M. G. Campbell, Private, Captain Thos. L. Leeds' Company (Orleans Light Horse),* enlisted March 22, 1862 at New Orleans for 90 days, paid July 25, for the period 1 July to 15 July at the rate of $24/Mo., $12.00, discharged July 25, 1862 by reason of being 17 years of age, exempt, born in New Orleans, La., 5' 8", light complexion, grey eyes, light hair, profession left blank, no other records

Notation on one card as Private in Southern Cadela Louisiana Militia

The command was located at Camp Leeds near Corinth March 25, 1862

* This company subsequently became Capt. Greenleaf's Company (Orleans Light Horse) Louisiana

M320: Compiled Service Records of Confederate Soldiers Who Served in Organizations from the State of Louisiana

Note: The records for Dubecq's Co., Cavalry & Capt. Greenleaf's Co., (Orleans Light Horse) Cavalry are both found on
one Microfilm Roll, M320 Roll #32. This might explain why you suspect he served in both units.