Givaudan-Roure Lecture - Association for Chemoreception Sciences

5 Slide [ ] Olfactory Bulb Physiology
MAIN OLFACTORY BULB DETECTION OF SOCIAL
RECOGNITION CUES IN MOUSE URINE
Lin D. 1, Katz L.C. 1 1Neurobiology, Duke University, Durham, NC
In rodents, chemicals present in urine play a critical role in
reproductive behaviors and mediating aggressive interactions. Both
behavioral tests and immediate early gene expression indicate that the
main olfactory bulb (MOB) participates in individual identification.
Little is known about how urine responsive neurons are organized in the
MOB, or which semiochemicals in urine carry important information.
To address these issues, we examined extracellular activity of mitral
cells in the mouse MOB in response to volatile components of urine
from different sexes and strains of mice. Recordings from more than
one thousand cells revealed that less than 5% of neurons responded
selectively to different sources of urine. The urine responsive cells were
confined to a small region in the ventral and lateral parts of the MOB.
To ascribe a role to specific chemicals present in urine, we combined
gas chromatography with extracellular recording in the MOB, so that
the activity of individual mitral cells could be monitored while
delivering the separated urinary components. The majority of neurons
which showed an excitatory response to complete urine responded
identically to just a single peak out of the hundreds present in the gas
chromatogram of mouse urine. Surprisingly, over 20% of the urine
responsive cells responded to one particular component, which has been
implicated as a mouse pheromone. Preliminary behavioral data indicate
the concentration of this pheromone in male mouse urine significantly
correlates with the duration of female mice investigation of the urine.
Thus, mitral cells selectively respond to individual components in
mouse urine, and a disproportionate number of these neurons are
involved in detecting a volatile pheromone.
6 Slide [ ] Olfactory Bulb Physiology
SPATIO-TEMPORAL FIRING RATE INTERACTIONS
AMONGST AN ENSEMBLE OF MITRAL/TUFTED CELLS
MAY SUBSERVE ODORANT DISCRIMINATIONS.
Lehmkuhle M.J. 1, Normann R.A. 1, Maynard E.M. 1 1Bioengineering,
University of Utah, Salt Lake City, UT
Populations of output neurons in the mammalian olfactory bulb (OB)
exhibit distinct spatial and temporal activation patterns when stimulated
with enantiomers of the same odorant. If, as has recently been
suggested, a two-stage network of inhibitory and excitatory centersurround
connections link spatially distributed glomerular activity with
underlying mitral and tufted neurons within olfactory bulb, then it is
likely that these interactions affect the ensemble response to odorant
stimulation. Here we investigate in the anesthetized rat the rate
response temporal kinetics in neuronal ensembles by comparing pairwise
response similarity of a population of single- and multi-unit
mitral/tufted cells aligned to breathing in the presence and absence of
enantiomers of limonene. Such comparisons can be used to quantify
differences in the kinetics of the response of one neuron from other
neurons in the recorded population. It is shown that aligning unit
responses to the inhalation phase of the animals´ breathing tends to
synchronize unit responses. Instances of high-similarity and
dissimilarity within the population are enantiomer-specific with these
instances occurring for pairs of units recorded over electrode
separations of 400 µm – 1.7 mm. These results support the centersurround
hypothesis and indicate that spatio-temporal firing rate
interactions amongst an ensemble of OB neurons produce odorant
representations beyond simple firing rates that may subserve odorant
discrimination.
2
7 Slide [ ] Olfactory Bulb Physiology
PRESYNAPTIC CENTER-SURROUND INHIBITION SHAPES
ODORANT-ELICITED INPUT TO THE MOUSE OLFACTORY
BULB
Vucinic D. 1, Cohen L.B. 1, Kosmidis E. 1 1Cellular & Molecular
Physiology, Yale University, New Haven, CT
Synaptic transmission from olfactory primary afferents onto neurons
of the olfactory bulb is modulated by presynaptic GABA receptors
B
(e.g. Wachowiak and Cohen, 1999; Ennis et al., 2001; Wachowiak et
al., 2002). To study the role of this modulatory circuit in vivo we
recorded the fluorescent signal from Calcium Green-1 dextran, loaded
into the axon terminals of olfactory receptor neurons, in response to
odorant presentations to the nose. We bath-applied agonists and
antagonists of the GABA receptor onto the olfactory bulb and looked
B
for an effect of these agents on the amplitude, spatial map and time
course of odorant-elicited signals. The GABA antagonist CGP46381
B
caused a significant and long-lasting increse in the average amplitude of
glomerular activation in most preparations. Large changes in signal
amplitude were accompanied by a change in the input map such that
many weakly activated glomeruli underwent relatively larger increases
in signal amplitude than the strongy activated ones. We find that the
magnitude of this effect correlates with how strongly activated the
surround of a glomerulus is. This finding indicates that a form of
GABA-mediated center-surround inhibition modifies the sensory input
map even before the first synaptic transmission, increasing its contrast.
Supported by NIH grants NS07455 and DC05259.
8 Slide [ ] Olfactory Bulb Physiology
LONG-TERM ODOR EXPOSURE INCREASES SURVIVAL
AND FUNCTIONAL INTEGRATION OF INTERNEURONS IN
THE OLFACTORY BULB.
Mirich J. 1, Illig K.R. 1, Brunjes P.C. 1 1Psychology, University of
Virginia, Charlottesville, VA
While our previous work indicates that activity is critical for the
survival of bulbar interneurons, the rules by which new neurons become
integrated into existing neural circuits remain unclear. If olfactory
activity guides the functional integration and survival of newly born
cells, then repeated exposure to an odorant should increase the number
of cells that participate in the coding of that odor. Adult subjects
received daily injections of BrdU for 5 days to label a cohort of newly
born neurons. They were then exposed daily to menthyl isovalerate, ßpinene,
butyric acid, or mineral oil (control) for 3 weeks. For half of the
animals in each group, the odorant was paired with Froot Loops to
increase salience. On the last day, animals were exposed to ultra-pure
odorants intermittently for 1hr, and tissue stained for BrdU and Fos
protein. Long-term odor exposure doubled the survival of interneurons
compared with controls. Double-label immunohistochemistry showed a
statistically significant increase (44%; p < 0.05) in BrdU/Fos positive
cells, demonstrating integration of newly born cells during the training
period. Additional analyses confirmed that new neurons integrated
specifically into the areas of the bulb activated by the odorant
presented. This study demonstrates that survival and integration of
newly born bulbar neurons depends on the odor environment present
during their development. We conclude that repeated activation of
synaptic ensembles might change neural requirements, thereby
influencing the cellular milieu. Supported by NIH grants DC0338
(NIDCD) and HD07323 (NICHD).