Manifestation of hemispheric laterality in chewing side preference and handedness.

Introduction: Humans manifest a behavioral inclination towards more utility of one side of the body, in relation with the dominant hemisphere of the brain. The current investigation assessed handedness together with chewing preference which have not been evaluated in various food textures before. Methods: Nineteen young and healthy volunteers chewed hard (walnut) and soft (cake) foods, during surface electromyography recording from masseter muscles. The side of the first and all chews in the two food types were determined and compared with the side of the dominant hand. Results: Results indicated the two lateralities in the same side considerably (60%-70%), implying the solidarity in the control of the dominant hemisphere of the brain. The unilaterality was more prominent in the assessment of all chews in hard food, with higher statistical agreement and correlation. Conclusion: Thereupon masticatory preference is found with probable origins in the dominant hemisphere of the brain.

Post-weaning environmental enrichment improves BDNF response of adult male rats.

The environment could have long lasting effects on the individual phenotype through developmental plasticity. Early environmental enrichment exerts profound biological effects, most of which are quite beneficial ones. To explore the enduring effects of rearing condition quality on BDNF(1) responses, we reared male Wistar rats from weaning to young-adulthood in three different environmental conditions: 1. Enriched 2. Standard, and 3. Isolated. Then, at the age of 16 weeks, 10 rats from each group were randomly chosen and allocated to six common mix cages. They were kept together for 14 weeks. At the end of the experiment, each rat received ten inescapable foot-shocks. Twelve hours later, the BDNF contents of the amygdala and CA1 sub-region of the dorsal hippocampus were measured. The serum BDNF levels, hematocrit values as well as brain and testis weights were also measured. Results showed that the environmental enrichment led to stronger dorsal hippocampal BDNF response and higher serum BDNF levels, while rats from standard laboratory condition showed higher amygdala BDNF response. Also, enriched animals showed higher brain weight compared to isolation reared rats as well as higher testis weight and hematocrit value compared to animals reared in standard laboratory condition. Rats showed less body weights in isolated condition. In conclusion, the BDNF profile of enriched animals might represent the neurobiological correlate of resilience phenotype under a stressful situation.

Voluntary drinking versus imposed drinking in the methodology of investigations about the drinking-induced thermoregulatory sweating.

UNLABELLED: Studies have shown that dehydrated humans or animals in a warm environment begin to sweat within seconds to minutes after drinking. This phenomenon is one of the drinking-induced thermoregulatory responses; being investigated from different aspects. Our objective is to show the difference of voluntary drinking and imposed drinking in the methodology of these experiments. Six healthy subjects 23.7 ± 0.6 yr old and 80.7 ± 5.7 kg wt were dehydrated by performing mild exercise (ergometer cycling) in a hot and humid chamber (38-40°C, 20-28% relative humidity). We incorporated two protocols: after dehydration, subjects were allowed to drink water with 1) imposed volumes of 1, 3, 5 ml/kg and 2) voluntary volumes; on four separate days. The sweating rate was measured on the forehead area before and after drinking. Sweating increased markedly just a few minutes after the onset of drinking. The mean sweat rates of the imposed volumes of 1, 3, 5 ml/Kg were 0.33 ± 0.15, 0.31 ± 0.17, 0.47 ± 0.21 respectively and for the voluntary volume it was 0.54 ± 0.19. The mean intake in the voluntary trial was 6.58 ± 1.14 ml/Kg, more than the imposed volume of 5 ml/Kg. The trend of the rate of the sweating response in the imposed trials was distinct from the response in the voluntary trial. CONCLUSION: There exists a difference between voluntary drinking and imposed drinking in the sweating response that follows rehydration. So it is suggested to use the methods of voluntary drinking in the investigations of this phenomenon, to reveal the natural events that happen in the actual circumstances.

The effect of water temperature and voluntary drinking on the post rehydration sweating.

During heat stress and dehydration, thermoregulation is partly suppressed to save body fluid and circulation. Drinking induces the recovery of thermoregulatory responses including sweating. Our objective is to investigate the effect of water temperature and voluntary drinking on the extent of the drinking-induced sweating. Six healthy subjects 23.7 ± 0.6 yr old and 80.7 ± 5.7 kg wt were dehydrated by performing mild exercise (ergometer cycling) in a hot and humid chamber (38-40°C, 20-28% relative humidity). After dehydration, subjects were allowed to drink water with temperatures of 5, 16, 26, 58°C on four separate days. The sweating rate was measured on the forehead area before and after drinking. Also, blood samples were collected during the experiments and plasma osmolality was measured. Sweating increased markedly just a few minutes after the onset of drinking. The rate of this response was lower in ingested water temperature of 5°C (0.43 ± 0.03 g, p = 0.000). Different intake occurred with different water temperatures (respectively 4.2, 6.4, 3.1, 1.8 ml/kg). Water at 16°C induced higher intake (6.4 ml/kg) together with lower sweating (0.54 ± 0.03 g), which can result in optimum level of hydration. Conclusion- When dehydrated subjects drink water with different temperatures, there are different sweating responses together with different voluntary intakes. According to our results, consuming 16°C water, cool tap water, could be suggested in dehydration.

Chewing side preference in first and all mastication cycles for hard and soft morsels.

Preferred chewing side is a still controversial matter and various methods used have yielded some inconsistencies. The aim of this study is to compare the preference determined in different conditions. Nineteen healthy subjects were offered hard (walnut) and soft (cake) foods, while the electromyography was recorded from their masseter muscles, in 2009 in the Research Center of Physical Medicine and Rehabilitation, Tabriz University of Medical Sciences, Tabriz, Iran. Four occurrences were determined as the side of the first chews/all chews in the two food types, and then analyzed for correlations and agreements. For hard food 73.68% and for soft food 57.89% of the subjects showed preference. The comparison of all chews showed a highly significant preference towards the right side in both food types (p=0.000 & 0.003). There was both correlation and agreement between the first chew preferences in both food types, and an agreement between the first and all chew preferences in the hard food. Therefore, there seems to exist some laterality in mastication, which is more explicit when using hard food and assessing all chews.

Water temperature, voluntary drinking and fluid balance in dehydrated taekwondo athletes.

Voluntary drinking is one of the major determiners of rehydration, especially as regards exercise or workout in the heat. The present study undertakes to search for the effect of voluntary intake of water with different temperatures on fluid balance in Taekwondo athletes. Six young healthy male Taekwondo athletes were dehydrated by moderate exercise in a chamber with ambient temperature at 38-40°C and relative humidity between 20-30%. On four separate days they were allowed to drink ad libitum plane water with the four temperatures of 5, 16, 26, and 58°C, after dehydration. The volume of voluntary drinking and weight change was measured; then the primary percentage of dehydration, sweat loss, fluid deficit and involuntary dehydration were calculated. Voluntary drinking of water proved to be statistically different in the presented temperatures. Water at 16°C involved the greatest intake, while fluid deficit and involuntary dehydration were the lowest. Intake of water in the 5°C trial significantly correlated with the subject's plasma osmolality change after dehydration, yet it showed no significant correlation with weight loss. In conclusion, by way of achieving more voluntary intake of water and better fluid state, recommending cool water (~16°C) for athletes is in order. Unlike the publicly held view, drinking cold water (~5°C) does not improve voluntary drinking and hydration status. Key pointsFor athletes dehydrated in hot environments, maximum voluntary drinking and best hydration state occurs with 16°C water.Provision of fluid needs and thermal needs could be balanced using 16°C water.Drinking 16°C water (nearly the temperature of cool tap water) could be recommended for exercise in the heat.

Effect of spatial learning on hippocampal testosterone in intact and castrated male rats.

BACKGROUND: Sex steroids and their receptors exist in hippocampus and affect spatial learning and memory. This study was designed to measure testosterone level of CA1 and to assess the effect of spatial learning on its amount in left and right hippocampus of adult male rats. METHODS: Sixteen rats were divided into two intact and castrated groups, and then trained in Morris water maze (MWM). Another 40 animals were divided into four groups and their right or left hippocampus cannulated. Half of the animals in each group were castrated simultaneously. All the animals were trained in MWM. Microdialysis was performed and steroid contents of hippocampal dialysate were analyzed through HPLC/ultraviolet detection device method. RESULTS: Results showed no significant differences between control and castrated animals in spatial learning after four days of training. Gonadectomy did not change testosterone level in CA1 region of hippocampus. Spatial learning decreased testosterone levels in CA1 region of hippocampus in right hippocampus of the non-castrated group. Significant differences were indicated in testosterone level between left and right hippocampus, in favor of left side in all groups. CONCLUSION: Castration does not affect learning. Testosterone, as a neuromodulator, exists in CA1 region of hippocampus and training can decrease its level only in right hippocampus significantly. Lesser testosterone content of right hippocampus may show the conversion of it to other metabolites.

Long-term regular exercise promotes memory and learning in young but not in older rats.

BACKGROUND AND OBJECTIVE: By aging, some functions in nervous system like spatial memory are reduced. It has been shown that short-time physical activity can improve memory but there is much less data on the long-term exercising. In the present study, the aim was to clarify the effect of regular long-term physical activity on spatial memory and learning of young and middle aged and older male Wistar rats. MATERIALS AND METHODS: Sixty 3 months old rats were randomly divided in six equal groups. Experimental groups were treadmill exercised at speed 22m/min for 1h 6 days per week, and the program lasted 3, 6 and 9 months, respectively. At the end of training period, spatial memory of rats was tested using Morris Water Maze. RESULTS: Results indicated that regular physical activity significantly increased spatial memory (p<0.05) in young rats (6 months old) as compared to controls, but not in the older ones (9 and 12 months old). Nonetheless, spatial memory of these rats was significantly better than in younger ones in both groups (p<0.05). CONCLUSION: Spatial memory and learning increased due regular exercise in young rats. With progression of age up to 9 and 12 months the memory improved, but the programmed exercise had no positive effect on learning.