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PubMed1993

Thalamic- and cerebellar-projecting interpolaris neuron responses to afferent inputs.

Thalamic- and cerebellar-projecting interpolaris neuron responses to afferent inputs from the temporomandibular joint (TMJ) and/or the masseter muscle (Mm) were examined in rats. Of 230 neurons tested, 24 could be antidromically stimulated from the contralateral ventral posteromedial thalamic nucleus (VPM), and 27 of 91 neurons tested were stimulated from the ipsilateral posteromedial part of crus II of the cerebellar cortex. None had dual projections. The thalamic-projecting neurons were recorded in the dorsomedial region of the interpolaris; most cerebellar-projecting neurons were at the medial border of the interpolaris. Ten of 24 thalamic- and 17 of 27 cerebellar-projecting neurons received nociceptive information. Afferent inputs from the TMJ and the Mm converged on 6 of 24 thalamic-projecting neurons and on 16 of 27 cerebellar-projecting neurons. In both the thalamic- and cerebellar-projecting neurons, there was no difference between the non-nociceptive and nociceptive neurons in mean antidromic latency. The results suggest that the interpolaris integrates and relays afferent inputs from deep oral structures.

Afferent Pathways↗
PubMed1995

Projections of the individual vestibular end-organs in the brain stem of the squirrel monkey.

The central nervous system (CNS) projections of primary afferent neurons from individual vestibular receptors were studied using horseradish peroxidase (HRP) or biocytin labeling in 14 ears from 7 adult squirrel monkeys using the technique developed in the chinchilla (Lee et al., 1989, 1992). The specificity of labeling was verified by examining the location of the labeled fibers and cell bodies in the vestibular nerve and Scarpa's ganglion. Labeled fibers and cells were restricted to nerves and areas belonging to groups of cells in either the superior or the inferior ganglion of the vestibular nerve. In the vestibular nerve root, labeled primary afferent fibers also exhibited a receptor-dependent segregation at the entrance to the medulla. Fibers from the HSC and the SSC were found rostrally and those from the PSC and the SAC were found in the caudal area. The UTR fibers were situated intermediate between these two groups of fibers. (A bundle of fibers, probably vestibular efferents, was identified immediately rostrally and ventromedially to the UTR fibers.) The primary afferent fibers bifurcated into secondary ascending and descending fibers at the lateral border of the vestibular nuclei, forming a longitudinal rostrocaudal vestibular tract. The secondary fibers from individual end-organs occupied specific locations in the tract: the UTR fibers were dorsal to the SSC and the HSC fibers, PSC fibers were found most medially, and the SAC fibers occupied the lateralmost area. The secondary UTR fibers overlapped considerably with those of the SSC and the HSC. The orderly receptor-dependent segregation of fibers was more prominent in the descending tracts than in the ascending tracts. In the vestibular nuclei complex the location of the tertiary branches of various end-organs exhibited considerable overlap within the major vestibular nuclei (SN, superior nucleus; LN, lateral nucleus; MN, medial nucleus; DN, descending nucleus). There were still differences, however, in the projection pattern. Fibers from the SAC ran primarily in the lateral area, fibers from the SSC and the UTR were found ventromedially to the SAC fibers, and the HSC projected slightly medially to the fibers from the SSC. The PSC fibers projected most medially. The UTR and SAC sent numerous fibers to the cerebellum. Fibers from the semicircular canals projected through the rostrodorsal region of the SN and presumably also projected to the cerebellum. The precise termination of fibers was evaluated by studying the location of labeled boutons, which were identified in all major vestibular nuclei. Labeled boutons from all the receptors were in the rostral and central areas of the SN, and in the MN mainly in the rostral two-thirds. In the LN, boutons from all the receptors were in the rostroventral part, most of which were from the UTR and SAC. No labeled boutons were in the caudodorsal part of this nucleus. Labeled boutons in the DN primarily surrounded the descending tract fibers and were particularly prominent medially. In specimens in which superior vestibular nerve receptor organs were scratched vestibular efferent fibers were also labeled. These fibers traveled in the most ventral part of the vestibular nerve root and projected in the ventral aspect of the LN to labeled soma in the ipsilateral and contralateral brain stem. Specificity the in projection patterns of efferent fibers from different end-organs could not be ascertained.

Animals↗
PubMed1990

Formation of crossed and uncrossed projections in the central nervous system.

Cellular mechanisms for decision of laterality of projections are discussed based on the observation of corticorubral and interpositorubral projections in the kitten. In both systems unilateral projections in adults appear to emerge from bilateral projections which occur early in development. Early unilateral lesions of the cerebral cortex or the interpositus nucleus cause persistent bilateral projections. Thus the neurons which eventually make a unilateral projection have the capability of forming synaptic connections with their target cells on both sides of the brain. Aberrant crossed (or uncrossed) projections in neonatal animals retract without forming complex axonal arbors, while those in lesioned animals form complex axonal arbors. Thus, success or failure in forming axonal arbors may be crucial for the maintenance of the aberrant crossed (or uncrossed) projections.

Animals↗
PubMed2004

Separate populations of neurons in the rostral ventromedial medulla project to the spinal cord and to the dorsolateral pons in the rat.

Activation of neurons in the rostral ventromedial medulla (RVM) directly modulates spinal nociceptive transmission by projections to the spinal cord dorsal horn and indirectly by projections to neurons in the dorsolateral pons (DLP) that project to the spinal cord dorsal horn. However, it is not known whether the same neurons in the RVM produce both direct and indirect modulation of nociception. Deposits of the retrograde tracers Fluoro-Gold (FG) in the spinal cord dorsal horn and DiI in the DLP were used to determine whether the same RVM neurons project to both of these regions. Only 0.9+/-0.1% of RVM neurons retrogradely labeled with Fluoro-Gold from the spinal cord were also labeled with DiI placed in the DLP. In addition, spinally projecting RVM neurons were significantly larger than RVM neurons that project to the DLP. Finally, spinally projecting neurons were found predominantly on the midline and within the RVM; neurons that project to the DLP had a wider distribution and were present both within and outside of the RVM. Thus, separate and morphologically distinct populations of RVM neurons appear to modulate nociception by direct and indirect descending pathways.

Animals↗
PubMed2006

Topographic organization of the projections from the interstitial system of the spinal trigeminal tract to the parabrachial nucleus in the rat.

Neurons in the paratrigeminal nucleus are known to project to the parabrachial region, but both these areas are heterogeneous, and the subnuclei that account for these connections are not known. To characterize better these projections, we injected small amounts of fluorogold or latex beads labeled with rhodamine or fluorescein into the parabrachial area in the rat and evaluated the retrograde transport of tracer to the paratrigeminal nucleus and neighboring regions. The results show that the rostral part of the paratrigeminal nucleus projects to the medial subnucleus of the parabrachial nucleus. The intermediary part of the paratrigeminal nucleus projects to both the external lateral and to the external medial subnuclei of the parabrachial nucleus. The caudal part of the paratrigeminal nucleus projects to the ventral lateral subnucleus of the parabrachial nucleus. The dorsal paramarginal nucleus projects to the external lateral and the extreme lateral subnuclei of the parabrachial nucleus. Lamina I and II of the spinal trigeminal nucleus also project to the external lateral and the extreme lateral subnuclei of the parabrachial nucleus. In conclusion, the rostral, intermediate, and caudal parts of the paratrigeminal nucleus and the dorsal paramarginal nucleus each have clearly different projection patterns and presumably have different functions.

Animals↗
PubMed2005

Delivering sustainability therapy in sustainable development projects.

This paper explores the apparent contradiction between the 'linearity' of most Sustainable Development projects, with time-bound and defined outputs achieved at a fixed cost, and an implied 'circularity' of the theory whereby there is no 'end'. Projects usually have clear parameters within which they are implemented, and the inclusion of elements such as the need for accountability, measurable impact and 'value for money' have grown in importance. It could be argued that we live in a 'projectified' and therefore linear world. The paper explores the potential contradiction between 'linearity' and 'circularity', and suggests that one way around this is to frame the project within a form of the Kolb Learning Cycle heuristic. This will facilitate a rationalisation from those implementing the sustainable development project as to why decisions are being made and for whom. If these questions are opened up to the project stakeholders, including beneficiaries, then the Kolb cycle could encourage learning and understanding by all involved. It could also provide Sustainability Therapy to those trapped in processes, which they find orthogonal to their own perceptions. It is suggested that such learning, therapy and reflective practice should be a valid output of the sustainable development project, although typically the focus is only upon the final outputs and how they feed into policy. Ironically funders would be well advised to take a broader perspective in order to achieve true 'value for money' within such projects, even if learning is not an easily measurable or tangible outcome. These points are explored within the context of the wider literature and experience with a sustainable development project undertaken in Malta.

Conservation of Natural Resources↗
PubMed2006

Projections of glutamate decarboxylase positive and negative cerebellar neurons to the pretectum in the cat.

The pretectum is one of the primary visual centers, and plays an important role in the visuomotor reflexes. It also receives projections from the cerebellar nuclei that are considered to regulate these reflexes. Gamma aminobutylic acid (GABA) and glutamate are supposed to be two major neurotransmitters of the projection neurons of the cerebellar nuclei. We double labeled the projecting neurons with a tracer, biotinylated dextran amine (BDA), and with an antiserum to glutamate decarboxylase (GAD), the enzyme that synthesizes GABA. The results indicated that about 40% of the pretectal-projecting neurons of the cerebellar nuclei were GAD immunoreactive. The GAD positive pretectal-projecting neurons were significantly smaller than the GAD negative projecting neurons. Our findings thus suggest the existence of two distinct cerebello-pretectal projection systems: one is mediated by GABAergic inhibitory projections, while the other is mediated by non-GABAergic, probably glutamatergic excitatory ones.

Animals↗
PubMed2004

Projections from estrogen receptor-alpha immunoreactive neurons in the periaqueductal gray to the lateral medulla oblongata in the rhesus monkey.

The periaqueductal gray (PAG) contains numerous estrogen receptor-alpha immunoreactive (ER-alpha IR) neurons that are distributed in a species-specific way. These neurons might modulate different types of behavior that are mediated by the PAG such as active and passive coping responses, analgesia, and reproductive behavior. In primates, it is not known whether ER-alpha IR PAG neurons represent local interneurons and/or neurons that project to brainstem areas that control these behaviors. In this double labeling study, we asked whether ER-alpha IR neurons in the PAG of the rhesus monkey project to the nucleus retroambiguus (NRA), an area in the ventrolateral caudal medulla oblongata that is involved in expiration, vocalization, and reproductive behavior. Tracer was injected into the caudal lateral medulla oblongata to retrogradely label PAG neurons, and ER-alpha was visualized immunohistochemically. Although ER-alpha IR neurons and NRA-projection neurons were present at similar levels of the PAG, their distributions hardly overlapped. ER-alpha IR PAG neurons that project to the lateral caudal medulla represented less than 2% of ER-alpha IR PAG neurons. These double-labeled neurons were mainly located in the ipsilateral caudal PAG. The cluster of neurons in the medial part of the lateral PAG that projects specifically to the NRA-region did not contain double-labeled cells. The results indicate that only a few ER-alpha IR PAG neurons project to the NRA-region. This might be related to the modest effects of estrogen on mating-related behavior in primates compared most other mammalian species. Remaining ER-alpha IR PAG neurons might act locally on other PAG neurons, or they might represent neurons that project to other areas. Furthermore, the finding that the distributions of ER-alpha IR neurons and neurons that project to premotor neurons in the NRA-region scarcely overlap illustrates that the PAG in primates is very highly organized into anatomically distinct regions compared with other species.

Animals↗
PubMed2004

Rat trigeminal lamina I neurons that project to thalamic or parabrachial nuclei contain the mu-opioid receptor.

Ligands of the mu-opioid receptor are known to inhibit nociceptive transmission in the dorsal horn, yet the cellular site(s) of action for this inhibition remain to be fully elucidated. Neurons located in lamina I of the dorsal horn are involved in distinct aspects of nociceptive transmission. Neurons projecting to the thalamus are thought to be involved in sensory-discriminative aspects of pain perception, while neurons projecting to the parabrachial nucleus are thought to be important for emotional and/or autonomic responses to noxious stimuli. The present study examined these two populations of lamina I projection neurons in the trigeminal dorsal horn to determine if the mu-opioid receptor protein (MOR1) is differentially located in these populations of neurons. Lamina I projection neurons were identified using the retrograde tracer FluoroGold (FGold). FGold was injected into either the contralateral thalamus (ventral posterolateral (VPM)/ventral posterolateral (VPL) thalamic region) or into the ipsilateral parabrachial nuclei. The distribution of MOR1 in these neurons was determined using immunocytochemistry. The distribution of MOR1-ir within these two populations of lamina I projection neurons was examined by both confocal and electron microscopy. We found that both populations of projection neurons contained MOR1. Immunogold analyses revealed the presence of MOR1-ir at membrane sites and within the cytoplasm of these neurons. Cytoplasmic receptor labeling may represent sites of synthesis, recycling or reserve populations of receptors. MOR1 was primarily found in the somata and proximal dendrites of projection neurons. In addition, these neurons rarely received synaptic input from MOR1-containing axon terminals. These results indicate that lamina I neurons in trigeminal dorsal horn that project to the thalamic and parabrachial nuclei contain MOR1 and are likely sites of action for MOR ligands that modulate sensory and/or autonomic aspects of pain transmission in the trigeminal dorsal horn.

Animals↗
PubMed2006

Forebrain projections of tuberoinfundibular peptide of 39 residues (TIP39)-containing subparafascicular neurons.

Neurons containing tuberoinfundibular peptide of 39 residues (TIP39) constitute a rostro-caudally elongated group of cells in the posterior thalamus. These neurons are located in the rostral part of the subparafascicular nucleus and in the subparafascicular area, caudally. Projections of the caudally located TIP39 neurons have been previously identified by their disappearance following lesions. We have now mapped the projections of the rat rostral subparafascicular neurons using injections of the anterograde tracer biotinylated dextran amine and the retrograde tracer cholera toxin B subunit, and confirmed the projections from more caudal areas previously inferred from lesion studies. Neurons from both the rostral subparafascicular nucleus and the subparafascicular area project to the medial prefrontal, insular, ecto- and perirhinal cortex, nucleus of the diagonal band, septum, central and basomedial amygdaloid nuclei, fundus striati, basal forebrain, midline and intralaminar thalamic nuclei, hypothalamus, subthalamus and the periaqueductal gray. The subparafascicular area projects more densely to the amygdala and the hypothalamus. In contrast, only the rostral part of the subparafascicular nucleus projects significantly to the superficial layers of prefrontal, insular, ectorhinal and somatosensory cortical areas. Double labeling showed that anterogradely labeled fibers from the rostral part of the subparafascicular nucleus contain TIP39 in many forebrain areas, but do not in hypothalamic areas. Injections of the retrograde tracer cholera toxin B subunit into the lateral septum and the fundus striati confirmed that they were indeed target regions of both the rostral subparafascicular nucleus and the subparafascicular area. In contrast, TIP39 neurons did not project to the anterior hypothalamic nucleus. Our data provide an anatomical basis for the potential involvement of rostral subparafascicular neurons in limbic and autonomic regulation, with TIP39 cells being major subparafascicular output neurons projecting to forebrain regions.

Animals↗
PubMed2006

[Remodeling of the nasal lobule using cartilaginous grafts on tip projection].

OBJECTIVES: Nasal tip projetion and definition are essential parameters which should be considered in the preoperative rhinoplasty plan. Jonhson and Toriumi have defined a technique of rhinoplasty to restructure the lobule using columellar strut and tip grafts. The aim of this study was to define the influence of this procedure on nasal tip projection, using the Goode method (objective measurement of the tip projection). METHODS: Forty patients underwent primary rhinoplasty, by open approach, with remodeling of the lobule using cartilagenous grafts, according to Jonhson and Torium technique. Goode ratio was calculated to assess tip projection preoperatively and postoperatively, based on photographic analysis. Moreover, postoperatively, all patients were clinically evaluated at 2, 4 and 6 months, and based on photographs of face at 2 and 6 months. RESULTS: Five hypoprojected preoperative nasal tips (Goode ratio (GR): 0,45 to 0,51) had a normal nasal tip projection postoperatively (GR: 0,55 to 0,59). Among the eight normal projected preoperative nasal tips (GR: 0,56 to 0,60), six had a normal postoperative nasal tip projection while two showed a hyperprojection (GR: 0,62 and 0,63). Among the 27 hyperprojected preoperative nasal tips (GR: 0,62 to 0,75), 17 showed a normal projection of the nasal tip postoperatively while 10 remained hyperprojected despite a decreased Goode ratio. CONCLUSION: Restructuration of the lobule, using cartilagenous grafts, is a reliable and reproducible technique allowing satisfying aesthetic results and objective measurements of the changes in nasal tip projection using the Goode method.

Adult↗
PubMed1999

Correlation and quantification of projected 2-dimensional radiographic images with actual 3-dimensional Y-axis vertebral rotations.

BACKGROUND: Historically, measurement of 2-dimensional (2-D) radiographic images on the anteroposterior radiograph has been made to assess 3-dimensional (3-D) y-axis vertebral rotations. OBJECTIVES: To correlate and quantify measurements of the projected 2-D radiographic image with the degree of 3-D y-axis rotation. STUDY DESIGN: A computer model was positioned in a simulated x-ray beam. Points of model contact with the simulated beam were projected onto a line in the neutral position and the first 7 degrees of both positive and negative y-axis rotation using two different axes of rotation. A larger model, a shape-altered model, and a decreased source-object-distance model were also studied. RESULTS: 3-D y-axis rotation of vertebrae causes an off-center displacement of the 2-D projected lamina junction in relation to the projected vertebral body. The magnitude of displacement increases with increasing degrees of rotation. In our model, no clinically significant difference was found in the amount of the projected off-center displacement of the lamina junction between either of our two chosen axes of rotation. However, significant differences in the projected offset were found between vertebrae with the same degree of rotation as a result of changes in vertebral shape, size, and positioning. The projected lamina junction off-centering at a given rotation is quantified for our model. CONCLUSION: Use of millimetric measurement of the projected lamina offset on the anteroposterior radiograph is an inaccurate method for the assessment of the degree of 3-D y-axis vertebral rotation.

Biomechanical Phenomena↗
PubMed1992

Topographical organization of the projections from physiologically identified areas of the motor cortex to the striatum in the rat.

The present study was undertaken to determine in the rat the topography of the neostriatal projections originating from the motor cortex. For that purpose, anterograde tracers (Phaseolus vulgaris leucoagglutinin: PHA-L; wheat germ agglutinin conjugated to horseradish peroxidase: WGA-HRP) were deposited in discrete cortical sites physiologically identified by microstimulation. Five major motor areas were considered in this study: the rostral (RFL) and caudal (CFL) forelimb areas, the hindlimb (HL) area, the vibrissae motor-frontal eye field (V-FEF) region and the jaw, lips and tongue (JLT) area (according to the nomenclature of Neafsey et al.). The results indicate that functionally different regions of the motor cortex project to different sectors of the caudate putamen (CPU). All 3 distinct limb areas RFL, CFL and HL project to the dorsolateral quarter of the CPU, V-FEF area projects to the dorsomedial quarter, whereas the JLT area projects to the ventrolateral quarter. The pattern of terminal labeling is relatively consistent, whatever the cortical area in which the tracer is deposited. This pattern is characterized by the presence of two or more labeled bands which are obliquely oriented along a ventrolateral-dorsomedial axis. Control experiments were also undertaken in which a retrograde tracer (WGA-HRP) was deposited in various neostriatal loci. The results are congruent with the findings of the anterograde study and further indicate that a given neostriatal sector receives projections from cytoarchitectonically different but functionally related regions of the neocortex. The somatotopic features of both motor and somatosensory corticostriatal projections appear to be in register. In addition, the striatal distribution of motor cortical fibers was compared in 6 experimental cases to the compartmental subdivision of the striatum in patches and matrix, following immunohistochemical localization of calbindin 28 kDa. The calbindin-immunoreactivity is extremely weak in the dorsolateral sector but is higher in the central and ventrolateral parts of the CPU. In these deep striatal regions receiving fibers from V-FEF, JLT and, to a lesser extent, from the limb areas, the cortical fibers are mostly directed to the matrix. The band-like organization of the projection from the motor cortex is correlated to the patch-matrix organization. The patches correspond to the bands of low density of terminal fibers and the matrix to the bands of high terminal density. The present results provide an anatomical basis to both electrophysiological and behavioral observations suggesting that functional distinctions can be established between subregions of the striatum.

Animals↗
PubMed1999

The scapulo-humeral rhythm: effects of 2-D roentgen projection.

OBJECTIVE: The objective of this study is to illustrate the low accuracy of two-dimensional (2-D) X-ray projection methods for the quantification of the three-dimensional (3-D) shoulder motions. BACKGROUND: The traditional method for the quantification of the gleno-humeral motion is by means of 2-D X-ray recording. The motion was characterized by the scapulo-humeral rhythm: the ratio of the nett humeral elevation over nett scapular rotation. The method was based on the quantification of the planar projection of the spatial positions of X-ray dense structures of the scapula. The deformations introduced by the central projection method, a feature of X-ray projection, cannot be compensated for by calibration: the position of the scapula with respect to the camera setting is unknown, and skeletal landmarks of the scapula cannot uniquely be identified. The transformation from 3-D orientations to 2-D angles will, therefore, be inaccurate. METHODS: A 2-D X-ray projection of the scapula during a typical arm abduction was simulated. The 3-D motion was obtained by means of palpation and subsequent digitization of skeletal landmarks of the scapula. The 3-D positions of the recorded landmarks were projected on a plane by a simulation based on the parameters of the X-ray equipment. The scapulo-humeral rhythm was calculated for the different scapular landmarks, and for the orientation of the subject with respect to the projection axis. The results were compared with previous published scapulo-humeral rhythms. RESULTS: The scapulo-humeral rhythm depends both on the choice of the skeletal landmarks, used to quantify the scapular rotations, and on the orientation of the subject in the X-ray setting. The full range of results obtained from earlier published experiments could be obtained from a simulation based on a single 3-D arm abduction. CONCLUSIONS: The 2-D scapulo-humeral rhythm, obtained from planar X-ray projection, is an inaccurate parameter to define the scapular motions. RELEVANCE: The 2-D scapulo-humeral rhythm is an insensitive parameter to identify clinical disorders in the gleno-humeral motions, 3-D motion recording should be applied. Only when stringent precautions are taken with respect to repeatability of positioning of the subjects, can the method be used to study intra-individual effects, e.g., the follow-up of patients during treatment.

Biomechanical Phenomena↗
PubMed2000

Limited collateralization of neurons in the rat prefrontal cortex that project to the nucleus accumbens.

The specificity and selectiveness of a neuronal message depends in part on the number of recipient neurons that simultaneously receive this message. Hence, projections involved in higher order cognitive processes might be expected to exhibit a lower degree of collateralization than projections that mediate more basic brain functions. This study sought to determine the degree to which neurons projecting from the prefrontal cortex to the nucleus accumbens collateralize to major cortical and subcortical regions: the contralateral prefrontal cortex, the basolateral amygdala or the ventral tegmental area. Fluoro-Gold and cholera toxin-b were used to label prefrontal cortex neurons that project to these targets, and the proportion of neurons singly and dually labeled by immunofluorescence for these tracers was determined. The prefrontal cortex neurons projecting to these regions exhibited a partially complementary laminar distribution. Furthermore, of the neurons projecting to the nucleus accumbens, 13% sent a collateralized projection to the contralateral prefrontal cortex, 7% collateralized to the basolateral amygdala, and 3% sent a branched projection to the ventral tegmental area. No differences were observed in the degree of collateralization of neurons in superficial versus deep layers.Thus, the degree of collateralization of corticoaccumbens neurons was overall limited, but significantly greater to a cortical target than to subcortical regions. These branching patterns provide anatomical substrates for temporal and spatial coordination of activity in limbic circuits.

Amygdala↗
PubMed2000

Cortical projections from the suprasylvian gyrus to the reticular thalamic nucleus in the cat.

The cat's suprasylvian gyrus was injected iontophoretically with either 4% wheat germ agglutinin-horseradish peroxidase, 4% dextran-fluororuby or 4% dextran-biotin. The locations of labelled fibres, presumed terminals and cell bodies were determined with the aid of a camera lucida attachment and computer aided stereometry. Cells from the crown of the suprasylvian gyrus project to the dorsal-most portion of the rostral half of the reticular nucleus. The region or 'sector' is distinct, albeit with some overlap, from the visual sector of the reticular nucleus defined by projections from adjacent extrastriate visual cortices. The projection from the suprasylvian gyrus to the reticular nucleus has a rough topography such that the caudal areas project to the more caudal aspects of the sector and rostral areas project to the more rostral areas of the reticular nucleus. There is a large degree of overlap of rostrocaudal projections from the suprasylvian gyrus within the sector, however, the projections originating from rostral sites are situated in a more ventral location compared to the projection originating from the caudal suprasylvian gyrus. Analysis of the distribution of biotin labelled presumptive terminals did not support the notion of 'slabs' or regional variation in terminal density across the mediolateral thickness of the reticular nucleus. In addition, a number of presumptive terminals were found within the internal capsule which coincided with the position of retrogradely labelled cells in the internal capsule following thalamic injections and appears to be part of the perireticular nucleus. The results suggest that the reticular nucleus may be segregated into sectors connected with modality specific cortical areas (e.g. striate and extrastriate visual areas) and nonspecific sectors connected with polymodal (e.g. area 7) cortical regions. The reticular nucleus and its connections with the suprasylvian gyrus may form an important link in binding eye movements to sensory integrative process through visuomotor and auditory thalamic connections.

Animals↗
PubMed2002

Quantitative analysis of the dendritic morphology of corticocortical projection neurons in the macaque monkey association cortex.

The polymodal association areas of the primate cerebral cortex are heavily interconnected and play a crucial role in cognition. Area 46 of the prefrontal cortex in non-human primates receives direct inputs from several association areas, among them the cortical regions lining the superior temporal sulcus. We examined whether projection neurons providing such a corticocortical projection differ in their dendritic morphology from pyramidal neurons projecting locally within area 46. Specific sets of corticocortical projection neurons were identified by in vivo retrograde transport in young macaque monkeys. Full dendritic arbors of retrogradely labeled neurons were visualized in brain slices by targeted intracellular injection of Lucifer Yellow, and reconstructed three-dimensionally using computer-assisted morphometry. Total dendritic length, numbers of segments, numbers of spines, and spine density were analyzed in layer III pyramidal neurons forming long projections (from the superior temporal cortex to prefrontal area 46), as well as local projections (within area 46). Sholl analysis was also used to compare the complexity of these two groups of neurons. Our results demonstrate that long corticocortical projection neurons connecting the temporal and prefrontal cortex have longer, more complex dendritic arbors and more spines than pyramidal neurons projecting locally within area 46. The more complex dendritic arborization of such neurons is likely linked to their participation in cortical networks that require extensive convergence of multiple afferents at the cellular level.

Animals↗
PubMed2002

Projection neurons and interneurons in the lateral geniculate nucleus undergo distinct forms of degeneration ranging from retrograde and transsynaptic apoptosis to transient atrophy after cortical ablation in rat.

The cytological responses of thalamic interneurons to selective degeneration of thalamocortical projection neurons after cortical damage in the adult brain are poorly understood. We used a unilateral neocortical lesion model (occipital cortex ablation) in the adult rat to test the hypothesis that interneurons and projection neurons in the lateral geniculate nucleus undergo distinct forms of degeneration. In situ nuclear DNA fragmentation in neurons in the lateral geniculate occurs maximally at 7 days postlesion. Geniculocortical projection neurons that are identified by the retrograde tracer Fluorogold die primarily with a morphology of endstage apoptosis prominent at 7 days postlesion. In contrast, interneurons, identified by their particular nuclear ultrastructure and by glutamic acid decarboxylase immunoreactivity, undergo an atrophic vacuolar pathology starting early during the period of projection neuron death and peaking after the projection neuron death is complete. This degeneration of interneurons is transient, because these neurons exhibit structural recovery and their numbers are not changed significantly postlesion. A rare subset of interneurons (less than one in 100 interneurons and less than one in 100 apoptotic cells) undergoes apoptosis concurrently with the projection neurons. We conclude that different types of neurons within the same thalamic nucleus respond differently to focal cortical target deprivation. Unlike the apoptosis-prone projection neurons, most interneurons undergo transient transsynaptic atrophy and recovery rather than cell death. Nevertheless, a small subset of lateral geniculate interneurons undergoes transsynaptic apoptosis in response to projection neuron apoptosis. The pathological responses of thalamic neurons to cortical trauma vary depending on cell type.

Animals↗