Axonal Transport Of Horseradish Peroxidase Research Articles

Choice-selective sequences dominate in cortical relative to thalamic inputs to NAc to support reinforcement learning.

SUMMARYHow are actions linked with subsequent outcomes to guide choices? The nucleus accumbens, which is implicated in this process, receives glutamatergic inputs from the prelimbic cortex and midline regions of the thalamus. However, little is known about whether and how representations differ across these input pathways. By comparing these inputs during a reinforcement learning task in mice, we discovered that prelimbic cortical inputs preferentially represent actions and choices, whereas midline thalamic inputs preferentially represent cues. Choice-selective activity in the prelimbic cortical inputs is organized in sequences that persist beyond the outcome. Through computational modeling, we demonstrate that these sequences can support the neural implementation of reinforcement-learning algorithms, in both a circuit model based on synaptic plasticity and one based on neural dynamics. Finally, we test and confirm a prediction of our circuit models by direct manipulation of nucleus accumbens input neurons.

Spatial Organization of the Projections of the Dorsal Raphe Nucleus to Functionally Diverse Areas of the Basal Ganglia in Dogs

Objective. To study the projections of individual subregions of the dorsal raphe nucleus (DRN) to functionally diverse areas of the basal ganglia in the dog brain. Materials and methods. A method based on the retrograde axonal transport of horseradish peroxidase (HRP) was used in 43 mongrel dogs given injections into functionally diverse areas of the basal ganglia to study the spatial organization of the projections from different parts of the DRN to these structures. At 48 h after perfusion of the brain, tetramethylbenzidine was used for the histochemical detection of HRP in DRN neurons in frontal serial sections of the brain and the numbers of labeled neurons in each area, as identified on serial frontal celloidin brain sections stained with toluidine, were counted under the microscope. Results. The spatial organization of projections to functionally diverse areas of the basal ganglia from individual functionally diverse parts of the DRN was studied in dogs using a method based on the retrograde axonal transport of HRP. The topographic characteristics of projection connections were identified, pointing to the possible segregated conduction of information from the dorsal part of the DRN, which has connections with limbic structures, i.e., limbic subareas of the corpus striatum. The overlapping of the terminal fields of neurons from all parts of the DRN receiving and sending functionally diverse information to the basal ganglia and structures connected to them seen in the entopeduncular nucleus, the ventral pallidum, the deep mesencephalic nucleus, and the medial part of the pedunculopontine nucleus of the tegmentum is evidence that this information may be integrated in these nuclei. The structural basis for information processing in the morphofunctional system of the basal ganglia was analyzed. Conclusions. Data are presented on the topographical organization of projections directed to functionally diverse areas of the basal ganglia from different parts of the DRN, providing evidence of the possible influences of different parts of the DRN on a wide spectrum of behavioral and physiological processes involving the basal ganglia. The connection system identified here is involved in conducting information and integrating it in the morphofunctional system of the basal ganglia and provides the structural basis for understanding the mechanisms of their functioning in health and disease.

Organization of the Connections of the Rostromedial Tegmental Nucleus with Structures of the Morphofunctional Basal Ganglia System in the Dog Brain

The spatial organization of the projections of the rostromedial tegmental nucleus (RMTg) to functionally diverse segments of the structures of the basal ganglia in dogs (n = 25) were studied by retrograde axonal transport of horseradish peroxidase. Connections between the limbic segments of the RMTg and the limbic segments of the zona incerta and the pallidum constituted evidence pointing to the segregated conduction of limbic information. In addition, these studies showed that the projections of the limbic medial and motor lateral segments of the RMTg overlap, within the pedunculopontine and entopeduncular nuclei, with fibers arriving in these nuclei from neurons in functionally diverse nuclei. The presence of labeled sparsely branched, long-axon “reticular” RMTg neurons projecting to the structures of interest is also evidence that this nucleus has an integrative function. Thus, the morphological substrate for information processing in the morphofunctional system of the basal ganglia underlying the mechanisms of their functioning was analyzed.

Organization of the Projections of the Lateral Midbrain Tegmental Nuclei to the Basal Ganglia in the Dog Brain

The organization of the projections of the lateral nuclei of the midbrain tegmentum (the peripeduncular and perilemniscal nuclei, the nucleus of the brachium of the posterior colliculus) to the functionally diverse nuclei of the basal ganglia system of the brain was studied in dogs (n = 34) using a method based on the retrograde axonal transport of horseradish peroxidase. The study nuclei of the midbrain were found to be involved in functionally diverse circuits whose components include the basal ganglia. These nuclei innervate the area of the putamen, globus pallidus, cuneate nucleus, and subcuneate nucleus, which on the basis of their predominant connections with the motor or limbic nuclei of the brain are classified as motor or limbic nuclei, as well as the area of the caudate and accumbens nuclei and the compact zone of the pedunculopontine nucleus, which receive projections from functionally diverse structures. Analysis of Nissl-stained frontal sections allowed the topographical anatomy of the individual lateral nuclei of the midbrain tegmentum to be refined. Histochemical reactions for NADPH diaphorase was used to determine the cholinergic nature of their neurons.

Neuron Populations Giving Rise to Corticothalamic Projections to the Partially Deafferented Ventrolateral Nucleus of the Thalamus

The characteristics of the distribution and morphological composition of neuron populations in the motor cortex projecting to the cerebellar recipient site, the ventrolateral nucleus of the thalamus, after its partial deafferentation were studied in adult cats. Partial deafferentation of the ventrolateral nucleus was produced by prior (three months) electrolytic lesioning of the contralateral intermediate nucleus of the cerebellum. A retrograde axonal horseradish peroxidase transport method with local administration of marker into the ventrolateral nucleus of the thalamus was used. All labeled neurons were members of the populations of nonpyramidal and pyramidal neurons, and most were of small or intermediate size and were located in the deep cortical layers – the lower subdivision of layer V and, mainly, layer VI. Labeled neurons were seen in cortical fi elds 4γ and 6αβ. These data demonstrate the absence of any structural reorganization of cortical projections to the deafferented ventrolateral nucleus of the thalamus. It is suggested that this is due to the high level of specialization of this movement program-triggering system. Neuroplastic changes were apparent in anomalous transformations of the proximal parts of dendrites and the presence of larger numbers of “paired” pyramidal neurons than in intact animals.

Organization of Projections of the Rostromedial Tegmental Nucleus to the Striatum in the Dog Brain

The organization of the projections of the rostromedial tegmental nucleus (RMTg) to functionally diverse areas of striatal structures in dogs (n = 26) was studied by a method based on retrograde axonal transport of horseradish peroxidase and fluorochromes. Projection fibers from neurons in the limbic medial part of the RMTg were found to be directed only to the limbic segments of the caudate nucleus, putamen, and nucleus accumbens. However, most segments of striatal structures showed convergence of projection fibers running from neurons in functionally diverse parts of the RMTg. Thus, the motor dorsolateral segment of the caudate nucleus, as well as striatal segments innervated by fibers from neurons in functionally diverse structures (the ventrolateral segment of the caudate nucleus and the lateral segment of the nucleus accumbens) received fibers from neurons in the motor lateral part of the RMTg and limbic medial part of the RMTg. The possible pathways conducting functionally diverse information and integrating it in the projection systems studied here are assessed.

Organization of the Projections of the Substructures of the Deep Mesencephalic Nucleus to the Striatum in the Dog Brain

Method of retrograde axonal transport of horseradish peroxidase was used to study the organization of the projections of the individual substructures of the deep mesencephalic nucleus complex to the functionally diverse regions of striatal structures of the dog brain (n=20). It was shown that the projection fibers of the neurons of the nucleus profundus mesencephali were directed to the ventro-lateral segment of the nucleus caudatus and the ventral segment of the putamen. The dorsal segment of the putamen obtains the fibers from the neurons of the nucleus cuneiformis, while the lateral segment of the nucleus accumbens received them from the neurons of the nucleus subcuneiformis. The possible pathways for conduction of the functionally diverse information and its integration in the investigated projection systems are discussed.

Interaction of the Pallidum, Pedunculopontine Nucleus, Zona Incerta, and Deep Mesencephalic Nucleus – Structures of the Morphofunctional Basal Ganglia System

The organization of the projections of substructures of the zona incerta (ZI), pedunculopontine nucleus (PPN), and the deep mesencephalic nucleus (NPM) complex and functionally diverse pallidal structures of the dog brain (n = 20) were studied by a method based on anterograde and posterograde axonal transport of horseradish peroxidase. The globus pallidus and entopeduncular nucleus were found to be connected by reciprocal connections with the dorsal, ventral, and caudal sectors of the ZI and with the NPM, and the lateral segment of the diffuse zone and the compact zone of the PPN. These same pallidal nuclei were connected to the rostral sector of the ZI, the cuneate and subcuneate nuclei of the NPM, the medial segment of the diffuse zone of the PPN via ipsilateral projections. Of all the structures studied, reciprocal connections with the ventral pallidum were seen only with the lateral segment of the diffuse zone and the compact zone of the PPN. The possible pathways for conduction of functionally diverse information and its integration in the projection systems studied here are discussed.

Striopallidal Projections of the Zona Incerta of the Dog Diencephalon

The projections of individual sectors of the zona incerta (ZI) in dog diencephalon to the functionally different striatal segments were studied by the method of the antero- and retrograde axonal transport of horseradish peroxidase. The data on the interconnections of ZI with all striopallidal structures, obtained by the author before and in the present work were summarized. Among all the striatal nuclei, the the rostral, ventral and caudal ZI sectors contained the neurons that projected their fibers only to the dorsal segments of the putamen. Not a single striatal structure was found to form projections to ZI. ZI and the dorsal pallidal nuclei (globus pallidus, nucleus entopeduncularis) are reciprocally connected with almost all ZI sectors. The connections of the ventral pallidum with the ZI were not detected.

Location of Neurons in the Central Nucleus of the Amygdaloid Body Projecting to the Paraventricular Nucleus of the Hypothalamus

Experiments were performed on rats using retrograde axonal transport of horseradish peroxidase with the aim of identifying cells in the individual structures of the central nucleus of the amygdaloid body (CNAB) innervating the paraventricular nucleus of the hypothalamus. Labeled cells were seen in the ipsilateral CNAB throughout its rostrocaudal extent. The largest number of labeled neurons was seen in the middle third of the nucleus in the area corresponding to the intermediate subnucleus of the CNAB. Occasional cells were located in the medial and lateral subnuclei of the CNAB. Labeled neurons in the intermediate subnucleus were oval cells or cells of indeterminate shape.

Projections of the basal ganglia to the zona incerta of the dog diencephalon

Retrograde axonal transport of horseradish peroxidase was used to show that the projections of the globus pallidus, entopeduncular nucleus, substantia nigra, and pedunculopontine tegmental nucleus in dogs are directed to all segments of the zone incerta. The experiments reported here identified no topical features in the organization of these projections in dogs, as application of marker to different areas of the zona incerta yielded similar distributions of labeled neurons in the basal ganglia. No striatal projections to the zone incerta were found.

Efferent innervation of the cervical segment of the trachea in early postnatal ontogenesis

A method based on retrograde axonal transport of horseradish peroxidase was used to study the efferent innervation of the cervical segment of the trachea in neonatal kittens and kittens aged 10, 20, and 30 days and two months. Labeled neurons in all animals were located in the cranial cervical, middle cervical, and cervicothoracic sympathetic ganglia on the right and left sides, at the level of the medulla oblongata, and in the dorsal and ambiguus nuclei of the vagus nerves. Up to age 30 days, neurons were also seen in the ventral horns of the spinal cord in segments C1 to C5. The number of sympathetic neurons innervating the trachea increased from the moment of birth, reaching a maximum by 10-20 days and then decreasing to age two months. The number of parasympathetic neurons gradually decreased during ontogenesis.

Projections of striatopallidal structures to the pedunculopontine nucleus of the tegmentum of the midbrain in dogs

A method based on retrograde axonal transport of horseradish peroxidase was used to study the striatopallidal afferent projections of the pendunculopontine nucleus of the midbrain (PPN) in dogs. The major source of these projections was found to be the pallidum, as both the compact and diffuse zones of this nucleus received projections from all of its structures: the entopeduncular nucleus, the globus pallidus, and the ventral pallidum. The striatal complex, specifically the nucleus accumbens, showed only occasional labeled neurons, projecting exclusively to the compact part of the PPN. Since the distribution of projection fibers arising from the functionally diverse territories of the striatopallidum and directed to individual structural subdivisions of the PPN showed no topical elements, identification of functionally specific (motor and limbic) areas of the PPN was not possible on the basis of the present analysis.

Localization of the spinal nucleus of accessory nerve in rat: a horseradish peroxidase study

The spinal nucleus of the accessory nerve (SNA) comprises the group of somata (perikarya) of motor neurons that supply the sternocleidomastoid and trapezius muscles. There are many conflicting views regarding the longitudinal extent and topography of the SNA, even in the same species, and these disagreements prompted the present investigation. Thirty Sprague-Dawley rats (15 males, 15 females) were used. The SNA was localized by retrograde axonal transport of horseradish peroxidase. Longitudinally, the SNA was found to be located in the caudal part (caudal 0.9-1.2 mm) of the medulla oblongata, the whole lengths of cervical spinal cord segments C1, C2, C3, C4, C5 and rostral fourth of C6. In the caudal part of the medulla oblongata, the SNA was represented by a group of perikarya of motor neurons lying immediately ventrolateral to the pyramidal fibres that were passing dorsolaterally after their decussation. In the spinal cord, the motor neuronal somata of the SNA were located in the dorsomedial and central columns at C1, in the dorsomedial, central and ventrolateral columns at C2 and in the ventrolateral column only at C3, C4, C5 and rostral quarter of C6. The perikarya of motor neurons supplying the sternocleidomastoid were located in the caudal part (caudal 0.9-1.2 mm) of the medulla oblongata ventrolateral to the pyramidal fibres that were passing dorsolaterally after their decussation. They were also located in the dorsomedial and central columns at C1, in the dorsomedial, central and ventrolateral columns at C2 and only in the ventrolateral column at the rostral three-quarters of C3. The perikarya of motor neurons supplying the trapezius muscle were located in the ventrolateral column only in the caudal three-quarters of C2, the whole lengths of C3, C4 and C5, and in the rostral quarter of C6.

歯科脳科学入門―中脳路核の歯髄ニューロンの話

In 1994 we developed a useful new subject for the sixth-year dental students, Brain Science of Dentistry, which included lectures and laboratory practice concerning the relation between feeding and brain functions. As an example of the contents of the lectures, how dental pulp neurons were discovered in the mesencephalic trigeminal nucleus will be described.It has been generally accepted that the tooth pulp is supplied by small myelinated Aδ and unmyelinated C fibers, which elsewhere in the body are involved in nociception. However, several histological and physiological studies have shown the presence of a substantial proportion of pulpal afferents with conduction velocities and diameters which would be expected for Aβ processes. Additionally, a related structure, the periodontal ligament, has been demonstrated to receive a dual innervation from the trigeminal ganglion (TG) and the mesencephalic trigeminal nucleus (MTN). Based on these findings, we suspected the existence of afferent processes innervating the tooth pulp whose cell bodies are part of the MTN. We examined this possibility in the adult cat using retrograde axonal transport of horseradish peroxidase (HRP). There are at least two decisive problems to overcome if one is to demonstrate HRP-labeled tooth pulp neurons in the TG and MTN after depositing HRP in pulp chambers of the permanent teeth:(1) preventing an inhibition of axonal transport of HRP due to acute pulpitis following the surgical procedures required to apply HRP to pulp tissues, and (2) controlling leakage of HRP through the apical foramina into the surrounding periodontal tissues. To solve the first problem, prednisolone, an anti-inflammatory synthetic steroid, was given (5 mg/kg, i.m.) immediately after surgery and every 12 h throughout the survival period of 3 days. In all prednisolone-treated cats, a considerable number of labeled neurons were found in both the TG and MTN, ipsilaterally. On the other hand, no labeled neurons were observed in the MTN in cats receiving no steroids. To check the presence of HRP leakage, we used two techniques. All teeth injected with HRP and the surrounding alveolar bone were decalcified, sectioned serially, and processed using the TMB technique. Examination under dark-field illumination revealed no evidence of HRP spread as far distally as the apical foramina and periodontal ligaments. The HRP-gel implant method is considered to be easier for localizing the spread of HRP, compared to the fluid injection method. In two additional steroid-treated cats, 1μl of 30% HRP entrapped in 5% polyacrylamide gel was placed in the pulp horn of the mandibular left canine. This procedure resulted in the labeling of 10 and 13 MTN neurons in the respective cats. When the number of HRP-labeled tooth pulp neurons in the MTN and TG were compared among five different mammalian species (rats, rabbits, cats, dogs, and monkeys), a conspicuous species difference was found in the tooth pulp innervation by the MTN. In cats, dogs and monkeys, HRP-labeled neurons were found in both the TG and MTN, but no labeled neurons were counted in the MTN of rats and rabbits. In conclusion, dual innervation of the tooth pulp by the TG and MTN occurs in the cat, dog, and monkey, but not in the rat and rabbit. This species difference in pulpal innervation might be brought about by a cumulative dominance over the teeth closely associated with feeding habits.

Organization of the efferent projections of the pedunculopontine tegmental nucleus of the midbrain of the dog pallidum

Studies of the pedunculopontinopallidal projections of the dog brain based on the retrograde axonal transport of horseradish peroxidase demonstrated that the compact zone (PPNc) and the lateral area of the diffuse zone (PPNd) of the pedunculopontine tegmental nucleus (PPN) of the midbrain project to the globus pallidus, entopeduncular nucleus, and ventral pallidum. The medial area of the PPNd, adjacent to the chiasm of the upper cerebellar peduncles and seen in other animals as the mesencephalic extrapyramidal area (MEA), projects only to the globus pallidus. In dogs, this area of the tegmentum is not a major source of projections to the striopallidum, such that it is inappropriate to regard it as a separate structure, comment being restricted to the topical organization of PPNd projections to the pallidum. Projection fibers to pallidal structures arise from both cholinergic and non-cholinergic PPN neurons.

Afferent innervation of the trachea during postnatal development

Retrograde axonal transport of horseradish peroxidase was used in this study to determine the location and basic morphological parameters of neurons innervating the trachea in newborn, 10-, 20-, 30-day-old and 2-month-old kittens. Labeled neurons were detected in all animals in the nodose ganglion of the vagus nerve and in the spinal ganglia (C1–C7 and T1–T6 after injection of tracer into the cervical trachea, C5–C7 and T1–T8 with injection into the thoracic part of the trachea) from both sides. The content of vagal and spinal afferent neurons innervating the cervical part of trachea declined during development. The number of spinal afferent neurons with connections to the thoracic trachea did not change but the quantity of cells in nodose ganglion supplying the thoracic trachea increased from the moment of birth till 10 and 20 days and decreased later in postnatal development. In newborn, 10-day-old and 20-day-old animals, the largest number of afferent cells was connected with the cervical part of the trachea in comparison with the thoracic one, whereas in 2-month-old kittens the relation was opposite. We suggest that afferent innervation of the trachea is not morphologically complete at the moment of birth and does not become mature until the second month of life.

Preganglionic inputs to the stellate ganglion of the cat during postnatal ontogenesis

The localization of preganglionic neurons forming, connections with the stellate ganglion was studied using a method based on retrograde axonal transport of horseradish peroxidase in cats during postnatal ontogenesis from birth to six months of life. The number of preganglionic neurons and spinal cord segments connected to the ganglion increased from birth to 10 days of age, and then decreased. The proportion of preganglionic neurons in different spinal cord nuclei changed during life and became comparable with that in adults by age six months. This was accompanied by an increase in the proportion of cells in the nucleus intermediolateralis thoracolumbaris pars principalis, with a decrease in the number of neurons in the nucleus intermediolateralis thoracolumbaris parts funicularis and in the ventral horns of the spinal cord.

Plastic Reorganization in the Cerebellothalamic System after Partial Deafferentation of the Ventrolateral Nucleus of the Thalamus

A method based on the retrograde axonal transport of horseradish peroxidase after preliminary (three months) lesioning of the contralateral intermediate nucleus of the cerebellum or lateral vestibular nucleus of Deiters in adult cats demonstrated the formation of new ipsilateral thalamic projections from all three central nuclei of the cerebellum and the nuclei of the vestibular complex.

Cerebellar connections to the rostral reticular nucleus of the thalamus in the rat.

We studied the cerebellar connections to the reticular nucleus thalamus (RNT) by means of retrograde axonal transport of horseradish peroxidase (HRP) in the rat. Specific HRP pressure injections to the rostral RNT (1.6-1.8 mm caudal to bregma) resulted in retrograde labelling of neurones in the cerebellar nuclei. The rostral RNT showed specific topographical organization of its cerebellar connections. Microinjections into the rostral RNT, 1.6 mm caudal to bregma, produced numerous HRP-labelled neurones within the anterior interposed (emboliform nucleus) and scarce HRP-labelled neurones within the lateral (dentate nucleus) cerebellar nuclei, whereas injections into the rostral RNT, 1.8 mm caudal to bregma, produced numerous HRP-labelled neurones within the posterior interposed (globose nucleus) and scarce lightly HRP-labelled neurones within the lateral (dentate nucleus) cerebellar nuclei. Cerebellar connections with the rostral RNT were exclusively ipsilateral to the injection site. No HRP-labelled cells were detected in the medial (fastigial nucleus) cerebellar nucleus. The cerebellar connections reach the RNT via the superior cerebellar peduncle. By contrast, HRP injections into the anterior, posterior interposed and lateral cerebellar nuclei produced no labelled cells within the RNT. This study demonstrates the existence of direct cerebello-RNT but not RNT-cerebellar connections. The presence of the cerebello-RNT connections introduces a new route through which the cerebellum may influence RNT and thus cerebral cortical activity.