Effects of lesions on somatostatin-like immunoreactivity in the rat striatum

Substantial amounts of somatostatin have been demonstrated in the basal ganglia and immunocytochemistry has demonstrated both somatostatin staining neurons and nerve terminals. In order to study possible sources of somatostatin input to the striatum a series of lesions were made. Lesions of the substantia nigra produced with either 6-hydroxydopamine or ibotenic acid and hemisections at the level of the globus pallidus (6.2 mm anterior) had no effect on striatal levels of somatostatin-like immunoreactivity (SLI). Similarly dorsal frontal or hemicortectomies had no effect on SLI in the striatum. Kainic acid injected directly into the striatum at 2 dose levels resulted in a 60% depletion of SLI on the ipsilateral side and a 25% reduction on the contralateral side. These results suggest that about half of the SLI in the striatum is localizable to intrinsic neurons; the source of the remaining SLI is presently unknown but does not appear to arise in the dorsal cortex, thalamus or brainstem.     

Striatal modulation of cAMP-response-element-binding protein (CREB) after excitotoxic lesions: implications with neuronal vulnerability in Huntington's disease

Recent evidence has shown that the activity of cAMP responsive element-binding protein (CREB) and of CREB-binding protein (CBP) is decreased in Huntington's disease (HD) [Steffan et al. (2000)Proc. Natl Acad. Sci. USA, 97, 6763-6768; Gines et al. (2003)Hum. Mol. Genet., 12, 497-508; Rouaux et al. (2004) Biochem. Pharmacol., 68, 1157-1164; Sugars et al. (2004)J. Biol. Chem., 279, 4988-4999]. Such decrease is thought to reflect the impaired energy metabolism observed in a HD mouse model, where a decline in striatum cAMP levels has been observed [Gines et al. (2003)Hum. Mol. Genet., 12, 497-508]. Increased levels of CREB have also been demonstrated to exert neuroprotective functions [Lonze & Ginty (2002)Neuron, 35, 605-623; Lonze et al. (2002)Neuron, 34, 371-385]. Our study aimed to investigate the distribution of CREB in the neuronal subpopulations of the striatum in normal rats compared to the HD model of quinolinic acid lesion. Twenty-five Wistar rats were administered quinolinic acid 100 mm into the right striatum, and killed after 24 h, 48 h, 1 week, 2 weeks, and six weeks, respectively. The contralateral striata were used as controls. Dual-label immunofluorescence was employed using antibodies against phosphorylated CREB and each of the different neuronal subpopulations markers. Our results show that activated CREB levels decrease progressively in projection neurons and parvalbumin (PARV) and calretinin (CALR) interneurons, whereas such levels remain stable in cholinergic and somatostatin interneurons. Thus, we speculate that the ability of cholinergic interneurons to maintain their levels of CREB after excitotoxic lesions is one of the factors determining their protection in Huntington's disease.     

Striatal formation of 6-hydroxydopamine in mice treated with pargyline,pyrogallol and methamphetamine

Summary. Formation of 6-hydroxydopamine (6-OHDA) has been posited in the striatum following methamphetamine treatment and plays a critical role in methamphetamine-induced nigrostriatal dopaminergic toxicity. We used high performance liquid chromatography electrospray ionization tandem mass spectrometry (HPLC-ESI-MS/MS) to determine the formation of 6-OHDA by the treatments of methamphetamine combined with pargyline, a monoamine oxidase inhibitor, and pyrogallol, a catechol-O-methyl-transferase inhibitor, in female C57BL/6J mouse striatum. A substantial amount of 6-OHDA (9.9 ± 0.7 pg/mg wet tissue) was detected in mice treated with pargyline (100 mg/kg) and pyrogallol (25 mg/kg) in combination. Greater striatal 6-OHDA levels were observed in mice treated with combined pargyline, pyrogallol and methamphetamine (50 mg/kg) as compared to mice treated with combined pargyline and pyrogallol. However, mice treated with pargyline and pyragollol in combination followed by one and two doses of methamphetamine exhibited comparable striatal 6-OHDA levels (23.2 ± 4.3, 27.3 ± 1.3 pg/mg wet tissue) in our protocol. We conclude that blockade of the primary metabolic pathways of dopamine by inhibiting both monoamine oxidase and catechol-O-methyl-transferase activities is sufficient to induce 6-OHDA formation in the striatum. Acute 6-OHDA accumulation in the striatum can be potentiated by methamphetamine, a potent dopamine releaser, administration following such metabolic inhibitions. Received May 3, 2002; accepted November 10, 2002 Acknowledgements This study was supported by the NSC of Taiwan (grant No. NSC90-2413-H006-012) to Dr. L. Yu. Authors' address: Dr. L. Yu, National Cheng Kung University College of Medicine, Institute of Behavioral Medicine, 1 University Rd, Tainan 70101, Taiwan, e-mail: lungyu@mail.ncku.edu.tw     

Rapid shrinkage of rat striatal extracellular space after local kainate application and ischemia as recorded by impedance

Early changes in tissue extracellular space following exposure to the excitotoxin kainate in the striatum were compared to those following cardiac arrest of rats anesthetized by chloral hydrate. Tissue extracellular space was monitored by impedance measurements. The possible role of voltage-sensitive Na channels and energy metabolism was studied by local and systemic application of tetrodotoxine (TTX) and glucose, respectively. After both kainate intoxication and cardiac arrest the extracellular space (normally about 20%) became less than one-half within 15 min. TTX caused a delay in the effect of cardiac arrest, and a slight attenuation of that of kainate. Glucose was ineffective in both preparations. Parallel to a decrease in the extracellular space whole tissue Na/K ratio increased. These experiments show that excitotoxins and cardiac arrest cause similar (and not additive) changes in the extracellular space and that these changes are not mediated by Na channels. In cardiac arrest the onset of the extracellular space alterations is triggered by Na+ influx, thus presumably by neurotransmitter release. It is suggested that most (if not all) currently described protective measures against ischemic, hypoxic, or hypoglycemic brain damage are based on a prolongation of the time of onset leading to cell depolarization, rather than suppressing damaging processes during depolarization.     

Striatal injections of kainic acid selectively impair serial memory performance in the rat

Rats with bilateral injections of kainic acid into the striatum were trained on a schedule of either singly alternated or continuous reinforcement in a runway. Both the acquisition and the extinction rates of the kainate-treated rats did not significantly differ from those of control rats with either reinforcement schedule. However, the kainate-treated rats ran significantly more slowly than the controls, especially at the onset of the training sessions, and, in contrast to the controls, failed to show reliable speed alternation in the late trials of the sessions with reward alternation, thus indicating both a locomotor impairment and an impairment of serial memory performance. In addition to severe loss of striatal neurons, the kainate injections induced partial neuronal loss in the neocortex, globus pallidus, hippocampus, and pyriform cortex. The similarity of the kainate-induced behavioral and pathological alterations to those of Huntington's disease is discussed.     

Cellular localization of MAO A and B in brain: Evidence from kainic acid lesions in striatum

The cellular localization of the two forms of monoamine oxidase (MAO A and MAO B) was studied by measuring their activities in rat striatum following unilateral stereotaxic injection of kainic acid to produce selective degeneration of striatal neurons and subsequent proliferation of astrocytes. The results demonstrated a persistent loss of 15-20% in MAO A activity, whereas MAO B activity decreased initially by 25% and then increased to more than twice the control value by 54 days after lesions. The changes in activity were compared to parallel estimates of the postsynaptic neuronal enzyme markers glutamic acid decarboxylase (GAD) and neuron-specific enolase (NSE), astroglial enzyme markers glutamine synthetase (GS) and non-neuronal enolase (NNE), and the presynaptic enzyme marker DOPA decarboxylase (DDC). The results suggest that a small amount of striatal MAO A is present in kainic acid-sensitive postsynaptic striatal neurons and that MAO B is probably localized in both neurons and astrocytes.     

Striatal dopamine and homovanillic acid in Huntington's Disease

Summary Using tissue taken post mortem from patients with neuropathologically confirmed Huntington's disease and a series of appropriate control cases, GABA, dopamine and homovanillic acid were measured in the caudate nucleus and the putamen. The previously reported loss of GABA in Huntington's disease was confirmed, while no change in dopamine concentrations and a loss of homovanillic acid in these striatal regions were observed. This loss could not be explained on the basis of agonal state or previous drug treatment.     

Separation of the motor consequences from other actions of unilateral 6-hydroxydopamine lesions in the nigrostriatal neurones of rat brain

Male rats showed a clear preference for one forepaw when they were trained to press a lever for food reward. The preference was then changed by training, by local anaesthetic injection into the preferred paw, by lesions in the striatal output pathways in the brain, or by neurotoxin injection into the striatum contralateral to the side of the preferred paw. The pressing rate was not changed in spite of the change in paw use in any of these operations. This result is in marked contrast to the effect of reducing the dopamine concentration on the side contralateral to the preferred paw; in this case a marked reduction in responding is seen as well as the change in paw use. Thus medial forebrain bundle 6-hydroxydopamine lesions are more debilitating than either striatal damage or peripheral paralysis at least in the short term.     

Behavioral recovery following kainic acid lesions and fetal implants of the striatum occurs independent of dopaminergic mechanisms

Transplantation of fetal striatal tissue into rats with kainic acid lesions of the striatum reversed the spontaneous locomotor abnormalities caused by the lesions, but had no effect on the lesion-induced hyperactivity that followed amphetamine or apomorphine injection. Conversely, transplants into intact (non-lesioned) striatum led to abnormalities in spontaneous locomotion, but did not effect locomotion under amphetamine or apomorphine conditions. Dopamine autoradiography found a relative absence of dopamine receptors within the transplants. These results suggest that the mechanism which accounts for transplant-induced recovery of spontaneous locomotion is independent of striatal dopamine mechanisms.     

Long-term local and distal increases in tryptophan hydroxylase activity following intracerebral kainic acid injections in the rat

The administration of kainic acid (1–2 μg) into the right striatum of adult rats resulted in a marked local increase in tryptophan hydroxylase activity (+ 54–106%). This change was significant as soon as on the second day after the treatment and persisted for at least 12 days. In addition, long-lasting elevations of tryptophan hydroxylase activity were also observed in the anterior raphe area, septum and ipsilateral hippocampus and cerebral cortex. In contrast, the intrahippocampal injection of kainic acid (1 μg) induced a long-term increase in tryptophan hydroxylase activity only in the injected structure. In all cases, the changes in tryptophan hydroxylase activity were associated with significant increases in the V_max of the enzyme with no alteration of its apparent affinities for tryptophan and the pterin cofactor. Studies of the sensitivity of tryptophan hydroxylase from control and from kainic acid-treated rats to in vitro activating conditions (Ca⁺-dependent phosphorylation, partial trypsinization, exposure to sodium dodecyl sulfate) suggest that the intrastriatal injection of the neurotoxin induced a long-lasting activation of the enzyme.These findings indicate that intracerebral injections of kainic acid may be a valuable approach to explore further the mechanisms controlling tryptophan hydroxylase activity in vivo.     

Effects of D2 receptor antagonist haloperidol on hippocampal neuronal apoptosis in a rat model of temporal epilepsy

BACKGROUND： Dopamine receptors are divided into D1 and D2 subgroups. It has been reported that D2 receptors resist neural toxicity induced by excitatory amino acids and muscarine, and also alleviate epilepsy attacks following pilocarpine treatment. However, it has not yet been established whether D2 receptors regulate temporal epilepsy. OBJECTIVE： To observe the effects of the D2 antagonist haloperidol on hippocampal neuronal apoptosis and electrical brain activity in a rat model of kainic acid-induced temporal epilepsy. DESIGN, TIME AND SETTING： Randomized grouping and histopathological study were performed at the Neurology Medicine Institute of Zhujiang Hospital, Southern Medical University from August to December 2004. MATERIALS： Twenty-five adult, male, Sprague Dawley rats were selected for the present study. Kainic acid （Sigma, USA） was injected into the right lateral ventricle to establish models of temporal epilepsy. A PowerLah multiplying channel eleetrophysiolograph was provided by AD Instruments, Australia. METHODS： The rats were randomly divided into 5 groups （n = 5）： control, model, haloperidol hippocampus, haloperidol striatum, and haloperidol substantia nigra. Temporal epilepsy was established in all rats except the control group. Haloperidol was slowly injected into the hippocampus, striatum and substantia nigra, respectively, in three different injection groups. Normal saline was injected into the right lateral ventricle of the control rats. MAIN OUTCOME MEASURES： Hippocampal apoptosis was observed on the day 3 of treatment using TUNEL staining. Changes in electroencephalogram at 0, 0.5, 2, 6, and 12 hours following treatment onset were observed using a PowerLab multiplying channel electrophysiolograph. Animal behaviors were classified according to the Racine criteria. RESULTS： Twenty-five rats were included in the final analysis. Seizures did not occur in the control group. In the model group, 10 minutes after kainic acid injection to the lateral cerebral ventricle, epilep     

Neurotensin receptors in the rat striatum: lesion studies

The specific binding of [3H]neurotensin binding to the rat striatum was characterized and its localization investigated by using frontal cortex ablations and the neurotoxins kainic acid and 6-hydroxydopamine. Scatchard analysis indicated the existence of a single population of binding sites and the potencies of various neurotensin fragments in competing with [3H]neurotensin for its binding site were in good agreement with the potency values obtained in biological assays. The lesion studies indicated that more than 50% of striatal neurotensin receptors are localized on intrinsic neurones, approximately 30% on dopaminergic nerve terminals and 20% on corticostriatal nerve fibres.     

Activity of neuron-specific enolase in normal and lesioned rat brain

Rat brain contains 3 forms of enolase, a neuron-specific form (NSE), a hybrid form, and a non-neuronal form (NNE) which were separated by DEAE-cellulose column chromatography. The enolase activity corresponding to each form of the enzyme eluted from the columns was determined spectrophotometrically. Using this assay procedure, an activity ratio (%NNE/%NSE) was calculated for cerebellum, brainstem, sciatic nerve, adrenals and liver. The results indicated excellent agreement between this enzymatically determined ratio and published values of a similar ratio (NNE/NSE) determined by radioimmunoassay for enzyme protein. Following in vivo destruction of neurons by intracerebral injection of the selective neurotoxin, kainic acid, there was a significant decrease in the activity of NSE and hybrid enolase (neuronal forms) and no change in the activity of NNE (glial form). These data indicate that separation and measurement of enolase species is useful to determine levels of these species in normal tissue and to estimate neuronal damage biochemically in brain lesions.     

成年大鼠纹状体海人藻酸损伤后nestin的表达

目的　 研究成年大鼠纹状体海人藻酸 (kainicacid,KA)损伤后不同时间点nestin的表达并探讨其机制。方法　向成年SD大鼠纹状体内立体定位注射 0 .5 μlKA(1mg/ml) ,分别于手术后第 1、3、7、14天用免疫组织化学法检测纹状体内nestin表达的变化。结果　 正常纹状体内可观察到微弱的淡染nestin样免疫活性阳性细胞 ;大鼠纹状体KA损伤后 1d ,nestin样免疫活性增强 ;第 3天nestin样免疫活性达峰值 ,nestin样免疫活性阳性细胞的胞体肥大 ,突起粗大 ,分支增加 ;此后nestin样免疫活性阳性细胞染色强度减弱 ,其胞体和突起逐渐变小变细。 结论　 成年大鼠纹状体内注射海人藻酸可诱导nestin的大量表达 ,该表达可能与脑损伤后的自身修复相关。     

Striatal dopamine uptake and swim performance of the aged rat

The striatum and olfactory tubercle of 30-month-old F344 rats contain significantly (21-24%) less dopamine compared with young adult (8-month) animals. However, rats of the two age groups show identical Km and Vmax values for the kinetics of [3H]dopamine uptake into striatal homogenates; uptake into the olfactory tubercle also appeared unaffected in old age. The preservation of dopamine uptake despite reductions in content of the transmitter suggests that the forebrain dopaminergic nerve terminals are intact, but that reduced dopamine synthesis and/or enhanced degradation may occur in the existing terminals. Administration to senescent animals of the dopamine uptake blockers nomifensine or bupropion (but not the norepinephrine uptake blocker desmethylimipramine) improved their swim performance to levels comparable with young adult animals. The findings suggest that amine reuptake may limit the synaptic effectiveness of dopamine released in the aged striatum.     

Effects of unilateral 6-Hydroxydopamine lesions of the caudate-putamen on skilled forepaw use in the rat

This experiment reports a novel means of measuring the effect of unilateral striatal dopamine (DA) depletion on co-ordinated motor behaviour involving skilled forepaw use in rats. Hungry rats were trained to use their forepaws to remove small food pellets from a moving conveyor belt. Behaviour was scored by counting successful retrievals, attempted retrievals and omissions. The rats were trained to a stable baseline, and the forepaw which they used most accurately was determined over a period of 300 trials. 6-Hydroxydopamine (6-OHDA, 8 μg base in 2 μl vehicle (ascorbic acid/0.9% saline) was injected unilaterally into the head of the caudate nucleus to produce selective DA depletion, either ipsi- or contralateral to the preferred paw. A control group received vehicle alone. There was a significant change in paw use in the 6-OHDA treated rats, but not in the controls, even though accuracy was affected similarly in both sham and lesioned groups. Ipsilaterally injected rats showed increased use of the preferred paw (90% pre-operation to 98% post-operation, while contralaterally injected rats showed reduced use (86% pre-operation to 49% post-operation). These changes appeared on the first day postsurgery and were still present 3 months later.     

Morphological changes of rat neurosecretory neurones after stereotacix injection of kainic acid into the supraoptic nucleus or the supraoptico-hypophyseal tract

Kainic acid is a structural analogue of glutamic acid possessing neurotoxic property. In the present study, performed on rats, morphological changes of neurosecretory neurones after stereotaxic injection of kainic acid into the left supraoptic nucleus or into the left supraoptico-hypophyseal tract were investigated. It is shown that administration of kainic acid in a dose that leads to destruction of hippocampal pyramidal cells has no effects on supraoptic perikarya but does destroy neurosecretory axons. These results contradict the observations of many authors who reported that local injection of kainic acid into the brain causes degeneration of perikarya but leaves axons of passage unaffected.     

Effects of kainic acid lesions of the striatum on self-stimulation in the substantia nigra and ventral tegmental area

Unilateral kainic acid lesions of the dorsal striatum provided evidence for a dissociation of neural substrates of brain-stimulation reward at sites in the ventral tegmental area and substantia nigra. The lesions caused a significant increase in current intensity thresholds at substantia nigra placements, whereas similar lesions had no effect on self-stimulation thresholds at sites in the ventral tegmentum. In addition, the rate-increasing effects of d-amphetamine (0.1–1.0 mg/kg) on self-stimulation were determined before and after lesions to the dorsal striatum. No significant changes in dose-response curves were observed at either loci. Amphetamine-induced rotation was used to confirm damage to the dorsal striatum and lesioned animals were observed to rotate towards the side of the lesion. In contrast, sham-lesioned animals showed turning away from the side stimulated electrically in previous tests. The results of the self-stimulation and rotation experiments are discussed in the context of neural substrates of reward and motor activity.     

Excitotoxin lesions do not mimic the alteration of somatostatin in Huntington''s disease

Huntington's disease is accompanied by severe neuronal death in the striatum, but despite this cell loss, there is a marked increase in the striatal concentration of somatostatin-like immunoreactivity (SLI). We attempted to examine the mechanism of this increase by using kainic or ibotenic acid to effect a unilateral lesion in the rat neostriatum. Graded doses of toxin cause a proportional decrease in the concentration of somatostatin-like immunoreactivity to a maximum of 50% of control, which is stable over an interval of 3 months. The increased somatostatin-like immunoreactivity in Huntington's disease is not mimicked by the excitotoxin lesions in rats. In addition we find that unilateral kainic acid lesions in the striatum reduce SLI in the contralateral striatum as well, although histologic evidence and assay of choline acetyltransferase activity indicate that damage is confined to the injected side. Immunocytochemistry demonstrates a loss of somatostatin-containing neurons on the lesioned side but no discernible loss in the contralateral striatum. The bilateral decrease in SLI following unilateral lesions suggests damage to a somatostatin projection to the contralateral striatum or a compensatory interaction between the two striatal nuclei.