Cytoarchitecture of the substantia nigra pars lateralis in the opossum (Didelphis virginiana): A correlated light and electron microscopic study

Background: The substantia nigra has been divided into three subdivisions. However, the cytoarchitecture of one of these subdivisions, the pars lateralis (SNI), has not been previously examined in detail at the light and electron microscopic levels in any species. In the adult opossum, the three nigral subdivisions can be easily distinguished as distinct, rostrocaudally oriented cell groups separated by neuron-free zones. Thus it was possible to determine the boundaries of the SNI unambiguously. This report covers the results of an examination of the morphology and organization of the SNI in the opossum. Methods: Material from 13 opossums was used for this study. Eight of the animals had been previously stained for Nissl substance (n=4) or impregnated by the Golgi technique (n=4). The remaining five animals were prepared for electron microscopic studies using standard procedures. Results: Two cell types were identified on the basis of morphological differences, small and medium-large neurons. Small neurons (10–18 μm long axis) have large nuclei with moderate amounts of heterochromatin and a thin rim of cytoplasm. They have long (up to 500 μm), spine-free dendrites. Medium-large neurons (18–54 μm long axis) have rounded nuclei with electron-lucent nucleoplasm. Few indentations of the nuclear envelope were observed. The surrounding cytoplasm has dense arrays of organelles. Nissl bodies are particularly prominent in the form of pyramids with their bases at juxtanuclear positions and their apices directed toward emerging dendrites. Dendrites of medium-large neurons are long (some>1 mm in length), are primarily oriented in the frontal plane, and extend along the dorsal surface of or into the cerebral peduncle. Some cells have dendrites that are moderately spinous, whereas other neurons possess sparsely spinous dendrites. Relatively few synaptic profiles are observed to contact somata and proximal dendrites. Conclusion: This report provides added morphological support for the idea that the SNI is a distinct subdivision of the substantia nigra, a distinction previously made on the basis of the physiologically characterized relationship between the lateral substantia nigra and orienting behaviors and seizure-related function. © 1995 Wiley-Liss, Inc.     

A microiontophoretic study on the nature of the putative synaptic neurotransmitter involved in the pedunculopontine-substantia nigra pars compacta excitatory pathway of the rat

Summary The nature of the synaptic transmitter involved in the excitatory fibers linking the nucleus tegmenti pedunculopontinus (PPN) to the pars compacta of the substantia nigra (SNPC) was investigated using microiontophoretic techniques in rats anesthetized with ketamine. Among the SNPC cells activated orthodromically by PPN electrical stimulation, only a few cells were weakly excited by iontophoretically administered acetylcholine (Ach) while most were not affected. Conversely all cells were promptly and powerfully excited by short pulses of glutamate (GLU). The administration of the GLU antagonists glutamic acid diethylester (GDEE) and D--aminoadipic acid (DAA) reversibly and simultaneously suppressed both the PPN-evoked orthodromic response and the GLU-induced excitation of SNPC cells without affecting their response to iontophoretic Ach. GDEE was more effective than DAA in counteracting the synaptically evoked excitation. On the other hand, atropine, while antagonizing the Ach response in those cells which were cholinoceptive, did not affect either the PPN-evoked or the GLU-induced excitation. Hence, despite the presence of cholinergic cells in the PPN region, Ach does not appear to be involved in the excitatory PPNSNPC pathway. The present findings suggest that the excitatory PPN fibers innervating the SNPC may utilize GLU or a closely related amino acid as a neurotransmitter.Supported by grants from the Ministero della Pubblica Istruzione     

Cholinergic and non-cholinergic neurons in the rat pedunculopontine tegmental nucleus

Summary Choline acetyltransferase immunhistochemistry was employed at light and electron microscopic levels in order to determine the distribution of cholinergic neurons in two subdivisions of the rat pedunculopontine tegmental nucleus that were previously defined on cytoarchitectonic grounds, and to compare the synaptic inputs to cholinergic and non-cholinergic somata in the subnucleus dissipatus, which receives major input from the substantia nigra. Large cholinergic neurons were found in both the pars compacta and the pars dissipata of the pedunculopontine nucleus. However, they were intermingled with non-cholinergic neurons and did not respect the cytoarchitectural boundaries of the nucleus. Ultrastructural study showed that all cholinergic neurons in the subnucleus dissipatus exhibited similar features. The majority had large somata (largest diameter 20 m) containing abundant cytoplasmic organelles and nuclei displaying a few shallow invaginations. Synaptic terminals on the cholinergic cell bodies were scarce and unlabeled boutons containing spherical synaptic vesicles and establishing asymmetric synaptic junctions were the dominant type. In contrast, the non-cholinergic neurons presented prominent differences in the size of their somata as well as in the distribution of axosomatic synapses. Two almost equally represented classes of non-cholinergic neurons which are referred to as large (largest diameter 20 m) and small (largest diameter <20 m) were recognized. Large non-cholinergic cell bodies were ultrastructurally similar to the cholinergic ones, but they received rich synaptic input by unlabeled nerve terminals which contained pleomorphic vesicles and were engaged in symmetric synaptic junctions. Small non-cholinergic cell bodies were characterized by deeply invaginated nuclei surrounded by a narrow rim of cytoplasm, and were often found near or in direct apposition to the cholinergic somata. Their major input consisted of axosomatic boutons containing round synaptic vesicles. These results demonstrate that cells in the pedunculopontine tegmental nucleus are differentiated with regard to their axosomatic synaptic inputs which may influence their firing properties. Furthermore, they support previous suggestions that nigral afferents may be preferentially distributed to a subpopulation of the pedunculopontine neurons.Abbreviations cp cerebral peduncle - CG central gray - CNF cunei-form nucleus - LPB lateral parabrachial nucleus - ml medial lemn-iscus - MPB medial parabrachial nucleus - me5 mesencephalic tri-geminal tract - Me5 nucleus of the mesencephalic tract of the trige-minal nerve - Mo5 motor trigeminal nucleus - PPNc pedunculo-pontine nucleus, subnucleus compactus - PPNd pedunculopontinenucleus subnucleus dissipatus - rs rubrospinal tract - RPo pontinereticular nucleus, oral portion - RR retrorubral nucleus - RRF re-trorubral field - scp superior cerebellar peduncle - SNr substantianigra, pars reticulata - SPTg subpeduncular tegmental nucleus - 3n oculomotor nerve     

Inhibitory substantia nigra inputs to the pedunculopontine neurons

Summary Responses of 43 pedunculopontine area (PPN area) neurons to electrical stimulation of the substantia nigra (SN) were studied in anesthetized rats. An intracellular recording technique was used to demonstrate that SN stimulation evoked hyperpolarizing potentials, which were identified by intracellular injections as inhibitory postsynaptic potentials (IPSPs). These IPSPs were often followed by a rebound depolarization that originates several spike potentials. These IPSPs were characterized as monosynaptic, with latencies varying from 1.0 to 8.5 ms. Similar results were observed in some animals with chronic unilateral coronal lesion just rostral to subthalamic nucleus (STH), which severed the rostral afferents. PPN area neurons were also antidromically activated by SN stimulation. Two PPN area projection neurons were clearly identified. Mean latency of one group was 0.71 ms; mean latency of the second group was 5.16 ms. The morphological analysis of a neuron inhibited by SN stimulation and labeled with horseradish peroxidase (HRP) demonstrated that the soma was fusiform in shape, with the axon originating in the soma and collaterals and a large dendritic field extending in the ventrodorsalis direction. The results indicate that the PPN area is reciprocally connected with the SN, which elicits an inhibitory effect on PPN area neurons.     

Expression and localization of pChAT as a novel method to study cholinergic innervation of rat adrenal gland

Cholinergic innervation of the rat adrenal gland has been analyzed previously using cholinergic markers including acetylcholinesterase (AChE), choline acetyltransferase (ChAT) and vesicular acetylcholine transporter (VAChT). In the present study, we demonstrate putative cholinergic neurons in the rat adrenal gland using an antibody to pChAT, which is the product of a splice variant of ChAT mRNA that is preferentially localized in peripheral cholinergic nerves. Most of the ganglionic neurons as well as small single sporadic neurons in the adrenal gland were stained intensely for pChAT. The density of pChAT-immunoreactive (IR) fibers was distinct in the adrenal cortex and medulla. AChE-, cChAT- and VAChT-immunoreactivities were also observed in some cells and fibers of the adrenal medulla, while the cortex had few positive nerve fibers. These results indicate that ganglionic neurons of the adrenal medulla and nerve fibers heterogeneously express cholinergic markers, especially pChAT. Furthermore, the innervation of the adrenal gland, cortex and medulla, by some cholinergic fibers provides additional morphological evidence for a significant role of cholinergic mechanisms in adrenal gland functions.     

Light and electron microscopic immunohistochemical studies of serotonin nerve fibers in the substantia nigra of the rat, cat and monkey

Summary The distribution of serotonin-containing nerve fibers in the substantia nigra of the rat, cat and monkey was studied with a highly sensitive peroxidase-antiperoxidase immunohistochemical method. Serotonin fibers in the substantia nigra of all species consisted of fine varicose fibers and formed a fine network. In the zona compacta of all species, serotonin fibers were sparsely distributed. In the zone reticularis of the rat and cat, these fibers were densely distributed and their distributional pattern was almost uniform, while in the monkey such fibers were unevenly distributed and high and low dense areas were intermingled. In the pars lateralis of all species, serotonin fibers were diffusely distributed, and the distributional density was much higher in the cat and monkey than in the rat. Immunoelectron-microscopic studies further revealed that a majority of the labeled varicosities in the rat substantia nigra were in close apposition to peridendritic axon terminals and were also free in the neuropil; occasionally they exhibited symmetrical synapses of en passant type with non-immunoreactive dendrites or somata. Our results support a functional significance of serotonergic regulation of the substantia nigra in mammals.     

Collateral axons of cholinergic pontine neurones projecting to midline, mediodorsal and parafascicular thalamic nuclei in the rat

The organization of collateral axons projecting from neurones in the pontine laterodorsal tegmental nucleus (LDTg) has been examined using combinations of retrograde neuronal tracers with immunocytochemical markers for the acetylcholine-synthesizing enzyme choline acetyltranferase (CHAT), focussing on projections to the midline, mediodorsal and parafascicular thalamic nuclei and the ventral tegmental area. 25–59% of LDTg neurones projecting to the mediodorsal nucleus provided collaterals to the midline nuclei. Virtually all (87–96%) of these double retrogradely labelled neurones appeared cholinergic. 9–18% of LDTg neurones projecting to the parafascicular nuclei also provided a collateral to the midline nuclei and 50–78% of these double retrogradely labelled neurones stained for CHAT. 26–29% of the single LDTg neurones which projected collaterals to both the mediodorsal and midline nuclei, were found to project a third collateral to the ventral tegmental area. These anatomical findings, taken together with functional evidence, suggest that cholinergic terminals arising from LDTg are involved in coordinating thalamic mechanisms of brain state control; and in regulating dopaminergic pathways, both directly and via the thalamus.     

帕金森病大鼠黑质区神经干细胞分化的观察

目的:探讨帕金森病(Parkinson's disease,PD)大鼠中脑黑质区神经干细胞(NSCs)的分化情况.方法:将6-OHDA注入纹状体内制作PD大鼠模型.随机将成功模型分为3 d、5 d、7 d、14 d、28 d组,每组6只;另设假手术及正常对照组各3只.向成功模型鼠腹腔注射5-溴脱氧尿苷(Brdu).用Brdu/NeuN、Brdu/GFAP、Brdu/TH免疫双标组织化学方法检测黑质区内源性NSCs向神经元、神经胶质细胞和多巴胺(DA)能神经元的分化情况.结果:PD模型7 d组,在黑质区Brdu /GFAP 、Brdu /NeuN 细胞开始出现,14 d组双标的阳性细胞数量逐渐增加,28 d达到高峰,14 d、28 d组与其它组比较差异显著(P＜0.05).在这些双标细胞中,Brdu /GFAP 细胞数量较多,Brdu /NeuN 细胞数量较少(P＜0.05),未发现Brdu /TH 细胞.结论:PD大鼠模型黑质区NSCs多数分化为神经胶质细胞,少数分化为神经元,在没有诱导和干预下,未见有向DA能神经元分化.     

Cholinergic projections to the anterior thalamic nuclei in the rat: a combined retrograde tracing and choline acetyl transferase immunohistochemical study

Retrograde transport of horseradish peroxidase (HRP) was combined with choline acetyltransferase (ChAT) immunohistochemistry to study cholinergic projections to the anterior thalamic nuclei in the rat. Small iontophoretic injections of HRP placed into different subdivisions of the anterior thalamic nuclear complex resulted in distinct patterns of retrograde labelling in two major cholinergic cell groups of the mesopontine tegmentum, the laterodorsal tegmental nucleus (LDTg), in which a majority of the labelled cells was located, and the pedunculopontine tegmental nucleus (PPT). After injections into the posterior subdivision of the anteroventral thalamic nucleus (AVp), double-labelled neurons were present predominantly in the ipsilateral LDTg while a smaller number was found in the PPT. In the ipsilateral LDTg, 60–70% of ChAT-positive neurons were HRP-labelled, and 90–95% of the HRP-labelled neurons were ChAT-positive. In the contralateral LDTg, 30–40% of ChAT-positive neurons were HRP-labelled. After injections in the medial subdivision of the anteroventral thalamic nucleus (AVm), the pattern of labelling in LDTg was similar to that detected after injections in the AVp. The number of double-labelled neurons in the LDTg and PPT was much lower after injections into AVm than after injections into AVp. When injections were confined to the anterodorsal thalamic nucleus (AD), no HRP-labelled cells were present in the LDTg or PPT. These results show that the LDTg and PPT are the sources of the cholinergic input to the rat anterior thalamus. The major projection from LDTg and PPT is to the AVp, whereas there is a lighter cholinergic projection to the AVm. The AD does not receive a projection from cholinergic cells in the mesopontine tegmentum.Abbreviations AChE Acetylcholinestrase - AD anterodorsal thalamic · nucleus - AM anteromedial thalamic nucleus - ATN anterior thalamic nuclei - AVm medial subdivision of the anteroventral thalamic nucleus - AVp posterior subdivision of the anteroventral thalamic nucleus - CG central gray - ChAT choline acetyltransferase - DAB diaminobenzidine tetrahydrochloride - DR dorsal raphé nucleus - f fornix - HRP horseradish peroxidase - ic internal capsule - LD laterodorsal thalamic nucleus - LDTg laterodorsal tegmental nucleus - ml medial lemniscus - mlf medial longitudinal fasciculus - mt mamillothalamic tract - NRS normal rabbit serum - PPT pedunculopontine tegmental nucleus - PT paratenial thalamic nucleus - Re reuniens thalamic nucleus - Rh rhomboid thalamic nucleus - RPn raphé pontis nucleus - scp superior cerebellar peduncle - sm stria medullaris thalami - st stria terminalis - TAAB glutaraldehyde - TRN thalamic reticular nucleus - VL ventrolateral thalamic nucleus - VM ventromedial thalamic nucleus - xscp decussation of superior cerebellar peduncle     

Stimulants and lesions of the substantia nigra and red nucleus

The interaction of altered activity levels by stimulants and brainstem lesions was examined. Lesions of the substantia nigra and red nucleus significantly increased activity over control levels in albino rats. The stimulant action of d-amphetamine and methylphenidate was additive with lesion effects. In addition, stimulants disrupted the normal light-dark relationship with activity while the lesions did not. It is suggested that there are two functionally separate systems regulating locomotor activity.     

Damage of substantia nigra pars reticulata during pilocarpine-induced status epilepticus in the rat: immunohistochemical study of neurons,astrocytes and serum-protein extravasation

Summary The substantia nigra has a gating function controlling the spread of epileptic seizure activity. Additionally, in models of prolonged status epilepticus the pars reticulata of substantia nigra (SNR) suffers from a massive lesion which may arise from a massive metabolic derangement and hyperexcitation developing in the activated SNR. In this study, status epilepticus was induced by systemic injection of pilocarpine in rats. The neuropathology of SNR was investigated using immunohistochemical techniques with the major emphasis on the time-course of changes in neurons and astrocytes. Animals surviving 20, 30, 40, 60 min, 2, 3, 6 hours, 1, 2, and 3 days after induction of status epilepticus were perfusion-fixed, and brains processed for immunohistochemical staining of SNR. Nissl-staining and antibodies against the neuron-specific calcium-binding protein, parvalbumin, served to detect neuronal damage in SNR. Antibodies against the astroglia-specific cytoskeletal protein, glial fibrillary acidic protein (GFAP), and against the glial calcium-binding protein, S-100 protein, were used to assess the status of astrocytes. Immunohistochemical staining for serum-albumin and immunoglobulins in brain tissue was taken as indicator of blood-brain barrier disturbances and vasogenic edema formation. Immunohistochemical staining indicated loss of GFAP-staining already at 30 min after induction of seizures in an oval focus situated in the center of SNR while sparing medial and lateral aspects. At 1 h there was additional vacuolation in S-100 protein staining. By 2 hours, parvalbumin-staining changed in the central SNR indicating neuronal damage, and Nissl-staining visualized some neuronal distortion. Staining for serum-proteins occurred in a patchy manner throughout the forebrain during the first hours. By 6 h, vasogenic edema covered the lesioned SNR. By 24 h, glial and neuronal markers indicated a massive lesion in the center of SNR. By 48–72 h, astrocytes surrounding the lesion increased in size, and polymorphic phagocytotic cells invaded the damaged area. In a further group of animals surviving 1 to 5 days, conventional paraffin-sections confirmed the neuronal and glial damage of SNR. Additional pathology of similar quality was found in the globus pallidus. Since astrocytes were always damaged in parallel with neurons in SNR it is proposed that the anatomical and functional interrelationship between neurons and astrocytes is particularly tight in SNR. Both cell elements may suffer in common from metabolic disturbance and neurotransmitter dysfunction as occur during massive status epilepticus.     

Participation of the substantia nigra dopaminergic neurons in the occurrence of gastric mucosal erosions

Previous reports indicate that dopaminergic systems play an important role on gastric mucosal erosions. In the present study, the participation of intrinsic neurons of the substantia nigra (SN) and ventral tegmental area (VTA) on the occurrence of stomach ulceration was investigated. It was found that bilateral microinfusions of a neurotoxic dose (20 microg/microl) of N-methyl-D-aspartate (NMDA) into the SN, but not in the VTA, lead to gastric erosions 24 h after the surgery. A decrease in dopamine levels in the caudate 24 h after the microinfusion of NMDA into the SN was also observed. Destruction of SN cell bodies with 6-hydroxydopamine (6-OHDA) did not induce gastric ulceration or changes in dopamine levels in the caudate nucleus 24 h after the lesioning procedure. NMDA neurotoxicity is mediated by the acute excitatory or activational effects, in contrast to 6-OHDA, suggesting that the occurrence of gastric ulceration after the infusion of NMDA into the SN is not due to the cell death per se but is related to an overactivation of these cells that precede their death. Taken together, these results suggest that modulation of dopaminergic levels by neurons located within the SN may play an important role for the development of gastric erosions.     

NeuN is not a reliable marker of dopamine neurons in rat substantia nigra

Quantification of neuronal cell number is a key endpoint in the characterization of neurodegenerative disease models and neuroprotective regimens. Immunohistochemistry for phenotypic markers, followed by unbiased stereology is often used to quantify the relevant neuronal population. To control for loss of phenotypic markers in the absence of cell death, or to determine if other types of neurons are lost, a general neuronal marker is often desired. Vertebrate neuron-specific nuclear protein (NeuN) is reportedly expressed in most mammalian neurons. In Parkinson's disease models, NeuN has been widely used to determine if there is actual nigral dopamine neuron loss or simply loss of tyrosine hydroxylase expression, a prominent phenotypic marker. To date, the qualitative value of NeuN expression as such a marker in the substantia nigra has not been assessed. Midbrain tissue sections from control rats were stained for NeuN and tyrosine hydroxylase and assessed by light or confocal microscopy. Here we report that NeuN expression level in the rat substantia nigra was highly variable, with many faintly stained cells that would not be meet stereological scoring criteria. Additionally, dopamine neurons with little or no NeuN expression were readily identified. Subcellular compartmentalization of NeuN expression was also variable, with many cells dorsal and ventral to the nigra exhibiting expression in both the nucleus and cytoplasm. NeuN expression also appeared to be much higher in non-dopamine neurons within the ventral midbrain. This characterization of nigral NeuN expression suggests that it is not useful as a quantitative general neuronal marker in the substantia nigra.     

The pattern of innervation of the corpus striatum by the substantia nigra

Radioactive proteins seen in autoradiographs of the rat striatum after injection of radioactive leucine into the substantia nigra are not evenly distributed. Areas of more intense labelling are regularly spaced in the nucleus in rows parallel to the edge of the striatum.The pattern is reminiscent of the innervation in young animals where ‘intensely fluorescent islands’ are seen. It is suggested that the areas of higher activity may correspond to the areas of dense labelling reported by others in sections of the striatum stained for acetylcholinesterase.     

Cytology of embryonal rhabdomyosarcoma: a cytologic, light microscopic, electron microscopic, and immunohistochemical study of seven cases

A correlated cytologic and histologic study of seven cases of embryonal rhabdomyosarcoma is presented. The diagnosis of rhabdomyosarcoma was established by light and electron microscopy and immunohistochemistry of the operative specimens. The cytologic appearance of the smears corresponded well with the histopathologic findings. Cytologically, two main cell types were distinguished: a predominant primitive, small round cell with scant cytoplasm and a large cell with an abundant cytoplasm, sometimes tadpole- or ribbon-shaped. The tumor cells were often enclosed in a background of mucosubstances. The lack of cytologic features proving rhabdomyoblastic differentiation, such as cross-striation, necessitates the use of additional methods in the cytologic diagnosis of embryonal rhabdomyosarcoma. The value of the embedding technique for ultrastructural analysis and immunohistochemistry in the demonstration of desmin in aspirates is emphasized in the diagnosis of embryonal rhabdomyosarcoma.     

Collateral projections of neurons of the rat globus pallidus to the striatum and substantia nigra

Summary Double retrograde fluorescent tracing techniques were used to evaluate the possibility that ascending and descending projections from the globus pallidus arise from divergent axon collaterals. Appropriately placed injections of different tracers (True Blue, Nuclear Yellow) into the substantia nigra and the striatum resulted in the double labelling of neurons in the globus pallidus. Conversely, simultaneous injection of two different sites within the striatum did not produce significant double labelling of globus pallidus neurons. These results indicate that at least a portion of the neurons of the globus pallidus project to both the striatum and substantia nigra, and that individual pallidal neurons do not have widespread projections to the striatum.     

Spatial relationship between neurotensinergic axons and cholinergic neurons in the rat basal forebrain: a light microscopic study with three-dimensional reconstruction

Cholinergic neurons of the basal forebrain are known to project to the hippocampus and cerebral cortex wherein they play an important role in cortical activation, attention and memory. These neurons have been shown to possess neurotensin binding sites and to respond electrophysiologically to local application of neurotensin, indicating the presence of functional receptors on their membrane. In the present light microscopic study, the spatial relationship between neurotensinergic axons and cholinergic nerve cell bodies and proximal dendrites was investigated in the basal forebrain of the rat by dual immunostaining for neurotensin and choline acetyltransferase. Rostrally, neurotensinergic fibres were concentrated in the lateral septum and anterior substantia innominata, whereas cholinergic neurons were located in the medial septum, diagonal band of Broca and magnocellular preoptic nucleus. At high magnification, a few neurotensinergic axonal varicosities were observed in the region of cholinergic neurons, and fewer still in close proximity to cholinergic perikarya and proximal dendrites. Caudally, neurotensinergic fibres formed a dense plexus of varicose axons in the same region where cholinergic neurons were located in the posterior substantia innominata and in the ventral and caudal aspects of the globus pallidus. At high magnification, many of these neurotensinergic varicosities were seen in close proximity to the cholinergic perikarya. These results suggest that cholinergic cells receive a much denser neurotensinergic innervation in the caudal than in the rostral aspect of the basal forebrain. This differential distribution is not reflected in the uniform density of neurotensin receptors and potent responses to neurotensin through the cholinergic cell population, suggesting the possibility that neurotensin's effects are mediated in part by a paracrine mechanism.     

Origin,course and termination of dopaminergic substantia nigra neurons projecting to the amygdaloid complex in the cat

The organization of dopaminergic neurons projecting to the amygdala was examined using retrograde (horseradish peroxidase histochemistry) and anterograde ([³H]leucine autoradiography) transport methods and Falck-Hillarp histofluorescence techniques combined with microspectrofluorometry and radiofrequency lesions. Cell bodies located within the pars lateralis and pars compacta of the substantia nigra were found to project to the lateral and central amygdaloid nuclei, respectively. Both of these areas within the substantia nigra contained dopaminergic perikarya, while the central and lateral amygdaloid nuclei contained fluorescent varicosities with features indicative of dopaminergic neurons. Lesions restricted to the pars lateralis of the substantia nigra resulted in a loss of fluorescence in the lateral amygdaloid nucleus. Autoradiographic experiments revealed that the projections from the pars lateralis did not run with fibers originating from the pars compacta in the nigrostriatal tract but rather had their own course occupying a lateral position adjacent to the cerebral peduncle and joining the ventral amygdalo-fugal bundle.The data indicate that, in the cat, there are two separate dopaminergic projections to the amygdala arising from the substantia nigra.     

The TPc,the avian substantia nigra: Pharmacology and behavior

The nucleus tegmenti pedunculo-pontinus, pars compacta (TPc) may be the avian analogue of the mammalian substantia nigra (SN). The analogy is suggested by both comparative neuroanatomical and neurohistochemical observations. To test the proposed analogy certain drugs (agonists or antagonists of putative transmitters that modulate the dopaminergic and GABAergic systems in rat) were injected into the TPc of the pigeon and the behavior effects observed. Muscimol (a GABA agonist) injected into the caudal TPc induced contralateral rotation and postural asymmetries. Pre-treatment with subcutaneous injections of apomorphine hydrochloride enhanced and haloperidol suppressed the rotatory response, while the postural asymmetries were not altered by either drug. Muscimol injected into the rostral TPc induced contralateral rotation, marked ataxia, and postural asymmetries, particularly the head and neck, legs and wings. Whereas apomorphine (subcutaneous injection) was without effect on the rotatory response to muscimol, haloperidol suppressed the rotatory response. Neither drug effected the postural asymmetry. Following drug injections into either the pigeon TPc or the rat SN the behaviors induced in both bird and rat suggest that the TPc and SN are analogous.     

The adrenergic innervation of the rat central amygdaloid nucleus: a light and electron microscopic immunocytochemical study using phenylethanolamine N-methyltransferase as a marker

Using immunocytochemistry of phenylethanolamine N-methyltransferase for light and electron microscopy, investigations were carried out to document the morphology of adrenergic afferents innervating the rat central amygdaloid nucleus and to analyse the manner in which contacts with neurons of the nucleus are formed. With the light microscope, dense terminal plexus of phenylethanolamine N-methyltransferase-immunoreactive axons with typical large boutons (diameter>1 m) were found in the medial central nucleus, extending into its ventral subdivision and the adjacent intra-amygdaloid portion of the bed nucleus of the stria terminalis. Electron microscopy of the medial central nucleus showed phenylethanolamine N-methyltransferase-immunoreaction product in the cytoplasm of intervaricose axons and boutons. Large adrenergic boutons contained numerous small clear vesicles and, occasionally, large dense-cored vesicles. In serial sections, most boutons formed synaptic contacts. Synapses of immunoreactive terminals were mainly of the asymmetric type and localized preferentially on medium sized to small dendrites and dendritic spines. Structures postsynaptic to adrenergic boutons were often additionally contacted by non-labelled terminals. The study gives evidence that adrenergic afferents exert a direct synaptic influence on medial central nucleus neurons. The peripheral localization of the majority of adrenergic synapses, their asymmetric configuration, and the presence of non-adrenergic synapsing terminals in their immediate vicinity indicate that the major component of the adrenergic input is of an excitatory nature, and is integrated with innervation from other sources.Abbreviations BNST _i Intra-amygdaloid portion of the bed nucleus of the stria terminalis - CL lateral central amygdaloid nucleus - CLc lateral capsular central amygdaloid nucleus - CM medial central amygdaloid nucleus - CN central amygdaloid nucleus - CV ventral central amygdaloid nucleus - DAB diaminobenzidine - EM electron microscopy - ir immunoreactive - LM light microscopy - NPY neuropeptide tyrosine - PBS phosphate buffered saline - PFA paraformaldehyde - PNMT phenylethanolamine N-methyltransferase