Lateral Dorsal Tegmental Nucleus Research Articles

A cholinergic projection to the rat substantia nigra from the pedunculopontine tegmental nucleus

This study demonstrates the pedunculopontine tegmental nucleus (PPN) to be the source of a major cholinergic projection to the rat substantia nigra (SN). Neurons of the PPN were double-labeled utilizing choline acetyltransferase immunocytochemistry combined with retrograde transport of horseradish peroxidase (HRP). The cholinergic projection to the SN originates from neurons located in predominately the ipsilateral and rostral portions of the PPN. Other cholinergic neurons that were also retrogradely labeled with HRP were located in the caudal PPN and in the lateral dorsal tegmental nucleus. A non-cholinergic projection from this region was also identified. These findings indicate that the PPN may be topographically organized with respect to its efferent projections. In addition, this study provides evidence for an extrinsic source of acetylcholine to the basal ganglia and implicates the PPN as a source of potentially significant influence over basal ganglia function.

A cholinergic projection to the rat superior colliculus demonstrated by retrograde transport of horseradish peroxidase and choline acetyltransferase immunohistochemistry.

Acetylcholinesterase (AChE) has been localized by histochemistry in the superior colliculus and in the tegmentum of the caudal midbrain and rostral pons of the rat. The pattern of AChE localization in the superior colliculus was characterized by homogeneous staining in the superficial layers and patchlike staining in the intermediate gray layer. In the tegmentum, AChE was localized in the pedunculopontine nucleus (PPN), beginning rostrally at the caudal pole of the substantia nigra and extending caudally to the level of the parabrachial nuclei, and in the lateral dorsal tegmental nucleus (LDTN) of the central gray. The localization of AChE in these nuclei overlapped the distribution of neurons stained by immunohistochemistry using an antibody to choline acetyltransferase (ChAT), the synthesizing enzyme of the neurotransmitter acetylcholine. Other neighboring areas that were stained with AChE, but that did not contain ChAT-immunoreactive neurons, included the microcellular tegmental nucleus and the ventral tegmental nucleus. Neurons in the PPN and LDTN were determined to be potential sources of the cholinergic projection to the intermediate gray layer of the rat superior colliculus by double labelling with retrograde transport of horseradish peroxidase (HRP) combined with the immunohistochemical localization of ChAT. Three populations of neurons were identified. A predominantly ipsilateral ChAT-immunoreactive population was located in the pars compacta subdivision of PPN (PPNpc). Retrograde HRP-labelled neurons in the pars dissipata subdivision of the PPN (PPNpd), located ventral to the superior cerebellar peduncle (SCP) at the level of the inferior colliculus, composed a second population that was predominantly contralateral but was not ChAT immunoreactive. A third population of retrogradely labelled neurons was predominantly ipsilateral and ChAT immunoreactive and was located in the LDTN. These findings compared favorably with the full extent of the projection from this tegmental region revealed by retrograde transport of HRP from the superior colliculus when more compatible fixation and chromogen procedures were used. The results suggest that the PPN and the LDTN are two sources of the cholinergic input to the superior colliculus. Since the PPN also has extensive efferent, and afferent, connections with basal-ganglia-related structures, this cholinergic excitatory input to the superior colliculus, like the GABA-ergic inhibitory input from the substantia nigra pars reticulata, may provide the basis for an additional influence of the basal ganglia on visuomotor behavior.

Distribution of neuropeptide K-immunoreactivity in the rat central nervous system

The distribution of neuropeptide K (NPK), a 36-residue amidated peptide originally isolated from porcine brain, is described in the rat CNS by immunohistochemical methods. Antibodies were generated in rabbits to N-terminus and C-terminus regions of the peptide and the distribution of immunoreactive cell bodies and fibers was mapped in colchicine-treated and normal rat brains. Major areas of cell body staining included the medial habenular nucleus, the ventromedial nucleus of the hypothalamus, the interpeduncular nucleus, the lateral dorsal tegmental nucleus, the nucleus raphe pallidus, and the nucleus of the solitary tract. Some of the areas of dense NPK-fiber immunoreactivity included the ventral pallidum, the caudate-putamen, certain areas of the hypothalamus, the central and medial amygdaloid nuclei, the entopeduncular nucleus, the habenular nuclei, the substantia nigra pars reticulata, the caudal part of the spinal nucleus of the trigeminal nerve, the nucleus of the solitary tract and the dorsal horn of the spinal cord. A striking similarity exists between this pattern of immunoreactive staining and that described for substance P, suggesting that the tachykinin systems do not exist independently in the brain. The possible roles for multiple tachykinins in the brain are discussed.

Colocalization of atriopeptin-like immunoreactivity with choline acetyltransferase-and substance P-like immunoreactivity in the pedunculopontine and laterodorsal tegmental nuclei in the rat

Atriopeptin, the atrial natriuretic peptide, is a circulating hormone that plays an important role in the regulation of fluid and electrolyte balance. Immunohistochemical studies have shown that large, multipolar atriopeptin-like immunoreactive (APir) neurons are present in areas of the midbrain corresponding to the large neurons of the pedunculopontine tegmental (PPT) and lateral dorsal tegmental (TLD) nuclei, all of which can be stained immunohistochemically for choline acetyltransferase-like immunoreactivity (ChATir). A subpopulation of these cholinergic PPT and TLD neurons are also known to contain substance P-like immunoreactivity (SPir). Using an immunofluorescent technique that allows simultaneous localization of two antigens, we have studied the relationship between APir, SPir and ChATir in the pontine tegmentum of the rat. We have found that (i) the large multipolar APir neurons of the pontine tegmentum are identical to the ChATir neurons of the PT and TLD nuclei and (ii) a subpopulation of the APir neurons in PPT and TLD neurons are also SPir.

Ultrastructural localization and afferent sources of substance P in the rat parabrachial region

The ultrastructural morphology and afferent sources of terminals containing substance P-like immunoreactivity were examined in the rat parabrachial region. In the first portion of the study, a polyclonal antiserum to substance P was localized in the ventrolateral parabrachial region using the peroxidase-antiperoxidase labeling technique combined with electron microscopy. The antiserum was tested for cross-reaction with substance P, physalaemin, substance K and neuromedins B, C and K. Cross-reactivity was most intense with substance P. However, substance K, neuromedin K and physalaemin also exhibited limited cross-reactions with the antiserum. In the ventrolateral parabrachial region of untreated adult animals, substance P-like immunoreactivity was localized in axon terminals containing numerous small (40–60 nm) clear vesicle and 1–3 large (90–120 nm) dense-core vesicles. At least 54% of the labeled terminals formed asymmetric synapses with unlabeled dendrites; and at least 30% of the recipient dendrites received more than one labeled axon terminal. In addition, the labeled terminals were associated less frequently with other unlabeled soma, axon terminals and blood vessels. In the second part of the study, we examined whether or not perikarya in various extrinsic regions contributed to the substance P-like immunoreactivity in axon terminals in the parabrachial region. Wheat-germ agglutinin conjugated horseradish peroxidase was injected unilaterally into the parabrachial region of adult rats two days prior to being killed and one day prior to intraventricular injection of colchicine (100 μg in 7.5μ1 saline) which enhanced the detection of immunoreactivity in perikarya. Sections were first processed by a tetramethylbenzidine reaction stabilized with cobalt-diaminobenzidine for demonstration of the transported peroxidase then were immunocytochemically labeled for substance P. Perikarya containing both the black granular retrograde labeling and brown peroxidase-immunoreactivity were found in the nuclei of the solitary tracts, the caudal ventrolateral reticular formation, the lateral dorsal tegmental nucleus and the paraventricular, dorsomedial and lateral hypothalamic nuclei. The projections were largely, but not exclusively, from perikarya located on the same side as the parabrachial injection. We conclude that substance P, or a closely related tachykinin, is a putative transmitter or modulator within a number of pathways to the parabrachial region and that these afferents act primarily through axodendritic synapses with intrinsic neurons.

Cholinergic projections from the midbrain and pons to the thalamus in the rat, identified by combined retrograde tracing and choline acetyltransferase immunohistochemistry

The distribution of cholinergic neurons in the midbrain and pons which project directly to the thalamus was investigated in the rat using a procedure which allows the simultaneous detection of retrogradely transported horseradish peroxidase (HRP) and immunohistochemical demonstration of choline acetyltransferase (ChAT) in the same neurons. HRP injections were placed in the dorsal half of the anterior third of the thalamus on one side which included the anteroventral nucleus as well as portions of the rostral intralaminar and reticular nuclei. These thalamic nuclei showed the highest density of immunohistochemically detectable cholinergic fibers. Neurons containing both HRP and ChAT, which represented cholinergic neurons projecting directly to the thalamus, were found in the midbrain and pons in the lateral tegmental reticular formation, parabrachial region and lateral dorsal tegmental nucleus. Ipsilateral to the injection site over 91% of the HRP labeled neurons in all of these regions were cholinergic, while an average of 60% of the cholinergic neurons had transported HRP. Contralateral to the injection site 5–6% of the cholinergic neurons in these regions were also retrogradely labeled. These findings demonstrate direct cholinergic projections to the thalamus from neurons in several regions in the tegmentum and suggest that tegmental projections to the thalamus are predominantly cholinergic.

Diencephalic and brainstem afferents to the hippocampal formation of the rat

The afferents to the hippocampal formation (Ammon's horn and dentate gyrus) of the rat were studied with the horseradish peroxidase (HRP) retrograde tracing method. HRP was deposited microelectrophoretically in the dorsal or ventral hippocampal formation of adult female rats. In addition to well-known afferents (e.g., entorhinal cortex and septum), labeled neurons were found in the thalamus, hypothalamus, and brainstem. In the thalamus, extensive labeling was found in nucleus reuniens, paraventricular and paratenial nucleus, as well as a few scattered labeled neurons in the ventromedial nucleus, nucleus rhomboidus, and zona incerta. The projection from nucleus reuniens is topographically organized: the dorsomedial portion of the nucleus projects to dorsal hippocampus and the ventrolateral portion of the nucleus projects to ventral hippocampus. In the hypothalamus, scattered labeled neurons were found in most nuclei and areas. The supramammillary region contained the largest number of labeled cells. The projection from the supramammillary region is topographically organized: the anterior-lateral region projects primarily to dorsal hippocampus and the posterior-medial region projects principally to ventral hippocampus. In the brainstem, labeled neurons were observed in the mesencephalic raphe (both raphe dorsalis and central superior), nucleus locus coeruleus, the dorsal magnocellular dividion of the interpeduncular nucleus and surrounding regions, the lateral dorsal tegmental nucleus, and the region caudal to the nucleus raphe dorsalis apparently corresponding to the dorsal tegmental nucleus pars ventromedialis.

Afferent connections of the laterodorsal thalamic nucleus in the rat

The laterodorsal thalamic afferent connections have been studied by means of the retrograde transport of horseradish peroxidase (HRP). The following new sources of projections to the laterodosal thalamic nucleus (LD) were observed: the zona incerta, the lateral dorsal tegmental nucleus (bilaterally), the lateral hypothalamus and the precentral agranular cortex.