Investigation of the Interglomerular Lateral Inhibition in Rat Olfactory Bulb

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Investigation of the Interglomerular Lateral Inhibition in Rat Olfactory Bulb

The study investigated the presence and the mechanism of lateral inhibition between glomeruli in the rat olfactory bulb. Therefore, slices of olfactory bulb were prepared to analyze the inhibitory effects of nearby glomeruli. As control, the olfactory sensory neurons in a glomerulus were stimulated by an electrical stimulus. Afterwards, nearby glomeruli were stimulated by photoactivated glutamate release, using a 355 nm DPSL-355/30 laser (Rapp OptoElectronic) coupled to a Rapp OptoElectronic UGA-40 scanner based point illumination system. After this "conditioning" stimulus, the response of the initial glomerulus to the electrical stimulus was tested again to quantify lateral inhibitory effects. With this technique, it was demonstrated that conditioning stimuli applied to one or more glomeruli can suppress the stimulus-evoked excitation of mitral cells at other glomeruli located as far as 600 µ away.

 

Setup:

 

  • Zeiss Axioscope FS2 with a 40x water-immersion objective
  • Multiclamp 700B amplifier (Molecular Devices)

 

Rapp OptoElectronic components:

 

  • System:          UGA-40 (externally triggered via TTL)
  • Light source:   DPSL 355/30 (355 nm, 30 mW)
  • Optical fibre:   ø 200 µm (multimode)
  • Approx. 35 µm spot size on the sample @ 40x magnification

 

Techniques:

 

  • Slice preparation of olfactory bulb
  • Glutamate uncaging (MNI caged glutamate)
  • Patch clamp recording

 

 

 

Figure 1: Glutamate uncaging evokes lateral inhibitory postsynaptic currents (IPSCs) in external tufted (ET) cells, but in not mitral cells (MCs).  

A. Experimental design: IPSCs in MCs and ET cells were recorded in response to glutamate uncaging at a distant glomerulus (gray circle; recordings done in 100 µM MNI-glutamate, 35-µm-diameter laser spot). The uncaged glutamate can excite short axon cells in the conditioning glomerulus that project to the test glomerulus. MC recordings were done in slices with a cut through the external plexiform layer to isolate glomerular layer inhibition.  

B. Example of current recordings: (Vhold = -7 mV), showing an evoked IPSC in an ET cell (left), but not the MC (right). Three representative trials are shown at top, and averages are at bottom. The open bars below the averaged traces indicate the 100 ms laser pulse. The evoked IPSC in the ET cell occurred with a delay of ~30 ms following the start of the laser pulse, presumably reflecting the time it takes for glutamate to accumulate and activate SA cells at the conditioning glomerulus, either directly or via a polysynaptic mechanism. (Whitesell et al. 2013)

 

Data from Whitesell et al. (2013), J. Neurosci. 33, pp 1552-1563, DOI: 10.1523/JNEUROSCI.3410-12.2013

 
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