Shuji Takaori

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.

Influence of norepinephrine-containing neurons derived from the locus coeruleus on lateral geniculate neuronal activities of cats

Abstract Facilitatory influences of conditioning stimulation of LC on evoked potentials in LGN to OTS were demonstrated in cats. These influences were observed when the stimulating electrode had been placed in areas histologically ascertained as having NE-containing cell bodies. The coeruleus modulation of geniculate potentials was not observed after reserpine pretreatment. However, a rapid recovery of the facilitation was produced by an l -dopa or NE injection. Injection of fusaric acid, a potent dopamine-β-hydroxylase inhibitor, also decreased the LC effects. In these cats, only an intraventricular NE injection was effective for the coeruleus modulation. The responsiveness of relay neurons to OTS, studied by extracellular recordings, was also enhanced y LC stimulation. Type-A interneurons, which responded to both orthodromic and antidromic stimulation, received influences similar to those on relay neurons after LC stimulation. Type-B interneurons, which failed to respond by antidromic spike discharges, received depressive effects. In reserpine-pretreated cats, LC effects on neuronal activities in the LGN were not observed. In these cats, l -dopa injection was effective in restoring the coeruleus modulation. It is suggested from these findings that enhanced responsiveness of relay neurons is due to an inhibitory effect on type-B interneurons after activation of NE-containing neurons derived from the LC.

Effects of Antiepileptic Drugs on Absence‐Like and Tonic Seizures in the Spontaneously Epileptic Rat, a Double Mutant Rat

Summary: 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: zilzil, tm/tm,), a double mutant rat, which was obtained by mating the tremor hétérozygous animals {tml +) with the zitter homozygous animals (zi/zi), and to détérmine 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 intra‐peritoneally, 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.

Noradrenaline-mediated inhibition by locus coeruleus of spinal trigeminal neurons

Abstract Inhibitory effects of conditioning stimulation of the locus coeruleus (LC) on the neuron activity in spinal trigeminal nucleus (STN) were investigated in gallamine-immobilized cats. Field potentials of STN and spike potentials of single relay neurons in STN were orthodromically elicited by ipsilateral alveolar nerve stimulation and antidromically by stimulation of contralateral medial lemniscus. Conditioning stimuli were applied to LC and sensory cortex (SC) at various C-T intervals. In tracking experiments near the LC region, conditioning stimulation of LC itself produced the most pronounced decrease in amplitude of the STN field potentials. Orthodromic spikes of STN single neurons were significantly reduced by conditioning stimulation of LC as well as SC. In reserpine-treated animals, however, conditioning stimulation of LC failed to produce a decrease in the number of orthodromic spikes, while the inhibitory effect of SC conditioning stimulation remained unaffected. Under these circumstances, intravenous L -dopa and intraventricular noradrenaline reproduced an inhibitory effect of LC conditioning stimulation on orthodromic spike generation, while such an effect was not seen with either dopamine or serotonin. Antidromic spike was unaltered by any of these treatments. Histochemically, catecholamine fluorescence in LC was entirely eliminated after reserpine-treatment, but was restored after L -dopa injection. These results strongly suggest that noradrenaline released from the terminals of neurons originating in LC produces an inhibition of transmission in the STN relay neurons.

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.

Attenuation of morphine analgesia in rats with lesions of the locus coeruleus and dorsal raphe nucleus

The nociceptive reflex activity and analgesic effect of morphine were studied in rats using the hind paw stimulation test. The stimulation threshold was significantly increased in animals with bilateral destruction of the locus coeruleus (LC), and was reduced after lesion of the dorsal raphe nucleus (DR). LC lesions produced a selective lowering of noradrenaline (NA) content in the forebrain, while DR lesions resulted in a reduction in serotonin levels. Lesioning both LC and DR significantly reduced both NA and serotonin contents even when the stimulation threshold was not altered. Morphine produced a significant and dose-dependent elevation of the stimulation threshold in sham-operated animals, while morphine analgesia was almost completely inhibited by destruction of LC, DR and both the nuclei. These results imply that a depression of LC-mediated noradrenergic tone results in a decreased sensitivity to painful stimuli, whereas a reduction of raphe-derived serotonergic tone produces the opposite effect against LC. It is suggested, however, that both of these monoamines from the LC and DR are necessary for the analgesic effect of morphine.

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.

Locus coeruleus-induced inhibition of dorsal cochlear nucleus neurons in comparison with lateral vestibular nucleus neurons.

The effects of conditioning stimulation of the locus coeruleus (LC) on the neuron activity of dorsal cochlear nucleus (DCN), which is rich in noradrenergic nerve terminals, were compared with those on the lateral vestibular nucleus (LVN), devoid of such terminals, to determine whether or not noradrenaline is responsible for the LC-induced inhibition. The conditioning stimuli applied to the LC had no effect on either the field potential or the spike generation of mono- and polysynaptic neurons in the LVN elicited by VIIIth cranial nerve stimulation. In contrast, the spike firing of the DCN neurons with VIIIth cranial nerve stimulation was significantly inhibited by LC conditioning stimulation. The inhibition of spike generation was mainly observed in the DCN neurons which fired spikes with a longer latency. The inhibition of DCN neurons by LC conditioning stimulation did not occur in the cats pretreated with reserpine; however, a rapid recovery of the inhibition was produced by intraventricular application of noradrenaline. These results are in good agreement with the histochemical findings and support our previous conclusion that noradrenaline acts as an inhibitory transmitter or modulator on the nuclei where noradrenergic nerve terminals derived from the LC are located. In addition, the vestibular input in the primary relay nucleus is apparently not regulated by noradrenaline originating in the LC.

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.

Mediation of micturition reflex by central norepinephrine from the locus coeruleus in the cat

We examined whether norepinephrine originating in the locus coeruleus mediates the micturition reflex in anesthetized cats. 6-Hydroxydopamine, a catecholamine neurotoxin, injected bilaterally into the locus coeruleus markedly decreased catecholamine fluorescence in the lesioned area and induced urinary retention after 72 to 84 hr. At this time, there was no or only slight contraction of the urinary bladder induced by its distension, while the contraction was noted before the treatment. However, phenylephrine, an alpha 1-receptor agonist, applied intrathecally in 6-hydroxydopamine-treated animals induced moderate bladder contraction. In sham-operated animals, the bladder contraction on its distension was inhibited by intrathecally applied prazosin, an alpha 1-receptor antagonist. Thus, in the micturition reflex, norepinephrine derived from the locus coeruleus acts on the alpha 1-adrenergic receptors in the sacral cord, and induces urinary bladder contraction via activation of the sacral parasympathetic preganglionic neurons.