Long-lasting Effects of Early Environmental Stimulation on Cortical Spreading Depression in Normal and Early Malnourished Adult Rats

Effects of early monocular enucleation on cortical spreading depression in well-nourished and malnourished adult rats

Sensory development is a complex process that can influence physiological and pathological factors. In laterally-eyed mammals, monocular enucleation (ME) during development and the subsequent lack of external sensory stimuli can result in permanent morphological and physiological changes. Malnutrition, especially in early life, also can cause permanent morphofunctional changes due to inadequate nutrient intake in both hemispheres. This study investigated the effects of early (postnatal day 7) ME and malnutrition during the suckling period on cortical excitability in adulthood (110-140 days of life). For this, we compared the speed propagation of cortical spreading depression in the occipital and parietal cortex of malnourished and well-nourished adult rats, previously suckled small-sized litters with three pups (L3/dam) medium-sized litters with six pups (L6/dam), and large-sized litters with twelve pups (L12/dam). The CSD velocity was augmented by the ME in the contralateral side of the removed eye in the parietal and occipital cortex. These findings suggest that visual sensory input deprivation is associated with permanent functional changes in the visual pathways, which can alter cortical excitability and lead to modifications in CSD propagation.

Undernutrition - thirty years of the Regional Basic Diet: the legacy of Naíde Teodósio in different fields of knowledge

Undernutrition is characterized by an imbalance of essential nutrients with an insufficient nutritional intake, a disorder in which the clinical manifestations in most cases are the result of the economic and social context in which the individual lives. In 1990, the study by the medical and humanitarian Naíde Teodósio (1915-2005) and coworkers, which formulated the Regional Basic Diet (RBD) model for inducing undernutrition, was published. This diet model took its origin from the observation of the dietary habits of families that inhabited impoverished areas from the Pernambuco State. RBD mimics an undernutrition framework that extends not only to the Brazilian population, but to populations in different regions worldwide. The studies based on RBD-induced deficiencies provide a better understanding of the impact of undernutrition on the pathophysiological mechanisms underlying the most diverse prevalent diseases. Indexed papers that are analyzed in this review focus on the importance of using RBD in different areas of knowledge. These papers reflect a new paradigm in translational medicine: they show how the study of pathology using the RBD model in animals over the past 30 years has and still can help scientists today, shedding light on the mechanisms of prevalent diseases that affect impoverished populations.

Suckling in litters with different sizes, and early and late swimming exercise differentially modulates anxiety-like behavior, memory and electrocorticogram potentiation after spreading depression in rats

OBJECTIVE

Analyze the hypothesis that swimming exercise, in rats suckled under distinct litter sizes, alters behavioral parameters suggestive of anxiety and recognition memory, and the electrocorticogram potentiation that occurs after the excitability-related phenomenon that is known as cortical spreading depression (CSD).

METHODS

Male Wistar rats were suckled in litters with six or 12 pups (L₆ and L₁₂ groups). Animals swam at postnatal days (P) 8-23, or P60-P75 (early-exercised or late-exercised groups, respectively), or remained no-exercised. Behavioral tests (open field - OF and object recognition - OR) were conducted between P77 and P80. Between P90 and P120, ECoG was recorded for 2 hours. After this 'baseline' recording, CSD was elicited every 30 minutes over the course of 2 hours.

RESULTS

Early swimming enhanced the number of entries and the percentage of time in the OF-center (P < 0.05). In animals that swam later, this effect occurred in the L6 group only. Compared to the corresponding sedentary groups, OR-test showed a better memory in the L6 early exercised rats, and a worse memory in all other groups (P < 0.05). In comparison to baseline values, ECoG amplitudes after CSD increased 14-43% for all groups (P < 0.05). In the L₆ condition, early swimming and late swimming, respectively, reduced and enhanced the magnitude of the post-CSD ECoG potentiation in comparison with the corresponding L₆ no-exercised groups (P < 0.05).

DISCUSSION

Our data suggest a differential effect of early- and late-exercise on the behavioral and electrophysiological parameters, suggesting an interaction between the age of exercise and the nutritional status during lactation.

Physical Exercise Preserves Adult Visual Plasticity in Mice and Restores it after a Stroke in the Somatosensory Cortex

The primary visual cortex (V1) is widely used to study brain plasticity, which is not only crucial for normal brain function, such as learning and memory, but also for recovery after brain injuries such as stroke. In standard cage (SC) raised mice, experience-dependent ocular dominance (OD) plasticity in V1 declines with age and is compromised by a lesion in adjacent and distant cortical regions. In contrast, mice raised in an enriched environment (EE), exhibit lifelong OD plasticity and are protected from losing OD plasticity after a stroke-lesion in the somatosensory cortex. Since SC mice with an access to a running wheel (RW) displayed preserved OD plasticity during aging, we investigated whether physical exercise might also provide a plasticity promoting effect after a cortical stroke. To this end, we tested if adult RW-raised mice preserved OD plasticity after stroke and also if short-term running after stroke restored OD plasticity to SC mice. Indeed, unlike mice without a RW, adult RW mice continued to show OD plasticity even after stroke, and a 2 weeks RW experience after stroke already restored lost OD plasticity. Additionally, the experience-enabled increase of the spatial frequency and contrast threshold of the optomotor reflex of the open eye, normally lost after a stroke, was restored in both groups of RW mice. Our data suggest that physical exercise alone can not only preserve visual plasticity into old age, but also restore it after a cortical stroke.

Manipulation of rat litter size during suckling influences cortical spreading depression after weaning and at adulthood

Nutritional conditions early in life constitute one environmental factor that can influence brain electrophysiological features. Cortical spreading depression (SD) is a brain electrophysiological phenomenon that can be altered by the early nutritional status of organism. SD-velocity changes were presently studied in young (30-40 days old) and adult (90-120 days) rats suckled in litters formed by 3, 6, or 12 pups (called respectively small (S), medium (M) and large (L) litters). Body weights and SD propagation velocities in the 3 groups varied, respectively in an inverse and direct way, in relation to the litter sizes. The present investigation provides the first systematic description of the effectiveness of favorable and unfavorable lactation conditions (respectively suckling in S and L litters) in altering cortical SD-propagation. The results confirm previous evidence in favor of permanent or at least long-lasting SD-changes associated to the prevailing nutritional status during the period of fast brain development.

NADPH-diaphorase Histochemical Labeling Patterns in the Hippocampal Neuropil and Visual Cortical Neurons in Weaned Rats Reared during Lactation on Different Litter Sizes

Tissue distribution of nitric oxide-synthases was investigated in the rat hippocampus and visual cortex under nutritional changes induced by modification of the litter size. Young (30-45-days-old) rats, suckled in litters formed by 3,6 or 12 pups (called small, medium and large litters, respectively), were studied by using nicotine-adenine-dinucleotide phosphate-diaphorase histochemistry (shortly, diaphorase), a simple and robust procedure to characterize tissue distribution of nitric oxide-synthases. We assessed morphometric features of the diaphorase-positive cells in visual cortex, and the neuropil histochemical activity in hippocampal CA1 and dentate gyrus using densitometry analysis. In the large-litter group, the labeled-cell density in white matter of area 17 was higher, as compared to the small-litter group. There was a clear trend, in the large-litter group, to lower values of soma area, dendritic field and branches per neuron, but the differences were not significant. Densitometry analysis of hippocampus revealed a significant increase in the relative neuropil histochemical activity of the dentate gyrus molecular layer in the larger litters, which may be associated to increased compensatory blood flow in the hippocampus. The pathophysiological mechanisms of the observed changes remain to be investigated.

Malnutrition and REM-sleep Deprivation Modulate in Rats the Impairment of Spreading Depression by a Single Sub-convulsing Dose of Pilocarpine

This study aimed to investigate the effect of a single injection of pilocarpine upon the phenomenon of cortical spreading depression (SD), in adult rats submitted to early malnutrition and/or to REM-sleep deprivation for 72h prior to the SD-recordings. The SD was recorded continuously for 3-4h in 13 well-nourished (W) and 15 early-malnourished (M) adult rats. One to two hours after the beginning of the recording session, a sub-convulsing intraperitoneal (i.p.) injection of pilocarpine (190mg/kg) was applied and its effects on SD were studied during the rest of the recording session. Pilocarpine reduced markedly the ECoG amplitudes in all animals and decreased the SD velocity of propagation in the M-, but not in the W-rats, as compared with the pre-drug values for the same animals. In additional 9W- and 10 M-animals, REM-sleep deprivation was induced during the 72 h preceding the SD-recording session. This condition enhanced the pilocarpine effects on SD in the W-, but not in the M-rats, as compared to the respective non-deprived (ND) groups. The results indicate an important acute cholinergic influence on SD, acting by means of pilocarpine-activated muscarinic receptors. This effect seems to be differentially modulated by sleep deprivation and malnutrition.

Fluoxetine inhibits cortical spreading depression in weaned and adult rats suckled under favorable and unfavorable lactation conditions

Wistar rats (n = 58) were injected subcutaneously during the lactation period with fluoxetine (5, 10, 20 or 40 mg/kg/day) and cortical spreading depression (SD) was recorded immediately after weaning (25-30 days of life). An additional group (10 mg/kg; n = 8) was SD-recorded at 60-70 days. As compared to the saline-injected (n = 24) or "ingenuous" (n = 16) controls, fluoxetine dose-dependently reduced (P < 0.05) SD-velocities in the young rats by 4, 6, 16 and 15%, respectively, and in adult rats by 13%. In another experiment (26 adult rats), topical cortical application of fluoxetine (5 and 10 mg/ml solutions over the intact dura-mater for 10 min; n = 12 and 14, respectively) dose-dependently reduced SD-velocity (7.6% and 43.3% maximal reductions; P < 0.05). SD-propagation was blocked in 4 out of the 14 W-rats topically treated with the highest fluoxetine concentration (10 mg/ml). This topical fluoxetine effect was reverted after flushing the treated region with saline. In additional, 58 early-malnourished rats, fluoxetine applied during the suckling period (10 mg/kg/day, s.c.) and topically (10 mg/ml) also reduced (P < 0.05) SD-velocities by 18 and 22% for the systemic treatment (young and adult animals, respectively) and by 22.4% for the topical one. The present fluoxetine action supports the hypothesis of an antagonistic serotoninergic influence on SD, as previously suggested in experiments using other serotoninergic drugs. Data also suggest that early malnutrition does not greatly affect fluoxetine effects on SD.

Nutrition and brain function: a multidisciplinary virtual symposium

A few months ago, the Brazilian Society for Neuroscience and Behavior (SBNeC) promoted a "virtual symposium" (by Internet, under the coordination of R.C.A. Guedes) on "Nutrition and Brain Function". The discussions generated during that symposium originated the present text, which analyzes current topics on the theme, based on the multidisciplinary experience of the authors. The way the brain could be non-homogeneously affected by nutritional alterations, as well as questions like early malnutrition and the development of late obesity and hormone abnormalities were discussed. Also, topics like the role of essential fatty acids (EFAs) on brain development, increased seizure susceptibility and changes in different neurotransmitters and in cognitive performance in malnourished animals, as well as differences between overall changes in nutrient intake and excess or deficiency of specific nutrients (e.g. iodine deficiency) were analyzed. It was pointed out that different types of neurons, possibly in distinct brain structures, might be differently affected by nutritional manipulation, including not only lack-but also excess of nutrient intake. Such differences could help in explaining discrepancies between data on humans and in animals and so, could aid in determining the basic mechanisms underlying lesions or changes in brain function and behavior.

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.

Citalopram has an antagonistic action on cortical spreading depression in well-nourished and early-malnourished adult rats

Adult, well-nourished (W) and early-malnourished (M) male Wistar rats were injected intraperitoneally for 7 days with 20 mg/kg CIT and cortical spreading depression (CSD) was recorded for 4 h on the day following the treatment. M-animals presented lower body weights, as well as higher CSD velocities of propagation, than the W ones, as previously reported. Compared to saline-injected controls, rats treated with CIT for 7 days presented comparable body weights and lower mean CSD velocities, per hour of recording, the differences being significant at the second hour (3.29+/-0.31 versus 3.56+/-0.40 mm/min; P < 0.05). Topical, cortical application of CIT (1- and 5 mg/ml solutions over the intact dura-mater) reduced dose-dependently the CSD velocity (maximal reductions of 16.3 and 55.8% for the 1 and 5 mg/ml solutions, respectively; P < 0.05), as well as the amplitude of the CSD-slow potential change (58.2 and 88.3%). In three out of seven W-rats and in one out of seven M-rats, topical CIT (5 mg/ml) blocked CSD propagation. The effects were reverted by flushing the treated region with saline. In the M-groups, CIT affected CSD in the same manner as in the W ones. The results reinforce previous evidence for an antagonistic influence of the serotoninergic activity on CSD.