Relationship of arsenic and chromium availability with carbon functional groups, aluminum and iron in Little Washita River Experimental Watershed Reservoirs, Oklahoma, USA.

Sediment from three reservoirs located in the Little Washita River Experimental Watershed (LWREW) in Oklahoma, USA with contrasting dominant land uses were analyzed for total and extractable concentrations of arsenic (As) and chromium (Cr), and the potential ecologic risk to benthic organisms. Extractable As ranged from 0.24 to 1.21 mg kg-1, in the order grazing>cropland>forest and 0.13-0.58 mg kg-1 for extractable Cr, in the order of forest>grazing>cropland. However, only approximately < 1.5% of total As and < 4% of total Cr were extractable. Total As ranged from 16.2 to 141 mg kg-1 and total Cr ranged from 5.06 to 40.1 mg kg-1 both in the order of cropland>grazing>forest. The sediment exhibited an alkaline pH (8.0-8.7). As sorption exhibited a positive relationship with Al (r = 0.9995; P = 0.0001), Fe (r = 0.9829; P = 0.0001), and C (r = 0.4090; P = 0.0017) and Cr correlated positively with Al (r = 0.9676 P = 0.0001), Fe (r = 0.9818; P = 0.0001), and C (r = 0.3368; P = 0.0111). In addition, both As and Cr exhibited positive relationships with carbon (C) functional groups in the order of O-alkyl C> methoxyl C> alkyl C> aromatic C> carboxyl C> phenolic C. The sediment concentration analysis results illustrated that As in all reservoirs exceeded their respective Threshold Effect Level (TEL) and/or Probable Effect Level (PEL) indicating that existing concentrations of metals in these sediments were sufficiently high to cause adverse effects. However, Cr concentrations in all reservoirs evaluated was lower compared to the TEL and PEL.

Potential arsenic exposures in 25 species of zoo animals living in CCA-wood enclosures.

Animal enclosures are often constructed from wood treated with the pesticide chromated copper arsenate (CCA), which leaches arsenic (As) into adjacent soil during normal weathering. This study evaluated potential pathways of As exposure in 25 species of zoo animals living in CCA-wood enclosures. We analyzed As speciation in complete animal foods, dislodgeable As from CCA-wood, and As levels in enclosure soils, as well as As levels in biomarkers of 9 species of crocodilians (eggs), 4 species of birds (feathers), 1 primate species (hair), and 1 porcupine species (quills). Elevated soil As in samples from 17 enclosures was observed at 1.0-110mg/kg, and enclosures housing threatened and endangered species had As levels higher than USEPA's risk-based Eco-SSL for birds and mammals of 43 and 46mg/kg. Wipe samples of CCA-wood on which primates sit had dislodgeable As residues of 4.6-111µg/100cm(2), typical of unsealed CCA-wood. Inorganic As doses from animal foods were estimated at 0.22-7.8µg/kg bw/d. Some As levels in bird feathers and crocodilian eggs were higher than prior studies on wild species. However, hair from marmosets had 6.37mg/kg As, 30-fold greater than the reference value, possibly due to their inability to methylate inorganic As. Our data suggested that elevated As in soils and dislodgeable As from CCA-wood could be important sources of As exposure for zoo animals.

Cleaning-induced arsenic mobilization and chromium oxidation from CCA-wood deck: Potential risk to children.

Concern about children's exposure to arsenic (As) from wood treated with chromated-copper-arsenate (CCA) led to its withdrawal from residential use in 2004. However, due to its effectiveness, millions of American homes still have CCA-wood decks on which children play. This study evaluated the effects of three deck-cleaning methods on formation of dislodgeable As and hexavalent chromium (CrVI) on CCA-wood surfaces and in leachate. Initial wipes from CCA-wood wetted with water showed 3-4 times more dislodgeable As than on dry wood. After cleaning with a bleach solution, 9.8-40.3µg/100cm(2) of CrVI was found on the wood surface, with up to 170µg/L CrVI in the leachate. Depending on the cleaning method, 699-2473mg of As would be released into the environment from cleaning a 18.6-m(2)-deck. Estimated As doses in children aged 1-6 after 1h of playing on a wet CCA-wood deck were 0.25-0.41µg/kg. This is the first study to identify increased dislodgeable As on wet CCA-wood and to evaluate dislodgeable CrVI after bleach application. Our data suggest that As and CrVI in 25-year old CCA-wood still show exposure risks for children and potential for soil contamination.

Fusion of Na-ASP-2 with human immunoglobulin Fcγ abrogates histamine release from basophils sensitized with anti-Na-ASP-2 IgE.

Na-ASP-2 is a major protein secreted by infective third-stage larvae (L3) of the human hookworm Necator americanus upon host entry. It was chosen as a lead vaccine candidate for its ability to elicit protective immune responses. However, clinical development of this antigen as a recombinant vaccine was halted because it caused allergic reactions among some of human volunteers previously infected with N. americanus. To prevent IgE-mediated allergic reactions induced by Na-ASP-2 but keep its immunogenicity as a vaccine antigen, we designed and tested a genetically engineered fusion protein, Fcγ/Na-ASP-2, composed of full-length Na-ASP-2 and truncated human IgG Fcγ1 that targets the negative signalling receptor FcγRIIb expressed on pro-allergic cells. The chimeric recombinant Fcγ/Na-ASP-2 protein was expressed in Pichia pastoris and shared the similar antigenicity as native Na-ASP-2. Compared to Na-ASP-2, the chimeric fusion protein efficiently reduced the release of histamine in human basophils sensitized with anti-Na-ASP-2 IgE obtained from individuals living in a hookworm-endemic area. In dogs infected with canine hookworm, Fcγ/Na-ASP-2 resulted in significantly reduced immediate-type skin reactivity when injected intradermally compared with Na-ASP-2. Hamsters vaccinated with Fcγ/Na-ASP-2 formulated with Alhydrogel(®) produced specific IgG that recognized Na-ASP-2 and elicited similar protection level against N. americanus L3 challenge as native Na-ASP-2.

Stage-specific immune responses in human Necator americanus infection.

We describe how hookworms interact with their human hosts by comparing lymphocyte phenotyping, proliferative responses, and cytokine and chemokine secretion patterns in adults who are either mono-infected with Necator americanus or egg-negative controls resident in an area of high transmission in Brazil. Cellular immune responses against crude hookworm antigen extracts from different developmental stages were evaluated simultaneously. Principal component analysis (PCA) was used to reduce the standardized immune responses. Random effects multivariate regression was then used to investigate whether principal components (PC) differ between the two groups once potential confounders and effect modifiers have been accounted for. Although hookworm patients had reduced percentages of T and B cells, they had higher levels of activated CD4(+) T and CD19(+) B cells. This state of 'immune activation' coincided with lower proliferative responses, especially to third-stage larval antigen. Cytokine levels in mono-infected adults were also lower and characterized by a mixed Th1/Th2-type profile. Excretory/secretory antigen from adult worms was a potent modulator of the immune response, resulting in diminished TNF-alpha and IL-10 secretion in peripheral blood mononuclear cells (PBMC) from hookworm infected patients. We propose that the longevity of hookworms in their human hosts results from a stage-specific, down-modulation of the immune response.

The influence of unstable signals for electron spin resonance dosimetry with synthetic A-type carbonated apatite.

Synthetic A-type carbonated apatite prepared in controlled conditions was irradiated at room temperature with 60Co gamma rays. The ESR spectrum was associated to axial CO2- and orthorhombic CO3- species. Radicals used as dose markers in biological apatites are long-lived paramagnetic species. The stability of the post-irradiation signal of A-type apatite was investigated for almost 2 years. Measurements showed variations in the spectra attributed to unstable CO3- species, which can be eliminated by thermal treatments at 100 degrees C for 24 h. Results indicated the potential use of an A-type carbonated apatite as a dosemeter.

Atropine in exercise stress echocardiography? Case report.

Stress echocardiography is widely used in the investigation of coronary heart disease. Exercise stress echocardiography offers the advantage of visualizing myocardial motion abnormalities during physiological stress testing. The authors report the use of atropine, as an adjunct to exercise echocardiography, in risk stratification after myocardial infarction.

Effects of malnutrition during early lactation on development and feeding behavior under the self-selection paradigm.

Selection of food can be affected by several factors, and with the method of self-selection, qualitative changes in nutritional balance may be detected. The goal of the present study was to evaluate feeding preferences in weaning rats using three macronutrients (protein, carbohydrate, and fat), through a free-choice method, evaluating the alteration in their feeding patterns as compared with the previous nutritional status during the early lactation period. We analyzed the effects of protein restriction during lactation over the nitrogen balance after the weaning. The dams were assigned to one of two diet conditions (nourished or malnourished). At weaning, two pups from each litter were housed individually in metabolic cages, and they were maintained on self-selection under a free-choice paradigm and were provided with separate sources of macronutrients. The parameter for evaluating the nutritional effectiveness of the diets was nitrogen balance. We observed that protein intake tended to increase and consumption of carbohydrate and fat tended to decrease progressively during the 3 wk of experiment. In selecting their own food, growing rats and malnourished rats consumed a larger amount of protein than the other rats. Nourished rats selecting their diet had a larger nitrogen balance than nourished rats receiving a composed diet; no nitrogen balance difference was found between the self-selecting groups. Rats can choose an adaptive form when recovering from protein malnutrition.

[Assessment of aortic atherosclerosis with transesophageal echocardiography]. / Avaliação da aterosclerose aórtica por ecocardiografia transesofágica.

OBJECTIVE: To image the thoracic aorta by transesophageal echocardiography (TEE) and study atherosis (morphology and extent of atheroma plaques) and sclerosis (stiffness) and secondarily correlate them with serum lipid levels (cholesterol, HDL, LDL and triglycerides). METHODS: We studied 29 patients (pts) who underwent TEE electively (male 18 pts, age 57.8 +/- 14.6 years). The parameters evaluated were: the stiffness coefficient = ln (PAsist/PAdiast)/(Dsyst/Dmin), and the morphology, location and extent of atheroma plaques. The systolic distension (Dsyst) was the difference between the maximal and the minimal dimensions (Dmin) of the aortic diameter measured by M mode. The lesions were classified in 4 degrees (0-3): 0--normal intima, 1--intimal thickening, 2--atheroma, 3--complicated lesion. Five aortic segments were studied: arch, D1-D4 (descending aorta at 5 cm intervals from the first 25 cm distal of the incisors line). We calculated the individual score = 1 x theta 1/180 + 2 x theta 2/180 + 3 x theta 3/180, theta n represents the angles occupied by the lesions and n (1-3) the severity of atherosis of each lesion. The total atherosis index (TAI) was sigma scores/(n. degree of visualized segments). RESULTS: The arch was not visualized in 3 pts, and the segment D4 was only visualized in 3 pts. TAI mean = 0.82 +/- 0.74, stiffness coefficient mean (SC) = 9.56 +/- 15.072. There were no significant correlations between the lipid levels and the TAI or SC. The only significant positive correlations were: TAI vs age (r = 0.62, p < 0.001) and SC and diastolic blood pressure (BP) (r = 0.42, p < 0.05). CONCLUSIONS: The best visualized segments belong to the descending aorta (25 to 40 cm from the incisors). In this group of patients the lipid levels did not seem to be a preponderant factor in aortic atherosclerosis. The most important factors were age for atherosis and BP for sclerosis.

Malnutrition and environmental stimulation in rats: wave latencies of the brainstem auditory evoked potentials.

It has been shown that environmental stimulation may reduce the damage caused by malnutrition to morphological and behavioural parameters; however, there are no data on the effects of stimulation on the Brainstem Auditory Evoked Potentials (BAEPs). The aim of this study was to evaluate the effects of protein malnutrition, nutritional recovery and environmental stimulation on the BAEPs of the rat. On the first day of life, the animals were divided into Well-nourished (W) and Malnourished (M) groups. At weaning, half the M rats were submitted to nutritional recovery (R) until the test day. All groups were subdivided into Stimulated (S) and Non-Stimulated (N) rats. BAEPs was tested in animals exposed to clicks of 90, 80 and 70 dB of intensity. The BAEPs latencies of waves I, II, III and IV in the left ear were analysed in independent groups of rats on the 14th, 18th, 22nd, 32nd, and 42nd days of age. Statistical analysis showed diet and environmental stimulation interaction on the latencies of waves I, II, III and IV at all tested ages. WN rats showed longer latencies of waves I, II, III and IV than WS rats, and MN rats also showed longer latencies of these waves compared to WN, MS and RN at all tested ages. The results showed that malnutrition caused a delay in the latency of all BAEPs waves in rats of all ages. However, environmental stimulation reduced these latencies, reversing some damage caused by malnutrition. These data suggest that the auditory brainstem pathway is vulnerable to nutritional insults, and its structures show plasticity with environmental stimulation.

Ethological analysis of mother-pup interactions and other behavioral reactions in rats: effects of malnutrition and tactile stimulation of the pups.

Mother-pup interaction, as well as other behavioral reactions were studied during the lactation period in 24 litters of Wistar rats and their dams fed either a 16% (control - C; 12 litters) or a 6% (malnourished - M; 12 litters) protein diet. The diets were isocaloric. Throughout lactation there was a 36.4% weight loss of M dams and a 63% body weight deficit in the M pups when compared to control pups. During this period, half of the litters were exposed daily to additional tactile stimulation (CS or MS), while the other half were submitted to normal rearing conditions (CN or MN). The tactile stimulation of pups (handling) consisted of holding the animal in one hand and gently touching the dorsal part of the animal's body with the fingers for 3 min. A special camera and a time-lapse video were used to record litter behavior in their home cages. Starting at 6 p.m. and ending at 6 a.m., on days 3, 6, 12, 15, 18 and 21 of lactation, photos were taken at 4-s intervals. An increase in the frequency (154.88 +/- 16.19) and duration (455.86 +/- 18.05 min) of suckling was observed throughout the lactation period in all groups compared to birth day (frequency 24.88 +/- 2.37 and duration 376.76 +/- 21.01 min), but the frequency was higher in the C (84.96 +/- 8.52) than in the M group (43.13 +/- 4.37); however, the M group (470.2 +/- 11.87 min) spent more time suckling as compared with the C group (393.67 +/- 13.09 min). The M dams showed a decreased frequency of resting position throughout the lactation period (6.5 +/- 2.48) compared to birth day (25.42 +/- 7.74). Pups from the C group were more frequently observed separated (73.02 +/- 4.38) and interacting (258.99 +/- 20.61) more with their mothers than the M pups (separated 66.94 +/- 5.5 and interacting 165.72 +/- 12.05). Tactile stimulation did not interact with diet condition, showing that the kind of stimulation used in the present study did not lead to recovery from the changes induced by protein malnutrition. The changes in mother-pup interaction produced by protein malnutrition of both may represent retardation in neuromotor development and a higher dependence of the pups on their mothers. These changes may represent an important means of energy saving and heat maintenance in malnourished pups.

Tumorigenicity of sodium ascorbate in male rats.

Sodium ascorbate, like other sodium salts such as saccharin, glutamate, and bicarbonate, produces urinary alterations when fed at high doses to rats, which results in mild superficial urothelial cytotoxicity and regeneration but not tumors in a standard 2-year bioassay. Sodium saccharin was shown to produce a low incidence of bladder tumors in rats if administered in a two-generation bioassay. In the present study, we evaluated sodium ascorbate in a two-generation bioassay that involved feeding to the male and female parental F344 rats for 4 weeks before mating, feeding the dams during gestation and lactation, and then feeding the weaned (at 28 days of age) male F1 generation rats for the remainder of their lifetime (up to 128 weeks of the experiment). Dietary levels of 1.0, 5.0, and 7.0% sodium ascorbate were tested. At 5.0 and 7.0% sodium ascorbate, there was an increase in urinary bladder urothelial papillary and nodular hyperplasia and the induction of a few papillomas and carcinomas. There was a dose-responsive increase in renal pelvic calcification and hyperplasia and inhibition of the aging nephropathy of rats even at the level of 1% sodium ascorbate. Because the short-term urothelial effects of sodium ascorbate in rats are inhibited by treatments producing urinary acidification to pH < 6.0, we coadministered high doses of long-term NH4Cl to groups of rats with 5.0 or 7.0% sodium ascorbate to evaluate the long-term effects. The combination of 7.0% sodium ascorbate plus 2.78% NH4Cl in the diet was toxic, and the group was terminated early during the course of the experiment. The group fed 5.0% sodium ascorbate plus 2.04% NH4Cl showed complete inhibition of the urothelial effects of sodium ascorbate and significant inhibition of its renal effects. We also demonstrated the presence of a calcium phosphate-containing urinary precipitate in rats fed sodium ascorbate at all doses, in a dose-responsive manner. The formation of the precipitate was inhibited by coadministration with NH4Cl. The proliferative effects of sodium ascorbate on the male rat urinary tract in this study are similar to those seen with sodium saccharin when administered in a two-generation bioassay. Mechanistic information suggests that this is a high-dose, rat-specific phenomenon.

Selection of an intact casein or casein hydrolysate diet by rats submitted to protein deprivation and bowel resection.

The feeding preference of normal rats (n = 14), malnourished rats (n = 14), and enterectomized rats (n = 16) was determined in a situation of free choice of three complete solid diets which only differed in extent of protein polymerization: intact casein, casein hydrolysate, and an amino acid mixture with a composition similar to that of casein. The animals were housed in metabolic cages for 30 days and allowed to freely choose among the three diets presented simultaneously. All three groups showed an initial preference for the intact casein diet. The control group maintained this preference, whereas the malnourished and enterectomized groups reduced the ingestion of the intact casein diet and increased the ingestion of the amino acid diet. The nitrogen balance, which was always positive in all three groups, was constant in the control group (1.51 +/- 0.26 g) initially higher (1.77 +/- 0.19 g) in the malnourished group, with a subsequent fall (1.13 +/- 0.24 g), and lower in the enterectomized group (0.83 +/- 0.32 g). Although total intake was similar for the control and malnourished groups, the malnourished group presented a higher weight recovery (130.2%). In contrast, the food intake of the enterectomized group was much lower, with a small weight gain. After treatment that impairs the digestive tract, intact casein was the initially preferred nitrogen source, which later tended to be replaced with free amino acids. This change was accompanied by an improvement in nitrogen balance and body weight, especially after protein malnutrition. These data may suggest that, in clinical practice, the use of enteral diets containing fully hydrolyzed protein may be of benefit in terms of the recovery of malnourished patients and of patients with short bowel syndrome.

Short-Term Social Isolation Does Not Reduce Elevated Plus-Maze Exploration in Early Protein Malnourished Rats.

An increased number of visits and time spent in the open arms of the elevated plus-maze by malnourished rats has been used as indicative of lower anxiety or higher impulsiveness. In order to study how this behavior profile responds to an anxiogenic procedure (short-term social isolation), control (16% protein) and malnourished (6% protein) rats were socially isolated prior to the test in the maze. Litters (dam plus 6 male and 2 female pups) were fed the diets from birth to 49 days of age. From 50 days on, all rats were fed a lab chow diet. Social isolation consists in removing the rats from the group and placing them in individual cages for 2 h before the test. During the test each rat was individually placed on the center of the maze and allowed to explore for 5 min. The results showed higher open arms exploration and lower attempts to enter open arms by the malnourished rats than by the controls. Social isolation decreased open arm exploration and increased time spent on the central platform in control animals, but had no effect on the malnourished rats. The results reinforce the lower anxiety or higher impulsiveness of malnourished rats, as well as the anxiogenic effect of social isolation in control rats. However, the malnourished rats were unresponsive to the anxiogenic effects of social isolation, indicating that protein deficiency early in life not only induces lower anxiety or higher impulsiveness in the maze, but also changes the behavior of these animals in response to another environmentally-induced procedure of anxiety (social isolation).

Effects of Early Concurrent Protein Malnutrition and Environmental Stimulation on the Central Nervous System and Behavior.

A complex program of environmental and sensory stimulation was developed to study its potential effects in reversing some of the alterations produced by early protein malnutrition in the brain and behavior of rats. Litters (dam plus 6 male pups) were fed diets containing 8% (malnourished) or 25% (well-nourished) casein. After weaning, the animals were maintained on the same diets as their respective dams until 50 days of age. Environmental stimulation consisted of 3-min daily handling from birth to 50 days of age. Additional stimulation was provided from birth to 50 days of age by rearing the rats in an enriched living cage and exposing the animals to visual, auditory and olfactory stimuli. At 50 days of age the animals were submitted to locomotor and inhibitory avoidance tests. Animals of the same age were sacrificed, the brain removed and divided in telencephalon, brain steam and cerebellum. DNA and RNA were assessed in telencephalon and cerebellum. Protein malnutrition produced brain weight deficits that were partially reversed by environmental stimulation. DNA and RNA levels were reduced by protein malnutrition and increased by environmental stimulation. The behavioral measures showed lower locomotor activity and higher latencies in inhibitory avoidance for malnourished animals as compared to well-nourished animals. Environmental stimulation reduced the aversiveness in the inhibitory avoidance test as showed by lower latencies in the stimulated group of animals. These results suggest that early protein malnutrition impairs brain and behavior of rats and that a complex program of environmental stimulation is beneficial to reverse some of those impairments.

Effects of Different Levels of Protein and Environmental Stimulation on the Behavior of Young Rats Tested in the Elevated Plus-Maze.

UNLABELLED: The interaction between the effects of different levels of protein malnutrition and environmental stimulation was investigated in young male rats in the elevated plus-maze (EPM). Litters (dam plus 6 male and 2 female pups) were fed a 16% ( CONTROL: C), 10% (Malnourished: M10) or 6% (Malnourished: M6) protein diet. Half of the litters were daily exposed to additional stimulation (CS, MS10 or MS6), while the other half was maintained in normal rearing conditions (CN, MN10 or MN6). The stimulation (handling) consisted of holding the rat in one hand and gently touching the dorsal part of the body with the fingers for 3 min. On the 22nd day of life (weaning), two male pups from each group were tested in the plus-maze. Two male pups continued to receive the same diet as their mothers, and the other two were fed a non-purified lab chow diet until 35 days of age when they were tested in the plus-maze (LN, LS, LN10, LS10, LN6 and LS6 groups). Results showed that environmental stimulation increased open arms exploration both at 22 and 35 days of age, indicating an anxiolytic effect of this procedure. Younger rats (22 days of age) explored significantly more the open arms of the maze as compared with older rats (35 days of age), indicating an increase in anxiety with age. M6 animals showed significantly higher percentages of open arm entries and less frequent attempts to enter open arms in the maze as compared with C and M10 animals. These results suggest that even a short period of protein deficiency can produce alterations in the emotional response of rats in the elevated plus-maze. In addition, the data demonstrated that protein deficiency more severe than 10% is necessary to produce behavior alterations in the EPM test.

Food intake and weight of lactating rats maintained on different protein-calorie diets, and pup growth.

Studies on rats maintained on low-protein-calorie diets during the lactation period show that food intake decreases. This process results in weight loss and a delay in litter development. The purpose of the present study was to determine the alterations in food intake, maternal weight and litter growth during lactation when dams were exposed to diets with different levels of protein and carbohydrate. Female Wistar rats receiving one of 4 different diets, A (N = 14), B (N = 14), C (N = 9) and D (N = 9), were used. Diet A contained 16% protein and 66% carbohydrate; diet B, 6% protein and 77% carbohydrate; diet C, 6% protein and 66% carbohydrate; diet D, 16% protein and 56% carbohydrate. Thus, C and D diets were hypocaloric, while A and B were isocaloric. The intake of a low-protein diet in groups B and C affected the weight of dams and litters during the last two weeks of lactation, while the low-calorie diets limited the growth of D litters at 21 days compared with A litters, but had no effect on the weight of D dams. Group B showed an increase in intake during the first five days of lactation, resulting in a behavioral calorie compensation due to the increase in carbohydrate content, but the intake decreased during the last part of lactation. Food intake regulation predominantly involves the recruitment of a variety of peripheral satiety systems that attempt to decrease the central feeding command system.

Response threshold to aversive stimuli in stimulated early protein-malnourished rats.

Two animal models of pain were used to study the effects of short-term protein malnutrition and environmental stimulation on the response threshold to aversive stimuli. Eighty male Wistar rats were used. Half of the pups were submitted to malnutrition by feeding their mothers a 6% protein diet from 0 to 21 days of age while the mothers of the other half (controls) were well nourished, receiving 16% protein. From 22 to 70 days all rats were fed commercial lab chow. Half of the animals in the malnourished and control groups were maintained under stimulating conditions, including a 3-min daily handling from 0 to 70 days and an enriched living cage after weaning. The other half was reared in a standard living cage. At 70 days, independent groups of rats were exposed to the shock threshold or to the tail-flick test. The results showed lower body and brain weights in malnourished rats when compared with controls at weaning and testing. In the shock threshold test the malnourished animals were more sensitive to electric shock and environmental stimulation increased the shock threshold. No differences due to diet or environmental stimulation were found in the tail-flick procedure. These results demonstrate that protein malnutrition imposed only during the lactation period is efficient in inducing hyperreactivity to electric shock and that environmental stimulation attenuates the differences in shock threshold produced by protein malnutrition.

Response threshold to aversive stimulated early protein-malnourished rats

Two animal models of pain were used to study the effects of short-term protein malnutrition and environmental stimulation on the response threshold to aversive stimuli. Eighty male Wistar rats were used. Half of the pups were submitted to malnutrition by feeding their mothers a 6 per cent protein diet from 0 to 21 days of age while the mothers of the other half (controls) were well nourished, receiving 16 per cent protein. From 22 to 70 days all rats were fed commercial lab chow. Half of the animals in the malnourished and control groups were maintained under stimulating conditions, including a 3-min daily handling from 0 to 70 days and an enriched living cage after weaning. The other half was reared in a standard living cage. At 70 days, independent groups of rats were exposed to the shock threshold or to the tail-flick test. The results showed lower body and brain weights in malnourished rats when compared with controls at weaning and testing. In the shock threshold test the malnourished animals were more sensitive to electric shock and environmental stimulation increased the shock threshold. No differences due to diet or environmental stimulation were found in the tail-flick procedure. These results demonstrate that protein malnutrition imposed only during the lactation period is efficient in inducing hyperreactivity to electric, shock and that environmental stimulation attenuates the differences in shock threshold produced by protein malnutrition.

Active tactile exploration influences the functional maturation of the somatosensory system.

1. The hypothesis that active exploration of objects is required for the functional maturation of neuronal circuits subserving tactile perception was tested by subjecting 8- to 11-day old rats to a complete unilateral section of the facial nerve. This procedure selectively abolished whisker protraction movements without affecting the sensory innervation of the facial vibrissae, the tactile organs used by rats to discriminate object texture and shape. 2. Six to 14 mo after the facial nerve section, simultaneous recordings of neuronal ensembles located in the ventral posterior medial nucleus (VPM) of the thalamus revealed a marked reduction in receptive field (RF) size (in terms of number of whiskers), and the formation of abnormal RF surrounds, spanning the face and contiguous body regions. In addition, the directional organization of VPM RFs, represented by caudal to rostral shifts in RF centers over 30 ms following whisker stimulation, was greatly reduced in these animals. 3. These results suggest that neonatal active tactile exploration is required to establish normal spatiotemporal patterning of neuronal RFs within the somatosensory system, and consequently, to develop normal tactile perception.