The influence of early experience on the development of sensory systems

Once sensory stimuli become able to alter firing patterns in the developing brain, they can influence the maturation of neuronal circuits. Recent experimental studies add to our understanding of precisely which developmental events are affected by early experience. In particular, it appears that experience of the external environment can affect the brain earlier in development and at earlier stages of sensory processing than previously thought. These studies emphasise the developmental importance of the patterning of neuronal firing produced either by sensory stimuli or by spontaneous activity. The timing of action potentials is also an important aspect of several exciting studies describing the mechanisms - anatomical, synaptic, and molecular - by which early experience brings about alterations in the maturation of sensory circuitry. Importantly, this kind of approach can lead to predictions concerning the nature of sensory stimulation that is most effective in instructing brain development.     

The role of inhibition processes in the development of functional properties of neurons of the vibrissa projection area in the cat somatosensory cortex

The paper deals with the contribution of intracortical inhibitory processes to the organization of receptive fields in the vibrissae projection area of the somatosensory cortex. Inhibition blockade by means of microelectrophoretic application of picrotoxin and bicucullin was shown to lead to a loss of directional sensitivity of neurones. Activation of inhibition at remote glutamate application led to opposite changes: the neurones became directionally sensitive, and dependence was found between the spatial localization of activated neurones and the character of changes of detector parameters. Inhibitory processes caused by natural afferent stimulation led to similar changes of functional characteristics of neurones.     

The effect of ouabain on sensory neuron neurite growth in organotypic culture

Ouabain, a known inhibitor of Na+, K(+)-ATP, taken in a wide range of concentrations, was investigated in organotypic tissue culture of dorsal root ganglia cells of 10-11 day old chick embryos. Ouabain inhibited neurite growth in a dose-dependent manner. The Hill coefficient was defined as 1, and the Kp value was estimated as 1 x 10(-10) M. At inhibitor concentrations exceeding 1 x 10(-9) M, the growth of neurites was totally inhibited. It is assumed that Na+, K(+)-ATPase may play an important role in regulation of the process of neurite growth in sensory neurones.     

Studies of development and plasticity in the olfactory sensory neuron

The olfactory system is favorable for studying mechanisms of development, plasticity and regeneration. Monoclonal antibodies have been generated which differentially stain olfactory axons and can identify their earliest trajectories in the fetal rat. The developing olfactory pathway also shows differential metabolic activity, as revealed by the 2-deoxyglucose method, and these patterns show plasticity as judged by both physiological and behavioral measures. The sensory neurons undergo dieback and neurogenesis following axonal transection; electrophysiological methods are being used to reveal the membrane mechanisms underlying this unique capacity.     

Precise development of functional and anatomical columns in the neocortex

Sensory cortex is ordered into columns, each tuned to a subset of peripheral stimuli. To identify the principles underlying the construction of columnar architecture, we monitored the development of circuits in the rat barrel cortex, using laser-scanning photostimulation analysis of synaptic connectivity, reconstructions of axonal arbors, and in vivo whole-cell recording. Circuits impinging onto layer 2/3 neurons from layers 4 and 2/3 developed in a monotonic, precise progression, with little evidence for transient hyperinnervation at the level of cortical columns. Consistent with this, synaptic currents measured in layer 2/3 neurons at PND 8, just after these neurons ceased to migrate, revealed already spatially well-tuned receptive fields.     

Vibrissectomy in rats in early ontogeny leads to disordered functional properties of the cortical projection neurons

Vibrissae trimming during the first 20 days of postnatal life caused alternations of the properties of the receptive fields of single neurons in the barrel-field cortex in rats. The following changes were found in the deafferented cortex: (i) an extension of the receptive fields of single neurons as judged from an increase in the number of vibrissae with short-latency excitatory responses to stimulation and (ii) a depression of the inhibitory receptive field tuning mechanisms.     

The effect of X-rays and artificial hypotermia on lipids in rat neocortex

Lipid content of tissue and of fraction of microsomes in neocortex of Wistar rats was studies under artificial hypothermia, after X-ray irradiation in dose 8 Gy under conditions of normothermia and artificial hypothermia in 48 h. The condition of artificial hypothermia get by cooling of rats to 15-18 degrees C. It was shown, that in fraction of microsomes of hypothermia rats the content of phosphatidylinositol was decreased, and in 48 h after cooling of rats the amount of protein, total and individual phospholipids was increased. The lipid content in tissue and in fraction of microsomes of rats, which were irradiated in normotermia, had no changes after 48 h. In fraction of microsomes of rats, which were irradiated after hypothermia, the amount of protein, total phospholipids, sphingomyelin, phosphatidylcholine and phosphatidylserine is increased trustworthy. Thus, we think, that radioprotective effect of hypotermia may be connected with the accumulation of proteins and of phospholipids in the endoplasmic reticulum membranes of neocortex.     

The effect of neurotropic agents on evoked potentials of the association and projection regions of the cat neocortex]

Intensive non-specific inactivation of the cortex by means of its local cooling, in the cat anasthetized with nembutal, blocks in a similar way the early component of associative responses (ECAR) in the parietal area and the primary responses (PR) in the projection areas. In the case of local application of neurotropic drugs possessing specific and differentiated action on postsynaptic activity, the same ECAR changes require a somewhat higher concentration of the reagents as compared with the concentration that produces a similar PR transformation. The higher threshold of chemical sensitivity in ECAR than in the PR depends on the characteristics of the morpho-functional organization of the cortical formations. Dissimilar reactivity of the direct cortical response and of ECAR of the parietal area to the action of chemical drugs is related to the peculiarities of intracortical origin of these potentials which are due to the dissimilar nature of their generation in response to a direct and to a peripheral stimulation.     

Effect of early sensory experience on the exploratory activity in adult animals

It was previously found that the exploratory activity of adult Wistar rats with their vibrissae cut in the period from 9 to 20 postnatal days was characterized by lower intragroup variability in comparison with control rats [3]. The present study has shown that the earlier limitation of species-specific afferentation (whisker trimming on postnatal days 2–9) does not induce such changes. We conclude that high plasticity of the brain during the early postnatal period provides better adaptation to the deficit of sensory information.     

Afferent inhibition and functional properties of neurons in the vibrissae projection area of the cat somatosensory cortex]

The aim of this study was to investigate the role of inhibitory processes in S-1 cortex of cats. The inhibition was evoked by "natural" afferent stimulation of the fascial vibrissae. For this purpose, two neighboring vibrissae were sequentially stimulated by mechanical deflection; single unit activity was recorded simultaneously from the cortex. Results showed that conditioning by afferent stimulation significantly influenced the directional sensitivity of cortical neurons. These data and analysis of spatial pattern of stimulated vibrissa indicate that detector neurons could be quickly modified during sensory processing.     

Postnatal development of functional properties of the visual cortical cells of area 18 in kittens raised with or without visual experience

866 units were recorded extracellularly in area 18 of anaesthetized and paralysed kittens from 13 to 66 days of age. The development of their receptive field properties was studied in normally (EN) and dark-reared (EO) kittens. In addition to orientation selective (S) and non-selective (NS) cells, we found a number of non-selective units whose receptive field was surrounded by a peripheral zone (NSp) where stationary stimuli were effective. In EN kittens, the orientation selectivity developed with age and concomitantly, NS and NSp cells disappeared. Ocular dominance distribution was also gradually modified from a contralateral monocular dominance at 13 days of age to an adult-like binocularity at 58 days. In EO kittens, the early orientation selectivity began to decrease at the 5th week. From then on, the process of despecification started and progressed until nearly all cells were NS. Absence of visual experience also delayed the development of mature binocularity. In 6 week old EO kittens, a 6 hrs. visual exposure induced a fast but uncomplete specification with decrease of both NS and NSp cells and a slight modification of the ocular dominance distribution. The comparison of these results with those obtained in area 17 shows that functional properties vary more slowly in area 18 than in area 17.     

The development of components of the blood-brain barrier in the neocortex of the white rat

In formation and differentiation of the hematoencephalic barrier elements in white non-inbred rats of 14 age groups (55 animals) at the ultrastructural level certain regular phases of the process have been revealed. For example, morphological maturation of endotheliocytes and pericytes occurs on the 7th day of the postnatal life. Maximal decrease in permeability of the hematoencephalic barrier takes place on the 10th day, as a consequence of liquidation of the pericapillary space between the basal membrane and the glial tunic of the capillaries. Morphofunctional maturation of the hematoencephalic barrier (the 21st day) terminates in differentiation of the pericapillary astrocytic limbs, that surround up to 85% of the capillary perimeter.     

The effects of neomycin on membrane properties and discharge activity of an isolated sensory neuron

The effects of neomycin sulfate were examined upon the discharge activity and electrical membrane properties of an isolated invertebrate sensory neuron, the crayfish stretch receptor neuron. Neomycin depressed cell discharge activity in a concentration-dependent manner over the concentration range of 0.01-1.0 mM. Significant concentration-related increases were observed in the resting membrane potential and the width of the orthodromic action potential. There was a significant concentration-dependent decrease in the fast rising phase of the antidromic action potential. Significant changes also were observed in other electrical properties such as membrane resistance, but these were found not to be concentration related. The most significant change was membrane hyperpolarization, which could account for the depression of cell discharge activity. The observed changes are consistent with a neomycin-induced change in the membrane potassium conductance. It is proposed that the neural effect of neomycin is a selective interaction with the neuronal membrane phospholipids.     

The specification of sensory neuron identity in Drosophila

Different types of sense organs are present on the larva of Drosophila. Several genes that specify the type of sense organ that will form at a particular position have been recently identified. Here we review the functional and molecular analyses of these genes, and summarize the evidence which supports a role in the choice of which type of organ will be formed. Most or all of these genes are required for the appropriate specification of adult as well as larval sense organs, suggesting that the larval and adult systems share many gene requirements. Interestingly, the specifying genes identified so far in the peripheral nervous system are also expressed in subsets of cells in the central nervous system, where they might have similar roles.