Intracranial self-stimulation enhances neurogenesis in hippocampus of adult mice and rats

Running is known to promote neurogenesis. Besides being exercise, it results in a reward, and both of these factors might contribute to running-induced neurogenesis. However, little attention has been paid to how reward and exercise relate to neurogenesis. The present study is an attempt to determine whether a reward, in the form of intracranial self-stimulation (ICSS), influences neurogenesis in the hippocampus of adult rodents. We used bromodeoxyuridine labeling to quantify newly generated cells in mice and rats that experienced ICSS for 1 h per day for 3 days. ICSS increased the number of 5-bromodeoxyuridine (Brdu)-labeled cells in the hippocampal dentate gyrus (DG) of both species. The effect, when examined at 1 day, 1 week, and 4 weeks post-ICSS, was predominantly present in the side ipsilateral to the stimulation, although it was distributed to the contralateral side. We also found in rats that, 4 weeks after Brdu injection, surviving newborn cells in the hippocampal DG of the ICSS animals co-localized with a mature neuron marker, neuronal nuclei (NeuN), and these surviving cells in rats were double-labeled with Fos, a marker of neuronal activation, after the rats had been trained to perform a spatial task. The results demonstrate that ICSS can increase newborn neurons in the hippocampal DG that endure into maturity.

Roles of pedunculopontine tegmental cholinergic receptors in brain stimulation reward in the rat

RATIONALE

The brainstem pedunculopontine tegmental nucleus (PPTg) is proposed to mediate hypothalamic self-stimulation reward via cholinergic activation of the ventral tegmental area (VTA). However, to date there is little direct evidence to support this hypothesis.

OBJECTIVES

To further study the role of PPTg in hypothalamic self-stimulation reward.

METHODS

By using in vivo microdialysis, the levels of extracellular acetylcholine (ACh) in the PPTg and VTA were detected during lateral hypothalamic (LH) self-stimulation in rats. Rate-frequency curve shift procedure was used to evaluate the effects of nonselective muscarinic antagonist scopolamine (1 approximately 100 microg/microl) and nicotinic antagonist mecamylamine (5 approximately 100 microg/microl) microinjected into the PPTg on the rewarding efficacy of LH self-stimulation. Subsequently, the drugs were injected into the PPTg, and the extracellular ACh in the VTA was measured.

RESULTS

LH self-stimulation produced a concurrent ACh release in the PPTg and VTA. Intra-PPTg injection of scopolamine (100 microg/microl) significantly reduced the frequency threshold for LH self-stimulation reward, but nicotinic antagonist mecamylamine did not shift the threshold. However, mecamylamine (10, 25 microg/microl) injected into the PPTg robustly diminished the nicotine-potentiated LH self-stimulation reward. The extracellular ACh in the VTA was dramatically increased by intra-PPTg scopolamine (10, 100 microg/microl), but not by mecamylamine.

CONCLUSIONS

Results confirm that PPTg plays an important role in brain stimulation reward by modulating the cholinergic activity of the VTA. The PPTg muscarinic receptors contribute to an inhibitory modulation of reward effects by self-stimulation, whereas nicotinic receptors seem to be more involved in nicotine potentiation of brain stimulation reward.

Intracranial self-stimulation induces Fos expression in GABAergic neurons in the rat mesopontine tegmentum

The cholinergic neurons which originate in the mesopontine tegmentum and innervate the midbrain ventral tegmental area have been proposed to play a key role in intracranial self-stimulation reward. This mesopontine area also contains GABA neurons. Detailed information is still lacking, however, about the relationship of cholinergic and GABAergic neurons in this region to self-stimulation reward. Therefore, using double immunostaining for Fos as a marker of neuronal activity and choline acetyltransferase as a marker of cholinergic neurons, or for Fos and GABA, we investigated whether self-stimulation of the medial forebrain bundle induces Fos expression within cholinergic and GABAergic neurons in two regions of the mesopontine tegmentum, i.e., pedunculopontine tegmental nucleus and laterodorsal tegmental nucleus. Self-stimulation of the medial forebrain bundle for 1 h induced a large increase in the number of cells expressing Fos in both the pedunculopontine tegmental nucleus and laterodorsal tegmental nucleus, when compared to control brains. However, the self-stimulation-induced expression of Fos was restricted mostly to GABA-, but not choline acetyltransferase-, immunostained cells. We also examined, using microdialysis, whether self-stimulation increases acetylcholine efflux in the ventral tegmental area, a terminal region of the mesopontine tegmentum cholinergic pathway. One hour of self-stimulation significantly increased acetylcholine efflux from this terminal area. These results indicate that intracranial self-stimulation of the medial forebrain bundle may increase acetylcholine release without affecting expression of Fos in cholinergic neurons, while the same stimulation may induce Fos expression in GABAergic neurons of the mesopontine tegmentum. GABAergic as well as cholinergic neurons in this area appear to be activated by self-stimulation reward in the medial forebrain bundle.

Immunohistochemical characterisation of Fos-positive cells in brainstem monoaminergic nuclei following intracranial self-stimulation of the medial forebrain bundle in the rat

Fos immunostaining was used as a marker of neuronal activity following intracranial self-stimulation (ICSS) of the medial forebrain bundle (MFB) in the rat, and was combined with immunostaining for tyrosine hydroxylase (TH), serotonin (5-HT), gamma-aminobutyric acid (GABA), or NR1 (one of the glutamate N-methyl- D-aspartate receptor subunits) for purposes of neurochemical identification. ICSS induced a significant but different degree of increase in the number of Fos-immunopositive (Fos+) cells in the six brainstem monoaminergic nuclei examined, which included the ventral tegmental area (VTA), substantia nigra pars compacta (SNc), dorsal raphe nucleus (DR), median raphe nucleus (MR), locus coeruleus (LC), and A7 noradrenaline cells. Densely labelled Fos+ cells were observed in the LC following ICSS, and many of these Fos+ cells were colocalized with TH. Similarly, many of Fos+ cells in the A7 and DR/MR were colocalized with TH and 5-HT, respectively. By contrast, a smaller number of Fos+ cells was detected in the VTA and SNc following the ICSS, and in these regions the majority of Fos+ cells were not colocalized with TH. Although results among regions quantitatively differed, the ICSS induced a significant increase in the number of double-labelled cells (GABA+/Fos+ or NR1+/Fos+) in all of the VTA, DR, and LC, in which the ICSS produced an ipsilaterally weighted increase in Fos-like immunoreactivity. These results suggest that ICSS of the MFB induces differential Fos expression within monoaminergic and GABAergic neurons in brainstem monoaminergic nuclei under modulation by glutamatergic afferents.

Pigmented villonodular synovitis of the ankle in an adolescent

We report a case of pigmented villonodular synovitis (PVNS) in an adolescent with monarticular involvement of the ankle and without congenital anomalies or sibling involvement.

Intracranial self-stimulation increases differentially in vivo hydroxylation of tyrosine but similarly in vivo hydroxylation of tryptophan in rat medial prefrontal cortex, nucleus accumbens and striatum

We have examined using microdialysis the effect of intracranial self-stimulation (ICSS) on the in vivo hydroxylation rate of tyrosine and tryptophan in the medial prefrontal cortex (mPFC), nucleus accumbens (NAC) and striatum (STR). A decarboxylase inhibitor NSD-1015 was included in the perfusate, which enabled the simultaneous measurement of 3,4-dihydroxyphenylalanine (DOPA) and 5-hydroxytryptophan (5-HTP) as an index of the in vivo hydroxylation level of tyrosine and tryptophan. When rats were exposed to 1 h of ICSS at the medial forebrain bundle (MFB), their extracellular levels of DOPA significantly increased in the mPFC, NAC and STR, but with a different magnitude and time course. The same stimulation produced a delayed increase in extracellular 5-HTP, compared to DOPA, in these brain regions. The profile of 5-HTP response demonstrated no apparent difference among the regions. These findings indicate that ICSS of the MFB can increase differentially the in vivo hydroxylation of tyrosine but similarly the in vivo hydroxylation of tryptophan in the mPFC, NAC and STR.

Lack of glucocorticoids attenuates the self-stimulation-induced increase in the in vivo synthesis rate of dopamine but not serotonin in the rat nucleus accumbens

Our previous study demonstrated that intracranial self-stimulation of the medial forebrain bundle can increase the in vivo synthesis turnover rate of dopamine (DA) and serotonin (5-HT) in the nucleus accumbens of adrenal-intact rats. The present study examined using microdialysis whether such increases in DA and 5-HT syntheses are influenced by adrenal hormones, which are also activated following intracranial self-stimulation. A decarboxylase inhibitor, NSD-1015, was perfused through reversed microdialysis which enabled the simultaneous measurement of 3,4-dihydroxyphenylalanine (DOPA) and 5-hydroxytryptophan (5-HTP) as an index of the in vivo turnover rate of DA and 5-HT syntheses. Adrenalectomy (ADX) attenuated significantly the self-stimulation-induced increase in dialysate levels of DOPA but not 5-HTP. Corticosterone (Cort) replacement reversed the attenuation in DOPA levels in adrenalectomized rats. The finding indicates that activation of DA synthesis in vivo in the nucleus accumbens during intracranial self-stimulation is dependent on, whereas that of 5-HT synthesis is independent of glucocorticoid modulation.

Modest neuropsychological deficits caused by reduced noradrenaline metabolism in mice heterozygous for a mutated tyrosine hydroxylase gene

Tyrosine hydroxylase (TH) is the initial and rate-limiting enzyme for the biosynthesis of catecholamines that are considered to be involved in a variety of neuropsychiatric functions. Here, we report behavioral and neuropsychological deficits in mice carrying a single mutated allele of the TH gene in which TH activity in tissues is reduced to approximately 40% of the wild-type activity. In the mice heterozygous for the TH mutation, noradrenaline accumulation in brain regions was moderately decreased to 73-80% of the wild-type value. Measurement of extracellular noradrenaline level in the frontal cortex by the microdialysis technique showed a reduction in high K(+)-evoked noradrenaline release in the mutants. The mutant mice displayed impairment in the water-finding task associated with latent learning performance. They also exhibited mild impairment in long-term memory formation in three distinct forms of associative learning, including active avoidance, cued fear conditioning, and conditioned taste aversion. These deficits were restored by the drug-induced stimulation of noradrenergic activity. In contrast, the spatial learning and hippocampal long-term potentiation were normal in the mutants. These results provide genetic evidence that the central noradrenaline system plays an important role in memory formation, particularly in the long-term memory of conditioned learning.

Differential effect of immobilization stress on in vivo synthesis rate of monoamines in medial prefrontal cortex and nucleus accumbens of conscious rats

We have used microdialysis to measure the in vivo hydroxylation level of tyrosine and tryptophan in the medial prefrontal cortex and nucleus accumbens of conscious rats that were subjected to immobilization. The brain was perfused with an inhibitor of aromatic L-amino acid decarboxylase, 3-hydroxybenzylhydrazine, and the amount of 3,4-dihydroxyphenylalanine (DOPA) and 5-hydroxytryptophan (5-HTP) accumulating in the dialysate was measured as an index of the in vivo hydroxylation rate of tyrosine and tryptophan. One hour of immobilization caused a significant increase in extracellular DOPAin the medial prefrontal cortex but not nucleus accumbens. The same manipulation produced a significant and more prolonged elevation in extracellular 5-HTP in the nucleus accumbens as well as medial prefrontal cortex. The observed profile of stress-induced 5-HTP response was comparable in two brain regions. The results suggest that in vivo catecholamine synthesis is heterogenous, whereas in vivo serotonin synthesis is homogenous, with respect to responsiveness to stress in the medial prefrontal cortex and nucleus accumbens.

Regional differences in desensitization of c-Fos expression following repeated self-stimulation of the medial forebrain bundle in the rat

The acute self-stimulation of the medial forebrain bundle was reported to induce the expression of c-Fos, the protein product of c-fos, an immediate early gene, in the central nervous system. In the present study, we examined regional changes in c-Fos expression in several reward-related areas of rat brain in response to short- and long-term exposure to self-stimulation of the medial forebrain bundle. Short-term one-hour stimulation of the medial forebrain bundle for one day after training, which evoked steady self-stimulation behavior, significantly increased the number of c-Fos-positive neurons bilaterally in all of 15 brain structures assayed, as compared to the non-stimulation control. Among them, structures showing a larger number of the stained neurons on the stimulated side were the anterior olfactory nucleus, amygdala, medial caudate-putamen complex, lateral septum, bed nucleus of the stria terminals, ventral pallidum, substantia innominata, lateral preoptic area, medial preoptic area, lateral hypothalamus rostral to the stimulating electrodes, and substantia nigra. Long-term stimulation of the medial forebrain bundle once daily for five successive days, which maintained consistently stable self-stimulation behavior, also increased the number of c-Fos-positive neurons in the aforementioned structures, as compared to the control. However, the long-term rewarding stimulation diminished the increased number of labeled neurons, as compared to the short-term rewarding stimulation. Seven areas, medial caudate-putamen complex, ventral pallidum, substantia innominata, lateral preoptic area, medial preoptic area, rostral lateral hypothalamus and substantia nigra, showed asymmetrical, ipsilateral predominance after the short- and long-term stimulation. However, the stained neuron count in those areas after the long-term stimulation was reduced to less than 50% of that found after the short-term stimulation with the exception of lateral preoptic area and rostral lateral hypothalamus. The results suggest that the development of desensitization of c-Fos response may differ among the reward-relevant brain regions as a consequence of repeated self-stimulation. They also indicate that a larger portion of neurons in the lateral preoptic area and rostral lateral hypothalamus may be implicated in both short- and long-term self-stimulations of the medial forebrain bundle.

Generation of reactive oxygen species accounts for cytotoxicity of an endogenous dopaminergic neurotoxin, (R)-N-methylsalsolinol, to differentiated dopaminergic SH-SY5Y cells

The mechanism of the cytotoxicity of endogenous dopamine-derived (R)-1,2-dimethyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline [(R)-N-methylsalsolinol] to differentiated human dopaminergic neuroblastoma SH-SY5Y cells was studied using a reduction-oxidation indicator, Alamar Blue. N-Methylsalsolinol and its oxidation product, 1,2-dimethyl-6,7-dihydroxyisoquinolinium ion, were found to inhibit oxidative phosphorylation, as shown by the Redox capacity. Antioxidants, such as reduced glutathione, catalase, Tris and n-propyl gallate, reduced the cytotoxicity of N-methylsalsolinol, suggesting that hydroxyl radical was the major reactive oxygen species for the cytotoxicity. Deprenyl also protected the cells from the decrease of the Redox capavity by N-methylsalsolinol. However, antioxidants did not protect the cells from the cytotoxicity of the catechol isoquinolinium ion. The results suggest that oxidative stress induced by hydroxyl radical may be involved in the cell death of dopaminergic neurons by N-methylsalsolinol.

Characterization of beta-phenylethylamine-induced monoamine release in rat nucleus accumbens: a microdialysis study

In vivo microdialysis was used to investigate the effect of beta-phenylethylamine on extracellular levels of monoamines and their metabolites in the nucleus accumbens of conscious rats. At all doses tested (1, 10 and 100 microM), infusion of beta-phenylethylamine through the microdialysis probe significantly increased extracellular levels of dopamine in the nucleus accumbens. These increases were dose-related. The increase in dopamine levels induced by 100 microM beta-phenylethylamine was not affected by co-perfusion of 4 microM tetrodotoxin. The ability of 100 microM beta-phenylethylamine to increase the extracellular level of dopamine was comparable to that of the same dose of methamphetamine. On the other hand, beta-phenylethylamine had a much less potent enhancing effect on 5-hydroxytryptamine (5-HT) than dopamine levels. Only the highest dose (100 microM) caused a statistically significant effect on 5-HT levels. Over the dose range tested (1, 10 and 100 microM), beta-phenylethylamine had no effect on extracellular metabolite levels of dopamine and 5-HT. The results suggest that beta-phenylethylamine increases the efflux of monoamines, preferentially dopamine, without affecting monoamine metabolism, in the nucleus accumbens.

Cytotoxicity of endogenous isoquinolines to human dopaminergic neuroblastoma SH-SY5Y cells

Endogenous isoquinolines with and without catechol structure have been proposed to be neurotoxins specific for dopamine neurons. In this paper they were examined for the cytotoxicity of human dopaminergic neuroblastoma SH-SY5Y cells. The cytotoxicity was quantitatively determined using Alamar Blue assay, by which the reduction-oxidation potency in the living cells can be measured spectrometrically. 1,2-Dimethyl-6,7-dihydroxyisoquinolinium ion [1,2-DMDHIQ+], an oxidation product of a parkinsonism-inducing isoquinoline, 1(R),2(N)-dimethyl-6,7-dihydroxy-1,2,3,4-tetrahroisoquinoline [N-methyl-(R)salsolinol, NM(R)Sal] was found to be the most potent toxin among isoquinolines examined. In general, catechol isoquinolines were more toxic than isoquinolines without catechol structure. With and without catechol structure, the oxidized isoquinolinium ion having methyl groups at C-1 and N-2 positions proved to be more cytotoxic than the simple isoquinolines. The involvement of 1,2-DMDHIQ+ to the neurotoxicity of NM(R)Sal was suggested and discussed.

Dopamine-derived endogenous 1(R),2(N)-dimethyl-6,7-dihydroxy- 1,2,3,4-tetrahydroisoquinoline, N-methyl-(R)-salsolinol, induced parkinsonism in rat: biochemical, pathological and behavioral studies

Dopamine-derived 1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (salsolinol, Sal) and related compounds were examined for their selective neurotoxicity to dopamine neurons by injection into the rat striatum. Among salsolinol analogs examined, only N-methyl-(R)- salsolinol (NM(R)Sal) induced behavioral changes very similar to those in Parkinson's disease: hypokinesia, stiff tail, limb twitching at rest and postural abnormality. Biochemical analysis showed that after NM(R)Sal injection, NM(R)Sal itself and its oxidation product, 1-2-dimethyl-6,7-dihydroxyisoquinolinium ion (DMDHIQ+) accumulated in the striatum, and also in the substantia nigra definite amount of DMDHIQ+ was detected. Dopamine and noradrenaline were reduced in the striatum and more markedly in the substantia nigra, whereas serotonin and its metabolite were not affected. Morphological analysis revealed selective reduction of tyrosine hydroxylase (TH)-containing neurons in the substantia nigra after continuous NM(R)Sal administration in the striatum. These results demonstrate the selective cytotoxicity of NM(R)Sal to the dopamine neurons in the substantia nigra, and the possible involvement of this 6,7-dihydroxy-isoquinoline in the pathogenesis of Parkinson's disease is discussed.

Effects of moclobemide on forced-swimming stress and brain monoamine levels in mice

Moclobemide [Ro 11-1163, p-chloro-N-(2-morpholinoethyl)benzamide, AURORIX] is known as an antidepressant and a reversible inhibitor of type A monoamine oxidase. In the present study, a forced swimming test was applied to mice to evaluate behavioral and neurochemical effects of this drug. During forced swimming posture of immobility, a typical behavioral change, was observed, and biochemical analysis of the brain revealed significant changes in the monoamine levels. The norepinephrine concentration was reduced, while that of its product was increased, indicating increase in norepinephrine turnover. The stress increased the levels of dopamine, serotonin, and their metabolites. Moclobemide significantly improved the immobility elicited by the test, and it could prevent the changes in the turnover of norepinephrine, dopamine, and serotonin induced by the stress. These results suggest that moclobemide may improve the behavioral changes induced by the forced swimming through its effects on monoamine metabolism.

N-methyl-4-phenylpyridinium and an endogenously formed analog, N-methylated beta-carbolinium, inhibit striatal tyrosine hydroxylation in freely moving rats

The effects of N-methyl-4-phenylpyridinium (MPP+) and its endogenous analog, 2,9-di-methyl-norharmanium (2,9-Me2NH+), on in vivo tyrosine hydroxylation were evaluated in freely moving rats. MPP+ gradually but almost completely reduced tyrosine hydroxylation, even at a dose as low as 0.05 mM. This effect was considered to be caused by the inhibition of tyrosine hydroxylase (TH) activation. On the contrary, 1 mM 2,9-Me2NH+ rapidly reduced 3,4-dihydroxyphenylalanine production to 10% of the basal level only during its perfusion, indicating direct inhibition of TH activity. The present study revealed that MPP+ and 2,9-Me2NH+ were taken up into dopaminergic neurons and then inhibited in vivo dopamine synthesis prior to cell death possibly in different manners.

Toluene induces behavioral activation without affecting striatal dopamine metabolism in the rat: behavioral and microdialysis studies

We examined the effects of toluene on the release of dopamine (DA) and its metabolites in rat striatum using microdialysis. Intraperitoneal injection of 800 mg/kg toluene significantly increased motor activity in rats, as did methamphetamine (MAP) (1 mg/kg). However, 800 mg/kg toluene did not affect the extracellular levels of DA, 3,4-dihydroxyphenylacetic acid, homovanillic acid, or 5-hydroxyindoleacetic acid. This is in contrast to MAP, which significantly increased extracellular DA and decreased the extracellular levels of its metabolites. These results suggest that toluene-induced behavioral augmentation may not be associated with alterations in DA or serotonin neurochemistry such as are associated with MAP-induced behavioral augmentation.

Biochemical and immunocytochemical changes induced by intrastriatal 6-hydroxydopamine injection in the rat nigrostriatal dopamine neuron system: evidence for cell death in the substantia nigra

Biochemical and immunocytochemical changes after unilateral 6-hydroxydopamine (6-OHDA) injection into the striatum were investigated in the rat nigrostriatal dopamine (DA) neuron system. Four weeks after 6-OHDA injection into the striatum, concentrations of DA and its metabolites were specifically decreased in the substantia nigra (SN), as well as in the striatum, ipsilateral to the injection. Immunocytochemistry of tyrosine hydroxylase (TH) revealed a marked decrease in the number of TH-immunoreactive neuronal cell bodies in the SN ipsilateral to the injection; this effect appeared 2 weeks after the injection and remained even 10 months after the injection. Electron microscopic study of these periods demonstrated degenerative neurons in the SN pars compacta, suggesting that the degenerative changes persisted for a long time after a single injection of 6-OHDA into the striatum. The results showed that degeneration of the dopaminergic terminals in the striatum may lead to cell death of the parent cell bodies in the SN and suggest that the striatum may be the initial site in which the neurodegeneration occurs in Parkinson's disease.

Peripherally administered (6R)-tetrahydrobiopterin increases in vivo tyrosine hydroxylase activity in the striatum measured by microdialysis both in normal mice and in transgenic mice carrying human tyrosine hydroxylase

The intraperitoneal administration of (6R)-L-erythro-5,6,7,8-tetrahydrobiopterin (6R-BH4), the natural cofactor of tyrosine hydroxylase (TH), increased the accumulation of L-3,4-dihydroxyphenylalanine (DOPA) measured using microdialysis under the inhibition of aromatic L-amino acid decarboxylase by NSD-1015 (in vivo TH activity) in the striatum both of transgenic mice carrying human TH gene and of non-transgenic mice, to a similar extent by about 4-fold. The results indicate that the peripherally administered 6R-BH4 activates in vivo TH activity in the nigrostriatal dopamine neurons in both non-transgenic and transgenic mice.

Characterization of the in vivo action of (R)-salsolinol, an endogenous metabolite of alcohol, on serotonin and dopamine metabolism: a microdialysis study

Using a microdialysis-HPLC technique in conscious rats, we examined the action of (R)-1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline, (R)-salsolinol (R-Sal), a possible endogenous metabolite of alcohol, on serotonin (5-HT) and dopamine (DA) metabolism in four regions of the brain: the striatum, the substantia nigra, the hippocampus and the hypothalamus. Following 1 mM R-Sal perfusion, the dialysate level of 5-HT in the striatum markedly increased from non-detectable levels to 4259.2 +/- 617.5 nM, while DA increased from 3.4 +/- 0.9 nM to 206.0 +/- 56.5 nM. This increase was one order of magnitude larger in 5-HT than in DA. Conversely, the output of 5-hydroxyindoleacetic acid decreased markedly to non-detectable levels, while 3,4-dihydroxyphenylacetic acid and homovanillic acid outputs decreased below 40% of basal levels. These effects were dose-related to R-Sal (1 microM to 1 mM) and were confirmed also in 3 other brain regions. The R-Sal-induced responses in the striatum were observed even after pretreatment of 2 microM tetrodotoxin, a blocker of nerve-firing activity, via the dialysis membrane. The repetitive perfusion with 1 mM R-Sal into the striatum induced the reproducible response of 5-HT and DA. Furthermore, the potencies of 1 mM R-Sal to increase the output of 5-HT and DA were approximately 783.0-fold and 2.6-fold stronger, respectively, than those of the same dose of methamphetamine. The results suggest that R-Sal acts to stimulate a release of monoamines, 5-HT preferentially, with inhibition of monoamine oxidase and catechol-O-methyltransferase activities.

Endogenous synthesis of N-methylnorsalsolinol in rat brain during in vivo microdialysis with epinine

The in vivo metabolic pathway for the synthesis of N-methylnorsalsolinol, an analogue of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), was studied in the rat brain. N-Methyldopamine (epinine) was perfused at the striatum of the rat brain by in vivo microdialysis. N-Methylnorsalsolinol (NMNSAL) was identified in the brain dialysate after epinine perfusion using gas chromatography-selected-ion monitoring mass spectrometry (GC-SIM-MS). We demonstrated that NMNSAL could be synthesized from epinine with an aldehyde by the Piclet-Spengler condensation reaction in the rat brain.

A new metabolic pathway of L-threo-3,4-dihydroxyphenylserine, a precursor amino acid of norepinephrine, in the brain. Studies by in vivo microdialysis

The metabolism and the effects of L-threo-3,4-dihydroxyphenylserine (L-threo-DOPS) were studied in the rat brain striatum by in vivo microdialysis. In the brain L-threo-DOPS was metabolized by 3 different enzymes; aromatic L-amino acid decarboxylase, catechol-O-methyltransferase, and DOPS-aldolase. DOPS-aldolase was the main enzyme which metabolizes L-threo-DOPS. The amounts of the metabolites by L-amino acid decarboxylase (norepinephrine and its metabolites) were 0.4% of the total amounts of metabolites detected in the dialysate, while those by catechol-O-methyltransferase, 2.1%, and by DOPS-aldolase, 97.5%, after 100 min perfusion of L-threo-DOPS. L-threo-DOPS was found to increase extracellular levels of dopamine and serotonin, and to inhibit monoamine catabolism in the brain. Inhibition of DOPS-aldolase should improve its effectiveness as the supplement therapy of norepinephrine.

Simultaneous determination of in vivo hydroxylation of tyrosine and tryptophan in rat striatum by microdialysis-HPLC: relationship between dopamine and serotonin biosynthesis

Using a microdialysis technique, the rat striatum was perfused with NSD-1015, an inhibitor of aromatic L-amino acid decarboxylase, and the amount of L-3,4-dihydroxyphenylalanine (L-DOPA) and 5-hydroxytryptophan (5-HTP) accumulating in dialysate was measured as an index of in vivo activities of tyrosine hydroxylase and tryptophan hydroxylase. NSD-1015 increased the concentration of L-DOPA much higher than that of 5-HTP in a dose-related manner (1-100 mumol/L). In order to examine the relationship between dopaminergic and serotonergic neurons in the striatum, either 5-HTP or L-DOPA was injected intraperitoneally to rats pretreated with benserazide, an inhibitor of peripheral decarboxylase. 5-HTP administration increased 5-HTP, but decreased L-DOPA in a dose-dependent manner. Conversely, 5-HTP concentration decreased in an association with the increased content of L-DOPA following L-DOPA administration. The decrease of 5-HTP caused by L-DOPA administration was not as remarkable as that of L-DOPA by 5-HTP injection. These results suggest that L-DOPA and 5-HTP, the precursor amino acids for catecholamines and indoleamines, could affect mutually each other neuronal activity through the inhibition of their rate-limiting enzymes.

Changes in monoamine levels in mouse brain elicited by forced-swimming stress, and the protective effect of a new monoamine oxidase inhibitor, RS-8359

As a stress model, a forced swimming test was applied to mice; and a typical behavioral change, an immobile posture, was recognized. This affected the brain monoamine levels significantly. The norepinephrine concentration was reduced, while that of its product was increased; and in the case of dopamine, both the amount of the amine and its product were increased. Stress increased the levels of serotonin and its product in the brain. The effects of RS-8359, (+/-)-4-(4-cyanophenyl)amino-6,7-dihydro-7-hydroxy-5H-cyclopenta[d ]- pyrimidine, a new inhibitor of type A monoamine oxidase, on the behavioral and biochemical changes caused by forced swimming were also investigated. RS-8359 significantly improved the immobile posture elicited by the forced swimming test. It reduced the increased turnover of norepinephrine and serotonin systems caused by swimming. These results suggest that the effect of RS-8359 on behavioral and biochemical changes by stress may be mainly due to its effects on norepinephrine and serotonin systems, presumably by the inhibition of type A monoamine oxidase.

Normalization of tyrosine hydroxylase activity in vivo in the striatum of transgenic mice carrying human tyrosine hydroxylase gene: a microdialysis study

Using a microdialysis method, we observed a similar steady-state L-3,4-dihydroxyphenylalanine accumulation in the striatum of transgenic mice carrying the human tyrosine hydroxylase (TH) gene after NSD-1015 perfusion (10(-4) M) as compared to nontransgenic mice. Basal extracellular levels of 3,4-dihydroxyphenylacetic acid before the perfusion of NSD-1015 were also comparable in both transgenic and non-transgenic striata. The results suggest that the in vivo activity of TH in the striatum of transgenic mice was retained to the normal level by some regulatory mechanism(s) in spite of the increased expression of the enzyme protein.

Naturally-occurring isoquinolines perturb monamine metabolism in the brain: studied by in vivo microdialysis

Naturally occurring isoquinolines affected the monoamine metabolism in the rat striatum, as proved by in vivo microdialysis technique. By analysis of monoamines and their metabolites in the dialysate, dopamine-derived 6,7-dihydroxy-1,2,3,4-tetrahydroisoquinolines were found to inhibit monoamine oxidase and catechol-O-methyltransferase activity. 1-Methyl- and 2-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline were found to inhibit activity of type A monoamine oxidase most markedly. To compare the structure-activity relationship, corresponding isoquinolines without a catechol structure were also examined. The inhibition by catechol isoquinolines was more manifest than those without a catechol structure. Among latter isoquinolines, N-methyl-isoquinolinium ion was the most potent inhibitor of monoamine oxidase. In addition, catechol isoquinolines increased monoamine levels in the brain. The number and the site of the methyl group are essentially required for the inhibition of monoamine oxidase and a catechol structure for that of catechol-O-methyl-transferase. These results are discussed in relation to possible involvement of these isoquinolines to the clinical features of some neuro-psychiatric diseases, such as alcoholism or in L-DOPA therapy.

The mechanism of perturbation in monoamine metabolism by L-dopa therapy: in vivo and in vitro studies

In the cerebrospinal fluid of the patients with Parkinson's disease treated with L-DOPA, L-3-O-methyldopa was the major metabolite of administered L-DOPA. Using a dopaminergic cell model, clonal rat phenochromocytoma PC 12h cells, and by microdialysis of the rat striatum it was proved that L-3-O-methyldopa was taken up into monoamine neurons by transport system specific for aromatic L-amino acids and inhibited transport of L-DOPA and other amino acids competitively. L-3-O-Methyldopa depleted allosteric regulation of the biopterin cofactor on activity of tyrosine hydroxylase, the rate-limiting enzyme of catecholamine synthesis. Depletion of the allostery may perturb the buffer action of endogenous L-DOPA synthesis that stabilizes dopamine level in the brain. By these mechanisms L-3-O-methyldopa may reduce clinical effectiveness of administered L-DOPA and be involved in wearing-off phenomenon. L-DOPA inhibited the activity of tryptophan hydroxylase and thus serotonin synthesis, which may be related to psychiatric side-effects in the patients under L-DOPA therapy.

Selective release of serotonin by endogenous alkaloids, 1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinolines, (R)- and (S)salsolinol, in the rat striatum; in vivo microdialysis study

Dopamine-derived 1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinolines, (R)- and (S)salsolinol, released an enormous amount of serotonin in the rat striatum; the concentration of serotonin increased from undetectable level to 2.53 +/- 0.12 and 3.69 +/- 0.01 microM after perfusion of (R)- and (S)salsolinol, respectively. Salsolinols increased extracellular dopamine level, but to a much lesser degree than serotonin. Other naturally occurring isoquinolines with catechol structure released serotonin and dopamine, but salsolinols were the most potent and selective releaser of serotonin. Serotonin release by salsolinols may be involved in some psychiatric symptoms in L-DOPA therapy or alcoholism.

N-methylation of dopamine-derived 6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline, (R)-salsolinol, in rat brains: in vivo microdialysis study

N-Methylation of (R)-1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline [(R)-salsolinol] derived from dopamine was proved by in vivo microdialysis study in the rat brain. The striatum was perfused with (R)-salsolinol and N-methylated compound was identified in the dialysate using HPLC and electrochemical detection with multichanneled electrodes. N-Methylation of (R)-salsolinol was confirmed in three other regions of the brain, the substantia nigra, hypothalamus, and hippocampus. In the substantia nigra, the amount of N-methylated (R)-salsolinol was significantly larger than in the other three regions. These results indicate that around dopaminergic neurons, particularly in the substantia nigra, (R)-salsolinol was methylated into N-methyl-(R)-salsolinol, which has a chemical structure similar to that of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, the selective dopaminergic neurotoxin. N-Methylation of tetrahydroisoquinolines and beta-carbolines have already been proven to increase their toxicity to dopaminergic neurons and N-methylation might be an essential step for these alkaloids to increase their toxicity. On the other hand, after perfusion of (R)-salsolinol, release of dopamine and 5-hydroxytryptamine was observed and inhibition of monoamine oxidase was indicated. (R)-Salsolinol and its derivatives may be candidates for being dopaminergic neurotoxins.

Endogenous synthesis of N-methylsalsolinol, an analogue of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, in rat brain during in vivo microdialysis with salsolinol, as demonstrated by gas chromatography-mass spectrometry

N-Methylsalsolinol, an analogue of 1,2,3,6-tetrahydropyridine, is present in the brains of patients with Parkinson's disease. To determine the metabolic pathway for the synthesis of N-Methylsalsolinol in the brain, salsolinol was perfused through the striatum or the substantia nigra of the rat brain by in vivo microdialysis. N-Methylsalsolinol was detected in the brain dialysate samples during microdialysis with salsolinol using gas chromatography-mass spectrometry with selected-ion monitoring. These results demonstrate that endogenous N-methylation of salsolinol into N-methylsalsolinol occurs in the brain in vivo.

Mutations on the second chromosome affecting the Drosophila eye

In the developing eye of Drosophila, cell interactions appear to be responsible for organising undifferentiated cells into unit eyes, or ommatidia. Extensive mutagenesis has been used to search for mutations affecting the development and differentiation of ommatidia. These mutations have been characterized using sections of adults and immunocytochemistry of imaginal discs. Fourteen loci on the second chromosome are described that affect the spacing of the preclusters, the differentiation of ommatidial cells, orientation of the ommatidia, or architecture of the adult retina, that cause retinal degeneration in larval or pupal eye discs, or that cause homeotic transformation of part of the head.

Differential effect of self-stimulation on dopamine release and metabolism in the rat medial frontal cortex, nucleus accumbens and striatum studied by in vivo microdialysis

Changes in the extracellular levels of dopamine (DA) and its metabolites in the dopaminergic terminal regions, the medial frontal cortex (MFC), nucleus accumbens (NAC), and striatum (STR), were measured by microdialysis during self-stimulation of the medial forebrain bundle (MFB) in rats pretreated with the DA uptake inhibitor, nomifensine (1 mg/kg, i.p.). Self-stimulation of the MFB in nomifensine-pretreated rats caused an increase in the extracellular DA level in the MFC and NAC but not in the STR. Self-stimulation also increased the extracellular concentrations of the main DA metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) to a similar extent in the MFC and NAC and to a lesser extent in the STR. Thus, there was a regional difference in the neurochemical changes following self-stimulation with either the MFC or the NAC showing larger extracellular levels of DA, DOPAC, and HVA than the STR. Furthermore, these changes were observed on both hemispheres ipsilateral and contralateral to the stimulation. The results indicate that self-stimulation of the MFB preferentially activates the mesocorticolimbic DA systems, thereby bilateral increases in the release of DA and its metabolism being produced in their terminal regions, the MFC and NAC.

The effect of methamphetamine on serotonin and its metabolite in the suprachiasmatic nucleus: a microdialysis study

The suprachiasmatic nucleus (SCN) has been identified as a major circadian pacemaker. Methamphetamine has been shown to modify the behavior of circadian rhythms. We detected extracellular serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) in the SCN in freely moving rats, using a microdialysis method, to investigate biochemical effects of methamphetamine in the SCN. Methamphetamine infusion into the SCN dose-dependently increased extracellular 5-HT and decreased extracellular 5-HIAA.

[Methodological considerations in microdialysis]

Microdialysis has rapidly become popular in recent years as an in vivo technique to monitor endogenous substances in the extracellular space of the local brain region. The combination of this technique with a variety of highly sensitive detection methods has enabled us to measure in vivo release of various neurotransmitters. However, the technique involves several methodological problems. The first is that the concentrations of substances in the dialysate only partially reflect their true concentrations in the extracellular space. Therefore, neurotransmitters such as neuropeptides that are present at very low concentrations in the extracellular space are still difficult to detect. The second problem is the effects of tissue damage by the microdialysis probe. Though the probe has been miniaturized, severe disturbance in tissue metabolism cannot be neglected. Histological examination suggests that the most suitable time for commencing microdialysis is between 24 and 48 h after probe implantation. The third problem is that neurotransmitters recovered in the dialysate are sometimes not involved in neurotransmission. It is suggested that the dialysate concentration of a neurotransmitter which reflects neuronal activity should be both tetrodotoxin-sensitive and calcium-dependent. In the case of a neurotransmitter in the dialysate which does not show these characteristics, its concentration may be related to metabolic rather than neurogenic events. The fourth problem is that microdialysis has poor time resolution. Therefore, the method is not suitable for measurement of neurochemical events that rapidly change in short intervals such as milliseconds or seconds. Thus careful consideration has to be given to these problems in the actual laboratory use of microdialysis technique.

[Microdialysis: a method to construct a microdialysis probe and its applications]

This paper describes a removable microdialysis probe constructed inexpensively and easily from a commercially available iv catheter placement unit and flexible fused silica tubing. The probe is characterized in in vitro recovery tests. As an example of its applications, experimental results measuring extracellular dopamine concentrations in the nucleus accumbens of rats during intracranial self-stimulation behavior are reported.

Preferential release of neuroactive amino acids from the ventrolateral medulla of the rat in vivo as measured by microdialysis

The basal overflow of extracellular endogenous amino acids was measured from the ventrolateral medulla of urethane anaesthetized rats in vivo by microdialysis. Inclusion of a mercury salt, p-chloromercuriphenylsulphonic acid, in the dialysate (Krebs' solution), results in a preferential increase in the overflow of aspartate, glutamate, glycine and GABA. A smaller increase in the overflow of the glutamate precursor and metabolite, glutamine, was also found. There was no significant change in the basal extracellular levels of taurine, asparagine, alanine, serine, ornithine or lysine. Inclusion of a specific GABA uptake inhibitor, nipecotic acid, in the dialysate results in an immediate, dose dependent increase in the overflow of GABA, and to a lesser extent, taurine. Since it is likely that mercury salts increase neurotransmitter release by increasing free intracellular calcium ion concentrations, it is suggested that these results provide further evidence for a physiologically relevant neurotransmitter role for aspartate, glutamate, glycine and GABA in the ventrolateral medulla.

Effects of apomorphine on in vivo release of dopamine and its metabolites in the prefrontal cortex and the striatum, studied by a microdialysis method

The effects of apomorphine (0.1-2.5 mg/kg) on release of endogenous dopamine and extracellular levels of 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the prefrontal cortex and the striatum were examined in vivo by a microdialysis method. Apomorphine significantly reduced release of dopamine and the extracellular levels of dopamine metabolites, DOPAC and HVA, not only in the striatum, but also in the prefrontal cortex. These findings indicate that dopamine autoreceptors modulate in vivo release of dopamine in the prefrontal cortex.

The effect of uptake inhibition on dopamine release from the nucleus accumbens of rats during self- or forced stimulation of the medial forebrain bundle: a microdialysis study

Changes in dopamine (DA) release were measured in microdialysis samples taken from the nucleus accumbens (NAC) of rats pretreated with the DA uptake inhibitor, nomifensine (1 mg/kg, i.p.) during self- or forced stimulation of the medial forebrain bundle (MFB). Self-stimulation of the MFB in nomifensine-pretreated rats caused an increased release of DA in the NAC. In the same rats, similar increases in DA release were also found during forced stimulation, that is, during MFB stimulation in the absence of lever-pressing, but at current and rate parameters identical to those recorded in the previous self-stimulation session. The results indicate that self-stimulation of the MFB activates the mesolimbic DA system; similar neurochemical changes observed during self- and forced stimulation of the MFB suggest that the operant lever-pressing behavior itself did not influence DA release in the NAC.

Increased dopamine and serotonin metabolism in rat nucleus accumbens produced by intracranial self-stimulation of medial forebrain bundle as measured by in vivo microdialysis

In the present study, we have used a newly developed microdialysis system to perfuse the nucleus accumbens (NAC) of conscious rats during spontaneous intracranial self-stimulation of the medial forebrain bundle (MFB). Chromatographic (HPLC-ECD) analysis of the perfusates showed that dopamine (DA) release increased, but with an unstable pattern during the actual period of self-stimulation. On the other hand, the main DA metabolites, 3,4-dihydroxyphenylacetic acid and homovanillic acid, and a serotonin metabolite 5-hydroxyindoleacetic acid, were all markedly enhanced by self-stimulation, but with different time courses. These findings indicate that self-stimulation of the MFB in rats induces increases in both DA and serotonin activities in the NAC. Such changes may be involved in mediating self-stimulation of the MFB.

Effects of heterocyclic amines in food on dopamine metabolism in nigro-striatal dopaminergic neurons

We investigated the effects of 14 heterocyclic amines in food on nigro-striatal dopaminergic neurons. Among 14 compounds tested, 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) and 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2) caused substantial decreases in 3,4-dihydroxy-phenylalanine (DOPA) formation in striatal tissue slice system. When Trp-P-1 or Trp-P-2 was unilaterally infused in the rat striatum by an in vivo micro-dialysis technique, both compounds produced a transient increase of dopamine (DA) and continuous decreases in the metabolites, homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic acid (DOPAC) in the perfusate. This suggests that the two compounds inhibit monoamine oxidase (MAO) in vivo. Indeed they were found to be very potent inhibitors of MAO in vitro. Systemic administration of Trp-P-1 to C57 Black mice caused a marked decrease of DOPAC content and a significant increase of DA in the striatum, indicating inhibition of MAO in vivo. These results suggest that Trp-P-1 and Trp-P-2 contained in food could alter the metabolism of DA in the brain.

Inactivation of tyrosine hydroxylase in rat striatum by 1-methyl-4-phenylpyridinium ion (MPP+)

We report that 1-methyl-4-phenylpyridinium ion (MPP+), the active metabolite of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), inactivated tyrosine hydroxylase (TH) when MPP+ was directly infused into the striatum. We examined both in vitro TH activity and TH content measured by an enzyme immunoassay in the rat striatum after MPP+ was administered by an in vivo brain microdialysis probe. MPP+ caused the inhibition of TH activity but did not influence TH content in the ipsilateral striatum. These results indicate that MPP+ may cause an acute inactivation of TH after continuous exposure at the high concentrations.

Striatal dopamine release and metabolism in sinoaortic-denervated rats by in vivo microdialysis

The purpose of this study was to provide new evidence favoring the hypothesis that cardiovascular information from arterial baroreceptors is integrated with the nigrostriatal system that contributes to regulation of motor activity. Samples of extracellular striatal dopamine (DA) and its metabolites, dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), were collected by the technique of in vivo microdialysis and analyzed by high-performance liquid chromatography-electron capture detection. Rats were prepared with a guide tube placed in the caudate-putamen for subsequent insertion of microdialysis probes. During the 1st wk after sinoaortic denervation (SAD) or sham operation (SO), a microdialysis probe was inserted and perfused with Ringer solution at the rate of 2 microliter/min in the freely moving rats. Samples were collected every 20 min before and after injection of pargyline, 100 mg/kg ip. The results showed that SAD rats have approximately 50% less extracellular striatal DA, DOPAC, and HVA than SO rats (P less than 0.01). After blockade of monoamine oxidase activity with pargyline, striatal DA accumulated three times faster in SO than SAD rats suggesting DA synthesis is reduced in SAD rats. These data provide further evidence that the arterial baroreceptor system affects dopaminergic metabolism in the nigrostriatal system possibly as a means for integration of cardiovascular and motor activity.

Effects of attention and background verbal stimuli on event-related potentials to tone pips in humans

The effects of attention and background verbal stimuli on event-related potentials (ERPs) following tone pips were assessed under four conditions: tone pips presented alone when attending and ignoring the tones and tone pips plus verbal stimuli when attending the tones and attending the verbal stimuli. The data were quantified in terms of the N1-P2 amplitude and the similarity (correlation) between ERPs in corresponding placements over the two hemispheres. The main results were that attention influenced the ERP amplitude only with the verbal stimuli, that interhemispheric similarity was greatest with the tones only, and that similarity was greater under the tone plus verbal stimuli condition during tone-attention instructions.

Acute effects of 1-methyl-4-phenylpyridinium ion (MPP+) on dopamine and serotonin metabolism in rat striatum as assayed in vivo by a micro-dialysis technique

The acute effect of 1-methyl-4-phenylpyridinium ion (MPP+), a neurotoxin derived from 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), was examined by the in vivo micro-dialysis technique. A dialysis cannula was implanted into rat striatum, and the changes in the concentrations of dopamine (DA), 3, 4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA) in the perfusate every 20 min after administration of MPP+ were determined by high-performance liquid chromatography with electrochemical detection (HPLC-ED). After MPP+ administration the levels of DOPAC, HVA and 5-HIAA were markedly decreased. On the contrary the level of DA was markedly increased and reached a maximum 40 min after beginning of the MPP+ administration. By postmortem analysis of the striatal tissue MPP+ was proved to cause the inhibition of monoamine oxidase (MAO), especially MAO-B. These results suggest that the acute biochemical changes induced by MPP+ in vivo were MAO inhibition and release of DA.

Differential behavioral responsiveness to ipsilateral and contralateral visual stimuli produced by unilateral rewarding hypothalamic stimulation in the rat

Rats were trained to respond to a visual cue signalling availability of brain reward on the left or the right side of a small chamber. Most of the rats began to respond more accurately to the visual cue presented on the side contralateral to brain stimulation than to the ipsilateral cue as the training progressed. The facilitation of the rat's response to the contralaterally presented visual cue was more evident when tested with visual cues presented simultaneously in both ipsilateral and contralateral sides. However, when tested with visual cues removed from both sides, this tendency became unclear. Additionally, monocular training gave evidence of identifying the visual cue ipsilateral to the open eye, irrespective of the electrode side. The results are interpreted as signifying that the ipsilateral hemisphere is activated by the brain stimulus and leads to improved discrimination of the contralateral visual cue because the visual system in the rat is crossed.

Alterations of amygdaloid kindling phenomenon following repeated electroconvulsive shocks in rats

In this study we investigated the effect of the electroconvulsive shock (ECS) soon after each amygdaloid stimulation (KS) upon the development of a kindling phenomenon. Thirty male Wistar albino rats were used in this study. Once daily stimulation of 200 microA, 1 msec, 60 Hz, 2 sec train by the right amygdaloid stimulation electrodes and the recording of the EEG were done. Rats of the Kindling + ECS group received the ECS through the clipped ears for five minutes after the KS. Behavioral manifestations, the duration of afterdischarge and the numbers of spikes were counted for five minutes at the time of every stimulation. The numbers of times the KS required to develop each stage were stage 1:4.8, stage 2:8, stage 3:8.6, stage 4:9.6, stage 5:12.6, respectively, on the kindling group. On the ECS-treated group, those were stage 1:8, stage 2:17, stage 3:18, stage 4: more than 20. The ECS soon after the amygdaloid stimulation retarded the process of kindling significantly. This result is consistent with the hypothesis that the electroconvulsive shocks disturb the information of the synaptic pathway before the consolidation of a central neuroplastic change underlying kindling.