CT-like images based on T1-weighted gradient echo MRI sequences for the assessment of fractures of the hand and wrist compared to CT.

OBJECTIVE: To evaluate the performance of a 3D T1-weighted gradient-echo (3D T1GRE) computed tomography (CT)-like magnetic resonance imaging (MRI) sequence for detecting and assessing wrist and hand fractures compared to conventional CT. METHODS: Subjects with acute wrist or hand fracture in CT underwent additional 3 T MRI including a CT-like 3D T1GRE sequence and were compared to patients without fractures. Two radiologists assessed fracture morphology on both modalities according to the Arbeitsgemeinschaft Osteosynthese (AO) and graded image quality and diagnostic confidence on a 5-point Likert scale. Besides diagnostic test evaluation, differences in image quality and diagnostic confidence between CT-like MRI and CT were calculated using the Wilcoxon test. Agreement of AO classification between modalities and readers was assessed using Cohen's Kappa. RESULTS: Twenty-eight patients with 43 fractures and 43 controls were included. Image quality (3D T1GRE 1.19 ± 0.37 vs. CT 1.22 ± 0.42; p = 0.65) and diagnostic confidence (3D T1GRE 1.28 ± 0.53 vs. CT 1.28 ± 0.55; p = 1.00) were rated excellent for both modalities. Regarding the AO classification, intra- (rater 1 and rater 2, κ = 0.89; 95% CI 0.80-0.97) and interrater agreement were excellent (3D T1GRE, κ = 0.82; 95% CI, 0.70-0.93; CT, κ = 0.85; 95% CI, 0.75-0.94). CT-like MRI showed excellent sensitivity, specificity and accuracy for fracture detection (reader 1: 1.00, 0.92, 0.96; reader 2: 0.98, 0.94, 0.96). CONCLUSION: CT-like MRI is a comparable alternative to CT for assessing hand and wrist fractures, offering the advantage of avoiding radiation exposure.

Long-range inhibition within the zebra finch song nucleus RA can coordinate the firing of multiple projection neurons.

The zebra finch forebrain song control nucleus RA (robust nucleus of the archistriatum) generates a phasic and temporally precise neural signal that drives vocal and respiratory motoneurons during singing. RA's output during singing predicts individual notes, even though afferent drive to RA from the song nucleus HVc is more tonic, and predicts song syllables, independent of the particular notes that comprise the syllable. Therefore RA's intrinsic circuitry transforms neural activity from HVc into a highly precise premotor output. To understand how RA's intrinsic circuitry effects this transformation, we characterized RA interneurons and projection neurons using intracellular recordings in brain slices. RA interneurons fired fast action potentials with steep current-frequency relationships and had small somata with thin aspinous processes that extended throughout large portions of the nucleus; the similarity of their fine processes to those labeled with a glutamic acid decarboxylase (GAD) antibody strongly suggests that these interneurons are GABAergic. Electrical stimulation revealed that RA interneurons receive excitatory inputs from RA's afferents, the lateral magnocellular nucleus of the anterior neostriatum (LMAN) and HVc, and from local axon collaterals of RA projection neurons. To map the functional connections that RA interneurons make onto RA projection neurons, we focally uncaged glutamate, revealing long-range inhibitory connections in RA. Thus these interneurons provide fast feed-forward and feedback inhibition to RA projection neurons and could help create the phasic pattern of bursts and pauses that characterizes RA output during singing. Furthermore, selectively activating the inhibitory network phase locks the firing of otherwise unconnected pairs of projection neurons, suggesting that local inhibition could coordinate RA output during singing.

Differential activation of glutamate receptor subtypes on a single class of cells enables a neural oscillator to produce distinct behaviors.

Electric fish generate different types of abrupt modulations of their electric organ discharge (EOD) rhythm to convey specific social signals. Intracellular recordings were made from neurons of the medullary pacemaker nucleus, which generates and transmits the rhythm that drives the EOD, to study the neuronal basis of two such modulations of the regular EOD rhythm, sudden accelerations, and abrupt interruptions. Recordings were both in vivo, and in a new in vitro brain preparation of Hypopomus pinnicaudatus (order Gymnotiformes). In vivo recordings during triggered behaviors indicated that abrupt modulations of the EOD rhythm are generated in the medullary pacemaker nucleus at the level of the relay cells, which are the projection cells of the nucleus, and not the pacemaker cells. In the in vitro brain stem preparation, cells of the pacemaker nucleus were spontaneously and rhythmically active as in the intact animal. Distinct modulations of the pacemaker nucleus rhythm that closely resembled those seen during natural behaviors could be triggered by electrical stimulation of afferent fibers. Modulations of the rhythm also could be triggered by direct pharmacological activation of the relay cells. When non-N-methyl-D-aspartate (NMDA) receptors were activated, relay cells were transiently depolarized and generated bursts of synchronized action potentials. NMDA receptor activation, alternatively, initiated a prolonged depolarization in the relay cells, during which time they failed to relay the regular pacemaker rhythm. The two firing states of the relay cell directly correlate with sudden accelerations and abrupt interruptions of the EOD.

Bird song: of tone and tempo in the telencephalon.

Songbirds learn a new song by matching the sound they produce to a memorized model. A distributed central pattern-generating circuit has now been identified that governs song production; the new results have important implications for the way songs are learned.

Immunolocalization of NMDA receptors in the central nervous system of weakly electric fish: functional implications for the modulation of a neuronal oscillator.

Using a monoclonal antibody raised against the R1 subunit of the rat NMDA receptor, we mapped the distribution of NMDA receptors in the brains of three genera of electric fish. On Western blots, the antibody recognized a glycoprotein of approximately 105 kDa throughout the CNS. On tissue sections, it strongly labeled a number of neuronal somata and dendrites in the medulla, with weaker immunoreactivity in the forebrain and across much of the rest of the nervous system. At the ultrastructural level, reaction product was localized, though not exclusively, to the postsynaptic region of synapses. To study the role of NMDA receptors in a specific neural circuit, we focused on the medullary pacemaker nucleus. Neurons in this nucleus, which fire action potentials regularly and trigger each electric organ discharge (EOD), receive glutamatergic input from identified premotor areas. Activity in these areas can cause the pacemaker nucleus to produce outputs with distinct temporal dynamics, which are observed in the behaving animal as modulations of the EOD. The projection cells of the pacemaker nucleus, the relay cells, were heavily labeled with the anti-NMDA R1 antibody in all genera studied. These results are consistent with the previous finding that a particular EOD modulation mediated by the connection from one premotor area of the brain to the relay cells is blocked by application to the pacemaker nucleus of NMDA receptor blockers. Our results complement ongoing efforts to study this nucleus and provide additional evidence for the role of NMDA receptors in diverse neural circuits.