Mossy cell axon synaptic contacts on ectopic granule cells that are born following pilocarpine-induced seizures

• Published in: Neuroscience letters 2007-07, Vol.422 (2), p.136-140
• Main Authors: Pierce, Joseph P., Punsoni, Michael, McCloskey, Daniel P., Scharfman, Helen E.
• Format: Article
• Language: English
• Subjects: Action Potentials - physiology; Animals; Biological and medical sciences; Biomarkers - analysis; Biomarkers - metabolism; Calbindins; Calcitonin Gene-Related Peptide - metabolism; CGRP; Choristoma - metabolism; Choristoma - pathology; Choristoma - physiopathology; Convulsants; Dendrites - metabolism; Dendrites - pathology; Dentate gyrus; Dentate Gyrus - metabolism; Dentate Gyrus - pathology; Dentate Gyrus - physiopathology; Disease Models, Animal; Epilepsy - chemically induced; Epilepsy - pathology; Epilepsy - physiopathology; Fundamental and applied biological sciences. Psychology; Headache. Facial pains. Syncopes. Epilepsia. Intracranial hypertension. Brain oedema. Cerebral palsy; Hippocampus - metabolism; Hippocampus - pathology; Hippocampus - physiopathology; Male; Medical sciences; Microscopy, Immunoelectron; Mossy Fibers, Hippocampal - metabolism; Mossy Fibers, Hippocampal - pathology; Mossy Fibers, Hippocampal - physiopathology; Nervous system (semeiology, syndromes); Neural Pathways - metabolism; Neural Pathways - pathology; Neural Pathways - physiopathology; Neurogenesis; Neurology; Pilocarpine; Presynaptic Terminals - metabolism; Presynaptic Terminals - pathology; Rats; Rats, Sprague-Dawley; S100 Calcium Binding Protein G - metabolism; Status epilepticus; Status Epilepticus - metabolism; Status Epilepticus - pathology; Status Epilepticus - physiopathology; Synaptic Transmission - physiology; Temporal lobe epilepsy; Vertebrates: nervous system and sense organs
• ISSN: 0304-3940; 1872-7972
• DOI: 10.1016/j.neulet.2007.06.016

Granule cell neurogenesis increases following seizures, and some newly born granule cells develop at abnormal locations within the hilus. These ectopic granule cells (EGCs) demonstrate regular bursts of action potentials that are synchronized with CA3 pyramidal cell burst discharges and the bursts of hilar neurons, including mossy cells. Such findings suggest that mossy cells may participate in circuits that activate EGCs. Electron microscopic immunolabeling was therefore used to determine if mossy cell axon terminals form synapses with hilar EGC dendrites, using animals that underwent pilocarpine-induced status epilepticus. Pilocarpine was administered to adult male rats, and those which developed status epilepticus were perfused 5–7 months later, after the period of EGC genesis. Hippocampal sections were processed for dual electron microscopic immunolabeling (using calcitonin gene-related peptide (CGRP) as a marker for mossy cells and calbindin (CaBP) as a marker for EGCs). Light microscopic analysis revealed large CGRP-immunoreactive cells in the hilus, with the appearance and distribution of mossy cells. Electron microscopic analysis revealed numerous CaBP-immunoreactive dendrites in the hilus, some of which were innervated by CGRP-immunoreactive terminals. The results suggest that mossy cells participate in the excitatory circuits which activate EGCs, providing further insight into the network rearrangements that accompany seizure-induced neurogenesis in this animal model of epilepsy.