Ld. Brewer et Jl. Larimer, ESTIMATION OF THE SIZE AND DIRECTIONAL OUTPUT OF FUNCTIONAL-GROUPS OFINTERNEURONS UNDERLYING ABDOMINAL POSITIONING BEHAVIORS IN CRAYFISH, The Journal of experimental zoology, 278(3), 1997, pp. 119-132
Quantitative studies were made of a large population of interneurons t
hat controls postural flexion and extension of the crayfish abdomen. T
he number of interneurons needed to produce a motor program was estima
ted by stimulating a single abdominal positioning interneuron and reco
rding interneuronal activity that was evoked from rostral and caudal c
onnectives in an isolated abdominal nerve cord. We also examined the r
ole that these functional groups have in producing a stronger motor ou
tput in either a rostral or caudal direction and thus specifying vario
us abdominal geometrics. The average number of interneurons responding
to stimulation of a single abdominal positioning interneuron was 32 (
range: 3-50; n = 27). The average number of interneurons that decrease
d activity was 10 (range: 2-32). Of 653 activated interneurons from 20
preparations, approximately 43% fired between 2 and 5 Hz, 33% fired b
etween 6 and 15 Hz, and 25% fired >15 Hz. The size of a recruited grou
p was usually but not always correlated with the strength of its motor
response or with the direction of motor bias. Therefore, the contribu
tion of a group may depend upon the number of active elements as well
as synaptic efficacy. (C) 1997 Wiley-Liss, Inc.