Isoxazolyl, oxazolyl, and thiazolylpropionic acid derivatives as potent alpha(4)beta(1) integrin antagonists.

A series of isoxazolyl, oxazolyl, and thiazolylpropionic acid derivatives derived from LDV was found to be a potent antagonist of the alpha(4)beta(1) integrin. The synthesis and SAR leading up to 3-[3-(1-[-[3-methoxy-4-(3-o-tolyl-ureido)-phenyl]-acetylamino]-3-methyl-butyl)-isoxazol-5-yl]-propionic acid (22) are reported. In an allergic mouse model, compound 22 was efficacious delivered systemically (58% inhib @ 10 mg/kg, sc) as well as by intra-tracheal instillation (ED(50)=2 microg/kg).

Direct innervation of identified tectothalamic neurons in the inferior colliculus by axons from the cochlear nucleus.

The present study sought to identify tectothalamic neurons in the rat inferior colliculus that receive their innervation directly from the cochlear nuclei and to identify the axons that provide the innervation. A direct projection would bypass the binaural interactions of the superior olivary complex and provide the quickest route to the neocortex. Axons, primarily from the dorsal cochlear nucleus, were labeled with anterograde transport of dextran and terminated in the central nucleus of the inferior colliculus in a laminar pattern. Most labeled axons were thin and simply branched. Other axons were thicker, gnarly, less frequently observed and probably originated from the ventral cochlear nucleus. None had concentrated endbulbs or a nest of endings. Both types of axons terminated primarily in the central nucleus and layer 3 of the external cortex. This pattern suggests that the combination of these subdivisions in the rat are equivalent to the central nucleus as defined in other species. Tectothalamic neurons in the inferior colliculus in the same animals were identified by retrograde transport from the medial geniculate body and intracellular injection of Lucifer Yellow. A number of different cell types act as tectothalamic neurons and receive contacts from cochlear nucleus axons. These include flat cells (disc-shaped), less-flat cells and stellate cells. Two innervation patterns were seen: a combination of axosomatic and axodendritic contacts, and predominantly axodendritic contacts. Both patterns were seen in the central nucleus, but axosomatic contacts were seen less often in the other subdivisions. This is the first study to show direct connections between cochlear nuclear axons and identified tectothalamic neurons. The layers of axons from cochlear nuclei may provide convergent inputs to neurons in the inferior colliculus rather than the heavy inputs from single axons typical of lower auditory nuclei. Excitatory synapses made by axons from the cochlear nuclei on tectothalamic neurons may provide a substrate for rapid transmission of monaural information to the medial geniculate body.

Axons from anteroventral cochlear nucleus that terminate in medial superior olive of cat: observations related to delay lines.

The differences in path length of axons from the anteroventral cochlear nuclei (AVCN) to the medial superior olive (MSO) are thought to provide the anatomical substrate for the computation of interaural time differences (ITD). We made small injections of biotinylated dextran into the AVCN that produced intracellular-like filling of axons. This permitted three-dimensional reconstructions of individual axons and measurements of axonal length to individual terminals in MSO. Some axons that innervated the contralateral MSO had collaterals with lengths that were graded in the rostrocaudal direction with shorter collaterals innervating more rostral parts of MSO and longer collaterals innervating more caudal parts of MSO. These could innervate all or part of the length of the MSO. Other axons had restricted terminal fields comparable to the size of a single dendritic tree in the MSO. In the ipsilateral MSO, some axons had a reverse, but less steep, gradient in axonal length with greater axonal length associated with more rostral locations; others had restricted terminal fields. Thus, the computation of ITDs is based on gradients of axonal length in both the contralateral and ipsilateral MSO, and these gradients may account for a large part of the range of ITDs encoded by the MSO. Other factors may be involved in the computation of ITDs to compensate for differences between axons.

Simultaneous anterograde labeling of axonal layers from lateral superior olive and dorsal cochlear nucleus in the inferior colliculus of cat.

The laminar organization of the central nucleus of inferior colliculus includes layers of axons that may be important in shaping the responses of neurons. Depending on their source, some layered axons are afferents that are superimposed and terminate on the same postsynaptic neurons, while other layered afferents, such as those from the ipsilateral and contralateral lateral superior olive, terminate side-by-side. The specific pattern of convergence may dictate which populations of axons are presynaptic to layered disc-shaped neurons in the central nucleus. We compared the distribution of afferent axons from the dorsal cochlear nucleus and the lateral superior olive to the contralateral inferior colliculus in the cat. Injection sites in cochlear nucleus and superior olive were physiologically characterized by extracellular recordings of single and multiple units in response to monaural and binaural acoustic stimulation. Two separate injections were made in each case, and both injection sites contained units with overlapping best frequencies. Biotinylated dextran, fluorescent dextran, 3H-leucine, and wheat germ agglutinin conjugated to horseradish peroxidase were used as anterograde tracers. The present results show that layered axons from the dorsal cochlear nucleus and lateral superior olive are superimposed in part of the contralateral central nucleus. Both projections were arranged in rostro-caudally oriented axonal layers that converged in the ventral part of the central nucleus. However, in the dorsal part of the central nucleus, the same layer of axons from the dorsal cochlear nucleus did not terminate with afferents from the lateral superior olive. Within the overlapping layers in the ventral central nucleus, the overlap of axons from the dorsal cochlear nucleus and the lateral superior olive was uniform except for small patches that were usually smaller than the dendritic fields of disc-shaped neurons. These data suggest that the layers may create specific functional zones in the central nucleus of the inferior colliculus. One zone may contain neurons with binaural responses that combine the properties of the inputs from the contralateral lateral superior olive and the dorsal cochlear nucleus. A second zone may contain inputs from the cochlear nucleus but lack those of the lateral superior olive.

Axonal projections from the lateral and medial superior olive to the inferior colliculus of the cat: a study using electron microscopic autoradiography.

The superior olivary complex is the first site in the central auditory system where binaural interactions occur. The output of these nuclei is direct to the central nucleus of the inferior colliculus, where binaural inputs synapse with monaural afferents such as those from the cochlear nuclei. Despite the importance of the olivary pathways for binaural information processing, little is known about their synaptic organization in the colliculus. The present study investigates the structure of the projections from the lateral and medial superior olivary nuclei to the inferior colliculus at the electron microscopic level. Stereotaxic placement and electrophysiological responses to binaural sounds were used to locate the superior olive. Anterograde axonal transport of 3H-leucine was combined with light and electron microscopic autoradiography to reveal the location and morphology of the olivary axonal endings. The results show that the superior olivary complex contributes different patterns of synaptic input to the central nucleus of the inferior colliculus. Each projection from the superior olivary complex to the colliculus differs in the number and combinations of endings. Axonal endings from the ipsilateral medial superior olive were exclusively the round (R) type that contain round synaptic vesicles and make asymmetrical synaptic junctions. This morphology is usually associated with excitatory synapses and neurotransmitters such as glutamate. Endings from medial superior olive terminate densely in the central nucleus. The projection from the contralateral lateral superior olive also terminates primarily as R endings. This projection also includes small numbers of pleomorphic (PL) endings that contain pleomorphic synaptic vesicles and usually make symmetrical synaptic junctions. The PL morphology is associated with inhibitory synapses and transmitters such as gamma-aminobutyric acid and glycine. All endings from the contralateral lateral superior olive terminate much less densely than endings from the medial olive. In contrast, the projection from the ipsilateral lateral superior olive contributes both R and PL endings in roughly equal proportions. These ipsilateral afferents are heterogeneous in density and can terminate in lower or higher concentrations than endings from the contralateral side. These data show that the superior olive is a major contributor to the synaptic organization of the central nucleus of the inferior colliculus. The ipsilateral projections of the medial and lateral superior olive may produce higher concentrations of R endings than other inputs to the central nucleus. Such endings may participate in excitatory synapses. The highest concentrations of PL endings come from the ipsilateral lateral superior olive.(ABSTRACT TRUNCATED AT 400 WORDS)

Connectivity of neurons in identified auditory circuits studied with transport of dextran and microspheres plus intracellular injection of lucifer yellow.

The components of a neural circuit are usually distinguished in separate experiments to identify long connections, presynaptic, and postsynaptic components. We describe a procedure to visualize these components in the same experiment. Neurons in the inferior colliculus the axons of which project to the medial geniculate body were identified by retrograde transport of latex microspheres, while their innervation from the cochlear nucleus was simultaneously visualized by anterograde transport of dextrans. In aldehyde-fixed slices, the microsphere-labeled neurons near dextran-labeled axons were injected with biotinylated Lucifer Yellow. Subsequent avidin-biotin histochemistry allowed permanent visualization. The specific neurons involved in this circuit and the axonal contacts they received were easily visualized with the light microscope. This method allows the study of complex innervation patterns in the mammalian central nervous system.

Morphology of GABAergic neurons in the inferior colliculus of the cat.

The goal of the present study was to provide a comprehensive and quantitative description of neurons immunoreactive for gamma-aminobutyric acid (GABA) in the inferior colliculus (IC) of the cat. Neurons were investigated with two different antisera and two different incubation methods. Free-floating frozen or vibratome-cut sections were incubated either with an antiserum to glutamic acid decarboxylase (GAD) or to GABA conjugated to protein with glutaraldehyde. Additional 1.5-microns-thick sections were incubated with the GABA antiserum after embedding and removal of the plastic. Quantitative data were obtained from much of this material. Despite the use of these different antisera and reaction methods, the results obtained were remarkably similar. The results show that GAD- or GABA-positive neurons represent a significant population of cells in the central nucleus of the IC, up to 20% of the neurons. Most of these neurons have large or medium-sized perikarya. In contrast, immunonegative neurons are medium-sized or small. Many GABA-positive neurons had proximal dendrites or somata oriented in parallel to the fibrodendritic laminae of the central nucleus and are presumed to be disc-shaped neurons. Other have an orthogonal orientation and are presumed to be stellate cells. Large GABA-positive neurons form two groups, those with many axosomatic endings and those with few. Collectively, these observations suggest that there are several types of GABAergic neuron in the central nucleus and, by extension, that these may participate in many types of inhibitory circuits.

Fine structure of GABA-labeled axonal endings in the inferior colliculus of the cat: immunocytochemistry on deplasticized ultrathin sections.

Antisera to GABA conjugates and postembedding techniques were used to identify GABA-containing axonal endings at the electron microscopic level in the inferior colliculus. Over 90% of the GABA-labeled axonal endings had a similar morphology. They contained pleomorphic synaptic vesicles and made symmetrical synapses. The exceptional endings contained round vesicles and made symmetrical synaptic contacts or had pleomorphic vesicles with asymmetrical contacts. The majority of GABA-labeled axonal endings synapsed on dendrites; however, a few labeled axosomatic synapses were also found. Potential sources for these GABAergic synapses are neurons intrinsic to the inferior colliculus or from the dorsal nucleus of the lateral lemniscus. These findings suggest a basic similarity for most GABAergic endings in the inferior colliculus despite their possible origin from different cell types.