The number, distribution and size of Golgi tendon organs in developing and adult rat muscles

The number, distribution and size of Golgi tendon organs (TOs) were studied in two hindlimb muscles of the rat from the first postnatal day until 5 months after birth. No significant differences in the number of TOs were found after the third postnatal day onwards and the data from day 3 to 150 were therefore pooled. The soleus (SOL) muscle contained 15.4 +/- 0.6 TOs (mean +/- S.E.); the extensor digitorum longus (EDL) had 14.0 +/- 0.5 TOs on the average. However, the number of TOs often varied in muscles from the rats of the same age group, especially those from different litters. In both muscles, TOs were distributed nearly equally along the proximal and distal aponeurosis; as a rule, the percentage of TOs was slightly higher at the proximal aponeurosis (54% of TOs in the SOL and 58% of TOs in the EDL). The TOs grew in length and width during their development and in 5-month-old rats measured 506.1 +/- 14.0 micrometers in length and 64.4 +/- 1.9 micrometers in diameter on the average. The distance of the ends of muscle fibres connected with the receptor from the tendinous pole was was 1 064.9 +/- 49.0 micrometers on the average. These were considerable differences among individual TOs in the length, diameter and in the distance of the muscle-fibre ends from the receptor tendinous pole. The largest TOs were 2 to 3 times longer than the smallest receptors. These differences in size were found in all age groups, but they were most prominent in adult rats. Beside differences in size, great variability in the shape of TOs was also observed, and the longer receptors tended to be relatively slender than smaller TOs. The statistical evaluation of size parameters measured showed their close correlation, but the functional significance of the size and/or shape variability of the TOs remains to be elucidated.