Corpus Glomerulosum Research Articles

Modelling the geometric features and investigating electrical properties of dendrites in a fish thalamic neuron

A certain pacific fish has a thalamic nerve cell with a unique dendritic geometry. Instead of the cell having a branching dendritic structure, the large cell of the corpus glomerulosum has, generally, a single dendritic stalk with a large bulbous tip. We formulate a cable-theory model that incorporates the geometry, and then, we solve the problem for a single, localized synaptic current source at the bulb. From the solution representation, we numerically examine the characteristics of the postsynaptic potential due to the presence of the bulbous tip.

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.

Slow removal of Na(+) channel inactivation underlies the temporal filtering property in the teleost thalamic neurons.

It has been previously shown that the "large cell" in the corpus glomerulosum (CG) of a teleost brain has a low-pass temporal filtering property. It fires a single spike only in response to temporally sparse synaptic inputs and thus extracts temporal aspects of afferent activities. To explore the ionic mechanisms underlying this property, we quantitatively studied voltage-gated Na(+) channels of the large cell in the CG slice preparation of the marine filefish by means of whole-cell patch clamp recordings in the voltage-clamp mode. Recorded Na(+) current was well described using the Hodgkin-Huxley "m(3)h" model. It was revealed that the Na(+) channels have a novel feature: remarkably slow recovery from inactivation. In other words, the time constant for the "h" gate was extremely large (approximately 100 ms at -80 to -50 mV). In order to test whether the analysed Na(+) current serves as a mechanism for filtering, the behaviour of the membrane model incorporating the Na(+) channel was simulated using a computer program called NEURON. In response to current injections, the membrane model displayed low-pass filtering and firing properties similar to those reported in real cells. The present results suggest that slow removal of Na(+) channel inactivation serves as a crucial mechanism for the low-pass temporal filtering property of the large cell. The simulation study also suggested that velocity and/or amplitude of a spike propagating though an axon expressing Na(+) channels of this type could potentially be modulated depending on the preceding activities of the cells.

Imaging postsynaptic activities of teleost thalamic neurons at single cell resolution using a voltage-sensitive dye

Optical recording of neuronal activities using voltage-sensitive dyes (VSDs) is a useful method for simultaneous multi-site recording. However, it has been rather difficult to distinguish optical signals from individual, identified cells. We applied the optical recording technique using a high-speed charge coupled device (CCD) imaging system to a teleost thalamic nucleus, corpus glomerulosum (CG) which has a well-defined histological organization and large postsynaptic dendrites. Patch-like dye (di-4-ANEPPS) signals were observed in the dendritic layer of the CG in response to afferent nerve stimulations. These responses were completely blocked by an α-amino-3-hydroxy-5-methyl-4-isoxazole-proprionate (AMPA) receptor antagonist, did not propagate, and the size of the patches were close to that of a single dendritic tip of the ‘large cell’. Thus, we found that these patch-like VSD signals most likely represent postsynaptic potentials at individual dendritic tips of the large cells.

Effects of characteristic dendritic tip geometry on the electrical properties of teleost thalamic neurons.

Of the factors that characterize the properties and functions of neurons, dendritic geometry is one of the most critical. We used simulations employing the multi-compartment model to study the effects of dendritic tip geometry on the electrical properties of the "large cell" in a teleost thalamic nucleus from the corpus glomerulosum. We demonstrated a dramatic geometrical "boosting" effect; passive propagation of the synaptic inputs from the dendritic tip to the soma through the dendritic stalk is less attenuated in cells with larger tips.

Encoding of different aspects of afferent activities by two types of cells in the corpus glomerulosum of a teleost brain.

The corpus glomerulosum (CG) is an expansive nucleus in acanthopterigian teleosts that has been suggested to be involved in vision-related information processing and the control of the hypothalamic function. The CG has only two types of constituent cells, the large cell and the small cell, and well-defined afferent/efferent fiber connections. One of the three types of teleostean CG, type III has additional outstanding morphological characters: clearly laminated organization and giant (>50 microm in diameter) tips of postsynaptic dendrites. Although such histological architecture is potentially advantageous for the study of information processing in a brain nucleus based on the physiological properties of identified cells and synapses, previous studies on the CG have been limited to anatomy. In this study, we developed a slice preparation of the type III CG in a teleost, Stephanoplepis cirrhifer, and studied the morphology and physiology of individual cells and synaptic transmission by means of dendritic intracellular and somatic whole cell recordings. The characteristic morphology of the two types of cells was revealed by intracellular staining. While both of them received similar glutamatergic and GABAergic projections from the nucleus corticalis mediated by AMPA, N-methyl-D-aspartate, and GABA(A) receptors, they showed quite distinctive firing properties and postsynaptic responses with current injection and synaptic inputs: the large cell fired a single spike, and the small cell fired a spike train whose frequency was dependent on the stimulus intensity. Furthermore, the large cell showed low-pass temporal filtering properties with paired stimuli. These results suggest that the large cell and the small cell may encode different aspects of the corticalis activities.

Fiber Connections of the Inferior Lobe in a Percomorph Teleost, Thamnaconus (Navodon) modestus

Afferent and efferent fiber connections of the lobus inferior (LI) were studied in a percomorph teleost, Thamnaconus (Navodon) modestus. The LI of Thamnaconus is composed of the nucleus diffusus lobi inferioris (NDLI), the nucleus recessus lateralis pars lateralis et medialis (NRLl and NRLm), and the nucleus centralis lobi inferioris pars anterior et posterior (NCa and NCp). The NDLI receives projections from the secondary gustatory nucleus, preglomerular tertiary gustatory nucleus, corpus glomerulosum, dorsal region of the area dorsalis telencephali pars medialis (dDm), and area dorsalis telencephali pars lateralis. Different subdivisions of the dorsal telencephalon project to discrete regions of the NDLI. The NDLI projects to the corpus mamillare, NRLl, NCa, and NCp. Thus the NDLI could be regarded as an intrahypothalamic relay nucleus. The NCa receives projections from the NDLI and projects to the preglomerular tertiary gustatory nucleus, secondary gustatory nucleus, nucleus lateralis valvulae, and NRLl. The NCa appears to be primarily an extrahypothalamic projection nucleus. The NCp receives projections from the NDLI. Efferent connections of the NCp remain to be studied. The NRLl receives projections from the NDLI, and projects to the nucleus ruber (NR) of Goldstein [1905] and the preglomerular tertiary gustatory nucleus. Dense projections of the NR to the stratum opticum and stratum fibrosum et griseum superficiale of the optic tectum are demonstrated. The NRLm receives projections from the medial part of the dDm. Efferent connections of the NRLm remain unclear. The LI as a whole receives projections from the locus coeruleus and nucleus raphe superior. These results suggest that the LI receives gustatory and/or general visceral information from the secondary and tertiary gustatory nuclei, visual and somatosensory inputs from the corpus glomerulosum. Inputs from the dorsal telencephalic subdivisions could be of various modalities (e.g. visual, acousticolateral, gustatory and/or general visceral). The present study also suggests that information processed in the LI is transmitted to the optic tectum via the NR, to the corpus mamillare, to the secondary and tertiary gustatory nuclei, and to the cerebellum via the nucleus lateralis valvulae.

Corpus glomerulosum in a teleost brain: Novel preparation for the study of neuronal processing in brain nuclei

Corpus glomerulosum in a teleost brain: Novel preparation for the study of neuronal processing in brain nuclei

Tectal projections in teleosts: Responses of some target nuclei to direct tectal stimulation

The optic tectum of Eugerres and Holocentrus was electrically stimulated, and field and unitary potentials were recorded from nucleus prethalamicus and nucleus isthmi; field potentials were also recorded from dorsolateral tegmental nuclei and corpus glomerulosum. Recording sites were verified by dye markings. The responses found are characteristics of, and limited to, each cell group in particular, and can thus be used for accurate location of such cell groups in the course of recording, stimulating or injecting experiments. In general, tectal stimulation leads to postsynaptic excitation at target nuclei. This is followed by further excitation mixed with inhibition in the case of nucleus prethalamicus. In the case of nucleus isthmi, excitation leads to repetitive firing which appears to arise at the dendrites and to be synchronized with firing of neighboring neurons.

Telencephalic projections in two teleost species.

The efferent pathways of the telencephalon were investigated in the percomorph Eugerres and the berycomorph Holocentrus. One telencephalic hemisphere was resected by suction and the animals were perfused 7-35 days thereafter. The brains were processed according to a modification (Method 7 in Ebbesson, '70) of the Fink-Heimer ('67) technique for selective silver impregnation of degenerating axons and terminals. Some fibers emerging from the lesioned telencephalic hemisphere terminate upon the contralateral hemisphere. The large bulk of efferent fibers, however, descends into the ipsilateral diencephalon and gives off the so-called strio-tectal bundle (STB) as well as the medial forebrain bundle (MFB). The remaining contingent eventually splits into the so-called strio-lobar bundle (SLB) and the lateral forebrain (LFB), but, previous to splitting, it contributes most of the telencephalic projection to the optic tectum in Eugerres, and gives abundant terminals to the ipsilateral nucleus rotundus or prethalamicus in both Eugerres and Holocentrus. The STB conveys all telencephalo-tectal fibers in Holocentrus, and some of them in Eugerres. Telencephalic efferents teminate ipsilaterally in the middle level of the tectum's stratum griseum centrale; in Holocentrus there is also a small projection to the stratum opticum. The MFB terminates at the caudal hypothalamus and gives terminals all along its course. The LFB also gives terminals all along its course and terminates upon a nucleus located between the midline and the corpus glomerulosum. The SLB spreads out and terminates in the inferior lobe of the hypothalamus.