Structural characteristics and development of ampullary organs in Acipenser naccarii.

Ampullary organs of Acipenser naccarii sturgeons were examined by optical and electronic microscopy (transmission electron microscopy and scanning electron microscopy) from hatching until 1 month later when the juvenile phase is completely established. It was observed that, when A. naccarii begins to feed actively, the ultrastructural characteristics of ampullary organs already correspond to those of adult animals. These organs may, therefore, be functional and, together with taste buds, facilitate food search after exhaustion of yolk sac food reserves. Mature ampullary organs of A. naccarii are formed by an ampulla that communicates with the exterior by means of a short channel. These ampullae correspond to the sensory portion of these receptors and are formed by two cell types: receptor cells and support cells. Receptor cells present a kinocilium on their free surface and establish ribbon synapses with axon nerve endings that arise from the underlying conjunctive tissue. Support cells enclose receptor cells, bear stereocilia and occasional cilia, and are of a secretory nature. The mucus associated with ampullary organs mainly comprises neutral mucopolysaccharides, whereas mucopolysaccharides are usually acid in other fish groups.

Erratum to "changes in cutaneous sensory nerve fibers induced by skin-scratching in mice".

BACKGROUND: Skin-scratching behavior, a common response observed in patients with pruritus, is supposed to promote the sprouting of cutaneous sensory nerve fibers. Thus, it sometimes exacerbates the original lesions. However, the precise changes that develop in cutaneous sensory nerve fibers after skin-scratching have not yet been elucidated. OBJECTIVE: To investigate how and what kinds of cutaneous sensory nerve fibers increase and how nerve growth factor (NGF) and its receptors change after skin-scratching. METHODS: After scratching the dorsal skin of anesthetized ICR mice, change in cutaneous nerve fibers was detected by immunofluorescence for protein gene product 9.5 (PGP9.5), substance P (SP) and/or calcitonin gene-related peptide (CGRP). To investigate the involvement of NGF signaling, the production of NGF and the expression of its receptors were examined using ELISA and/or immunofluorescence, respectively. RESULTS: Skin-scratching dramatically induced the sprouting of cutaneous nerve fibers. Both dermal and epidermal nerve fibers began to increase and reached a peak at days 3-7. At the same time, nerve fibers containing SP or CGRP increased significantly. NGF in the scratched skin increased immediately and reached a peak at days 1-3. The expression of NGF receptors, such as phosphorylated trk A and p75, on nerve fibers was remarkably upregulated within 2 days. CONCLUSIONS: Skin-scratching induced the sprouting of cutaneous sensory nerve fibers in the skin within several days, thus possibly leading to enhanced neurogenic inflammation. Analysis of the expression of NGF and its receptors suggest that NGF signaling may be, at least in part, involved in these changes.

Gastric preloads of corn oil and mineral oil produce different patterns of increases of c-Fos-like immunoreacitve cells in the brain of 9-12 day-old rats.

Equivolumetric gastric preloads of corn oil and mineral oil administered to rats on postnatal day 12 (P12) inhibited intake equally during a 30-min test of independent ingestion (II), but preloads of corn oil inhibited intake significantly more than preloads of mineral oil on P15 and P18 [Weller, A., Gispan, I.H., Armony-Sivan, R., Ritter, R.C., Smith, G.P., 1997. Preloads of corn oil inhibit independent ingestion on postnatal day 15 in rats. Physiol. Behav. 62, 871-874]. It is possible that the equivalent inhibition of intake by the oil preloads on P12 resulted from the failure of the preabsorptive sensory properties of the preloads to be discriminated by peripheral or central sensory mechanisms. To investigate this possibility, we administered equivolumetric gastric preloads of 25% corn oil and 25% mineral oil to pups on P9-12 and counted the number of c-Fos-like immunoreactive (CFLI) cells in central sites that are activated by food intake and postingestive preabsortive mechanisms in adult rats and in pups on P10-11. The major result was that preloads of 25% corn oil and 25% mineral oil that produced equivalent inhibition of II intake produced differential increases of CFLI cells in the forebrain and hindbrain. Specifically, preloads of corn oil increased the number of CFLI cells in the caudal Nucleus Tractus Solitarius significantly more than preloads of mineral oil. Furthermore, preloads of corn oil increased the number of CFLI cells in the Paraventricular and Supraoptic nuclei, but preloads of mineral oil did not. This differential pattern of increases of CFLI cells is evidence that the brain discriminates the preabsorptive sensory properties of preloads of corn oil and mineral oil on P9-12.

Changes in cutaneous sensory nerve fibers induced by skin-scratching in mice.

BACKGROUND: Skin-scratching behavior, a common response observed in patients with pruritus, is supposed to promote the sprouting of cutaneous sensory nerve fibers. Thus, it sometimes exacerbates the original lesions. However, the precise changes that develop in cutaneous sensory nerve fibers after skin-scratching have not yet been elucidated. OBJECTIVE: To investigate how and what kinds of cutaneous sensory nerve fibers increase and how nerve growth factor (NGF) and its receptors change after skin-scratching. METHODS: After scratching the dorsal skin of anesthetized ICR mice, change in cutaneous nerve fibers was detected by immunofluorescence for protein gene product 9.5 (PGP9.5), substance P (SP) and/or calcitonin gene-related peptide (CGRP). To investigate the involvement of NGF signaling, the production of NGF and the expression of its receptors were examined using ELISA and/or immunofluorescence, respectively. RESULTS: Skin-scratching dramatically induced the sprouting of cutaneous nerve fibers. Both dermal and epidermal nerve fibers began to increase and reached a peak at days 3-7. At the same time, nerve fibers containing SP or CGRP increased significantly. NGF in the scratched skin increased immediately and reached a peak at days 1-3. The expression of NGF receptors, such as phosphorylated trk A and p75, on nerve fibers was remarkably upregulated within 2 days. CONCLUSIONS: Skin-scratching induced the sprouting of cutaneous sensory nerve fibers in the skin within several days, thus possibly leading to enhanced neurogenic inflammation. Analyses of the expression of NGF and its receptors suggest that NGF signaling may be, at least in part, involved in these changes.

Age-related changes in tactile spatial resolution from 6 to 16 years old.

The aim of this study was to determine age-related changes in tactile spatial resolution from 6 to 16 years old. Two hundred and twenty-two healthy children (105 boys and 117 girls) were assessed. The tactile spatial resolution threshold was determined using a classic set of JVP domes with a procedure adapted for children. Preadolescence appears to be an important step in tactile spatial resolution since children aged between 6 and 9 years old had a worse tactile spatial resolution than older children. Both peripheral and central explanations for this improvement of tactile spatial resolution with age are considered. The authors suggest that cortical maturational processes are likely to explain the better results of older children.

Axon guidance during establishment of electroreceptor innervation in the catfish Kryptopterus.

The principles were studied, according to which the characteristic electroreceptor distribution pattern consisting of organ rows and clusters on the tail of the catfish Kryptopterus spec. is formed. As each electroreceptor is induced by its future afferent ('electrosensory') nerve fibre at the site where the outgrowing fibre reaches the epidermis, it is the fibre navigation which controls the organ distribution. Three navigation principles of the outgrowing electrosensory fibres were found. (i) The electrosensory fibre courses are bound to the tail segmentation. Nerve displacement experiments suggest that the fibres are guided by the intersegmental connective tissue sheaths, i.e. the myosepta and myocommata. (ii) The individual fibres have no specificity for a certain route or target area on the tail, but can grow in any direction and into any tail area and induce organs there. This is indicated by experiments with nerve elimination and nerve deflection. (iii) An outgrowing fibre's only orientation is towards a nearby 'free site'; i.e. it aims for a place in clusters with fewer organs than their actual capacity allows. The capacity increases continuously with the specimen's age, so that free sites progressively develop. So, it depends on chance which outgrowing fibre occupies which 'free site'; a free site is targeted by whatever outgrowing fibre happens to be the nearest. The mechanisms of development of the somatotopic projection of the electrosensory fibres to the central nervous system (CNS) are discussed.

Effects of neurotrophin-3 gene mutation in the expression of neurocalcin.

Neurocalcin (NC) is a neuron-specific "EF-hand" calcium-binding protein present in a non-fully characterized subpopulation of dorsal root ganglion (DRG) neurons, some kinds of mechanoreceptors and proprioceptors, and in motor end-plates. In the present study we have characterized NC expression in spinal sensory and motor neurons, and their endings in newborn mouse. Because the neurotrophic factor neurotrophin-3 (NT-3) appears to plays a major role in the development and maturation of sensory and motor neuronal populations, we have studied NC immunoreactivity in newborn NT-3 null mutant. In NT-3 deficient animals the overall number of NC-immunoreactive DRG neurons was reduced by as much as 70% including all large neurons, but subpopulations of NC expressing small and intermediate-sized neurons survived. As expected no muscle spindles were found in NT-3 mutant mice while they were present and normally innervated by NC-positive nerve fibers in wild-type animals. On the other hand, NC immunoreactivity was dramatically decreased in motoneurons of the spinal cord, ventral root nerves and motor end-plates in the absence of NT-3. The present results demonstrate that NC-containing DRG neurons include all proprioceptive, and a subset of mechanoreceptive and proprioceptive. Furthermore, they strongly suggest that NT-3 is involved in the maturation of motor end-plates.

Histogenesis of the oropharyngeal cavity taste buds and the relevant nerves and brain centers in substrate-brooding and mouth-brooding cichlid fish (Cichlidae, Teleostei).

This study follows the histogenesis of the oropharyngeal cavity taste buds, along with the development of the relevant neural centers and gustatory nerves, in two cichlid species: the substrate-brooding Cichlasoma cyanoguttatum and the mouth-brooding Astatotilapia flavijosephi, from fertilization to 20-day-old juveniles, grown at a temperature of 26 degrees C. Significant differences in pace of development were shown between the two social types: Substrate-brooders complete embryogenesis and hatch 48 h after fertilization (HAF) and begin to swim 120 HAF, with the yolk sac disappearing 160 HAF, whereas mouth-brooders hatch 84 HAF and begin to swim 196 HAF, with the yolk sac disappearing 360 HAF. Histogenesis of primordial taste buds occurs 75 HAF and 160 HAF in C. cyanoguttatum and A. flavijosephi, respectively. Accordingly, the related sensory ganglia and nerves (VII, IX, and X) develop much earlier in the substrate-brooded larvae and postlarvae. Nerve and brain development in juvenile A. flavijosephi of 13 mm total length (TL) closely resemble those of 8-mm-TL C. cyanoguttatum. These differences in development continue throughout the early stages of growth. Similar differences are observed in the ripening and increase in number of taste buds and dentition on the jaws and pharyngeal bones. The possible triggers and causes of such differences in development, as well as the inductors of taste bud development, are discussed.

Lateral line receptors: where do they come from developmentally and where is our research going?

The lateral line system is composed of both mechanoreceptors, which exhibit little variation in structure between taxonomic groups, and electroreceptors, which exhibit considerably more variation. Cathodally sensitive ampullary electroreceptors are the primitive condition and are found in agnathans, chondrichthyans, and most osteichthyans. Aquatic amphibians also have ampullary electroreceptors for at least part of their life cycle. The more recently evolved anodally sensitive ampullary electroreceptors and tuberous electroreceptors are only found in four groups of teleost fishes. The basic ontogenetic unit of lateral line development is the dorsolateral placode. Primitively, there are six pairs of placodes, which pass through sequential stages of development into lateral line receptors. There is no question about the origin of primitive mechanoreceptors or electroreceptors, however, we do not have a good understanding of the origin of teleost mechanoreceptors and their ampullary or tuberous electroreceptors; do they come exclusively from dorsolateral placodes or from neural crest or even general ectoderm? A second intriguing lateral line question is how certain teleost fish groups evolved tuberous electroreceptors. Electroreception appears to have re-evolved at least twice in teleosts after being lost during the neopterygian radiation. It has been suggested that the development of tuberous electroreceptors might be due to changes in placodal patterning or a change in the general ectoderm that placodes arise from. Unfortunately, our understanding of lateral line origins in fishes is very sketchy, and, if we are to answer such an evolutionary question, we first need more complete information about lateral line development in a variety of fishes, which can then be combined with gene expression data to better interpret lateral line receptor development.

Development of the lateral line system in the shovelnose sturgeon.

The lateral line systems of aquatic amphibians and all chondrichthyan and osteichthyan fish present a similar array of mechanoreceptors. However, electroreceptors, the second major component of the lateral line system, have clearly undergone more significant evolutionary change. Chondrichthyans and non-neopterygian fish possess primitive ampullary organ electroreceptors, whereas significantly different 'new' ampullary organs and tuberous electroreceptors are found in a few groups of teleosts (mormyrids, gymnotids and some catfish). The pairing of mechano- and electroreceptors in the lateral line system, as well as the morphologically and physiologically distinct electroreceptors of teleosts have inspired several recent studies on the origin and evolution of the lateral line receptors. We described the development of the lateral line system in sturgeon (Scaphirhynchus platorynchus) as part of an outgroup analysis of lateral line development in three taxa: vertebrates that have both mechanoreceptive neuromasts and primitive electroreceptors; neopterygian fish that only have mechanoreceptors; and teleosts that have re-evolved new electroreceptors. Development in Scaphirhynchus was consistent with previously studied taxa in that the lateral line system developed from a series of six dorsolateral placodes. Interestingly, we found that the octaval placode was bound rostrally and caudally by large placodal fields, out of which the six lateral line placodes arose. This finding supports recent suggestions for a common placodal primordium for all placodes. Each of the six placodes gave rise to the lateral line nerves before elongating into sensory ridges, which contained neuromast primordia. The ampullary organ fields of Scaphirhynchus arose from the lateral zones of the anterodorsal, anteroventral, otic and supratemporal sensory ridges, which is also consistent with recently studied taxa. Comparisons of the lateral line system of Scaphirhynchus and close relatives, Acipenser and Polyodon, indicate that variation in some aspects of lateral line receptor numbers and distribution are related to changes in head morphology and feeding strategy, whereas other changes, such as a reduction in receptor number without a change in placode field size, indicate changes in placode development.

Muscle twitches during sleep shape the precise muscles of the withdrawal reflex.

Very precise nociceptive skin reflexes that withdraw the skin from a harmful stimulus are formed through an experience-dependent mechanism that develops around two weeks after birth in rodents. Tactile input paves the way for the nociceptive reflex, and nociceptive stimuli are not required for the reflex to be formed. Petersson et al. show that the tactile input produced during muscle twitches occurring during sleep are essential for this process to develop.

Rescue of NGF-deficient mice I: transgenic expression of NGF in skin rescues mice lacking endogenous NGF.

Mice lacking a functional NGF gene (ngf-/- mice) have less than one third of the normal complement of sensory neurons, few sympathetic postganglionic neurons and die shortly after birth. We report here that transgenic expression of NGF under control of the K14 keratin promoter can rescue some elements of the peripheral nervous system and restore normal growth and viability to ngf-/- mice. While hybrid transgenic-ngf-/- mice (ngfTKOs) displayed marginal rescue of trigeminal ganglion neurons, the percentage of CGRP-positive neurons was restored to normal. Restoration of CGRP-positive terminals in skin and spinal cord was also found and accompanied by recovery of behavioral responses to noxious stimuli. ngfTKO mice displayed a normal number of superior cervical ganglion neurons and recovery of sympathetic innervation of skin. These results demonstrate that substitution of a functional NGF locus by a transgene directing expression largely to skin can result in normal growth and viability. Thus, the most vital functions of NGF are not dependent on faithful recapitulation of the normal spatiotemporal pattern of gene expression.

Patent ductus arteriosus remodels cardiac sensory neuronal chemotransduction.

We sought to determine the capacity of neonatal ventricular sensory nerve endings (neurites) to transduce the cardiac milieu in the presence of cardiovascular pathology. The spontaneous activity generated by nodose ganglion cardiac afferent neurons was identified in situ using extracellular recording techniques in two groups of piglets approximately 2 weeks old: (i). controls that underwent sham operations (n=19 piglets) 2 weeks earlier and (ii). a pathological model of patent ductus arteriosus stented open for about 2 weeks (n=16 piglets). The capacity of ventricular sensory neurites associated with nodose ganglion afferent neurons to transduce local mechanical (including alterations in right or left ventricular volumes) or chemical stimuli was studied in both groups. The average conduction velocity of afferent axons associated with identified neuronal somata was estimated to be 1.5+/-0.6 or 2.9+/-1.3 m s(-1). Ventricular afferent neurons transduced mechanical stimuli similarly in both groups. In control animals, ventricular afferent neurons transduced the following chemicals: the sodium channel modifier veratridine (delta 23+/-7 impulses min(-1)), the P(1)-purinoceptor agonist adenosine (Delta 24+/-8 impulses min(-1)), and the beta-adrenoceptor agonist isoproterenol (delta 18+/-7 impulses min(-1)). On the other hand, patent ductus arteriosus cardiac afferent neurons did not transduce these chemicals. It is concluded that neonatal cardiac afferent neuronal chemosensory-as opposed to mechanosensory-transduction remodels in the presence of a patent ductus arteriosus. The reduced capacity of neonatal cardiac afferent neurons to transduce chemicals in the presence of a patent ductus arteriosus should be taken into account when considering neonatal cardiovascular control in such a state.

Neural plasticity in the gustatory system.

Sensory systems adapt to changing environmental influences by coordinated alterations in structure and function. These alterations are referred to as plastic changes. The gustatory system displays numerous plastic changes even in receptor cells. This review focuses on the plasticity of gustatory structures through the first synaptic relay in the brain. Unlike other sensory systems, there is a remarkable amount of environmentally induced changes in these peripheral-most neural structures. The most consistent and largest changes occur to stimuli that also impact on homeostatic systems, especially when the environmental manipulation is instituted during early development.

Development of catfish lateral line organs: electroreceptors require innervation, although mechanoreceptors do not.

In amphibians the lateral line sense organs, i.e., mechanoreceptors (neuromasts) and electroreceptors, develop autonomously from placodal tissue, with no need for innervating nerve fibers. The present study deals with the question whether or not the mechano- and the (ampullary) electroreceptors develop in the same manner in teleosts. On the tail of larval catfish, Silurus, the first mechano- and electroreceptors appear several days after hatching in two longitudinal rows, one along the outgrowing main branch of the lateral line nerve and one along its ventral branch. Prevention of outgrowth of both nerve branches by repeated nerve sectioning, before the receptors form, shows (1) that the mechanoreceptors can develop without innervation as in amphibians, and (2) that the electroreceptors do not develop without innervation, unlike amphibian electroreceptors. These results are discussed with regard to the placodal origin and the phylogeny of the two sense organs.

Postnatal maturation of neuroepithelial bodies and carotid body innervation: a quantitative investigation in the rabbit.

The intrapulmonary airways contain oxygen-sensitive chemoreceptors which may be analogous to the arterial chemoreceptors: the neuroepithelial bodies (NEB). While the NEB are prominent in the neonatal lung, physiological studies indicate that the carotid bodies are still relatively inactive at birth. This points to an unequal degree of development of both during the early neonatal period. As a reflexogenic chemoreceptor function depends on a well-developed innervation, we undertook a comparative investigation of the development of the NEB and the carotid body glomus cell innervation. Two morphological aspects of the innervation of NEB and carotid body glomus cells were quantified in rabbits of different age groups. The total sectional area of intracorpuscular and intraglomerular nerve endings per NEB or glomus cell group, respectively, was measured and the area percentage of mitochondria and synaptic vesicles was determined. In the NEB, no significant difference in total sectional area of the nerve endings between the age groups was observed, while in the carotid body there was a significant increase in the adult age group. In addition, the area percentage of mitochondria and synaptic vesicles of the nerve endings did not change significantly with age in the NEB, while in the carotid body these increased and decreased, respectively, with age. These observations point to a shift from morphologically efferent nerve endings, rich in synaptic vesicles, to morphologically afferent nerve endings, rich in mitochondria. Our interpretation of these findings is that, at birth, the NEB innervation is more mature than the carotid body glomus cell innervation and that the latter matures at a later time than the former. These findings support the theory that the NEB may act as complementary chemoreceptors to the carotid body during the early postnatal period.

[The effect of the limitation of afferent inflow in early ontogeny on the evoked activity of projective neurons depends on the degree of the maturity of the sensory inputs]. / Vliianie ogranicheniia afferentnogo pritoka v rannem ontogeneze na vyzvannuiu aktivnost' proektsionnykh neironov zavisit ot stepeni zrelosti sensornykh vkhodov.

The study is focused on the influence of a partial limitation of the sensory inflow in rat pups on the development of the sensory systems, which mature earlier and later. In accordance with the ontogenetic rule of proximal-distal maturation, the sensory inflow from the forelimbs matures faster than that from the hindlimbs. Fourteen Wistar rat pups (from 28) were deafferented on the 13th day of postnatal ontogeny (a small portion of the median nerve was unilaterally dissected). The background and evoked activity of single neurons was recorded in 26-47-day-old pups in the somatosensory cortex (in the projection areas of the intact n. medianus, which matures earlier, and n. ischiadicus, which matures later). The changes in firing activity produced by deafferentation were observed. In the projection area of the intact forelimb of the denervated rats, the incidence of inhibitory responses significantly increased, whereas the incidence of completes responses significantly decreased. In the hindlimb projection area of the denervated animals the background firing rate was significantly lower and the incidence of activation responses was increased.

A developmental study using three antibodies (VOBM1, VOBM2, and VOM2): immunocytochemical and electron microscopical analysis of the luminal surface of the rat vomeronasal sensory epithelium.

The development of the rat vomeronasal organ was studied morphologically and immunocytochemically, using the monoclonal antibodies (MAbs) VOBM1, VOBM2 and VOM2 that react with the luminal surface of the vomeronasal sensory epithelium. Postnatal day (P) 7, 14, 21, 28, 35 and adult animals were examined. The vomeronasal organ and the blood vessel of the organ markedly increased in size and the vomeronasal glands increased in number between P7 and P14. At P35, the shape of the vomeronasal organ was similar to that of the adult but its size was slightly smaller. Electron microscopy showed that only a few scattered microvilli were present on supporting cells, and receptor cells were immature at P7. At P21, well-branched microvilli of the receptor cells and many microvilli of the supporting cells were observed on the luminal surface of the sensory epithelium. At P35, most apical endings of supporting cells and receptor cells were covered with numerous microvilli. Less developed areas were also present at the luminal surface of the epithelium at P35. At P7, immunoreactivities of the three antibodies were observed as discontinuous thin-layered bands only on the luminal surface of the sensory epithelium and no immunoreactivity was observed in other regions of the vomeronasal organ. Immunoreactivities of the VOBM1, VOBM2 and VOM2 increased with age and were observed as continuous thin-layered bands on the luminal surface of the epithelium by P35. These finding suggest that the development of the vomeronasal organ continues after birth and that the organ may reach maturity just before puberty (P42-49).

Fine structure and distribution of antennal sensilla of the desert locust, Schistocerca gregaria (Orthoptera: Acrididae).

The fine structure and distribution of various types of antennal sensilla in three nymphal stages and in adults of both solitary-reared (solitary) and crowd-reared (gregarious) phases of the desert locust, Schistocerca gregaria, were investigated by scanning and transmission electron microscopy. Four types of sensilla were identified: sensilla basiconica, s. trichodea, s. coeloconica and s. chaetica. S. basiconica contain up to 50 sensory neurons, each of which displays massive dendritic branching. The sensillar wall is penetrated by a large number of pores. In contrast, s. trichodea contain one to three sensory neurons that branch to give five or six dendrites in the sensillar lumen; the sensillum wall is penetrated by relatively few pores. The s. coeloconica are situated in spherical cuticular pits on the antennal surface. The s. coeloconica are of two types: one type contains one to three sensory neurons with double sensillar walls penetrated by slit-like pores, whereas the second type contains four sensory neurons with non-porous double sensillar walls. The s. chaetica have a flexible socket and a thick non-porous sensillum wall and contain four sensory neurons that send unbranched dendrites to a terminal pore. A fifth sensory neuron of the s. chaetica terminates in a tubular body at the base of the hair. S. basiconica and coeloconica are normally distributed over the entire antennal flagellum, with a concentration in the middle segments; s. trichodea have three areas of concentration on the 5th, 10th and 14th flagellar segments. Sensilla chaetica are most abundant on the terminal segment. Locusts raised in solitary conditions have more olfactory sensilla (s. basiconica and s. coeloconica) than crowd-reared locusts. The difference in sensillar numbers is more evident in adults than in nymphs. These results suggest that differences in the odour-mediated behaviour of nymphs and adults, and between the phases of S. gregaria, may be attributable to differences at the sensory input level.

[The formation of motor units in vertebrates (a histophysiological analysis)]. / Formirovanie dvigatel'nykh edinits u pozvonochnykh (gistofiziologicheskii analiz).

In motor unit anlage successive formation of morphophysiological and biochemical components of system-forming units (histophysiological compartments) occurs. Simultaneously functional differentiation of motor units takes place, based on morphological, biochemical and functional heterogeneity of nervous, muscular and synaptic motor unit components. Intrinsic genetic programmes of main nervous and skeletal muscular tissue differons are the leading ones in early stages of embryogenesis. Morphofunctional base for realization of neurogenic control of skeletal musculature fibres histochemical differentiation forms in muscle anlage. Genetic programmes of two tissues development come to direct (contact) interaction through outer regions of cell membranes: motor neurons participation in skeletal muscular tissue histogenesis, especially on the stage of muscular tubules differentiation into muscular fibres of certain histophysiological type is essential. Most complicated changes are observed in postsynaptic membrane area. This allows to emphasize the development of the symphast nucleo-sarcoplasmic compartment. In further, adaptive changes and morphological manifestations of skeletal muscular tissue genetic programme realization arise in myogenesis with motor neurons role progressively increasing and becoming the predominant one.