Influences of environmental complexity and visual stimulation on development of occipital cortex in rat

Environmental Enrichment and Epigenetic Changes in the Brain: From the Outside to the Deep Inside

The brain plays a vital role in maintaining homeostasis and effective interaction with the environment, shaped by genetic and environmental factors throughout neurodevelopment and maturity. While genetic components dictate initial neurodevelopment stages, epigenetics-specifically neuroepigenetics-modulates gene expression in response to environmental influences, allowing for brain adaptability and plasticity. This interplay is particularly evident in neuropathologies like Rett syndrome and CDKL5 deficiency syndrome, where disruptions in neuroepigenetic processes underline significant cognitive and motor impairments. The environmental enrichment paradigm, introduced by Donald Hebb in the late 1940s, demonstrates how enriching stimuli-such as complex sensory, social, and cognitive inputs-affect brain structure and function. Despite methodological variability, evidence reveals that enriched environments catalyze beneficial changes in behavior and neuroanatomy, including increased synaptic plasticity, enhanced motor coordination, and improved cognitive performance in rodent models. Additionally, environmental enrichment induces epigenetic modifications that facilitate these outcomes, highlighting the necessity of understanding the mechanisms driving gene expression changes within the context of enriched experiences. Ultimately, this manifold relationship between environment, neuroepigenetic modulation, and brain function highlights the brain's capacity for change, reinforcing the importance of considering environmental factors in studies of neurodevelopment and therapy for neurological disorders.

Non-invasive sensory neuromodulation in epilepsy: Updates and future perspectives

Epilepsy, one of the most common neurological disorders, often is not well controlled by current pharmacological and surgical treatments. Sensory neuromodulation, including multi-sensory stimulation, auditory stimulation, olfactory stimulation, is a kind of novel noninvasive mind-body intervention and receives continued attention as complementary safe treatment of epilepsy. In this review, we summarize the recent advances of sensory neuromodulation, including enriched environment therapy, music therapy, olfactory therapy, other mind-body interventions, for the treatment of epilepsy based on the evidence from both clinical and preclinical studies. We also discuss their possible anti-epileptic mechanisms on neural circuit level and propose perspectives on possible research directions for future studies.

Effects of enriched housing on the neuronal morphology of mice that lack zinc transporter 3 (ZnT3) and vesicular zinc

In the central nervous system, certain neurons store zinc within the synaptic vesicles of their axon terminals. This vesicular zinc can then be released in an activity-dependent fashion as an intercellular signal. The functions of vesicular zinc are not entirely understood, but evidence suggests that it is important for some forms of experience-dependent plasticity in the brain. The ability of neurons to store and release vesicular zinc is dependent on expression of the vesicular zinc transporter, ZnT3. Here, we examined the neuronal morphology of mice that lack ZnT3. Brains were collected from mice housed under standard laboratory conditions and from mice housed in enriched environments - large, multilevel enclosures with running wheels, numerous objects and tunnels, and a greater number of cage mates. Golgi-Cox staining was used to visualize neurons for analysis of dendritic length and dendritic spine density. Neurons were analyzed from the barrel cortex, striatum, basolateral amygdala, and hippocampus (CA1). ZnT3 knockout mice, relative to wild type mice, exhibited increased basal dendritic length in the layer 2/3 pyramidal neurons of barrel cortex, independently of housing condition. Environmental enrichment decreased apical dendritic length in these same neurons and increased dendritic spine density on striatal medium spiny neurons. Elimination of ZnT3 did not modulate any of the effects of enrichment. Our results provide no evidence that vesicular zinc is required for the experience-dependent changes that occur in response to environmental enrichment. They are consistent, however, with recent reports suggesting increased cortical volume in ZnT3 knockout mice.

Extinction of Contextual Fear with Timed Exposure to Enriched Environment: A Differential Effect

BACKGROUND

Extinction of fear memory depends on the environmental and emotional cues. Furthermore, consolidation of extinction is also dependent on the environmental exposure. But, the relationship of the time of the exposure to a variety of environmental cues is not well known. The important region involved in facilitation of extinction of fear memory is through diversion of the flow of information leaving the lateral nucleus of amygdala.

PURPOSE

The study aimed to address a question to explain how these brain regions react to environmental stimulation during the retention and extinction of fear memory.

METHODS

An enriched environment (EE) is assumed to mediate extinction of fear memory, we examined the apparent discrepancy between the effects of defensive response, the freezing behavior induced by Pavlovian classical fear conditioning by subjecting them to variance in the timing to EE. The different timing of EE exposure was 10 days of EE either before fear conditioning and/or after extinction training to the rats. The local field potentials was recorded from CA1 hippocampus, lateral nucleus of amygdala and infralimbic region of medial prefrontal cortex (mPFC) during the fear learning and extinction from the control rats and rats exposed to EE before and after fear conditioning.

RESULTS

Exposure to EE before the fear conditioning and after extinction training was more effective in the extinction fear memory. In addition, we also found switching from exploratory locomotion to freezing during retention of contextual fear memory which was associated with decreased theta power and reduced synchronized theta oscillations in CA1-hippocampus, lateral nucleus of amygdala, and infralimbic region of mPFC.

CONCLUSION

Thus, we propose that the timing of exposure to EE play a key role in the extinction of fear memory.

The Transitional Age Brain: "The Best of Times and the Worst of Times"

Over the past two decades, there have been substantial developments in the understanding of brain development and the importance of environmental inputs and context. This paper focuses on the neurodevelopmental mismatch that occurs during the epoch we term the 'transitional age brain' (ages 13-25) and the collateral behavioral correlates. We summarize research findings supporting the argument that, because of this neurodevelopmental mismatch, transitional age youth are at high risk for engaging in behaviors that lead to negative outcomes, morbidity, and mortality. We highlight the need to develop new, neuroscience-inspired health promotion and illness prevention approaches for transitional age youth.

Developmental neurobiology of the rat attachment system and its modulation by stress

Stress is a powerful modulator of brain structure and function. While stress is beneficial for survival, inappropriate stress dramatically increases the risk of physical and mental health problems, particularly when experienced during early developmental periods. Here we focus on the neurobiology of the infant rat's odor learning system that enables neonates to learn and approach the maternal odor and describe the unique role of the stress hormone corticosterone in modulating this odor approach learning across development. During the first nine postnatal days, this odor approach learning of infant rats is supported by a wide range of sensory stimuli and ensures attachment to the mother's odor, even when interactions with her are occasionally associated with pain. With maturation and the emergence of a stress- or pain-induced corticosterone response, this odor approach learning terminates and a more adult-like amygdala-dependent fear/avoidance learning emerges. Strikingly, the odor approach and attenuated fear learning of older pups can be re-established by the presence of the mother, due to her ability to suppress her pups' corticosterone release and amygdala activity. This suggests that developmental changes in stress responsiveness and the stimuli that produce a stress response might be critically involved in optimally adapting the pup's attachment system to its respective ecological niche.

Opposing actions of environmental enrichment and Alzheimer's disease on the expression of hippocampal microRNAs in mouse models

Alzheimer's disease (AD) is the most common form of dementia in the elderly. Although there are no drugs that modify the disease process, exposure to an enriched environment (EE) can slow the disease progression. Here, we characterize the effects of AD and EE on the post-transcriptional regulators, microRNAs (miRNAs), which may contribute to the detrimental and beneficial effects of AD and EE, respectively, on synaptic plasticity-related proteins and AD pathology. We found for the first time miRNAs that were inversely regulated in AD and EE, and may affect synaptic proteins and modulators, molecular factors associated with AD pathology, and survival and neuroprotective factors. MiRNAs that were upregulated only in 3xTgAD mice model of AD compared with their control mice were localized to synapses, predicted to downregulate essential synaptic proteins and are highly associated with regulating apoptosis, AD-associated processes and axon guidance. Studying the progressive change in miRNAs modulation during aging of 3xTgAD mice, we identified miRNAs that were regulated in earlier stages of AD, suggesting them as potential AD biomarkers. Last, we characterized AD- and EE-related effects in the mouse hippocampus on tomosyn protein levels, an inhibitor of the synaptic transmission machinery. While EE reduced tomosyn levels, tomosyn levels were increased in old 3xTgAD mice, suggesting a role for tomosyn in the impairment of synaptic transmission in AD. Interestingly, we found that miR-325 regulates the expression levels of tomosyn as demonstrated by a luciferase reporter assay, and that miR-325 was downregulated in AD and upregulated following EE. These findings improve our understanding of the molecular and cellular processes in AD pathology, following EE, and the interplay between the two processes, and open new avenues for the studies of understanding and controlling AD.

VEGF reverts the cognitive impairment induced by a focal traumatic brain injury during the development of rats raised under environmental enrichment

The role of VEGF in the nervous system is extensive; apart from its angiogenic effect, VEGF has been described as a neuroprotective, neurotrophic and neurogenic molecule. Similar effects have been described for enriched environment (EE). Moreover, both VEGF and EE have been related to improved spatial memory. Our aim was to investigate the neurovascular and cognitive effects of intracerebrally-administered VEGF and enriched environment during the critical period of the rat visual cortex development. Results showed that VEGF infusion as well as enriched environment induced neurovascular and cognitive effects in developing rats. VEGF administration produced an enhancement during the learning process of enriched animals and acted as an angiogenic factor both in primary visual cortex (V1) and dentate gyrus (DG) in order to counteract minipump implantation-induced damage. This fact revealed that DG vascularization is critical for normal learning. In contrast to this enriched environment acted on the neuronal density of the DG and V1 cortex, and results showed learning enhancement only in non-operated rats. In conclusion, VEGF administration only has effects if damage is observed due to injury. Once control values were reached, no further effects appeared, showing a ceiling effect. Our results strongly support that in addition to neurogenesis, vascularization plays a pivotal role for learning and memory.

The development and neurobiology of infant attachment and fear

Survival of altricial infants depends on attachment to the caregiver - a process that requires infants to identify, learn, remember, and approach their attachment figure. Here we review the neurobiology of attachment in infant rats where learning about the caregiver is supported by a specialized attachment neural circuitry to promote the infant-caregiver relationship. Specifically, the attachment circuit relies on infants acquiring learned preferences to the maternal odor, and this behavior is supported by the hyperfunctioning locus coeruleus and generous amounts of norepinephrine to produce experience-induced changes in the olfactory bulb and anterior piriform cortex. Infants also possess a reduced ability to acquire learned aversions or fear, and this behavior is facilitated through attenuated amygdala plasticity to block fear learning. Presumably, this attachment circuitry constrains the infant animal to express only learned preferences regardless of the quality of care received. As pups mature, and begin to travel in and out of the nest, the specialized attachment learning becomes contextually confined to when pups are with the mother. Thus, when outside the nest, these older pups show learning more typical of adult learning, presumably to prepare for independent life outside the nest. The quality of attachment can alter this circuitry, with early life stress prematurely terminating the pups' access to the attachment system through premature functional activation of the amygdala. Overall, the attachment circuit appears to have a dual function: to keep pups close to the caregiver but also to shape pups' behavior to match the environment and define long-term emotion and cognition.

Visual deprivation alters dendritic bundle architecture in layer 4 of rat visual cortex

The effect of visual deprivation followed by light exposure on the tangential organisation of dendritic bundles passing through layer 4 of the rat visual cortex was studied quantitatively in the light microscope. Four groups of animals were investigated: (I) rats reared in an environment illuminated normally--group 52 dL; (II) rats reared in the dark until 21 days postnatum (DPN) and subsequently light exposed for 31 days-group 21/31; (III) rats dark reared until 52 DPN and then subsequently light exposed for 3 days--group 3 dL; and (IV) rats totally dark reared until 52 DPN--group 52 DPN. Each group contained five animals. Semithin 0.5-1-μm thick resin-embedded sections were collected from tangential sampling levels through the middle of layer 4 in area 17 and stained with Toluidine Blue. These sections were used to quantitatively analyse the composition and distribution of dendritic clusters in the tangential plane. The key result of this study indicates a significant reduction in the mean number of medium- and small-sized dendritic profiles (diameter less than 2 μm) contributing to clusters in layer 4 of groups 3 dL and 52 dD compared with group 21/31. No differences were detected in the mean number of large-sized dendritic profiles composing a bundle in these experimental groups. Moreover, the mean number of clusters and their tangential distribution in layer 4 did not vary significantly between all four groups. Finally, the clustering parameters were not significantly different between groups 21/31 and the normally reared group 52 dL. This study demonstrates, for the first time, that extended periods of dark rearing followed by light exposure can alter the morphological composition of dendritic bundles in thalamorecipient layer 4 of rat visual cortex. Because these changes occur in the primary region of thalamocortical input, they may underlie specific alterations in the processing of visual information both cortically and subcortically during periods of dark rearing and light exposure.

Defining age limits of the sensitive period for attachment learning in rat pups

Enhanced odor preference learning and attenuated fear learning characterizes rat pups' attachment learning Sensitive Period for learning the maternal odor. This period terminates at 10 days old (PN10) with increasing endogenous levels of the stress hormone, corticosterone. Increasing Sensitive Period pups' corticosterone prematurely terminates the Sensitive Period, while decreasing corticosterone in older pups delays Sensitive Period termination. Here we extend these findings and define the age range corticosterone alters learning and question whether corticosterone permanently terminates the Sensitive Period. Pups were odor-0.5 mA shock conditioned with either corticosterone increased (PN5-6; 4 mg/kg vs. saline) or decreased (PN15-16; naturally by maternal presence or corticosterone synthesis blocker, Metyrapone). Finally, PN7-8 pups were conditioned with corticosterone and reconditioned without corticosterone to assess whether the Sensitive Period was permanently terminated. Results indicate developmental limits for corticosterone regulation of pup learning are PN6 through PN15. Furthermore, inducing precocious corticosterone induced fear learning was not permanent, since reconditioning without corticosterone enabled odor preference learning. Results suggest pups are protected from learning aversions to maternal odor until approaching weaning.

Examining the Neuroscience Evidence for Sensory-Driven Neuroplasticity: Implications for Sensory-Based Occupational Therapy for Children and Adolescents

When Ayres first presented the theory of sensory integration (SI), she grounded it in the neuroscience literature. Neuroplasticity was then, and is today, considered to be at the heart of this theory. This evidence-based review sought to critically examine the basic science literature to specifically identify evidence for the assumptions and tenets of Ayres’ theory of SI. We reviewed literature between 1964 and 2005, within psychological, physiological, and biomedical areas, addressing neuroplasticity. The review focused on sensorimotor-based neuroplasticity; explored the data that addressed the links among sensory input, brain function, and behavior; and evaluated its relevance in terms of supporting or refuting the theoretical premise of occupational therapy using an SI framework (OT/SI) to treatment. Although direct application from basic science to OT/SI is not feasible, we concluded that there was a basis for the assumptions of Ayes’ SI theory.

Transitions in sensitive period attachment learning in infancy: the role of corticosterone

Survival of altricial infants, including humans and rats, depends on attachment to the caregiver - a process that requires infants to recognize, learn, and remember their attachment figure. The demands of a dynamic environment combined with a maturing organism require frequent neurobehavioral reorganization. This restructuring of behavior and its supporting neural circuitry can be viewed through the unique lens of attachment learning in rats in which preference learning is enhanced and aversion learning is attenuated. Behavioral restructuring is well adapted to securing the crucial infant-caregiver relationship regardless of the quality of care. With maturation and the end of the infant-caregiver attachment learning period, the complex interplay of neural structures, hormones, and social behavior coordinates the developing rat's eventual transition to life outside of the nest. Nevertheless, early-life environmental and physiological stressors can alter the resilient nature of this system, particularly with respect to the amygdala, and these changes may provide important clues to understanding the lasting effects of early stress.

Is exposure to enriched environment beneficial for functional post-lesional recovery in temporal lobe epilepsy?

Exposure to enriched environment has been shown to induce robust neuronal plasticity in both intact and injured adult central nervous system, including up-regulation of multiple neurotrophic factors, enhanced neurogenesis in the dentate gyrus of the hippocampus, and improved spatial learning and memory function. Neuronal plasticity, though mostly adaptive and abnormal, also occurs during certain neurodegenerative conditions such as the temporal lobe epilepsy (TLE). The TLE is characterized by hippocampal neurodegeneration, aberrant mossy fiber sprouting, spontaneous recurrent motor seizures, cognitive deficits, and abnormally enhanced neurogenesis during the early phase and dramatically declined neurogenesis during the chronic phase of the disease. As environmental enrichment has been found to be beneficial for treating animal models of Alzheimer's, Parkinson's, and Huntington's diseases, there is considerable interest in determining the efficacy of this strategy for preventing or treating chronic TLE after the initial precipitating brain injury. This review first discusses the proof of principle behind the potential application of the environmental enrichment strategy for preventing or treating TLE after brain injury. The subsequent chapters confer the portrayed beneficial effects of enrichment for functional post-lesional recovery in TLE and the possible complications which may arise from housing epilepsy-prone or epileptic rats in enriched environmental conditions. The final segment discusses studies that are essential for further understanding the efficacy of this approach for preventing or treating TLE.

Enviromimetics: exploring gene environment interactions to identify therapeutic targets for brain disorders

There is a growing awareness of the central role played by environmental factors in many of the most debilitating neural disorders. Epidemiological studies have suggested a complex balance between genetic and environmental factors in the pathogenesis of neurological and psychiatric conditions. The use of accurate animal models, combined with experimental manipulations such as environmental enrichment, has shown that increased sensory, cognitive and motor stimulation has beneficial effects in a range of CNS disorders, including Huntington's, Alzheimer's, Parkinson's and other neurodegenerative diseases. Various studies have identified molecular, structural and functional correlates of this experience-dependent plasticity. The authors propose that the molecular systems which mediate the therapeutic effects of environmental enrichment may provide novel targets for pharmacotherapies. More specifically, they elaborate a theoretical framework for the development of 'enviromimetics', therapeutics that mimic or enhance the beneficial effects of environmental stimulation, targeted towards a wide range of nervous system disorders.

Neurobiology of infant attachment

A strong attachment to the caregiver is critical for survival in altricial species, including humans. While some behavioral aspects of attachment have been characterized, its neurobiology has only recently received attention. Using a mammalian imprinting model, we are assessing the neural circuitry that enables infant rats to attach quickly to a caregiver, thus enhancing survival in the nest. Specifically, the hyper-functioning noradrenergic locus coeruleus (LC) enables pups to learn rapid, robust preference for the caregiver. Conversely, a hypo-functional amygdala appears to prevent the infant from learning aversions to the caregiver. Adult LC and amygdala functional emergence correlates with sensitive period termination. This study suggests the neonatal brain is not an immature version of the adult brain but is uniquely designed to optimize attachment to the caregiver. Although human attachment may not rely on identical circuitry, the work reviewed here suggests a new conceptual framework in which to explore human attachments, particularly attachments to abusive caregivers.

Enhancement of auditory fear conditioning after housing in a complex environment is attenuated by prior treatment with amphetamine

Prior exposure to drugs of abuse has been shown to occlude the structural plasticity associated with living in a complex environment. Amphetamine treatment may also occlude some cognitive advantages normally associated with living in a complex environment. To test this hypothesis we examined the influence of prior exposure to amphetamine on fear conditioning in rats housed in either a standard or complex environment. Housing in a complex environment facilitated fear learning to an auditory conditioned stimulus (CS), but not to the training context, relative to animals housed singly or in a social group. Prior treatment with amphetamine eliminated this effect. These results indicate that living in a complex environment facilitates conditional freezing to an auditory CS, and that this effect is abolished by pretreatment with amphetamine.

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.

Estimulação psicossocial e plasticidade cerebral em desnutridos

RESUMO: É feita uma revisão sobre as estratégias e efeitos da estimulação sensorial e ambiental de indivíduos desnutridos. Reportam os autores evidências provenientes de experimentos com modelos animais e de estudos em seres humanos, mostrando os benefícios da administração da estimulação sensorial ou psicossocial programadas sobre as funções neuro-comportamentais. Mostram ainda a importante participação que a plasticidade cerebral pode ter neste processo. Finalmente enfatizam que as evidências eletrofisiológicas - obtidas pela técnica da depressão alastrante cortial em animais - e as observações em seres humanos indicam que as regiões cerebrais comportam-se diferencialmente nesta recuperação. Daí, sugerem uma abordagem nos cuidados médicos em indivíduos desnutridos levando em conta estas peculiaridades regionais do cérebro.

Effect of environmental complexity on size of the superior colliculus

The present study examined effects of environmental complexity on the size of the superior colliculus, a subcortical structure involved in visuomotor functions. Long-Evans hooded rats raised together in a complex environment for 48 weeks were compared with their littermates housed in individual cages. The depth and area of the superficial gray layer of the superior colliculus were about 5-6% greater in the group from the complex environment, while the deeper layers of the superior colliculus showed no significant differences. The magnitude of the differences approached those reported for the neocortex, which has been considered to be distinctive in its morphological responsiveness to differential environmental complexity. The findings also extend previous observations that visual deprivation leads to shrinkage of the superficial gray layer and indicate that the morphology of this subcortical visual area is responsive to varying degrees of environmental stimulation.

Effect of early locomotor training on evoked potentials and structural organization of visual cortex dendrites of rats during ontogeny

The effect of early locomotor training (running in a squirrel cage from an age of 1 month for 3-6 months) on evoked potentials of the rat visual cortex during ontogeny was investigated. It was established that intensified proprioceptive afferentation causes a statistically significant reduction of both the latent periods and the recovery cycles of excitability of primary responses of the visual cortex to paired light flashes, whereupon the increase in functional activity is more pronounced with respect to the indices of the excitability recovery cycle than with respect to the latent periods or primary responses. The indicated functional changes correlate with the quantitative increase in the density of dendritic spines on neurons of the visual cortex of both layer V, which are primarily the integrative-triggering apparatus of the cortex, and of the complex of layers II + III, which are primarily associative with respect to their functional significance.

Cortical depth changes in enriched and isolated mice

The occipital cortical depth was determined in laboratory mice at both 14 and 20 days of age and after various periods of postweaning exposure to enrichment or isolation. The depth was found to be maximal at 20 days of age. It declined thereafter, irrespective of environment, but the isolate cortical depth decreased faster than the enriched. The postweaning depth of the occipital cortex appears to be determined by an inevitable age-related decrease whose rate of decline may be attenuated by sensory stimulation. The postweaning cortical depth may reflect the extent of cortical neuronal development and associated metabolic activity.

Rehabilitation following brain damage: some neurophysiological mechanisms. The effects of repetitive stimulation in recovery from damage to the central nervous system

There is a growing body of evidence that the central nervous system (CNS), even in the adult animal, is capable of adaptation and reorganization not only as a result of partial damage to the CNS but also in response to stimulation. Environmental stimulation produces changes including expansion of visual cortex, increases in dendritic branching, glia and cholinesterase. Environmental stimulation also produces behavioural changes. Experimental electrical stimulation produces changes in synapse size, synaptic vesicle change, dendritic branching and changes in synaptic transmission. In man, repetitive electrical stimulation via epidural electrodes increases plasma levels of norepinephrine, epinephrine, and dopamine, and CSF levels of norepinephrine. Repetitive electrical stimulation in man dates back to 1967 and has been used for the control of pain, to improve spasticity, bladder control, motor deficit and the autonomic hyperreflexia of spinal cord injury. In addition, improvement has been reported in epilepsy, cerebral palsy, torticollis and peripheral vascular diseases. The best controlled studies are in multiple sclerosis and peripheral vascular disease, and these results will be presented in more detail.

Recovery from experimentally induced problem-solving deficits in neonatal Peking ducklings as a function of environmental stimulation

Neonatal Peking ducklings were reared in 3 different environments containing varied light and sound stimulation. One group was exposed to the stimulative environment only during the last 3 prenatal days, 1 group was placed in the stimulative environment at the time of hatching, and the 3rd group was exposed to the stimulative environment both pre- and postnatally. No differences in performance in a detour learning task were noted between controls and experimentals from the 1st 2 groups (prenatal stimulation only and postnatal stimulation only); however, the group receiving both pre- and postnatal stimulation solved the detour task significantly faster than their controls. This learning improvement as a function of the stimulative environment represents a partial recovery from the deficit produced as a result of the experimental paradigm in which the shell covering the air space was replaced with clear plastic wrap, a procedure which has been shown to reduce oxygen consumption and lead to learning retardation.

Injury and insult--considerations of the neuropathological aetiology of mental subnormality

We have gone far in getting to grips with the nature of the error underlying mental handicap in many conditions. In a number of these, this has given scope, for example, for treatment based on biochemical correction, and for valuable preventive measures. The cause of the condition of many mentally handicapped patients, however, remains mysterious when neither history-taking nor investigations have led to any clues.

The interaction between sensory and nonsensory factors in the determination of brain structure and chemistry: a review

Contrary to previous thinking, the brain is now recognized as a plastic organ whose structure and function adapt to the functional demands of the sensory environment. This paper examines the interaction between sensory and nonsensory brain-modifying factors in determining the psychobiological outcome in animals reared under conditions of environmental complexity and deprivation. Stimulant drugs appear to enhance complexity effects and depressants to reduce them. Hormones affected by hypophysectomy or castration do not appear to interfere with sensory effects, though a progestogen norethynodrel does appear to interact with them. For genetic effects, strain, species and sex may interact, with male hybrids being perhaps most susceptible to environmental effects. The picture which is emerging is of the brain as inextricably linked to its environment and suggests that a full study demands a recognition of the ecological context. This picture of multiway inter-dependencetrain species and sex may interact, with male hybrids being perhaps most susceptible to environmental effects. The picture which is emerging is of the brain as inextricably linked to its environment and suggests that a full study demands a recognition of the ecological context. This picture of multiway inter-dependencetrain species and sex may interact, with male hybrids being perhaps most susceptible to environmental effects. The picture which is emerging is of the brain as inextricably linked to its environment and suggests that a full study demands a recognition of the ecological context. This picture of multiway inter-dependence and interdetermination or "omnideterminism" is similar to the holistic orgnaismic picture of the universe of the millenia-old yogi-consciousness disciplines and of modern physics.

Effects of early visual and complex stimulation on learning, brain biochemistry, and electrophysiology

A complex stimulation regimen (visual, auditory, and somesthetic-kinesthetic with forced movements, 30 times for 30 min each within 14 days) increased significantly the amplitudes of visual cortical evoked potentials (EPs) in adult rats if applied during the second postnatal fortnight. The EP increase after stimulation during the first 14 days after birth was not significant. Visual stimulation alone was compared with complex stimulation (visual plus forced movements) during the 2nd postnatal fortnight. More specific local changes in the visual cortex were revealed in brain biochemistry (lower DNA concentration, more RNA and protein per cell) and cortical electrogenesis (enhanced visual EPs) after visual stimulation alone, whereas complex stimulation induced more diffuse changes and rather profoundly influenced higher nervous functions (viz., memory retrieval - improved 24-h). Involvement of both specific and nonspecific mechanisms in the aftereffects of early stimulation is indicated.

Brain-specific proteins in the occipital cortex of rats housed in enriched and impoverished environments

The occipital cortex was dissected from the brain of rats housed in either enriched or impoverished environment for four weeks. In environmentally enriched rats the weight of occipital cortex was found to be increased 5.7%, compared to environmentally impoverished rats, and the amount of protein was increased 6.0%. The amount of six nervous system-specific proteins was measured by crossed immunoelectrophoresis. Synaptin increased 4.7%, D3 increased 8.3%, and D1 increased 9.6%, whereas D2 was not significantly increased. Compared to D2, D3 and D1 were still increased significantly, although all were present in synaptosomal membrane fractions. The protein S-100 was increased 3.4% and the neuronal protein 14-3-2 was increased 12.2% for the cathodal component whereas the anodal component was not increased. The results were interpreted as representing delayed development of environment-dependent neurons in the environmentally impoverished rats.

The effects of dark rearing on the development of the visual cortex of the rat

The effects of dark rearing on the development of the visual cortex has been studied in Wistar rats, as have the effects of subsequent light exposure on recovery. Five groups of animals were used: (1) light exposed until 30-40 days post partum (dpp) (2) dark reared until 30-40 ddp (3) dark reared until 80-120 dpp (4) dark reared to 21 dpp, then light exposed until 40 dpp (5) light exposed to 21 dpp and then dark reared until 40 dpp. Golgi-Cox impregnations of layer IV stellate cell dendritic fields were analysed and total neuronal and glial counts were also done within layer IV of the primary visual cortex. Normal visual stellate cell dendritic fields were radially organised, with the highest dendritic density being recorded below the soma. In short term visually deprived animals and in the exposed only for 21 dpp and then reared in light until 40 dpp the radial distribution of dendrites was maintained but the peak density shifted to above the soma. In all other experimental groups this abnormal polarisation was still present but not as marked. Measurement of branching indices suggested that these field changes resulted from increased branching and growth in the superficial domain and not from the reorientation of dendrites. Differential glial counts revealed a significantly higher number of microglia in dark reared animals than in controls. Neuronal numbers were not affected.

The effects of reduced climbing and parallel fibre input on Purkinje cell dendritic growth

The effects of afferent fibre depletion on the development of the dendritic trees of Purkinje cells in the cerbellum were investigated. Parallel fibres were reduced by postnatal administration of a schedule of low level X-irradiation. Climbing fibers were prevented from innervating the cerebellum by lesioning the olivo-cerebellar tract. Network analysis was performed on Purkinje cells in Golgi-Cox preparations of the vermis of 30-day-old animals. tin the irradiated cerebella Purkinje cells with a 'weeping willow' type morphology predominated. Purkinje cells devoid of their climbing fibre contact exhibited large spines on their main dendritic trunks. In both experimental situations the size of the dendritic tree was reduced. This diminution was the result of a decrease in the total number of dendritic segemnts. Individual segment lengths were largely unalteral. Topological type analysis revealed that the trees had arisen in a manner indistinguishable from terminal dichotomous branching and that the 'weep-willow' pattern was produced by a deviation of branching from a purely random form. The interaction of intrinsic and extrinsic factors in the formation of segments and on the nature of branching were discussed.

The effects of psychomotor stimulants on stereotypy and locomotor activity in socially-deprived and control rats

Using measures of locomotor activity and stereotypy, dose-response curves to several psychomotor stimulant drugs were obtained on rats reared in deprived or normal environments. At both 0.5 and 1.5 mg/kg d-amphetamine, the deprived rats exhibited more intense stereotyped behavior than the control rats. At 5.0 mg/kg, both groups showed maximum response. However, there was no significant difference between the two groups in locomotor response. A similar pattern of results was found for pipradrol, cocaine, and apomorphine. The findings show that different social and environmental experience can modify the response to dopaminergic stimulating agents. The results also suggest that stereotyped behavior should not be considered on the same continuum as locomotor activity. These two behaviors may be mediated by different mechanisms.