John S. Kauer

Globose basal cells are neuronal progenitors in the olfactory epithelium: A lineage analysis using a replication-incompetent retrovirus

We have used a replication-incompetent retrovirus to analyze the lineage of olfactory receptor neurons in young rats. At 5-40 days after infection, clusters of infected cells comprised two major types: one consisted of 1-2 horizontal basal cells, and a second consisted of variable numbers of globose basal cells and immature and mature sensory neurons. Olfactory nerve lesion (which enhances neuronal turnover) increased the frequency of the globose-sensory neuron clusters as well as the number of cells in such clusters. No clusters contained both horizontal and globose basal cells, and none contained sustentacular cells. These data suggest, at least in young rats, that horizontal basal cells are not precursors of olfactory neurons, that there is a lineage path from globose cells to mature neurons, and that sustentacular cells may arise from a separate lineage.

Responses of olfactory bulb neurones to odour stimulation of small nasal areas in the salamander

1. Previous experiments have suggested that one way odours may be discriminated is by different spatial patterns of response at both the olfactory bulb and receptor level. The present experiments were designed to test to what extent the position of an odour on the receptor mucosa can influence the activity of olfactory bulb neurones.

Contributions of topography and parallel processing to odor coding in the vertebrate olfactory pathway

Odor information appears to be encoded by activity distributed across many neurons at each level in the olfactory pathway. Thus olfactory circuits function as parallel distributed processors. New methods for observing distributed activity in such systems permit computer simulations to be constructed that are constrained by patterns of activity observed in the real system. Analysis of the system using a combination of physiological measurements and computational approaches might elucidate the principles by which odors are discriminated.

Suckling pheromone stimulation of a modified glomerular region in the developing rat olfactory bulb revealed by the 2-deoxyglucose method

Topographic analysis of olfactory bulb activation, based on the [14C]2-deoxy-Dglucose (2DG) autoradiographic method of Kennedy et al. s, has provided new insight into the funcitonal organization of this system. Recent experiments have shown that odor stimulation produces localized sites of activity-related glucose metabolism within the glomerular layer; and that for specific odors, such as amyl acetate and camphor, the autoradiographs reveal overlapping but distinguishable spatial patterns of enhanced uptake, which vary in a systematic fashion with odor concentra*ion14As, 17. In the present study we have extended this technique in order to examine the olfactory bulb of 9-18-day-old rats. There were two main objectives of this undertaking. First, we sought to determine whether the developing olfactory bulb would show localized uptake of 2DG in response to amyl acetate, and whether the topographical pattern of activation was similar to that seen in adults. Secondly, we wished to determine whether a specific pattern would be induced by a behaviorally-significant odor, such as a pheromone. Behavioral studies have shown that olfaction is a dominant sensory modality for nipple attachment by rat pups, and that the nipples are coated by a lipid soluble substance that must be present in order for rat pups to effectively attach to a nipple 14. Removal of this scent by chemical lavage virtually eliminates attachment in pups of all ages, whereas application of a vacuum-distilled extract of the wash fluid fully restores suckling a,19,20. Both behavioral and chemical investigations indicate that this nipple cue satisfies nearly all proposed criteria for a pheromone 2 which acts by directing and permitting nipple attachmenta,vA0,16, ~s-20. We therefore examined the 2DG patterns induced in the olfactory bulbs of rat pups during nipple attachment and suckling. The results have provided evidence for a specific activity site associated with a macroglomerular complex in rat pup olfactory bulb under these conditions.

Current trends in `artificial-nose' technology

Basic principles derived from biological olfaction, such as combining semiselective sensor arrays with pattern recognition, have been used to develop instrumentation capable of broad-band chemical detection and quantification. Commercially available instruments are useful in areas including quality control in the food, beverage and fragrance industries, environmental monitoring, chemical-purity and -mixture analysis, and medical diagnostics. Ongoing research is aimed at the development of more-advanced instruments that are smaller, cheaper, faster and more stable and reliable. These second-generation instruments are likely to find an increasing number of applications, including the on-line monitoring of fermentation and other bioprocesses.

Response patterns of amphibian olfactory bulb neurones to odour stimulation.

1. Responses of 199 single olfactory bulb neurones in the frog were observed with odour stimulation.

Day-night variation in prepro vasoactive intestinal peptide/peptide histidine isoleucine mRNA within the rat suprachiasmatic nucleus☆

Neurons within the suprachiasmatic nuclei of the hypothalamus (SCN) appear to function as a circadian clock that controls the timing of many physiological systems. The SCN contain several chemically distinct neuronal subpopulations, including a large group of interneurons within the ventrolateral SCN that exhibit co-localizable immunoreactivity for both vasoactive intestinal peptide (VIP) and peptide histidine isoleucine (PHI). The purpose of the present study was to determine whether VIP/PHI neurons within the rat SCN exhibit rhythmicity in the cellular levels of the messenger RNA encoding the precursor from which both VIP and PHI are derived. Using both quantitative in situ and solution hybridization prepro-VIP/PHI mRNA levels early in the dark phase were demonstrated to be significantly higher than those 5 h after the onset of the daily light period. Since no statistically reliable (P greater than 0.05) day-night variation was observed in the levels of prepro-VIP/PHI mRNA within cortex, these data suggest that the rhythmicity in prepro-VIP/PHI mRNA is an intrinsic property of VIP/PHI-containing SCN neurons, or rhythmically driven by local synaptic events within the SCN.

Real-time imaging of evoked activity in local circuits of the salamander olfactory bulb

The encoding of olfactory information in the central nervous system (CNS) depends on spatially distributed patterns of activity generated simultaneously in many neuronal circuits11–4. Optical neurophysiological recording permits analysis of neural activity non-invasively and with high spatial and temporal resolution5. Here, a video method for imaging voltage-sensitive dye fluorescence in vivo is used to map neuronal activity in local circuits of the salamander olfactory bulb. The method permits the imaging of simultaneous ensemble transmembrane activity in real time. After electrical stimulation of the olfactory nerve, activity spreads centripetally from the sites of synaptic input to generate non-homogeneous response patterns that are presumably mediated by local circuits within the bulbar layers. The results also show the overlapping temporal sequences of activation of cell groups in each layer. The method thus provides high resolution, sequential video images of the spatial and temporal progression of transmembrane events in neuronal circuits after afferent stimulation and offers the opportunity for studying ensemble events in other brain regions.

Generating Sensor Diversity through Combinatorial Polymer Synthesis

A new approach for rapid, simple generation of uniquely responding sensors for use in polymer-based sensor arrays has been developed. Polymerization reactions between different combinations of two starting materials have been found to lead to many new, unique sensors with responses not simply related to the proportion of the starting materials. This approach is demonstrated in two ways:  (a) the use of discrete polymer sensing cones each comprised of a specific monomer combination and (b) the fabrication of a gradient sensor, containing all combinations between the starting and ending monomer concentrations. Gradient sensors were fabricated using two different binary monomer systems, with both systems showing regions of broadly diverse fluorescence responses to organic vapor pulses.

Odor-elicited activity monitored simultaneously from 124 regions of the salamander olfactory bulb using a voltage-sensitive dye.

In response to controlled, odor pulse stimulation of the olfactory receptor mucosa, large fluorescence signals were recorded simultaneously from 124 contiguous anatomical regions of the salamander olfactory bulb using the potentiometric probe RH 414. The amplitudes and waveforms of the signals varied systematically across the bulbar surface in apparent correspondence with the laminae of the bulbar neurons. Qualitatively similar results were obtained using both intact and decorporate preparations, although fluorescence signals obtained from intact animals were distorted by optical noise generated by mechanical disturbances related to the functioning cardiovascular system. These results indicate that multiple site optical recording can be used to obtain information about spatio-temporal patterning of bulbar electrical activity evoked by physiological odor stimulation of the receptor mucosa. This is the first demonstration that activity elicited by a single, one second odor stimulus at physiological concentration and duration can be measured across many elements in the olfactory bulb. Information provided by this approach, in combination with complementary data derived from 2-deoxyglucose and single unit studies, may yield a better understanding of how the vertebrate central nervous system extracts quality and concentration information from olfactory afferent input.