Biomedical subjects

L Dryer

Publications and source records attributed to L Dryer.

9 recordsLinked to original sources

PubMed1998

A novel family of ancient vertebrate odorant receptors.

Vertebrate odorant receptor (OR) genes have been isolated and characterized in several taxa, including bony fish and mammals. However, the search for more ancient vertebrate OR genes has been unsuccessful to date, indicating that these ancient genes share little sequence identity with previously isolated ORs. The lamprey (Lampetra fluviatilis) olfactory epithelium does not appear to express any of the modern vertebrate ORs previously identified in bony fish and mammals. We have isolated and characterized an ancient family of vertebrate membrane receptors from the olfactory epithelium of the lamprey. Sequence analysis reveals similarities with other Class A (rhodopsin-like) G protein-coupled receptors such as serotonin, dopamine, and histamine receptors, but the expression patterns of members of the new family, as well as certain conserved motifs, strongly suggest that the sequences encode ORs. Sequence similarity within the lamprey OR family is low, and Southern blot analysis suggests reduced-sized subfamilies. This novel vertebrate OR gene family, the most ancient isolated to date, is proposed to be involved in the detection of water-borne molecules in jawless fishes. Lamprey OR genes therefore represent a new level of diversity within the vertebrate OR gene family, but also provide clues as to how vertebrate ORs might have emerged.

Amino Acid Sequence↗

PubMed1998

Arachidonic acid-sensitive A-currents and multiple Kv4 transcripts are expressed in chick ciliary ganglion neurons.

A-currents (IA) of chick ciliary ganglion (CG) neurons were blocked reversibly by arachidonic acid and a non-metabolizable analog of arachidonic acid, 5,8,11,14-eicosatetraynoic acid. Inhibition of IA by both lipids was observed in whole-cell recordings and in excised inside-out patches, suggesting that Kv4 (Shal) subunits contribute to functional IA channels in CG neurons. Consistent with this, Kv4.2 and Kv4.3 cDNAs were isolated by RT-PCR from chick CG neurons.

Animals↗

PubMed1996

Information processing in mammalian olfactory system.

In recent years, considerable progress has been made in understanding how the olfactory system uses neural space to encode sensory information. In this review, we focus on recent studies aimed at understanding the organizational strategies used by the mammalian olfactory system to encode information. The odorant receptor gene family is discussed in the context of its genomic organization as well as the specificity of olfactory sensory neurons. These data have important consequences for the mechanisms of odorant receptor gene choice by a given sensory neuron. Division of the olfactory epithelium into zones that express different sets of odorant receptors is the first level of input organization. The topographical relationship between periphery and olfactory bulb represents a further level of processing of information and results in the formation of a highly organized spatial map of information in the olfactory bulb. There, local circuitry refines the sensory input through various lateral interactions. Finally, the factors that may drive the development of such a spatial map are discussed. The onset of expression and the establishment of the zonal organization of odorant receptor genes in the epithelium are not dependent upon the presence of the olfactory bulb, suggesting that the functional identity of olfactory sensory neurons is determined independently of target selection.

Animals↗

PubMed1996

Synaptology of the olfactory bulb of an elasmobranch fish, Sphyrna tiburo.

The ultrastructure of the elasmobranch olfactory bulb was examined in order to determine the synaptology of the olfactory circuitry in the bonnethead shark, Sphyrna tiburo. The compartmentalization of the bulb, together with the lack of mitral cell basal dendrites, suggests a different way of performing lateral communication between mitral cells of the olfactory bulb. The results show that granule cells assume an important role by directly interlinking mitral cells. A corollary of this is the segregation of the input onto the mitral cell dendritic arborization: afferent fibers synapse onto the intraglomerular mitral terminals, whereas most local circuit interactions utilize extraglomerular synapses located on the shafts and the somas of the mitral dendrites. Therefore, the elasmobranch synaptic pattern is different from that of higher vertebrates; This might represent the use of a different neural route to achieve the same processing task.

Animals↗

PubMed1996

Posttranslational regulation of Ca(2+)-activated K+ currents by a target-derived factor in developing parasympathetic neurons.

Macroscopic IK[Ca is not expressed in normal levels in chick ciliary ganglion (CG) neurons prior to synapse formation with target tissues, or in neurons developing in vitro or in situ in the absence of target tissues. Here, two chick CG slo partial cDNAs encoding IK[Ca channels were isolated, cloned, and sequenced. Both slo transcripts were readily detected in developing CG neurons prior to or in the absence of target tissue interactions. When CG neurons developed in vitro in the presence of target tissue (iris) extracts, a normal whole-cell IK[Ca was expressed. These effects did not require protein synthesis, and the activity was detectable throughout the stages of synapse formation in the iris. The active component has an apparent molecular weight of 40-60 kDa.

Amino Acid Sequence↗

PubMed1994

Mitral cell dendrites: a comparative approach.

Phylogenetically persistent structures such as the mitral cells of the vertebrate olfactory bulb undergo changes in their dendritic arbor in the course of evolution. The morphology of mitral cells and the main elements of the olfactory bulb circuit in all classes of vertebrates are reviewed in this paper. Most of the neuronal elements found in the mammalian olfactory bulb are present in anamniotes. However, in contrast to those of amniotes, the mitral cells of most anamniotes lack basal dendrites, and periglomerular cells are absent in fish. This suggests a different circuitry and therefore drastic changes in the processing of olfactory information within the olfactory bulb. Lateral inhibition, conferred by basal dendrites in anamniotes, must then utilize other mechanisms in anamniotes. Moreover, the marked segregation of olfactory inputs onto mammalian mitral cells is less obvious in mitral cells of anamniotes that lack basal dendrites. The general role of dendrites, including those of mitral cells, is discussed in the light of increasing evidence for dendritic excitability. The evolutionary significance of mitral cell basal dendrites is also discussed.

Animals↗

PubMed1994

Projections of the olfactory bulb in an elasmobranch fish, Sphyrna tiburo: segregation of inputs in the telencephalon.

We have previously shown that the morphological compartmentalization of the elasmobranch olfactory bulb is accompanied by a topographical arrangement of the primary olfactory projections onto the bulb. If this spatial arrangement is significant for the processing of the information, one would expect it to be preserved in the secondary olfactory centers of the telencephalon. In this paper, we describe the elasmobranch secondary projections from the olfactory bulb to the telencephalon, focusing on their spatial arrangements within the forebrain. Results show that the olfactory input onto the telencephalon are segregated. The medial olfactory tract projects rostrally onto the superficial layer of the dorsal pallium and onto the lateral pallium. The lateral olfactory tract projects caudally onto the lateral pallium, the striatum and the area superficialis basalis. Thus, the secondary olfactory projections are segregated within the telencephalon, with an overlapping of the secondary fibers in the main projection area, the lateral pallium.

Animals↗

PubMed1994

Influence of the olfactory organ on brain development.

The olfactory epithelium is a unique sensory structure that has the intrinsic ability to renew its receptor neurons naturally throughout the vertebrate lifetime. The olfactory epithelium is also a neurogenetic matrix that generates various cell populations during embryonic development and adulthood. Some of these cell types migrate to the forebrain and therefore contribute to brain formation. The molecules involved in cell migration and continuous reconnection of olfactory receptor neurons to the bulb are discussed. Experiments involving removal or transplants of the olfactory placode in amphibians suggest that the olfactory organ influences the development of the telencephalon. We believe that the olfactory organ has a morphogenetic influence and even possibly an inducing effect on the forebrain. This effect could be mediated by a number of organizing factors that we discuss. The profound influence of the olfactory organ on brain development underlines the importance of the olfactory organ for survival.

Aging↗

PubMed1993

A pilot study on morphological compartmentalization and heterogeneity in the elasmobranch olfactory bulb.

The olfactory bulb of many elasmobranch fishes is morphologically subdivided into distinct units or sub-bulbs immediately adjacent to the olfactory epithelium. We investigated this morphological feature in two species of shark and one species of ray in order to understand its impact on the arrangement of the primary olfactory projections onto the bulb. Using anterograde tracing methods in vitro (biocytin) as well as in fixed tissue (DiI), we observed a direct segregated projection of the olfactory afferents onto the bulb. Application of tracers to the lateral part of the olfactory epithelium resulted in staining restricted to this region of the bulb, whereas the same tracers applied to the medial part of the epithelium resulted in staining of the medial olfactory bulb. The sub-bulbs appear to be individual anatomical units that each receive input from the olfactory lamellae. Nissl and myelin staining as well as the Golgi method show that the cytoarchitecture of the sub-bulbs is not substantially different from that of other anamniotes. However, we did note the existence of two types of mitral cell, based on the morphology of their dendritic arborization. Type L cells exhibit a loose dendritic arborization, whereas type T cells are characterized by a dense, bush-like dendritic arborization. Both types of mitral cells lack basal dendrites.

Animals↗