Dorsal Posterior Thalamic Nuclei Research Articles

Afferent and efferent connections of the nucleus posterior tuberis in the firemouth cichlid, Thorichthys meeki

The nucleus posterior tuberis (NPT) in teleost fishes, also called posterior tuberal nucleus, is situated in the posterior tuberculum of the diencephalon. It is fused across the midline and densely packed with small cells, but little is known about its connections. In this study, the afferent and efferent connections of the NPT were examined by means of tracer applications of the carbocyanine dye DiI in the firemouth cichlid, Thorichthys meeki. Retrogradely labeled cell bodies were found in the corpus mamillare and nucleus periventricularis of the inferior lobe; and anterogradely labeled terminal fibers were detected in the medial zone of the dorsal telencephalon, medial part of the nucleus lateralis tuberis, dorsal posterior thalamic nucleus, torus lateralis, medial part of the nucleus diffusus of the inferior lobe, and tectum opticum. All these connections show an ipsilateral tendency. The NPT is apparently a significant relay nucleus in the diencephalon of T. meeki, and possibly involved in a variety of feedback circuits. It seems also to be part of a tecto-hypothalamo-telencephalic pathway in cichlids.

The Mormyrid Optic Tectum Is a Topographic Interface for Active Electrolocation and Visual Sensing.

The African weakly electric fish Gnathonemus petersii is capable of cross-modal object recognition using its electric sense or vision. Thus, object features stored in the brain are accessible by multiple senses, either through connections between unisensory brain regions or because of multimodal representations in multisensory areas. Primary electrosensory information is processed in the medullary electrosensory lateral line lobe, which projects topographically to the lateral nucleus of the torus semicircularis (NL). Visual information reaches the optic tectum (TeO), which projects to various other brain regions. We investigated the neuroanatomical connections of these two major midbrain visual and electrosensory brain areas, focusing on the topographical relationship of interconnections between the two structures. Thus, the neural tracer DiI was injected systematically into different tectal quadrants, as well as into the NL. Tectal tracer injections revealed topographically organized retrograde and anterograde label in the NL. Rostral and caudal tectal regions were interconnected with rostral and caudal areas of the NL, respectively. However, dorsal and ventral tectal regions were represented in a roughly inverted fashion in NL, as dorsal tectal injections labeled ventral areas in NL and vice versa. In addition, tracer injections into TeO or NL revealed extensive inputs to both structures from ipsilateral (NL also contralateral) efferent basal cells in the valvula cerebelli; the NL furthermore projected back to the valvula. Additional tectal and NL connections were largely confirmatory to earlier studies. For example, the TeO received ipsilateral inputs from the central zone of the dorsal telencephalon, torus longitudinalis, nucleus isthmi, various tegmental, thalamic and pretectal nuclei, as well as other nuclei of the torus semicircularis. Also, the TeO projected to the dorsal preglomerular and dorsal posterior thalamic nuclei as well as to nuclei in the torus semicircularis and nucleus isthmi. Beyond the clear topographical relationship of NL and TeO interconnections established here, the known neurosensory upstream circuitry was used to suggest a model of how a defined spot in the peripheral sensory world comes to be represented in a common associated neural locus both in the NL and the TeO, thereby providing the neural substrate for cross-modal object recognition.

Distribution of endomorphin-like-immunoreactive neurones in the brain of the cichlid fish Oreochromis mossambicus.

Endomorphins (EMs) are tetrapeptides involved in pain and neuroendocrine responses with a high affinity for μ-opioid receptors in mammals. In the present study, we investigated the distribution of EM-like-immunoreactive (EM-L-IR) neurones in the brain of the cichlid fish Oreochromis mossambicus. Application of antisera against EM-1 and 2 (EM-1-2) revealed the presence of EM-L-IR somata and fibres throughout the different subdivisions of the olfactory bulb, such as the olfactory nerve layer and the granule cell layer. Although the extensions of EM-L-IR fibres were seen along the medial olfactory tract, intensely labelled EM-L-IR somata were found in different subdivisions of the telencephalon. In the diencephalon, intensely stained EM-L-IR neurones were noted in the preoptic area, the nucleus preopticus pars magnocellularis, the suprachiasmatic nucleus, the nucleus lateralis tuberis pars lateralis and the nucleus lateralis tuberis pars medialis regions, whereas projections of EM-L-IR fibres were also seen along the hypothalamic-hypophyseal tract, suggesting a possible hypophysiotrophic role for these neurones. Intense to moderately stained EM-L-IR neurones were noted in different subdivisions of thalamic nucleus, such as the dorsal posterior thalamic nucleus, commissura posterior, ventromedial thalamic nucleus, nucleus posterior tuberis, ventrolateral thalamic nucleus and medial preglomerular nucleus. Numerous intensely stained perikarya and axonal fibres were also noted throughout the inferior lobe, along the periventricular margin of the reccessus lateralis and in the nucleus recesus lateralis regions. In addition, numerous moderately labelled EM-like neuronal populations were found in the secondary gustatory nucleus and rostral spinal cord. The widespread distribution of EM-L-IR neurones throughout the brain and spinal cord indicates the diverse roles for these cells in neuroendocrine and neuromodulatory responses for the first time in fish. The present study provides further insights into the possible existence of EM-like peptides in early vertebrate lines and suggests that these peptides might have been well-conserved during the course of evolution.

Descending projections to the hindbrain and spinal cord in the paddlefish Polyodon spathula

In vertebrates, almost all motor neurons innervating skeletal muscles are located in the hindbrain and spinal cord, and all brain centers that control behavior have descending projections into these parts of the central nervous system. With tracer injections into the spinal cord and hindbrain, we have studied cell groups with descending projections in the paddlefish. Spinal cord injections reveal retrogradely labeled cells in all reticular and raphe nuclei, as well as the nucleus of the medial longitudinal fascicle. Additional cell groups with projections to the spinal cord are the nucleus of the fasciculus solitarius, descending trigeminal nucleus, several octavolateral nuclei, the dorsal hypothalamic nucleus, and the pretectum. The only primary sensory fibers with descending projections are trigeminal fibers. Hindbrain injections reveal a number of additional cell groups in di- and mesencephalon. The most prominent source is the mesencephalic tectum. Other descending cells were found in the dorsal posterior thalamic nucleus, ventral thalamus, torus semicircularis, lateral mesencephalic nucleus, and the central gray of the mesencephalon. Our data show that descending spinal projections are comparable to those of other vertebrates and that the tectum is the most important motor control center projecting to the hindbrain. A surprising result was that the dorsal posterior thalamic nucleus also projects to the hindbrain. This nucleus is thought to be a center that relays sensory information to the telencephalon. Further studies are needed to determine the complete set of projections of the dorsal thalamus in paddlefish and other fishes to gain insights into its functional role.

Efferent Connections of the Cerebellum of the Goldfish, Carassius auratus

Efferent fiber connections of the corpus and valvula cerebelli in the goldfish, Carassius auratus, were studied using an anterograde neural fiber tracing technique. Efferent targets of the corpus cerebelli are the posterior parvocellular preoptic nucleus, the ventromedial and ventrolateral thalamic nucleus, dorsal posterior thalamic nucleus, periventricular nucleus of posterior tuberculum, dorsal periventricular pretectal nucleus, inferior lobe, optic tectum, torus semicircularis, nucleus of the medial longitudinal fascicle, nucleus ruber, dorsal tegmental nucleus, nucleus lateralis valvulae, reticular formation, torus longitudinalis, and the medial and lateral lobe of the valvula cerebelli. Projections to the posterior parvocellular preoptic nucleus and the periventricular nucleus of posterior tuberculum are not reported in previous studies. Efferent targets of the medial lobe of the valvula cerebelli are similar to that of the corpus cerebelli except for lacking a projection to the inferior lobe and torus longitudinalis, but showing one to the corpus cerebelli. On the other hand, the lateral lobe of the valvula cerebelli projects only to the dorsal zone of the periventricular hypothalamus, the diffuse nucleus of the inferior lobe, corpus mamillare, vagal lobe and the corpus cerebelli. There are topographical projections from the lateral valvula to the inferior lobe. These results suggest that the function of the corpus and medial lobe of the valvula cerebelli include not only motor control but also functions similar to the mammalian higher cerebellum. This study also suggests that there are obvious functional divisions between the medial and lateral lobes of the valvula cerebelli.

Connections of the basal forebrain of the weakly electric fish, Eigenmannia virescens

The organization of the ventral nucleus of the ventral telencephalon (Vv) was examined in the weakly electric fish, Eigenmannia virescens. This nucleus, which is considered the teleost homologue to the basal forebrain nuclei of other vertebrates, was subdivided into dorsal and ventral subdivisions, based upon cytoarchitectonic, immunohistochemical, and connectional criteria. Afferent projections were observed from the medial olfactory bulb as well as the terminal nerve ganglion. Telencephalic afferents to the Vv were very restricted, consisting of the supracommissural and the dorsal intermediate nuclei of the ventral telencephalon, the nucleus taenia, and the medial region of the posterior nucleus of the dorsal telencephalon. However, the major afferents to the Vv were diencephalic, particularly those originating from the rostral preoptic area and other hypothalamic nuclei. Additional afferents included the posterior tubercular nucleus, the locus coeruleus, the medial perilemniscal nucleus, and the periventricular nucleus of the posterior tuberculum. Relatively weak projections were observed from the ventral thalamus and the dorsal posterior thalamic nucleus. As described previously, the diencephalic complex of the central posterior thalamic nucleus/prepacemaker nucleus (CP/PPn), which also has cells that innervate the pacemaker circuitry controlling the production of an electric organ discharge, projects to the Vv. Terminal fields of the Vv were observed to be coextensive with afferent cell groups in the preoptic area, lateral and caudal hypothalamic nuclei, and thalamus. An additional efferent target of the Vv was the pretectal nucleus electrosensorius. That many cell groups that are connected with the Vv are also connected with the CP/PPn, particularly the preoptic and hypothalamic nuclei, suggests that the electrocommunicatory system is intimately linked with basal forebrain limbic pathways. J. Comp. Neurol. 389:49–64, 1997. © 1997 Wiley-Liss, Inc.

Connections of the basal forebrain of the weakly electric fish,Eigenmannia virescens

The organization of the ventral nucleus of the ventral telencephalon (Vv) was examined in the weakly electric fish, Eigenmannia virescens. This nucleus, which is considered the teleost homologue to the basal forebrain nuclei of other vertebrates, was subdivided into dorsal and ventral subdivisions, based upon cytoarchitectonic, immunohistochemical, and connectional criteria. Afferent projections were observed from the medial olfactory bulb as well as the terminal nerve ganglion. Telencephalic afferents to the Vv were very restricted, consisting of the supracommissural and the dorsal intermediate nuclei of the ventral telencephalon, the nucleus taenia, and the medial region of the posterior nucleus of the dorsal telencephalon. However, the major afferents to the Vv were diencephalic, particularly those originating from the rostral preoptic area and other hypothalamic nuclei. Additional afferents included the posterior tubercular nucleus, the locus coeruleus, the medial perilemniscal nucleus, and the periventricular nucleus of the posterior tuberculum. Relatively weak projections were observed from the ventral thalamus and the dorsal posterior thalamic nucleus. As described previously, the diencephalic complex of the central posterior thalamic nucleus/prepacemaker nucleus (CP/PPn), which also has cells that innervate the pacemaker circuitry controlling the production of an electric organ discharge, projects to the Vv. Terminal fields of the Vv were observed to be coextensive with afferent cell groups in the preoptic area, lateral and caudal hypothalamic nuclei, and thalamus. An additional efferent target of the Vv was the pretectal nucleus electrosensorius. That many cell groups that are connected with the Vv are also connected with the CP/PPn, particularly the preoptic and hypothalamic nuclei, suggests that the electrocommunicatory system is intimately linked with basal forebrain limbic pathways.

Visual and electrosensory circuits of the diencephalon in mormyrids: An evolutionary perspective

Mormyrids are one of two groups of teleost fishes known to have evolved electroreception, and the concomitant neuroanatomical changes have confounded the interpretation of many of their brain areas in a comparative context, e.g., the diencephalon, where different sensory systems are processed and relayed. Recently, cerebellar and retinal connections of the diencephalon in mormyrids were reported. The present study reports on the telencephalic and tectal connections, specifically in Gnathonemus petersii, as these data are critical for an accurate interpretation of diencephalic nuclei in teleosts. Injections of horseradish peroxidase into the telencephalon retrogradely labeled neurons ipsilaterally in various thalamic, preglomerular, and tuberal nuclei, the nucleus of the locus coeruleus (also contralaterally), the superior raphe, and portions of the nucleus lateralis valvulae. Telencephalic injections anterogradely labeled the dorsal preglomerular and the dorsal tegmental nuclei bilaterally. Injections into the optic tectum retrogradely labeled neurons bilaterally in the central zone of area dorsalis telencephali and ipsilaterally in the torus longitudinalis, various thalamic, pretectal, and tegmental nuclei, some nuclei in the torus semicircularis, the nucleus of the locus coeruleus, the nucleus isthmi and the superior reticular formation, basal cells in the ipsilateral valvula cerebelli, and eurydendroid cells in the contralateral lobe C4 of the corpus cerebelli. Weaker contralateral projections were also observed to arise from the ventromedial thalamus and various pretectal and tegmental nuclei, and from the locus coeruleus and superior reticular formation. Tectal injections anterogradely labeled various pretectal nuclei bilaterally, as well as ipsilaterally the dorsal preglomerular and dorsal posterior thalamic nuclei, some nuclei in the torus semicircularis, the dorsal tegmental nucleus, nucleus isthmi, and, again bilaterally, the superior reticular formation. A comparison of retinal, cerebellar, tectal, and telencephalic connections in Gnathonemus with those in nonelectrosensory teleosts reveals several points: (1) the visual area of the diencephalon is highly reduced in Gnathonemus, (2) the interconnections between the preglomerular area and telencephalon in Gnathonemus are unusually well developed compared to those in other teleosts, and (3) two of the three corpopetal diencephalic nuclei are homologues of the central and dorsal periventricular pretectum in other teleosts. The third is a subdivision of the preglomerular area, rather than an accessory optic or pretectal nucleus, and is related to electroreception. The preglomerulo-cerebellar connections in Gnathonemus are therefore interpreted as uniquely derived characters for mormyrids.

Visual pathways in elasmobranchs: Organization and phylogenetic implications

Although earlier experimental studies of the visual system in elasmobranch fishes suggested that these fishes possess fewer primary retino-recipient nuclei than other gnathostome vertebrates, recent studies utilizing more sensitive tracing methods indicate that most elasmobranch species possess ten primary retinofugal targets in addition to the optic tectum. Furthermore, many species appear to exhibit bilateral retinal projections to these nuclei. Similarly, initial claims that the organization of the visual thalamus of elasmobranchs is more primitive than that of most other gnathostomes--in that elasmobranchs possess only a single thalamic nucleus that receives both retinal and tectal inputs and that only a single thalamo-telencephalic projection exists to the telencephalon--have been refuted. Many, if not all, elasmobranchs possess a rostrally located dorsal thalamic nucleus (anterior thalamic nucleus), that receives retinal and tectal inputs and projects bilaterally to the dorsal and medial pallium, and a more caudally and dorsally located thalamic nucleus, the dorsal posterior thalamic nucleus, that receives bilateral tectal input and projects to the ventrolateral periventricular area and/or dorsal pallium of the telencephalon. Thus the thalamic organization of elasmobranch fishes is similar to that of other gnathostomes.