Genevieve S. Young

Blood phospholipid fatty acid analysis of adults with and without attention deficit/hyperactivity disorder.

Several psychiatric disorders, including juvenile Attention Deficit/Hyperactivity Disorder (ADHD), have been associated with abnormalities of certain long-chain PUFA (LCPUFA). Despite this reported association, the FA levels of patients with the adult form of ADHD have not previously been evaluated. In this study we measured the total blood phospholipid FA concentrations in 35 control subjects and 37 adults with ADHD symptoms to determine whether adults with ADHD symptoms would show abnormalities of FA relative to control subjects. In the serum phospholipids, adults with ADHD symptoms had significantly lower levels of total saturated, total polyunsaturated, and total omega-6 (n−6) FA, as well as the omega-3 (n−3) LCPUFA DHA (22∶6n−3), and significantly higher levels of total monounsaturated FA and the n−3 LCPUFA docosapentaenoic acid (22∶5n−3). In the erythrocyte membrane phospholipids, adults with ADHD symptoms had significantly lower levels of total PUFA, total n−3 FA, and DHA, and significantly higher levels of total saturated FA. Neither serum nor erythrocyte membrane phospholipid DHA was related to ADHD symptom severity (as assessed by the Amen questionnaire) in ADHD subjects. Although the exact cause of these variations is unknown, both environmental and genetic factors may be involved.

The role of dietary niacin intake and the adenosine-5'-diphosphate-ribosyl cyclase enzyme CD38 in spatial learning ability: is cyclic adenosine diphosphate ribose the link between diet and behaviour?

The pyridine nucleotide NAD+ is derived from dietary niacin and serves as the substrate for the synthesis of cyclic ADP-ribose (cADPR), an intracellular Ca signalling molecule that plays an important role in synaptic plasticity in the hippocampus, a region of the brain involved in spatial learning. cADPR is formed in part via the activity of the ADP-ribosyl cyclase enzyme CD38, which is widespread throughout the brain. In the present review, current evidence of the relationship between dietary niacin and behaviour is presented following investigations of the effect of niacin deficiency, pharmacological nicotinamide supplementation and CD38 gene deletion on brain nucleotides and spatial learning ability in mice and rats. In young male rats, both niacin deficiency and nicotinamide supplementation significantly altered brain NAD+ and cADPR, both of which were inversely correlated with spatial learning ability. These results were consistent across three different models of niacin deficiency (pair feeding, partially restricted feeding and niacin recovery). Similar changes in spatial learning ability were observed in Cd38- / - mice, which also showed decreases in brain cADPR. These findings suggest an inverse relationship between spatial learning ability, dietary niacin intake and cADPR, although a direct link between cADPR and spatial learning ability is still missing. Dietary niacin may therefore play a role in the molecular events regulating learning performance, and further investigations of niacin intake, CD38 and cADPR may help identify potential molecular targets for clinical intervention to enhance learning and prevent or reverse cognitive decline.

Use of salient and non-salient visuospatial cues by rats in the Morris Water Maze

In the Morris Water Maze (MWM), an animal learns the location of a hidden platform relative to distal visual cues in a process known as spatial learning. The visual cues used in MWM experiments are invariably salient in nature, and non-salient cues, such as subtle environmental variations, have not traditionally been considered to play a significant role. However, the role of non-salient cues in spatial navigation has not been adequately investigated experimentally. The objective of this experiment was therefore to determine the relative contribution of salient and non-salient visual cues to spatial navigation in the MWM. Animals were presented with an environment containing both types of visual cues, and were tested in three successive phases of water maze testing, each with a new platform location. Probe tests were used to assess spatial accuracy, and several cue variation trials were run in which both salient and non-salient visual cues were manipulated. It was observed that removal of the salient visual cues did not cause a significant deterioration in performance unless accompanied by disruption of the non-salient visual cues, and that spatial navigation was unimpaired when only the salient visual cues were removed from view. This suggests that during place learning in Long-Evans rats, non-salient visual cues may play a dominant role, at least when salient cue presentation is limited to four cues.

Modifications to Increase the Efficiency of the Fluorometric Cycling Assay for Cyclic ADP-Ribose

Cyclic ADP-ribose (cADPR) is an intracellular messenger that triggers the release of calcium ions from intracellular stores in a variety of cell types. The fluorometric cycling assay has become the preferred method for measuring cADPR due to its high level of sensitivity (in the sub-nanomolar range) and its use of commercially available reagents. Additionally, the assay is performed in multiwell plates, making it suitable for high throughput screening using a fluorescence plate reader. The findings reported in this paper present several problems that may be encountered during various stages of the assay, and provide solutions to these problems. Modifications to the assay address reduced recovery of sample and cADPR with removal of perchloric acid (PCA) using organic solvent, reduction in diaphorase activity with heat treatment, and effects on resorufin fluorescence by pH range. Using these modifications, we report an increase of approximately 15% in recovery of brain cADPR, and show that between-subject variability is greatly reduced. We hope that these observations will encourage more widespread application of this valuable assay.

The guinea-pig is a poor animal model for studies of niacin deficiency and presents challenges in any study using purified diets

The guinea-pig was previously reported as being sensitive to a niacin-deficient (ND), high-protein diet, suggesting that it is a suitable model for the low tryptophan to NAD+ conversion observed in human subjects. However, these studies were based on growth rates and mortality. The objective of the present study was to determine whether guinea-pigs are suitable for ND studies based on measurements of blood and bone marrow NAD+. Using a 20 % casein diet, ND decreased blood NAD+ after 4 weeks, but this parameter returned to normal after 9 weeks of feeding, while bone marrow was decreased by 35 % at this time point. Using a 15 % casein diet, 7 weeks of ND caused 44 and 42 % decreases in blood and bone marrow NAD+. Using a 10 % casein diet, ND decreased NAD+ by 32 % in blood and 62 % in bone marrow at 7 weeks. Growth rates were directly related to the dietary tryptophan content, with the lowest growth rates seen with the 10 % casein diet. Changes in guinea-pig NAD+ are comparable with the rat model at similar levels of dietary tryptophan, while mortality rates were dramatically higher in the guinea-pig model. The present study concludes that mortality in ND guinea-pigs is not indicative of poor tryptophan conversion, but is due to environmental stresses in guinea-pigs that are not observed with rats. We conclude that guinea-pigs are not suitable for research on niacin deficiency and they present challenges for any study requiring purified diets and wire-bottomed cages.