Molecular layer interneurons shape the spike activity of cerebellar Purkinje cells

Abstract

Purkinje cells receive synaptic input from several classes of interneurons. Here, we address the roles of inhibitory molecular layer interneurons in establishing Purkinje cell function in vivo. Using conditional genetics approaches in mice, we compare how the lack of stellate cell versus basket cell GABAergic neurotransmission sculpts the firing properties of Purkinje cells. We take advantage of an inducible Ascl1CreER allele to spatially and temporally target the deletion of the vesicular GABA transporter, Vgat, in developing neurons. Selective depletion of basket cell GABAergic neurotransmission increases the frequency of Purkinje cell simple spike firing and decreases the frequency of complex spike firing in adult behaving mice. In contrast, lack of stellate cell communication increases the regularity of Purkinje cell simple spike firing while increasing the frequency of complex spike firing. Our data uncover complementary roles for molecular layer interneurons in shaping the rate and pattern of Purkinje cell activity in vivo.

Purkinje cell neurotransmission patterns cerebellar basket cells into zonal modules that are defined by distinct pinceau sizes

“…To test this hypothesis, we used a genetic fate mapping approach to selectively mark basket cells and specifically to highlight the boundaries of their cell membranes with a conditional reporter (Figure 7). We recently showed that an Ascl1 CreERT2 allele can be used to mark basket cells based on their birth date during late embryogenesis (Brown et al, 2019). Ascl1 , also known as Mash1 , encodes a member of the basic helix-loop-helix (BHLH) family of transcription factors.…”

“…A knock-in allele of CreER into the Ascl1 locus faithfully reports on the differentiation of GABAergic neurons in the cerebellum, and it has a dual function in labeling different subsets of inhibitory neurons at the time of their birth (Sudarov et al, 2011). Here, we crossed the Ascl1 CreERT2 mice to a mouse line that expresses myristoylated GFP (mGFP) in differentiated neurons (Hippenmeyer et al, 2005), but only after recombination is induced upon tamoxifen administration to the mice (Brown et al, 2019). We chose this genetic strategy because oral gavage of tamoxifen to pregnant dams when their embryos are embryonic day (E) 18.5 labels a rich population basket cells with recombination at ∼43% across the entire cerebellum (Brown et al, 2019; the genetic strategy is schematized in Figure 7E), and the mGFP reporter impressively fills the entire axons of even the finest projections in the cerebellum (Sillitoe et al, 2009).…”

“…Here, we crossed the Ascl1 CreERT2 mice to a mouse line that expresses myristoylated GFP (mGFP) in differentiated neurons (Hippenmeyer et al, 2005), but only after recombination is induced upon tamoxifen administration to the mice (Brown et al, 2019). We chose this genetic strategy because oral gavage of tamoxifen to pregnant dams when their embryos are embryonic day (E) 18.5 labels a rich population basket cells with recombination at ∼43% across the entire cerebellum (Brown et al, 2019; the genetic strategy is schematized in Figure 7E), and the mGFP reporter impressively fills the entire axons of even the finest projections in the cerebellum (Sillitoe et al, 2009). After inducing basket cell recombination during development, we followed the marked cells into adulthood to examine their architecture using triple staining with a pan Purkinje cell marker, GFP expression, and a Purkinje cell zone marker.…”

“…More than three decades later, advanced slice electrophysiology recording methods revealed an unexpected ultra-fast ephaptic mode of axon-to-axon communication between basket cells and Purkinje cells (Blot and Barbour, 2014). Accordingly, the collective repertoire of contacts between the two cell types makes a substantial functional contribution, as genetic silencing of GABAergic basket cell output alters Purkinje cell firing in vivo (Brown et al, 2019). There is also evidence showing that basket cells play an essential role in controlling cerebellar cortical output during motor behavior (Barmack and Yakhnitsa, 2008).…”

Morphological pseudotime ordering and fate mapping reveals diversification of cerebellar inhibitory interneurons

“…days and trace their locations and patterns of axon morphogenesis. We used the tamoxifen-inducible Ascl1-CreER line to activate Cre in MLI progenitors at the time of terminal division(Sudarov et al 2011;Brown et al 2019). Consistent with previous studies, tamoxifen (TMX) injection of Ascl1-CreER; Ai4 flox-STOP-TdTomato animals at P0 enriched for the labelling of BCs that innervate the lower ML, while delivery at P4 and P7 marked SC-like cells restricted to the upper ML (…”