Showing papers by "Dalhousie University published in 1993"

Refractive indices of water and ice in the 0.65- to 2.5-µm spectral range.

Abstract: New accurate values of the imaginary part, k, of the refractive index of water at T = 22 °C, supercooled water at T = −8 °C and polycrystalline ice at T = −25 °C are reported. The k spectrum for water in the spectral region 0.65–2.5 μm is found to be in excellent agreement with those of previous studies. The k values for polycrystalline ice in the 1.44–2.50-μm region eliminate the large uncertainties existing among previously published conflicting sets of data. The imaginary part of refractive index of supercooled water shows a systematic shift of absorption peaks toward the longer wavelengths compared with that of water at warmer temperatures.

Mechanical model for the tectonics of doubly vergent compressional orogens

Abstract: A mechanical model of crustal shortening and deformation driven by the relative convergence of rigid, underlying mantle plates explains many features of convergent orogens. Results based on numerical models and supported by sandbox models show that a Coulomb crustal layer subject to basal velocity boundary conditions corresponding to asymmetric detachment and subduction of the underlying mantle passes through three stages of orogenic growth: (1) block uplift bounded by step-up shear zones; (2) development of a low-taper wedge over the underthrusting mantle plate; and (3) development of a low-taperwedge overlying the overthrusting mantle plate and verging in the opposite direction. When modified by isostasy, basal viscous flow, surface erosion and denudation, and sedimentation, the resultant model orogens exhibit a variety of styles with characteristics in common with small, rapidly denuded orogens, large orogens with plateaus and extensional characteristics, and active subduction margins with doubly vergent accretionary wedges and deformed fore-arc basins.

Sutural biology and the correlates of craniosynostosis

Abstract: The purpose of this paper is to provide a new perspective on craniosynostosis by correlating what is known about sutural biology with the events of craniosynostosis per se. A number of key points emerge from this analysis: 1) Sutural initiation may take place by overlapping, which results in beveled sutures, or by end-to-end approximation, which produces nonbeveled, end-to-end sutures. All end-to-end sutures occur in the midline (e.g., sagittal and metopic) probably because embryonic biomechanical forces on either side of the initiating suture tend to be equal in magnitude. A correlate appears to be that only synostosed sutures of the midline have pronounced bony ridging. 2) Long-term histologic observations of the sutural life cycle call into question the number of layers within sutures. The structure varies not only in different sutures, but also within the same suture over time. 3) Few, if any, of the many elegant experimental research studies in the field of sutural biology have increased our understanding of craniosynostosis per se. An understanding of the pathogenesis of craniosynostosis requires a genetic animal model with primary craniosynostosis and molecular techniques to understand the gene defect. This may allow insight into pathogenetic mechanisms involved in primary craniosynostosis. It may prove to be quite heterogeneous at the basic level. 4) The relationship between suture closure, cessation of growth, and functional demands across sutures poses questions about various biological relationships. Two conclusions are provocative. First, cessation of growth does not necessarily, or always lead to fusion of sutures. Second, although patent sutures aid in the growth process, some growth can take place after suture closure. 5) In an affected suture, craniosynostosis usually begins at a single point and then spreads along the suture. This has been shown by serial sectioning and calls into question results of studies in which the affected sutures are only histologically sampled. 6) Craniosynostosis is etiologically and pathogenetically heterogeneous. Known human causes are reviewed. Is craniosynostosis simply normal suture closure commencing too early?(ABSTRACT TRUNCATED AT 400 WORDS)

On the convergence of von Neumann's alternating projection algorithm for two sets

Abstract: We give several unifying results, interpretations, and examples regarding the convergence of the von Neumann alternating projection algorithm for two arbitrary closed convex nonempty subsets of a Hilbert space. Our research is formulated within the framework of Fejer monotonicity, convex and set-valued analysis. We also discuss the case of finitely many sets.

Heat-shock response and limitation of tissue necrosis during occlusion/reperfusion in rabbit hearts.

Abstract: BACKGROUNDInduction of stress proteins, such as heat-shock protein 71 (HSP71), is associated with cardioprotection in isolated ischemic myocardium. We tested this hypothesis in rabbits pretreated w...

Growth in pinnipeds.

Abstract: This review presents summary figures of, and fits growth curves to, data on body lengths (as standard length, SL, whenever possible) of pinnipeds at ages estimated to O.I y. (1) Generalized von Bertalanffy (vB) growth curves are fitted to most data: Lx = L infinity (I - ea(x-x0)b, Lx is length at age x, x0 is the origin of the curve (here chosen a priori as time of initiation of embryonic growth), L infinity is asymptotic length, a (which is negative) determines rate of approach to the asymptote, and b influences the 'shape' of the approach. (2) No single monotonic growth equation suffices for growth in length, which is linear before birth and remains so during early life. The vB equation is only suitable to describe mean lengths of newborns, and animals one or more years old. (3) Also, for males of polygynous species, two functions are needed to account for accelerated growth at puberty. Generally a Gompertz equation is adequate for adult males of these species. (4) The fitted growth equations permit statistical comparisons of sizes and growth rates, as well as of individual variability (as growth-curve residuals), among populations and species. (5) For the following species (including different populations when available), the reliability of data is assessed and parameters of growth curves are presented (with sexes separated where significantly different): walrus, California and Steller sea lions, Antarctic, subantarctic and northern fur seals, Hawaiian monk seal, crabeater, Weddell and Leopard seals, southern and northern elephant seals, bearded, hooded, ringed, Baikal, Caspian, spotted, harbour, harp, ribbon and grey seals. (6) Some novel findings pertain to individual species as follows. Although the Pacific walrus is generally stated to be the larger subspecies, females from Hudson Bay and males from Foxe Basin, in the eastern Canadian Arctic, may be as long as those from the Bering Sea. Although female Weddell seals have been assumed to grow larger than males, there is no significant difference in growth curves fitted to the most complete data. Uniquely among populations examined, the relative variability (absolute growth curve residuals/predicted lengths) of male southern elephant seals is amplified with age. Among ringed seals from Svalbard, the eastern, western and high Canadian Arctic, and the Bering, Chukchi, Okhotsk, Barents and Baltic Seas, asymptotic sizes are larger among those that breed on land-fast ice rather than floes, and size may be more variable in more extreme Arctic environments. The Baikal seal is confirmed as the smallest species of pinniped.(ABSTRACT TRUNCATED AT 400 WORDS)

RNA editing in plant mitochondria and chloroplasts.

Abstract: In the mitochondria and chloroplasts of flowering plants (angiosperms), transcripts of protein-coding genes are altered after synthesis so that their final primary nucleotide sequence differs from that of the corresponding DNA sequence. This posttranscriptional mRNA editing consists almost exclusively of C-to-U substitutions. Editing occurs predominantly within coding regions, mostly at isolated C residues, and usually at first or second positions of codons, thereby almost always changing the amino acid from that specified by the unedited codon. Editing may also create initiation and termination codons. The net effect of C-to-U RNA editing in plants is to make proteins encoded by plant organelles more similar in sequence to their nonplant homologs. In a few cases, a strong argument can be made that specific C-to-U editing events are essential for the production of functional plant mitochondrial proteins. Although the phenomenon of RNA editing in plants is now well documented, fundamental questions remain to be answered: What determines the specificity of editing? What is the biochemical mechanism (deamination, base exchange, or nucleotide replacement)? How did the system evolve? RNA editing in plants, as in other organisms, challenges our traditional notions of genetic information transfer.

Pfeiffer syndrome update, clinical subtypes, and guidelines for differential diagnosis

Abstract: Steven Pfeiffer syndrome pedigrees (three 3 generation and four 2 generation) have been recorded to date in addition to at least a dozen sporadic cases. Autosomal dominant inheritance with complete penetrance is characteristic of the 7 familial instances. Variable expressivity has involved mostly the presence or absence of syndactyly and the degree of syndactyly when present. Classic Pfeiffer syndrome is designated type I. Type 2 consists of cloverleaf skull with Pfeiffer hands and feet together with ankylosis of the elbows. Such patients do poorly with an early death. All reported instances to date have been sporadic. Type 3 is similar to type 2 but without cloverleaf skull. Ocular proptosis is severe in degree and the anterior cranial base is markedly short. These patients also do poorly and tend to have an early death. To date all cases have occurred sporadically. Although these 3 clinical subtypes do not have status as separate entities, their diagnostic and prognostic implications are important. Type 1 is commonly associated with normal intelligence, generally good outcome, and can be found dominantly inherited in some families. Types 2 and 3 generally have severe neurological compromise, poor prognosis, early death, and sporadic occurrence. Recognition of type 3 is particularly important because extreme ocular proptosis in the absence of cloverleaf skull but with various visceral anomalies can result in failure to diagnose Pfeiffer syndrome and labeling the patient as an "unknown" or as a "newly recognized entity."(ABSTRACT TRUNCATED AT 250 WORDS)

Requirements for leukocyte adhesion molecules in nephrotoxic nephritis.

Abstract: Requirements for leukocyte adhesion molecules as well as cytokines have been determined in the rat model of acute nephrotoxic nephritis. Proteinuria (at 24 h) and neutrophil accumulation in renal glomeruli (at 6 h) have been used as the endpoints. For full accumulation in glomeruli of neutrophils as well as full development of proteinuria, requirements have been demonstrated for TNF alpha, (but not IL-1), CD11b (but not CD11a), very late arising-4 (CD49d/CD29), and intercellular adhesion molecule-1 but not endothelial leukocyte adhesion molecule-1 (E-selectin). By immunohistochemical approaches, infusion of antibody to glomerular basement membrane induced glomerular upregulation of intercellular adhesion molecule-1, endothelial leukocyte adhesion molecule-1, and vascular adhesion molecule-1. Treatment of rats with anti-TNF alpha or soluble recombinant human TNF receptor-1 blocked this expression. Renal arterial infusion of TNF alpha induced glomerular expression of all three endothelial adhesion molecules, but infusion of IL-1 beta did not. These data suggest that, in neutrophil and complement-dependent anti-glomerular basement membrane-induced acute nephritis in rats, there are selective requirements for cytokines, beta 1 and beta 2 integrins, and endothelial adhesion molecules. These requirements contrast with those found in other vascular beds in which complement and neutrophil-induced vascular injury has been induced by deposition of immune complexes.

Effects of alterations in auditory feedback and speech rate on stuttering frequency

Abstract: This study investigated the effects of altered auditory feedback on stuttering frequency during speech production at two different speech rates. Nine stutterers, who exhibited at least 5% dysfluenc...

Expression of four growth factors during fracture repair.

Abstract: Fracture repair offers an opportunity to study the physiology of bone formation at the fracture site. Isolation of growth factors from bone matrix has implicated growth factors as participants in bone physiology. We therefore examined the expression patterns of aFGF, IGF-I, PDGF, and TGF-beta during fracture repair. An animal model has been developed to study repair of tibial fractures. The model provides both reproducible and quantifiable results, allowing the fracture repair process to be divided into four stages (Bourque et al., Lab. Anim. Sci 42: 369-374, 1992). Fractured tibiae were examined immunohistochemically with polyclonal antibodies to four growth factors. PDGF was visualized in macrophages in close proximity to the periosteum during stage 1. aFGF was visualized in cells of the expanded cambial layer and was associated with a rapid increase in the population of fibroblast-like mesenchymal cells during stage 2. IGF-I was visualized in young chondroblasts at the edge of the cartilage mass replacing the fibrous callus during stage 3. TGF-beta was visualized in calcified matrix producing chondrocytes at the edge of ossification fronts penetrating the cartilage callus during stage 4. The immunohistochemical results suggest that these growth factors act as local simulators of the repair process.

What are human express saccades

Abstract: When a fixation point is removed 200 msec prior to target onset (the gap condition), human subjects are said to produce eye movements that have a short latency (80-120 msec), that form the early peak of a bimodal latency distribution, and that have been labeled "human express saccades" (see, e.g., Fischer, 1987; Fischer & Breitmeyer, 1987; Fischer & Ramsperger, 1984, 1986). In three experiments, we sought to obtain this express saccade diagnostic pattern in the gap condition. We orthogonally combined target location predictability with the presence versus absence of catch trials (Experiment 1). When target location was fixed and catch trials were not used, we found mostly anticipations. In the remaining conditions, where responses were under stimulus control, bimodality was not frequently observed, and, whether it was or not, latencies were not in the express saccade range. Using random target locations, we then varied stimulus luminance and the mode of stimulus presentation (LEDs vs. oscilloscope) in the gap and overlap (fixation is not removed) conditions (Experiment 2). Bimodality was rarely observed, the gap effect (overlap minus gap reaction time) was additive with luminance, and only the brightest targets elicited saccades in the express range. When fixed locations and no catch trials were combined with latency feedback (Experiment 3), we observed many responses in the express saccade range and some evidence for bimodality, but the sudden introduction of catch trials revealed that many early responses were not under stimulus control. Humans can make stimulus-controlled saccades that are initiated very rapidly (80-120 msec), but unless catch trials or choice reaction time is used, it is not possible to distinguish such saccades from anticipatory responses that are prepared in advance and timed to occur shortly after target onset. Because the express saccade diagnostic pattern is not a characteristic feature of human saccadic performance, we urge investigators to focus their attention on the robust gap effect.

The occurrence and duration of symptoms in elderly patients with delirium.

Abstract: BACKGROUND: This study attempts to estimate the incidence, prevalence, and average duration of delirium in elderly patients; to assess the sensitivity of DSM-III and DSM-III-R in the diagnosis of delirium; and to compare the estimates of the duration of delirium using DSM-III and DSM-III-R criteria. METHODS: A 12-month prospective descriptive study of 168 consecutively admitted patients and 5 additional patients with delirium was conducted in the Geriatric Assessment Unit of a teaching hospital. The duration in days of DSM-III and DSM-III-R symptoms for each delirious patient was assessed by two clinicians. The Barthel Index, Mini-Mental State Examination, and Trezpacz Delirium Symptom Rating Scale scores were also recorded. RESULTS: The prevalence of delirium was 18% and the incidence was 7%. Compared to clinical judgment DSM-III-R showed 100% sensitivity. The mean duration of delirium was 8 +/- 9 days (DSM-III-R); the DSM estimate was 7 +/- 7 days. Complete symptom recovery was seen in only 52% of surviving patients. Prolonged memory impairment was common. CONCLUSIONS: As operationalized in this study, DSM-III-R delirium criteria were more sensitive than DSM-III. Persistent symptoms are common in elderly patients with delirium.

Determination of the major groups of phytoplankton pigments from the absorption spectra of total particulate matter

Abstract: The contributions of detrital particles and phytoplankton to total light absorption are retrieved by nonlinear regression on the absorption spectra of total particles from various oceanic regions. The model used explains more than 96% of the variance in the observed particle absorption spectra. The resulting absorption spectra of phytoplankton are then decomposed into several Gaussian bands reflecting absorption by phytoplankton pigments. Such a decomposition, combined with high-performance liquid chromatography data on phytoplankton pigment concentrations, allows the computation of specific absorption coefficients for chlorophylls a, b, and c and carotenoids. The spectral values of these in vivo absorption coefficients are then discussed, considering the effects of secondary pigments which were not measured quantitatively. We show that these coefficients can be used to reconstruct the absorption spectra of phytoplankton at various locations and depths. Discrepancies that do occur at some stations are explained in terms of particle size effect. These coefficients can be used to determine the concentrations of phytoplankton pigments in the water, given the absorption spectrum of total particles.

Joint-Attentional States and Lexical Acquisition at 18 Months.

Abstract: Two groups of 18-month-old infants were observed during a relatively natural play session with an adult experimenter and several toys. A novel object associated with one of the toys was labeled a dodo by the experimenter using either an attention-following strategy (i.e., introducing the label when the infant was focused on the dodo object) or an attention-switching strategy (i.e., introducing the label when the infant was focused on an alternative object). With factors such as frequency of exposure to the object label and infant compliance equivalent across the groups, infants in the attention-following procedure were more likely to correctly identify the dodo object in a subsequent comprehension task

A Device for Precision Splitting of Micropaleontological Samples in Liquid Suspension

Abstract: The impetus for writing this paper has come from many people who have shown an interest in the device we describe; prior to this paper, we had no reference to provide for interested parties. The original device was described in Elmgren (1973) and illustrated in Thomas (1986). These papers are not readily available to many micropaleontologists; hence, we felt the need to redescribe it here with a few modifications. Traditionally, foraminiferal researchers, especially those working in fossil deposits, work on samples that are first processed and then dried. To split these dry samples to aliquots of manageable numbers of foraminifera, they use the well-known “Otto” microsplitter, which provides accurate splits plus or minus 10–20 percent.

Evidence for the importance of bubbles in increasing air–sea gas flux

Abstract: Two models have been proposed to account for gas exchang between the atmosphere and the oceans: one involves direct transport of the gas through a surface boundary layer1; the other also includes a substantial enhancement of the gas flux due to bubbles formed by breaking waves2,3. In a long time-series of dissolved oxygen measurements, Wallace and Wirick4 observed sharply increased fluxes that seemed to be associated with wave activity. But the lack of vertical resolution meant that they could not rule out water advection and entrapment, rather than bubble-mediated air injection, as the cause of the increased flux. They were also unable to calculate transfer coefficients. Here we report simultaneous in situ observations from a vertical array of dissolved-gas sensors and a variety of other instruments during a single storm event. Our results confirm the importance of bubbles for the gas-transfer process. They also imply that existing transfer coefficients underestimate the transfer of weakly soluble gases during periods of bubble penetration.

Comparative three-dimensional analysis of CT-scans of the calvaria and cranial base in Apert and Crouzon syndromes

Abstract: Summary The purpose of this study is to describe and analyze Apert and Crouzon skulls from three-dimensional (3-D) reconstructions of CT-scans. 12 Apert patients and 19 with Crouzon syndrome were included in the study. The age range was 0 to 23 years. All CT-scannings were carried out according to the same protocol with a slice thickness of 2 or 4 mm and 3-D reconstructions of the craniofacial region included midsagittal and horizontal cuts. A number of qualitative characteristics of the calvaria and cranial base were recorded and the cranial base angle was measured on the 3-D models. Our results showed that Apert and Crouzon syndromes are very different in cranial development and their dysmorphology is highly age dependent. We suggest that cartilage abnormalities, especially in the anterior cranial base, play a primary role in cranial development in the Apert syndrome from very early intrauterine life. Several cranial anomalies observed postnatally, however, are caused by the resultant dysmorphic and compensatory growth and are probably compounded by early cranial deformation. The primary abnormality in Crouzon syndrome appears to be premature fusion of sutures and synchondroses. Based on the findings at birth and early infancy it would seem that such fusions occur relatively late in fetal life. The adult cranial form in Crouzon 's patients is explainable by resultant dysmorphic and compensatory growth changes. Very early release of the coronal suture areas with advancement of the frontal bone is advocated in both syndromes but for somewhat different reasons. In Apert syndrome, the primary indication for such treatment is to reduce further dysmorphic growth changes in the calvaria and cranial base, whereas the risk for increased intracranial pressure is low considering the large midline calvarial defect found in early infancy. In contrast, newborns with Crouzon syndrome develop multiple suture synostoses and fused synchondroses, and early surgery is most often indicated to prevent or treat increased intracranial pressure.

VLA-4 integrin can mediate CD11/CD18-independent transendothelial migration of human monocytes.

Abstract: The migration of human monocytes across unactivated and activated human umbilical vein endothelium (HUVE) in response to chemotactic factors was studied, and the adhesion molecules involved were characterized. Migration of blood monocytes or U937 cell line-derived monocytes across unactivated HUVE induced by C5a, was partially inhibited (by 75%) by mAbs (R15.7 or 60.3) to CD18 of the CD11/CD18 complex on the monocyte. However, when the HUVE was pretreated for 5 h with IL-1 alpha (0.1 ng/ml), TNF-alpha (100 U/ml), or LPS (1 ng/ml), migration induced by C5a was no longer inhibited; i.e., migration became CD18 independent. The monocyte CD18-independent migration was completely blocked by mAbs against alpha 4 or beta 1 integrin chains of VLA-4. This migration was also partially inhibited by mAbs against vascular cell adhesion molecule-1 (VCAM-1), a major counter-receptor on HUVE for VLA-4, but not by mAbs to E-selectin or intercellular adhesion molecule-1. The significant CD18-independent migration across "unactivated" HUVE was also inhibited by mAbs against alpha 4 or beta 1 chains of VLA-4, although mAbs against VCAM-1 did not inhibit under these conditions. Finally, considerable VLA-4-dependent transendothelial migration to C5a was also observed with monocytes from a patient with CD18 deficiency (leukocyte adhesion deficiency). These results suggest that (a) there is a major CD18-independent component in monocyte chemotactic factor-dependent migration across activated and unactivated endothelium; (b) that VLA-4 integrin on the monocyte has a major role in this migration; and (c) that VCAM-1 on activated endothelium functions as a counter-receptor in this process, but other ligands for VLA-4, especially on unactivated endothelium, may also be involved.

Role of β1 β2 integrins and ICAM-1 in lung injury after deposition of IgG and IgA immune complexes

Abstract: After intrapulmonary deposition of IgG or IgA immune complexes, injury has been recently shown to be CD18-dependent in both cases and E-selection-dependent only in the former case. In our studies further evaluation of the requirements for beta 1 and beta 2 integrins and intercellular adhesion molecule-1 (ICAM-1) has been undertaken. In the IgG immune complex model, which is neutrophil dependent, anti-CD11a reduced injury (as measured by changes in permeability and hemorrhage) by 61 and 43%, respectively, whereas a newly developed anti-CD11b produced minimal protection (16 and 19%, respectively). Treatment of rats with increasing doses (1.5- and 3.0-fold) of antibody to rat CD11b failed to demonstrate additional protective effects in this model of injury. Anti-ICAM-1 reduced the parameters of injury by 61 and 78%, respectively, while anti-VLA-4 reduced the injury parameters by 40 and 35%, respectively. There were reductions in lung content of myeloperoxidase, roughly corresponding to the protective effects of the interventions. In the IgA immune complex model of injury, in which lung macrophages appear to be the effector cells, anti-CD11a reduced the injury parameters (permeability and hemorrhage) by 36 and 33%, respectively, whereas anti-CD11b reduced the parameters of injury by 63 and 67%, respectively. In this model, anti-ICAM-1 reduced the parameters of injury by 61 and 56%, respectively, while anti-VLA-4 reduced the parameters by 77 and 62%, respectively. The cell content of bronchoalveolar lavage fluids revealed changes that have been shown to reflect protective interventions in both models of immune complex-induced injury. These findings suggest that, in IgG and IgA immune complex models of lung injury, both VLA-4 and ICAM-1 are required, although lymphocyte function-associated Ag-1 is the predominant beta 2 integrin requirement in the IgG immune complex-induced model of injury and Mac-1 is the predominant requirement for IgA immune complex-induced lung injury. Thus, engagement in the lung of adhesion molecules in a manner leading to injury depends on the nature of the inflammatory stimulus and the type of phagocytic cells involved in the development of injury.

Editing of transfer RNAs in Acanthamoeba castellanii mitochondria.

Abstract: With the discovery of RNA editing, a process whereby the primary sequence of RNA is altered after transcription, traditional concepts of genetic information transfer had to be revised. The known RNA editing systems act mainly on messenger RNAs, introducing sequence changes that alter their coding properties. An editing system that acts on transfer RNAs is described here. In the mitochondria of Acanthamoeba castellanii, an amoeboid protozoan, certain transfer RNAs differ in sequence from the genes that encode them. The changes consist of single-nucleotide conversions (U to A, U to G, and A to G) that appear to arise posttranscriptionally, are localized in the acceptor stem, and have the effect of correcting mismatched base pairs. Editing thus restores the base pairing expected of a normal transfer RNA in this region.

Localization of cholinergic neurons in the forebrain and brainstem that project to the suprachiasmatic nucleus of the hypothalamus in rat.

Abstract: In mammals, the suprachiasmatic nucleus is responsible for the generation of most circadian rhythms and their entrainment to environmental cues. Cholinergic agents can alter circadian rhythm phase, and fibres immunoreactive for choline acetyltransferase, the biosynthetic enzyme for acetylcholine, are present in the suprachiasmatic nucleus. Since there are no cholinergic somata in the suprachiasmatic nucleus, these fibres must represent the terminals of cholinergic neurons whose cell bodies are located elsewhere in the brain. This study was aimed at locating the cholinergic neurons that project to the suprachiasmatic nucleus by retrograde and anterograde tract-tracing and immunohistochemistry for choline acetyltransferase in the rat. After injection of fluorogold, a retrograde tracer, into the suprachiasmatic nucleus, retrogradely labelled neurons that were immunopositive for choline acetyltransferase were located throughout the rostrocaudal extent of the cholinergic basal nuclear complex, with highest densities in the substantia innominata and the nucleus basalis magnocellularis. A few cells were also located in the medial septum and in the vertical and horizontal limbs of the diagonal band of Broca. In the brainstem, double-labelled neurons were located in the laterodorsal tegmental nucleus, pedunculopontine tegmental nucleus and the parabigeminal nucleus. Injections of the anterograde tracer biocytin in these three brainstem nuclei resulted in fibre labelling in the suprachiasmatic nucleus, consistent with the retrograde findings. No clearly double-labelled cells were located in the retina. These results suggest that the suprachiasmatic nucleus receives cholinergic afferents from both the basal forebrain and mesopontine tegmentum which may mediate cholinergic effects on circadian rhythms.