Retinal input induces three firing patterns in neurons of the superficial superior colliculus of neonatal rats.
By using an in vitro isolated brain stem preparation, we recorded extracellular responses to electrical stimulation of the optic tract (OT) from 71 neurons in the superficial superior colliculus (SC) of neonatal rats (P1-13). At postnatal day 1 (P1), all tested neurons (n = 10) already received excitatory input from the retina. Sixty-nine (97%) superficial SC neurons of neonatal rats showed three response patterns to OT stimulation, which depended on stimulus intensity. A weak stimulus evoked only one spike that was caused by activation of non-N-methyl-D-aspartate (NMDA) glutamate receptors. A moderate stimulus elicited a short train (<250 ms) of spikes, which was induced by activation of both NMDA and non-NMDA receptors. A strong stimulus gave rise to a long train (>300 ms) of spikes, which was associated with additional activation of L-type high-threshold calcium channels. The long train firing pattern could also be induced either by temporal summation of retinal inputs or by blocking gamma-aminobutyric acid-A receptors. Because retinal ganglion cells show synchronous bursting activity before eye opening at P14, the retinotectal inputs appear to be sufficient to activate L-type calcium channels in the absence of pattern vision. Therefore activation of L-type calcium channels is likely to be an important source for calcium influx into SC neurons in neonatal rats.
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Department of Cell Biology and Anatomy, Louisiana State University, Medical Center, New Orleans, Louisiana 70112, USA.
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D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D000831:Animals, Newborn; D001640:Bicuculline / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D004558:Electric Stimulation; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018756:GABA Antagonists / Q000494:pharmacology; D066298:In Vitro Techniques; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D009568:Nitrendipine / Q000494:pharmacology; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011963:Receptors, GABA-A / Q000187:drug effects / Q000378:metabolism; D012160:Retina / Q000187:drug effects / Q000502:physiology*; D013477:Superior Colliculi / Q000187:drug effects / Q000502:physiology*
D002121:Calcium Channel Blockers; D018691:Excitatory Amino Acid Antagonists; D018756:GABA Antagonists; D011810:Quinoxalines; D011963:Receptors, GABA-A; C056723:FG 9041; D015763:2-Amino-5-phosphonovalerate; D009568:Nitrendipine; D001640:Bicuculline