Information coding in the vertebrate olfactory system.

The olfactory systems of vertebrates are able to discriminate a vast array of structurally diverse odorants. This perceptual acuity derives from a series of information-processing events that occur within distinct neural structures through which olfactory sensory information flows. This review discusses current knowledge concerning the mechanisms by which olfactory stimuli are initially detected and transduced into electrical signals that are transmitted to the olfactory bulb of the brain.

Volatile and intravenous anesthetics decrease glutamate release from cortical brain slices during anoxia.

Background: Extracellular accumulation of the excitatory neurotransmitter L-glutamate during cerebral hypoxia or ischemia contributes to neuronal death. Anesthetics inhibit release of synaptic neurotransmitters but it is unknown if they alter net extrasynaptic glutamate release, which accounts for most of the glutamate released during hypoxia or ischemia. The purpose of this study was to determine if different types of anesthetics decrease hypoxia-induced glutamate release from rat brain slices.

Does the sulfhydryl or the adenine moiety of CoA enhance firefly luciferase activity?

Light production by firefly luciferase is limited by product release resulting in flash kinetics. Several compounds (CoA, PPi, and nucleotides) transform the flash-form of light production into continuous light production. The sulfhydryl group of CoA is required; however, since nucleotides are also active, at least two mechanisms (sites) must exist.

Target-independent pattern specification in the olfactory epithelium.

In mammals, odors are detected by approximately 1000 different types of odorant receptors (ORs), each expressed by a fraction of neurons in the olfactory epithelium. Neurons expressing a given OR are confined to one of four spatial zones but are distributed randomly throughout that zone. In the olfactory bulb, the axons of neurons expressing different ORs synapse at different sites, giving rise to a highly organized and stereotyped information map.

Spatial patterning and information coding in the olfactory system.

The ability of mammals to discriminate thousands of structurally diverse odorants appears to derive from the existence of a multigene family that encodes approximately 1000 different odorant receptors. Recent studies have used this family to explore how the olfactory system organizes sensory information. These studies reveal striking patterns of organization suggesting that incoming sensory information is first broadly organized in the nose and is then transformed in the olfactory bulb into a stereotyped and highly organized spatial map.

Role of adenosine in NMDA receptor modulation in the cerebral cortex of an anoxia-tolerant turtle (Chrysemys picta belli).

Accumulation of the neuromodulator adenosine in the anoxia-tolerant turtle brain may play a key role in a protective decrease in excitatory neurotransmission during anoxia. Since excitatory neurotransmission is mediated largely by Ca2+ entry through N-methyl-D-aspartate (NMDA) receptors, we measured the effect of adenosine on NMDA-mediated Ca2+ transients in normoxic and anoxic turtle cerebrocortical sheets. Intracellular [Ca2+] was measured fluorometrically with the Ca2+-sensitive dye Fura-2.

Information coding in the olfactory system: evidence for a stereotyped and highly organized epitope map in the olfactory bulb.

In the mammalian olfactory system, information from approximately 1000 different odorant receptor types is organized in the nose into four spatial zones. Each zone is a mosaic of randomly distributed neurons expressing different receptor types. In these studies, we have obtained evidence that information highly distributed in the nose is transformed in the olfactory bulb of the brain into a highly organized spatial map.

Effects of isoflurane and hypothermia on glutamate receptor-mediated calcium influx in brain slices.

Background: To understand how volatile anesthetics protect neurons during cerebral ischemia, we studied the effects of isoflurane on cerebral glutamate receptor-mediated calcium influx. Calcium influx via these key excitatory receptors may mediate pain transmission, memory, and the pathophysiologic sequelae of cerebral anoxia or ischemia. Because cerebral protection by hypothermia may involve a decrease in glutamate receptor activity, we also examined the interaction of temperature and isoflurane on glutamate receptor inhibition.

Comparisons of freshly isolated strains of Lactobacillus acidophilus of human intestinal origin for ability to assimilate cholesterol during growth.

Fecal isolates of Lactobacillus acidophilus were obtained from human volunteers and tested for bile tolerance, the ability to deconjugate bile salts, and the ability to assimilate (take up) cholesterol during growth. One hundred and twenty-three of the 304 isolates of lactobacilli obtained were identified as L. acidophilus.

A second subunit of the olfactory cyclic nucleotide-gated channel confers high sensitivity to cAMP.

Sensory transduction in olfactory neurons is mediated by intracellular cAMP, which directly gates a nonselective cation channel. A cDNA encoding a cyclic nucleotide-gated (CNG) ion channel subunit (rOCNC1) has been cloned previously from rat olfactory epithelium. However, differences between the functional properties of rOCNC1 and the native olfactory CNG channel suggest that the native channel could be composed of several distinct subunit types.

A molecular dissection of spatial patterning in the olfactory system.

The identification and cloning of genes encoding odorant receptors has provided molecular probes with which to examine the molecular mechanisms and organizational strategies underlying olfactory information processing. Recent studies using odorant receptor genes have revealed unexpected patterns of expression that provide new insights into how information may be organized in the nose and in the axonal projection from the nose to the brain.

Substrate and acute temperature effects on turtle heart and liver mitochondria.

The oxidative properties of heart and liver mitochondria from the Western painted turtle (Chrysemys picta bellii) were characterized on the basis of substrate preferences and temperature sensitivity. Turtle heart and liver mitochondria oxidize most substrates at 2- and 10-fold less, respectively, than rates obtained from the corresponding rat mitochondria. Krebs cycle intermediates, ketone bodies, and glutamate were oxidized at similarly high rates by turtle heart mitochondria (70.

Odorant receptor diversity and patterned gene expression in the mammalian olfactory epithelium.

The mammalian olfactory system is capable of discriminating a vast array of structurally diverse odors. We have identified a novel multigene family whose unusual size and diversity suggest that odor discrimination may rely heavily on the existence of many hundreds of different types of odorant receptors which are differentially expressed by olfactory sensory neurons in the nasal cavity. We have found that the members of this family are segregated in their expression into a series of distinct, and highly specified, zones within the olfactory epithelium.

Anoxic suppression of Na(+)-K(+)-ATPase and constant membrane potential in hepatocytes: support for channel arrest.

The maintenance of ion gradients across the plasma membrane by the Na(+)-K(+)-ATPase has been shown to utilize a large fraction of the total cellular energy demand. In view of the importance of ion gradients to cellular function, and the remarkable anoxia tolerance of Chrysemys picta bellii (western painted turtle) and hepatocytes isolated from this species, it was of interest to determine if in response to anoxia 1) ion gradients were maintained and 2) if the activity of the plasma membrane Na(+)-K(+)-ATPase changed to aid in ion gradient maintenance. From normoxic hepatocyte suspensions the ouabain-inhibitable 86Rb+ uptake (a measure of Na(+)-K(+)-ATPase activity) was determined, and the rate of ATP utilization was 19.

Microcalorimetric measurement of reversible metabolic suppression induced by anoxia in isolated hepatocytes.

The metabolic suppression due to anoxia in hepatocytes from the anoxia-tolerant turtle Chrysemys picta bellii was measured directly using microcalorimetric techniques. The normoxic heat flux from hepatocytes in suspension (25 degrees C) was 1.08 +/- 0.

Anoxia-tolerant hepatocytes: model system for study of reversible metabolic suppression.

Chrysemys picta bellii is well known for its ability to survive extended anoxic periods and has been widely used as a model system to study anoxic metabolism. Described here is a method for the isolation of anoxia-tolerant hepatocytes from this species. Freshly isolated hepatocytes were determined to be viable based on trypan blue exclusion, gluconeogenic capacity from [14C]lactate, responsiveness to epinephrine and glucagon, and maintenance of cellular adenylate concentrations.

Response of protein synthesis to anoxia and recovery in anoxia-tolerant hepatocytes.

Hepatocytes from the western painted turtle (Chrysemys picta bellii) display a profound metabolic suppression under anoxia. Fractional rates of protein synthesis fell by 92% during 12 h anoxia at 25 degrees C and were indistinguishable from the rate obtained with cycloheximide. Normoxic recovery saw protein synthesis increase to 160% of control values and return to normal after 2 h.

A zonal organization of odorant receptor gene expression in the olfactory epithelium.

The mechanisms by which mammals discriminate a vast array of diverse odors are poorly understood. To gain insight into the organizational strategies underlying this discriminatory capacity, we have examined the spatial distribution of odorant receptor RNAs in the mouse olfactory epithelium. We have observed topographically distinct patterns of receptor RNAs suggesting that the nasal cavity is divided into a series of expression zones.

The family of genes encoding odorant receptors in the channel catfish.

The anatomical and numerical simplicity of the fish olfactory system has led us to examine the family of olfactory receptors expressed in the catfish. We have identified a family of genes encoding seven transmembrane domain receptors that share considerable homology with the odorant receptors of the rat. The size of the catfish receptor repertoire appears to be far smaller than in mammals.

Receptor diversity and spatial patterning in the mammalian olfactory system.

In order to gain insight into the mechanisms underlying olfactory perception in mammals, we have performed experiments to identify and characterize the basic receptive elements of the olfactory system, the odorant receptors. We have identified a novel multigene family that encodes odorant receptors on olfactory sensory neurons in the nasal cavity. The tremendous size and diversity of this family indicate that perceptual acuity in the olfactory system relies heavily on the differential binding properties of hundreds of different receptor types.

The olfactory multigene family.

A novel multigene family has been identified that is likely to encode odorant receptors on olfactory sensory neurons. Further studies on this gene family are likely to shed light on the molecular mechanisms underlying information coding in the mammalian olfactory system. This review is also published in Current Opinion in Genetics and Development 1992, 2:467-473.

The olfactory multigene family.

A novel multigene family has been identified that is likely to encode odorant receptors on olfactory sensory neurons. Further studies on this gene family are likely to shed light on the molecular mechanisms underlying information coding in the mammalian olfactory system. This review is also published in Current Opinion in Neurobiology 1992, 2:282-288.