Complementary Distribution of Calbindin D-28k and Parvalbumin in the Basal Forebrain and Midbrain of the Squirrel Monkey

Neurochemistry and circuit organization of the lateral spiriform nucleus of birds: A uniquely nonmammalian direct pathway component of the basal ganglia

We used diverse methods to characterize the role of avian lateral spiriform nucleus (SpL) in basal ganglia motor function. Connectivity analysis showed that SpL receives input from globus pallidus (GP), and the intrapeduncular nucleus (INP) located ventromedial to GP, whose neurons express numerous striatal markers. SpL-projecting GP neurons were large and aspiny, while SpL-projecting INP neurons were medium sized and spiny. Connectivity analysis further showed that SpL receives inputs from subthalamic nucleus (STN) and substantia nigra pars reticulata (SNr), and that the SNr also receives inputs from GP, INP, and STN. Neurochemical analysis showed that SpL neurons express ENK, GAD, and a variety of pallidal neuron markers, and receive GABAergic terminals, some of which also contain DARPP32, consistent with GP pallidal and INP striatal inputs. Connectivity and neurochemical analysis showed that the SpL input to tectum prominently ends on GABAA receptor-enriched tectobulbar neurons. Behavioral studies showed that lesions of SpL impair visuomotor behaviors involving tracking and pecking moving targets. Our results suggest that SpL modulates brainstem-projecting tectobulbar neurons in a manner comparable to the demonstrated influence of GP internus on motor thalamus and of SNr on tectobulbar neurons in mammals. Given published data in amphibians and reptiles, it seems likely the SpL circuit represents a major direct pathway-type circuit by which the basal ganglia exerts its motor influence in nonmammalian tetrapods. The present studies also show that avian striatum is divided into three spatially segregated territories with differing connectivity, a medial striato-nigral territory, a dorsolateral striato-GP territory, and the ventrolateral INP motor territory.

Corticotropin-releasing factor-dopamine interactions in male and female macaque: Beyond the classic VTA

Dopamine (DA) is involved in stress and stress-related illnesses, including many psychiatric disorders. Corticotropin-releasing factor (CRF) plays a role in stress responses and targets the ventral midbrain DA system, which is composed of DA and non-DA cells, and divided into specific subregions. Although CRF inputs to the midline A10 nuclei ("classic VTA") are known, in monkeys, CRF-containing terminals are also highly enriched in the expanded A10 parabrachial pigmented nucleus (PBP) and in the A8 retrorubral field subregions. We characterized CRF-labeled synaptic terminals on DA (tyrosine hydroxylase, TH+) and non-DA (TH-) cell types in the PBP and A8 regions using immunoreactive electron microscopy (EM) in male and female macaques. CRF labeling was present mostly in axon terminals, which mainly contacted TH-negative dendrites in both subregions. Most CRF-positive terminals had symmetric profiles. In both PBP and A8, CRF symmetric (putative inhibitory) synapses onto TH-negative dendrites were significantly greater than asymmetric (putative excitatory) profiles. This overall pattern was similar in males and females, despite shifts in the size of these effects between regions depending on sex. Because stress and gonadal hormone shifts can influence CRF expression, we also did hormonal assays over a 6-month time period and found little variability in basal cortisol across similarly housed animals at the same age. Together our findings suggest that at baseline, CRF-positive synaptic terminals in the primate PBP and A8 are poised to regulate DA indirectly through synaptic contacts onto non-DA neurons.

Ultrastructural localization of glutamate delta 1 (GluD1) receptor immunoreactivity in the mouse and monkey striatum

The glutamate receptor delta 1 (GluD1) is strongly expressed in the striatum. Knockout of GluD1 expression in striatal neurons elicits cognitive deficits and disrupts the thalamostriatal system in mice. To understand the potential role of GluD1 in the primate striatum, we compared the cellular and subcellular localization of striatal GluD1 immunoreactivity (GluD1-IR) in mice and monkeys. In both species, striatal GluD1-IR displayed a patchy pattern of distribution in register with the striosome/matrix compartmentation, but in an opposite fashion. While GluD1 was more heavily expressed in the striosomes than the matrix in the monkey caudate nucleus, the opposite was found in the mouse striatum. At the electron microscopic level, GluD1-IR was preferentially expressed in dendritic shafts (47.9 ± 1.2%), followed by glia (37.7 ± 2.5%), and dendritic spines (14.3 ± 2.6%) in the matrix of the mouse striatum. This pattern was not statistically different from the labeling in the striosome and matrix compartments of the monkey caudate nucleus, with the exception of a small amount of GluD1-positive unmyelinated axons and axon terminals in the primate striatum. Immunogold staining revealed synaptic and perisynaptic GluD1 labeling at putative axo-dendritic and axo-spinous glutamatergic synapses, and intracellular labeling on the surface of mitochondria. Confocal microscopy showed that GluD1 is preferentially colocalized with thalamic over cortical terminals in both the striosome and matrix compartments. These data provide the anatomical substrate for a deeper understanding of GluD1 regulation of striatal glutamatergic synapses, but also suggest possible extrasynaptic, glial, and mitochondrial GluD1 functions.

Characterization of the relaxin family peptide receptor 3 system in the mouse bed nucleus of the stria terminalis

The bed nucleus of the stria terminalis (BNST) is a critical node involved in stress and reward-related behaviors. Relaxin family peptide receptor 3 (RXFP3) signaling in the BNST has been implicated in stress-induced alcohol seeking behavior. However, the neurochemical phenotype and connectivity of BNST RXFP3-expressing (RXFP3+) cells have yet to be elucidated. We interrogated the molecular signature and electrophysiological properties of BNST RXFP3+ neurons using a RXFP3-Cre reporter mouse line. BNST RXFP3+ cells are circumscribed to the dorsal BNST (dBNST) and are neurochemically heterogeneous, comprising a mix of inhibitory and excitatory neurons. Immunohistochemistry revealed that ~48% of BNST RXFP3+ neurons are GABAergic, and a quarter of these co-express the calcium-binding protein, calbindin. A subset of BNST RXFP3+ cells (~41%) co-express CaMKIIα, suggesting this subpopulation of BNST RXFP3+ neurons are excitatory. Corroborating this, RNAscope® revealed that ~35% of BNST RXFP3+ cells express vVGluT2 mRNA, indicating a subpopulation of RXFP3+ neurons are glutamatergic. RXFP3+ neurons show direct hyperpolarization to bath application of a selective RXFP3 agonist, RXFP3-A2, while around 50% of cells were depolarised by exogenous corticotrophin releasing factor. In behaviorally naive mice the majority of RXFP3+ neurons were Type II cells exhibiting I_h and T type calcium mediated currents. However, chronic swim stress caused persistent plasticity, decreasing the proportion of neurons that express these channels. These studies are the first to characterize the BNST RXFP3 system in mouse and lay the foundation for future functional studies appraising the role of the murine BNST RXFP3 system in more complex behaviors.

Beyond the Classic VTA: Extended Amygdala Projections to DA-Striatal Paths in the Primate

The central extended amygdala (CEA) has been conceptualized as a 'macrosystem' that regulates various stress-induced behaviors. Consistent with this, the CEA highly expresses corticotropin-releasing factor (CRF), an important modulator of stress responses. Stress alters goal-directed responses associated with striatal paths, including maladaptive responses such as drug seeking, social withdrawal, and compulsive behavior. CEA inputs to the midbrain dopamine (DA) system are positioned to influence striatal functions through mesolimbic DA-striatal pathways. However, the structure of this amygdala-CEA-DA neuron path to the striatum has been poorly characterized in primates. In primates, we combined neuronal tracer injections into various arms of the circuit through specific DA subpopulations to assess: (1) whether the circuit connecting amygdala, CEA, and DA cells follows CEA intrinsic organization, or a more direct topography involving bed nucleus vs central nucleus divisions; (2) CRF content of the CEA-DA path; and (3) striatal subregions specifically involved in CEA-DA-striatal loops. We found that the amygdala-CEA-DA path follows macrostructural subdivisions, with the majority of input/outputs converging in the medial central nucleus, the sublenticular extended amygdala, and the posterior lateral bed nucleus of the stria terminalis. The proportion of CRF+ outputs is >50%, and mainly targets the A10 parabrachial pigmented nucleus (PBP) and A8 (retrorubal field, RRF) neuronal subpopulations, with additional inputs to the dorsal A9 neurons. CRF-enriched CEA-DA projections are positioned to influence outputs to the 'limbic-associative' striatum, which is distinct from striatal regions targeted by DA cells lacking CEA input. We conclude that the concept of the CEA is supported on connectional grounds, and that CEA termination over the PBP and RRF neuronal populations can influence striatal circuits involved in associative learning.

Optogenetic Dissection of the Basal Forebrain Neuromodulatory Control of Cortical Activation, Plasticity, and Cognition

The basal forebrain (BF) houses major ascending projections to the entire neocortex that have long been implicated in arousal, learning, and attention. The disruption of the BF has been linked with major neurological disorders, such as coma and Alzheimer's disease, as well as in normal cognitive aging. Although it is best known for its cholinergic neurons, the BF is in fact an anatomically and neurochemically complex structure. Recent studies using transgenic mouse lines to target specific BF cell types have led to a renaissance in the study of the BF and are beginning to yield new insights about cell-type-specific circuit mechanisms during behavior. These approaches enable us to determine the behavioral conditions under which cholinergic and noncholinergic BF neurons are activated and how they control cortical processing to influence behavior. Here we discuss recent advances that have expanded our knowledge about this poorly understood brain region and laid the foundation for future cell-type-specific manipulations to modulate arousal, attention, and cortical plasticity in neurological disorders.

SIGNIFICANCE STATEMENT

Although the basal forebrain is best known for, and often equated with, acetylcholine-containing neurons that provide most of the cholinergic innervation of the neocortex, it is in fact an anatomically and neurochemically complex structure. Recent studies using transgenic mouse lines to target specific cell types in the basal forebrain have led to a renaissance in this field and are beginning to dissect circuit mechanisms in the basal forebrain during behavior. This review discusses recent advances in the roles of basal forebrain cholinergic and noncholinergic neurons in cognition via their dynamic modulation of cortical activity.

The non-human primate striatum undergoes marked prolonged remodeling during postnatal development

We examined the postnatal ontogeny of the striatum in rhesus monkeys (Macaca mulatta) to identify temporal and spatial patterns of histological and chemical maturation. Our goal was to determine whether this forebrain structure is developmentally static or dynamic in postnatal life. Brains from monkeys at 1 day, 1, 4, 6, 9, and 12 months of age (N = 12) and adult monkeys (N = 4) were analyzed. Nissl staining was used to assess striatal volume, cytoarchitecture, and apoptosis. Immunohistochemistry was used to localize and measure substance P (SP), leucine-enkephalin (LENK), tyrosine hydroxylase (TH), and calbindin D28 (CAL) immunoreactivities. Mature brain to body weight ratio was achieved at 4 months of age, and striatal volume increased from ∼1.2 to ∼1.4 cm(3) during the first postnatal year. Nissl staining identified, prominently in the caudate nucleus, developmentally persistent discrete cell islands with neuronal densities greater than the surrounding striatal parenchyma (matrix). Losses in neuronal density were observed in island and matrix regions during maturation, and differential developmental programmed cell death was observed in islands and matrix regions. Immunohistochemistry revealed striking changes occurring postnatally in striatal chemical neuroanatomy. At birth, the immature dopaminergic nigrostriatal innervation was characterized by islands enriched in TH-immunoreactive puncta (putative terminals) in the neuropil; TH-enriched islands aligned completely with areas enriched in SP immunoreactivity but low in LENK immunoreactivity. These areas enriched in SP immunoreactivity but low in LENK immunoreactivity were identified as striosome and matrix areas, respectively, because CAL immunoreactivity clearly delineated these territories. SP, LENK, and CAL immunoreactivities appeared as positive neuronal cell bodies, processes, and puncta. The matrix compartment at birth contained relatively low TH-immunoreactive processes and few SP-positive neurons but was densely populated with LENK-immunoreactive neurons. The nucleus accumbens part of the ventral striatum also showed prominent differences in SP, LENK, and CAL immunoreactivities in shell and core territories. During 12 months of postnatal maturation salient changes occurred in neurotransmitter marker localization: TH-positive afferents densely innervated the matrix to exceed levels of immunoreactivity in the striosomes; SP immunoreactivity levels increased in the matrix; and LENK-immunoreactivity levels decreased in the matrix and increased in the striosomes. At 12 months of age, striatal chemoarchitecture was similar qualitatively to adult patterns, but quantitatively different in LENK and SP in caudate, putamen, and nucleus accumbens. This study shows for the first time that the rhesus monkey striatum requires more than 12 months after birth to develop an adult-like pattern of chemical neuroanatomy and that principal neurons within striosomes and matrix have different developmental programs for neuropeptide expression. We conclude that postnatal maturation of the striatal mosaic in primates is not static but, rather, is a protracted and dynamic process that requires many synchronous and compartment-selective changes in afferent innervation and in the expression of genes that regulate neuronal phenotypes.

Amygdala projections to the lateral bed nucleus of the stria terminalis in the macaque: comparison with ventral striatal afferents

The lateral bed nucleus of the stria terminalis (BSTL) is involved in mediating anxiety-related behaviors to sustained aversive stimuli. The BSTL forms part of the central extended amygdala, a continuum composed of the BSTL, the amygdala central nucleus, and cell columns running between the two. The central subdivision (BSTLcn) and the juxtacapsular subdivision (BSTLJ) are two BSTL regions that lie above the anterior commissure, near the ventral striatum. The amygdala, a heterogeneous structure that encodes emotional salience, projects to both the BSTL and ventral striatum. We placed small injections of retrograde tracers into the BSTL, focusing on the BSTLcn and BSTLJ, and analyzed the distribution of labeled cells in amygdala subregions. We compared this to the pattern of labeled cells following injections into the ventral striatum. All retrograde results were confirmed by anterograde studies. We found that the BSTLcn receives stronger amygdala inputs relative to the BSTLJ. Furthermore, the BSTLcn is defined by inputs from the corticoamygdaloid transition area and central nucleus, while the BSTLJ receives inputs mainly from the magnocellular accessory basal and basal nucleus. In the ventral striatum, the dorsomedial shell receives inputs that are similar, but not identical, to inputs to the BSTLcn. In contrast, amygdala projections to the ventral shell/core are similar to projections to the BSTLJ. These findings indicate that the BSTLcn and BSTLJ receive distinct amygdala afferent inputs and that the dorsomedial shell is a transition zone with the BSTLcn, while the ventral shell/core are transition zones with the BSTLJ.

Localization of type-III sodium-dependent phosphate transporter 2 in the mouse brain

Type-III sodium-dependent phosphate transporters 1 and 2 (PiT-1 and PiT-2, respectively) are proteins encoded by SLC20A1 and SLC20A2, respectively. The ubiquitous distribution of PiT-1 and PiT-2 mRNAs in mammalian tissues is in agreement with the housekeeping maintenance of homeostasis of intracellular inorganic phosphate (Pi), which is absorbed from interstitial fluid for normal cellular functions. Recently, mutations of SLC20A2 have been found in patients with idiopathic basal ganglia calcification (IBGC), also known as Fahr's disease. However, the localization of PiT-2 in the brain has not been clarified yet. Therefore, the aim of this study is to clarify the distribution of PiT-2 expression in the mouse brain. Our biochemical and immunohistochemical analyses using a polyclonal antibody (Ab) and a monoclonal Ab showed that PiT-2 was ubiquitously expressed throughout the brain. In terms of the cellular type, PiT-2 was predominantly detected in neurons; it colocalized with β-tubulin III in the cerebral cortex and with calbindin D-28K in Purkinje cells. Additionally, PiT-2 immunopositivity was detected in the microtubule-associated protein 2-positive neuronal dendrites in the cerebral cortex. However, colocalization with PiT-2 immunopositivity was not observed in the synaptophysin-positive nerve terminals. PiT-2 was also expressed in astrocytes and vascular endothelial cells. Our results indicate that PiT-2 plays an important role in the maintenance of cellular Pi homeostasis in neurons, astrocytes, and endothelial cells. This finding is a milestone in the study of the function of PiT-2 in the normal mouse brain and particularly in the brains of patients with Fahr's disease.

Neurochemical characterization of the tree shrew dorsal striatum

The striatum is a major component of the basal ganglia and is associated with motor and cognitive functions. Striatal pathologies have been linked to several disorders, including Huntington’s, Tourette’s syndrome, obsessive–compulsive disorders, and schizophrenia. For the study of these striatal pathologies different animal models have been used, including rodents and non-human primates. Rodents lack on morphological complexity (for example, the lack of well defined caudate and putamen nuclei), which makes it difficult to translate data to the human paradigm. Primates, and especially higher primates, are the closest model to humans, but there are ever-increasing restrictions to the use of these animals for research. In our search for a non-primate animal model with a striatum that anatomically (and perhaps functionally) can resemble that of humans, we turned our attention to the tree shrew. Evolutionary genetic studies have provided strong data supporting that the tree shrews (Scadentia) are one of the closest groups to primates, although their brain anatomy has only been studied in detail for specific brain areas. Morphologically, the tree shrew striatum resembles the primate striatum with the presence of an internal capsule separating the caudate and putamen, but little is known about its neurochemical composition. Here we analyzed the expression of calcium-binding proteins, the presence and distribution of the striosome and matrix compartments (by the use of calbindin, tyrosine hydroxylase, and acetylcholinesterase immunohistochemistry), and the GABAergic system by immunohistochemistry against glutamic acid decarboxylase and Golgi impregnation. In summary, our results show that when compared to primates, the tree shrew dorsal striatum presents striking similarities in the distribution of most of the markers studied, while presenting some marked divergences when compared to the rodent striatum.

Immunohistochemical localization of AMPA-type glutamate receptor subunits in the striatum of rhesus monkey

Corticostriatal and thalamostriatal projections utilize glutamate as their neurotransmitter. Their influence on striatum is mediated, in part, by ionotropic AMPA-type glutamate receptors, which are heteromers composed of GluR1-4 subunits. While the cellular localization of AMPA-type subunits in the basal ganglia has been well characterized in rodents, the cellular localization of AMPA subunits in primate basal ganglia is not. We thus carried out immunohistochemical studies of GluR1-4 distribution in rhesus monkey basal ganglia in conjunction with characterization of each major neuron type. In striatum, about 65% of striatal neurons immunolabeled for GluR1, 75%-79% immunolabeled for GluR2 or GluR2/3, and only 2.5% possessed GluR4. All neurons the large size of cholinergic interneurons (mean diameter 26.1 microm) were moderately labeled for GluR1, while all neurons in the size range of parvalbuminergic interneurons (mean diameter 13.8 microm) were intensely rich in GluR1. Additionally, somewhat more than half of the neurons in the size range of projection neurons (mean diameter 11.6 microm) immunolabeled for GluR1, and about one third of these were very rich in GluR1. About half of the neurons the size of cholinergic interneurons were immunolabeled for GluR2, and the remainder of the neurons that were immunolabeled for GluR2 coincided with projection neurons in size and shape (GluR2 diameter=10.7 microm), indicating that the vast majority of striatal projection neurons possess immunodectible GluR2. Similar results were observed with GluR2/3 immunolabeling. Half of the neurons the size of cholinergic interneurons immunolabeled for GluR4 and seemingly all neurons in the size range of parvalbuminergic interneurons possessed GluR4. These results indicate that AMPA receptor subunit combinations for striatal projection neurons in rhesus monkey are similar to those for the corresponding neuron types in rodents, and thus their AMPA responses to glutamate are likely to be similar to those demonstrated in rodents.

Basal ganglia pathology in schizophrenia: dopamine connections and anomalies

Schizophrenia is a severe mental illness that affects 1% of the world population. The disease usually manifests itself in early adulthood with hallucinations, delusions, cognitive and emotional disturbances and disorganized thought and behavior. Dopamine was the first neurotransmitter to be implicated in the disease, and though no longer the only suspect in schizophrenia pathophysiology, it obviously plays an important role. The basal ganglia are the site of most of the dopamine neurons in the brain and the target of anti-psychotic drugs. In this review, we will start with an overview of basal ganglia anatomy emphasizing dopamine circuitry. Then, we will review the major deficits in dopamine function in schizophrenia, emphasizing the role of excessive dopamine in the basal ganglia and the link to psychosis.

Amygdala projections to central amygdaloid nucleus subdivisions and transition zones in the primate

In rats and primates, the central nucleus of the amygdala (CeN) is most known for its role in responses to fear stimuli. Recent evidence also shows that the CeN is required for directing attention and behaviors when the salience of competing stimuli is in flux. To examine how information flows through this key output region of the primate amygdala, we first placed small injections of retrograde tracers into the subdivisions of the central nucleus in Old world primates, and examined inputs from specific amygdaloid nuclei. The amygdalostriatal area and interstitial nucleus of the posterior limb of the anterior commissure (IPAC) were distinguished from the CeN using histochemical markers, and projections to these regions were also described. As expected, the basal nucleus and accessory basal nucleus are the main afferent connections of the central nucleus and transition zones. The medial subdivision of the central nucleus (CeM) receives a significantly stronger input from all regions compared to the lateral core subdivision (CeLcn). The corticoamygdaloid transition zone (a zone of confluence of the medial parvicellular basal nucleus, paralaminar nucleus, and the sulcal periamygdaloid cortex) provides the main input to the CeLcn. The IPAC and amygdalostriatal area can be divided in medial and lateral subregions, and receive input from the basal and accessory basal nucleus, with differential inputs according to subdivision. The piriform cortex and lateral nucleus, two important sensory interfaces, send projections to the transition zones. In sum, the CeM receives broad inputs from the entire amygdala, whereas the CeLcn receives more restricted inputs from the relatively undifferentiated corticoamygdaloid transition region. Like the CeN, the transition zones receive most of their input from the basal nucleus and accessory basal nucleus, however, inputs from the piriform cortex and lateral nucleus, and a lack of input from the parvicellular accessory basal nucleus, are distinguishing afferent features.

The primate centromedian-parafascicular complex: anatomical organization with a note on neuromodulation

In addition to the cerebral cortex, the striatum receives excitatory input from the thalamus. The centromedian (centre median, CM) and parafascicular (Pf) nuclei are an important source of thalamostriatal projections. Anterograde tract-tracing indicates the CM-Pf complex provides dense afferents to the matrix compartment of the striatum. Whereas CM projects to the entire sensorimotor territory of the striatum, the Pf provides complementary input to the entire associative sector. The Pf also provides lighter input to the nucleus accumbens. Both CM and Pf provide light to moderately dense inputs to other components of the basal ganglia in a largely complementary manner, covering motor or associative-limbic territories of the subthalamic nucleus, globus pallidus and ventral midbrain. In turn, the CM and Pf receive mainly segregated input from parallel motor and associative-limbic circuits of the basal ganglia. The CM and Pf may therefore be considered important participants in parallel processing of motor and associative-limbic information in the basal ganglia. Connections of the CM and Pf with other thalamic nuclei suggest they also participate in integrative functions within the thalamus. In addition, inputs from the brainstem reticular core, reciprocal connections with the cerebral cortex and reticular thalamic nucleus suggest a role in state-dependant information processing. Consideration of the differential connections of the CM and Pf, and better understanding of their role in pathophysiology, may eventually lead to development of an important new target for relief of a variety of neurological and psychiatric disorders.

Supplementary motor area and presupplementary motor area: targets of basal ganglia and cerebellar output

We used retrograde transneuronal transport of neurotropic viruses in Cebus monkeys to examine the organization of basal ganglia and cerebellar projections to two cortical areas on the medial wall of the hemisphere, the supplementary motor area (SMA) and the pre-SMA. We found that both of these cortical areas are the targets of disynaptic projections from the dentate nucleus of the cerebellum and from the internal segment of the globus pallidus (GPi). On average, the number of pallidal neurons that project to the SMA and pre-SMA is approximately three to four times greater than the number of dentate neurons that project to these cortical areas. GPi neurons that project to the pre-SMA are located in a rostral, "associative" territory of the nucleus, whereas GPi neurons that project to the SMA are located in a more caudal and ventral "sensorimotor" territory. Similarly, dentate neurons that project to the pre-SMA are located in a ventral, "nonmotor" domain of the nucleus, whereas dentate neurons that project to the SMA are located in a more dorsal, "motor" domain. The differential origin of subcortical projections to the SMA and pre-SMA suggests that these cortical areas are nodes in distinct neural systems. Although both systems are the target of outputs from the basal ganglia and the cerebellum, these two cortical areas seem to be dominated by basal ganglia input.

Long-term effects of a single adult methamphetamine challenge: minor impact on dopamine fibre density in limbic brain areas of gerbils

BACKGROUND

The aim of the study was to test long-term effects of (+)-methamphetamine (MA) on the dopamine (DA) innervation in limbo-cortical regions of adult gerbils, in order to understand better the repair and neuroplasticity in disturbed limbic networks.

METHODS

Male gerbils received a single high dose of either MA (25 mg/kg i.p.) or saline on postnatal day 180. On postnatal day 340 the density of immunoreactive DA fibres and calbindin and parvalbumin cells was quantified in the right hemisphere.

RESULTS

No effects were found in the prefrontal cortex, olfactory tubercle and amygdala, whereas the pharmacological impact induced a slight but significant DA hyperinnervation in the nucleus accumbens. The cell densities of calbindin (CB) and parvalbumin (PV) positive neurons were additionally tested in the nucleus accumbens, but no significant effects were found. The present results contrast with the previously published long-term effects of early postnatal MA treatment that lead to a restraint of the maturation of DA fibres in the nucleus accumbens and prefrontal cortex and a concomitant overshoot innervation in the amygdala.

CONCLUSION

We conclude that the morphogenetic properties of MA change during maturation and aging of gerbils, which may be due to physiological alterations of maturing vs. mature DA neurons innervating subcortical and cortical limbic areas. Our findings, together with results from other long-term studies, suggest that immature limbic structures are more vulnerable to persistent effects of a single MA intoxication; this might be relevant for the assessment of drug experience in adults vs. adolescents, and drug prevention programs.

Neurochemical characterization of dopaminergic neurons in human striatum

We examined the neurochemical phenotype of striatal neurons expressing tyrosine hydroxylase (TH) mRNA to determine if they form a distinct class of neurons within the human striatum. Double in situ hybridization (ISH) and immunohistochemical (IHC) procedures were used to know if TH mRNA-positive striatal neurons express molecular markers of mature neurons (MAP2 and NeuN), dopaminergic neurons (DAT and Nurr1) or immature neurons (TuJ1). All TH mRNA-labeled neurons were found to express NeuN, DAT and Nurr1, whereas about 80% of them exhibited MAP2, confirming their neuronal and dopaminergic nature. Only about 30% of TH mRNA-labeled neurons expressed TuJ1, suggesting that this ectopic dopaminergic neuronal population is principally composed of mature neurons. The same double ISH/IHC approach was then used to know if these dopamine neurons display markers of well-established classes of striatal projection neurons (GAD65 and calbindin) or local circuit neurons (GAD65, calretinin, somatostatin and parvalbumin). Virtually all TH-labeled neurons expressed GAD65 mRNA, about 30% of them exhibited calretinin, but none stained for the other striatal neuron markers. These results suggest that the majority of TH-positive neurons intrinsic to the human striatum belong to a distinct subpopulation of striatal interneurons characterized by their ability to produce dopamine and GABA.

Bcl-2 immunoreactive neurons are differentially distributed in subregions of the amygdala and hippocampus of the adult macaque

The amygdala and hippocampus are key limbic structures of the temporal lobe, and are implicated in the pathology of mood disorders. Bcl-2, an intracellular protein, has recently been identified in the primate amygdala and hippocampus, and is now recognized as an intracellular target of mood stabilizing drugs. However, there are few data on the cellular phenotypes of bcl-2-expressing cells, or their distribution in specific subregions of the amygdala and hippocampus. We used a number of histochemical markers to define specific subregions of the primate amygdala and hippocampus, and examined phenotype-specific distributions of bcl-2 immunoreactive cells within each subregion. Immature-appearing bcl-2 labeled neurons, which co-contain class III beta-tubulin immunoreactivity, are found in distinct subregions in each structure. In the amygdala, bcl-2 positive neurons with an immature morphology are densely distributed in the paralaminar nucleus and intercalated cell islands, the parvicellular basal nucleus, and the ventral periamygdaloid cortex and amygdalohippocampal area. In the hippocampus, immature-appearing bcl-2-labeled cells are confined to the polymorph layer (subgranular zone), and base of the granule cell layer in the dentate gyrus. Well-differentiated neurons also express bcl-2. In the amygdala, labeled cells with mature phenotypes are concentrated in the parvicellular basal nucleus, the accessory basal nucleus, and the periamygdaloid cortex. The medial nucleus and central extended amygdala also contain many well-differentiated bcl-2 positive cells. In the hippocampus, the dentate gyrus and Ammon's horn contain many bcl-2 immunoreactive nonpyramidal cells. These are preferentially distributed in the rostral hippocampus. CA3 and CA2 contain relatively higher concentrations of bcl-2-labeled cells than CA1 and the subiculum. Bcl-2 is thus important in intrinsic circuitry of the hippocampus, and in amygdaloid subregions modulated by the hippocampus. In addition, the extended amygdala, a key amygdaloid output, is richly endowed with bcl-2 positive cells. This distribution suggests a role for bcl-2 in circuits mediating emotional learning and memory which may be targets of mood stabilizing drugs.

Calbindin D-28k positive projection neurones and calretinin positive interneurones of the rat globus pallidus

Immunohistochemistry for three calcium-binding proteins calbindin D-28k, calretinin, and parvalbumin revealed neuronal heterogeneity within the GP. Each neurone appeared to express either a single type of calcium binding protein or none at all. The co-localisation of calcium binding proteins was not observed. Combined immunohistochemistry and retrograde tract tracing using colloidal gold particles injected into the projection fields, the substantia nigra or subthalamic nucleus, revealed that projection neurones could be labelled with either calbindin or parvalbumin. These cells were of medium size (22 x 12 microm), multipolar and moderate varicose dendritic trees. In contrast, calretinin-positive neurones were never retrogradely labelled, even in regions where neuronal colloidal gold deposits were numerous. This, combined with their rarity (<1%) and small size (11 x 9 microm), suggests that calretinin may be a neurochemical marker for putative rat globus pallidus interneurones. Calcium-binding proteins are known to have unique buffering characteristics that may confer specific functional properties upon pallidal neurones. Indeed, differential calcium binding protein expression may underlie the electrophysiological heterogeneity observed in the rat globus pallidus.

Perineuronal nets in the rhesus monkey and human basal forebrain including basal ganglia

Perineuronal nets of extracellular matrix have been shown to characterize the microenvironment of individual neurons and the chemoarchitecture of brain regions such as basal forebrain nuclei. Previous work has also demonstrated that neurons in the human cerebral cortex ensheathed by perineuronal nets rarely undergo cytoskeletal changes in Alzheimer's disease, suggesting a neuroprotective effect of extracellular matrix components. It is not known, however, whether or not perineuronal nets are absent in the microenvironment of the cholinergic basal forebrain neurons that are involved early in the cascade of neurodegeneration in humans. Therefore, the present study was undertaken to examine the distribution patterns of perineuronal nets in the basal forebrain of the higher primates, rhesus monkey and human. Cytochemical staining was performed with the lectin Wisteria floribunda agglutinin and a polyclonal antibody to core proteins of chondroitin sulfate proteoglycans in the perfusion-fixed tissue of rhesus monkeys. In human brains, perineuronal nets were only stained with the immunoreaction for chondroitin sulfate proteoglycans. The results showed similar characteristics in distribution patterns of perineuronal nets in the medial septum, the diagonal band of Broca, the basal nucleus of Meynert (Ch1-Ch4), the lateral septum, the caudate-putamen, and the globus pallidus in both species. Double-labelling revealed that the vast majority of cholinergic neurons, labelled either with antibodies to choline acetyltransferase or the low-affinity neurotrophin receptor p75(NTR), were not ensheathed by perineuronal nets. A small subpopulation of net-associated neurons in close proximity to or intermingled with cholinergic neurons of the Ch1-Ch4 cell groups was found to be immunoreactive for parvalbumin. In the caudate-putamen, a large number of the parvalbumin-positive neurons were surrounded by perineuronal nets, whereas in the external and internal segments of the globus pallidus the coincidence of both markers was nearly complete. The study demonstrates that perineuronal nets of extracellular matrix are associated with different types of non-cholinergic neurons in the primate basal forebrain. The absence of nets around cholinergic basal forebrain neurons may be related to their slow modulatory activity but may also contribute to their susceptibility to degeneration in Alzheimer's disease.

Neurochemical organization of the human basal ganglia: anatomofunctional territories defined by the distributions of calcium-binding proteins and SMI-32

The distribution of the calcium-binding proteins calbindin-D28K (CB), parvalbumin (PV) and calretinin (CR), and of the nonphosphorylated neurofilament protein (with SMI-32) was investigated in the human basal ganglia to identify anatomofunctional territories. In the striatum, gradients of neuropil immunostaining define four major territories: The first (T1) includes all but the rostroventral half of the putamen and is characterized by enhanced matriceal PV and SMI-32 immunoreactivity (-ir). The second territory (T2) encompasses most part of the caudate nucleus (Cd) and rostral putamen (PuT), which show enhanced matriceal CB-ir. The third and fourth territories (T3 and T4) comprise rostroventral parts of Cd and PuT characterized by complementary patch/matrix distributions of CB- and CR-ir, and the accumbens nucleus (Acb), respectively. The latter is separated into lateral (prominently enhanced in CB-ir) and medial (prominently enhanced in CR-ir) subdivisions. In the pallidum, parallel gradients also delimit four territories, T1 in the caudal half of external (GPe) and internal (GPi) divisions, characterized by enhanced PV- and SMI-32-ir; T2 in their rostral half, characterized by enhanced CB-ir; and T3 and T4 in their rostroventral pole and in the subpallidal area, respectively, both expressing CB- and CR-ir but with different intensities. The subthalamic nucleus (STh) shows contrasting patterns of dense PV-ir (sparing only the most medial part) and low CB-ir. Expression of CR-ir is relatively low, except in the medial, low PV-ir, part of the nucleus, whereas SMI-32-ir is moderate across the whole nucleus. The substantia nigra is characterized by complementary patterns of high neuropil CB- and SMI-32-ir in pars reticulata (SNr) and high CR-ir in pars compacta (SNc) and in the ventral tegmental area (VTA). The compartmentalization of calcium-binding proteins and SMI-32 in the human basal ganglia, in particular in the striatum and pallidum, delimits anatomofunctional territories that are of significance for functional imaging studies and target selection in stereotactic neurosurgery.

Bed nucleus of the stria terminalis and extended amygdala inputs to dopamine subpopulations in primates

The 'extended amygdala', a forebrain continuum implicated in complex motivational responses, is comprised of the bed nucleus of the stria terminalis and its sublenticular extension into the centromedial amygdala. Dopamine is also involved in motivated behavior, and is increased in several brain regions by emotionally relevant stimuli. To examine how the extended amygdala influences the dopamine cells, we determined the organization of inputs from subdivisions of the bed nucleus of the stria terminalis and sublenticular extended amygdala to the dopamine subpopulations in monkeys. Inputs from the bed nucleus of the stria terminalis and corresponding regions of the sublenticular extended amygdala are differentially organized. The medial bed nucleus of the stria terminalis and its medial sublenticular extension have a mediolateral organization with the densest inputs to the medial substantia nigra, pars compacta, and relatively few inputs to the central and lateral substantia nigra. In contrast, the lateral bed nucleus of the stria terminalis (and its continuation into the sublenticular extended amygdala) projects across the mediolateral extent of the substantia nigra. The subnuclei of the lateral bed nucleus of the stria terminalis also have differential projections to the dopamine cells. While the central core of the lateral bed nucleus of the stria terminalis has restricted inputs, the surrounding dorsolateral, capsular and juxtacapsular subdivisions project strongly to the dorsal tier dopamine neurons. The posterior subdivision of the lateral bed nucleus of the stria terminalis and its continuation into the central sublenticular extended amygdala project more broadly to both the dorsal tier and densocellular region of the ventral tier. From these results we suggest that specific subdivisions of the bed nucleus of the stria terminalis have differential influences on the dopamine subpopulations, influencing dopamine responses in diverse brain regions.

GABA promotes survival but not proliferation of parvalbumin-immunoreactive interneurons in rodent neostriatum: an in vivo study with stereology

Amino-acid neurotransmitters regulate a wide variety of developmental processes in the mammalian CNS including neurogenesis, cell migration, and apoptosis. In order to investigate the role of GABA in early development of forebrain interneurons, we determined the survival of parvalbumin-immunoreactive GABAergic interneurons in the adult rat striatum following prenatal exposure to either GABA(A) receptor agonist or antagonist. Unbiased stereology was used to quantify parvalbumin-immunoreactive neuron number in the neostriatum of adult rats exposed to the drugs in utero, and the results were compared to pair-fed or vehicle controls. Embryos were exposed to the GABA(A) antagonist (bicuculline) or agonist (muscimol) during previously defined proliferative or post-proliferative periods for parvalbumin-immunoreactive interneurons. Unbiased stereology using the optical fractionator was used to estimate the total number of parvalbumin-immunoreactive neurons in neostriatum of experimental and control rats. No significant alteration in parvalbumin-immunoreactive neuron number was observed in rats treated with either bicuculline (1 or 2mg/kg/day) or muscimol (1mg/kg/day) during the proliferative phase. Administration of bicuculline during the post-proliferative phase significantly reduced parvalbumin-immunoreactive neuron number in the neostriatum. A concomitant decrease in neostriatal volume was also observed, suggesting that the effect is not restricted to parvalbumin-immunoreactive interneurons. Positional analysis revealed loss of normal regional distribution gradients for parvalbumin-immunoreactive neurons in neostriatum of rats exposed to bicuculline in the embryonic post-proliferative phase. This data collectively suggests that GABA promotes survival but not proliferation of parvalbumin-immunoreactive progenitors. GABA may also promote migration of subpopulations of interneurons that ultimately populate the ventral telencephalon.

Chemical anatomy of striatal interneurons in normal individuals and in patients with Huntington's disease

This paper reviews the major anatomical and chemical features of the various types of interneurons in the human striatum, as detected by immunostaining procedures applied to postmortem tissue from normal individuals and patients with Huntington's disease (HD). The human striatum harbors a highly pleomorphic population of aspiny interneurons that stain for either a calcium-binding protein (calretinin, parvalbumin or calbindin D-28k), choline acetyltransferase (ChAT) or NADPH-diaphorase, or various combinations thereof. Neurons that express calretinin (CR), including multitudinous medium and a smaller number of large neurons, are by far the most abundant interneurons in the human striatum. The medium CR+ neurons do not colocalize with any of the known chemical markers of striatal neurons, except perhaps GABA, and are selectively spared in HD. Most large CR+ interneurons display ChAT immunoreactivity and also express substance P receptors. The medium and large CR+ neurons are enriched with glutamate receptor subunit GluR2 and GluR4, respectively. This difference in AMPA GluR subunit expression may account for the relative resistance of medium CR+ neurons to glutamate-mediated excitotoxicity that may be involved in HD. The various striatal chemical markers display a highly heterogeneous distribution pattern in human. In addition to the classic striosomes/matrix compartmentalization, the striosomal compartment itself is composed of a core and a peripheral region, each subdivided by distinct subsets of striatal interneurons. A proper knowledge of all these features that appear unique to humans should greatly help our understanding of the organization of the human striatum in both health and disease states.

Cyto- and chemoarchitecture of basal forebrain cholinergic neurons in the common marmoset (Callithrix jacchus)

The cyto- and chemoarchitecture of basal forebrain cholinergic neurons (BFCN) was investigated in the lower primate, the common marmoset (Callithrix jacchus). A large population of magnocellular, hyperchromic, and choline acetyltransferase (ChAT)-positive neurons was detected in the marmoset basal forebrain. The distribution of these neurons was similar to those in higher primates. Thus, ChAT-positive neurons were observed in the medial septum (Ch2), the vertical (Ch2) and horizontal (Ch3) limbs of the diagonal band of Broca, and the nucleus basalis of Meynert (Ch4). The Ch4 complex was relatively well differentiated and displayed distinct sectors. We detected anterior (Ch4a, with a medial and a lateral subdivision), intermediate (Ch4i, with a dorsal and a ventral subdivision), and posterior (Ch4p) sectors in the marmoset Ch4. The Ch4i was relatively small while the Ch4p was large. Similar to the rodent, the marmoset Ch1 extended quite a distance posteriorly, and the Ch4p displayed a major interstitial component distributed within the globus pallidus, its medullary laminae, and the internal capsule. Virtually all of the marmoset BFCN displayed acetylcholinesterase activity, and low affinity (p75(NTR)) and high affinity (Trk) neurotrophin receptor immunoreactivity. A majority contained immunoreactivity for calbindin-D(28K) and calretinin. Many of the Ch4 neurons also displayed tyrosine hydroxylase immunoreactivity. The BFCN lacked galanin immunoreactivity, but were innervated by galanin-positive fibers. None of the marmoset BFCN were NADPH-d-positive. Thus, the BFCN display major anatomical and biochemical differences in the marmoset when compared with higher primates. The marmoset BFCN also display many characteristics common to other primates. This fact, combined with the relatively short life span of the marmoset, indicates that this species may be ideal for studies of age-related changes in the BFCN.

The core-shell dichotomy of nucleus accumbens in the rhesus monkey as revealed by double-immunofluorescence and morphology of cholinergic interneurons

Double-immunolabelling experiments for the combinations, calretinin (CR)-calbindin, CR-tyrosine hydroxylase (TH) and calbindin-TH, were performed in rhesus monkeys to compare the chemical organization of the nucleus accumbens (ACC) in primates and rodents. Additionally, the soma sizes and numbers of primary dendrites of cholinergic neurons in the subregions of ACC were compared with those of caudate-putamen. Our findings subserve the shell-core concept also in the primate ACC, as like in the rat, CR immunoreactivity (-ir) due to intense neuropil labelling is very strong in the shell of rhesus monkey, but poor in the core. The staining intensity of this marker decreases in dorsoventral direction. An almost complementary pattern was noted in sections of the monkey ACC immunostained for both calbindin and TH. The cholinergic interneurons of the nucleus caudatus-putamen are clearly distinguished from those of the ACC and insula Calleja magna by their much bigger soma sizes and higher numbers of primary dendrites. Cholinergic neurons of the shell were found to be slightly, but significantly, larger than those of the core that also subserves subdivision of the primate ACC into shell and core. A low proportion of tyrosine-hydroxylase-immunostained cells, already previously described below the rostral ACC, co-expressed CR but not calbindin. A CR-immunoreactive neuronal population, intermingled with these cells, extends as a stripe medially to the ACC along the septal part of corpus callosum into the lateral septal area. The presumed origin of CR-immunoreactive fibres in the shell of ACC is discussed.

Regional and cellular localisation of GABA(A) receptor subunits in the human basal ganglia: An autoradiographic and immunohistochemical study

The regional and cellular localisation of gamma-aminobutyric acid(A) (GABA(A)) receptors was investigated in the human basal ganglia using receptor autoradiography and immunohistochemical staining for five GABA(A) receptor subunits (alpha(1), alpha(2), alpha(3), beta(2, 3), and gamma(2)) and other neurochemical markers. The results demonstrated that GABA(A) receptors in the striatum showed considerable subunit heterogeneity in their regional distribution and cellular localisation. High densities of GABA(A) receptors in the striosome compartment contained the alpha(2), alpha(3), beta(2, 3), and gamma(2) subunits, and lower densities of receptors in the matrix compartment contained the alpha(1), alpha(2), alpha(3), beta(2,3), and gamma(2) subunits. Also, six different types of neurons were identified in the striatum on the basis of GABA(A) receptor subunit configuration, cellular and dendritic morphology, and chemical neuroanatomy. Three types of alpha(1) subunit immunoreactive neurons were identified: type 1, the most numerous (60%), were medium-sized aspiny neurons that were immunoreactive for parvalbumin and alpha(1), beta(2,3), and gamma(2) subunits; type 2 (38%) were medium-sized to large aspiny neurons immunoreactive for calretinin and alpha(1), alpha(3), beta(2,3), and gamma(2) subunits; and type 3 (2%) were large sparsely spiny neurons immunoreactive for alpha(1), alpha(3), beta(2,3), and gamma(2) subunits. Type 4 neurons were calbindin-positive and immunoreactive for alpha(2), alpha(3), beta(2,3), and gamma(2) subunits. The remaining neurons were immunoreactive for choline acetyltransferase (ChAT) and alpha(3) subunit (type 5) or were neuropeptide Y-positive with no GABA(A) receptor subunit immunoreactivity (type 6). The globus pallidus contained three types of neurons: types 1 and 2 were large neurons and were immunoreactive for alpha(1), alpha(3), beta(2,3), and gamma(2) subunits and for parvalbumin alone (type 1) or for both parvalbumin and calretinin (type 2); type 3 neurons were medium-sized and immunoreactive for calretinin and alpha(1), beta(2, 3), and gamma(2) subunits. These results show that the subunit composition of GABA(A) receptors displays considerable regional and cellular variation in the human striatum but are more homogeneous in the globus pallidus.

Calbindin-D 28kD immunofluorescence in ventral mesencephalic neurons labeled following injections of Fluoro-Gold in nucleus accumbens subterritories: inverse relationship relative to known neurotoxin vulnerabilities

The shell and core of the nucleus accumbens exhibit different vulnerabilities to neurotoxins. Calcium binding proteins are reported to offer some neuroprotection against excitotoxicity by suppressing or buffering intracellular calcium. Differences in the distributions of the calbindin-D 28kD (CB) and calretinin (CR) might be related to the different vulnerabilities to neurotoxins of dopaminergic neurons in the ventral mesencephalon that project to the core and medial shell of the nucleus accumbens. To address this possibility, Fluoro-Gold (FG) was injected into accumbens subterritories and numbers of retrogradely labeled neurons in the ventral tegmental area containing CB and CR immunoreactivities (ir) were expressed as a percentage of total numbers of labeled neurons. The perikaryal diameters and lengths of the immunoreactive dendrites of FG labeled neurons were also measured. About 70% and 35% of retrogradely labeled cells observed following core and medial shell injections, respectively, exhibited CB immunoreactivity. Differences were not observed in the percentages of FG labeled cells exhibiting CR immunoreactivity following medial shell (13%) and core (15%) injections. The mean perikaryal diameters and median summed lengths of dendrites of retrogradely labeled neurons containing CB were smaller than in labeled neurons lacking CB following injections in both core and medial shell of the nucleus accumbens. The data indicate that the different 6-hydroxydopamine (6-OHDA) vulnerabilities of ventral mesencephalic dopaminergic neurons are not obviously related to the presence of CB and CR.

The internal globus pallidus is affected in progressive supranuclear palsy and Parkinson's disease

Our structural studies of the substantia nigra in parkinsonian patients identified previously unsuspected changes in the pars reticulata, suggesting significant dysfunction in this basal ganglia output. There have been few similar structural studies of the other major basal ganglia output, the internal segment of the globus pallidus. This is despite significant evidence that this basal ganglia region is crucially important for generating parkinsonian symptoms. In fact current surgical interventions target this region in Parkinson's disease. The cellular anatomy of the internal globus pallidus was compared among five controls, six patients with Parkinson's disease, and five patients with progressive supranuclear palsy. Neurons and pathological structures were quantified using the unbiased fractionator method. Only cases with progressive supranuclear palsy had detectable pathology within the internal globus pallidus in the form of tau-positive neuronal and glial tangles and substantial neurodegeneration. Cases with Parkinson's disease had a significant reduction in the proportion of neurons containing parvalbumin but were without significant neurodegeneration, consistent with dysfunction of both basal ganglia output nuclei in advanced parkinsonism. Surgical ablation of the internal globus pallidus for Parkinson's disease appears at odds with the significant neurodegeneration in the similarly akinetic and rigid patients with progressive supranuclear palsy. The results are discussed in association with current hypotheses of basal ganglia function and recent experimentation in patients undergoing pallidotomy for hyperkinetic disorders.

The external globus pallidus in patients with Parkinson's disease and progressive supranuclear palsy

Underactivity of the external segment of the globus pallidus is thought to contribute to the generation of parkinsonian hypokinetic symptoms in association with striatal dopaminergic dysfunction and overactivity of the subthalamus. These symptoms can be corrected by neurosurgical techniques aimed at normalizing subthalamic overactivity. The aim of the present study was to compare the amount of neurodegeneration and changes in the calcium-binding protein parvalbumin in the external segment of the globus pallidus in parkinsonian disorders. Cases with progressive supranuclear palsy were compared with cases with Parkinson's disease and control subjects. The number of neurones and neurofibrillary tangles was estimated using unbiased stereologic techniques. The external segment of the globus pallidus in Parkinson's disease was not significantly different from that in control subjects. In contrast, most patients with progressive supranuclear palsy had significant neurodegeneration of the external pallidum, particularly patients with significant degeneration of both the subthalamus and substantia nigra. These results suggest that the parkinsonian symptoms in progressive supranuclear palsy are caused by the degeneration of the external segment of the globus pallidus because such degeneration would increase thalamic inhibition through the basal ganglia output nuclei, particularly in patients with a loss of excitatory drive from the subthalamus.

The concepts of the ventral striatopallidal system and extended amygdala

The concepts of the ventral striatopallidal system and extended amygdala have significantly improved our understanding of basal forebrain organization. As a result of these and other advances during the last twenty years, many of the most prominent basal forebrain structures, including the nucleus accumbens, olfactory tubercle, and amygdaloid body, have all but lost their relevance as independent functional anatomical units. In order to appreciate the distinct differences that exist between the ventral striatopallidal system and the extended amygdala, and as a way of explaining the choice of the terms ventral striatopallidal system and extended amygdala, we will review the discovery and subsequent elaboration of these two systems. On the background of these discussions, we will then proceed to dispel some recently published misgivings regarding the usefulness of the extended amygdaloid concept.

Thalamic inputs to striatal interneurons in monkeys: synaptic organization and co-localization of calcium binding proteins

Recent studies indicate that extrinsic inputs from sensorimotor regions of the cerebral cortex and the centromedian intralaminar thalamic nucleus terminate preferentially upon specific subpopulations of striatal output neurons in monkeys. The objective of the present study was to verify whether this specificity of innervation also characterizes the synaptic interactions between thalamic inputs from the centromedian nucleus and the four major populations of striatal interneurons. This was achieved by double labelling techniques at the electron microscope level, combining the anterograde transport of biotinylated-dextran amine with the immunostaining for specific markers of striatal interneurons (somatostatin, parvalbumin, choline acetyltransferase and calretinin). Injections of biotinylated-dextran amine in the centromedian nucleus led to dense bands of anterograde labelling which, in double immunostained sections, largely overlapped with the four populations of interneurons in the post-commissural region of the putamen. In the electron microscope, biotinylated-dextran amine-containing terminals formed asymmetric axo-dendritic synapses with somatostatin-, parvalbumin-, and choline acetyltransferase-containing elements. However, synapses between anterogradely labelled terminals and calretinin-positive neurons were not found. In sections processed to localize biotinylated-dextran amine and parvalbumin or calretinin, double-labelled terminals (biotinylated-dextran amine/parvalbumin and biotinylated-dextran amine/calretinin), morphologically similar to thalamostriatal boutons, were found in the striatum indicating that calcium binding proteins may be expressed by thalamostriatal neurons. To test this possibility, we combined the retrograde transport of lectin-conjugated horseradish peroxidase from the putamen with parvalbumin and calretinin immunostaining and found that, indeed, most of the retrogradely labelled cells in the centromedian nucleus displayed parvalbumin and calretinin immunoreactivity. Moreover, co-localization studies revealed that calretinin and parvalbumin co-exist in single neurons of the centromedian nucleus. In conclusion, striatal interneurons immunoreactive for somatostatin, parvalbumin and choline acetyltransferase, but not those containing calretinin, receive strong inputs from the centromedian nucleus in monkeys. Moreover, our findings indicate that parvalbumin and calretinin co-exist in individual thalamostriatal neurons. In combination with our previous data, these results suggest that thalamic information may be conveyed to striatal projection neurons both, directly via excitatory synaptic inputs, or indirectly via striatal interneurons. The relative importance of those direct and indirect thalamic influences upon the activity of striatal output neurons remains to be established.

CART peptide-immunoreactive neurones in the nucleus accumbens in monkeys: ultrastructural analysis, colocalization studies, and synaptic interactions with dopaminergic afferents

Cocaine- and amphetamine-regulated transcript (CART) is a novel mRNA whose level of expression was found to be increased in the striatum after acute administration of psychomotor stimulants in rats. To define better the potential role of CART peptides in behavioural and physiologic changes induced by psychomotor stimulants, we analyzed the distribution, ultrastructural features, synaptic connectivity, and transmitter content of CART peptide-immunoreactive neurones in the nucleus accumbens in monkeys. Medium-sized CART peptide-immunoreactive neurones within a rich plexus of labelled varicosities were found mostly in the medial division of the shell of the nucleus accumbens in monkeys. At the electron microscope level, CART peptide immunoreactivity was exclusively associated with neuronal structures that included perikarya, dendrites, spines as well as nerve terminals packed with electron-lucent and dense-core vesicles. Most CART peptide-containing somata displayed the ultrastructural features of striatal output neurones. The majority of labelled terminals formed symmetric axodendritic synapses and displayed gamma-aminobutyric acid (GABA) immunoreactivity. CART peptide-immunoreactive somata were not immunoreactive for parvalbumin and somatostatin, two markers of striatal interneurones, nor for calbindin D-28k, a marker of a subpopulation of projection neurones. In double-immunostained sections, CART peptide-immunoreactive dendrites were found to be contacted by tyrosine hydroxylase-positive terminals which displayed the ultrastructural features of dopamine-containing boutons. These findings strongly suggest that CART peptides may be a cotransmitter with GABA in a subpopulation of projection neurones in the monkey accumbens. Furthermore, the fact that CART peptide-immunoreactive neurones receive direct synaptic inputs from dopaminergic afferents and are particularly abundant in the caudomedial division of the shell of the nucleus accumbens suggest that CART peptides might be involved in neuronal and behavioural changes that underlie addiction to psychomotor stimulants and feeding in primates.

The midbrain dopaminergic cell groups in the baboon Papio ursinus

The present study evaluates the cytoarchitecture of midbrain dopaminergic regions in baboons using similar methodology to that recently applied to compare humans and rats. This information is relevant for the interpretation of nonhuman primate models of Parkinson's disease (PD). The midbrains of four alpha male baboons were serially sectioned into 10 evenly spaced series of 50 microm sections. Series were stained with either cresyl violet or immunohistochemically reacted for tyrosine hydroxylase, substance P, calbindin-D28k, or parvalbumin. The organization of dopaminergic cell groups and the distribution of proteins within these groups were found to be very similar to that previously described in humans [McRitchie et al., J. Comp. Neurol. 364:121-150; 1996]. Dorsal and ventral tiers of the A9 substantia nigra (SN) pars compacta and all divisions of the A8 and A10 cell groups were identified revealing a high degree of homology in the arrangement of chemically distinct midbrain neurons between primates. The major difference between the organization of human and baboon midbrain dopaminergic neurons is the anteroposterior extent of the dense cell clusters within the SN pars compacta. In baboons the dorsomedial cell cluster is absent at posterior levels. The ventral tier cell clusters, which are targeted by PD in humans, are restricted to the posterior and ventral regions of the SN pars compacta of the baboon. In humans these cell clusters are found throughout the rostrocaudal extent of the SN. These ventral cell clusters have been previously shown to have reciprocal connections with sensorimotor regions of the putamen.

Structural and functional evolution of the basal ganglia in vertebrates

While a basal ganglia with striatal and pallidal subdivisions is 1 clearly present in many extant anamniote species, this basal ganglia is cell sparse and receives only a relatively modest tegmental dopaminergic input and little if any cortical input. The major basal ganglia influence on motor functions in anamniotes appears to be exerted via output circuits to the tectum. In contrast, in modern mammals, birds, and reptiles (i.e., modern amniotes), the striatal and pallidal parts of the basal ganglia are very neuron-rich, both consist of the same basic populations of neurons in all amniotes, and the striatum receives abundant tegmental dopaminergic and cortical input. The functional circuitry of the basal ganglia also seems very similar in all amniotes, since the major basal ganglia influences on motor functions appear to be exerted via output circuits to both cerebral cortex and tectum in sauropsids (i.e., birds and reptiles) and mammals. The basal ganglia, output circuits to the cortex, however, appear to be considerably more developed in mammals than in birds and reptiles. The basal ganglia, thus, appears to have undergone a major elaboration during the evolutionary transition from amphibians to reptiles. This elaboration may have enabled amniotes to learn and/or execute a more sophisticated repertoire of behaviors and movements, and this ability may have been an important element of the successful adaptation of amniotes to a fully terrestrial habitat. The mammalian lineage appears, however, to have diverged somewhat from the sauropsid lineage with respect to the emergence of the cerebral cortex as the major target of the basal ganglia circuitry devoted to executing the basal ganglia-mediated control of movement.

Chemical phenotype of calretinin interneurons in the human striatum

We recently reported the existence of a new class of aspiny interneurons characterized by their immunoreactivity for the calcium-binding protein calretinin (CR) in human striatum. This group is composed of numerous medium-sized (10-20 microm) neurons with poorly branched dendrites and a smaller number of large-sized (24-42 microm) neurons with highly ramified dendrites. We further demonstrated the selective sparing of the medium-sized, but not all the large-sized, CR+ striatal neurons in Huntington's disease. In the present study, we applied a double-antigen localization method to postmortem striatal tissue obtained from normal individuals to further characterize the chemical phenotype of these two subsets of CR+ neurons. Our results reveal that in the medium-sized neurons, CR is not colocalized with any of the following current markers of striatal neurons: calbindin, parvalbumin, beta-nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d), or choline acetyltransferase (ChAT). Furthermore, quantitative estimates show that the medium-sized CR+ neurons are by far the most abundant type of interneurons in the human striatum. In contrast, CR is colocalized with ChAT in about 80% of the large-sized CR+ neurons. Thus, the medium-sized CR+ neurons appear to form a distinct class of striatal interneurons, whereas most of the large-sized CR+ neurons belong to the population of giant cholinergic neurons. This study has provided the first exhaustive characterization of the chemical phenotype of the CR + neurons in the human striatum.

Distribution of calbindin D-28k and parvalbumin neurons and fibers in the rat basal ganglia

This review deals with the distribution of immunoreactivity for calbindin D-28k (CB) and parvalbumin (PV) in the different nuclei of the rodent basal ganglia analyzed with the data available after the use of single and double antigen procedures applied to single sections. These findings reveal that CB and PV are distributed according to a highly heterogeneous pattern in the caudate putamen complex (CPu), globus pallidus (GP), entopeduncular nucleus (EP), subthalamic nucleus (STh) and substantia nigra (SN) of the rat. In each basal ganglia structure, the two calcium-binding proteins label different neuronal subsets. Therefore, the use of CB and PV immunohistochemistry may be considered as an excellent tool to define distinct chemoarchitectonic and functional domains within the complex organization of the basal ganglia. Double immunohistochemical methods are also useful to illustrate the relationships between the different chemical subdivisions of the CPu, GP, EP, STh and SN and the chemically characterized connections with each other and with other forebrain and brainstem structures. However, specific rules should be followed when combining single and double immunostaining procedures, and the results of such studies must be evaluated with caution. When they are used properly, these methods can reveal hitherto unknown principles of organization of the basal ganglia and thus shed new light on the anatomical and functional organization of this set of subcortical structures involved in the control of motor behavior.

Relative resistance of striatal neurons containing calbindin or parvalbumin to quinolinic acid-mediated excitotoxicity compared to other striatal neuron types

To evaluate the relative ability of those striatal neuron types containing calbindin or parvalbumin to withstand a Ca(2+)-mediated excitotoxic insult, we injected the NMDA receptor-specific excitotoxin quinolinic acid (QA) into the striatum in mature adult rats and 2 months later examined the relative survival of striatal interneurons rich in parvalbumin and striatal projection neurons rich in calbindin. To provide standardization to the survival of striatal neuron types thought to be poor in Ca2+ buffering proteins, the survival was compared to that of somatostatin-neuropeptide Y (SS/NPY)-containing interneurons and enkephalinergic projection neurons, which are devoid of or relatively poorer in such proteins. The various neuron types were identified by immunohistochemical labeling for these type-specific markers and their relative survival was compared at each of a series of increasing distances from the injection center. In brief, we found that parvalbuminergic, calbindinergic, and enkephalinergic neurons all showed a generally comparable gradient of neuronal loss, except just outside the lesion center, where calbindin-rich neurons showed significantly enhanced survival. In contrast, striatal SS/NPY interneurons were more vulnerable to QA than any of these three other types. These observed patterns of survival following intrastriatal QA injection suggest that calbindin and parvalbumin content does not by itself determine the vulnerability of striatal neurons to QA-mediated excitotoxicity in mature adult rats. For example, parvalbuminergic striatal interneurons were not impervious to QA, while cholinergic striatal interneurons are highly resistant and SS/NPY+ striatal interneurons are highly vulnerable. Both cholinergic and SS/NPY+ interneurons are devoid of any known calcium buffering protein. Similarly, calbindin does not prevent striatal projection neuron vulnerability to QA excitotoxicity. Nonetheless, our data do suggest that calbindin may offer striatal neurons some protection against moderate excitotoxic insults, and this may explain the reportedly slightly greater vulnerability of striatal neurons that are poor in calbindin to ischemia and Huntington's disease.

Ultrastructural study of nitric oxide synthase-containing striatal neurons and their relationship with parvalbumin-containing neurons in rats

Single- and double-label electron microscopic immunocytochemistry was used to examine the ultrastructure of striatal neurons containing nitric oxide synthase (NOS+) and evaluate the synaptic relationship of NOS+ striatal neurons with those containing parvalbumin (PV+). In both the single-label and double-label studies, NOS+ perikarya were observed to possess polylobulated nuclei. In the single-label studies, NOS+ terminals were seen forming synaptic contacts with dendritic shafts and dendritic spines that did not contain NOS, but not with NOS+ perikarya or dendrites. In the double-label studies (using diaminobenzidine and silver intensified immunogold as markers), nitric oxide synthase and parvalbumin immunoreactions were found in two different populations of medium-sized aspiny striatal neurons. The PV+ axon terminals were seen forming symmetric synapses on the dendritic spines of neurons devoid of PV or NOS labeling, on PV+ dendrites, and on NOS+ soma and dendrites. In contrast, NOS+ terminals were not observed to form synaptic contacts with the dendrites or soma of either PV+ or NOS+ neurons. These findings suggest that NOS+ striatal interneurons form synaptic contact with the spines and presumably the dendrites of striatal projection neurons, but not with the dendrites or soma of PV+ or NOS+ striatal interneurons. NOS+ neurons do, however, receive synaptic input from PV+ neurons.

Neurochemical compartments in the human forebrain: evidence for a high density of secretoneurin-like immunoreactivity in the extended amygdala

Secretoneurin is a 33-amino acid neuropeptide produced by endoproteolytic processing from secretogranin II, which is a member of the chromogranin/ secretogranin family. In this immunocytochemical study we investigated the localization of secretoneurin-like immunoreactivity in the human substantia innominata in relation to the ventral striatopallidal system, the bed nucleus-amygdala complex and the basal nucleus of Meynert. A high density of secretoneurin immunostaining was found in the medial part of the nucleus accumbens. All subdivisions of the bed nucleus of the stria terminalis displayed a very prominent immunostaining for secretoneurin, whereas substance P and enkephalin showed a more restricted distribution. A high concentration of secretoneurin immunoreactivity was also observed in the central and medial amygdaloid nuclei. In the lateral bed nucleus of the stria terminalis and the sublenticular substantia innominata, the appearance of secretoneurin immunoreactivity was very similar to that of enkephalin-like immunoreactivity, exhibiting mostly peridendritic and perisomatic staining. The ventral pallidum and the inner pallidal segment displayed strong secretoneurin immunostaining. Secretoneurin did not label cholinergic neurons in the basal forebrain. This study demonstrates that secretoneurin-like immunoreactivity is prominent in the bed nucleus-amygdala complex, referred to as extended amygdala. The distribution of secretoneurin-like immunoreactivity in comparison with that of other neuroanatomical markers suggests that this forebrain system is a discret compartment in the human forebrain.

Parvalbumin and calbindin D-28k in the entopeduncular nucleus, subthalamic nucleus, and substantia nigra of the rat as revealed by double-immunohistochemical methods

The cellular localization of calbindin D-28k (CB) and parvalbumin (PV) was analyzed by means of double-immunohistochemical techniques applied to single sections in the entopeduncular nucleus (EP), the subthalamic nucleus (STh), and the substantia nigra (SN) of the rat. In EP, PV-positive cells abounded centrally, where CB immunostaining was minimal. The medial and ventral sectors of EP were markedly enriched with CB neuropil but devoid of PV-positive cells. CB-positive neurons abounded particularly in the rostral pole of EP. In STh, PV-positive neurons and neuropil were concentrated in the lateral two thirds of this nucleus. Only a few PV-positive cells were detected in sectors of STh devoid of PV-positive neuropil. The STh was completely devoid of CB immunostaining. In the rostral two thirds of SN, PV-positive neurons were largely confined to the lateral half of the pars reticulata (SNR), and occurred more ventrally and medially in the caudal third. Intense CB-immunoreactive neuropil was found in medial and dorsal parts of rostral SNR, and CB-positive cells were observed in the SN pars compacta and the ventral tegmental area. PV and CB cells were also observed in the pars lateralis of SN. The markedly heterogeneous pattern of distribution of PV and CB in EP, STh, and SN suggests that these two calcium-binding proteins may label distinct functional domains in each of these three components of the rat basal ganglia.

Colocalization of somatostatin, neuropeptide Y, neuronal nitric oxide synthase and NADPH-diaphorase in striatal interneurons in rats

The neuropeptides somatostatin (SS), neuropeptide Y (NPY), the enzyme neuronal nitric oxide synthase (nNOS) and enzymatic activity for NADPH diaphorase (NADPHd) are extensively colocalized in striatal interneurons, which has led to the widespread tendency to operationally treat all four substances as being completely colocalized within a single class of striatal interneurons. We have explored the validity of this assumption in rat striatum using multiple-labeling methods. Conventional epi-illumination fluorescence microscopy was used to examine tissue triple labeled for SS, NPY and nNOS, or double-labeled for SS and nNOS or for SS and NPY. In tissue double-labeled for SS and nNOs, confocal laser scanning microscopy (CLSM) images of SS and nNOS labeling were compared to subsequent NADPHd labeling. We found that SS, NPY and nNOS co-occurred extensively, but a moderately abundant population of neurons containing SS and nNOS but not NPY was also observed, as were small populations of SS only and nNOS only neurons. About 80% of SS+ neurons contained NPY, and no NPY neurons were devoid of SS or nNOS. All neurons containing nNOS in rat striatum were found to contain NADPHd. Combining our various quantitative observations, we found that of those striatal neurons containing any combination of SS, NPY, nNOS and NADPHd in rats, about 73% contained all four, 16% contained SS, nNOS and NADPHd, 5% contained SS only, and 6% contained only nNOS and NADPHd. These results indicate that while there is a large population of striatal neurons in which SS, NPY, nNOS and NADPHd are colocalized in rats, there may be smaller populations of striatal neurons devoid of NPY in which SS or nNOS/NADPHd are found individually or together.

Calcium-binding proteins in primate basal ganglia

This paper describes the distribution of the calcium-binding proteins calbindin-D28k. Parvalbumin and calretinin in primate basal ganglia. The data derive from immunocytochemical studies undertaken in squirrel monkeys (Saimiri sciureus) and in normal human individuals. In the striatum, calbindin labels medium-sized spiny projection neurons whereas parvalbumin and calretinin mark two separate classes of aspiny interneurons. The striatal matrix compartment is markedly enriched with calbindin while striatal patches (striosomes) display a calretinin-rich neuropil. In the pallidum, virtually all neurons contain parvalbumin but none express calbindin. Calretinin occurs only in a small subpopulation of both large and small pallidal neurons. In the subthalamic nucleus, there exists a multitude of parvalbumun-positive cells and fibers but the number of calretinin and calbindin-positive neuronal elements is small. In the substantia nigra/ventral tegmental area complex, calbindin and calretinin occur principally in dopaminergic neurons of the dorsal tier of the pars compacta and in those of the ventral tegmental area. Parvalbumin is strictly confined to the GABAergic neurons of the pars reticulata and lateralis. Calbindin-rich fibers abound in the pars reticulata and lateralis, while calretinin-positive axons are confined to the pars compacta. These results indicate that calbindin and parvalbumin are distributed according to a strikingly complementary pattern in primate basal ganglia. Calretinin is less ubiquitous but occurs in all basal ganglia components where it labels distinct subsets of neurons. Such highly specific patterns of distribution indicate that calbindin, parvalbumin and calretinin may work in synergy within primate basal ganglia.

Distribution and neurochemical character of substance P receptor (SPR)-immunoreactive striatal neurons of the macaque monkey: accumulation of SP fibers and SPR neurons and dendrites in "striocapsules" encircling striosomes

The striatal distribution of the substance P receptor (SPR) protein was examined in relation to its ligand, the neuro-peptide SP, as well as to the neurochemical and compartmental composition of the neostriatum in rhesus monkeys (Macaca mulatta) in immunohistochemical experiments. About 2% of striatal neurons, displaying varicose, virtually spine-free dendrites characteristic of large and medium-sized aspiny interneurons, expressed SPR immunoreactivity. SPR/choline acetyltransferase, SPR/somatostatin, SPR/GABA, SPR/calbindin D28k, and SPR/parvalbumin double immunolabeling experiments demonstrated that SPR-positive cells are either cholinergic or somatostatinergic. Comparison of SP and SPR immunoreactivities in double-labeled and adjacent single-labeled sections revealed compartment-specific match and mismatch between the densities of the peptide and receptor. A matching high density of SP fibers and SPR cells and dendrites was only observed in the rim of the striosome compartments. To our knowledge, this is the first evidence for an anatomical border comprised of dendritic processes that separate striatal compartments. We have termed these zones "striocapsules," because they encircle and encapsulate striosomal cell islands. In the striatal matrix, an abundance of SPR-labeled profiles was complemented with light SP staining. By contrast, in the core of the striosomes, SPR labeling was sparse and SP staining intense. SP-positive axon-like puncta frequently contacted SPR-positive dendrites in all striatal compartments. The SP receptor/ligand match indicates a sharp increase in the efficacy of SP action in the striocapsules, and suggests that the influence of SP might be heightened in this striatal subcompartment.