Table 2.
Timelines for landmarks in spinal cord sensorimotor development in human and rodent
| Human age (gestational weeks) | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11–13 | 14 | 15.5 | 17 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Rat age ( days) | E13 | E14 | E15 | E16 | E17 | E18 | E19 | E20–P0 | P1 | P2 | P3 |
| Human | Birth of motoneurones | Segregation of lat., med., central motor columns Some motoneurones express Er81 | Thickening of proximal dendrites Segregation of somata | ||||||||
| Rat (mouse) | Lumbar motoneurone production | Outgrowth of motor axons Expression of EPHA4 | Segregation of lat., med., central motor columns | Elimination of proximal gap junction coupling between motoneurones | |||||||
| Human | PV positive proprioreceptive afferents enter intermediate zone | PV afferents contact motoneurones Most PV sensory neurones express Er81 | |||||||||
| Five fold increase in synapses in the ventral horn | |||||||||||
| Rat (mouse) | Motor, sensory axons contact muscle. Induction of Er81 expression | PV expression in Proprioreceptive afferents | Sensory axons enter intermediate zone | Sensory axons contact motoneurones. DR stimulation elicits fEPSPs in motoneurones | Fast, heteronymous stretch reflex connections to antagonist muscles detectable | ||||||
| Human | Emergence of independent limb movements | Stimulation of palm/foot elicits finger/toe movement | Effective grasp reflex | ||||||||
| Rat | Stretch reflex appears | Stretch reflex reaches max. amplitude before decreasing | |||||||||
| Human | Identifiable Clarke's column neurones innervated by PV afferents | Clarke's column axons enter lateral funiculus | |||||||||
This table makes a comparison between human and rodent development and attempts to put into register the different rates of development of the species. Similar information for each species is grouped in adjacent, parallel bands. The majority of information on rodent development concerns the rat. Text in italics refers to the mouse, which develops at a slightly faster rate, and therefore the age given may be slightly more mature than the equivalent stage in rat. Information on the development of Clarke's column is very limited in rodent and so it is not included. The information presented was taken from the present study and the following references: Altman & Bayer (2001), Chang et al. (1999), Chen et al. (2003), Eberhart et al. (2002), Kudo & Yamada (1985), Kudo & Yamada (1987), Okado (1980), Snider et al. (1992), Vinay et al. (2000), Zhang et al. (1990) and Ziskind-Conhaim (1990).