Motor, but not sensory, cortical potentials are amplified by high-protein diet

Diet influences cocaine withdrawal behaviors in the forced swimming test

The effects of drugs of abuse might depend on several environmental factors, among them the individual's feeding habits. It was our objective to study the influence of the diet on cocaine acute behavioral effects and during the first 5 days of withdrawal after prolonged treatment. Rats were fed a balanced diet, high-protein diet, high-carbohydrate diet or high-fat diet from weaning to adulthood. Adult rats were injected with 15 mg/kg cocaine 24, 5 and 1 h before the forced swimming retest or the drug was administered daily during 15 days and the animals were evaluated in the forced swimming test on five daily occasions after drug withdrawal. Diets alone did not induce significant behavioral differences in locomotion, immobility, swimming, climbing or head shakes. Acute cocaine reduced immobility during the forced swimming test and increased locomotion demonstrating a nonspecific antiimmobility effect related to hyperactivity. Acute cocaine reduced head shakes of rats fed high-protein and high-carbohydrate diets. After cocaine withdrawal, head shakes were decreased for rats fed any of the diets and rats were more immobile if fed a high-fat diet and were less immobile if fed a high-protein or high-carbohydrate diet. In conclusion, differences in the amounts of macronutrients in the diet may cause different behavioral outcomes after acute cocaine and during cocaine withdrawal.

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.

Short-term consumption of a diet rich in fat decreases anxiety response in adult male rats

Short- and long-term changes in the composition of dietary macronutrients [protein (P), carbohydrate (C), and fat (F)] alter neurochemistry and behavior in animals. We examined whether short-term intake of a diet rich in P, C, or F affected their anxiety response (AR). AR of Sprague-Dawley rats was measured in an elevated plus maze. Rats were placed in the black compartment facing the wall opposite the aperture, and the time (max. 360 s) it took to enter the white compartment with all four paws was noted. Rats were fed Purina chow and tap water unless otherwise indicated. On repeated testing (three times on the same day) AR increased and, consequently, most rats spent the entire 360 s in the dark. Whereas most rats exhibited low anxiety response in trial 1, which increased during successive trials (low-high group), some exhibited high initial anxiety that remained unchanged (high-high group). To determine whether macronutrients may alter AR, groups of low-high and high-high rats were tested three times on the same day and then put on a P, C, or F diet for 7 days. On day 8, they were again tested for AR in a single trial and the results compared with those of the third trial of the previous test (preC: 302 +/- 39, post-C: 294 +/- 42, p > 0.05; pre-P: 305 +/- 35, post-P: 297 +/- 43, p > 0.05; pre-F: 321 +/- 17, post-F: 241 +/- 24sec, p = 0.009; n = 30; mean +/- SEM). The results show that a diet rich in F, but not P or C, decreases AR in rats.

Differential modulation of dopaminergic systems in the rat brain by dietary protein

Rats that consume a diet 50% rich in protein exhibit hyperactivity and hyperresponsiveness to nociceptive stimuli, in which facilitation of dopaminergic activity has been implicated. We studied the regional changes in the concentrations of dopamine (DA) and its metabolites, dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the brains of rats that were maintained on high-protein (HP, 50% casein), normal-protein (NP, 20% casein), and low-protein (LP, 8% casein) diets for 36 weeks. Brain nuclei that represented different DAergic systems were punch-dissected and analyzed using HPLC. In the substantia nigra, the striatum, and the dentate gyrus, DA concentrations decreased and increased, respectively, with a decrease and increase in dietary protein (p < 0.05 compared to the NP diet). Similar trends in the effect of the HP diet were observed in the ventral tegmental area, amygdala, frontal cortex, subiculum, centromedial nucleus (CM) of the thalamus, and inferior colliculi (IC), although the differences in DA concentrations were not statistically significant. These brain areas also showed a pattern of decreased DA concentration in association with the LP diet, and the differences were statistically significant (p < 0.05) in the CM and IC. DA concentrations in most regions of the midbrain and brainstem were not different between the diet groups, nor were consistent trends observed in those regions. Also, there were no consistent relationships between DOPAC/DA and HVA/DA ratios and dietary protein level. These data suggest that only discrete dopaminergic neuronal circuits in the rat forebrain were sensitive to changes in dietary protein level.

Can dietary macronutrient preference profile serve as a predictor of voluntary alcohol consumption?

A diet rich in protein has been shown to increase voluntary alcohol consumption (VAC) in a variety of animal species. Macronutrient preference (MP) profile varies widely among different outbred rats of the same strain. Using outbred Sprague-Dawley rats and two inbred selected strains of rats (P and NP) that are known for large differences in alcohol preference, we have examined whether 1) there is a relationship between MP profile and VAC and 2) MP profile can be a predictor of VAC. Results of these studies show 1) wide animal-to-animal variations in both the MP and VC and 2) the presence of an association between MP profile and VAC in P and NP but not Sprague-Dawley rats. Therefore, we conclude that MP profile may not serve as a reliable predictor of VAC in a nonselected population.

Alterations in dendritic spine density in the rat brain associated with protein malnutrition

Rats that consume a high-protein diet are hyperactive, hyperresponsive to noxious stimuli, and demonstrate elevated basal arousal levels. Although the mechanism involved in dietary protein-induced changes in behavior is unclear, it may involve many changes including abnormal dendrite morphology in the brain. Three groups of rats were pair-fed with isocaloric diets containing 8%, 20% and 50% casein for 4 weeks. Their brains were processed for examination of dendritic spine densities in the frontal, parietal, and entorhinal cortices, the striatum, and the septum. Animals on the 50% casein diet showed increased spine densities in all areas investigated (P less than 0.05), compared to the animals on normal (20%) casein. In contrast, animals maintained on the 8% casein diet showed increased spine densities (P less than 0.05) only in the striatum and entorhinal cortex, and exhibited normal densities in the frontal and parietal cortices, and the medial septum.