Non-linear developmental trajectory of electrical phenotype in rat substantia nigra pars compacta dopaminergic neurons

Abstract

Neurons have complex electrophysiological properties, however, it is often difficult to determine which properties are the most relevant to neuronal function. By combining current-clamp measurements of electrophysiological properties with multi-variate analysis (hierarchical clustering, principal component analysis), we were able to characterize the postnatal development of substantia nigra dopaminergic neurons' electrical phenotype in an unbiased manner, such that subtle changes in phenotype could be analyzed. We show that the intrinsic electrical phenotype of these neurons follows a non-linear trajectory reaching maturity by postnatal day 14, with two developmental transitions occurring between postnatal days 3–5 and 9–11. This approach also predicted which parameters play a critical role in phenotypic variation, enabling us to determine (using pharmacology, dynamic-clamp) that changes in the leak, sodium and calcium-activated potassium currents are central to these two developmental transitions. This analysis enables an unbiased definition of neuronal type/phenotype that is applicable to a range of research questions.DOI: http://dx.doi.org/10.7554/eLife.04059.001

Robustness to Axon Initial Segment Variation Is Explained by Somatodendritic Excitability in Rat Substantia Nigra Dopaminergic Neurons

“…3 D, E). Consistent with previous observations (Amendola et al, 2012;Dufour et al, 2014), both AP amplitude and AP halfwidth displayed significant cell-to-cell variability, ranging from 48 to 78 mV (mean ϭ 62 Ϯ 7.2 mV, n ϭ 54) and 0.9 to 1.8 ms (mean ϭ 1.3 Ϯ 0.2 ms, n ϭ 54), respectively, but were not correlated ( Fig. 3D).…”

“…Recordings were obtained from coronal midbrain slices in the presence of synaptic blockers (picrotoxin and kynurenate) to isolate intrinsically generated activity. Recordings and reconstructions were performed on P19-P21 rats (mean age ϭ P20), as both electrophysiological properties and morphological features have been described to reach a mature stage by the end of the second postnatal week (Tepper et al, 1994;Dufour et al, 2014). Although the axon of SNc DA neurons has been previously identified based on its (1) absence of spines, (2) small diameter, and (3) angle of branching from dendrite (Häusser et al, 1995), we performed ankyrinG immunostainings on every recorded neuron to unambiguously identify the axon (Fig.…”

Female mice are resilient to age-related decline of substantia nigra dopamine neuron firing parameters

“…Dopamine neurons were identified in the ventral half of the SN of coronal midbrain slices based on their large cell bodies, characteristic slow firing rate (<7Hz) (Grace & Onn, 1989) and the presence of a large voltage sag as a result of the hyperpolarization-activated cation current, IH (Dufour, Woodhouse, Amendola, & Goaillard, 2014). Recorded cells were also filled with neurobiotin to confirm their dopaminergic identity through post hoc immunostaining for tyrosine hydroxylase (TH), the rate limiting enzyme of dopamine synthesis (Dufour et al, 2014;Fig 1A).…”

Information topology of gene expression profile in dopaminergic neurons

“…All recordings were performed as already described previously 33 . Picrotoxin and Kynurenate were present for all recordings to prevent contamination of the intrinsic activity by spontaneous glutamatergic and GABAergic synaptic activity.…”