Figure 4

Neuronal activity in inhibitory, biphasic and excitatory LPeD1 cells and the corresponding activity pattern expressed as 1/interspike interval.

(A) Neuronal electrical activity observed over a 12 hour period of VD4 and LPeD1 cells that responded to acetylcholine with inhibitory, biphasic and excitatory responses. VD4 and LPeD1 neurons were cultured overnight on MEAs in DM and control recordings were obtained in DM followed by CM exposure. The responses of LPeD1 cells to ACh were tested 10 hours following CM addition. Each measure of activity represents the average number of action potentials recorded per a 2 hour period. Note the different responses of LPeD1 cells exposed to CM among the various different LPeD1 phenotypes. Next, to examine activity over an extended period of time, the interspike interval (ISI; time elapsed between two action potentials) was calculated and the inverse of the ISI was taken to give a measure of frequency. Using this protocol, we examined the firing pattern and found that a characteristic of (Bi) excitatory LPeD1 neurons was a progression of activity towards a tightly regulated firing rate of approximately 1 Hz, while the firing frequency of (Bii) inhibitory cells did not undergo this change in pattern and neurons continued to fire at a highly variable rate. After fingerprinting this pattern, we correlated the patterned activity with receptor expression using blinded scoring. It can be seen that (C) excitatory receptor expressions is significantly correlated with patterned activity. Significant differences are denoted with an asterisk (*) and significance is assumed if p < 0.05. Non-significantly different groups were designated with “n.s.”.