Multiple patterns and components of persistent inward current with serotonergic modulation in locomotor activity-related neurons in Cfos-EGFP mice.
Using CFos-EGFP transgenic mice (P6-P12), we targeted persistent inward current (PIC) in the spinal interneurons activated by locomotion. Following a locomotor task, whole cell patch-clamp recordings were obtained from ventral EGFP+ neurons in spinal cord slices (200-250 μm from T₁₃-L₄). PIC was recorded by a family of 10 s voltage bi-ramps starting from -70 mV with 30 mV steps. PIC could be classified as ascending and descending forms based on the rising and falling phases of the bi-ramps. Multiple patterns of PIC with various hystereses were found in EGFP+ neurons. A novel form of PIC, single PIC crossing both phases of the bi-ramps, was described in this study. PIC was found in 82% of EGFP+ neurons (n = 129) with no significant difference in laminar distribution. PIC activated at -56.7 ± 8 mV with an amplitude of 85.3 ± 59 pA and time constant of 657.0 ± 272 ms (n = 63). PIC in lamina VIII neurons activated significantly lower (-60.2 ± 7 mV) than in lamina VII (-54.8 ± 6 mV) and lamina X (-55.8 ± 9 mV) neurons. PIC could be differentiated as calcium dependent (Ca-PIC) by bath application of 1-5 μM TTX or sodium dependent (Na-PIC) by administration of 20-30 μM dihydropyridine. Ca-PIC activated at -40.2 ± 19 mV (n = 49), whereas Na-PIC activated at -46.8 ± 16 mV (n = 17). Composite-, Ca-, and Na-PICs were significantly different in activation but not amplitude and time constant. Bath application of 5-HT (10-30 μM) enhanced PIC (n = 32) by hyperpolarizing onset (4.2 ± 6 mV) and increasing amplitude (16%). 5-HT-increased amplitude seemed to be significantly larger in lamina VII neurons (32%) than VIII (6%) and X (14%) neurons. 5-HT enhancement of Ca-PIC (n = 6) and Na-PICs (n = 4) was also observed in EGFP+ neurons. This study unveiled unique properties of PICs in EGFP+ neurons. The lamina-related PIC activation and variable effects of 5-HT on PIC amplitude provides insight into the ionic basis on which locomotion could be generated.
Dai
Yue
Y
Dept. of Physiology, Univ. of Manitoba, Winnipeg, Manitoba R3E0J9, Canada.
Jordan
Larry M
LM
D000818:Animals; D000831:Animals, Newborn; D005456:Fluorescent Dyes; D049452:Green Fluorescent Proteins; D007395:Interneurons / Q000166:cytology / Q000502:physiology*; D051379:Mice; D008822:Mice, Transgenic; D023421:Models, Animal; D009043:Motor Activity / Q000187:drug effects* / Q000502:physiology; D009431:Neural Conduction / Q000502:physiology*; D018408:Patch-Clamp Techniques; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics / Q000502:physiology*; D012701:Serotonin / Q000502:physiology*; D018490:Serotonin Agents / Q000494:pharmacology*; D012702:Serotonin Antagonists / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000494:pharmacology
D005456:Fluorescent Dyes; D016760:Proto-Oncogene Proteins c-fos; D018490:Serotonin Agents; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins; D012701:Serotonin