Glycaemic indices of different varieties of rice grown in Sri Lanka

OBJECTIVE

Varieties of red raw rice are widely believed to have a better nutritional quality. The physiological effects of consuming different varieties of rice may not be so. The glycaemic index has been developed as an indicator of the physiological effect of foods. It is the glycaemic response of a 50 g carbohydrate portion of food expressed as a percentage of that of a standard. The objective of this study was to determine the glycaemic indices of different varieties of rice grown in Sri Lanka.

DESIGN

Digestible carbohydrate content of 11 varieties of rice flour and bread were determined. Fasting blood samples followed by half-hourly samples for two hours were drawn after giving portions of either cooked rice or bread containing 50 g carbohydrate each.

SETTING

Fibre mill in Gampaha district.

SUBJECTS

Twenty-two fibre mill workers aged between 25 and 50 years.

MEASUREMENTS

The area under the blood glucose curve (AUC) for varieties of rice for a subject was calculated. Average AUC of 3 values for bread were calculated. Glycaemic index of each variety of rice was determined from the above variables.

RESULTS

Glycaemic indices of varieties of rice differ. The glycaemic indices of varieties of red raw rice varied between 56 and 73 and the variety Bg 350 had the lowest glycaemic index. There was no significant difference between mean glycaemic index of varieties of white raw and some varieties of red raw rice (p = 0.2). Parboiled varieties of red raw rice had a significantly lower glycaemic index than white raw rice (p = 0.04) and some of the red raw rice (p = 0.005).

CONCLUSIONS

The glycaemic index cannot be predicted from the colour of the rice grain. Red parboiled varieties of rice and Bg 350 can be recommended for patients with diabetes.

Characterization of D3 Autoreceptor Function in Whole Zebrafish Brain with Fast-Scan Cyclic Voltammetry

Zebrafish (Danio rerio) are ideal model organisms for investigating nervous system function, both in health and disease. Nevertheless, functional characteristics of dopamine (DA) release and uptake regulation are still not well-understood in zebrafish. In this study, we assessed D3 autoreceptor function in the telencephalon of whole zebrafish brains ex vivo by measuring the electrically stimulated DA release ([DA]max) and uptake at carbon fiber microelectrodes with fast-scan cyclic voltammetry. Treatment with pramipexole and 7-OH-DPAT, selective D3 autoreceptor agonists, sharply decreased [DA]max. Conversely, SB277011A, a selective D3 antagonist, nearly doubled [DA]max and decreased k, the first-order rate constant for the DA uptake, to about 20% of its original value. Treatment with desipramine, a selective norepinephrine transporter blocker, failed to increase current, suggesting that our electrochemical signal arises solely from the release of DA. Furthermore, blockage of DA uptake with nomifensine-reversed 7-OH-DPAT induced decreases in [DA]max. Collectively, our data show that, as in mammals, D3 autoreceptors regulate DA release, likely by inhibiting uptake. The results of this study are useful in the further development of zebrafish as a model organism for DA-related neurological disorders such as Parkinson's disease, schizophrenia, and drug addiction.

Impaired Dopamine Release and Latent Learning in Alzheimer's Disease Model Zebrafish

Alzheimer's disease (AD) is a progressive, fatal, neurodegenerative disorder for which only treatments of limited efficacy are available. Despite early mentions of dementia in the ancient literature and the first patient diagnosed in 1906, the underlying causes of AD are not well understood. This study examined the possible role of dopamine, a neurotransmitter that is involved in cognitive and motor function, in AD. We treated adult zebrafish (Danio rerio) with okadaic acid (OKA) to model AD and assessed the resulting behavioral and neurochemical changes. We then employed a latent learning paradigm to assess cognitive and motor function followed by neurochemical analysis with fast-scan cyclic voltammetry (FSCV) at carbon fiber microelectrodes to measure the electrically stimulated dopamine release. The behavioral assay showed that OKA treatment caused fish to have lower motivation to reach the goal chamber, resulting in impeded learning and decreased locomotor activity compared to controls. Our voltammetric measurements revealed that the peak dopamine overflow in OKA-treated fish was about one-third of that measured in controls. These findings highlight the profound neurochemical changes that may occur in AD. Furthermore, they demonstrate that applying the latent learning paradigm and FSCV to zebrafish is a promising tool for future neurochemical studies and may be useful for screening drugs for the treatment of AD.

Dopamine Release Impairments Accompany Locomotor and Cognitive Deficiencies in Rotenone-Treated Parkinson's Disease Model Zebrafish

In this work, we carried out neurochemical and behavioral analysis of zebrafish (Danio rerio) treated with rotenone, an agent used to chemically induce a syndrome resembling Parkinson's disease (PD). Dopamine release, measured with fast-scan cyclic voltammetry (FSCV) at carbon-fiber electrodes in acutely harvested whole brains, was about 30% of that found in controls. Uptake, represented by the first order rate constant (k) and the half-life (t1/2) determined by nonlinear regression modeling of the stimulated release plots, was also diminished. Behavioral analysis revealed that rotenone treatment increased the time required for zebrafish to reach a reward within a maze by more than 50% and caused fish to select the wrong pathway, suggesting that latent learning was impaired. Additionally, zebrafish treated with rotenone suffered from diminished locomotor activity, swimming shorter distances with lower mean velocity and acceleration. Thus, the neurochemical and behavioral approaches, as applied, were able to resolve rotenone-induced differences in key parameters. This approach may be effective for screening therapies in this and other models of neurodegeneration.

Caged Zn2+ Photolysis in Zebrafish Whole Brains Reveals Subsecond Modulation of Dopamine Uptake

Free, ionic zinc (Zn2+) modulates neurotransmitter dynamics in the brain. However, the sub-s effects of transient concentration changes of Zn2+ on neurotransmitter release and uptake are not well understood. To address this lack of knowledge, we have combined the photolysis of the novel caged Zn2+ compound [Zn(DPAdeCageOMe)]+ with fast scan cyclic voltammetry (FSCV) at carbon fiber microelectrodes in live, whole brain preparations from zebrafish (Danio rerio). After treating the brain with [Zn(DPAdeCageOMe)]+, Zn2+ was released by application of light that was gated through a computer-controlled shutter synchronized with the FSCV measurements and delivered through a 1 mm fiber optic cable. We systematically optimized the photocage concentration and light application parameters, including the total duration and light-to-electrical stimulation delay time. While sub-s Zn2+ application with this method inhibited DA reuptake, assessed by the first-order rate constant (k) and half-life (t1/2), it had no effect on the electrically stimulated DA overflow ([DA]STIM). Increasing the photocage concentration and light duration progressively inhibited uptake, with maximal effects occurring at 100 μM and 800 ms, respectively. Furthermore, uptake was inhibited 200 ms after Zn2+ photorelease, but no measurable effect occurred after 800 ms. We expect that application of this method to the zebrafish whole brain and other preparations will help expand the current knowledge of how Zn2+ affects neurotransmitter release/uptake in select neurological disease states.