[Verse 1] Before the granule cells exist, entorhinal axons arrive Swimming through the marginal zone, prenatal and alive Cajal-Retzius guideposts waiting in lacunosum-moleculare Reelin signals mark the spot where terminals declare Lateral takes the outer band, medial middle ground Ephrin gradients draw the map, topography is found [Chorus] Lamina-specific, topographically precise Molecular instructions guide each axon splice Semaphorins repel and push, Netrins pull them near Slit and Robo mark the lanes, pathways crystal clear Birth order sets the sequence, loop formation flows From perforant to return, each connection knows [Verse 2] Mossy fibers wake up late, postnatal pioneers Growing into stratum lucidum through the early years Giant boutons detonate on CA3 proximal trees Class 3 Semaphorins fence the zone, keep them from the breeze Granule cells born after birth, two to three weeks long Must find their narrow targeting, detonator strong [Chorus] Lamina-specific, topographically precise Molecular instructions guide each axon splice Semaphorins repel and push, Netrins pull them near Slit and Robo mark the lanes, pathways crystal clear Birth order sets the sequence, loop formation flows From perforant to return, each connection knows [Bridge] Schaffer collaterals branch from CA3 pyramids Seeking CA1 radiatum, where their synapse lives Guidance cues in layers stack like geological time Each pathway finds its destined band, molecular sublime Return fibers close the loop, subicular relay Hippocampal circuit wired in systematic way [Verse 3] Eph receptors read the code, position maps align Neuropilins catch the scent of chemorepulsive signs DCC receptors chase Netrin, attractive force so strong Robo sensors dodge the Slit, keep axons moving along Guidepost cells illuminate the roads between each zone Pioneer pathfinders carve routes through tissue unknown [Verse 4] Activity shapes the final form, use-dependent change Silent synapses compete while connections rearrange NMDA gates swing open when pre and post align Calcium floods trigger growth, molecular design Pruning cuts the excess back, refines the growing tree Developmental programs end, adult circuitry [Chorus] Lamina-specific, topographically precise Molecular instructions guide each axon splice Semaphorins repel and push, Netrins pull them near Slit and Robo mark the lanes, pathways crystal clear Birth order sets the sequence, loop formation flows From perforant to return, each connection knows [Outro] Four pathways interwoven, guidance symphony complete Molecular choreography makes the circuit sweet
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