Muscle stretch receptor function in the neonatal rat

Abstract

Since the early investigations of muscle spindle function (Matthews, 1933) the principal focus of study has been on a detailed analysis of receptor responses in adult animal (for reviews see Matthews, 1972, Boyd, 1980), while the only systematic study of developing spindle function was performed in kittens (Skoglund, 1960), and indicated the absence of a slowly-adapting response earlier than 6–10 days post-natally. It was suggested (Landon, 1972) that the lack of a static response was due to the relative immaturity of the nuclear chain fibres when compared with the nuclear bag ones. However, while the spindles of the kitten show some bag/chain differentiation at birth, those of the rat show little, with differentiation occurring during the first two postnatal weeks (Zelená, 1957, Landon, 1972, Kronnie et al., 1982), suggesting the possibility of a lesser functional maturity in the rat than in the kitten neonatally.