Relationships between thalamostriatal neurons and pedunculopontine projections to the thalamus: a neuroanatomical tract-tracing study in the rat

The present study aimed to investigate whether the pedunculopontine projection to the thalamus overlaps with identified thalamostriatal neurons. These projections were studied using a dual tract-tracing procedure combining anterogradely transported biotinylated dextran amine (pedunculopontine projections) and retrogradely transported Fluoro-Gold (thalamostriatal projections). Overlapping thalamic territories between thalamostriatal neurons and the axon terminals arising from the pedunculopontine tegmental nucleus were observed in the midline (paraventricular) and in the intralaminar (centrolateral, central medial, paracentral and parafascicular) thalamic nuclei. Other thalamic nuclei, such as the ethmoid, intermediodorsal, mediodorsal, paratenial, posteromedian, ventromedian, ventrolateral and rhomboid thalamic nuclei, displayed a lesser degree of overlap. These observations suggest the existence of presumptive contacts between thalamostriatal neurons and axons emerging from the pedunculopontine tegmental nucleus, therefore supporting the possible existence of feedback circuits in the rat basal ganglia in which the tegmento-thalamic projection would play a major role

Re-examination of the thalamostriatal projections in the rat with retrograde tracers

Topographical arrangements of thalamostriatal projection neurons was examined in the rat by the retrograde tract-tracing method. After injecting Fluoro-Gold (FG) and/or cholera toxin beta-subunit (CTB) in different regions of the caudate-putamen (CPu), distribution of retrogradely labeled neurons was observed in the thalamus. The main findings were as follows: (1) Retrogradely labeled neurons were seen in the midline-intralaminar thalamic nuclei in all rats examined in the present study. Neurons in the ventral lateral and posterior thalamic nuclear groups were also labeled in the rats which were injected with the tracer into the dorsal part of Cpu, but not in the rats which were injected with the tracer into the nucleus accumbens (Acb) and its adjavent regions in the ventromedial part of the Cpu. (2) Topographical organization was observed in the projections from the midline-intralaminar thalamic nuclei to the CPu. After the tracer injection into the dorsal part of the CPu or the ventral part of the CPu (including the Acb), labeled neurons in the midline-intralaminar thalamic nuclei were distributed predominantly in the lateral part of the intralaminar nuclei or the midline nuclei, respectively. On the other hand, after the tracer injection into the medial or the lateral part of the CPu, labeled neurons in the midline-intralaminar nuclei were distributed mainly in the dorsal or the ventral part of these nuclei, respectively. (3) Topographical organization was also observed in the thalamostriatal projections from the ventral and Pos. After the tracer injection into the rostral part of the CPu, labeled neurons were distributed mainly in the rostral part of the ventral nuclear group. On the other hand, after the tracer injection into the caudal part of the CPu, labeled neurons were distributed mainly in the caudal part of the ventral nuclear group, as well as in the posterior nuclear group

Striatal input from the ventrobasal complex of the rat thalamus

We have analyzed whether caudal regions of the caudate putamen receive direct projections from thalamic sensory relay nuclei such as the ventrobasal complex. To this aim, the delivery of the retrograde neuroanatomical tracer Fluoro-Gold into the caudal caudate putamen resulted in the appearance of retrogradely labeled neurons in the ventral posteromedial and ventral posterolateral thalamic nuclei. These projections were further confirmed with injections of the anterograde tracers biotinylated dextran amine or Phaseolus vulgaris leucoagglutinin into these thalamic nuclei, by showing the existence of axonal terminal fields located in the caudal striatum. These results support the existence of direct projections linking the thalamic ventrobasal complex and the caudal striatum in the rat, probably via collateralization of thalamocortical axons when passing through the caudate putamen, and therefore supporting the putative involvement of the caudal striatum in sensory-related functions

Multiple axonal tracing: simultaneous detection of three tracers in the same section

Multiple neuroanatomical tract-tracing methods are important tools for elucidating the connectivity between different populations of neurons. Evaluation of the question as to whether two specific fiber inputs converge on a particular, identified population of projection neurons requires the application of a triple-staining procedure that allows the unequivocal detection of three markers in a single section. The present report deals with a combination of tracing methods using anterogradely transported Phaseolus vulgaris leucoagglutinin and biotinylated dextran amine in conjunction with retrogradely transported Fluoro-Gold. These tracers were simultaneously detected according to a three-color paradigm, which includes the use of three different peroxidase substrates (nickel-enhanced diaminobenzidine, diaminobenzidine, and Vector VIP), thus resulting in three distinct precipitates: black, brown, and purple. We illustrate this method by showing convergence of projections arising from neurons located in two separate basal ganglia-related nuclei onto identified thalamostriatal projection neurons

Thalamic interaction between the input and the output systems of the basal ganglia

The striatal return through the thalamus is largely neglected in current studies dealing with basal ganglia function, and its role within this circuitry remains obscure. In this contribution the thalamus is regarded as an important place of interaction between the input and the output organization of the basal ganglia. In support of this idea, a brief overview is provided of some of the most recent findings concerning the thalamus in relation to the basal ganglia circuitry. In particular, we have focused on the thalamostriatal projections themselves, on the output of the basal ganglia to the thalamus and also on the overlapping territories between the thalamic projection of the output nuclei and the thalamostriatal neurons. These data support the existence of several thalamic feedback circuits within the basal ganglia neural system. Finally, some considerations are provided upon the functional significance of these thalamic feedback circuits in the overall organization of the basal ganglia

Complex brain circuits studied via simultaneous and permanent detection of three transported neuroanatomical tracers in the same histological section.

Experimental neuroanatomical tracing methods lie at the basis of the study of the nervous system. When the scientific question is relatively straightforward, it may be sufficient to derive satisfactory answers from experiments in which a single neuroanatomical tracing method is applied. In various scientific paradigms however, for instance when the degree of convergence of two different projections on a particular cortical area or subcortical nucleus is the subject of study, the application of single tracing methods can be either insufficient or uneconomical to solve the questions asked. In cases where chains of projections are the subjects of study, the simultaneous application of two tracing methods or even more may be compulsory. The present contribution focuses on combinations of several neuroanatomical tract-tracing strategies, enabling in the end the simultaneous, unambiguous and permanent detection of three transported markers according to a three-color paradigm. A number of combinations of three tracers or of two tracers plus the immunocytochemical detection of a neuroactive substance can be conceived; we describe several of these combinations implemented by us using the present multitracer protocol

El núcleo tegmental pedunculopontino. Anatomía, consideraciones funcionales e implicaciones fisiopatológicas

El núcleo tegmental pedúnculopontino está constituido por un conjunto de neuronas colinérgicas y no colinérgicas, localizadas en el tegmento pontomesencefálico caudal, rodeando al pedúnculo cerebeloso superior. Es un núcleo considerado parte integral de la formación reticular del tronco del encéfalo, con extensas conexiones anatómicas y funciones muy variadas. Mediante las proyecciones ascendentes que envía al tálamo, interviene en la regulación del ciclo vigilia-sueño. Además, constituye el núcleo más caudal del neuroeje que recibe conexiones de los ganglios basales, por lo que ha atraído el interés de aquellos investigadores que se ocupan del estudio de estas estructuras. Gracias a sus conexiones recíprocas con los ganglios basales, así como a sus proyecciones descendentes a diversas estructuras de la protuberancia, bulbo y médula espinal, se ha relacionado al núcleo tegmental pedúnculopontino con el control de la locomoción. Recientemente, se le ha considerado un posible centro de integración de la información motora que le aporta el estriado dorsal con la información motivacional o límbica proveniente del estriado ventral, para permitir su acceso directo a centros motores bulbares o medulares. En este trabajo vamos a revisar sus características anatómicas y funcionales así como su implicación en algunas enfermedades del sistema nervioso como la narcolepsia, la parálisis supranuclear progresiva, la esquizofrenia y la enfermedad de Parkinson.Pedunculopontine tegmental nucleus is formed by an ensemble of cholinergic and non-cholinergic neurons located in the caudal pontomesencephalic tegmentum, surrounding the superior cerebellar peduncle. It is an integral part of the reticulate formation of the brain stem, with extensive anatomical connections and highly varied functions. By means of ascendant projections that it sends to the thalamus, it intervenes in the waking-sleep cycle. Besides, it constitutes the most caudal nucleus of the neuroaxis, receiving connections from the basal ganglia, for which reason it has attracted the interest of those researchers concerned with the study of these structures. Thanks to its reciprocal connections with the basal ganglia, as well as to its descending projections to different structures of the pons, medulla and spinal cord; it has been related to the control of locomotion. Recently, it has also been considered as a possible centre for the integration of the motor information provided by the dorsal striatum with the motivational or limbic information proceeding from the ventral striatum, to permit its direct access to bulbar or spinal motor centres. In this work we will review its anatomical and functional characteristics, as well as its implication in some diseases of the nervous system such as narcolepsy, progressive supranuclear paralysis, schizophrenia and Parkinson's disease

El núcleo tegmental pedunculopontino. Anatomía, consideraciones funcionales e implicaciones fisiopatológicas

El núcleo tegmental pedúnculopontino está constituido por un conjunto de neuronas colinérgicas y no colinérgicas, localizadas en el tegmento pontomesencefálico caudal, rodeando al pedúnculo cerebeloso superior. Es un núcleo considerado parte integral de la formación reticular del tronco del encéfalo, con extensas conexiones anatómicas y funciones muy variadas. Mediante las proyecciones ascendentes que envía al tálamo, interviene en la regulación del ciclo vigilia-sueño. Además, constituye el núcleo más caudal del neuroeje que recibe conexiones de los ganglios basales, por lo que ha atraído el interés de aquellos investigadores que se ocupan del estudio de estas estructuras. Gracias a sus conexiones recíprocas con los ganglios basales, así como a sus proyecciones descendentes a diversas estructuras de la protuberancia, bulbo y médula espinal, se ha relacionado al núcleo tegmental pedúnculopontino con el control de la locomoción. Recientemente, se le ha considerado un posible centro de integración de la información motora que le aporta el estriado dorsal con la información motivacional o límbica proveniente del estriado ventral, para permitir su acceso directo a centros motores bulbares o medulares. En este trabajo vamos a revisar sus características anatómicas y funcionales así como su implicación en algunas enfermedades del sistema nervioso como la narcolepsia, la parálisis supranuclear progresiva, la esquizofrenia y la enfermedad de Parkinson.Pedunculopontine tegmental nucleus is formed by an ensemble of cholinergic and non-cholinergic neurons located in the caudal pontomesencephalic tegmentum, surrounding the superior cerebellar peduncle. It is an integral part of the reticulate formation of the brain stem, with extensive anatomical connections and highly varied functions. By means of ascendant projections that it sends to the thalamus, it intervenes in the waking-sleep cycle. Besides, it constitutes the most caudal nucleus of the neuroaxis, receiving connections from the basal ganglia, for which reason it has attracted the interest of those researchers concerned with the study of these structures. Thanks to its reciprocal connections with the basal ganglia, as well as to its descending projections to different structures of the pons, medulla and spinal cord; it has been related to the control of locomotion. Recently, it has also been considered as a possible centre for the integration of the motor information provided by the dorsal striatum with the motivational or limbic information proceeding from the ventral striatum, to permit its direct access to bulbar or spinal motor centres. In this work we will review its anatomical and functional characteristics, as well as its implication in some diseases of the nervous system such as narcolepsy, progressive supranuclear paralysis, schizophrenia and Parkinson's disease

Re-examination of the thalamostriatal projections in the rat with retrograde tracers

Topographical arrangements of thalamostriatal projection neurons was examined in the rat by the retrograde tract-tracing method. After injecting Fluoro-Gold (FG) and/or cholera toxin beta-subunit (CTB) in different regions of the caudate-putamen (CPu), distribution of retrogradely labeled neurons was observed in the thalamus. The main findings were as follows: (1) Retrogradely labeled neurons were seen in the midline-intralaminar thalamic nuclei in all rats examined in the present study. Neurons in the ventral lateral and posterior thalamic nuclear groups were also labeled in the rats which were injected with the tracer into the dorsal part of Cpu, but not in the rats which were injected with the tracer into the nucleus accumbens (Acb) and its adjavent regions in the ventromedial part of the Cpu. (2) Topographical organization was observed in the projections from the midline-intralaminar thalamic nuclei to the CPu. After the tracer injection into the dorsal part of the CPu or the ventral part of the CPu (including the Acb), labeled neurons in the midline-intralaminar thalamic nuclei were distributed predominantly in the lateral part of the intralaminar nuclei or the midline nuclei, respectively. On the other hand, after the tracer injection into the medial or the lateral part of the CPu, labeled neurons in the midline-intralaminar nuclei were distributed mainly in the dorsal or the ventral part of these nuclei, respectively. (3) Topographical organization was also observed in the thalamostriatal projections from the ventral and Pos. After the tracer injection into the rostral part of the CPu, labeled neurons were distributed mainly in the rostral part of the ventral nuclear group. On the other hand, after the tracer injection into the caudal part of the CPu, labeled neurons were distributed mainly in the caudal part of the ventral nuclear group, as well as in the posterior nuclear group

Relationships between thalamostriatal neurons and pedunculopontine projections to the thalamus: a neuroanatomical tract-tracing study in the rat

The present study aimed to investigate whether the pedunculopontine projection to the thalamus overlaps with identified thalamostriatal neurons. These projections were studied using a dual tract-tracing procedure combining anterogradely transported biotinylated dextran amine (pedunculopontine projections) and retrogradely transported Fluoro-Gold (thalamostriatal projections). Overlapping thalamic territories between thalamostriatal neurons and the axon terminals arising from the pedunculopontine tegmental nucleus were observed in the midline (paraventricular) and in the intralaminar (centrolateral, central medial, paracentral and parafascicular) thalamic nuclei. Other thalamic nuclei, such as the ethmoid, intermediodorsal, mediodorsal, paratenial, posteromedian, ventromedian, ventrolateral and rhomboid thalamic nuclei, displayed a lesser degree of overlap. These observations suggest the existence of presumptive contacts between thalamostriatal neurons and axons emerging from the pedunculopontine tegmental nucleus, therefore supporting the possible existence of feedback circuits in the rat basal ganglia in which the tegmento-thalamic projection would play a major role