Endocannabinoid signaling controls pyramidal cell specification and long-range axon patterning

Abstract

Endocannabinoids (eCBs) have recently been identified as axon guidance cues shaping the connectivity of local GABAergic interneurons in the developing cerebrum. However, eCB functions during pyramidal cell specification and establishment of longrange axonal connections are unknown. Here, we show that eCB signaling is operational in subcortical proliferative zones from embryonic day 12 in the mouse telencephalon and controls the proliferation of pyramidal cell progenitors and radial migration of immature pyramidal cells. When layer patterning is accomplished, developing pyramidal cells rely on eCB signaling to initiate the elongation and fasciculation of their long-range axons. Accordingly, CB 1 cannabinoid receptor (CB1R) null and pyramidal cellspecific conditional mutant (CB 1R f/f,NEX-Cre ) mice develop deficits in neuronal progenitor proliferation and axon fasciculation. Likewise, axonal pathfinding becomes impaired after in utero pharmacological blockade of CB 1Rs. Overall, eCBs are fundamental developmental cues controlling pyramidal cell development during corticogenesis.excitation ͉ glutamate ͉ layer patterning ͉ neocortex ͉ neurogenesis P yramidal cell specification follows a sequential scenario in the developing cerebrum: commitment of progenitor cells to the neuronal lineage occurs in the subcortical proliferative ventricular zone (VZ) and subventricular zone (SVZ). Immature pyramidal cells undergo radial migration to populate the cortical plate (CP) (1), where they acquire layer-specific neurochemical and morphological diversity (2). Pyramidal cell positioning and patterning of their corticofugal and intracortical axons is in part achieved via transcriptional control acting throughout cellular identification (2). However, epigenetic microenvironmental cues, provided by neural progenitors, radial glia, and immature neurons, are also fundamental in attaining cortical cell identity with particularly robust effects on pathfinding and directional growth of long-range axons (3).Endocannabinoids [eCBs; anandamide (AEA) and 2-arachidonoylglycerol] control various forms of synaptic plasticity at cortical glutamatergic synapses in the postnatal brain (4) through functional CB 1 cannabinoid receptors (CB 1 Rs) (5). During brain development, eCBs control neuronal fate decision (6), interneuron migration (7), and axonal specification (8). Developmental eCB actions are underpinned by a temporally defined assembly of functional eCB signaling networks with coincident expression of sn-1-diacylglycerol lipases (DAGL␣/␤) (9) and N-arachidonoyl-phosphatidyl ethanolamine (NAPE)-selective phospholipase D involved in eCB synthesis, fatty-acid amide hydrolase (FAAH) (an enzyme preferentially degrading AEA), and CB 1 Rs (8). The selective axonal targeting of CB 1 Rs and DAGLs in immature neurons suggests that eCBs may function in either cell-autonomous (6, 9) or target-derived (8) manner to control axonal elongation and postsynaptic target selection, respectively.Although recent findings in both mammals (8) and nonmammalian v...

Prenatal Ethanol Exposure Persistently Alters Endocannabinoid Signaling and Endocannabinoid-Mediated Excitatory Synaptic Plasticity in Ventral Tegmental Area Dopamine Neurons

“…Furthermore, several studies report increased excitatory synaptic strength in VTA DA neurons after cocaine, ethanol, or stress exposure, conditions known to increase addiction risk. Increased excitatory synaptic strength in VTA DA neurons after drug or stress exposure appears to be mediated by elevated calcium-permeable AMPA receptor (CP-AMPAR) expression in VTA DA neurons (Ortiz et al, 1995;Bellone and Lüscher, 2006;Argilli et al, 2008), which have larger conductance than calciumimpermeable AMPARs (Cull-Candy et al, 2006).…”

Differential Pharmacological Regulation of Sensorimotor Gating Deficit in CB1 Knockout Mice and Associated Neurochemical and Histological Alterations

“…Another type of GABAergic neurons are the PV-ir chandelier cells that synapse the axon initial segment of the pyramidal neurons (Inda et al, 2009). Recent data show that migrating neurons express CB1r during neocorticogenesis and that the endocannabinoid signaling control not only pyramidal positioning but also long-range axon patterning (Berghuis et al, 2007;Mulder et al, 2008;Oudin et al, 2011). Interestingly, in CB1KO mice, the density of pyramidal neurons in superficial layers decreased whereas it increased in deep cortical layers as a result of abnormal radial migration (Mulder et al, 2008).…”

“…Recent data show that migrating neurons express CB1r during neocorticogenesis and that the endocannabinoid signaling control not only pyramidal positioning but also long-range axon patterning (Berghuis et al, 2007;Mulder et al, 2008;Oudin et al, 2011). Interestingly, in CB1KO mice, the density of pyramidal neurons in superficial layers decreased whereas it increased in deep cortical layers as a result of abnormal radial migration (Mulder et al, 2008). Abnormal radial migration also causes blurred layering in the neocortex (Berbel et al, 2001).…”

Assay and Inhibition of the Purified Catalytic Domain of Diacylglycerol Lipase Beta

“…For example, DAGL-dependent eCB signalling regulates axonal growth and guidance during development [1][2][3][4][5][6] . In the adult two forms of plasticity are controlled by DAGL-dependent eCB signalling and these are synaptic plasticity in the form of retrograde synaptic transmission throughout the brain 7,8 and cellular plasticity in the form of adult neurogenesis in the hippocampus and sub-ventricular zone 1,7,9,10 .…”

“…It is noteworthy that DAGLα and DAGLβ make distinct tissue specific contributions towards 2-AG and AA levels and therefore selective modulators for these enzymes are likely to be essential to harness their therapeutic potential from both a safety and efficacy perspective 7,25 . For instance, recent studies have highlighted DAGLβ as a target for inflammatory diseases via mechanisms independent of the cannabinoid receptors whereas DAGLα is responsible for 2-AG mediated CB1 signalling at the synapse and therefore non-selectively targeting DAGLβ (over DAGLα) could risk 5 disrupting CB1 signalling at the synapse 13,[23][24][25] . It is therefore crucial to factor in selectivity assays to address this in drug discovery programmes.…”