Performance measurement of the microPET focus 120 scanner.

The microPET Focus 120 scanner is a third-generation animal PET scanner dedicated to rodent imaging. Here, we report the results of scanner performance testing. METHODS: A (68)Ge point source was used to measure energy resolution, which was determined for each crystal and averaged. Spatial resolution was measured using a (22)Na point source with a nominal size of 0.25 mm at the system center and various off-center positions. Absolute sensitivity without attenuation was determined by extrapolating the data measured using an (18)F line source and multiple layers of absorbers. Scatter fraction and counting rate performance were measured using 2 different cylindric phantoms simulating rat and mouse bodies. Sensitivity, scatter fraction, and noise equivalent counting rate (NECR) experiments were repeated under 4 different conditions (energy window, 250 approximately 750 keV or 350 approximately 650 keV; coincidence window, 6 or 10 ns). A performance phantom with hot-rod inserts of various sizes was scanned, and several animal studies were also performed. RESULTS: Energy resolution at a 511-keV photopeak was 18.3% on average. Radial, tangential, and axial resolution of images reconstructed with the Fourier rebinning (FORE) and filtered backprojection (FBP) algorithms were 1.18 (radial), 1.13 (tangential), and 1.45 mm full width at half maximum (FWHM) (axial) at center and 2.35 (radial), 1.66 (tangential), and 2.00 mm FWHM (axial) at a radial offset of 2 cm. Absolute sensitivities at transaxial and axial centers were 7.0% (250 approximately 750 keV, 10 ns), 6.7% (250 approximately 750 keV, 6 ns), 4.0% (350 approximately 650 keV, 10 ns), and 3.8% (350 approximately 650 keV, 6 ns). Scatter fractions were 15.9% (mouse phantom) and 35.0% (rat phantom) for 250 approximately 750 keV and 6 ns. Peak NECR was 869 kcps at 3,242 kBq/mL (mouse phantom) and 228 kcps at 290 kBq/mL (rat phantom) at 250 approximately 750 keV and 6 ns. Hot-rod inserts of 1.6-mm diameter were clearly identified, and animal studies illustrated the feasibility of this system for studies of whole rodents and mid-sized animal brains. CONCLUSION: The results of this independent field test showed the improved physical characteristics of the F120 scanner over the previous microPET series systems. This system will be useful for imaging studies on small rodents and brains of larger animals.     

Effects of acute barbiturate administration, tolerance and dependence on brain GABA system: comparison to alcohol and benzodiazepines

Central nervous system depressants, e.g., barbiturates, alcohol and benzodiazepines, have a wide spectrum of activity in humans and animals. Evidence accumulated suggests that some of the pharmacological actions exerted by these agents may be mediated through GABA system by mimicking GABAergic transmission. This review attempts to summarize the evidence available as to how the GABA system plays a part in the barbiturate actions and the development of tolerance to and physical dependence on barbiturates. The comparisons of the effects of alcohol, barbiturates and benzodiazepines at different steps of GABA synapse are also presented. Furthermore, the results which have been reported in the literature are inconsistent. This may be due to differences in: (a) animal models used; (b) brain regions used; (c) protocols (dose, duration, form and route of administration, etc.) used in treating animals and/or (d) techniques (pharmacological, biochemical, physiological, etc.) used.     

Inhibition of hepatic glucose production by SDZ 51641

The new oral hypoglycemic agent SDZ 51641 was evaluated in nondiabetic rats and a rat model of human non-insulin-dependent diabetes mellitus. Diabetes was induced with a single injection of 37.5 mg/kg streptozocin, and the rats exhibited hyperglycemia in the fed state with normal insulin levels. Treatment of nondiabetic animals with 100 mg/kg SDZ 51641 given orally significantly decreased serum glucose and ketone levels within 4 h without affecting insulin levels. Nonesterified fatty acids increased more than twofold during the same period. Its effect on ketone and fatty acid levels suggests that SDZ 51641 acts as an inhibitor of fatty acid oxidation. Diabetic rats treated with SDZ 51641 exhibited a significant acute hypoglycemic response, which was more pronounced after 3 days of treatment. The compound also significantly decreased serum cholesterol and triglyceride levels 27 and 53%, respectively. When endogenous hepatic glucose production was assessed in nondiabetic and diabetic animals via continuous infusion of [3-3H]glucose, we found that hepatic glucose production was elevated 43% in diabetic compared with control animals. When diabetic rats were treated with 100 mg/kg SDZ 51641, hepatic glucose production decreased to normal levels within 6 h. Hyperinsulinemic-euglycemic clamp studies indicated that SDZ 51641 had no effect on insulin-stimulated glucose utilization. Measurement of [1-14C]oleate oxidation in isolated hepatocytes demonstrated that SDZ 51641 inhibited long-chain fatty acid oxidation in a concentration-dependent manner. The compound was ineffective at inhibiting long-chain fatty acid oxidation in epitrochlearis or soleus muscles.(ABSTRACT TRUNCATED AT 250 WORDS)     

Anatomic relationship of the oculomotor nuclear complex and medial longitudinal fasciculus in the midbrain.

PURPOSETo compare the MR characteristics of the oculomotor nucleus with its appearance on anatomic images.METHODSSpecimens of cadaveric brains were imaged in a 3.0-T MR imager equipped with a 3.0-cm solenoid coil. The specimens were sectioned, stained, and examined histologically. On anatomic sections, the oculomotor nuclei, medial longitudinal fasciculus, red nuclei, and oculomotor nerve were identified. The MR images were then compared with the anatomic sections.RESULTSThe oculomotor nuclei, medial longitudinal fasciculus, red nuclei, and oculomotor nerve could be identified on MR images by their size, shape, signal intensity, and location.CONCLUSIONMR images show the anatomic relationship of the oculomotor nerve complex, medial longitudinal fasciculus, and related structures in the brain stem.     

EMG myokymia as a cause of ptosis in hypothyroidism

Ptosis is known to be associated with thyroid disorders. We describe two biochemically corrected hypothyroid patients presenting with isolated bilateral ptosis. EMG of the orbicularis oculi showed continuous grouped motor unit potentials. In the absence of obvious aetiology, it is hypothesised that focal demyelination of terminal branches to the orbicularis oculi may play a role in the generation of the discharges.