Fig. 4
Electrophysiological and immunohistochemical identification of dopaminergic neurons. (A) Representation of in vivo single action potential (average of 20 successive spike traces) from nigral mDA neuron in control mice. The spike was identified as originating from a dopaminergic neuron based on specific properties, including its large biphasic shape, an inflection on the positive phase driven by a Ca2+ conductance, and a prominent negative phase. Moreover, the spike time duration exceeded 2 ms, and its initial phase (from the start to the end of hyperpolarisation) had values greater than 1.1 ms. (B) Scatterplot representing the distribution of total spike (TS), initial spike (IS), and half spike (HS) durations for 20 control mDA neurons (black dots) and 18 grafted mDA neurons (black triangles), along with their respective mean and SD values. Each plot represents the average of 20 successive spike traces. An unpaired t-test with Welch’s correction showed no statistical differences between control mDA and grafted mDA neurons in TS ((t, df) = 1.233, 35.79; p = 0.2257), IS ((t, df) = 0.444, 28.11; p = 0.6605), and HS ((t, df) = 0.5710, 34.07; p = 0.5717). The inset shows an example of the spike waveform recorded from a grafted mDA neuron with the different spike durations (TS, IS, HS). The raw trace represents the average of 20 successive spikes in the recording sequence. (C) Spike shape variability in grafted mDA and control mDA neurons. For each experimental condition, three examples of recorded spike shapes are shown. Different representative variant points are annotated: 1 (post-hyperpolarisation rebound), 2 (notch prominence), 3 (amplitude between depolarisation and hyperpolarisation maxima), and 4 (post-hyperpolarisation duration). (D) Immunolabelling identification of recorded grafted mDA neurons. The image shows the merging of neurobiotin (Nb)-filled recorded grafted mDA neuron (in red), co-expressing HuNu (in blue) and TH (in green). Scale bar: 50 μm