Synapses in the rat substantia nigra

The composition and organization of the input to the rat substantia nigra were studied with the electron microscope. Four distinct types of synaptic boutons were described. The first contained small (381 A), clear synaptic vesicles. The second type contained the small, clear vesicles and several large, dense-core vesicles. The third ending contained large, dense-core vesicles and larger (581 A) clear vesicles. The fourth ending, found on the axon hillock and other terminal boutons, contained slightly elongated, clear synaptic vesicles. The presence of these four boutons was discussed in light of the known afferent input and neurochemical composition of the substantia nigra.     

Transient contralateral rotation following unilateral substantia nigra lesion reflects susceptibility of the nigrostriatal system to exhaustion by amphetamine

Following unilateral 6-OHDA induced SN lesion, a transient period of contralateral rotation has been reported to precede the predominant ipsilateral circling. In order to clarify the nature of this initial contralateral rotation we examined the effect of the duration of recovery period after the lesion, on amphetamine-induced rotational behavior. Three days post lesion, most rats circled predominantly contralaterally to the lesion. Such contralateral rotation may result from either degeneration-induced breakdown of the DA pool, or lesion-induced increase of DA turnover in the spared neurons. A substantial degree of contralateral preference was still evident when amphetamine was administered for the first time 24 days after lesioning, indicating involvement of spared cells in the contralateral rotation. However, regardless of the duration of recovery (and irrespective of either lesion volume, amphetamine dose, or post-lesion motor exercise), amphetamine-induced rotation tended to become gradually more ipsilateral as the observation session progressed, and all rats circled ipsilaterally to the lesion in response to further amphetamine injections. These findings suggest that amphetamine has an irreversible effect on the post-lesion DA pool contributing to contralateral rotation.     

Peripheral iron dextran induced degeneration of dopaminergic neurons in rat substantia nigra

Iron accumulation is considered to be involved in the pathogenesis of Parkinson's disease. To demonstrate the relationship between peripheral iron overload and dopaminergic neuron loss in rat substantia nigra (SN), in the present study we used fast cyclic voltammetry, tyrosine hydroxylase (TH) immunohistochemistry, Perls' iron staining, and high performance liquid chromatography-electrochemical detection to study the degeneration of dopaminergic neurons and increased iron content in the SN of iron dextran overloaded animals. The findings showed that peripheral iron dextran overload increased the iron staining positive cells and reduced the number of TH-immunoreactive neurons in the SN. As a result, dopamine release and content, as well as its metabolites contents were decreased in caudate putamen. Even more dramatic changes were found in chronic overload group. These results suggest that peripheral iron dextran can increase the iron level in the SN, where excessive iron causes the degeneration of dopaminergic neurons. The chronic iron overload may be more destructive to dopaminergic neurons than the acute iron overload.     

Effect of chronic neuroleptic or L-DOPA administration on GABA levels in the rat substantia nigra

Male albino rats were administered daily with haloperidol, clozapine or L-DOPA and sacrificed 18 hours after the last dose of the drug. Acutely haloperidol (5mg/kg, i.p.) greatly lowered nigral GABA levels whereas after 167 daily doses the nigral GABA levels were not significantly different from controls, but were significantly increased as compared with the acutely treated animals. In contrast, acute L-DOPA (2 × 100mg, p.o.) greatly raised nigral GABA levels whereas after chronic L-DOPA (167 days) nigral GABA levels were not significantly different from controls and were significantly lower as compared with the animals receiving the acute treatment. Clozapine (20 mg/kg, i.p. either acutely or chronically) did not have as marked an effect on nigral GABA levels as did haloperidol. Of these various drug regimens only chronic L-DOPA significantly affected nigral GAD activity, producing a moderate decrease.     

Chronic intrastriatal dopamine infusions in rats with unilateral lesions of the substantia nigra

This study examined the effects of continuously supplied dopamine delivered directly into the dopamine-deficient striatum. Rats received unilateral lesions of the substantia nigra by stereotaxic administration of 6-hydroxydopamine and were tested for apomorphine-induced rotational behavior and general activity. Osmotic mini-pumps were filled with dopamine in various concentrations, implanted subcutaneously and connected to a cannula implanted directly into the striatum. The system delivered solution at a rate of .5 microliter/hr for two weeks. Dopamine in a dosage of 0.5 microgram/per hour reduced apomorphine-induced rotational behavior by a mean of 52 +/- 5.8% (mean +/- SEM, n = 20) with a maximal individual decrease of 99%. There was no change in general activity or increase in stereotyped behavior. Infusions of vehicle solutions did not decrease rotational behavior. Spread of the infused dopamine and its metabolites was estimated by adding 3H-dopamine to the pumps in tracer quantities. Radioactivity was highly concentrated at the infusion site and decreased rapidly within a few mm from the infusion site. Continuous infusion methods may eventually prove to be effective in the treatment of nigro-striatal degenerative disease.     

The effects of lesioning both the superior colliculus and the substantia nigra of cats on turning behavior

In twenty two adult cats, distributed in four groups, stainless steel electrodes were implanted in the superior colliculus and the substantia nigra of both sides in order: 1) to find the current intensity threshold values necessary to evoke turning behavior, and record their variations after lesion of the cited structures; 2) to study the effects of lesioning two of these structures, specifically related to the direction of turning behavior, and 3) to assess the time-course of recovery from postural asymmetry after damaging two structures involved in rotation behavior, located either in the same or in the opposite side, as well as the importance of performing these lesions simultaneously or at different periods. Three main results were observed: 1) a large proportion of lesioned cats showed an increase in threshold values necessary to evoke rotation of the implanted structures located either in the same or in the opposite side; 2) the lesions induced in a significant number of cats a transient postural asymmetry. After lesioning the superior colliculus, the direction of turning was towards the damaged hemisphere. Apomorphine injected fourteen days later demonstrated the existence of an occult asymmetry, and the direction of turning was maintained. In the substantia nigra lesioned animals, the direction of turning, was towards the non-lesioned side. Apomorphine reversed the direction of turning; 3) the cats showed a remarkable capacity to recover from the postural asymmetry produced by the lesion. This experimental series further support the hypothesis of a close functional relationship between structures of both cerebral hemispheres related to turning behavior.     

Effect of single and repeated methamphetamine treatment on neurotransmitter release in substantia nigra and neostriatum of the rat

There are tissue specific discrepancies in expression of tryptophan hydroxylase (TPH) between the pineal gland and brainstem. TPH mRNA levels in the pineal are much higher than in the brainstem, however, the two tissues contain comparable protein levels. This discrepancy could result from different translation efficiency of two of the TPH mRNA isoforms. Using PCR-based methods, we analyzed the relative expression, in pineal and brainstem, of two TPH mRNA isoforms differing in the length of their untranslated region (5'UTR). The levels of the TPHalpha were found to be 960-fold more abundant than the 51-nucleotide longer TPHbeta, in the pineal. TPHbeta was also detected for the first time in the brainstem, where TPHbeta/TPHalpha was about five-fold higher than in the pineal. To study the role of the different 5'UTRs, each was cloned in-frame upstream of luciferase, and transfected into PC12 cells. Both 5'UTRs enhanced luciferase activity, with TPHbeta 5'UTR being more effective than TPHalpha 5'UTR, indicating selective regulation of translation efficiency. We also examined whether physiological manipulations alter the distribution of the TPH mRNA isoforms. Repeated stress had no effect in pineal, but led to a marked preferential induction of TPHbeta in brainstem. Modulation of TPH gene expression in serotonergic neurons could result from selective and tissue specific regulation of its mRNA isoforms.     

大鼠黑质多巴胺能神经元的二型性

成年哺乳动物的某些脑区存在性别差异,即二型性,但中脑黑质是否存在性分化目前不清楚。本文旨在探讨成年大鼠中脑黑质是否存在二型性。将60只成年大鼠分成5组：（1）正常雌鼠对照组：（2）正常雄鼠对照组：（3）去卵巢组;（4）去睾丸组;（5）去卵巢后回补雌激素组,该组大鼠在去卵巢后的第7天开始连续3d给予生理剂量的雌激素回补。所有大鼠在右侧黑质埋置记录电极,在清醒和安静的生理状态下连续14d记录黑质的P50听觉诱发电位（P50）,之后作黑质酪氨酸羟化酶（tyrosine hydroxylase,TH）免疫组织化学染色,检查TH阳性（TH^＋）细胞数量和形态变化。结果表明,正常成年雄鼠黑质的TH^＋细胞数量较雌鼠少22．47％（P〈0．05）,P50的T／C值也低34．72％（P〈0．01）,提示正常成年大鼠黑质在结构和功能上存在二型性。与正常雄鼠相比,去睾丸大鼠黑质的TH^＋细胞数量、形态和P50的T／C值无显著性变化（P〉0．05）。与正常雌鼠相比,去卵巢大鼠黑质TH^＋细胞数量减少28．09％（P〈0．01）,P50的T／C值降低30．85％（P〈0．01）。在大鼠去卵巢后的短时间内给予3d生理剂量的雌激素,15-20d后可观察到其黑质TH^＋细胞数量、形态和P50的T／C值基本恢复到去卵巢前水平。结果提示,大鼠中脑黑质的多巴胺能神经元在数量、结构和功能活动上存在性别差异：内源性雌激素在维持黑质多巴胺系统完整性及调节其功能活动中起重要作用。     

The fine structure of the neurons in the rat substantia nigra

Three distinct neurons were identified in the substantia nigra of the rat using Golgi, light, and electron microscopic techniques. A large neuron, found in the pars reticulata, is characterized by well-developed RER, a tubular cytoplasmic inclusion, and somatic and dendritec thorns. A medium-sized neuron, found in the pars compacta, has an eccentric nucleus, distinct Nissl bodies, and an inclusion composed of whorls of concentric cisternae. A small neuron, found in both nigral regions, contains a highly invaginated nucleus, fibrous nuclear inclusion, and paucity of cytoplasmic organelles. Its axon synapses around other nigral dendrites. The presence of these neurons was correlated with the efferent projections and function of the substantia nigra.     

Phencyclidine-induced ipsilateral rotation in rats with unilateral 6-hydroxydopamine-induced lesions of the substantia nigra

The effect of phencyclidine (PCP) on rotational behavior in rats with unilateral 6-hydroxydopamine (6-OHDA)-induced lesions of the substantia nigra was examined and compared to the effects of d-amphetamine and apomorphine. PCP, like d-amphetamine, induced ipsilateral rotation indicating a presynaptic effect on dopamine (DA) neurons whereas apomorphine, a direct acting agonist, caused contralateral rotation. Pretreatment with alpha-methyparatyrosine inhibited PCP-induced rotation approximately to the same extent as it inhibited d-amphetamine-induced rotation, but did not significantly reduce apomorphine-induced contralateral turning, further indicating that PCP has a presynaptic effect on DA neurons. Anti-cholinergic effects on PCP may also contribute to the ipsilateral rotation noted.     

Feeding behaviour following substantia nigra and globus pallidus stimulation in chronic cats

It is known that the lesion of the nigrostriatal and pallidofugal systems causes an experimental condition comparable to the hypothalamic sindrome, with severe aphagia and adipsia. It was considered of interest to study the effects of the low frequency long-duration stimulation of the substantia nigra and the globus pallidus on feeding behaviour. Experiments were performed on eight chronic cats with electrodes implanted in SN (pars compacta) and in the GP (pars externa). In the 2 hours of observation the food intake and the number of food-taking acts were calculated. The stimulation was induced continuously in the former hour. The modification in food intake, also on the basis of somatic behavioural observations may be ascribed to motor impairment rather than to involvement of a motivational state.     

Morphological and functional effects of PACAP in 6-hydroxydopamine-induced lesion of the substantia nigra in rats

Pituitary adenylate cyclase activating polypeptide (PACAP) has several different actions in the nervous system, including neuroprotective effects. In the present study, we investigated the effects of different doses of PACAP on the functional and morphological outcome in a rat model of Parkinson's disease. Rats were given unilateral injections of 6-hydroxydopamine (6-OHDA) into the substantia nigra. PACAP-treated animals received 1, 0.1 or 0.01 microg PACAP as a pretreatment. Control animals without PACAP treatment displayed severe hypokinesia at 1 and 10 days post-lesion when compared to normal animals or those receiving saline only. PACAP treatment resulted in less severe acute hypokinesia, and complete recovery by 10 days. Asymmetrical signs were observed in all lesioned animals 1 day post-lesion. PACAP-treated animals, however, showed better recovery as they ceased to display asymmetrical signs 10 days later and showed markedly less apomorphine-induced rotations. Best behavioral outcome was observed in animals treated with 0.1 microg PACAP. Tyrosine-hydroxylase (TH) immunohistochemistry revealed increased number of dopaminergic neurons in the substantia nigra pars compacta and in the ventral tegmental area in all PACAP-treated rats in contrast to the severe cell loss in control animals. These results indicate that PACAP may be a promising therapeutic agent in Parkinson's disease.     

Loss of striatal mu1 opiate binding by substantia nigra lesions in the rat

Opiate receptors have been identified within the striatum and some have been localized presynaptically to nigrostriatal neurons. Using unilateral ablative lesions of the substantia nigra, we examined binding in the ipsilateral and contralateral striata. Lesions significantly lowered both 3H[D-Ala2,MePhe4,Gly(ol)5]enkephalin (DAGO) and 3H[D-Ala2,Leu5]enkephalin (DADL) binding. The inclusion of competitors in these assays revealed a decrease in both mu1 and mu2 receptors. Mu1 binding was slightly more sensitive to the lesioning than mu2 binding. Selective mu1 and mu2 binding assays supported these observations. No change in delta binding was observed in the lesioned striata. These studies raise the possibility that both mu1 and mu2, but not delta, receptors are localized presynaptically on nigrostriatal neurons.     

雌激素对6-羟基多巴胺损伤黑质多巴胺能神经元的保护作用

本研究以P50听觉诱发电位(P50 auditory evoked potential, P50)和酪氨酸羟化酶(tyrosine hydroxylase, TH)阳性细胞计数作为黑质功能和形态学指标,动态追踪研究雌激素对6-羟基多巴胺(6-hydroxydopamine, 6-OHDA)损伤黑质多巴胺(dopamine, DA)能神经元的作用.将大鼠分为4组:(1)正常雌性大鼠对照组;(2)单纯帕金森氏病(Parkinson's disease, PD)模型组;(3)双侧去卵巢PD模型组;(4)去卵巢回补3d雌激素的PD模型组.在大鼠清醒和安静的生理状态下连续14d记录黑质的P50,并检测黑质TH 细胞数目的变化.结果显示:单纯PD模型大鼠黑质P50的T/C值较正常雌鼠降低40.60%(P<0.01),其损伤侧黑质TH 细胞数目减少64.74%(P<0.01);去卵巢PD模型大鼠黑质P50的T/C值较单纯PD模型大鼠进一步降低45.88%(P<0.01),同时其黑质TH 细胞数目值也进一步减少57.26%(P<0.01),表明急性缺乏生理水平性腺雌激素将增大6-OHDA损伤黑质DA能神经元的程度,同时使黑质的感觉门控(sensory gating, SG)功能明显受损;去卵巢后回补3d生理剂量雌激素,可明显改善大鼠黑质的SG功能,提高TH 细胞数量(与去卵巢PD模型大鼠比较,P<0.01),其黑质损伤程度与单纯PD模型大鼠相当.以上结果提示,生理水平的雌激素具有提高黑质DA能神经元对伤害性刺激耐受性的神经保护作用.缺乏性腺源性的雌激素时,及时给予生理剂量的雌激素可以减轻神经毒素6-OHDA对黑质DA能神经元结构和功能的损伤.     

短暂的糖氧剥夺导致小鼠黑质核团的即时性损伤

为研究运动控制关键核团黑质在代谢负荷下发生的即时性损伤,研制了多通道组织灌流槽,改进了以MTT、甲酚紫染色考察脑组织损伤的方法,获得了20 min的短时程糖氧剥夺所引起的小鼠黑质区即时性功能和形态损伤的组织化学依据。1)MTT检测显示,糖氧剥夺使黑质区域MTT与线粒体琥珀酸脱氢酶的反应产物甲臜晶体密度减少,并且这种减少在黑质的中部到吻侧的背部区域最为明显(约42.5%);2)甲酚紫染色结果表明,糖氧剥夺不影响脑片黑质区面积和着色斑块的数密度,而使斑块的平均面积减低(6.9%)。上述研究结果提示短时程糖氧剥夺可导致黑质区空间依存性的线粒体功能损伤,并且具有与凋亡相似的形态学特征。     

Differentiation gradient of dopaminergic neurons in substantia nigra of rat

The chemical differentiation featured by the appearance of tyrosine hydroxylase (TH) and the distribution pattern of the dopaminergic cells of rat substantia nigra (SN) were studied with combined immunocytochemical and electronmicroscopic techniques. Under the light microscope, the earliest TH-positive cells at embryonic day 13 are localized at the ventral part of rostral midbrain. Later appearing TH-positive cells join the earlier ones dorsally and caudally. As to the stain intensity and morphology of the labeled cells in the region of the SN, there exists a ventral to dorsal and lateral to medial spatiotemporal gradient, namely the cells in the ventral and lateral parts, compared with the dorsal and medial ones, have more intense staining, larger cell bodies with smaller nuclei and more and longer processes. The earliest nigrostriatal projection fibers stem from the most laterally located SN cells. Under electron microscope, rough endoplasmic reticula are always seen within the positively stained cells. With the progression of development, the cells show more intense staining and contain more rough endoplasmic reticula and other organelles. Together with the results reported on the neurogenesis and migration of the SN cells, the present study indicates that the chemical differentiation of SN cells, with a spatiotemporal gradient, starts after the completion of cell migration, a process paralleling to their morphological differentiation.     

Effect of dopamine agonists and antagonists on DOPA formation in the substantia nigra

Abstract: The effect of different psychotropic drugs on the rate of DOPA accumulation after administration of a decarboxylase inhibitor (NSD 1015) was compared in the substantia nigra (SN) and caudate nucleus (CN) by a new radioenzymatic method. Inhibition of monoamine oxidase with pargyline or stimulation of dopamine (DA) receptors with apomorphine, N -n-propyl-norapomorphine or d -amphetamine reduced DOPA formation in the CN and SN to the same extent. Vice versa, both inhibition of DA receptors with haloperidol or (-)sulpiride and depletion of DA concentration with reserpine enhanced DOPA formation to a greater extent in the CN than in the SN. Apomorphine antagonized not only the effect of haloperidol and (-)sulpiride, but also, and even more effectively, that of reserpine. The results indicate that DA synthesis in the SN is controlled by both end-product inhibition and DA receptor-mediated mechanisms.     

Activity of substantia nigra pars reticulata neurons after lesion of the ipsilateral neostriatum by kainic acid in rats

Huntington's chorea is a degenerative disorder of the human brain characterized by a marked loss of intrinsic neostriatal neurons. This situation can be reproduced by kainic acid injection in the caudate nucleus. Activity of pars reticulata neurons ipsilateral to the injected neostriatum was studied in normal, control (saline-injected) and lesioned rats. They were identified by electrophysiological and histological criteria (Fig. 1). Results obtained in normal and control rats were very similar (Table I). As previously described, the mean frequency of these neurons was high. An important percentage (respectively 72.5 and 73%) and these neurons presented the characteristics of a regular firing pattern (so called "organized neurons"). Results obtained in kainic acid lesioned rats were significantly different (Table I). The mean frequency was lower and only 11% of reticulata cells remained organized after neostriatal lesion. This important dysfunction may be explained in various ways: The neostriato-nigral pathway's destruction involves both the inhibitory GABAergic tract and the excitatory substance P tract (GALE et al., 1978). Other inputs arising from many structures in the brain continue to exert their own action on SN neurons, resulting in an unbalance in the SN inputs. It is well known that the nigral dopamine influences the neuronal activity of pars reticulata neurons (Ruffieux et Schultz, 1980; Waszczak et Walters, 1983). Doudet et al. (1984 b) previously reported a dysfunction of neuronal activity of dopaminergic cells after striatal lesion. A disturbance in the electrical activity may induce a similar disturbance in the intranigral dendritic release of DA.(ABSTRACT TRUNCATED AT 250 WORDS)