Effects of preweaning sensorimotor stimulation on behavioral and neuronal development in motor and visual cortex of the rat

The role of enriched environment in neural development and repair

In addition to genetic information, environmental factors play an important role in the structure and function of nervous system and the occurrence and development of some nervous system diseases. Enriched environment (EE) can not only promote normal neural development through enhancing neuroplasticity but also play a nerve repair role in restoring functional activities during CNS injury by morphological and cellular and molecular adaptations in the brain. Different stages of development after birth respond to the environment to varying degrees. Therefore, we systematically review the pro-developmental and anti-stress value of EE during pregnancy, pre-weaning, and “adolescence” and analyze the difference in the effects of EE and its sub-components, especially with physical exercise. In our exploration of potential mechanisms that promote neurodevelopment, we have found that not all sub-components exert maximum value throughout the developmental phase, such as animals that do not respond to physical activity before weaning, and that EE is not superior to its sub-components in all respects. EE affects the developing and adult brain, resulting in some neuroplastic changes in the microscopic and macroscopic anatomy, finally contributing to enhanced learning and memory capacity. These positive promoting influences are particularly prominent regarding neural repair after neurobiological disorders. Taking cerebral ischemia as an example, we analyzed the molecular mediators of EE promoting repair from various dimensions. We found that EE does not always lead to positive effects on nerve repair, such as infarct size. In view of the classic issues such as standardization and relativity of EE have been thoroughly discussed, we finally focus on analyzing the essentiality of the time window of EE action and clinical translation in order to devote to the future research direction of EE and rapid and reasonable clinical application.

Forced activity and environmental enrichment mildly improve manifestation of rapid cerebellar degeneration in mice

Exercise therapy represents an important tool for the treatment of many neurological diseases, including cerebellar degenerations. In mouse models, exercise may decelerate the progression of gradual cerebellar degeneration via potent activation of neuroprotective pathways. However, whether exercise could also improve the condition in mice with already heavily damaged cerebella remains an open question. Here we aimed to explore this possibility, employing a mouse model with dramatic early-onset cerebellar degeneration, the Lurcher mice. The potential of forced physical activity and environmental enrichment (with the possibility of voluntary running) for improvement of behaviour and neuroplasticity was evaluated by a series of behavioural tests, measuring BDNF levels and using stereological histology techniques. Using advanced statistical analysis, we showed that while forced physical activity improved motor learning by ∼26 % in Lurcher mice and boosted BDNF levels in the diseased cerebellum by 57 %, an enriched environment partially alleviated some behavioural deficits related to behavioural disinhibition. Specifically, Lurcher mice exposed to the enriched environment evinced reduced open arm exploration in elevated plus maze test by 18 % and increased immobility almost 9-fold in the forced swim test. However, we must conclude that the overall beneficial effects were very mild and much less clear, compared to previously demonstrated effects in slowly-progressing cerebellar degenerations.

Environment and Brain Plasticity: Towards an Endogenous Pharmacotherapy

Brain plasticity refers to the remarkable property of cerebral neurons to change their structure and function in response to experience, a fundamental theoretical theme in the field of basic research and a major focus for neural rehabilitation following brain disease. While much of the early work on this topic was based on deprivation approaches relying on sensory experience reduction procedures, major advances have been recently obtained using the conceptually opposite paradigm of environmental enrichment, whereby an enhanced stimulation is provided at multiple cognitive, sensory, social, and motor levels. In this survey, we aim to review past and recent work concerning the influence exerted by the environment on brain plasticity processes, with special emphasis on the underlying cellular and molecular mechanisms and starting from experimental work on animal models to move to highly relevant work performed in humans. We will initiate introducing the concept of brain plasticity and describing classic paradigmatic examples to illustrate how changes at the level of neuronal properties can ultimately affect and direct key perceptual and behavioral outputs. Then, we describe the remarkable effects elicited by early stressful conditions, maternal care, and preweaning enrichment on central nervous system development, with a separate section focusing on neurodevelopmental disorders. A specific section is dedicated to the striking ability of environmental enrichment and physical exercise to empower adult brain plasticity. Finally, we analyze in the last section the ever-increasing available knowledge on the effects elicited by enriched living conditions on physiological and pathological aging brain processes.

Neonatal Food Restriction Induces Hypoplasia in Developing Facial Motor Neurons of Rats

The effects of neonatal food restriction upon the dendritic development of facial nucleus (FN) motor neurons of Wistar rats were analyzed. Rats neonatally underfed by daily (12 h) mother-litter separation in an incubator from 5-30 days after birth exhibited, in brain stem Golgi-Cox sections, significant reductions in the number and extension of stellate, triangular and bipolar FN neuronal dendritic prolongations with negligible effects upon perikarya measurements. Data suggest that in the underfed newborn, the ability of FN neurons to establish synaptic contacts with afferent fibers is reduced, which then interferes with their capacities for the integration and triggering of nerve impulses to modulate facial motor expression in response to sensory cues.

Alterations in the Solitary Tract Nucleus of the Rat Following Perinatal Food Restriction and Subsequent Nutritional Rehabilitation

Newborn of altricial species maintain functional gustatory communication with the mother because the neural substrate and the capacity to discriminate and promote gustofacial responses are already operating. Because little is known about the effects of perinatal food restriction upon gustatory neuronal brain stem structures, we characterized neuronal Golgi-Cox alterations of the solitary tract rostral portion (NSTr) where gustatory information is known to convey in neonatal Wistar rats. Pre-and neonatally undernourished rats exhibited a general reduction in the number and extension of distal dendrites particularly in small neurons but little effect upon perikarya measurements of the NSTr neuronal population. By contrast, in nutritional and sensory rehabilitated rats the number of distal dendrites increased, although the dendritic extensions were less affected compared to perinatally underfed and control subjects. The data indicate that perinatal food restriction interferes with the NSTr dendritic arbor organization, while nutritional and sensorial rehabilitation given by normally lactating dams induced plastic changes presumably modifying the integrative processes underlying early taste discriminative capabilities. Moreover, since perinatal food restriction is a powerful stressor influence and the NST forms a part of a complex system underlying adaptive stress responses, the neuronal alterations observed here may be partly due to this noxious perinatal influence.

Frequency Modulation and Spatiotemporal Stability of the sCPG in Preterm Infants with RDS

The nonnutritive suck (NNS) is an observable and accessible motor behavior which is often used to make inference about brain development and pre-feeding skill in preterm and term infants. The purpose of this study was to model NNS burst compression pressure dynamics in the frequency and time domain among two groups of preterm infants, including those with respiratory distress syndrome (RDS, N = 15) and 17 healthy controls. Digitized samples of NNS compression pressure waveforms recorded at a 1-week interval were collected 15 minutes prior to a scheduled feed. Regression analysis and ANOVA revealed that healthy preterm infants produced longer NNS bursts and the mean burst initiation cycle frequencies were higher when compared to the RDS group. Moreover, the initial 5 cycles of the NNS burst manifest a frequency modulated (FM) segment which is a significant feature of the suck central pattern generator (sCPG), and differentially expressed in healthy and RDS infants. The NNS burst structure revealed significantly lower spatiotemporal index values for control versus RDS preterm infants during FM, and provides additional information on the microstructure of the sCPG which may be used to gauge the developmental status and progression of oromotor control systems among these fragile infants.

Suck Predicts Neuromotor Integrity and Developmental Outcomes

Neonatal motor behavior predicts both current neurological status and future neurodevelopmental outcomes. For speech pathologists, the earliest observable patterned oromotor behavior is suck. Suck production requires effective coordination of an infant's oral sensorimotor system and is subject to a variety of neuromodulatory inputs. Demonstration and practice of coordinated suck serves as a biomarker for oral feeding skills neural integrity and is being assessed for its relation to neurodevelopmental outcomes (speech, cognition, and learning) by research teams in the United States, Europe, Japan, and Brazil. Suck may also serve as an intervention point to prevent feeding disorders and mitigate speech-language delays and disorders.

Respiratory treatment history predicts suck pattern stability in preterm infants

Sensory deprivation and motor restriction associated with extensive oxygen therapy may lead to poor oromotor control in preterm infants. Non-nutritive suck is one of the first complex oromotor behaviors infants perform. This study determined the spatiotemporal variability of non-nutritive suck (NNS) pressure trajectories in three preterm groups with differing oxygen histories-one control group with minimal or no O(2) therapy, and two Respiratory Distress Syndrome (RDS) groups with either a mild/moderate (RDS1) or moderate/severe (RDS2) O(2) history. The Non-nutritive Suck Spatiotemporal Index (NNS STI) quantifies spatial and temporal variability across kinematic trajectories, and was calculated from digital representations of infants' suck pressure signals. An ANCOVA revealed a significant effect for group (p < .001) on the NNS STI measure, with RDS2 infants showing highly variable NNS patterning, and thus relatively underdeveloped suck. Extensive oxygen therapy, which alters the oral sensory environment and reduces motor experiences, disrupts the development of coordinated NNS in preterm infants.

Synthetic orocutaneous stimulation entrains preterm infants with feeding difficulties to suck

BACKGROUND

Prematurity can disrupt the development of a specialized neural circuit known as suck central pattern generator (sCPG), which often leads to poor feeding skills. The extent to which suck can be entrained using a synthetically patterned orocutaneous input to promote its development in preterm infants who lack a functional suck is unknown.

OBJECTIVE

To evaluate the effects of a new motorized 'pulsating' pacifier capable of entraining the sCPG in tube-fed premature infants who lack a functional suck and exhibit feeding disorders.

METHODS

Prospective cohort study of 31 preterm infants assigned to either the oral patterned entrainment intervention (study) or non-treated (controls) group, matched by gestational age, birth weight, oxygen supplementation history and oral feed status. Study infants received a daily regimen of orocutaneous pulse trains through a pneumatically controlled silicone pacifier concurrent with gavage feeds.

RESULTS

The patterned orocutaneous stimulus was highly effective in accelerating the development of non-nutritive suck (NNS) in preterm infants. A repeated-measure multivariate analysis of covariance revealed significant increases in minute rates for total oral compressions, NNS bursts, and NNS cycles, suck cycles per burst, and the ratiometric measure of NNS cycles as a percentage of total ororhythmic output. Moreover, study infants also manifest significantly greater success at achieving oral feeds, surpassing their control counterparts by a factor of 3.1 x (72.8% daily oral feed versus 23.3% daily oral feed, respectively).

CONCLUSION

Functional expression of the sCPG among preterm infants who lack an organized suck can be induced through the delivery of synthetically patterned orocutaneous pulse trains. The rapid emergence of NNS in treated infants is accompanied by a significant increase in the proportion of nutrient taken orally.

Pacifier Stiffness Alters the Dynamics of the Suck Central Pattern Generator

Variation in pacifier stiffness on non-nutritive suck (NNS) dynamics was examined among infants born prematurely with a history of respiratory distress syndrome. Three types of silicone pacifiers used in the NICU were tested for stiffness, revealing the Super Soothie™ nipple is 7 times stiffer than the Wee™ or Soothie™ pacifiers even though shape and displaced volume are identical. Suck dynamics among 20 preterm infants were subsequently sampled using the Soothie™ and Super Soothie™ pacifiers during follow-up at approximately 3 months of age. ANOVA revealed significant differences in NNS cycles/min, NNS amplitude, NNS cycles/burst, and NNS cycle periods as a function of pacifier stiffness. Infants modify the spatiotemporal output of their suck central pattern generator when presented with pacifiers with significantly different mechanical properties. Infants show a non-preference to suck due to high stiffness in the selected pacifier. Therefore, excessive pacifier stiffness may decrease ororhythmic patterning and impact feeding outcomes.

Non-Nutritive Suck Parameter in Preterm Infants with RDS

OBJECTIVE: To characterize the integrity of non-nutritive suck (NNS) parameters among three groups of preterm infants ranging from normal to those with progressive degrees of respiratory distress syndrome (RDS). STUDY DESIGN: NNS compression waveforms were sampled from 55 infants in the neonatal intensive care unit using a silicone pacifier electronically instrumented for intraluminal pressure. Seven select NNS parameters were measured at two different sessions, and statistically analyzed using a General Linear Model Analysis of Covariance. RESULTS AND CONCLUSIONS: Preterm infants with a more extensive history of RDS and oxygen therapy manifest significantly (p≤0.001) degraded performance on six of the seven NNS measures. This trend was disproportionately amplified in preterm infants with moderate-to-severe RDS. Prolonged periods of RDS requiring oxygen therapy may cause maladaptive orosensory experiences, and restrict oral movements which may contribute to delayed NNS development.

Respiratory Distress Syndrome Degrades the Fine Structure of the Non-Nutritive Suck In Preterm Infants

AIMS AND OBJECTIVES: Suck development is a challenging hurdle for preterm infants who endure an extensive oxygen history due to respiratory distress syndrome (RDS). The fine structure of the non-nutritive suck (NNS) was studied in preterm infants according to RDS severity. DESIGN AND METHODS: Recordings of NNS were completed cribside in the neonatal intensive care unit (NICU) in 55 preterm infants distributed among one healthy control group and two RDS infant groups. NNS pressure amplitude (cmH(2)0) and within-burst suck cycle period (ms) were the dependent measures extracted from digitized records of pacifier nipple compression pressure. RESULTS AND CONCLUSIONS: RDS preterm infants demonstrated significant differences in NNS suck pressure amplitude compared to healthy preterm infants. Periods of oxygen supplementation restrict orofacial movement and limit orosensory experiences necessary for suck development and neural maturation. RDS infants may be excellent candidates for patterned oral stimulation programs designed to advance the maturation of sucking skills.

Contributions of undernutrition and handling to huddling development of rats

When newborn rats are separated from the mother, they consistently exhibit the huddling response to maintain body temperature and physical contact. Therefore, we investigated if preweaning handling/sensory stimulation may overcome the huddling deficiencies associated to neonatal undernourishment/maternal deprivation of Wistar rats maintained at constant temperature (30 degrees C). The data indicated that initial and final temperatures in the pile of undernourished (U) and undernourished stimulated (Us) pups was reduced compared to their controls (C and Cs, respectively). Huddling latency was prolonged at 5 days of age in the Us group and at 20 days of age in the U pups. On postpartum day 5, U and Us subjects were similar in battery and pile-huddling performance compared to their controls; thereafter, the frequency of battery type was low and pile type was high (in frequency) in all experimental treatments. The frequency of recycling from the pile in the Us pups in most of the ages was significantly reduced compared to U and C subjects, suggesting that early sensory stimulation possibly accelerates the maturation of thermoregulatory brain structures underlying the huddling response and causing increased physical contacts. The data provide evidence that both neonatal undernutrition/maternal deprivation and early sensory stimulation may modify the huddling response by reducing or increasing, respectively, brain mechanisms underlying huddling. The amount of physical contact the newborns receive from their littermates and the mother may be a fundamental source of sensory cues for neuronal maturation and brain functioning.

Neonatal food restriction and binaural ear occlusion interfere with the maturation of cortical motor pyramids in the rat

Golgi-Cox-impregnated pyramidal neurons of layer five motor cortical area were investigated in control, binaural ear-occluded control, undernourished and binaural ear-occluded undernourished Wistar rats of 12, 20 and 30 days of age. In neonatally undernourished, binaural ear-occluded-undernourished and partly in ear-occluded-control subjects, there were significant reductions in both the number and extent of the distal part of the dendritic branches of motor pyramids compared to their controls. Moreover, minimal effects on perikarya measurements were observed. These findings suggest that neonatal undernutrition and the concurrent reduction of auditory cues affect dendritic arbor development and possibly the convergence of the auditory experience upon motor pyramids and may interfere with the neocortical modulation of postural and movements activities.

A paradigm of undernourishing and neonatal rehabilitation in the newborn rat

Perinatal undernutrition as a deficiency of nutrient availability, affects body and brain developmental processes and promotes recurrent health problems. Thus, altered mother-litter bonds and deficient environmental interactions may interfere with the brain pluripotential capabilities of the newborn. To gather information concerning the mechanisms underlying perinatal undernutrition we designed a paradigm of undernutrition and neonatal rehabilitation in the rat. An underfed group came from pregnant Wistar rats fed with 50% of the diet from G6 to G12 and with 60% from G13 until G21. After birth, pups were daily undernourished during 12 h daily by rotating a pair of lactating well-nourished dams which had one of their nipples subcutaneously ligated. The rehabilitated animals were undernourished pups neonatally fed by a pair of normally lactating dams. Controls received plenty of food during the pre- and neonatal periods. Pups were sacrificed at 12, 20 and 30 days of age. Perinatal underfeeding significantly reduced body and brain weights and neuronal morphometric parameters. Normal neonatal feeding in the newborn ameliorated the damages associated to food deprivation. The current undernourishing paradigm may be helpful to assess brain development alterations, as well as to study the compensatory mechanisms associated to salutary epigenetic influences.

Neonatal nutritional rehabilitation of morphological features in facial motoneurons altered by prenatally food deprivation in the rat

Undernutrition alters facial motoneurons development. Here, we evaluated the plastic characteristics of facial motoneurons in response to neonatal rehabilitation. Prenatally undernourished rat pups derived from pregnant rats fed with 50% of the diet from gestational days G6 to G12, and with 60% of food from G13 to G21 and rehabilitated after birth by a pair of control lactating foster dams. Morphological features of 640 Golgi-Cox impregnated motoneurons from 12, 20 and 30 days old pups were analyzed. Neonatal food rehabilitation increased the number and extension of the dendritic branches (main neuronal reception area) without altering significantly soma measurements (main neuronal firing area), suggesting that food and sensory maternal disponibility after birth ameliorates the damage due to prenatal deprivation. Findings showed that neonatal rehabilitation in addition to intense maternal polysensorial stimuli from the foster mothers partially diminished the morphological alterations associated to prenatal undernutrition, and provide evidence of plastic properties of facial motoneurons to the influence of environmental cues.

Mothering begets mothering: the transmission of behavior and its neurobiology across generations

Early experiences exert their effects on adult parental behavior in part by altering the development of neurobiological mechanisms that initiate or support the initiation and sustenance of adult parental behavior. The effects of parental behavior on sensory, perceptual and emotional mechanisms in offspring constitute an experientially based mechanism by which neurobiological factors regulating behavior can be transferred from generation to generation somewhat independently of genetic endowment.

Effects of enriched environment and fluid percussion injury on dendritic arborization within the cerebral cortex of the developing rat

We have recently demonstrated that fluid percussion injury (FPI) sustained early in life prevents the neural plasticity response associated with rearing in an enriched environment (EE). In order to determine if this reduction in plasticity capacity is reflected in alterations in dendritic arborization, the present study examined dendritic changes in response to EE, FPI, and FPI followed by EE. Twenty postnatal day 19-20 rat pups were subjected to FPI or sham injury and were subsequently housed in EE (17 days) or standard conditions. Brains were processed according to the Golgi-Cox method and were analyzed using dendritic density (Sholl) and dendritic branching analyses in frontal, parietal, and occipital cortices. Rearing in EE induced an increase in dendritic density, primarily within the occipital cortex. FPI induced an increase in dendritic density, primarily in regions remote from the injury site, namely contralateral parietal cortex and ipsilateral and contralateral occipital cortex. In injured animals subsequently housed in EE, FPI appeared to inhibit the experience-dependent dendritic density effects of EE. However, an unexpected enhancement of dendritic density was seen in the ipsilateral occipital cortex, indicating a unique response of this region based on its distance-specific sensitivity to injury-induced plasticity and its region-specific sensitivity to experience-dependent plasticity. These results suggest that dendritic changes mediate the anatomical and behavioral changes characteristic of impaired developmental plasticity following FPI, and that these changes are dependent on location within the cerebral cortex.

Recovery of long-term maternal behavioral deficiencies of neonatally underfed rats by early sensory stimulation: effects of successive parturitions

The study examines the effects of two paradigms of neonatal food deprivation (daily mother-litter separation, Experiment 1 or nipple-ligation of mothers, Experiment 2) associated or not to early sensory stimulation (daily handling or the exposure to an enriched sensory environment) during the pre-weaning period of Wistar strain female rats. The effects of experimental manipulations were evaluated by measuring the nest building, retrieving latencies and nursing time of adult dams along three successive parturitions. Undernourished dams of Experiment 1, showed significant alterations in maternal responsiveness in the first delivery, which were attenuated by the maternal experience of two additional parturitions. Moreover, maternal alterations were importantly compensated by the association to early sensory stimulation (except nest building). Underfed mothers of Experiment 2 exhibited less alterations of the maternal response during the first parturition, and these were ameliorated by the maternal experience of successive parturitions. Additionally, complete recovery of maternal responsiveness alterations was obtained when sensory stimulation was associated to the maternal experience. Data suggest differential vulnerability to neonatal food and sensory deprivation of the neural mechanisms underlying maternal performance.

Preweaning enrichment has no lasting effects on adult hippocampal neurogenesis in four-month-old mice

Since both living in an enriched environment and physical activity stimulate hippocampal neurogenesis in adult mice, we endeavored to examine whether pre-weaning enrichment, a sensory enrichment paradigm with very limited physical activity, had similar effects on neurogenesis later in life. Mice were removed from the dams for periods of increasing length from post-natal day 7 to 21, and exposed to a variety of sensory stimuli. At the age of 4 months, significant differences could be found between previously enriched and nonenriched animals when spontaneous activity was monitored. Enriched mice moved longer distances, and spent more time in a defined center zone of the open field. Adult neurogenesis was examined by labeling proliferating cells in the dentate gyrus with bromodeoxyuridine (BrdU). Cell proliferation, survival of the newborn cells, and net neurogenesis were similar in both groups. Volumetric measurements and stereological assessment of total granule cell counts revealed no difference in size of the dentate gyrus between both groups. Thus, in contrast to postweaning enrichment, preweaning enrichment had no lasting measurable effect on adult neurogenesis. One of the parameters responsible for this effect might be the lack of physical activity in preweaning enrichment. As physical activity is an integral part of postweaning enrichment, it might be a necessary factor to elicit a neurogenic response to environmental stimuli. The result could also imply that baseline adult hippocampal neurogenesis is independent of the changes induced by preweaning enrichment and might not contribute to the sustained types of plasticity seen in enriched animals.

Intergenerational effects of complete maternal deprivation and replacement stimulation on maternal behavior and emotionality in female rats

The present study investigated the effects of early rearing experiences on the development of maternal behavior in Sprague-Dawley female rats. Pups from individual litters were assigned to four different groups on Day 3 of life. From days 4 to 20 of life, these were reared artificially, without mother and receiving minimal "licking-like" tactile stimulation (AR-MIN), or maximal stimulation (AR-MAX) or were reared with their mothers (MR-CONTROL and MR-SHAM). At 70-100 days all AR and MR animals were mated and then observed with their own offspring, culled to eight pups. After maternal testing open-field tests were conducted. The female offspring in these litters (all raised by their MR and AR mothers) were reared to adulthood and then observed interacting with their offspring. Results show that in adulthood AR mothers engaged in significantly fewer pup-retrievals and less pup-licking (genital and body), and crouching, but significantly more non-maternal tail-chasing, digging, and hanging/climbing. As well, they were more active in the open field. Comparisons between the two AR groups and the MR groups, showed that most of the differences were between the AR-MIN and MR groups, with the AR-MAX animals showing levels of behavior between the two, and differing from neither. Analyses of covariance indicated that early experience and adult emotional behavior both influence adult maternal behavior, but their effects are independent of one another. A cross-generational effect of artificial rearing was also found. Daughters of AR and MR mothers that were observed after the birth of their own litters in adulthood showed a pattern of behavior that mimicked the pattern shown by their mothers. These results are discussed in terms of the variety of possible behavioral, endocrine, and neurochemical mechanisms that mediate the effects of early experiences on adult maternal behavior.

Role of an enriched environment on the restoration of behavioral deficits in Lurcher mutant mice

Lurcher mutant mice, characterized by massive degeneration of the cerebellar cortex, and normal littermate controls were reared from birth either in standard conditions or in an enriched environment. The effects of this manipulation on motor functions, landmark water maze learning, exploration, and anxiety were evaluated at 3 months of age. Under standard conditions, Lurcher mutants were impaired in comparison to controls on tests of sensorimotor function and had altered exploratory tendencies. The enriched housing improved the motor coordination of Lurcher mutants and decreased the number of trials before reaching criterion in the landmark water maze. In addition to its effects in Lurcher mutants, enriched rearing also increased some behavioral abilities in normal mice. It is hypothesized that enriched housing altered brain morphology or neurochemistry in both normal and cerebellar-damaged animals.