Acetylcholinesterase-containing neurons, substance P and enkephalin fibers in the ventral horns of developing human embryos and fetuses

Early human motor development: From variation to the ability to vary and adapt

This review summarizes early human motor development. From early fetal age motor behavior is based on spontaneous neural activity: activity of networks in the brainstem and spinal cord that is modulated by supraspinal activity. The supraspinal activity, first primarily brought about by the cortical subplate, later by the cortical plate, induces movement variation. Initially, movement variation especially serves exploration; its associated afferent information is primarily used to sculpt the developing nervous system, and less to adapt motor behavior. In the next phase, beginning at function-specific ages, movement variation starts to serve adaptation. In sucking and swallowing, this phase emerges shortly before term age. In speech, gross and fine motor development, it emerges from 3 to 4 months post-term onwards, i.e., when developmental focus in the primary sensory and motor cortices has shifted to the permanent cortical circuitries. With increasing age and increasing trial-and-error exploration, the infant improves its ability to use adaptive and efficicient forms of upright gross motor behavior, manual activities and vocalizations belonging to the native language.

Neural substrate and clinical significance of general movements: an update

General movements are present from early fetal life to 3 to 5 months corrected age. Atypical general movements, especially in the last, so-called fidgety general movement phase, are predictive of cerebral palsy (CP). This review updates knowledge on the neural substrate and clinical significance of typical and atypical general movements. Typical general movements are primarily characterized by complexity and variation. Presumably these core characteristics are initially induced by modulating activity of the cortical subplate. When the subplate gradually dissolves between 3 months before term and 3 months corrected age the cortical plate takes over. This coincides with the fidgety general movement phase. Conceivably, fidgety activity reflects 'sparsification', i.e. fragmentation of cortical network activity. The quintessential feature of atypical general movements is reduced complexity and variation. This is attributed to impaired integrity of extensive cortical-subcortical networks, in which the subplate and periventricular white matter play a prominent role. The most serious forms of network impairment are associated with absent fidgety movements.

WHAT THIS PAPER ADDS

The emergence of fidgety movements reflects a developmental transition from widespread to fragmented cortical network activity. Atypical general movements characterized by reduced complexity and variation are attributed to impaired integrity of extensive cortical-subcortical networks.

Functional corticospinal projections are established prenatally in the human foetus permitting involvement in the development of spinal motor centres

From studies of subhuman primates it has been assumed that functional corticospinal innervation occurs post-natally in man. We report a post-mortem morphological study of human spinal cord, and neurophysiological and behavioural studies in preterm and term neonates and infants. From morphological studies it was demonstrated that corticospinal axons reach the lower cervical spinal cord by 24 weeks post-conceptional age (PCA) at the latest. Following a waiting period of up to a few weeks, it appears they progressively innervate the grey matter such that there is extensive innervation of spinal neurons, including motor neurons, prior to birth. Functional monosynaptic corticomotoneuronal projections were demonstrated neurophysiologically from term, but are also likely to be present from as early as 26 weeks PCA. At term, direct corticospinal projections to Group Ia inhibitory interneurons were also confirmed. Independent finger movements developed much later, between 6 and 12 months post-natally. These data do not support the proposal that in man, establishment of functional corticomotoneuronal projections occurs immediately prior to and provides the capacity for the expression of fine finger movement control. We propose instead that such early corticospinal innervation occurs to permit cortical involvement in activity dependent maturation of spinal motor centres during a critical period of perinatal development. Spastic cerebral palsy from perinatal damage to the corticospinal pathway secondarily involves disrupted development of spinal motor centres. Corticospinal axons retain a high degree of plasticity during axon growth and synaptic development. The possibility therefore exists to promote regeneration of disrupted corticospinal projections during the perinatal period with the double benefit of restoring corticospinal connectivity and normal development of spinal motor centres.

Early appearance of acetylcholinergic, serotoninergic, and peptidergic neurons and fibers in the developing human central nervous system

Animal experiments have already shown that neurotransmitters and neuropeptides are not only important for normal functioning of the adult central nervous system (CNS) but are also crucial to its development. However, information on the spatio-temporal distribution of these endogenous substances in the developing human CNS is still scarce. With the use of immunocytochemical staining and a constant supply of properly fixed human abortuses from southern China, an early appearance of acetylcholinesterase, enkephalin, and substance P immunoreactivities was detected first in the spinal cord (weeks 5 to 7 of gestation), then in the brainstem nuclei (weeks 11 to 12). Their overlapping localizations in many regions of the CNS suggest possible interactions among neurons containing these substances, which are in turn important for the proper establishment of the neuronal circuitry. Immunoreactivity for neuropeptide Y appeared initially in the lateral region of upper segments of the spinal cord at week 12 of gestation, then spread latero-medially and cranio-caudally to the sacral region. In the hippocampus, neuropeptide Y neurons appeared from week 15 onwards. Serotoninergic neurons were found in the dorsal raphe nucleus at week 10 and then decreased in number as the fetus grew older. Somatostatin releasing inhibitory factor, vasopressin, and oxytocin were detected in the hypothalamus from weeks 12 to 14 onwards, and monoamine oxidase, succinic dehydrogenase, parvalbumin, calbindin D28K, and vasoactive intestinal peptide were found in the visual cortex at midgestation. The early appearance and the abundance of the neurotransmitters and neuropeptides in the developing CNS indicate that they may play a key role in neuronal differentiation.

Tachykinins, neurotrophism and neurodegenerative diseases: a critical review on the possible role of tachykinins in the aetiology of CNS diseases

The tachykinins are a family of undecapeptides that are widely distributed throughout the body, including the central nervous system (CNS). They have several well defined roles in non-CNS sites as well as in the dorsal horn, where they are involved in the transmission of nociceptive information. However their function(s) in other CNS sites is unclear, but there is some evidence that they function as neuromodulators rather than neurotransmitters. This neuromodulation includes a possible role in maintaining the integrity of neuronal populations, analogous to the functions of neurotrophic factors. This review critically evaluates the role of tachykinins as neurotrophic factors, with particular reference to the common neurodegenerative diseases of the CNS.

Immunohistochemical studies of GABA and parvalbumin in the developing human cerebellum

The localization of GABA and parvalbumin was studied in the developing cerebellum of human fetuses from 16 to 28 weeks of gestation. The avidin-biotin complex immunohistochemical method combined with silver staining were used to reveal the presence of GABA- and parvalbumin-positive neurons and nerve fibres. As early as the 16th week of gestation, GABA immunopositivity was observed in the cerebellar cortex and the deep nuclei. GABA-positive neurons included Purkinje cells, stellate and basket cells of the cerebellar cortex and neurons in the deep nuclei. The gradient of immunoreactivity increased with the maturing cells, being weak at 16 weeks and becoming markedly pronounced at 28 weeks of gestation. GABA-immunopositive mossy fibres were observed in the granular cell layer at 16 weeks, and by 28 weeks, a robust fibre network was present in the cortex and deep nuclei. Immunohistochemical localization for parvalbumin indicates that weak immunoreactivity was observed in Purkinje cells, stellate and basket cells at 16 weeks of gestation, increasing in intensity with advancing age, notably in the Purkinje cells which had acquired an elaborate arbor of neurites at 28 weeks of gestation. In the deep nuclei, parvalbumin-positive cells and nerve fibres were observed throughout the 16 to 28 week period. These results indicate that GABA- and parvalbumin-positive neurons and fibres appeared as early as 16 weeks of gestation, expressing a high degree of immunoreactivity by the 28 week of fetal age.