Abstract-Lesion composition plays a significant role in atherosclerotic lesion instability and rupture. Current clinical techniques cannot fully characterize lesion composition or accurately identify unstable lesions. This study investigates the use of time-resolved fluorescence spectroscopy for unstable atherosclerotic lesion diagnosis. The fluorescence of human coronary artery samples was induced with nitrogen laser and detected in the 360-to 510-nm wavelength range. The samples were sorted into 7 groups according to the AHA classification: normal wall and types I, II a (fatty streaks), III (preatheroma), IV (atheroma), V a (fibrous), and V b (calcified) lesions. Spectral intensities and time-dependent parameters [average lifetime f ; decay constants: 1 (fast-term), 2 (slow-term), A 1 (fast-term amplitude contribution)] derived from the time-resolved spectra of coronary samples were used for tissue characterization. We determined that a few intensity values at longer wavelengths (Ͼ430 nm) and time-dependent parameters at peak emission region (390 nm) discriminate between all types of arterial samples except between normal wall and type I lesions. The lipid-rich lesions (more unstable) can be discriminated from fibrous lesions (more stable) on the basis of time-dependent parameters (lifetime and fast-term decay). We inferred that features of lipid fluorescence are reflected on lipid-rich lesion emission. Our results demonstrate that analysis of the time-resolved spectra may be used to enhance the discrimination between different grades of atherosclerotic lesions and provide a means of discrimination between lipid-rich and fibrous lesions. Key Words: atherosclerosis Ⅲ lesion instability Ⅲ time-resolved laser-induced fluorescence Ⅲ spectroscopy R upture of coronary atherosclerotic lesions leads to the acute coronary syndromes of unstable angina, acute myocardial infarction, and ischemic sudden death. [1][2][3] Evidence suggests that lesion composition plays a crucial role in lesion instability and that lipid-rich lesions are more prone to rupture than fibrous lesions. [1][2][3] Current clinical techniques (angiography, angioscopy, ultrasound) are limited in their ability to characterize lesion composition and identify lipidrich lesions. 3 Various techniques are currently under study as potential new tools for identification of lipid-rich lesions (MRI, 4 near-infrared spectroscopy, 5 Raman spectroscopy 6 ) or markers of instability, such as macrophage activation in fibrous cap (local thermography 7 ).Several groups have investigated laser-induced fluorescence spectroscopy (LIFS) as a tool for analyzing plaque composition in the attempt to guide laser angioplasty and to evaluate the likelihood of restenosis. 8 -13 The research was carried out for both ex vivo 8 -12 and in vivo 12,13 conditions. These early studies have demonstrated the potential of LIFS to characterize a few types of atherosclerotic lesions (fibrous, atheromatous, calcified) and to discriminate those from the normal arterial wall. These studies,...

Autoradiographs are conventionally analyzed by a region-of-interest (ROI) analysis. However, definition of ROIs on an image set is labor intensive, is subject to potential inter-rater bias, and is not well suited for anatomically variable structures that may not consistently correspond to specific ROIs. Most importantly, the ROI method is poorly suited for whole-brain analysis, where one wishes to detect all activations resulting from an experimental paradigm. A system developed for analysis of imaging data in humans, Statistical Parametric Mapping (SPM), avoids some of these limitations but has not previously been adapted as a tool for the analysis of autoradiographs. Here, we describe the application of SPM to an autoradiographic data set mapping cerebral activation in rats during treadmill walking. We studied freely moving, non-tethered rats that received injections of the cerebral blood flow tracer [ 14 C]-iodoantipyrine, while they were performing a treadmill task (n = 7) or during a quiescent control condition (n = 6). Results obtained with SPM were compared to those previously reported using a standard ROI-based method of analysis [J. Cereb. Blood Flow Metab. 23 (2003) 925]. The SPM method confirmed most areas detected as significant using the ROI approach. However, in the subcortex, SPM detected additional significant regions that, because of their irregular structures, fell short of statistical significance when analyzed by ROI. The SPM approach offers the ability to perform a semi-automated whole-brain analysis, and coupled with autoradiography, provides an effective means to globally localize functional activity in small animals.

Exercise training (ET) causes functional and morphologic changes in normal and injured brain. While studies have examined effects of short-term (same day) training on functional brain activation, less work has evaluated effects of long-term training, in particular treadmill running. An improved understanding is relevant as changes in neural reorganization typically require days to weeks, and treadmill training is a component of many neurorehabilitation programs. Adult, male rats (n=10) trained to run for 40 min/day, 5 days/week on a Rotarod treadmill at 11.5 cm/s, while control animals (n=10) walked for 1 min/day at 1.2 cm/s. Six weeks later, [(14)C]-iodoantipyrine was injected intravenously during treadmill walking. Regional cerebral blood flow-related tissue radioactivity was quantified by autoradiography and analyzed in the three-dimensionally reconstructed brain by statistical parametric mapping. Exercised compared to nonexercised rats demonstrated increased influence of the cerebellar-thalamic-cortical (CbTC) circuit, with relative increases in perfusion in deep cerebellar nuclei (medial, interposed, lateral), thalamus (ventrolateral, midline, intralaminar), and paravermis, but with decreases in the vermis. In the basal ganglia-thalamic-cortical circuit, significant decreases were noted in sensorimotor cortex and striatum, with associated increases in the globus pallidus. Additional significant changes were noted in the ventral pallidum, superior colliculus, dentate gyrus (increases), and red nucleus (decreases). Following ET, the new dynamic equilibrium of the brain is characterized by increases in the efficiency of neural processing (sensorimotor cortex, striatum, vermis) and an increased influence of the CbTC circuit. Cerebral regions demonstrating changes in neural activation may point to alternate circuits, which may be mobilized during neurorehabilitation.

Preclinical drug development for visceral pain has largely relied on quantifying pseudoaffective responses to colorectal distension (CRD) in restrained rodents. However, the predictive value of changes in simple reflex responses in rodents for the complex human pain experience is not known. Male rats were implanted with venous cannulas and with telemetry transmitters for abdominal electromyographic (EMG) recordings. [ 14 C]-iodoantipyrine was injected during noxious CRD (60 mmHg) in the awake, nonrestrained animal. Regional cerebral blood flow (rCBF)-related tissue radioactivity was quantified by autoradiography and analyzed in the threedimensionally reconstructed brain by statistical parametric mapping. 60-mmHg CRD, compared with controls (0 mmHg) evoked significant increases in EMG activity (267 ± 24% vs. 103 ± 8%), as well as in behavioral pain score (77 ± 6% vs. 3 ± 3%). CRD elicited significant increases in rCBF as expected in sensory (insula, somatosensory cortex), and limbic and paralimbic regions (including anterior cingulate cortex and amygdala). Significant decreases in rCBF were seen in the thalamus, parabrachial nucleus, periaqueductal gray, hypothalamus and pons. Correlations of rCBF with EMG and with behavioral pain score were noted in the cingulate, insula, lateral amygdala, dorsal striatum, somatosensory and motor regions. Our findings support the validity of measurements of cerebral perfusion during CRD in the freely moving rat as a model of functional brain changes in human visceral pain. However, not all regions demonstrating significant group differences correlated with EMG or behavioral measures. This suggests that functional brain imaging captures more extensive responses of the central nervous system to noxious visceral distension than those identified by traditional measures.

Diaphragm and latissimus dorsi muscle functions, histochemistries, and morphometries were studied in anesthetized male Yucatan minipigs with congestive heart failure (CHF) induced by supraventricular tachycardia (n = 5). Sham-operated animals served as a control group (n = 5). In CHF animals, transdiaphragmatic pressure measured during supramaximal phrenic stimulation was reduced by 40% at low frequencies (< or = 20 Hz) and by 60% at higher frequencies. Twitch amplitude and half-relaxation time were also decreased. The cross-sectional areas of type I, IIa, and IIb fibers were reduced in the diaphragm. The proportion of type I fibers increased, whereas type IIa fibers decreased. Succinate dehydrogenase activity was elevated in type IIa and IIb fibers, but diaphragmatic fatigability was not altered. CHF reduced latissimus dorsi isometric force by 40% for stimulation frequencies > or = 30 Hz. The cross-sectional area of latissimus dorsi type IIb fibers was decreased, but twitch characteristics, fiber type composition, succinate dehydrogenase activity, and fatigability were unchanged. Experimental CHF appears to cause greater intrinsic adaptive changes in the diaphragm compared with those in the latissimus dorsi in the minipig. For both muscles, reduced contractile function was associated with atrophy. Impaired performance of the diaphragm may also be attributed to an increase in the relative contribution of type I fibers to the total tension-generating capacity of the muscle and to the pathophysiological mechanisms underlying the shortened relaxation time of the twitch response.

Summary:A dilemma in functional neuroimaging is that immobilization of the subject, necessary to avoid movement artifact, extinguishes all but the simplest behaviors. Recently, we developed an implantable microbolus infusion pump (MIP) that allows bolus injection of radiotracers by remote activation in freely moving, nontethered animals. The MIP is examined as a tool for brain mapping in rats during a locomotor task. Cerebral blood flow-related tissue radioactivity (CBF-TR) was measured using [14 C]-iodoantipyrine with an indicator-fractionation method, followed by autoradiography. Rats exposed to walking on a treadmill, compared to quiescent controls, showed increases in CBF-TR in motor circuits (primary motor cortex, dorsolateral striatum, ventrolateral thalamus, midline cerebellum, copula pyramis, paramedian lobule), in primary somatosensory cortex mapping the forelimbs, hindlimbs and trunk, as well as in secondary visual cortex. These results support the use of implantable pumps as adjunct tools for functional neuroimaging of behaviors that cannot be elicited in restrained or tethered animals.

Studies in healthy human subjects and patients with irritable bowel syndrome suggest sex differences in cerebral nociceptive processing. Here we examine sex differences in functional brain activation in the rat during colorectal distention (CRD), a preclinical model of acute visceral pain. [14C]-iodoantipyrine was injected intravenously in awake, nonrestrained female rats during 60-mmHg or 0-mmHg CRD while electromyographic abdominal activity (EMG) and pain behavior were recorded. Regional cerebral blood flow related tissue radioactivity was analyzed by statistical parametric mapping from autoradiographic images of 3-dimensionally reconstructed brains. Sex differences were addressed by comparing current data with our previously published data collected from male rats. While sex differences in EMG and pain scores were modest, significant differences were noted in functional brain activation. Females showed widespread changes in limbic (amygdala, hypothalamus) and paralimbic structures (ventral striatum, nucleus accumbens, raphe), while males demonstrated broad cortical changes. Sex differences were apparent in the homeostatic afferent network (parabrachial nucleus, thalamus, insular and dorsal anterior cingulate cortices), in an emotional-arousal network (amygdala, locus coeruleus complex), and in cortical areas modulating these networks (prefrontal cortex). Greater activation of the ventromedial prefrontal cortex and broader limbic/paralimbic changes in females suggest greater engagement of affective mechanisms during visceral pain. Greater cortical activation in males is consistent with the concept of greater cortical inhibitory effects on limbic structures in males, which may relate to differences in attentional and cognitive attribution to visceral stimuli. These findings show remarkable similarities to reported sex differences in brain responses to visceral stimuli in humans.

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