Cadmium is a toxic environmental and industrial pollutant. Cadmium toxicity has been reported to produce biochemical and behavioral dysfunction that may cause adverse effects on several organs including the central nervous system. The present study was designed to investigate the neurotoxic effects of Cadmium Chloride (CdCl2) at three different doses by using different behavioral models. Lipid peroxidation (LPO), superoxide dismutase (SOD) and acetylcholinesterase (AChE) activities were also monitored following acute intraperitoneal injection of cadmium. Twenty four adult locally bred Albino Wistar rats were divided into control and 3 test groups (n = 6). Control rats were injected intraperitoneally with saline (0.9% NaCl) and test groups were injected with CdCl2 (1 mg/kg, 2 mg/kg and 3 mg/kg) dissolved in physiological solution. Behavioral activities of rats were monitored after 1 h of cadmium injection. Locomotor activity and depression-like symptoms were measured by Open Field Test (OFT) and Forced Swimming Test (FST) respectively. Anxiety like behavior was monitored using Light-dark Transition (LDT) test and memory functions of rats were assessed by Morris Water Maze test (MWM). In the present study acute cadmium administration dose dependently increased anxiety in rats as compared to control rats. A significant increase in depression-like symptoms was also exhibited by cadmium treated rats. These behavioral dysfunctions may be attributed to the decreased superoxide dismutase (SOD) activity and simultaneously increased brain lipid peroxidation (LPO). Moreover learning and memory assessed by MWM showed dose dependent impairment in memory function in cadmium treated rats as compared to control rats. Acetylcholinesterase (AChE) activity was also decreased in brains of cadmium administered rats. It is suggested in this study that behavioral, biochemical and neurochemical dysfunctions caused by acute cadmium administration occur in a dose dependent manner.

It has been shown in various studies that increase in serotonergic neurotransmission is associated with increased memory consolidation whereas low brain 5HT impairs memory performance. In the first phase of our study we found that tryptophan (TRP) administration for 6 weeks increased plasma TRP and whole brain TRP, 5HT and 5HIAA levels. Many brain regions are involved in the learning process but particularly the hippocampus is known to have key role in learning and memory. The present study was therefore designed to investigate the effects of TRP loading particularly on hippocampal 5HT metabolism and cognitive performance in rats. TRP-treated rats demonstrated spatial enhancement as evidenced by a significant decrease in time to find the hidden food reward in radial arm maze test (RAM). The important finding of the present study was the greater increase in the 5HT metabolism in hippocampus than in any other brain region of the TRP-treated rats. This increased 5HT metabolism in the hippocampus emphasizes the involvement of this region in memory process.

Lead toxicity is known to induce a broad range of physiological, biochemical and behavioral dysfunctions that may result in adverse effects on several organs, including the central nervous system. Long-term exposure to low levels of lead (Pb(2+)) has been shown to produce behavioral deficits in rodents and humans by affecting hypothalamic-pituitary-adrenal (HPA) axis. These deficits are thought to be associated with altered brain monoamine neurotransmission and due to changes in glucocorticoids levels. This study was designed to investigate the effects of Pb(2+)exposure on growth rate, locomotor activity, anxiety, depression, plasma corticosterone and brain serotonin (5-HT) levels in rats. Rats were exposed to lead in drinking water (500 ppm; lead acetate) for 5 weeks. The assessment of depression was done using the forced swimming test (FST). Estimation of brain 5-HT was determined by high-performance liquid chromatography with electrochemical detection. Plasma corticosterone was determined by spectrofluorimetric method. The present study showed that long term exposure to Pb(2+) significantly decreased the food intake followed by the decrease in growth rate in Pb(2+)exposed rats as compared to control group. No significant changes in open field activity were observed following Pb(2+)exposure while significant increase in anxiogenic effect was observed. Increased plasma corticosterone and decreased 5-HT levels were exhibited by Pb(2+)exposed rats as compared to controls. A significant increase in depressive like symptoms was exhibited by Pb(2+)exposed rats as compared to control rats. The results are discussed in the context of Pb(2+) inducing a stress-like response in rats leading to changes in plasma corticosterone and brain 5-HT levels via altering tryptophan pyrrolase activity.

Memory impairment is a major problem afflicting mankind. The association between memory functions and neurotransmitter functions is of great interest for understanding brain function. Serotonergic pathways play an important role in the modulation of memory functions but the importance of its receptor types and subtypes on memory functions is still unclear. Activation and blockade of various serotonin (5-HT) receptors has been reported to alter cognitive processes and 5-HT receptor antagonism could be beneficial in the treatment of cognitive diseases. The role of 5-HT on memory functions is complicated. Among the 5-HT receptors subtypes, 5-HT(1A) receptors are of special interest because these receptors are present in the brain areas involved in learning and memory functions such as hippocampus and cortex. The present study was therefore designed to investigate the effect of activation and blockade of somatodendritic and/or postsynaptic 5-HT(1A) receptor on learning and memory functions in rats using modified version of water maze. In this study, 8-OH-DPAT (8-hydroxy-2-(di-N-propylamino) tetralin) at 0.3 mg/kg significantly enhanced learning acquisition (LA), short-term memory (STM) and long term memory (LTM) of rats pre-injected with saline suggesting that the activation of pre-synaptic 5-HT(1A) receptors by its agonist enhanced the memory functions of rats. Conversely, rats injected with 8-OH-DPAT at 1.0 mg/kg exhibited impaired LA and STM and had no effect on LTM. It was also shown in this study that blockade of 5-HT(1A) receptors by spiperone enhanced LA, had no effect on STM but impaired the LTM, which showed that the blockade of 5-HT(1A) receptors by its antagonist exerts different effect on different types of memory. This study suggests that 5-HT(1A) receptor could be used as a significant pharmacological target for the treatment of CNS diseases. Unraveling the role of serotonin in cognition and memory disorders could provide better therapy and it may lead to new insights in our understandings of learning and memory.

Conclusion NTM were present in at least 1.3% of all smear positive samples. It is important for public health programs to recognize the avoidable burden on logistics, infrastructure and finances caused by this. Detection and quantification of this burden would help design an appropriate strategy for optimal tuberculosis control.