title: A sodium afterdepolarization in rat superior colliculus neurons and its contribution to population activity.
abstract: The mammalian superior colliculus (SC) is a midbrain structure that integrates multimodal sensory inputs and computes commands to initiate rapid eye movements. SC neurons burst with the sudden onset of a visual stimulus, followed by persistent activity that may underlie shifts of attention and decision making. Experiments in vitro suggest that circuit reverberations play a role in the burst activity in the SC, but the origin of persistent activity is unclear. In the present study we characterized an afterdepolarization (ADP) that follows action potentials in slices of rat SC. Population responses seen with voltage-sensitive dye imaging consisted of rapid spikes followed immediately by a second distinct depolarization of lower amplitude and longer duration. Patch-clamp recordings showed qualitatively similar behavior: in nearly all neurons throughout the SC, rapid spikes were followed by an ADP. Ionic and pharmacological manipulations along with experiments with current and voltage steps indicated that the ADP of SC neurons arises from Na(+) current that either persists or resurges following Na(+) channel inactivation at the end of an action potential. Comparisons of pharmacological properties and frequency dependence revealed a clear parallel between patch-clamp recordings and voltage imaging experiments, indicating a common underlying membrane mechanism for the ADP in both single neurons and populations. The ADP can initiate repetitive spiking at intervals consistent with the frequency of persistent activity in the SC. These results indicate that SC neurons have intrinsic membrane properties that can contribute to electrical activity that underlies shifts of attention and decision making.
authors.affiliation: Department of Neuroscience and Neuroscience Training Program, The University of Wisconsin, Madison, Wisconsin; and.
authors.forename: Nima
authors.initials: N
authors.lastname: Ghitani
authors.affiliation: Department of Neuroscience and Neuroscience Training Program, The University of Wisconsin, Madison, Wisconsin; and.
authors.forename: Peter O
authors.initials: PO
authors.lastname: Bayguinov
authors.affiliation: Department of Psychiatry and Biobehavioral Sciences and Department of Neurobiology, The Fuster Laboratory for Cognitive Neuroscience, The Semel Institute for Neuroscience and Human Behavior, and The Brain Research Institute, The David Geffen School of Medicine, University of California, Los Angeles, California.
authors.forename: Michele A
authors.initials: MA
authors.lastname: Basso
authors.affiliation: Department of Neuroscience and Neuroscience Training Program, The University of Wisconsin, Madison, Wisconsin; and meyer.jackson@wisc.edu.
authors.forename: Meyer B
authors.initials: MB
authors.lastname: Jackson
mesh_terms: D000818:Animals; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000378:metabolism*; D026941:Sodium Channel Blockers / Q000494:pharmacology; D015222:Sodium Channels / Q000378:metabolism; D013477:Superior Colliculi / Q000187:drug effects / Q000502:physiology*; D046509:Tissue Culture Techniques; D056969:Voltage-Sensitive Dye Imaging
chemical_list: D026941:Sodium Channel Blockers; D015222:Sodium Channels; D012964:Sodium
keywords: Na+ channels; eye movements; persistent activity