of the ampullae.

Coexistence of inhibitory dopamine D-1 and excitatory D-2 receptors on the same caudate nucleus neurons

Microiontophoretic studies using cats anesthetized with alpha-chloralose were performed to determine whether or not dopamine D-1 and D-2 receptors co-exist in the same caudate nucleus (CN) neurons that receive inputs from the substantia nigra (SN), and in which spikes elicited by SN stimulation were blocked by domperidone, a selective D-2 antagonist. Iontophoretic application of dopamine produced a dose-dependent inhibition of spontaneous firing in 2 of 4 spontaneously active CN neurons and an increase in firing in the remaining 2 neurons. However, dopamine inhibited the glutamate-induced firing in 31 of 32 CN neurons that were not spontaneously active. Similar inhibition with iontophoretically applied SKF 38393, a selective D-1 agonist, was observed in 33 of 34 spontaneously inactive neurons tested. When the effects of dopamine, SKF 38393 and bromocriptine (D-2 agonist) were examined on the same CN neurons, the inhibitory effects of both dopamine and SKF 38393 were seen in 14 of 15 neurons, and both an inhibition by SKF 38393 and an excitation by bromocriptine were observed in 15 of 17 neurons. The inhibitory effects of dopamine and SKF 38393 were antagonized by haloperidol and SCH 23390 (D-1 antagonist) without being affected by domperidone. Furthermore, the dopamine-induced inhibition was converted to an excitation during simultaneous application of SCH 23390 in 6 of 10 CN neurons, and this excitation was antagonized by domperidone. These results strongly suggest that the inhibitory D-1 and excitatory D-2 receptors co-exist on the same CN neurons receiving inputs from the SN.

Acute effects of methamphetamine applied microiontophoretically to nucleus accumbens neurons in rats

Microiontophoretic studies were performed to elucidate the acute effects of methamphetamine on the nucleus accumbens (Acc) neurons receiving input from the parafascicular nucleus (Pf) of the thalamus using rats anesthetized with chloral hydrate. Spike generation upon Pf stimulation was inhibited by conditioning stimuli applied to the ventral tegmental area (VTA), which is rich in dopamine-containing neurons, and by iontophoretic application of methamphetamine as well as dopamine. The VTA-, methamphetamine- and dopamine-induced inhibition of the spikes elicited by Pf stimulation was antagonized during simultaneous application of haloperidol. Glutamate-induced firing was also inhibited during iontophoretic application of methamphetamine and dopamine in neurons receiving input from the Pf, and the inhibition was blocked by simultaneously applied haloperidol. In the reserpine-treated animals, however, the Pf-induced spikes were not affected by methamphetamine, but inhibited by dopamine. These results indicate that methamphetamine inhibits the Acc neurons receiving input from the Pf, probably by releasing dopamine from dopaminergic nerve terminals from the VTA.

Solubilization and separation of ethacrynic acid (EA) highly sensitive and EA less sensitive Mg2+-ATPases in the rat brain

Rat brain microsomal Mg2+-ATPases with two distinct activities: ethacrynic acid (EA) highly sensitive and EA less sensitive Mg2+-ATPase activities were solubilized by the combined treatment with 10 mM 3-(3-chlolamidopropyl)-dimethylammonio-1-propane-sulfate (CHAPS) and 30 mM octyl-beta-D-glucoside. The solubilized enzymes had properties similar to those of the membrane-bound enzyme in microsomes with respect to the sensitivity to EA and Cl-, although the optimal pH and the affinity to ATP were slightly altered after the solubilization. Fast protein liquid chromatography of the solubilized enzymes on an anion-exchanger (Mono Q) column with a linear NaCl gradient (0-1.0 M) yielded separate peaks for EA highly sensitive and EA less sensitive Mg2+-ATPase activities at 0.1 and 0.35 M NaCl, respectively. Polyacrylamide gradient gel electrophoresis of the samples from the peak-fractions of EA highly sensitive and EA less sensitive Mg2+-ATPase activities yielded prominent bands at 600 and 70 kDa, respectively. These results indicate that EA highly sensitive Mg2+-ATPase is solubilized and separated from EA less sensitive Mg2+-ATPase as a large enzyme molecule with anion-sensitive sites.

A new model of petit mal epilepsy: spontaneous spike and wave discharges in tremor rats

A mutant rat, which was found in a colony of Kyoto:Wistar rats and genetically defined as a tremor rat (tm/tm), developed tremor of the whole body at 2 weeks of age but the tremor gradually disappeared between 6 and 8 weeks of age. The electroencephalogram (EEG) recorded using chronically implanted electrodes showed a 5-7 Hz (mostly 6 Hz) spike and wave complex synchronously in the cerebral cortex and hippocampus accompanied by absence-like seizure in all six tremor rats examined. The spike and wave complex appeared 0.8-1.9 times per minute and lasted for 1-17 s. However, normal EEG activity was observed in the intervening periods, free of absence-like seizure. Thus the tremor rat is considered to be a possible model for studying the pathogenesis and therapy of petit mal epilepsy in humans.

Characteristics of ethacrynic acid highly sensitive Mg2+-ATPase in microsomal fractions of the rat brain: functional molecular size, inhibition by SITS and stimulation by Cl-

Studies were performed to characterize ethacrynic acid (EA) highly sensitive Mg2+-ATPase isolated from microsomal fractions of the rat brain. The functional molecular sizes of the EA highly sensitive and EA less sensitive Mg2+-ATPases, estimated by a radiation inactivation method, were 480 and 80 kDa, respectively. An anion transport inhibitor, 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS) inhibited the EA highly sensitive Mg2+-ATPase activity. The type of inhibition was uncompetitive with respect to ATP, and the inhibition was suppressed by anions such as Cl-, Br- and I-. Chloride ions stimulated enzyme activity with an increase in Vmax, but not in Km, for ATP. Anions tested also increased the enzyme activity in the following order of decreasing potency: Cl- greater than Br- greater than CH3COO- = I- greater than SO4(2-) = HCO3- greater than SO3(2-). These results suggest that EA highly sensitive Mg2+-ATPase is a relatively large molecule with anion-sensitive sites that affect the ATP hydrolyzing activity and the SITS binding capacity through anions, with Cl- being the most potent.