Aging/metabolism; Brain/metabolism; Cranial Nerves/metabolism; Embryonic and Fetal Development; Gene Expression Regulation, Developmental; Membrane Glycoproteins/genetics; Membrane Transport Proteins; Neuropeptides; Spinal Cord/metabolism; Transcription, Genetic; Animals; Animals, Newborn; Brain/embryology; Brain/growth & development; Cranial Nerves/embryology; Cranial Nerves/growth & development; In Situ Hybridization; Limbic System/embryology; Limbic System/growth & development; Limbic System/metabolism; Membrane Glycoproteins/biosynthesis; Neurotransmitter Agents/biosynthesis; Oligonucleotide Probes; Organ Specificity; RNA Probes; RNA, Messenger/biosynthesis; Rats; Rats, Sprague-Dawley; Reverse Transcriptase Polymerase Chain Reaction; Spinal Cord/embryology; Spinal Cord/growth & development; Vesicular Biogenic Amine Transport Proteins; Vesicular Monoamine Transport Proteins