Immunocytochemical properties and network bursting in Organotypic (OT) hindbrains + spinal cords of embryonic mice

In OT spinal cord explants bursting discharge probably depends upon distributed properties of neuronal networks; this is in contrast to circumscribed pacemaker function underlying respiration-like output from acute in-vitro neonatal rodent hindbrains. Nonetheless, burst patterns in the present OT preparation, which includes both hindbrain and upper cord regions of E14 mice, share several neuropharmacological characteristics (Neurosciences abstracts: 23:875, 1997) with respiratory output of the acute neonatal hindbrain. To evaluate viability and potential circuitry that might contribute to bursting, preparations maintained for 2-4 weeks were fixed and sectioned transversely (30 μm). Sections were immunostained for choline acetyl transferase (CHAT), glutamate decarboxylase (GAD), synaptic terminals (synapsin), and astrocyte fibers (GFAP). Results showed large CHAT containing neurons, probably motor neurons, at the caudal hindbrain / upper cord level. GAD-containing neurons were concentrated at or near the exposed surface of the preparation. Synapsin surrounded cells, even in the thickest portion (approx. 150-200 um, dorsal-ventral) of the preparation, and GFAP could be observed throughout the matrix. Augmentation of network bursts and effects on burst frequency, when GABA_A receptors are blocked in the present OT preparation, may arise from interruption of output from a relatively discrete layer. However, other synaptic interactions, with potential relevance to bursting activity may occur throughout the tissue.