Central actions of liver-derived insulin-like growth factor I underlying its pro-cognitive effects

Increasing evidence indicates that circulating insulin-like growth factor I (IGF-I) acts as a peripheral neuroactive signal participating not only in protection against injury but also in normal brain function. Epidemiological studies in humans as well as recent evidence in experimental animals suggest that blood-borne IGF-I may be involved in cognitive performance. In agreement with observations in humans, we found that mice with low-serum IGF-I levels due to liver-specific targeted disruption of the IGF-I gene presented cognitive deficits, as evidenced by impaired performance in a hippocampal-dependent spatial-recognition task. Mice with serum IGF-I deficiency also have disrupted long-term potentiation (LTP) in the hippocampus, but not in cortex. Impaired hippocampal LTP was associated with a reduction in the density of glutamatergic boutons that led to an imbalance in the glutamatergic/GABAergic synapse ratio in this brain area. Behavioral and synaptic deficits were ameliorated in serum IGF-I-deficient mice by prolonged systemic administration of IGF-I that normalized the density of glutamatergic boutons in the hippocampus. Altogether these results indicate that liver-derived circulating IGF-I affects crucial aspects of mature brain function; that is, learning and synaptic plasticity, through its trophic effects on central glutamatergic synapses. Declining levels of serum IGF-I during aging may therefore contribute to age-associated cognitive loss.

Nifedipine-mediated mobilization of intracellular calcium stores increases spontaneous neurotransmitter release at neonatal rat motor nerve terminals

The modulation of spontaneous release of acetylcholine by specific Ca2+ channel blockers was studied at neonatal rat neuromuscular junction. During early postnatal periods (0-4 days), blockers of N- and P/Q-type Ca2+ channels did not affect miniature endplate potential (MEPP) frequency. Unexpectedly, treatment with the L-type Ca2+ channel antagonist nifedipine, although not when treated with isradipine, nitrendipine, or calciseptine, resulted in strong increase in MEPP frequency. The potentiation effect of nifedipine was dose-dependent with a 56-fold maximum effect with 15 microM. The effect decreased during the first two postnatal weeks and disappeared by the third. The effect of nifedipine was not dependent on extracellular Ca2+ and was not altered by the presence of other Ca2+ channel blockers. In contrast, it was abolished by depleting intracellular Ca2+ stores with 2 microM thapsigargin and was partially inhibited by 10 microM ryanodine. In conclusion, we report a new ryanodine receptor-mediated effect of nifedipine on neonatal neuromuscular junction that may indicate the developmental expression of a specific receptor channel that interacts with intracellular Ca2+ stores. This effect of nifedipine should also be considered when using this drug as either a therapeutic or a research tool.

Effect of time on liver clearance of technetium-99m-tetrofosmin in patients with acute chest pain: when should imaging begin?

OBJECTIVE

Due to stable myocardial retention and technetium imaging characteristics, 99mTc-tetrofosmin has been considered potentially useful for acute chest pain imaging. Tetrofosmin also has favorable biokinetics with reported rapid liver clearance, 5 min poststress and 30-45 min post-rest injection. Since comparable data are not available, the effect of time on liver clearance was evaluated in patients with acute chest pain.

METHODS

One hundred six patients received an intravenous injection of 25-30 mCi 99mTc-tetrofosmin to evaluate acute chest pain. SPECT imaging was performed 15-120 min after injection of the tracer. Patient images were grouped according to the time of acquisition after acute injection: 15-30 min, 31-45 min, 46-60 min, 61-90 min and > 90 min. Quantitative analysis was performed of a similar anterior projection for each patient consisting of 6 X 6-pixel region of interest over the myocardium and adjacent liver. Average counts per pixel were determined and a heart/liver (H/Li) ratio was calculated.

RESULTS

The mean H/Li ratio was < 1.0 for patient images acquired 15-45 min after injection, and > 1.0 for patient images acquired after 45 min. The difference was statistically significant (p < 0.05).

CONCLUSION

Quantitative analysis suggests that the optimal imaging time should be at least 45 min after the injection of 99mTc-tetrofosmin to allow adequate liver clearance before image acquisition of acute chest pain syndromes.

[Bronchiolitis obliterans with organizing pneumonia associated with idiopathic thrombocytopenic purpura]

We report a case of a 35 year-old woman with idiopathic thrombocytopenic purpura (ITP) who, under treatment with immunosuppressive drugs, developed bilateral interstitial pulmonary disease. Previously she had been splenectomized and treated with corticosteroids and cyclosporin. During the clinical course, the patient developed alterations of the hepatogram and presented a positive serology for Epstein-Barr virus. The lung biopsy showed the histologic pattern of obliterative bronchiolitis, interstitial inflammatory infiltration and intraalveolar pneumonia (BOOP). We could not find in the literature a previous report in which ITP was associated with BOOP. Of interest was the spontaneous remission of the pulmonary disease after suppression of cyclosporin and positive serology for Epstein-Barr virus.