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Biomedical subjects

M Leon

Publications and source records attributed to M Leon.

At least 145 records · Page 8Linked to original sources
PubMed1987

Evidence of lateral synaptic interactions in olfactory bulb output cell responses to odors.

Lateral inhibitory circuits are found throughout the nervous system. While the neuroanatomical basis for lateral inhibitory interactions exists in the olfactory bulb of Norway rats, there has been no direct demonstration of lateral inhibition in the responses of olfactory bulb output neurons to odor stimulation. In this report we recorded the extracellular activity of a large number of sequentially recorded mitral/tufted cells in response to odor stimuli at two different concentrations, as well as the inter-cell distance between these cells. The probability of recording two cells with excitatory responses to the same odor was then determined for inter-cell distances up to 500 microns. For cells stimulated with high concentration odors, the probability of two cells 100-200 microns apart both being excited by the same odor was significantly lower than that predicted if all cells responded independently. Cells separated by greater or shorter inter-cell distances did not differ from the predicted value. Responses to the low odor concentration were not dependent on inter-cell distance. These results demonstrate that lateral synaptic interactions within the olfactory bulb influence output cell responses to odor stimulation.

Animals↗
PubMed1987

Glycogen phosphorylase activity in the olfactory bulb of the young rat.

The activity of glycogen phosphorylase, the enzyme that controls glycogen breakdown, was histochemically mapped in the olfactory bulbs of 19-day-old rats. The effect of early odor experience on subsequent olfactory bulb phosphorylase activity was also examined. The highest level of phosphorylase staining in the bulb (and seemingly the highest in the brain) was in the glomerular layer, followed by the external plexiform, internal plexiform, granule cell, and olfactory nerve layers. Virtually no activity was visible in the large output neurons of the bulb, mitral, and tufted cells. Early peppermint odor experience, previously shown to increase metabolic activity in specific glomerular foci as measured by 2-deoxyglucose uptake, had no apparent effect on glomerular-layer phosphorylase activity. In some odor-familiar animals, however, patches of activity were seen in the internal plexiform layer in the area of the bulb where foci of high deoxyglucose uptake are seen in response to peppermint. The patches were directly in line with modified glomerular clusters often seen to underlie foci of enhanced deoxyglucose uptake. The existence of particularly heavy activity in the peripheral third of the glomerular layer, where glycogen-containing modified Schwann cells have been localized, raises the possibility that the glomerular-layer activity is at least partially glial in origin. Finally, because of its rich noradrenaline and serotonin innervation and high density of insulin receptors, the olfactory bulb is proposed as a model system to study the interaction of glycogen/glucose metabolism with neural activity in a relatively well-defined neuronal circuit.

Age Factors↗
PubMed1987

One-trial olfactory learning enhances olfactory bulb responses to an appetitive conditioned odor in 7-day-old rats.

The expression of a conditioned odor preference and focal uptake of [14C]2-deoxyglucose (2-DG) within the olfactory bulb was assessed in neonatal rat pups that had undergone a single olfactory classical conditioning trial. At 6 days of age, rat pups were simultaneously exposed for 10 min to an odor (peppermint) and to a reinforcing tactile stimulation similar to that received from the dam. Three control groups received only the odor, only the stimulation, or neither of these stimuli. The next day, pups were either assessed for differential olfactory bulb activity using the 2-DG technique or tested for their olfactory preference behavior. Only pups that received simultaneous odor and tactile stimulation exhibited an attraction to the conditioned odor in the two-odor choice test. Furthermore, such pups had greater focal 2-DG uptake in the olfactory bulb glomeruli that were responsive to the odor than pups in all other groups. Thus, the olfactory bulb responds differentially to an odor which has acquired attractive value.

Age Factors↗
PubMed1987

Abrupt decrease in synaptic inhibition in the postnatal rat olfactory bulb.

Olfactory bulb responses to paired-pulse stimulation of the lateral olfactory tract were examined in urethane-anesthetized rats, aged 5 days to adult. Brief inter-pulse intervals resulted in a depression of test responses at all ages. The magnitude of this depression decreased dramatically between postnatal days 19 and 20 to approach adult levels. Longer inter-pulse intervals resulted in a facilitation of test response amplitude in adult animals. This facilitation was evident at adult levels by postnatal day 10. These results suggest that both inhibitory and facilitatory synaptic mechanisms appear early in the course of rat olfactory bulb development. Furthermore, presumed granule cell-mediated inhibition is present at unusually high levels in the developing bulb, decreasing sharply between days 19 and 20.

Aging↗
PubMed1987

Single-unit analysis of postnatal olfactory learning: modified olfactory bulb output response patterns to learned attractive odors.

Neonatal rats learn to approach odors associated with stimulation normally provided by their mother. The present report describes changes in olfactory bulb single-unit activity following olfactory learning in young rats. Rat pups were exposed from postnatal day 1 to 18 to either (1) peppermint-scented air while receiving tactile stimulation (Pepp-Stroked), (2) peppermint-scented air with no tactile stimulation (Pepp-Only), (3) clean air and tactile stimulation (Stroked-Only), or (4) clean air and no tactile stimulation (Naive). On day 19, single-unit activity was recorded from mitral/tufted cells in urethane-anesthetized, freely breathing pups in response to either peppermint or a novel orange odor. Mitral/tufted cell response patterns to peppermint were significantly altered in Pepp-Stroked animals compared to control pups. Peppermint exposure alone, not associated with tactile stimulation (Pepp-Only), did not affect subsequent single-cell response patterns to that odor. In addition, the modification of response patterns was specific to peppermint and was not associated with a change in respiration rate. Furthermore, Pepp-Stroked pups had a relative behavioral preference for peppermint on day 19 compared to control pups. These results demonstrate that postnatal olfactory learning selectively modifies the subsequent response patterns of olfactory bulb output cells to the attractive odor. Furthermore, these results indicate that the initial coding of an odor's attractive value occurs within the olfactory bulb.

Animals↗
PubMed1986

Enhanced neural response by adult rats to odors experienced early in life.

The enhanced olfactory bulb neural response to familiar odors by young rats persists into adulthood. Ninety-day-old rats who had received neonatal odor exposure had an enhanced uptake of [14C]2-deoxyglucose (2-DG) when exposed to the familiar odor. The odor-familiar rats did not have an increased respiration rate during the 2-DG test. A long-lasting change in neuronal response is consistent with the observation of behavioral effects of early odor experience persisting into adulthood.

Aging↗
PubMed1986

Metabolic strategies of pallid bats (Antrozous pallidus) during reproduction.

Both lactating and non-lactating pallid bats defend a high body temperature in a cool ambient temperature during the summer months by increasing their metabolism. Metabolism decreased between August and September in captive females maintained under constant conditions and melatonin implants accelerated this shift from homeothermy to heterothermy. There appears to be an endogenous change in metabolism which can be accelerated by a rise in circulating melatonin levels.

Animals↗
PubMed1986

Endocrine response to acute cold exposure by lactating and non-lactating Norway rats.

Plasma levels of corticosterone, prolactin and thyroxine (T4) were measured in lactating and non-lactating Norway rats at 22 degrees C and 4 degrees C. Acute cold exposure increased corticosterone secretion in all groups, although non-lactating female levels rose higher than those of mother rats. While prolactin levels are unaffected by acute cold exposure in non-lactating females, mothers with their litters had lower prolactin levels in the cold. T4 levels increased during cold exposure in lactating females, suggesting that the low T4 levels observed during lactation may not be due to lactational competition for available iodine.

Animals↗
PubMed1986

Thermal control of mother-young contact in Norway rats: factors mediating the chronic elevation of maternal temperature.

The chronically elevated heat production of lactating Norway rats makes them vulnerable to acute hyperthermia during pup contact and thereby limits the duration of such interactions. High lactational levels of progesterone and corticosterone may act in concert to increase maternal heat load. Specifically, progesterone appears to increase maternal thermal set point and corticosterone is necessary for the increase in maternal heat production. Thyroid hormones and brown adipose tissue do not seem to contribute to the chronic increase in maternal heat production. While mammary tissue does contribute to maternal heat load, it is no more hypermetabolic than other maternal tissues.

Adipose Tissue, Brown↗
PubMed1986

Olfactory bulb responses after odor aversion learning by young rats.

The increased olfactory bulb response by young rats to familiar odors was not observed in response to odors which have attained their familiarity in aversive situations. Odor experience associated with toxicosis induced a behavioral aversion to the odor which was not accompanied by the enhanced uptake of [14C]2-deoxyglucose (2-DG) that accompanies attractive familiar odors. A single odor exposure on day 17 was sufficient to induce a small increase in 2-DG uptake in specific glomerular areas. We hypothesize that a different neural substrate underlies familiarity associated with an aversive odor than that associated with an attractive odor.

Aging↗
PubMed1986

Odor specificity of the enhanced neural response following early odor experience in rats.

The enhanced neural response in the olfactory bulbs of rat pups following early olfactory experience is specific to the familiar odor. Pups were exposed daily to either peppermint or cyclohexanone odor for the first 18 postnatal days. On day 19, peppermint-familiar pups exposed to peppermint had significantly higher [14C]2-deoxyglucose (2-DG) uptake in a focal glomerular area compared with the response to peppermint by cyclohexanone-familiar pups. We also found that cyclohexanone-experienced pups had a subsequent enhanced response to cyclohexanone odor in glomerular areas medial and caudal to those responding to peppermint. None of the 2-DG uptake differences were attributable to respiration differences between the groups during any part of the odor test.

Animals↗
PubMed1986

Early olfactory learning induces an enhanced olfactory bulb response in young rats.

During postnatal days 1-18, pups were simultaneously exposed to an odor and reinforcing tactile stimulation similar to that normally received from the dam. Control pups received only the odor, only the stimulation, or neither of these stimuli. On postnatal day 19, pups that had previously received simultaneous odor and tactile stimulation displayed both a behavioral odor preference and an enhanced 2-deoxyglucose uptake in specific olfactory bulb glomeruli to subsequent presentation of that odor. These results suggest that early olfactory learning enhances the neural response to odors that have acquired attractive value.

Animals↗
PubMed1986

Early appearance of inhibition in the neonatal rat olfactory bulb.

The functional development of inhibition in the rat olfactory bulb was examined in the present study. Inhibition of presumed mitral cell spontaneous activity following stimulation of the lateral olfactory tract was present by postnatal day 5, the youngest age tested. The duration of this inhibition was greatest in young animals, decreasing after postnatal day 15. Possible mechanisms of this enhanced inhibition in neonates were discussed.

Action Potentials↗