Activation of multiple neuromodulatory systems in alert rats acquiring conditioned taste aversion revealed by positron emission tomography.

Conditioned taste aversion (CTA) is an essential ability for animals to consume food safely and is regulated by neuromodulatory systems including the dopamine, noradrenaline, serotonin, and acetylcholine systems. However, because few studies focused on a comprehensive understanding of whole-brain activities, how these neuromodulators contribute to the process of CTA remains an open issue. 18F-fluorodeoxyglucose (FDG)-positron emission tomography (PET) can visualize activated regions within the whole brain simultaneously and noninvasively. This study aimed to understand the mechanisms of CTA, especially focusing on the retrieval process after CTA acquisition by FDG-PET imaging. CTA was established in rats who received an intraoral application of saccharin solution (IOAS) on the first day (Day 1), a LiCl i.p. injection after an IOAS on Day 2, and an IOAS on Day 3 (CTA group). The subtraction images of Day 3 of the SHAM group, which received a 0.9 % NaCl (saline) injection instead of a LiCl on Day 2, from those of Day 3 of the CTA group revealed increases in FDG signals in multiple brain regions including the substantia nigra, ventral tegmental area, locus coeruleus, dorsal raphe, and nucleus basalis magnocellularis, in addition to the hippocampus and nociception-related regions, including the parabrachial nucleus and solitary nucleus. On the other hand, the visceral pain induced by the LiCl injection increased FDG signals in the primary and secondary somatosensory and insular cortices in addition to the parabrachial nucleus and solitary nucleus. These results suggest that the retrieval process of CTA induces brain regions producing neuromodulators and pain-related brainstem.

A voxel-based analysis of brain activity in high-order trigeminal pathway in the rat induced by cortical spreading depression.

Cortical spreading depression (SD) is a self-propagating wave of depolarization that is thought to be an underling mechanism of migraine aura. Growing evidence demonstrates that cortical SD triggers neurogenic meningeal inflammation and contributes to migraine headaches via subsequent activation of trigeminal afferents. Although direct and indirect evidence shows that cortical SD activates the trigeminal ganglion (peripheral pathway) and the trigeminal nucleus caudalis (TNC, the first central site of the trigeminal nociceptive pathway), it is not yet known whether cortical SD activates the high-order trigeminal nociceptive pathway in the brain. To address this, we induced unilateral cortical SD in rats, and then examined brain activity using voxel-based statistical parametric mapping analysis of FDG-PET imaging. The results show that approximately 40h after the induction of unilateral cortical SD, regional brain activity significantly increased in several regions, including ipsilateral TNC, contralateral ventral posteromedial (VPM) and posterior thalamic nuclei (Po), the trigeminal barrel-field region of the primary somatosensory cortex (S1BF), and secondary somatosensory cortex (S2). These results suggest that cortical SD is a noxious stimulus that can activate the high-order trigeminal nociceptive pathway even after cortical SD has subsided, probably due to prolonged meningeal inflammation.

Positron emission tomography study on pancreatic somatostatin receptors in normal and diabetic rats with 68Ga-DOTA-octreotide: a potential PET tracer for beta cell mass measurement.

Diabetes mellitus (DM) is a metabolic disorder characterized by hyperglycemia, and the loss or dysfunction of pancreatic beta cells has been reported before the appearance of clinical symptoms and hyperglycemia. To evaluate beta cell mass (BCM) for improving the detection and treatment of DM at earlier stages, we focused on somatostatin receptors that are highly expressed in the pancreatic beta cells, and developed a positron emission tomography (PET) probe derived from octreotide, a metabolically stable somatostatin analog. Octreotide was conjugated with 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA), a chelating agent, and labeled with (68)Gallium ((68)Ga). After intravenous injection of (68)Ga-DOTA-octreotide, a 90-min emission scan of the abdomen was performed in normal and DM model rats. The PET studies showed that (68)Ga-DOTA-octreotide radioactivity was highly accumulated in the pancreas of normal rats and that the pancreatic accumulation was significantly reduced in the rats administered with an excess amount of unlabeled octreotide or after treatment with streptozotocin, which was used for the chemical induction of DM in rats. These results were in good agreement with the ex vivo biodistribution data. These results indicated that the pancreatic accumulation of (68)Ga-DOTA-octreotide represented specific binding to the somatostatin receptors and reflected BCM. Therefore, PET imaging with (68)Ga-DOTA-octreotide could be a potential tool for evaluating BCM.

Functional neuroimaging of aversive taste-related areas in the alert rat revealed by positron emission tomography.

Among noninvasive functional brain imaging techniques, (18) F-fluorodeoxyglucose (FDG)-positron emission tomography (PET) has a comparative advantage in detecting active brain regions in freely locomoting animals. We developed an [(18) F]FDG-PET protocol that visualizes active brain regions that respond preferentially to citrate-induced multiple behaviors in freely locomoting rats. In addition, c-Fos immunohistochemistry, an activity-dependent mapping, was performed to examine whether the areas detected by PET correspond to regions with c-Fos-immunopositive neurons. Citrate (0.1 M) was intraorally applied to detect activated brain regions responding to gustation and the rejection behaviors including gaping and tongue protrusion, which would potently activate the limbic system. PET images during citrate stimulation were subtracted from those obtained during free locomotion or during application of distilled water. Citrate increased FDG signals in multiple gustation-related regions: the nucleus accumbens (core and shell), the ventromedial nucleus of the thalamus, the basolateral and central nuclei of the amygdala, the hypothalamus, and the insular cortex. In addition, the ventrolateral striatum and the cingulate and entorhinal cortices, which have received less attention in the field of gustatory studies, also showed an increase in FDG signals. As expected, c-Fos-immunopositive cells were also found in these regions, suggesting that increased FDG signals induced by intraoral citrate injection are likely to reflect neural activity in these regions. Our [(18) F]FDG-PET protocol reveals the contributions of multiple brain regions responding to aversive taste in freely locomoting rats, and this approach may aid in the identification of unknown neural networks especially relating to the limbic information processing.

Synthesis of an (11) C-labeled antiprion GN8 derivative and evaluation of its brain uptake by positron emission tomography.

A radiolabeled PET! A (11) C-labeled derivative of N,N'-(methylenedi-4,1-phenylene)bis[2-(1-pyrrolidinyl) acetamide] (GN8), an antiprion agent currently under development, was synthesized by palladium-catalyzed rapid methylation of aryltributylstannane and assessed for brain penetration and organ distribution in rats by positron emission tomography (PET).

Stoichiometry-focused (18)F-labeling of alkyne-substituted oligodeoxynucleotides using azido([(18)F]fluoromethyl)benzenes by Cu-catalyzed Huisgen reaction.

A novel method for (18)F-radiolabeling of oligodeoxynucleotides (ODNs) by a Cu-catalyzed Huisgen reaction has been developed by using the lowest possible amount of the precursor biomolecule for the realization of stoichiometry-oriented PET (positron emission tomography) chemistry. Under the optimized cyclization conditions of p- or m-azido([(18)F]fluoromethyl)benzene and alkyne-substituted ODN (20nmol) at 40°C for 15min in the presence of CuSO(4), TBTA [tris((1-benzyl-1H-1,2,3-triazol-4-yl)methyl)amine], and sodium ascorbate (2:1:2), the synthesis of (18)F-labeled ODNs with sufficiently high radioactivities of 2.1-2.5GBq and specific radioactivities of 1800-2400GBq/µmol have been accomplished for use in animal and human PET studies.