CART peptide and opioid addiction: Expression changes in male rat brain.

Previous studies have shown the prominence of cocaine- and amphetamine-regulated transcript (CART) peptide in rewarding and reinforcing effects of drugs of abuse specially psychostimulants. The data regarding the effects of different stages of opioid addiction on CART expression and the interconnection between CART and opioids are not much available. Here we have studied the changes in the expression level of CART mRNA and protein in various parts of the brain reward pathway in different stages of opioid addiction. Groups of male rats received acute low-dose (10mg/kg), acute high-dose (80mg/kg) and chronic escalating doses of morphine. In addition, withdrawal and abstinence states were evaluated after injection of naloxone (1mg/kg) and long-term maintenance of addicted animals, respectively. Expression of CART mRNA in the brain was measured by real-time PCR method. Western blotting was used to quantify the protein level. CART mRNA and protein were both up-regulated in high-dose morphine-administered animals and also in the withdrawal group in the nucleus accumbens (NAc), striatum and prefrontal cortex (PFC). In the addicted group, CART mRNA and protein were both down-regulated in NAc and striatum. In the abstinent group, CART mRNA was down-regulated in NAc. In the hippocampus, the only observed change was the up-regulation of CART mRNA in the withdrawal group. We suggest that the modulatory role of CART peptide in rewarding and reinforcing effects of opioids weakens when opioids are used for a long time and is stimulated when acute stress such as naloxone-induced withdrawal syndrome or acute high-dose administration of morphine occurs to the animal.

Effect of circadian rhythm disturbance on morphine preference and addiction in male rats: Involvement of period genes and dopamine D1 receptor.

It is claimed that a correlation exists between disturbance of circadian rhythms by factors such as alteration of normal light-dark cycle and the development of addiction. However, the exact mechanisms involved in this relationship are not much understood. Here we have studied the effect of constant light on morphine voluntary consumption and withdrawal symptoms and also investigated the involvement of Per1, Per2 and dopamine D1 receptor in these processes. Male wistar rats were kept under standard (LD) or constant light (LL) conditions for one month. The plasma concentration of melatonin was evaluated by enzyme-linked immunosorbent assay (ELISA). Real-time PCR was used to determine the mRNA expression of Per1, Per2 and dopamine D1 receptor in the striatum and prefrontal cortex. Morphine preference (50mg/L) was evaluated in a two-bottle-choice paradigm for 10 weeks and withdrawal symptoms were recorded after administration of naloxone (3mg/kg). One month exposure to constant light resulted in a significant decrease of melatonin concentration in the LL group. In addition, mRNA levels of Per2 and dopamine D1 receptor were up-regulated in both the striatum and prefrontal cortex of the LL group. However, expression of Per1 gene was only up-regulated in the striatum of LL rats in comparison to LD animals. Furthermore, after one month exposure to constant light, morphine consumption and preference ratio and also severity of naloxone-induced withdrawal syndrome were significantly greater in LL animals. It is concluded that exposure to constant light by up-regulation of Per2 and dopamine D1 receptor in the striatum and prefrontal cortex and up-regulation of Per1 in the striatum and the possible involvement of melatonin makes animals vulnerable to morphine preference and addiction.

Compact and integrated 2-D photonic crystal super-prism filter-device for wavelength demultiplexing applications.

A two-dimensional photonic crystal (PhC) super-prism integrated with one-dimensional photonic crystal microcavity filters has been designed using the plane wave expansion (PWE) and 2-D Finite Difference Time Domain (FDTD) methods based on Silicon-on-Insulator (SOI) technology. The super-prism operates as a coarse spatial filter with an average response bandwidth of 60 nm, while the 1-D PhC microcavity filters operate as narrow band-pass transmission filters with an average filter response line-width of 10 nm. This work demonstrates the simultaneous operation of two photonic devices for de-multiplexing applications on a single platform that could be useful in future Photonic Crystal Integrated Circuits (PCICs).

MMI multiplexer for dual-channel erbium-doped waveguide amplifiers.

A multimode interference coupler is proposed for pumping two erbium-doped waveguide amplifiers from a single 980 nm pump channel. Simulations predict that a device less than 2500 microm long can be made with signal and pump power losses of 0.28 dB and 0.63 dB respectively. The calculated 1 dB excess loss bandwidth of the device is 57 nm.