Prenatal Development of Spontaneous and Evoked Activity in the Rat (Rattus Norvegicus Albinus)

Abstract

I. The characteristics of prenatal spontaneous activity of rat fetuses of 16 through 20 days of gestation, and the development of responses to cutaneous stimulation are discussed and tabulated. In early fetuses of 16 and 17 days, only few activity bursts occur between long intervals of inactivity. The frequency of activity bursts increases greatly at day 18 and attains a peak at this stage, whereupon it declines to a lower level from day 19 through term. 2. Qualitatively, the movements appear to be unintegrated. Three types of activity have been distinguished: Total, generalized or mass movements, when all parts that are capable of movements participate; regional when only one body region such as the head and forelimbs are in motion, and local movements of single parts. In the earliest stage, only head and forelimb movements are observed. There is a gradual extension of motility in rostro-caudal and proximodistal direction, but there are exceptions to this rule. The movements in the rat fetus seem to be more smooth compared with those of the chick embryo where the movements are more jerky. 3. Our recordings show that no clear, or one-to-one correlation exists between fetal activity and uterine contractions. Amnion contractions do not occur in the rat fetus. 4. The first evoked responses in the rat fetus are interpreted as an incipient total or regional pattern. In later stages of development, discrete, low-amplitude unintegrated local responses are identifiable. At 17 and 18 days the local responses are frequently combined with regional and total mass body movements, but by day 19, total movements are less frequently elicited, and the local responses are more complex, resembling mature and fully integrated action patterns. The conclusion is made that in the rat fetus local complex patterns are built up from less complex units. 5. Spontaneous motility in other mammalian embryos and the origin of integrated specialized local action patterns are discussed in relation to the development of the structure and organization of the spinal cord.

Ultrasonographic observations of the maturation of basic movements in guinea pig fetuses

“…The craniocaudal direction of the appearance of movement in guinea pig fetuses were also observed in two previous studies [3,4]. Among rat fetuses, cutaneous reflexes as well as spontaneous movements also has a craniocaudal sequence of appearance [7,8]. Alternating movements occur first in forelimbs, then in hind limbs during prenatal development of rat fetuses [2].…”

Glycinergic and GABAergic Synaptic Activity Differentially Regulate Motoneuron Survival and Skeletal Muscle Innervation

“…Glycine/GABA A receptor activation increases lumbar motor burst frequency in early embryonic mouse (Hanson and Landmesser, 2003) and rat (Narayanan et al, 1971;Nishimaru et al, 1996); this response changes to decreased burst frequency only 1-2 d before birth (Nishimaru et al, 1996;Nishimaru and Kudo, 2000). In contrast, glycine/GABA A receptor activation depresses respiratory motor frequency at earlier stages of embryonic development, from E16 onward (Ren and Greer, 2003).…”

Developmental Adaptation of Rat Nociceptive Withdrawal Reflexes after Neonatal Tendon Transfer

“…It is conceivable that this temporal correlation leads to a selective strengthening of the efficacy of appropriate connections and a reduction in the efficacy of inappropriate ones. Indeed, nonreflexogenic spontaneous limb movements (Hamburger, 1970) are a common feature of normal development and appear around embryonic day 15 in the rat, i.e., at approximately the time at which reflex activity can first be evoked (Angulo y Gonzalez, 1932;Narayanan et al, 1971).…”