Kensaku Mori

Membrane and synaptic properties of identified neurons in the olfactory bulb

Abbreviations 275

Subclasses of olfactory receptor cells and their segregated central projections demonstrated by a monoclonal antibody

A library of monoclonal antibodies (MAbs) was generated against a homogenate of the rabbit olfactory bulb. One of them immunohistochemically distinguished a subgroup of olfactory nerves. Both in the olfactory bulb and the epithelium, this MAb labeled most olfactory receptor axons in the lateral but only a small fraction in the medial portion. These findings demonstrate a molecular heterogeneity among olfactory receptor cells and suggest a functional division between the lateral and the medial portions of the epithelium and the bulb.

Centrifugal influence on olfactory bulb activity in the rabbit.

(1) Regions which exert centrifugal influences on the olfactory bulb activity were studied by applying systematic stimulation to various areas of the ipsilateral telencephalon in the rabbit. By delivering electric stimuli to the anterior commissure (AC), the deep lying structures in the projection areas of the lateral olfactory tract (LOT) and the medial forebrain bundle situated between the lateral hypothalamic area and the lateral preoptic area, negative field potentials were evoked in the granule cell layer (GCL) of the bulb. (2) Intracellular recordings from the mitral cells and the GCL neurons in the olfactory bulb were performed in order to clarify the modes of the centrifugal influences on the olfactory bulb neurons. (3) EPSPs were recorded in the GCL neurons by stimulation of the deep-lying structure of the prepiriform cortex as well as by stimulation of the AC. The onset time and duration of the EPSPs corresponded well to those of the negative field potentials in the GCL. Thus, it was suggested that these negative potentials were caused by the EPSPs of the number of granule cells. (4) In almost all of the mitral cells, IPSPs were recorded by stimulation of the AC and the deep-lying structures of the LOT projection areas. The onsets of the IPSPs were found with delays of several milliseconds from those of the negative field potentials in the GCL. (5) It was postulated that the excitation of the centrifugal system mainly exerts a depressive influence on the activity of the mitral cell, and that the GCL neuron (presumably the granule cell) seems to be an inhibitory interneuron interpolated between the extrinsic fibers from the telencephalon and the mitral cell.

Immunochemical identification of subgroups of vomeronasal nerve fibers and their segregated terminations in the accessory olfactory bulb

Vomeronasal nerve (VNN) fibers and their terminations in the accessory olfactory bulb (AOB) were studied immunohistochemically using 3 monoclonal antibodies (MAbs). One MAb (R2D5) labeled all VNN fibers. Another MAb (R4B12) labeled a subgroup of the VNN fibers which terminated in the rostrolateral glomeruli in the AOB. The third MAb (R5A10) recognized a complementary subgroup of the VNN which terminated in the caudomedial portion of the AOB. These results for the first time show occurrence of subtypes in the VNN axons with segregated terminations in the AOB.

Projections of two subclasses of vomeronasal nerve fibers to the accessory olfactory bulb in the rabbit

The organization of the projections of subclasses of vomeronasal nerve fibers to the accessory olfactory bulb was analysed using monoclonal antibodies generated against a homogenate of the rabbit olfactory bulb. Monoclonal antibody R2D5 labels all the somata of vomeronasal receptor cells in the vomeronasal organ as well as all their axons (vomeronasal nerve fibers). Another monoclonal antibody (R4B12), which has been shown to selectively bind and thus identify a subclass of olfactory nerve fibers, also labels a subclass of vomeronasal nerve fibers. The R4B12-positive subclass of vomeronasal nerve fibers project to the glomeruli in the rostrolateral part of the accessory olfactory bulb. The third monoclonal antibody (R5A10) recognizes a complementary subclass of vomeronasal nerve fibers projecting to the glomeruli in the caudomedial part of the accessory bulb. In contrast to the clearly segregated terminations in the accessory bulb, the two subclasses of vomeronasal nerve fibers are intermingled with each other in the vomeronasal nerve bundles. Retrograde labeling of vomeronasal receptor cell somata following injection of horseradish peroxidase within the rostrolateral (R4B12-positive) part of the accessory bulb indicates that vomeronasal receptor cells of this subtype are widely distributed in the vomeronasal sensory epithelium. These results demonstrate the heterogeneity of vomeronasal receptor cells and the specificity of projections arising from subclasses of vomeronasal nerve fibers to the accessory olfactory bulb.

Monoclonal antibodies (2C5 and 4C9) against lactoseries carbohydrates identify subsets of olfactory and vomeronasal receptor cells and their axons in the rabbit

Monoclonal antibodies (MAbs) against lactoseries carbohydrates were used to study immunohistochemically the olfactory and vomeronasal receptor cells and their axons in the rabbit. MAb 2C5, which recognizes Gal alpha 1----3Gal beta 1----4G1cNAc----R structure, selectively labeled a subset of olfactory receptor cells and the majority of vomeronasal receptor cells. MAb 4C9, which reacts with fucosyl poly-N-acetyllactosamine, identified a subset of vomeronasal receptor cells. The above two MAbs also labeled the axons of these chemosensory receptor cells and thus revealed their axonal projection sites in the main and accessory olfactory bulbs.

The morphology and physiology of the granule cells in the rabbit olfactory bulb revealed by intracellular recording and HRP injection

Abstract The synaptic potentials of granule cells in the rabbit olfactory bulb were recorded intracellularly. The granule cells were then injected with horseradish peroxidase and their processes were reconstructed. Granule cells showed a depolarizing potential with one or a few spikes following the stimulation of either the lateral olfactory tract or the anterior commissure. In some granule cells, the depolarizing potential was followed by a hyperpolarizing potential.

Axonal projection of anterior olfactory nuclear neurons to the olfactory bulb bilaterally

Abstract The axonal projection of anterior olfactory nuclear (AON) neurons to the ipsilateral and contralateral olfactory bulbs and to the prepiriform cortex was analyzed electrophysiologically in the rabbit. Of 117 AON neurons which sent their axons to the anterior commissure, 46 cells (39%) and 55 cells (47%) were activated antidromically by ipsilateral and contralateral olfactory bulb stimulation, respectively, and 22 AON neurons (19%) were activated antidromically from both. The mean axonal conduction velocity of the AON neurons was 2.8 m/s in the AON—anterior commissure axonal segment, 1.6 m/s in the AON—contralateral offactory bulb segment, and 1.0 m/s in the AON—ipsilateral bulb segment. These results and the collision tests between the antidromically evoked spikes indicate that a number of AON neurons send their axons to the contralateral olfactory bulb via the anterior commissure and that the same neurons send thin axon collaterals to the ipsilateral bulb. These axonal projections are significant in relation to the synaptic influences of these axons upon olfactory bulb neurons.

LectinUlex europaeus agglutinin I specifically labels a subset of primary afferent fibers which project selectively to the superficial dorsal horn of the spinal cord

To examine differential carbohydrate expression among different subsets of primary afferent fibers, several fluorescein-isothiocyanate conjugated lectins were used in a histochemical study of the dorsal root ganglion (DRG) and spinal cord of the rabbit. The lectin Ulex europaeus agglutinin I specifically labeled a subset of DRG cells and primary afferent fibers which projected to the superficial laminae of the dorsal horn. These results suggest that specific carbohydrates containing L-fucosyl residue is expressed selectively in small diameter primary afferent fibers which subserve nociception or thermoception.

Modulation by prostaglandin D2 of mitral cell responses to odor stimulation in rabbit olfactory bulb

Recent work in our laboratory has demonstrated that prostaglandin (PG) D2 and the enzyme activities for its biosynthesis and inactivation are highly concentrated in the olfactory bulb and that the mitral cell layer of the bulb is enriched with PGD2-binding protein. We therefore investigated the role of PGD2 in the processing of odor signals in the rabbit olfactory bulb by an electrophysiological technique. Iontophoretic (-100 nA, 20 s), intra-arterial (0.0125-0.1 mg/kg) and intravenous (i.v., 0.05-0.3 mg/kg) administration of PGD2 enhanced and prolonged the responses of mitral cells to some of the olfactory stimuli tested. The extent and duration of granule cell inhibition of mitral cells were assessed by recording field potential responses in the bulb to paired lateral olfactory tract volleys. The i.v. administration of indomethacin or diclophenac, both of which are inhibitors of PG biosynthesis, resulted in prolongation of the granule cell inhibition of mitral cells without any significant change of the conditioning amplitudes. It also caused the reduction of the spike responses of mitral cells to olfactory stimuli. After treatment with indomethacin, the i.v. administration of PGD2 (1 mg/kg) rapidly reduced the duration of the granule cell inhibition of mitral cells. These results indicate that PGD2 plays a modulatory role in the mitral cell responses to odor stimuli by suppressing the inhibitory synaptic inputs from granule cells to mitral cells.