Biomedical Engineering Reference
In-Depth Information
Fig. 3.5. Comparison of Vm and [Ca
2
+
]
i
signals from same dendritic locations. (
A
) A composite image of a neuron
(voltage-sensitive dye excitation). (
B
) Low resolution images (bis-fura-2 excitation) of the dendritic arbor in recording
position. Representative recording locations marked by white ovals; the position of the extracellular electrode shown
schematically. (
C
)Vmsignalsand[Ca
2
+
]
i
signals related to backpropagated action potentials (bAP, gray traces), EPSP
train (dashed traces, shown only for [Ca
2
+
]
i
signals), and paired EPSP-AP activity (dark traces). Vm signals (100 ms)
during paired activity are superimposed with the recordings of bAP signals alone. Calcium recordings (400 ms) are
shown above Vm traces - signals during three stimulation protocols (bAPs, EPSP train, paired) are superimposed. (
D
)Vm
recordings of bAPs on the expanded time scale superimposed on the same baseline to show region-specific changes
in the peak membrane depolarization during paired activity (upper traces). Traces are shifted horizontally with respect
to each other for clarity. Lower traces: The first spike signals (unpaired and paired) aligned to indicate the difference in
baseline-to-peak amplitude (EPSP signal subtracted).
APs (
Fig. 3.5C
; middle set of traces). At the same time, a dra-
matic reduction in the baseline-to-peak local AP amplitude was
observed during the paired stimulation. The reduction in the size
of the backpropagated AP during paired activity is illustrated in
Fig. 3.5D
. The spike signals corresponding to backpropagated
APs evoked alone and during paired activity are superimposed on
the baseline membrane potential before the EPSP train (upper
traces) and on the baseline membrane potential immediately pre-
ceding the spikes evoked during the last two EPSPs in a train
(lower traces). Clearly, a supralinear increase in [Ca
2
+
]
i
that serves
as a trigger for LTP induction did not require boosting in bAP
baseline-to-peak amplitude. This initial result was followed by a
series of experiments carried out to characterize the relationship
between electrical signals and related [Ca
2
+
]
i
transients during
