Czesnik D et al. (2003), Neuronal representation of odourants in the olf...

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Eur J Neurosci 2003 Jan 01;171:113-8. doi: 10.1046/j.1460-9568.2003.02448.x.

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Neuronal representation of odourants in the olfactory bulb of Xenopus laevis tadpoles.

Czesnik D , Rössler W , Kirchner F , Gennerich A , Schild D .

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When an odourant enters the nose, olfactory receptor neurons (ORNs) convey information about it to the olfactory bulb (OB), where this information is processed and where the first central representations of the odourant are generated. In this paper we show how odourants are represented by ensembles of OB neurons, in particular mitral cells (MCs) which are the output neurons of the OB. We were able to demonstrate for the first time that the intracellular calcium concentrations ([Ca2+]i) in the somata of these neurons undergo specific changes and that different stimuli are represented by different neuronal [Ca2+]i patterns. The similarity of patterns was assessed by cross-correlation analysis. We further show that noradrenaline (NA), which is reported to be involved in olfactory memory formation and to modulate synaptic transmission at dendrodendritic synapses in the OB, profoundly changes the representation of odourants at the level of MCs.

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Species referenced: Xenopus laevis
Genes referenced: fh gabarap syp

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	FIG. 1. Brain slice preparation including the olfactory epithelia (OE), the olfactory bulbs (OB) and the brain of Xenopus laevis tadpoles. (A) Xenopus laevis tadpole. The black rectangle indicates the block of tissue that was cut out for the experiments. (B) Higher magnification of the anterior part of the noseâ€“brain preparation showing the OB with the top sliced open, the olfactory epithelia, and the olfactory nerves (ON). (C) OB double labelled with an antibody to synaptophysin (green) and propidium iodide (red) showing the glomerular layer (GL) and the organization of cell nuclei in the mitral (MCL) and granule (GCL) cell layers. MOB, main OB; AOB, accessory OB. Scale bars, 1.5mm (A), 750 mm (B), 200 mM (C).
	FIG. 2. Imaging of changes in somatic [Ca2Ã¾]i in OB neurons reveals spatial and temporal patterns of cells activated in response to stimulation with natural odourants. (A) Fluorescence of neuronal cell bodies (F380) loaded with Fura- 2. The white box indicates the region imaged. N, nerve layer, MOB, main OB; MCL, mitral cell layer; GCL, granule cell layer; V, ventricle; AOB, accessory OB (for comparison, see Fig. 1C). The dotted lines indicate the borders of the mitral and granule cell layers, the ventricle, and the AOB. (B) Ratio image R of the selected region of interest. (CâH) [Ca2Ã¾]i activation patterns in response to stimulation with methionine (100 mM) at different times (in s) before, during and after odourant application. The stimulus was applied at tÂ¼22 s for 7 s. The delta ratio, DR(t)Â¼R(t)Ro, highlights the changes in [Ca2Ã¾]i. Green spots indicate neuronal cell bodies showing an increase in [Ca2Ã¾]i whereas red indicates a decrease in [Ca2Ã¾]i. For better orientation, the response patterns are superimposed on the first ratio image.
	FIG. 3. Time courses of increasing or decreasing [Ca2Ã¾]i respones imaged in single neuronal cell bodies within the mitral cell layer. (AâC and E) Examples of an increase in [Ca2Ã¾]i. (D) A cell responding with a decrease in [Ca2Ã¾]i. The corresponding cell bodies are indicated in Fig. 2D. The horizontal bar indicates the time and duration of methionine application (100 mM). Scale bars, tÂ¼10 s, DRÂ¼0.05.
	FIG. 4. Responses to repeated olfactory stimulation with the same odour (methionine, 100 mM). Similar [Ca2Ã¾]i time courses of cell 1, 2 and 3. Cell 4 showed a large [Ca2Ã¾]i excursion in one of three trials. This [Ca2Ã¾]i transient started prior to stimulus application and was thus uncorrelated to it. Scale bars, tÂ¼10 s, DRÂ¼0.1.
	FIG. 5. Responses to repeated olfactory stimulation with the same odour. (A and B) [Ca2Ã¾]i activation patterns in response to two stimulations with methionine (100 mM). The time interval between the stimulations was 8 min.
	FIG. 6. Olfactory stimulation with different amino acids give rise to different [Ca2Ã¾]i response patterns of OB neuron somata. [Ca2Ã¾]i activation pattern in response to stimulation with (A) methionine (met, 100 mM), (B) leucine (leu, 100 mM), (C) histidine (his, 100 mM) and (D), arginine (arg, 100 mM). All patterns are shown at the time of maximum activation.
	FIG. 7. Olfactory stimulations of different concentrations of stimuli of the same odour lead to different patterns. (A) [Ca2Ã¾]i activation patterns in response to stimulation with methionine (50 mM); (B) [Ca2Ã¾]i activation patterns in response to stimulation with methionine (100 mM); (C) [Ca2Ã¾]i activation patterns in response to stimulation with methionine (200 mM).
	FIG. 8. The GABAA receptor antagonist picrotoxin (PicTx) alters neuronal activation patterns in response to olfactory stimulation with amino acids. (A) [Ca2Ã¾]i activation pattern in response to olfactory stimulation with histidine (100 mM) before and (C) after application of PicTx (100 mM). (B) [Ca2Ã¾]i activation pattern in response to a mixture of 15 amino acids (mix, 100 mM each) before and (D) after application of PicTx (100 mM). All patterns are shown at the time of maximum activation.
	FIG. 9. The a2-receptor agonists aMeNA modulates lateral inhibition of odour-induced activation in OB neurons. (A) [Ca2Ã¾]i activation pattern in response to stimulation with arginine (100 mM) before and (B) after application of aMeNA (10 mM). All patterns are shown at the time of maximum activation of neurons.
	FIG. 10. Olfactory stimulation of both the left and the right olfactory epithelium and resulting activity patterns in the olfactory bulbs. (A and B) Left OB, [Ca2Ã¾]i activation patterns in response to stimulation with mix of amino acids (A, 100 mM) and with methionine (B, 100 mM). (C and D) Right OB, [Ca2Ã¾]i activation patterns in response to stimulation with mix of amino acids (C, 100 mM) and with methionine (D, 100 mM).