This review presents a schematic attempt to classify the major pain pathways, based on the results of recent studies in our laboratory, with a special emphasis on the parabrachial system. Our view is based on results from experiments in the rat, using very small iontophoretic injections of anterograde tracers. As illustrated in this report, we have found a very dramatic difference between ascending projections originating from deep laminae compared with those arising from lamina I of the dorsal horn. We propose three main pain systems and discuss their functional‐anatomical relationships. The first system is centred on the projection from deep laminae to three caudal reticular areas – the lateral reticular nucleus (LRN), the subnucleus reticularis dorsalis (SRD) and the gigantocellular lateral paragigantocellular reticular nuclei (NGc) – and the parabrachial internal lateral subnucleus (PBil). The second system is centred on the projection from lamina I to the ventral posterolateral nucleus (VPL), the ventral posteromedial (VPM), the posterior nuclear group (Po) and triangular posterior nucleus (PoT) of the thalamus. The third system is centred on the projection from lamina I to the lateral parabrachial area. We also present the four main projections from the latter area to the extended amygdala, the hypothalamus, the periaqueductal grey matter (PAG), and the ventrolateral medulla (VLM), and their involvement in emotional and autonomic (homeostatic) aspects of pain.

1. Neurons were recorded in the parabrachial (PB) area, located in the dorsolateral region of the pons (with the use of extracellular micropipette), in the anesthetized rat. Parabrachioamygdaloid (PA) neurons (n = 67) were antidromically identified after stimulation in the centralis nucleus of the amygdala (Ce). The axons of these neurons exhibit a very slow conduction velocity, between 0.26 and 1.1 m/s, i.e., in the unmyelinated range. 2. These PA neurons were located in a restricted region of the PB area: the subnuclei external lateral (PBel) and external medial (PBem). A relative somatotopic organization was found in this region. 3. These units were separated into two groups: 1) a group of nociceptive-specific (NS) neurons (69%), which responded exclusively to noxious stimuli, and 2) a group of nonresponsive (NR) neurons (31%). 4. The NS neurons exhibited low or lacked spontaneous activity. They responded exclusively to mechanical (pinch or squeeze) and/or thermal (waterbath or waterjet greater than 44 degrees C) noxious stimuli with a marked and sustained activation with a rapid onset and generally without afterdischarge. Noxious thermal stimuli generally induced a stronger response than the noxious mechanical stimuli. These neurons exhibited a clear capacity to encode thermal stimuli in the noxious range: 1) the stimulus-response function was always positive and monotonic; 2) the slope of the curve progressively increased up to a maximum where it was very steep, then the steepness of the slope decreased close to the maximum response; and 3) the mean threshold was 44.1 +/- 2 degrees C, and the point of steepest slope of the mean curve was around 47 degrees C. 5. The excitatory receptive fields of the NS neurons were large in the majority (70%) of the cases and included several areas of the body. A more marked activation was often obtained from stimuli applied to one part of the body, denoted as the preferential receptive field (PRF). In the other cases (30%), the excitatory receptive field was relatively small (SRF) and restricted to one part of the body (the tail, a paw, a hemiface, or the tongue). Both the PRF and SRF were more often located on the contralateral side. In addition, noxious stimuli applied outside the excitatory receptive field were found to strongly inhibit the responses of NS neurons. 6. All the NS neurons responded to intense transcutaneous electrical stimulation applied to the PRF or SRF with two peaks of activation.(ABSTRACT TRUNCATED AT 400 WORDS)

Single-unit extracellular recordings of spino-parabrachial (spino-PB) neurons (n = 53) antidromically driven from the contralateral parabrachial (PB) area were performed in the lumbar cord in anesthetized rats. All the spino-PB neurons were located in the lamina I of the dorsal horn. Their axons exhibited conduction velocities between 2.8 and 27.8 m/s, in the thin myelinated fibers range. They had an extremely low spontaneous activity (median = 0. 064 Hz) and a small excitatory receptive field (

V617F JAK2 mutation is a reliable molecular marker of polycythemia vera (PV), potentially useful to monitor the effect of treatments in this disease. In a phase 2 study of pegylated (peg) IFN-␣-2a in PV, we performed prospective sequential quantitative evaluation of the percentage of mutated JAK2 allele (%V617F) by realtime polymerase chain reaction (PCR). The %V617F decreased in 24 (89%) of 27 treated patients, from a mean of 49% to a mean of 27% (mean decrease of 44%; P < .001), and no evidence for a plateau was observed. In one patient, mutant JAK2 was no longer detectable after 12 months. In 3 patients homozygous for the mutation, reappearance of 50% of wildtype allele was observed during treatment. The results seem to confirm the hypothesis that IFN-␣ preferentially targets the malignant clone in PV and show that %V617F assessment using a quantitative method may provide the first tool to monitor minimal residual disease in PV. This trial was registered at www. clinicaltrials.gov as #NCT00241241. (Blood.