Projection neurons in lamina I, together with those in laminae III–IV that express the neurokinin 1 receptor (NK1r), form a major route through which nociceptive information reaches the brain. Axons of these cells innervate various targets, including thalamus, periaqueductal gray matter (PAG), and lateral parabrachial area (LPb), and many cells project to more than one target. The aims of this study were to quantify projections from cervical enlargement to PAG and LPb, to determine the proportion of spinothalamic neurons at lumbar and cervical levels that were labelled from PAG and LPb, and to investigate morphological differences between projection populations. The C7 segment contained fewer lamina I spinoparabrachial cells than L4, but a similar number of spino-PAG cells. Virtually all spinothalamic lamina I neurons at both levels were labelled from LPb and between one-third and one-half from PAG. This suggests that significant numbers project to all three targets. Spinothalamic lamina I neurons differed from those labelled only from LPb in that they were generally larger, were more often multipolar, and (in cervical enlargement) had stronger NK1r immunoreactivity. Most lamina III/IV NK1r cells at both levels projected to LPb, but few were labelled from PAG. The great majority of these cells in C7 and over one-fourth of those in L4 were spinothalamic, and at each level some projected to both thalamus and LPb. These results confirm that neurons in these laminae have extensive collateral projections and suggest that different neuronal subpopulations in lamina I have characteristic patterns of supraspinal projection. J. Comp. Neurol. 515:629–646, 2009.

The major ascending outputs from superficial spinal dorsal horn consist of projection neurons in lamina I, together with neurons in laminae III-IV that express the neurokinin 1 receptor (NK1r) and have dendrites that enter the superficial laminae. Some neurons in each of these populations belong to the spinothalamic tract, which conveys nociceptive information via the thalamus to cortical areas involved in pain. A projection from the cervical superficial dorsal horn to the posterior triangular nucleus (PoT) has recently been identified. PoT is at the caudal end of the thalamus and was not included in injection sites in many previous retrograde tracing studies. We have injected various tracers (cholera toxin B subunit, Fluoro-Gold, and fluorescent latex microspheres) into the thalamus to estimate the number of spinothalamic neurons in each of these two populations, and to investigate their projection targets. Most lamina I and lamina III/IV NK1r-immunoreactive spinothalamic neurons in cervical and lumbar segments could be labeled from injections centered on PoT. Our results suggest that there are 90 lamina I spinothalamic neurons per side in C7 and 15 in L4 and that some of those in C7 only project to PoT. We found that 85% of the lamina III/IV NK1r-immunoreactive neurons in C6 and 17% of those in L5 belong to the spinothalamic tract, and these apparently project exclusively to the caudal thalamus, including PoT. Because PoT projects to second somatosensory and insular cortices, our results suggest that these are major targets for information conveyed by both these populations of spinothalamic neurons. J. Comp. Neurol. 511:1-18, 2008. © 2008 Indexing terms: posterior triangular nucleus of thalamus; neurokinin 1 receptor; dorsal horn; confocal microscopyThe spinal dorsal horn receives a major input from primary afferent axons. This input is organized according to modality, with nociceptive afferents terminating mainly in laminae I and II (Rexed, 1954;Todd and Koerber, 2005). Although the axons of most dorsal horn neurons remain within the spinal cord, some of these cells (projection neurons) have axons that terminate in the brain, and these form an important output from the region. Projection neurons are not uniformly distributed within the dorsal horn, but are concentrated in lamina I and scattered throughout the deeper laminae (III-VI).The majority of lamina I projection neurons in the rat express the neurokinin 1 receptor (NK1r) on which substance P acts (Ding et al

Although most projection neurons in lamina I express the neurokinin 1 receptor (NK1r), we have identified a population of large multipolar projection cells that lack the NK1r, are characterized by the high density of gephyrin puncta that coat their cell bodies and dendrites, and express the transcription factor Fos in response to noxious chemical stimulation. Here we show that these cells have a very high density of glutamatergic input from axons with strong immunoreactivity for vesicular glutamate transporter 2 that are likely to originate from excitatory interneurons. However, they receive few contacts from peptidergic primary afferents or transganglionically labeled A␦ nociceptors. Unlike most glutamatergic synapses in superficial laminas, those on the gephyrin-coated cells contain the GluR4 subunit of the AMPA receptor. A noxious heat stimulus caused Fos expression in 38% of the gephyrin-coated cells but in 85% of multipolar NK1r-immunoreactive cells. These findings are consistent with the suggestion that there is a correlation between function and morphology for lamina I neurons but indicate that there are at least two populations of multipolar neurons that differ in receptor expression, excitatory inputs, and responses to noxious stimulation. Although there are only ϳ10 gephyrin-coated cells on each side per segment in the lumbar enlargement, they constitute ϳ18% of the lamina I component of the spinothalamic tract at this level, which suggests that they play an important role in transmission of nociceptive information to the cerebral cortex. Our results also provide the first evidence that postsynaptic GluR4-containing AMPA receptors are involved in spinal nociceptive transmission.

Objectives:To assess the prevalence of common radiological variants of sinonasal anatomy among Saudi population and compare it with the reported prevalence of these variants in other ethnic and population groups.Methods:This is a retrospective cross-sectional study of 121 computerized tomography scans of the nose and paranasal sinuses of patients presented with sinonasal symptoms to the Department of Otorhinolarngology, King Fahad Hospital of the University, Khobar, Saudi Arabia, between January 2014 and May 2014.Results:Scans of 121 patients fulfilled inclusion criteria were reviewed. Concha bullosa was found in 55.4%, Haller cell in 39.7%, and Onodi cell in 28.9%. Dehiscence of the internal carotid artery was found in 1.65%. Type-1 and type-2 optic nerve were the prevalent types. Type-II Keros classification of the depth of olfactory fossa was the most common among the sample (52.9%). Frontal cells were found in 79.3%; type I was the most common.Conclusions:There is a difference in the prevalence of some radiological variants of the sinonasal anatomy between Saudi population and other study groups. Surgeon must pay special attention in the preoperative assessment of patients with sinonasal pathology to avoid undesirable complications.