Table 1.

Motor neuron pool innervating forelimb muscles: Anatomical and in vivo electrophysiological assessment.

Muscle: Flexor carpi radialis (FCR)	# of FluoroGold-labelled motor neurons per animal
Animal 1	133
Animal 2	119
Animal 3	250
Animal 4	158
Mean	165 ± 34 (SEM)
Muscle: Flexor digitorum profundus (FDP)	# of FluoroGold-labelled motor neurons per animal
Animal 1	109
Animal 2	66
Animal 3	93
Animal 4	60
Animal 5	159
Animal 6	163
Mean	108 ± 20 (SEM)
Muscle: Palmaris longus (PL)	# of FluoroGold-labelled motor neurons per animal
Animal 1	72
Animal 2	78
Animal 3	42
Animal 4	57
Mean	62 ± 9 (SEM)
Summated Anatomical Motor Neuron # Count: FCR + FDP + PL	Electrophysiological Motor Neuron # Estimation:
336 ± 16 (SEM)	415 ± 8 (SEM)

Individual and mean numbers of Fluoro-Gold (FG)-labelled motor neurons ± standard error of the mean (SEM) were determined after FG injections into corresponding forelimb muscles: flexor carpi radialis m. (FCR), flexor digitorum profundus m. (FDP), and palmaris longus m. (PL). These anatomical counts were summated and compared with in vivo electrophysiological motor neuron counts for neurobiological validation. The anatomical count (336 ± 16 [SEM]) represents the summated mean number of FG-labelled motor neurons for all assessed wrist flexor muscles (FCR, FDP, PL), while the electrophysiological estimate (415 ± 8 [SEM]) represents the mean calculated MUNE (compound muscle action potential/average single motor unit potential) from ventromedial forearm wrist flexor muscle recordings.