[Investigation on the cytoarchitecture of the nucleus accumbens septi of rat (author's transl)].
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Abstract:
The nucleus accumbens septi of the normal adult rat was investigated by means of the rapid Golgi impregnation technique according to Valverde (1970). 5 neuron types could be differentiated: type 1: spiny neurons; type 2: few spiny neurons; type 3: aspiny giant neurons; type 4: spiny spindle shaped neurons; type 5: aspiny spidery neurons. The types 1, 4 and 5, resp., are considered, with respect to morphological criteria, to represent interneurons, whereas the types 2 and 3 are considered to be accumbens output neurons. The cytoarchitecture of the nc. accumbens septi thus displays striking similarities with the caudate-putamen-complex. An hypothetical correlation of these neurons in a functional -- biochemical sense as well as their position in the nc. accumbens which is suggested to be a transition area between limbic and extrapyramidal motor systems, is discussed.Keywords:
Cytoarchitecture
Medium spiny neuron
Putamen
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The striatum is critically involved in motor and motivational functions. The dorsal striatum, caudate-putamen, is primarily implicated in motor control and the learning of habits and skills, whereas the ventral striatum, the nucleus accumbens, is essential for motivation and drug reinforcement. The GABA medium-sized spiny neurons (MSNs, about 95% of striatal neurons), which are targets of the cerebral cortex and the midbrain dopaminergic neurons, form two pathways. The dopamine D(1) receptor-positive (D(1)R) striatonigral MSNs project to the medial globus pallidus and substantia nigra pars reticulata (direct pathway) and co-express D(1)R and substance P, whereas dopamine D(2) receptor-positive (D(2)R) striatopallidal MSNs project to the lateral globus pallidus (indirect pathway) and co-express D(2)R, adenosine A(2A) receptor (A(2A)R) and enkephalin (Enk). The specific role of the two efferent pathways in motor and motivational control remained poorly understood until recently. Indeed, D(1)R striatonigral and D(2)R striatopallidal neurons, are intermingled and morphologically indistinguishable, and, hence, cannot be functionally dissociated with techniques such as chemical lesions or surgery. In view of the still debated respective functions of projection D(2)R striatopallidal and D(1)R striatonigral neurons and striatal interneurons, both in motor control and learning but also in more cognitive processes such as motivation, the present review sum up the development of new models and techniques (bacterial artificial chromosome transgenesis, optogenetic, viral transgenesis) allowing the selective targeting of these striatal neuronal populations in adult animal brain to understand their specific roles.
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Subthalamic Nucleus
Medium spiny neuron
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Pars reticulata
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SUMMARY The striatum is the interface between dopamine reward signals and cortico-basal ganglia circuits that mediate diverse behavioral functions. Medium spiny neurons (MSNs) constitute the vast majority of striatal neurons and are traditionally classified as direct- or indirect-pathway neurons. However, that traditional model does not explain the anatomical and functional diversity of MSNs. Here, we defined molecularly distinct MSN types in the primate striatum, including (1) dorsal striatum MSN types associated with striosome and matrix compartments, (2) ventral striatum types associated with the nucleus accumbens shell and olfactory tubercle, and (3) an MSN-like type restricted to μ-opioid receptor rich islands in the ventral striatum. These results lay the foundation for achieving cell type-specific transgenesis in the primate striatum and provide a blueprint for investigating circuit-specific processing.
Medium spiny neuron
Ventral striatum
Putamen
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Medium spiny neuron
Ventral striatum
Putamen
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The nucleus accumbens septi of the normal adult rat was investigated by means of the rapid Golgi impregnation technique according to Valverde (1970). 5 neuron types could be differentiated: type 1: spiny neurons; type 2: few spiny neurons; type 3: aspiny giant neurons; type 4: spiny spindle shaped neurons; type 5: aspiny spidery neurons. The types 1, 4 and 5, resp., are considered, with respect to morphological criteria, to represent interneurons, whereas the types 2 and 3 are considered to be accumbens output neurons. The cytoarchitecture of the nc. accumbens septi thus displays striking similarities with the caudate-putamen-complex. An hypothetical correlation of these neurons in a functional -- biochemical sense as well as their position in the nc. accumbens which is suggested to be a transition area between limbic and extrapyramidal motor systems, is discussed.
Cytoarchitecture
Medium spiny neuron
Putamen
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The striatum includes the structures of the caudate, putamen, and nucleus accumbens (Nacb) and is a subset of the subcortical interconnected nuclei that make up the basal ganglia [39]. The striatum is one of the major input structures of the basal ganglia and integrates input from many cortical areas as well as the thalamus. In general, the dorsal striatum processes more input from the motor regions of the cortex, while the ventral striatum processes input predominantly from the limbic and cognitive areas of the brain [2].
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Caudate nucleus
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Medium spiny neuron
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Medium spiny neuron
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The striatum, the major input structure of the basal ganglia, is critically involved in motor control and learning of habits and skills, and is also involved in motivational and reward processes. The dorsal striatum, caudate-putamen, is primarily implicated in motor functions whereas the ventral striatum, the nucleus accumbens, is essential for motivation and drug reinforcement. Severe basal ganglia dysfunction occurs in movement disorders as Parkinson's and Huntington's disease, and in psychiatric disorders such as schizophrenia and drug addiction. The striatum is essentially composed of GABAergic medium-sized spiny neurons (MSNs) that are output neurons giving rise to the so-called direct and indirect pathways and are targets of the cerebral cortex and mesencephalic dopaminergic neurons. Although the involvement of striatal sub-areas in motor control and motivation has been thoroughly characterized, major issues remained concerning the specific and respective functions of the two MSNs sub-populations, D(2)R-striatopallidal (dopamine D(2) receptor-positive) and D(1)R-striatonigral (dopamine D(1) receptor-positive) neurons, as well as their specific regulation. Here, we review recent advances that gave new insight in the understanding of the differential roles of striatopallidal and striatonigral neurons in the basal ganglia circuit. We discuss innovative techniques developed in the last decade which allowed a much precise evaluation of molecular pathways implicated in motivational processes and functional roles of striatopallidal and striatonigral neurons in motor control and in the establishment of reward-associated behavior.
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