Basic Helix-Loop-Helix Transcription Factors/physiology; Neural Pathways/growth & development; Neuropeptides/physiology; Somatosensory Cortex/growth & development; Synapses/physiology; Thalamus/growth & development; 2-Amino-5-phosphonovalerate/pharmacology; Amino Acid Sequence; Amino Acids/metabolism; Animals; Animals, Newborn; Basic Helix-Loop-Helix Transcription Factors/deficiency; Blotting, Western/methods; CREB-Binding Protein/metabolism; Calcium Channel Blockers/pharmacology; Cells, Cultured; Chelating Agents/pharmacology; Chloramphenicol O-Acetyltransferase/metabolism; Drug Interactions; Egtazic Acid/pharmacology; Electric Stimulation/methods; Embryo, Mammalian; Excitatory Amino Acid Antagonists/pharmacology; GABA Antagonists/pharmacology; Gene Expression/drug effects; Immunohistochemistry/methods; In Vitro Techniques; Membrane Potentials/drug effects; Membrane Potentials/physiology; Membrane Potentials/radiation effects; Mice; Mice, Knockout; Models, Biological; Nerve Growth Factors/metabolism; Neurons/drug effects; Neuropeptides/deficiency; Nimodipine/pharmacology; Patch-Clamp Techniques/methods; Phosphopyruvate Hydratase/metabolism; Potassium Chloride/pharmacology; Pyridazines/pharmacology; Pyridinium Compounds/metabolism; Quinoxalines/pharmacology; Receptors, AMPA/metabolism; S100 Calcium Binding Protein beta Subunit; S100 Proteins/metabolism; Somatosensory Cortex/cytology; Transcriptional Activation/genetics; Transfection/methods; Vibrissae/growth & development; Vibrissae/innervation