Fiber connections of the corpus mamillare in a percomorph teleost, tilapia Oreochromis niloticus

Brain areas activated during visual learning in the cichlid fish Pseudotropheus zebra

The neural correlates of most cognitive functions in fish are unknown. This project aimed to identify brain regions involved in visual learning in the cichlid fish Pseudotropheus zebra. The expression of the protein pS6 was measured in 19 brain areas and compared between groups of individuals subjected to four different behavioral contexts (control, avoidance, trained, and novelty groups). Control group individuals were sacrificed with minimal interactions. Fish in the avoidance group were chased with a net for an hour, after which they were sacrificed. Individuals in the trained group received daily training sessions to associate a visual object with a food reward. They were sacrificed the day they reached learning criterion. Fish in the novelty group were habituated to one set of visual stimuli, then faced a change in stimulus type (novelty stimulus) before they were sacrificed. Fish in the three treatment groups showed the largest activation of pS6 in the inferior lobes and the tectum opticum compared to the control group. The avoidance group showed additional activation in the preoptic area, several telencephalic regions, the torus semicircularis, and the reticular formation. The trained group that received a food reward, showed additional activation of the torus lateralis, a tertiary gustatory center. The only area that showed strong activation in all three treatment groups was the nucleus diffusus situated within the inferior lobe. The inferior lobe receives prominent visual input from the tectum via the nucleus glomerulosus but so far, nothing is known about the functional details of this pathway. Our study showed for the first time that the inferior lobes play an important role in visual learning and object recognition.

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.

Calretinin immunoreactivity in the inferior lobe of the hypothalamus and associated nuclei of the firemouth cichlid, Thorichthys meeki

The distribution of the calcium-binding protein calretinin (CR) was examined by an immunohistochemical method using specific antibodies. CR is involved in the visual system, and the inferior lobe of the hypothalamus represents a multisensory integration center in cichlids. The focus of the present study was to analyze the distribution of CR immunoreactivity in a cichlid fish, the firemouth cichlid, Thorichthys meeki, for the hypothalamic inferior lobe and for the torus lateralis, nucleus glomerulosus, nucleus posterior tuberis, and corpus mamillare as associated nuclei of the hypothalamus. CR-immunoreactive (CR-ir) cell bodies were visualized in the lateral and medial part of the diffuse nucleus of the inferior lobe, ventral portion of the central nucleus of the inferior lobe, torus lateralis, nucleus glomerulosus, and nucleus posterior tuberis. CR-ir fibers could be detected in the dorsal portion of the central nucleus of the inferior lobe and corpus mamillare. The strongest labeling of CR-ir neuropil was observed in the lateral part of the diffuse nucleus of the inferior lobe, outer zone of the periventricular nucleus of the inferior lobe, torus lateralis, nucleus glomerulosus, and nucleus posterior tuberis. CR is abundantly present in the inferior lobe of the hypothalamus and associated nuclei. The role of CR in highly active processes in the inferior lobe of cichlids will be discussed.

Brain histopathology in red tilapia Oreochromis sp. experimentally infected with Streptococcus agalactiae serotype III

One of the clinical manifestations of streptococcosis is swimming errors of the infected fish, which is likely caused by lesions in the brain. As most studies described brain histopathology in streptococcosis as meningitis, with a limited description of lesions in the whole brain, the aim of this study was therefore to explore histopathology of the whole brain of red tilapia experimentally infected with Streptococcus agalactiae serotype III. Transcripts relating to motoneuron functions and inflammatory responses were also investigated. In the S. agalactiae-infected fish, the parenchyma of the whole brain and its associated meninx primitiva were found to be markedly infiltrated by mononuclear cells and Gram-positive cocci. Hemorrhage, neuronal necrosis, and localized spongiform histopathology were observed, especially within the midbrain and the cerebellum. The lesion was observed in the medial longitudinal fasciculus and its nucleus. Expressions of the transcripts CD166, GAP43, SMN, and SV2B of the infected fish did not change, while those of IL-1β and TNF-α were significantly upregulated. It is likely that S. agalactiae cause extensive damage to the fish brain, especially in areas that control swimming activities, through both direct invasion of the bacteria and acute inflammatory responses of the brain resident macrophages, or microglia.

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.

An ascending visual pathway to the dorsal telencephalon through the optic tectum and nucleus prethalamicus in the yellowfin goby Acanthogobius flavimanus (Temminck & Schlegel, 1845)

Dual visual pathways reaching the telencephalon appear to be an ancient vertebrate trait, but some teleost fish seem to possess only one pathway via the optic tectum. We undertook the present study to determine if and when this loss occurred during evolution. Tracer injection experiments to the optic nerve, the optic tectum, and the dorsal telencephalon were performed in the present study, to investigate ascending visual pathways to the dorsal telencephalon in an acanthopterygian teleost, the yellowfin goby Acanthogobius flavimanus (Temminck & Schlegel, 1845). We confirmed the presence of a nucleus prethalamicus (PTh) in the goby, which has been convincingly identified only in holocentrids, suggesting that this nucleus is present in other acanthopterygians. We found that the optic tectum projects to the PTh bilaterally. The PTh projects in turn to the dorsal telencephalon, ipsilaterally. These results suggest that the yellowfin goby possesses only an extrageniculate-like pathway, while a geniculate-like pathway could not be identified. This situation is common with that of holocentrids and may be a character common in acanthopterygians. It is possible that a geniculate-like system was lost in the common ancestor of acanthopterygians, although the scenario for the evolution of ascending visual systems in actinopterygians remains uncertain due to the lack of precise knowledge in a number of actinopterygian taxons.

Neural connections of the pretectum in zebrafish (Danio rerio)

The pretectum is a complex region of the caudal diencephalon which in adult zebrafish comprises both retinorecipient (parvocellular superficial, central, intercalated, paracommissural, and periventricular) and non-retinorecipient (magnocellular superficial, posterior, and accessory) pretectal nuclei distributed from periventricular to superficial regions. We conducted a comprehensive study of the connections of pretectal nuclei by using neuronal tracing with fluorescent carbocyanine dyes. This study reveals specialization of efferent connections of the various pretectal nuclei, with nuclei projecting to the optic tectum (paracommissural, central, and periventricular pretectal nuclei), the torus longitudinalis and the cerebellar corpus (paracommissural, central, and intercalated pretectal nuclei), the lateral hypothalamus (magnocellular superficial, posterior, and central pretectal nuclei), and the tegmental regions (accessory and superficial pretectal nuclei). With regard to major central afferents to the pretectum, we observed projections from the telencephalon to the paracommissural and central pretectal nuclei, from the optic tectum to the paracommissural, central, accessory and parvocellular superficial pretectal nuclei, from the cerebellum to the paracommissural and periventricular pretectal nuclei and from the nucleus isthmi to the parvocellular superficial and accessory pretectal nuclei. The parvocellular superficial pretectal nucleus sends conspicuous projections to the contralateral magnocellular superficial pretectal nucleus. The composite figure of results reveals large differences in connections of neighbor pretectal nuclei, indicating high degree of nuclear specialization. Our results will have important bearings in functional studies that analyze the relationship between specific circuits and behaviors in zebrafish. Comparison with results available in other species also reveals differences in the organization and connections of the pretectum in vertebrates.

Nucleus Ruber of Actinopterygians

Nucleus ruber is known as an important supraspinal center that controls forelimb movements in tetrapods, and the rubral homologue may serve similar functions in fishes (motor control of pectoral fin). However, two apparently different structures have been identified as 'nucleus ruber' in actinopterygians. One is nucleus ruber of Goldstein (1905) (NRg), and the other nucleus ruber of Nieuwenhuys and Pouwels (1983) (NRnp). It remains unclear whether one of these nuclei (or perhaps both) is homologous to tetrapod nucleus ruber. To resolve this issue from a phylogenetic point of view, we have investigated the distribution of tegmental neurons retrogradely labeled from the spinal cord in eight actinopterygian species. We also investigated the presence/absence of the two nuclei with Nissl- or Bodian-stained brain section series of an additional 28 actinopterygian species by comparing the morphological features of candidate rubral neurons with those of neurons revealed by the tracer studies. Based on these analyses, the NRg was identified in all actinopterygians investigated in the present study, while the NRnp appears to be absent in basal actinopterygians. The phylogenetic distribution pattern indicates that the NRg is the more likely homologue of nucleus ruber, and the NRnp may be a derived nucleus that emerged during the course of actinopterygian evolution.

Characterization of the hypothalamus of Xenopus laevis during development. II. The basal regions

The expression patterns of conserved developmental regulatory transcription factors and neuronal markers were analyzed in the basal hypothalamus of Xenopus laevis throughout development by means of combined immunohistochemical and in situ hybridization techniques. The connectivity of the main subdivisions was investigated by in vitro tracing techniques with dextran amines. The basal hypothalamic region is topologically rostral to the basal diencephalon and is composed of the tuberal (rostral) and mammillary (caudal) subdivisions, according to the prosomeric model. It is dorsally bounded by the optic chiasm and the alar hypothalamus, and caudally by the diencephalic prosomere p3. The tuberal hypothalamus is defined by the expression of Nkx2.1, xShh, and Isl1, and rostral and caudal portions can be distinguished by the distinct expression of Otp rostrally and Nkx2.2 caudally. In the mammillary region the xShh/Nkx2.1 combination defined the rostral mammillary area, expressing Nkx2.1, and the caudal retromammillary area, expressing xShh. The expression of xLhx1, xDll4, and Otp in the mammillary area and Isl1 in the tuberal region highlights the boundary between the two basal hypothalamic territories. Both regions are strongly connected with subpallial regions, especially those conveying olfactory/vomeronasal information, and also possess abundant intrahypothalamic connections. They show reciprocal connections with the diencephalon (mainly the thalamus), project to the midbrain tectum, and are bidirectionally related to the rhombencephalon. These results illustrate that the basal hypothalamus of anurans shares many features of specification, regionalization, and hodology with amniotes, reinforcing the idea of a basic bauplan in the organization of this prosencephalic region in all tetrapods.

The distribution of an AVT V1a receptor in the brain of a sex changing fish, Epinephelus adscensionis

The present study describes the distribution of an arginine vasotocin (AVT) V1a receptor (AVTr) throughout the brain of a sex-changing grouper, rock hind Epinephelus adscensionis. The objectives of this study were to describe the AVTr distribution in the brain of rock hind for potential linkages of the AVT hormone system with sex-specific behaviors observed in this species and to examine sex-specific differences that might exist. An antibody was designed for rock hind AVTr against the deduced amino acid sequence for the third intracellular loop. Protein expression, identified with immunohistochemistry showed high concordance with mRNA expression, identified with in situ hybridization. AVTr protein and mRNA expression was widely distributed throughout the brain, indicating that AVT may act as a neuromodulator via this V1a receptor subtype. AVTr protein and mRNA were present in regions associated with behavior, reproduction and spatial learning, as well as sensory functions such as vision, olfaction and lateral line sensory processing. We observed high AVTr expression in granular cell formations in the internal cellular layer of olfactory bulbs, torus longitudinalis, granular layer of the corpus cerebellum, valvula of the cerebellum, nuclei of the lateral and posterior recesses, and granular eminence. High protein and mRNA expression was also observed in the preoptic area, anterior hypothalamus, and habenular nucleus. No obvious sex differences were noted in any region of the rock hind brain.

Fiber connections of the corpus glomerulosum pars rotunda, with special reference to efferent projection pattern to the inferior lobe in a percomorph teleost, tilapia (Oreochromis niloticus)

Fiber connections of the corpus glomerulosum pars rotunda (GR) in a teleost, tilapia Oreochromis niloticus, were studied by biotinylated dextran amine injections into the GR and inferior lobe. After tracer injections into the GR, major groups of labeled somata were found bilaterally in the cortical nucleus and ipsilaterally in the nucleus intermedius. Numerous labeled terminals were found ipsilaterally in the central nucleus, nucleus of lateral recess, and diffuse nucleus (NDLI) of the inferior lobe. Some other connections were also elucidated in the present study, although these were less abundant. Notably, efferent projections to the inferior lobe were not evenly distributed within each lobar nucleus. Labeled terminals were confined to the cell body zone of central nucleus and the outer cell-sparse layer of the nucleus of lateral recess. The rostrolateral portion of NDLI and ventrolateral portion of middle to caudal NDLI received few GR fibers, the rostromedial portion of NDLI a moderate density of fibers, and the rest of the nucleus numerous fibers. These different portions of the NDLI, to some extent, also differed in other afferent and efferent connections, suggesting regional specialization of the nucleus. Furthermore, restricted injections to the lobar nuclei suggest different efferent projections of the component cells of the GR: large and small cells. The large cells project only to the central nucleus, whereas the small cells project to the NDLI and nucleus of lateral recess. Therefore, the two types of GR cells appear to constitute parallel pathways from the pretectum to the inferior lobe.

Expression of pcp4a in subpopulations of CNS neurons in zebrafish

The molecular organization of the zebrafish brain and its relation to neuroanatomical divisions are still largely unknown. In this study we have analyzed the expression of a small transcript encoding for the IQ containing polypeptide Pcp4a in developing and juvenile zebrafish. The transcript is exclusively expressed in neural structures with a pattern that is highly specific for restricted domains and cell populations throughout development, and it allows us to follow the development of these structures at different times. The expression of pcp4a characterizes the dorsocaudal telencephalon, dorsal habenula, pretectal nuclei, preglomerular complex, mammillary bodies, and deep layers of the optic tectum and is a hallmark of a subpopulation of reticulospinal neurons. In the telencephalon, comparison of the expression of pcp4a with other pallial markers showed a rostrocaudal gradient in the expression of these genes, which suggests that the dorsal telencephalon of zebrafish may be organized in distinct areas with different molecular natures. Pcp4 has been involved in modulating calcium signals and in binding to calmodulin, but its precise role in neuronal functions is not known. The analysis of pcp4a expression and localization in the zebrafish brain suggests that pcp4a may be a useful marker for sensory and some motor neuronal circuitries and for telencephalic areas processing sensory inputs.

Calretinin immunoreactivity in the brain of the zebrafish, Danio rerio: distribution and comparison with some neuropeptides and neurotransmitter-synthesizing enzymes. I. Olfactory organ and forebrain

The distribution of calretinin (CR) in the forebrain and the olfactory system of the adult zebrafish was studied by using immunocytochemical techniques. Previous studies in trout forebrain have indicated that CR-immunoreactive neurons acquire this phenotype rather early in development (Castro et al., J. Comp. Neurol. 467:254-269, 2003). Thus, precise knowledge of CR-expressing neuronal populations in adult zebrafish may help to decipher late stages of forebrain morphogenesis. For analysis of some forebrain nuclei and regions, CR distribution was compared with that of various ancillary markers: choline acetyltransferase, glutamic acid decarboxylase, tyrosine hydroxylase, neuropeptide Y, thyrotropin-releasing hormone, and galanin. The results reveal that calretinin is a specific marker of olfactory receptor neurons and of various neuronal populations distributed throughout the telencephalon and diencephalon. In addition, CR immunocytochemistry revealed characteristic patterns of fibers and neuropil in several telencephalic and diencephalic regions, indicating that it is a useful marker for characterizing a number of neural centers, pathways, and neuronal subpopulations in the zebrafish forebrain. Some ancillary markers also showed a distinctive distribution in pallial and subpallial regions, revealing additional aspects of forebrain organization. Comparison of the distribution of CR observed in the forebrain of zebrafish with that reported in other teleosts revealed a number of similarities and also some interesting differences. This indicates that various neuronal populations have maintained the CR phenotype in widely divergent teleost lines and suggests that CR studies may prove very useful for comparative analysis.

Projections of the sensory trigeminal nucleus in a percomorph teleost, tilapia (Oreochromis niloticus)

The sensory trigeminal nucleus of teleosts is the rostralmost nucleus among the trigeminal sensory nuclear group in the rhombencephalon. The sensory trigeminal nucleus is known to receive the somatosensory afferents of the ophthalmic, maxillar, and mandibular nerves. However, the central connections of the sensory trigeminal nucleus remain unclear. Efferents of the sensory trigeminal nucleus were examined by means of tract-tracing methods, in a percomorph teleost, tilapia. After tracer injections to the sensory trigeminal nucleus, labeled terminals were seen bilaterally in the ventromedial thalamic nucleus, periventricular pretectal nucleus, medial part of preglomerular nucleus, stratum album centrale of the optic tectum, ventrolateral nucleus of the semicircular torus, lateral valvular nucleus, prethalamic nucleus, tegmentoterminal nucleus, and superior and inferior reticular formation, with preference for the contralateral side. Labeled terminals were also found bilaterally in the oculomotor nucleus, trochlear nucleus, trigeminal motor nucleus, facial motor nucleus, facial lobe, descending trigeminal nucleus, medial funicular nucleus, and contralateral sensory trigeminal nucleus and inferior olive. Labeled terminals in the oculomotor nucleus and trochlear nucleus showed similar densities on both sides of the brain. However, labelings in the trigeminal motor nucleus, facial motor nucleus, facial lobe, descending trigeminal nucleus, and medial funicular nucleus showed a clear ipsilateral dominance. Reciprocal tracer injection experiments to the ventromedial thalamic nucleus, optic tectum, and semicircular torus resulted in labeled cell bodies in the sensory trigeminal nucleus, with a few also in the descending trigeminal nucleus.

Topography and connections of the telencephalon in a chondrostean,Acipenser baeri: An experimental study

Sturgeons belong to an ancient group of the extant actinopterygian fishes. Accordingly, the study of their brain connections is important to understand brain evolution in the line leading to teleosts. We examined the topography and connections of the various telencephalic regions of the Siberian sturgeon (Acipenser baeri). The telencephalic regions were characterized on the basis of acetylcholinesterase histochemistry and calbindin-D28k and calretinin immunohistochemistry. The telencephalic connections were investigated by using the fluorescent dye DiI (1,1'-dioctadecyl 3,3,3',3'-tetramethylindocarbocyanine perchlorate) in fixed brains. Application of DiI to different areas of the pallial (dorsal) regions of the telencephalic lobes showed that they have mostly intratelencephalic connections. A posterior pallial region is characterized by its similar hodology to that of the posterior zone of the teleosts dorsal telencephalon and those described in other ancient groups. Extratelencephalic connections of the pallium are scarce, although a few afferent and efferent connections with the diencephalon, mesencephalon, and rostral rhombencephalon were observed. DiI application to subpallial regions showed both intratelencephalic connections and connections with different brain regions. Afferents to the subpallium originate from the olfactory bulbs, preoptic area, thalamus, posterior tuberculum, hypothalamus, secondary gustatory nucleus, and raphe nuclei. Some of these connections are quite similar to those described for other vertebrates.

Improving seizure control in dogs with refractory epilepsy using gabapentin as an adjunctive agent

OBJECTIVE

To assess whether there is a change in seizure activity in dogs with refractory epilepsy that are receiving appropriate doses of phenobarbitone and/or potassium bromide, when gabapentin is added to the therapeutic regimen.

DESIGN

A prospective study of 17 dogs with a refractory seizure disorder, 16 of which have idiopathic epilepsy.

PROCEDURE

Patients were stabilised using phenobarbitone and/or potassium bromide to produce tolerable therapeutic serum concentrations and dosed additionally with gabapentin at 35 to 50 mg/kg/d (divided twice or three times daily) for 4 months. Owners recorded seizure activity and side effects during this period in a standardised diary. Patients underwent monthly physical examinations and venepuncture to assess selected serum biochemical analytes, as well as phenobarbitone and bromide concentrations. Patients were further monitored for long-term response to adjunctive gabapentin therapy.

RESULTS

There was no significant decrease in the number of seizures over the study period for the entire cohort, however three dogs stopped seizuring completely. There was a significant increase in the number of patients who showed an increase in the interictal period (P > 0.001). Serum alkaline phosphatase activity and triglyceride concentrations were elevated at baseline. There were no significant changes in biochemical analytes during the course of the study period. Side effects observed initially on addition of gabapentin included sedation and hind limb ataxia. The former resolved spontaneously after a few days; the latter after a slight reduction in bromide dose. Long-term, a further two patients became seizure free and ten patients remained on gabapentin indefinitely. No long-term side effects have become apparent.

CONCLUSION

Addition of gabapentin to phenobarbitone and/or potassium bromide increased the interictal period and shortened the post-seizure recovery in some canine epileptics. In some dogs, seizures were prevented completely, while in others there was an increase in interictal period. The short-half life of gabapentin has advantages for seizure control, however its present high cost may prohibit therapy in large dogs.

Experimental study of the connections of the preglomerular nuclei and corpus mamillare in the rainbow trout, Oncorhynchus mykiss

The preglomerular complex of trout consists of the anterior (aPGN) and medial (mPGN) preglomerular nuclei and the corpus mamillare (CM). In order to improve knowledge on this complex, we applied a lipophilic neuronal tracer (DiI) to the three nuclei. These nuclei received afferents from the medial part of the dorsal telencephalic area (Dm), the ventral part of the ventral telencephalic area (Vv), the preoptic nucleus, the periventricular layer of the rostral optic tectum and the central posterior thalamic nucleus. The aPGN also received numerous toral projections and, sent efferents to the anterior tuberal nucleus. In addition, both the aPGN and the mPGN nuclei gave rise to efferents to the dorsal region of the dorsal telencephalic area (Dd), whereas the medial preglomerular nucleus and the CM sent fibers to the torus lateralis and the diffuse nucleus, as confirmed by reciprocal labeling. A small mPGN/CM subgroup projected to the optic tectum. These results suggest close functional inter-relationship between the trout preglomerular complex and two telencephalic regions (Dm and Vv). In addition, all nuclei of the complex receive preoptic, tectal and dorsal thalamic afferents, whereas the aPGN and mPGN are related with acoustic-lateral ascending pathways, and the mPGN and CM with the central region of the dorsal telencephalic area and visceral/gustatory pathways.

Fiber connections of the central nucleus of semicircular torus in cyprinids

Fiber connections of the presumed auditory portion of the semicircular torus or the central nucleus (TSc) as well as other central and peripheral auditory structures were studied by tract-tracing methods in carp and goldfish. Major ascending projections to the TSc originated from the descending octaval nucleus (DO) and medullary secondary octaval population (SO). Toropetal neurons of the DO were within the saccular terminal zone. A small number of toropetal DO neurons might receive inputs from other inner ear and lateral line endorgans as well. Fibers from the DO terminated in a deep zone of the TSc, while those from the SO in both deep and superficial zones. Afferents to the TSc also arose from the rhombencephalic reticular formation, anterior octaval nucleus, isthmic reticular nucleus, perilemniscular nucleus, medial pretoral nucleus, anterior tuberal nucleus, and central posterior thalamic nucleus. The TSc projected ascending fibers to the medial pretoral nucleus, anterior tuberal nucleus, central posterior thalamic nucleus, and the preglomerular complex (anterior preglomerular nucleus, the caudomedial region of lateral preglomerular nucleus, and a medial zone of medial preglomerular nucleus). These parts of preglomerular complex appear structurally continuous sharing common hodological and cytoarchitectonic features, and thus might be regarded as a single neuronal population. Abundant descending pathways were also noted in the present study. Of particular note is the medial pretoral nucleus, which received fibers from diencephalic auditory nuclei. The nucleus gave rise to indirect descending pathways to a medial zone of the cerebellar crest where dendrites of crest cells in the SO ramify.

Fiber connections of the anterior preglomerular nucleus in cyprinids with notes on telencephalic connections of the preglomerular complex

Fiber connections of the anterior preglomerular nucleus (PGa) were studied in carp and goldfish by tracer injection experiments to the nucleus and telencephalon. The PGa received fibers from the central nucleus of semicircular torus, perilemniscular nucleus, anterior tuberal nucleus, and medial pretoral nucleus, all of which are presumed auditory structures. The PGa projected to the dorsal (dDm) and ventral (vDm) regions of medial part of dorsal telencephalic area. The caudomedial region of lateral preglomerular nucleus (PGl) and medial zone of medial preglomerular nucleus (PGm), which also receive auditory toral fibers, projected to the same telencephalic regions as did PGa. These preglomerular structures and the PGa also received in common descending fibers from a rostromedial portion of dDm. The PGa also received fibers from the parvocellular and magnocellular preoptic nuclei, and suprachiasmatic nucleus and projected to the anterior tuberal nucleus and medial inferior lobe, suggesting neurohormonal and circadian control on the PGa and auditory influences on hypothalamic functions. Of other diencephalic nuclei that receive auditory toral fibers, only small numbers of neurons were labeled in the central posterior thalamic nucleus and anterior tuberal nucleus even after large injections to the dorsal telencephalic area. Thus, the PGa and closely related preglomerular regions, not the dorsal thalamus, appear to constitute the major auditory relay station to the dorsal telencephalic area. The rostrolateral region of PGl, rostral and lateral zones of PGm, commissural preglomerular nucleus, and preglomerular tertiary gustatory nucleus, which do not receive auditory toral fibers, also projected to the dorsal telencephalic area.

Connections of the lateral and medial divisions of the goldfish telencephalic pallium

Biotinylated dextran amine and fluorescent carbocyanine dye (DiI) were used to examine connections of the lateral (Dl) and medial (Dm) divisions of the goldfish pallium. Besides numerous intrinsic telencephalic connections to Dl and Dm, major ascending projections to these pallial divisions arise in the preglomerular complex of the posterior tuberculum, rather than in the dorsal thalamus. The rostral subnucleus of the lateral preglomerular nucleus receives auditory input via the medial pretoral nucleus, lateral line input via the ventrolateral toral nucleus, and visual input via the optic tectum, and it projects to both Dl and Dm. The anterior preglomerular nucleus and caudal subnucleus of the lateral preglomerular nucleus receive auditory input via the central toral nucleus and project to Dm. This pallial division also receives chemosensory information via the medial preglomerular nucleus. The central posterior (CP) nucleus, which receives both auditory and visual inputs, also projects to Dm and is the only dorsal thalamic nucleus projecting to the pallium. Thus, both Dl and Dm clearly receive multisensory inputs. Major projections of CP and projections of all other dorsal thalamic nuclei are to the subpallium, however. Descending projections of Dl are primarily to the preoptic area and the caudal hypothalamus, whereas descending projections of Dm are more extensive and particularly heavy to the anterior tuber and nucleus diffusus of the hypothalamus. The topography and connections of Dl are remarkably similar to those of the hippocampus of tetrapods, whereas the topography and connections of Dm are similar to those of the amygdala.

Experimental study of the connections of the telencephalon in the rainbow trout (Oncorhynchus mykiss). II: Dorsal area and preoptic region

In this study and the accompanying article (Folgueira et al., 2004a), the fluorescent carbocyanine dye 1,1'-dioctadecyl 3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) was used in fixed tissue to comprehensively analyze the connections of the different regions of the telencephalic lobes and the preoptic region of the rainbow trout. Here, we analyze the connections of the dorsal area (D; pallium) of the telencephalon, and the preoptic region, as well as the telencephalic connections of several structures in the diencephalon and brainstem of juvenile trout. The dorsal plus dorsolateral pallial zone of D (Dd+Dl-d) receives afferents from contralateral Dd+Dl-d, the ventral area of the telencephalon, preoptic nucleus, suprachiasmatic nucleus, medial thalamus, preglomerular complex, anterior and lateral tuberal nuclei, posterior tuberal nucleus, posterior hypothalamic lobe, superior raphe nucleus, and the rhombencephalic central gray and reticular formation, and projects to the central zone of D (Dc), medial thalamus, and some caudomedial hypothalamic regions. The medial zone of D (Dm) maintains reciprocal connections with the preglomerular complex and also receives afferents from the preoptic nucleus, suprachiasmatic nucleus, anterior tuberal nucleus, preglomerular tertiary gustatory nucleus, posterior tubercle, superior raphe nucleus, locus coeruleus, and the rhombencephalic central gray, and reticular formation. Dc receives fibers mainly from Dd+Dl-d, preoptic nucleus, preglomerular complex, and torus semicircularis and projects to several extratelencephalic centers, including the paracommissural nucleus, optic tectum, torus semicircularis, thalamus, preglomerular complex, posterior tubercle nuclei, and inferior hypothalamic lobes. The posterior zone of D (Dp) is mainly connected with the olfactory bulbs, the ventral and supracommissural nuclei of the ventral area (subpallium), the preoptic nucleus, and the preglomerular complex and projects to wide hypothalamic and posterior tubercular regions. The preoptic nucleus projects to the olfactory bulb, to most regions of the telencephalic lobes, and to several diencephalic and brainstem structures. These results reveal complex and specialized connectional patterns in the rainbow trout dorsal telencephalon and preoptic region. Most of these connections have not been described previously in salmonids. These connections indicate that the salmonid telencephalon is involved in multisensorial processing and modulation of brain activity.

An experimental study of the connections of the telencephalon in the rainbow trout (Oncorhynchus mykiss). I: Olfactory bulb and ventral area

The fluorescent carbocyanine dye 1,1'-dioctadecyl 3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) was used in fixed tissue to comprehensively analyze the connections of the olfactory bulbs and the different regions of the ventral (V) area of the telencephalic lobes (subpallium) of the rainbow trout. With this goal, DiI was applied to the different telencephalic nuclei and zones, as well as to the olfactory nerve, the olfactory bulb, the retina, and to several structures in the diencephalon and brainstem of juvenile trout. The olfactory bulbs maintain reciprocal connections with several regions of the telencephalon [ventral nucleus of V (Vv), supracommissural nucleus (Vs), posterior zone of D (Dp), preoptic nucleus], and also project to the diencephalon (posterior tuberal nucleus, posterior hypothalamic lobe). Vv receives afferents from Vs, the dorsal nucleus of V (Vd), the preoptic nucleus, and from several nuclei in the diencephalon and brainstem (suprachiasmatic nucleus, anterior and lateral tuberal nuclei, preglomerular complex, tertiary gustatory nucleus, posterior tubercle, inferior hypothalamic lobes, thalamus, torus semicircularis, secondary gustatory nucleus, locus coeruleus, superior raphe nucleus, central gray, and reticular formation), and projects to dorsal (pallial) regions and most of the nuclei afferent to Vv. The dorsal nucleus of V (Vd) and Vs mainly project to the dorsal area. In an accompanying article (Folgueira et al., 2004), we present the results of application of DiI to dorsal (pallial) telencephalic regions, as well as of several experiments of tracer application to extratelencephalic regions. The results presented here, together with those of the accompanying article, reveal a complex connectional pattern of the rainbow trout ventral telencephalon, most of these connections having not been described previously in salmonids.

The anterograde and retrograde axonal transport of biotinylated dextran amine and biocytin in the nervous system of teleosts

Biotinylated dextran amine (BDA) and biocytin are well transported both retrogradely and anterogradely. Both tracers have stable molecular structure for long-term storage and examination, and their visualizations can be realized by simple histochemical reactions. Therefore, the BDA and biocytin are widely used in neuroanatomical studies as the tract-tracing markers. The results obtained by BDA and biocytin applications to various areas of the nervous system in teleosts were qualitatively identical, and the retrogradely and anterogradely labeled structures could be clearly identified with reference to the counter-staining. Iontophoretic injections or crystal insertions resulted in filling of cell bodies, dendrites and terminals in the core of injection side, revealing morphological details of the local and distant somata, dendritic arborizations and axonal terminals. However, biocytin exhibited superior to BDA in anterograde transport, and could label very thin axons, axonal collaterals and terminal ramifications. In contrast, retrograde transport of BDA was superior to that of biocytin, and resulted in more complete dendritic filling of retrograde labeled neurons including dendritic arborizations and spines.

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.

Have brain dynamics evolved? Should we look for unique dynamics in the sapient species?

Ongoing "spontaneous" electrical field potentials of assemblies of neurons in the brains of diverse animal groups differ widely in character and amplitude without obvious explanation. There may be correlates with other measures of brain complexity, such as histological differentiation, but so far there are no known differences between the EEGs of humans and other mammals or between mammals and reptiles, amphibians or fish, apart from amplitude. The proposition is defended that further search for descriptors or statistical, probably nonlinear features of the time series will reveal consistent differences, meaning that we have so far missed major features of the natural history of EEGs, just as we have thus far relatively neglected the identification of features of the physiology of the brain relevant to its evolution of complexity through major grades of phyla, classes, and orders.

Hypothalamic inferior lobe and lateral torus connections in a percomorph teleost, the red cichlid (Hemichromis lifalili)

The neuroanatomic connections of the inferior lobe and the lateral torus of the percomorph Hemichromis lifalili were investigated by 1,1', dioctadecyl-3,3,3',3'-tetramethylindo-carbocyanine perchlorate (DiI) tracing. The inferior lobe and the lateral torus both receive afferents from the secondary gustatory nucleus. Additional afferents reach the inferior lobe from the nucleus glomerulosus, nucleus suprachiasmaticus, dorsal and central posterior thalamic nucleus, nucleus lateralis valvulae, magnocellular part of the magnocellular nucleus of the preoptic region, caudal nucleus of the preglomerular region, posterior tuberal nucleus, area dorsalis of the telencephalon, and a tegmental nucleus (T2). Efferents from the inferior lobe and the lateral torus terminate in the dorsal hypothalamic neuropil and corpus mamillare. Furthermore, the inferior lobe projects to the medial nucleus of the lateral tuberal hypothalamus and perhaps makes axo-axonal synapses in the tractus tectobulbaris rectus. The inferior lobe and the torus lateralis have reciprocal connections with the preglomerular tertiary gustatory nucleus and posterior thalamic nucleus and are also mutually interconnected. The inferior lobe is also reciprocally connected with the medial nucleus of the preglomerular region, reticular formation and sparsely with the anterior dorsal thalamic and the ventromedial thalamic nuclei. Thus, whereas the lateral torus is exclusively connected with the gustatory system, the inferior lobe is of a multisensory nature. In comparison with the goldfish (Carassius auratus), the connectivity pattern of the inferior lobe of Hemichromis lifalili reflects its specialization with respect to the visual system, as it receives qualitative (i.e., dorsal posterior, anterior, and ventromedial thalamic nuclei) as well as quantitative (i.e., nucleus glomerulosus) additional visual input.

Afferent sources to the ganglion of the terminal nerve in teleosts

Afferent sources to the ganglion (ggl) of the terminal nerve (TN) were studied in percomorph teleosts the tilapia and dwarf gourami. After tracer applications to the TN-ggl and the surrounding bulbus olfactorius, retrogradely labeled neurons were present in the area dorsalis telencephali pars posterior (Dp), area ventralis telencephali pars ventralis et supracommissuralis (Vv and Vs), nucleus tegmento-olfactorius of Prasada Rao and Finger (1984), and locus coeruleus. In the contralateral bulbus olfactorius labeled cells were observed, and terminals were seen in the TN-ggl. Tracer injection experiments to the possible sources of origin to the TN-ggl were then performed. Tracer applications to the nucleus tegmento-olfactorius labeled abundant terminals in the TN-ggl but labeled very few in the bulbus olfactorius proper. Retrogradely labeled neurons were present in the nucleus ventromedialis thalami, nucleus commissurae posterioris, area pretectalis pars dorsalis et ventralis, nucleus sensorius nervi trigemini, and formatio reticularis pars superius et medius. Tracer applications to the Dp or Vs/Vv labeled terminals mainly in the bulbus olfactorius proper. However, terminals to the TN-ggl were supplied from labeled axons on their way to the bulbus olfactorius. Tracer injections to the locus coeruleus labeled only a few fibers around the TN-ggl. These results suggest that the TN-ggl receives somatosensory and visual inputs from the nucleus tegmento-olfactorius and olfactory inputs from the bulbus olfactorius and telencephalic subdivisions, which receive secondary olfactory projections. The locus coeruleus may also send fibers to the TN-ggl.