Effect of L-thyroxine administration on long-term potentiation and accompanying mitogen-activated protein kinases in rats.

The present study investigated the differences in the activation of c-Jun NH2-terminal kinases (JNK), p38 mitogen-activated protein kinases (p38MAPK ), and extracellular signal-regulated kinases 1/2 (Erk1/2) 1 hr after the induction of long-term potentiation (LTP) between rats with hyperthyroidism that was produced at two different stages of development. Hyperthyroidism was produced in rats by daily injections of L-thyroxine (T4, ip., 0.2 mg/kg) to their dams for lactation period or to the rats itself during the young adult period. LTP was induced by application of high-frequency stimulation protocol. Five-min averages of the excitatory postsynaptic potential (EPSP) slopes and population spike (PS) amplitudes at the end of recording were averaged to measure the magnitude of LTP. Total and phosphorylated levels of Erk1/2, JNK, and P38-MAPK were assessed via western blotting in these hippocampi. LTP was found to be impaired in both groups of hyperthyroidisms, but this impairment observed together with increased expression and phosphorylation of ERK1/2, and increased phosphorylation of JNK in rats treated maternally with T4 compared to those treated adultly. These results suggest that excessiveness of thyroid hormone has longstanding effects on hippocampal function and may account for failed LTP in both early and relatively late stage of development depending on various molecular pathways, such as ERK1/2 and JNK.

Maternal L-thyroxine treatment during lactation affects learning and anxiety-like behaviors but not spatial memory in adult rat progeny.

BACKGROUND: The present study compared behavioral and molecular indicators of hippocampal function in L-thyroxine treated rats to determine whether thyroid hormone excessiveness produces relatively stable lifelong changes. METHODS: Hyperthyroidism was induced in rats by daily injections of L-thyroxine (0.2 mg/kg) to their dams for lactation period (MOH: maternal-onset hyperthyroidism) or to the rats itself during the young adult period (AOH: adult-onset hyperthyroidism; between the day 39-60). Spatial learning was assessed in the Morris Water Maze (MWM). Levels of type 2 and type 3 deiodinases, Erk1/2, JNK and P38MAPK were assessed via western blotting in the hippocampus of trained rats. Measurements were all done in rats aged 60-66 days. RESULTS: In MWM, maternally treated rats with L-thyroxine swam more away from the hidden platform, with showing more anxiety-like behavior, as compared to the rats treated or no treated with L-thyroxine in young adulthood. In spite of impaired acquisition, MOH group was not significantly different from the other groups in probe trial. In Western blot of the hippocampus, a decreased the expression of P38MAPK was found in rats treated with L-thyroxine in young adulthood period. However, maternal treatment with L-thyroxine resulted in an increased expression of Type 2 deiodinase and a tendency toward decreased expression of total and phosphorylated ERK1/2. No detectable band for type 3 deiodinase, p-JNK and p-P38MAPK was observed in all three groups. CONCLUSION: These results suggest that perinatal excessiveness of thyroid hormone has longstanding effects on hippocampal function and may account for memory problems experienced by adolescents with lactational hyperthyroidism.

P50 variations in Behcet`s patients without neurologic findings.

OBJECTIVE: In the present study, subclinical lesion involvement was investigated using the P50 component in Behcet`s patients without neurological manifestation. METHODS: We performed this clinical research in Erciyes University, Faculty of Medicine between December 2000 and November 2001. The studies were carried out on 18 Behcet`s patients without neurologic findings and 18 volunteers for control. Standard Ag/AgCl electrodes in plastic cups were used for monopolar EEG derivations. They were attached with electrode paste and tape at the Cz (vertex) according to the 10-20 system. The auditory stimuli were delivered in pairs. The P50 waves, which may be taken from approximately 50 msec from the stimuli, were collected by computer system. Amplitudes and latencies of the P50 components were measured in the same system. RESULTS: This study showed that the suppression of P50 responses performed by the test stimuli, was significantly more decreased in Behcet`s patients than the control subjects. CONCLUSION: The decrease of the suppression of the auditory P50 response to repeated stimuli reflects a deficit in the central nervous system`s ability, such as attention, cognition, and sensory input in Behcet`s patients and can be used as a neurophysiological marker in subclinical lesions in these patients.

Sex-related differences in time estimation and the role of expectancy.

In this study, using auditory sequences, the authors designed an examination with three phases of stimulus-driven attention that is based on the possibility that involuntarily time shifts of attention are caused by nonunique stimulus properties. The purpose was to investigate whether attending and temporal expectancies are influenced by stimulus's properties and by sex. In each phase, an auditory stimulus train was presented, and the participant was asked to tap rhythmically in order to anticipate every fifth stimulus (or, in the third phase, the lack of it). The time between button pressing and stimulus onset was measured using a computer. Time estimation was accepted as a false response if the subject responded before 150 ms or 150 ms later from onset stimulus time. Error numbers were greater in Phase 3 and there was no significant difference between the male and female subjects for any of the phases when error numbers were compared. On the other hand, males pressed the button more accurately than females. Time estimation performance was affected by sex and expectancy-related motor responses are very important for time estimation.

Effects of cigarette smoking on cognitive processing.

Several previous studies have reported that cigarette smoking enhances performance of cognitive processing. These enhancements are generally attributed to the pharmacological effects of nicotine, while there is some debate whether the effects of smoking/nicotine are a result of recovery from abstinence. Evoked potentials (EPs) and event related potentials (ERPs) of the brain have been applied as an index of information processing in a wide variety of normal and cognitive impaired subjects. This study was carried out on 20 healthy students (23 +/- 2.3 years old) from the medical faculty of City University. Study population comprised ten chronic cigarette smokers consuming an average of 14 +/- 4.2 cigarettes per day, with a history of smoking for more than one year. Ten non -smokers served as control. Standard oddball paradigm was presented, and EEG activity was recorded at the Fz, Cz, Pz electrode sites. Twenty responses to target stimuli were averaged at each location. N1, P2, N2, and P300 components were evaluated in these recordings. Amplitudes were measured relative to prestimulus baseline, and peak latencies were defined as the time point of maximum amplitude. It was found that there were no significant differences between either N1, P2, N2, P300 amplitudes or peak latency values of cigarette smokers and non smokers. As a result, chronic cigarette smoking generally does not improve cognitive processing.

Evaluation of auditory evoked potentials from the inferior colliculus in rat.

This study aimed to investigate the usefulness of auditory evoked potentials (AEPs) in rats. To this end, N1, P2 latencies, and the N1-P2 amplitude of responses to different acoustic stimuli from rats, which were implanted with permanent electrodes in the inferior colliculus (IC), were evaluated and used to demonstrate the frequency characteristics of IC region. Permanent electrodes were implanted in IC regions of 7 male albino rats by the stereotaxic method. The animals were exposed to five tones series of stimuli (1000 Hz, 2000 Hz, 4000 Hz, 6000 Hz, and 8000 Hz tones with 1500 ms interstimulus intervals) of 70 dB with a duration of 1000 ms. AEPs) were recorded and analyzed with the Brain-Data Acquisition system. There were no statistically significant differences in N1, P2 latencies, and the N1-P2 amplitude of AEPs from IC regions of rats as a result of changes in the frequency of stimulus. It was determined that the dominant frequency activity of the IC to acoustic stimulus was theta-alpha band, with theta as the peak frequency.