Book of abstracts - British Neuroscience Association

31.03
Dopaminergic modulation of spinal neuronal excitability
Han P, Michelle A. Tran, Whelan P J
Rm 2068 Hotchkiss Brain Institute, University of Calgary, 3330
Hospital Drive,NW,Calgary, AB T2N4N1,CANADA
Although dopamine is well known to play a role in motor control it is
generally assumed that dopamine does not directly modulate spinal
motor circuits. However, in recent years several studies have
demonstrated a modulatory action of dopamine on spinal networks
and reflexes. DA fibres and receptors are present in the spinal cord
and evidence for DA release within the spinal cord has been
published. A critical gap is our lack of data regarding dopaminergic
modulation of intrinsic and synaptic properties of motoneurons and
ventral interneurons in the mammalian spinal cord. In this study, we
address this issue by examining the intracellular mechanisms
underlying DA’s excitatory effect on motor systems. We examine DA’s
effects on two classes of cells important for motor control,
motoneurons and Hb9 interneurons located in lamina VIII. We show
that DA can boost excitability in spinal motor systems by decreasing
the first spike latency and the AHP. Collectively, this leads to an
increase in the F-I slope. Our data suggest that these changes are
due to modulation of IA and SKCa currents. We also demonstrate that
DA modulates glutamatergic transmission by increasing both the
amplitude and frequency of miniature and spontaneous excitatory
postsynaptic currents suggesting that DA acts both pre and
postsynaptically. Collectively these data suggest that DA has
widespread actions on intrinsic and synaptic properties of spinal
neurons consistent with its ability to modulate and stabilize spinal
networks. In addition, dopaminergic therapy may provide promising
perspectives on spinal cord rehabilitation.
32.01
Stimulus timing-dependent plasticity in the adult auditory system
Dahmen J, Ahmed B, Hartley D E H, King A J
Department of Physiology, Anatomy and Genetics, Sherrington Building,
University of Oxford, Parks Road, Oxford OX1 3PT
Adult cortical circuits possess considerable plasticity over different time
scales, which can be induced by conditioning or task-specific training. For
instance, it has been shown that repetitive pairing of stimuli that differ either
in their orientation (Yao and Dan, 2001, Neuron 32:315-323) or location in
space (Fu et al., 2002, Science 296:1999-2003) can induce rapid shifts in
the orientation tuning and receptive field location, respectively, of neurons
in the primary visual cortex. The direction of those shifts was found to
depend on the order of stimulus presentation, while their magnitude
depended on the interval between the stimuli in each pair, with intervals
larger than about 20 ms being ineffective. This is consistent with the
temporal window of spike timing-dependent synaptic plasticity. To examine
whether stimulus timing-dependent plasticity also exists in the auditory
system, we recorded from neurons in primary auditory cortex of
anaesthetized adult ferrets. Presentation of ≥600 pairs of tones that differed
in frequency resulted in shifts in the best frequencies of the neurons. These
shifts were observed when stimulus onset asynchronies of up to 12 ms
were used and their direction depended on the order in which the tones in a
pair were presented. The shifts in frequency tuning persisted for several
minutes and appeared to be most pronounced in the supragranular layers
of the cortex. These data show that stimulus timing-dependent plasticity is
a property of the auditory cortex and exhibits a temporal specificity similar
to that observed in the visual system.
32.02
Regulation of CSPG expression in the developing barrel cortex
A Petrie, Matthews R L, Kind P C
1 & 3, University of Edinburgh,, Hugh Robson Building,, George
Square,, Edinburgh,, EH8 9XD,, 2, SUNY Upstate medical University,
New York
Chondroitin-sulphate proteoglycans (CSPGs) are a principle
component of the extracellular matrix (ECM) of the CNS. In adult
animals, CSPGs appears to restrict plasticity induced by monocular
deprivation (Pizzorusso et al 2002) and the expression of aggrecan, a
principle CSPG in adult brain, correlates well with the termination of
developmental plasticity (Sur et al 1988). Aggrecan localises to
perineuronal nets, a specialised ECM that surrounds soma and
proximal dendrites. We have used Cat-315, an antibody that labels an
epitope on aggrecan (Lander et al, 1997), to examine the role of this
molecule in cortical development. In mouse neocortex, staining
increases through development and, in adults, is highest in primary
somatosensory cortex (S1), retrosplenial cortex and motor cortex. In
S1, staining appears as two distinct bands of labelled soma, one
through layer 4 and the other through lower layer 5 and layer 6.
Staining with Cat-315 of tangential sections shows an intense staining
in a barrel-like pattern in S1.
We have previously shown that mGluR5 signalling via PLC-b1
regulates barrel formation. Aggrecan expression is known to be
dependent on synaptic activity (Sur et al., 1988; Kind et al., 1995)
raising the possibility that mGluR5 may regulate aggrecan expression.
To determine whether mGluR5 signalling via PLC- b1 also regulates
aggrecan expression we investigated Cat-315 expression in Mglur5-/-
and Plc-b1-/- mice. Qualitative assessment of Mglur5-/- show fewer
Cat-315 immunopositive cells and staining at a lower intensity than
Mglur5+/+, indicating mGluR5 may regulate the formation of
perineuronal nets in barrel cortex.
33.01
Space-Time Spike triggered covariance analysis of fly motion
selective neuron
Saleem A, Schultz S R
Department of Bioengineering,, Imperial College London,, UK SW7 2AZ
The H1 neuron of the fly lobula plate has been widely studied with an
interest to understand the motion detection systems of the visual system.
Most properties of H1 have been studied in the steady state through tuning
curve functions of the cells, which assume separability of the response
properties along the different dimensions. The spike triggered covariance
(STC) analysis of these cells avoids this. STC in the velocity-time domain is
also limited as it assumes velocity tuning of a neuron that is known to be
temporal frequency tuned. We carry out STC in the space-time domain,
thus making fewer assumptions about the properties of the cells.
We recorded extracellular activity of the H1 cells of blowflies while
presenting a bar stimulus: the contrasts of the bars changing as ternary
noise. We carry out STC analysis on this data. We recovered the spacetime
receptive fields of the cell. These show a temporal frequency tuning of
about 120 cycles/deg, which matches previous studies. We also observe
that the cell responds to changes is position that are within 8msec. We
recovered spatially separated excitatory and suppressive filters. We also
recovered the non-linear stage of a stochastic linear-nonlinear model of the
cell. We present a complete model of the cell recovered from the data.
The space-time STC analysis has been used to build models of cells in the
MT/V5 of the primate visual cortex, and hence we can directly compare our
results between the two systems.
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