Innervation and osteoclast distribution in the inferior pharyngeal jaw of the cichlid Nile tilapia (Oreochromis niloticus).

In addition to an oral jaw, cichlids have a pharyngeal jaw, which is used for crushing and processing captured prey. The teeth and morphology of the pharyngeal jaw bones adapt to changes in prey in response to changes in the growing environment. This study aimed to explore the possible involvement of the peripheral nervous system in remodeling the cichlid pharyngeal jaw by examining the innervation of the inferior pharyngeal jaw in the Nile tilapia, Oreochromis niloticus. Vagal innervation was identified in the Nile tilapia inferior pharyngeal jaw. Double staining with tartrate-resistant acid phosphatase and immunostaining with the neuronal markers, protein gene product 9.5, and acetylated tubulin, revealed that osteoclasts, which play an important role in remodeling, were distributed in the vicinity of the nerves and were in apposition with the nerve terminals. This contact between peripheral nerves and osteoclasts suggests that the peripheral nervous system may play a role in remodeling the inferior pharyngeal jaw in cichlids.

Postnatal development of thalamic reticular nucleus projections to the anterior thalamic nuclei in rats.

The thalamic reticular nucleus (TRN) projects inhibitory signals to the thalamus, thereby controlling thalamocortical connections. Few studies have examined the development of TRN projections to the anterior thalamic nuclei with regard to axon course and the axon terminal distributions. In the present study, we used parvalbumin (PV) immunostaining to investigate inhibitory projections from the TRN to the thalamus in postnatal (P) 2- to 5-week-old rats (P14-35). The distribution of PV-positive (+) nerve fibers and nerve terminals markedly differed among the anterior thalamic nuclei at P14. Small, beaded nerve terminals were more distributed throughout the anterodorsal nucleus (AD) than in the anteroventral nucleus (AV) and anteromedial nucleus (AM). PV+ fibers traveling from the TRN to the AD were observed in the AV and AM. Nodular nerve terminals, spindle or en passant terminals, were identified on the axons passing through the AV and AM. At P21, axon bundles traveling without nodular terminals were observed, and nerve terminals were distributed throughout the AV and AM similar to the AD. At P28 and P35, the nerve terminals were evenly distributed throughout each nucleus. In addition, DiI tracer injections into the retrosplenial cortex revealed retrogradely-labeled projection neurons in the 3 nuclei at P14. At P14, the AD received abundant projections from the TRN and then projected to the retrosplenial cortex. The AV and AM seem to receive projections with distinct nodular nerve terminals from the TRN and project to the retrosplenial cortex. The projections from TRN to the AV and AM with nodular nerve terminals at P14 are probably developmental-period specific. In comparison, the TRN projections to the AD at P14 might be related to the development of spatial navigation as part of the head orientation system.

Fiber Connections of the Caudal Corpus Cerebelli, with Special Reference to the Intrinsic Circuitry, in a Teleost (Oreochromis niloticus).

The caudal part of the corpus cerebelli of Nile tilapia can be divided into dorsal and ventral regions. The granule cell layer of the dorsal (dGL) and ventral (vGL) regions of the caudal corpus cerebelli is known to receive indirect inputs from the telencephalon relayed by the nucleus paracommissuralis. The descending pathways are topographically organized, and the dGL and vGL receive inputs from different dorsal telencephalic parts. The caudal corpus cerebelli, in turn, projects extracerebellar efferents. However, it remains unknown how the descending telencephalic inputs are processed within the cerebellum. Therefore, the present study investigated intrinsic connections of the caudal corpus cerebelli by injecting neural tracers into the molecular layer of dorsal and ventral regions. Injections of tracers into the ventral molecular layer resulted in labeled cells in the vGL and the ganglionic layer of the ventral corpus. The axonal trajectories from labeled cells in the ganglionic layer were analyzed in detail via single-axon reconstructions, which suggested that the terminal portions were confined to the ganglionic layer of the dorsal corpus. No labeled terminals were observed outside the caudal corpus cerebelli. Tracer applications to the dorsal molecular layer resulted in labeled cells not only in the ganglionic layer and the granule cell layer of the dorsal corpus but also in the ganglionic layer of the ventral corpus. The latter finding confirms the presence of intrinsic projections from the ventral region to the dorsal region in the caudal corpus cerebelli. We further revealed that the intrinsic projection neurons are Purkinje cells by immunohistochemistry for zebrin II (aldolase C), which is a marker of Purkinje cells, combined with tracer injections into the dorsal corpus. Unlike injections into the ventral corpus, injections into the dorsal corpus resulted in labeled terminals in extracerebellar structures, such as the nucleus of the medial longitudinal fascicle and reticular formation. The present study suggests that indirect inputs from different telencephalic parts received and processed by distinct regions of caudal corpus cerebelli are sent out of the corpus through the efferent neurons in the dorsal corpus.

Distributions of calcitonin gene-related peptide and substance P in the human maxillary sinus of Japanese cadavers.

BACKGROUND: Substance P (SP) and calcitonin gene-related peptide (CGRP) are released by the nociceptive sensory nerve and are involved in blood flow, pain and inflammation in the nasal mucosa. The purpose of this study was to assess the distribution of the SP and CGRP nerve fibres related to blood supply within human Schneiderian membrane of the maxillary sinus (MS). MATERIAL AND METHODS: In this study, the MS from Japanese cadavers was examined by whole-mount immunohistochemistry. Human male cadavers (ranging in age from 80 to 90 years) were used in this study. RESULTS: SP- and CGRP-positive fibres were found around large vessels of the medialis superior alveolar branches and also within the floor region of the MS. The floor region of the MS was composed of complex branches of these fibres. CONCLUSION: Our results give useful information for surgical sinus floor elevation in this region of the MS. These anatomical features may assist in the execution of a successful surgical procedure.

A morphological study of the blood vessels associated with periodontal probing depth in human gingival tissue.

Gingival tissues in human cadavers were examined the blood vessel diameter in the depths of the gingival pockets such as three groups: gingiva adjacent to a sulcus of 2 mm (Group 1); gingiva adjacent to a 2-4-mm sulcus (Group 2); and gingiva adjacent to a sulcus of > 4 mm (Group 3). A meaningful significant difference was seen observed in gingival pocket side, intermediate and outer layer side regions of the gingiva. A meaningful significant difference was seen found in intermediate part and the outer layer of the gingiva in Group 3. Other gingival biopsies were performed on a human body donation specimen to examine CD-31 positive endothelial cells of blood vessels by an immnohistochemical method. Our results suggest that the periodontal probing depth reflect the blood vessel organization of human gingival tissue.

Observing the bony canal structure of the human maxillary sinus in Japanese cadavers using cone beam CT.

We observed the location of the posterior superior alveolar artery (PSAA) and nerve at the macroscopic level between the maxillary sinus (MS) and surrounding bone of the anterior region of the maxilla. This study was completed using cone beam computed tomography (CBCT) imaging of 19 human cadavers with 38 sides of Japanese origin (ranging in age from 59-94 years, mean 77.7 +/- 9.8 years) that were prepared for this study. The bony canal structure of the inner surface of the maxilla was clearly apparent in our results, and the bony canals were classified into three types according to the structure along the course of the PSAA: canal-like, ditch-shaped tunnel and fragmented, and the lest sides were undefined. Calcitonin gene-related peptide (CGRP)-positive fibers were identified along the PSAA in the bony canal of the maxilla by immunohistochemistry. The presence of the bony structure and CGRP-positive nerve fibers along the PSAA suggests that there is risk to the PSAA during surgery involving graft implant in the floor of the maxillary sinus.

Evaluation of the blood and nerve supply patterns in the molar region of the maxillary sinus in Japanese cadavers.

The maxillary sinus (MS) in the maxilla bone is located near the orbit, the nasal cavity and the oral cavity; however, the positioning of the constituent bones is complex. The posterior superior alveolar branches of the maxillary artery and nerve are distributed in the lateral wall of the MS. The courses of these blood vessels and nerves are restricted by the morphology of the craniofacial bones, and the landmarks used in dental implant treatment of these courses mainly run along the lateral wall of the MS. In this study, 19 human cadavers with 34 sides of Japanese origin (ranging in age from 59-94 years, mean 77.7 +/- 9.8 years) were prepared for measurement of the MS, the superior alveolar artery and the infraorbital artery using cone beam computed tomography (CBCT). The posterior superior alveolar artery (PSAA) of the lateral wall of the MS can be classified into one of three groups based on the supply pattern. In the greatest number of cadavers, the PSAA ran mainly to the lateral surface of the zone between the superior border of the alveolar foramen and the inferior border of the MS (53.0%, 18/34). In others, the PSAA ran to the zone between the infraorbital foramen and the superior border of the alveolar foramen (17.6%, 6/34); in a third group, the PSAA ran to the zone between the inferior border of the MS and the greater palatine foramen (23.5%, 8/34). The lest of two sides are spread out in this area (5.9%, 2/34). CBCT is the most accurate tool to evaluate important anatomical parameters, such as the distance of the blood supply, for the implant of grafts in the floor of the MS during surgical procedures.

Understanding the formation of maxillary sinus in Japanese human foetuses using cone beam CT.

The formation of the maxillary sinus (MS) is tied to the maturation of the craniofacial bones during development. The MS and surrounding bone matrices in Japanese foetal specimens were inspected using cone beam computed tomography relative to the nasal cavity (NC) and the surrounding bones, including the palatine bone, maxillary process, inferior nasal concha and lacrimal bone. The human foetuses analysed were 223.2 ± 25.9 mm in crown-rump length (CRL) and ranged in estimated age from 20 to 30 weeks of gestation. The amount of bone in the maxilla surrounding the MS increased gradually between 20 and 30 weeks of gestation. Various calcified structures that formed the bone matrix were found in the cortical bone of the maxilla, and these calcified structures specifically surrounded the deciduous tooth germs. By 30 weeks of gestation, the uncinate process of the ethmoid bone formed a border with the maxilla. The distance from the midline to the maximum lateral surface border of the MS combined with the width from the midline to the maximum lateral surface border of the inferior nasal concha showed a high positive correlation with CRL in Japanese foetuses. There appears to be a complex correlation between the MS and NC formation during development in the Japanese foetus. Examination of the surrounding bone indicated that MS formation influences maturation of the maxilla and the uncinate process of the ethmoid bone during craniofacial bone development.

Novel localization of tenascin-X in adult mouse leptomeninges and choroid plexus.

Tenascin-X (Tn-X) belongs to the tenascin family of glycoproteins and is clearly associated with the human connective tissue disorder Ehlers-Danlos syndrome. Recently, human single nucleotide polymorphism analyses showed that Tn-X is associated with schizophrenia. Tn-X-related central nervous system (CNS) disorder has been reported in recent years. However, details of Tn-X localization are not clear in the adult cerebral cortex and its meninges. Using immunohistochemical techniques, we found novel localizations of Tn-X in the leptomeningeal trabecula (TB) of adult mice and in the connective tissue of the choroid plexus (CP) in the brains of mice. Subsequent immunohistochemical studies showed complementary localization of Tn-X in the leptomeninges and CP. Localization of tenascin-C was not detected in the leptomeningeal TB or in the connective tissue of the CP. These results might provide insight into the role of Tn-X in the pathogenesis of disorders in the CNS.

Distribution of LYVE-1 and CD31 in postnatal rat masseter muscle.

During the development of blood vascular systems in the masseter muscle, one functional property of the blood supply via capillaries is altered by the change in feeding pattern from suckling to mastication. The lymphatic vessel hyaluronan receptor-1 (LYVE-1) is a marker of lymphatic endothelial cells. The PECAM (CD31) is also an important marker of vascular endothelial cells and lymphatic cells. The mechanisms by which circulating lymphatic endothelial cells from blood vessels in masseter muscle form a network of lymphatic capillaries and vessels functioning in jaw muscle movement remain unknown. In our results, LYVE-1- and CD31- positive reactions were located in almost identical regions at the stages examined using double immunofluorescence staining. However, the level of protein for LYVE-1 and CD31 differed between superficial and deep regions in postnatal rat masseter muscle using Western blotting analysis. The different distribution of LYVE-1 and CD31 antibody reactions was found in the deep region in contrast to that of the superficial area in 3-7-week-old rat masseter muscles. Concomitant with the increased level of protein for CD31 in the deep region, many small vessels branch in this region during development in rat masseter muscle. Therefore, different levels of protein and immunohistochemical reactions for CD31- and LYVE-1-positive cells may reflect alterations in the functional properties of the blood supply and collection via capillaries due to the changes in feeding pattern.

Classifications of tunnel-like structure of human petrotympanic fissure by cone beam CT.

The discomallear ligament (DML) runs through a narrow space of bony petrotympanic fissure, which joins the articular disc of the temporomandibular joint (TMJ) and the malleus in the tympanic cavity. Previous report suggest that an anatomical feature gives rise to TMJ pain and dysfunction. Recently, the movement of the malleus caused by hypertension on the discomallear ligament is important to the function of the TMJ. The purpose of this study is to define its morphological features using the cone beam CT (CBCT) and anatomical dissection of Japanese cadavers. Petrotympanic fissure and DML were observed in 14 cadavers (eight males and six females). It is revealed that a wide tunnel-like structure was found on CBCT images in the middle region of the petrotympanic fissure to the malleus in the tympanic cavity consisting of mainly three types: a wide tunnel-shaped structure (29.2%, 7/24, type 1), a tunnel-shaped structure widely open in the entrance of the petrotympanic fissure to the mandibular fossa and gradually thinning out in the tympanic cavity (20.8%, 5/24, type 2), and a tunnel-shaped structure widely open in the entrance of the mandibular fossa, middle region with flat-shaped tunnel structure and narrow exit in the tympanic cavity (41.7%, 10/24, type 3). These structures between the entrance of the petrotympanic fissure and the exit at the tympanic cavity are important to define the limited movement of the malleus. Therefore, morphological feature of the ligaments in malleus may relate to TMJ pain, dysfunction and hearing function.

Distribution of slow muscle fiber of muscle spindle in postnatal rat masseter muscle.

We investigated the properties of the muscle spindle in the masseter muscle at an immunohistochemical level in rats fed for 6 weeks. Slow myosin heavy chain (MyHC) isoforms were measured and intrafusal fibers in the muscle spindle were studied to determine the relationship between the superficial and deep regions of rat masseter muscle after alternated feeding pattern. However, muscle spindles were found in both regions, mainly in the deep region of the posterior superficial region of masseter muscle. The total number of the slow fiber in the intrafusal fiber and number of muscle spindle in the deep region were high from 5 to 8 weeks old in spite of various dimensions of data such as diameter and the compositions of the intrafusal fiber. The relationship of the protein expression of slow MyHC in the two regions at 5 weeks old reversed five weeks later (10 weeks old). This period is an important stage because the mastication system in masseter muscle with muscle spindle may be changed during the alternated feeding pattern of suckling to mastication. The changes may be a marker of the feeding system and of the control by the tension receptor of muscle spindle in this stage of masseter muscle after postnatal development.

Giant neurons in the macaque pulvinar: a distinct relay subpopulation.

Calbindin positive (CB+) giant neurons are known to occur within the pulvinar nucleus in subhuman primates. Here, we demonstrate by combined retrograde tracing and immunocytochemistry that at least some of these are pulvinocortical relay neurons, and further report several distinctive features. First, in contrast with non-giant relay neurons, the giant neurons are often solitary and isolated from a main projection focus. The question thus arises of whether their cortical projections may be non-reciprocal or otherwise distinctive. Second, these neurons are positive for GluR4; but third, they are otherwise neurochemically heterogeneous, in that about one-third are positive for both parvalbumin (PV) and CB. Presumably, these subpopulations are also functionally heterogeneous. These results provide further evidence for the idea of multiple, interleaved organizations within the pulvinar; and they imply that thalamocortical projections are more disparate than has yet been appreciated. Finally, we found that giant CB+ neurons have a distinctive meshwork of large, PV+ terminations, prominent at the first dendritic branch point. In size and location, these resemble inhibitory terminations from the zona incerta or anterior pretectal nucleus (APT), as recently described in higher order thalamic nuclei in rats. One can speculate that giant neurons in the macaque pulvinar participate in a layer 5-APT-thalamus (giant neuron) extrareticular pathway, functionally distinct from the layer 6-reticular nucleus-thalamus network.

Long-range interneurons within the medial pulvinar nucleus of macaque monkeys.

Like other thalamic nuclei, the primate pulvinar is considered not to have long-range intrinsic connections, either excitatory or inhibitory. Injections of biotinylated dextran amine (BDA) in the medial pulvinar, however, reveal retrogradely filled neurons up to 2.0 mm from the injection edge. Serial section reconstruction (n = 18) confirmed that retrogradely filled neurons projected to the injection site and showed that they had additional long-range collaterals within the posterior pulvinar. Arrays of small, beaded terminations occurred in multiple foci along the collaterals. Terminal arrays were up to 1.0 mm in length; foci were separated by about 0.7 mm. Somata were large (average area = 220 microm2), and dendritic arbors were radiate and also large (about 1.0 mm in diameter), but without either the appendages of classical interneurons or the hairlike spines characteristic of radiate pulvinocortical projection neurons. Double labeling for BDA and parvalbumin (PV) or BDA and gamma-aminobutyric acid (GABA) indicated that these large neurons were positive for both PV and GABA. Double labeling for PV and GABA, or PV and glutamic acid decarboxylase 67 (GAD67) revealed a small number of similarly large neurons in the posterior pulvinar that were positive for both substances. Thus, we propose that these neurons are a novel class of inhibitory interneuron, longer range than the classic thalamic local circuit interneurons. Future questions include how these neurons relate to other inhibitory systems and specific postsynaptic populations and whether they are located preferentially within the posterior pulvinar, possibly related to the multimodal character of this thalamic region.

Afferent connections of the corpus cerebelli in holocentrid teleosts.

The holocentrid corpus cerebelli (CC) is composed of the dorsal (CCd) and ventral (CCv) lobes. In the present study, afferent connections of the CCd and CCv in holocentrid teleosts (Sargocentron rubrum and S. diadema) were examined by means of tract-tracing methods. Tracer injections into either lobe of the CC labeled neurons in the ipsilateral area pretectalis pars anterior et posterior, nucleus paracommissuralis (NPC), nucleus accessorius opticus and nucleus tegmentocerebellaris. Labeled neurons were also present in the bilateral nucleus lateralis valvulae (NLV), nucleus raphes, nucleus reticularis lateralis and inferior reticular formation, and in the contralateral inferior olive. Injections into the CCd labeled only a few neurons in the area pretectalis pars anterior et posterior, nucleus accessorius opticus and nucleus tegmentocerebellaris, whereas many labeled cells were seen in these nuclei after CCv injections. Injections into the CCv also revealed afferent connections that were not observed after CCd injections. The CCv injections labeled additional neurons in the ipsilateral torus longitudinalis and nucleus subeminentialis and in the bilateral nucleus subvalvularis and nucleus of the commissure of Wallenberg. These differences in afferent connections suggest functional differences between the CCd and CCv. After injections into the CCd, labeled neurons in the NPC were restricted to a medial portion of the nucleus. On the other hand, after injections into the CCv, labeled neurons were found throughout the NPC. Labeled neurons in the NLV were mainly located in its rostral portion following CCd injections, whereas labeled neurons were mainly distributed in the medial portion following CCv injections. These observations suggest topographical organizations of the NPC-CC and NLV-CC projections.

Fiber connections of the lateral valvular nucleus in a percomorph teleost, tilapia (Oreochromis niloticus).

Fiber connections of the lateral valvular nucleus were investigated in a percomorph teleost, the tilapia (Oreochromis niloticus), by tract-tracing methods. Following tracer injections into the lateral valvular nucleus, neurons were labeled in the ipsilateral dorsal part of dorsal telencephalic area, corpus glomerulosum pars anterior, dorsomedial thalamic nucleus, central nucleus of the inferior lobe, mammillary body, semicircular torus, valvular and cerebellar corpus, in the bilateral rostral regions of the central part of dorsal telencephalic area, dorsal region of the medial part of dorsal telencephalic area, habenula, anterior tuberal nucleus, posterior tuberal nucleus, and spinal cord, and in the contralateral lateral funicular nucleus. Labeled fibers and terminals were found in the ipsilateral cerebellar corpus and bilateral valvula of the cerebellum. Tracers were injected into portions of the telencephalon, pretectum, inferior lobe, and cerebellum to confirm reciprocally connections with the lateral valvular nucleus and to determine afferent terminal morphology in the lateral valvular nucleus. Telencephalic fibers terminated mainly in a dorsolateral portion of the lateral valvular nucleus. Terminals from the corpus glomerulosum pars anterior, central nucleus of the inferior lobe, and mammillary body showed more diffuse distributions and were not confined to particular portions of the lateral valvular nucleus. Labeled terminals in the lateral valvular nucleus were cup-shaped or of beaded morphology. These results indicate that the lateral valvular nucleus receives projections from various sources including the telencephalon, pretectum, and inferior lobe to relay information to the valvular and cerebellar corpus. In addition, the corpus glomerulosum pars anterior in tilapia is considered to be homologous to the magnocellular part of superficial pretectal nucleus in cyprinids.

Fiber connections of the torus longitudinalis and optic tectum in holocentrid teleosts.

Fiber connections of the torus longitudinalis (TL) and target(s) of toral recipient tectal neurons (pyramidal cells) in the optic tectum were examined by tract-tracing methods in holocentrids. Injections into the stratum marginale (SM) labeled neurons in the stratum opticum and stratum fibrosum et griseum superficiale (SFGS). They had superficial spiny dendrites, with a fan-shaped branching pattern in SM and a thick basal dendrite that gave rise to bushy horizontal branches at the boundary between the SFGS and the stratum griseum centrale (SGC), where an axon and a thin dendrite arose. The axon terminated in a middle cellular layer of the SGC, and the thin dendrite ramified slightly deeper to this cellular layer. The SM injections also labeled cells in the ipsilateral TL. Injections into either the lateral or the medial part of TL labeled terminals in the ipsilateral SM and neurons in the bilateral nucleus paracommissuralis (NPC) and nucleus subvalvularis and ipsilateral nucleus subeminentialis. Only medial TL injections labeled cells in the ipsilateral SGC. These neurons had a basal dendrite that branched in the middle cellular layer of SGC, suggesting that they receive inputs from the pyramidal cells and project back to the TL to form a closed circuit. Only lateral TL injections labeled terminals in the corpus cerebelli. A visual telencephalic portion projects to the NPC and sublayers of SGC, where dendrites of the pyramidal cells and SGC neurons ramify. The present results therefore suggest that the TL and SM are components of an intricate circuitry that exerts telencephalic descending visual influence on the optic tectum and corpus cerebelli.

Topographical organization of an indirect telencephalo-cerebellar pathway through the nucleus paracommissuralis in a teleost, Oreochromis niloticus.

The nucleus paracommissuralis (NPC) of teleosts is a relay nucleus of an indirect telencephalo-cerebellar pathway. However, cells of origin in telencephalic subdivisions and terminal patterns of the NPC fibers in the cerebellum remain unclear. We studied these issues by means of tract-tracing methods in a cichlid, tilapia (Oreochromis niloticus). After tracer injections into the NPC, retrogradely labeled cells were found bilaterally in dorsal and ventral regions of the area dorsalis telencephali pars centralis (dDc and vDc) and area dorsalis telencephali pars dorsalis (Dd). Anterogradely labeled terminals were found in a caudal part of the bilateral corpus cerebelli (CC). The labeled terminals were restricted in the granular layer, which can be divided into dorsal and ventral regions based on cytoarchitecture. We injected tracers separately into the three telencephalic portions (dDc, vDc, and Dd) and into the dorsal or ventral regions of granular layer in the caudal CC. The results revealed a topographical organization of the indirect telencephalo-cerebellar pathway. A medial portion of the NPC received fibers from the vDc and projected to the ventral region of the caudal CC. An intermediate portion of the NPC received fibers from the dDc and Dd, and in turn projected to the dorsal region of the caudal CC. A lateral portion of the NPC received fibers from the Dd and in turn projected to the dorsal region of the caudal CC. The Dc is known to receive visual input via the area dorsalis telencephali pars lateralis, and the Dd is presumably a multimodal telencephalic portion. The present study suggests that the indirect telencephalo-cerebellar pathway through the NPC might convey descending visual and multimodal information to the CC in a topographical manner. We also demonstrated other indirect telencephalo-cerebellar pathways through the nucleus lateralis valvulae and the area pretectalis.

Fiber connections of the torus longitudinalis in a teleost: Cyprinus carpio re-examined.

Fiber connections of the carp torus longitudinalis were re-examined by means of tract-tracing methods. The torus longitudinalis projected mainly to the stratum marginale of the optic tectum, area pretectalis, and corpus cerebelli. The stratum marginale was anterogradely labeled only by biocytin, but not by horseradish peroxidase. Because the stratum is composed of extremely fine axons of the small toral neurons, this may be ascribed to different molecular weights of the tracers. The main afferent sources to the torus longitudinalis were the nucleus subvalvularis, which was located beneath the nucleus lateralis valvulae, the nucleus subeminentialis pars magnocellularis, and neurons along the posterior mesencephalo-cerebellar tract. Some labeled cells also appeared in the area pretectalis, nucleus paracommissuralis, optic tectum, and torus semicircularis. In a previous paper, it was incorrectly reported that the valvula cerebelli was the main source of afferents to the torus longitudinalis. Here we report the reason for the previous mistake in relation to the techniques employed.