Caudal Cortex Research Articles

Evidence that Trigeminal Brainstem Interneurons Form Subpopulations to Produce Different Forms of Mastication in the Rabbit

To determine how trigeminal brainstem interneurons pattern different forms of rhythmical jaw movements, four types of motor patterns were induced by electrical stimulation within the cortical masticatory areas of rabbits. After these were recorded, animals were paralyzed and fictive motor output was recorded with an extracellular microelectrode in the trigeminal motor nucleus. A second electrode was used to record from interneurons within the lateral part of the parvocellular reticular formation (Rpc-alpha, n = 28) and gamma- subnucleus of the oral nucleus of the spinal trigeminal tract (NVspo-gamma, n = 68). Both of these areas contain many interneurons projecting to the trigeminal motor nucleus. The basic characteristics of the four movement types evoked before paralysis were similar to those seen after the neuromuscular blockade, although cycle duration was significantly decreased for all patterns. Interneurons showed three types of firing pattern: 54% were inactive, 42% were rhythmically active, and 4% had a tonic firing pattern. Neurons within the first two categories were intermingled in Rpc-alpha and NVspo-gamma: 48% of rhythmic neurons were active during one movement type, 35% were active during two, and 13% were active during three or four patterns. Most units fired during either the middle of the masseter burst or interburst phases during fictive movements evoked from the left caudal cortex. In contrast, there were no tendencies toward a preferred coupling of interneuron activity to any particular phase of the cycle during stimulation of other cortical sites. It was concluded that the premotoneurons that form the final commands to trigeminal motoneurons are organized into subpopulations according to movement pattern.

Morphochemical changes in brain structures and their correction by tuftsin in rats with hypofunction of the dopamine system

Chronic administration of haloperidol to Wistar rats induces specific changes in protein metabolism at the cortical-subcortical level (sensorimotor cortex—caudate nucleus), in associative and integrative triggering neurons, and in the cytoplasm and nucleus of the same neuron, judging from the state of structural proteins and aminopeptidase activity. Tuftsin reduces these changes only in the sensorimotor cortex.

Evidence of structural and material adaptation to specific strain features in cortical bone

Background Functionally induced strains provide epigenetic signaling for bone modeling and remodeling activities. Strain gauge documentation of the equine third metacarpal reveals a neutral axis passing through the craniolateral cortex, resulting in a narrow band of cortex loaded predominantly in tension, with the remainder of the cortex experiencing a wide range of compression strain magnitudes that are maximal in the caudomedial cortex. This predictable strain pattern provides a model for examining the hypothesis that strain mode, magnitude, and strain energy density are potential correlates of compact bone structural and material organization. Methods Structural and material variables were quantified in nine equine (standard breeds) third metacarpals for comparison with the in vivo strain milieu that was evaluated in thoroughbred horses. The variables quantified included secondary osteon population density (OPD), fractional area of secondary bone (FASB), fractional area of porous spaces, collagen fiber orientation, mineral content (% ash), and cortical thickness. Each bone was sectioned transversely at 50% of length, with subsequent quantification of eight radial sectors and three intracortical regions (periosteal, middle, endosteal). Linear regression analysis compared these variables to magnitudes of corresponding regional in vivo longitudinal strain, shear strain, and strain energy density values reported in the literature. Results The craniolateral (“tension”) cortex of this bone is distinguished by its 30% lower FASB and with the lateral cortex exhibits 20% darker gray level (more longitudinal collagen) compared with the average of all other locations. Conversely, the remaining (“compression”) cortices as a group have a high OPD, are more extensively remodeled, and contain more oblique-to-transverse collagen. The caudal cortices (caudomedial, caudal, caudolateral) are significantly thinner (P < 0.01) and have 4% lower mineral content (P < 0.05) than all other locations. Moderately strong correlations exist between collagen fiber orientation and normal strain (r = 0.752) and shear strain (r = 0.555). When normal and shear strains were transformed to their respective absolute values, thus eliminating the effects of strain mode (tension vs. compression), these correlation coefficients decreased markedly. Conclusions Collagen fiber orientation is related to strain mode and may function to accentuate rather than attenuate bending. These differences may represent adaptations that function synergistically with bone geometry to promote a beneficial strain distribution and loading predictability during functional loading. © 1996 Wiley-Liss, Inc.

Evidence of structural and material adaptation to specific strain features in cortical bone.

Functionally induced strains provide epigenetic signaling for bone modeling and remodeling activities. Strain gauge documentation of the equine third metacarpal reveals a neutral axis passing through the craniolateral cortex, resulting in a narrow band of cortex loaded predominantly in tension, with the remainder of the cortex experiencing a wide range of compression strain magnitudes that are maximal in the caudomedial cortex. This predictable strain pattern provides a model for examining the hypothesis that strain mode, magnitude, and strain energy density are potential correlates of compact bone structural and material organization. Structural and material variables were quantified in nine equine (standard breeds) third metacarpals for comparison with the in vivo strain milieu that was evaluated in thoroughbred horses. The variables quantified included secondary osteon population density (OPD), fractional area of secondary bone (FASB), fractional area of porous spaces, collagen fiber orientation, mineral content (% ash), and cortical thickness. Each bone was sectioned transversely at 50% of length, with subsequent quantification of eight radial sectors and three intracortical regions (periosteal, middle, endosteal). Linear regression analysis compared these variables to magnitudes of corresponding regional in vivo longitudinal strain, shear strain, and strain energy density values reported in the literature. The craniolateral ("tension") cortex of this bone is distinguished by its 30% lower FASB and with the lateral cortex exhibits 20% darker gray level (more longitudinal collagen) compared with the average of all other locations. Conversely, the remaining ("compression") cortices as a group have a high OPD, are more extensively remodeled, and contain more oblique-to-transverse collagen. The caudal cortices (caudomedial, caudal, caudolateral) are significantly thinner (P < 0.01) and have 4% lower mineral content (P < 0.05) than all other locations. Moderately strong correlations exist between collagen fiber orientation and normal strain (r = 0.752) and shear strain (r = 0.555). When normal and shear strains were transformed to their respective absolute values, thus eliminating the effects of strain mode (tension vs. compression), these correlation coefficients decreased markedly. Collagen fiber orientation is related to strain mode and may function to accentuate rather than attenuate bending. These differences may represent adaptations that function synergistically with bone geometry to promote a beneficial strain distribution and loading predictability during functional loading.

Evidence of strain-mode-related cortical adaptation in the diaphysis of the horse radius

The relative importance that certain strain features, including mode (e.g., tension vs. compression) and magnitude, have in affecting adaptive bone remodeling seen in normal skeletally mature bones remains controversial. The equine radius is used as a model because in vivo strain data show that the mid-to-proximal diaphysis receives a consistent history of predominantly cranial-caudal bending loads, in contrast to the distal diaphysis which receives relatively more torsional loading superimposed on cranial-caudal bending. Medial and lateral cortices serve as control regions because they correspond to a neutral axis of bending. Equine radii were sectioned transversely at 65% (proximal), 50%, and 35% (distal) of length and cortical bone from the cranial ("tension"), caudal ("compression"), medial, and lateral regions was examined to determine if one, of many, structural and material features could be distinguished as being consistently related to the distribution of the prevailing strain modes. Mineral content (percent ash) differences, though statistically significant (p < 0.01), vary less than 1% between regions of the cortex at all sections. Porosity is not significantly different between any of the regions (p = 0.13). In the 65% and 50% sections, secondary osteon population density (OPD, osteons per square millimeter) and fractional area of secondary bone (FASB) are each nearly two times as great in the caudal regions than in the other three regions (p < 0.01). The 35% section shows a pattern opposite of that in the other sections--there are more than two times as many osteons in the cranial cortex than in the caudal cortex.(ABSTRACT TRUNCATED AT 250 WORDS)

Neurotensin-like immunoreactivity in locust supraesophageal ganglion and optic lobes

A substance immunoreactive to antibodies directed against bovine neurotensin (NT) was localized in neurons in the supraesophageal ganglion (SEG) and optic lobes of larval and adult Locusta migratoria L. Two large somata were located in the caudal cortex, ventral to the calyces and symmetrical to the medium of the SEG. Four smaller somata also in the caudal cortex were located as two symmetrical pairs at the level of the central body. These somata formed a diffuse network of varicose fibers from the superior lateral to the ventro-lateral protocerebrum between the pedunculi and frontal cortical region. Some fibers crossed the median to the contralateral sides of the SEG. Another pair of immunoreactive somata whose terminating processes remained unclear was found at the level of the antennal lobes. Intrinsic networks of fibers were labeled in the accessory medulla and in layer 4/5 of the medulla. These fibers originated from 8–10 small somata near the dorso-frontal rim of the medulla. All larval stages contained these NT-like immunoreactive structures. Results from isoelectric focusing and press-blot analysis of SEG homogenates, synthetic neurotensin and neurotensin fragments indicate that this substance is similar to bovine neurotensin(1–13).

Spontaneous activity and evoked potentials in the caudal trigeminal nucleus, ventrobasal thalamus, and cerebral cortex of rats with neuropathic trigeminal neuralgia

Incomplete compression of the infraorbital nerve in rats leads to spontaneous neuronal activity in the form of bursts in the caudal trigeminal nucleus and to epileptiform activity in the ventrobasal thalamus and cerebral cortex. From the latter, afterdischarges are also recorded.

Radiographie study of homotypic variation of long bones in dogs

Summary Dogs have been used extensively as an experimental model for studying musculoskeletal disorders. Many of these studies incorporated sequential radiography to quantitate a particular treatment's effect, using the contralateral bone as the control condition. The contralateral bone can be used as a control only if there is bilateral symmetry between right and left limbs. We performed radiography (craniocaudal and lateromedial views) on 10 pairs of humeri, radii, femora, and tibiae from dogs, using an alignment jig, to radiographically determine homotypic geometric variations or long bones. The bones were divided into 5 regions: proximal epiphysis, proximal metaphysis, diaphysis, distal metaphysis, and distal epiphysis. The toal bone diameter, medullary diameter, and cortical width (total of medial + lateral cortex or total of cranial + caudal cortex) were measured at specified slices throughout each of these regions. Fourteen of 540 homotypic comparisons revealed significant differences between right and left bones at either a slice or region. Although there were only 14 significant differences between right and left bones at any region or slice, measurements were more precise with lower coefficients of variation in the diaphyseal and epiphyseal regions. Homotypic differences in diaphyseal and epiphyseal regions were &lt; 5.3 and 7.5%, respectively (power = 0.8). In metaphyseal regions, however, homotypic differences were larger; these differences could have been as large as 11.5% for total bone diameter, 15.6% for medullary diameter, and 80.0% for cortical width without achieving significant differences between populations (power = 0.8). This study validated the concept of using the contralateral limb as the control condition in orthopedic studies using dogs, particularly when evaluating the geometric properties of long bones radiographically.

Functional associations between collagen fibre orientation and locomotor strain direction in cortical bone of the equine radius.

A novel technique for determining the collagen fibre orientation pattern of cross-sections of cortical bone was used to study mid-diaphyseal sections from the equine radius. Several in vivo strain gauge studies have demonstrated that this bone is loaded in bending during locomotion in such a way that the cranial cortex is consistently subjected to longitudinal tensile strains and the caudal cortex to longitudinal compressive strains. Twenty-three radii from 17 horses were studied. All the bones obtained from adult horses exhibited a consistent pattern of collagen fibre orientation across the cortex. The cranial cortex, subjected to intermittent tension, and the lateral and medial cortices, through which the neutral axis passes, contained predominantly longitudinally oriented collagen fibres. The caudal cortex, subjected to longitudinal compression during life, contained predominantly oblique/transverse collagen. This pattern was less evident in bones from foals. Microscopic analysis of the bones studied showed that primary lamellar bone was composed of predominantly longitudinal collagen fibres, irrespective of cortex. However, there was a strong relationship between cortical location and fibre orientation within remodelled bone. Secondary osteons which formed in the caudal (compressive) cortex contained predominantly oblique/transverse collagen, while those which formed elsewhere contained longitudinal collagen. This observation explained the developmental appearance of the characteristic macroscopic pattern of collagen fibre orientation across the whole cortex in the adult. These findings provide evidence for the existence of a relationship between the mechanical function of a bone with its architecture, and now demonstrate that it extends to the molecular level.

Mechanical implications of collagen fibre orientation in cortical bone of the equine radius.

Mechanical test specimens were prepared from the cranial and caudal cortices of radii from eight horses. These were subjected to destructive tests in either tension or compression. The ultimate stress, elastic modulus and energy absorbed to failure were calculated in either mode of loading. Analysis was performed on the specimens following mechanical testing to determine their density, mineral content, mineral density distribution and histological type. A novel technique was applied to sections from each specimen to quantify the predominant collagen fibre orientation of the bone near the plane of fracture. The collagen map for each bone studied was in agreement with the previously observed pattern of longitudinal orientation in the cranial cortex and more oblique to transverse collagen in the caudal cortex. Bone from the cranial cortex had a significantly higher ultimate tensile stress (UTS) than that from the caudal cortex (160 MPa vs 104 MPa; P < 0.001) though this trend was reversed in compression, the caudal cortex becoming relatively stronger (185 MPa vs 217 MPa; P < 0.01). Bone from the cranial cortex was significantly stiffer than that from the caudal cortex both in tension (22 GPa vs 15 GPa; P < 0.001) and compression (19 GPa vs 15 GPa; P < 0.01). Of all the histo-compositional variables studied, collagen fibre orientation was most closely correlated with mechanical properties, accounting for 71% of variation in ultimate tensile stress and 58% of variation in the elastic modulus. Mineral density and porosity were the only other variables to show any significant correlation with either UTS or elastic modulus. The variations in mechanical properties around the equine radius, which occur in close association with the different collagen fibre orientations, provide maximal safety factors in terms of ultimate stress, yet contribute to greater bending of the bone as it is loaded during locomotion, and thus lower safety factors through the higher strains this engenders.

Effects of a fixed compression load on the osteogenic effect of autogenous cancellous bone grafts in dogs

Summary A standardized cortical defect was created on the caudal cortex of the proximal portion of each ulna in 5 adult mixed-breed dogs. One gram of autogenous cancellous bone graft (acbg) was obtained from the greater tubercle of the ipsilateral humerus. The cortical defect in the ulna of 1 limb was filled with 1 g of acbg that had been compressed with 2-MPa pressure for 30 seconds. One gram of noncompressed acbg was placed into the contralateral ulnar cortical defect. The compressed and noncompressed acbg recipient sites were radiographed at weekly intervals. Dogs were euthanatized 8 weeks after surgery, and the acbg recipient sites were harvested for histomor-phometric analysis. Optical densitometry was performed on all radiographs. There was no significant difference between compressed and noncompressed acbg with optical densitometry or histomorphometric analysis for total bone area. We concluded that there was no difference in osteogenic capability between compressed and noncompressed acbg of equal mass.

Cortical oscillations and temporal interactions in a computer simulation of piriform cortex.

1. A large-scale computer model of the piriform cortex was constructed on the basis of the known anatomic and physiological organization of this region. 2. The oscillatory field potential and electroencephalographic (EEG) activity generated by the model was compared with actual physiological results. The model was able to produce patterns of activity similar to those recorded physiologically in response to both weak and strong electrical shocks to the afferent input. The model also generated activity patterns similar to EEGs recorded in behaving animals. 3. In addition to replicating known physiological responses, it has been possible to use the simulations to explore the interactions of network components that might underlie these responses. This analysis suggests that the physiological properties of the cortex are dependent on the complex interaction of both network and cellular properties. In particular, we have found that the relationship between conduction velocities in intrinsic cortical fiber systems and the time constants of excitatory and inhibitory effects are critical for replicating physiological results. 4. Analysis of the model also suggests a correspondence between the 40-Hz oscillatory patterns of activity induced by low levels of odor-like stimulation and oscillatory patterns seen in lightly anesthetized cortex in response to weak electrical shocks to the afferent fiber system. 5. The specific relationships we have found between the different components of the model also support several speculations on their functional significance. The simulations suggest that during each 40-Hz cycle of EEG activity there is a convergence in rostral cortex of afferent information from the olfactory bulb and recurrent association fiber information from caudal cortex. This convergence could underlie an iterative process central to the recognition of complex olfactory stimuli.

Cortical folding, the lunate sulcus and the evolution of the human brain

Controversy over the placement of the lunate sulcus on the Taung australopithecine endocast has been central in the debate as to whether cortical reorganization occurred independently of and preceded the expansion of the human brain. A new technique, the gyrification index, measures the degree of cortical folding. A comparison of the index among extant great ape and human brains shows that the values of the two taxa overlap only in the caudal cortex where the lunate sulcus is found. The similarity in degree of cortical folding in the caudal cortex contrasts to differences in all the other portions where the human cortex has a higher degree of folding than found in ape brains. The conservation in the degree of caudal cortical folding is unexpected if, during human evolution, the parietal association cortex had enlarged independently of brain size so much that the lunate sulcus moved posteriorly. The findings are more consistent with interpretations that the major differences in folding between human and ape parietal and occipital cortices arose concurrently with changes in brain size. Although these data do not localize the position of the lunate sulcus on the Taung endocast, the similarity in degrees of folding among hominoids is consistent with interpretations that, given its small cranial capacity, the lunate sulcus of the Taung specimen is in a pongid position.

Cortical Gyrification in the Rhesus Monkey: A Test of the Mechanical Folding Hypothesis

A quantitative measure of the degree of cortical folding was used to test the mechanical hypothesis of cortical folding and to analyze structural properties of the rhesus monkey cortex. The rhesus monkey cortex has both its maximal degree of cortical folding and the largest ratios of supragranular laminae to the lower granular and infragranular layers in the caudal cortex, over the posterior parietal-anterior occipital regions. Low values for cortical folding and for the ratios of inner and outer cortical layers characterize frontal regions. Topographically intermediate regions are intermediate in both sets of values. Ratios of the amounts of white and gray matter have a topographic pattern that differs from those of cortical folding, suggesting that the sizes of subcortical axonal bundles are not directly associated with the degree of cortical folding. Whereas differences in mean degrees of cortical folding are correlated with brain weights among species of primates, the amount of folding is not associated with brain weight within the species.

Effect of Monosialoganglioside (GM1) on Transected Monoaminergic Pathways

The effects of exogenous monosialogangliosides (GM1) on transected monoaminergic cerebral cortical pathways were investigated in mice. Norepinephrine (NE), 5-hydroxytryptamine (5-HT), and 5-hydroxyindole-3-acetic acid (5-HIAA) contents were determined in cerebral cortex rostral and caudal to unilateral coronal transection sites. The transmitter contents were expressed as a ratio of those in the unlesioned contralateral cortex. In the caudal cortex, NE ratios fell to 70% within a week after transection and decreased further to 35-40% by 4 weeks. Treatment with exogenous GM1 for 2 weeks starting shortly after the lesion increased NE concentrations in the caudal cortex to 47.4-55.0% at 4 weeks, significantly greater than control animals (p less than 0.01, Mann-Whitney U-test). GM1 treatment for 2 and 4 weeks, starting 2 weeks after the lesion, yielded similar results. The 5-HT and 5-HIAA ratios in the caudal cortex also rose significantly after GM1 treatment. Thus, GM1 increased monoaminergic levels nonspecifically in the cortex caudal to the cortical lesion. The treatment effect did not depend on the timing or duration of treatment. These results indicate that exogenous GM1 treatment has a nonspecific restorative effect on the central nervous system after axonal lesions.

A Combined Tension Band and Lag Screw Technique for Fixation of Olecranon Osteotomies

A combined tension band and lag screw technique for fixation of olecranon osteotomies was used in six canine clinical patients weighing 4.5 to 19 kg. After the proximal part of the ulnar shaft was exposed, a screw hole was drilled and tapped just cranial to the caudal cortex of the olecranon. An osteotomy was performed and the hole in the olecranon fragment was overdrilled to form a gliding hole. For reconstruction, the olecranon was reduced anatomically and compressed with a screw placed in lag fashion. With the trochlear notch exposed, a Kirschner wire was inserted cranial to the screw, using care not to enter the elbow joint. A double-twist figure-eight tension band wire was placed around the Kirschner wire in five dogs and around the screw in one dog. In this dog, a spiked washer was used with the screw because a small olecranon fragment had been produced by incorrect osteotomy position. A painful soft tissue swelling over the prominent washer, which resolved after implant removal, was the only complication attributed to the technique. The combined tension band wire and lag screw technique was a rapid and reliable method for fixation of olecranon osteotomies.

Connections of the dorsal nucleus of the lateral lemniscus: an inhibitory parallel pathway in the ascending auditory system?

This study examines the dorsal nucleus of the lateral lemniscus (DNLL) and its afferent and efferent connections. In Nissl-stained material, DNLL has three parts: dorsal, ventral, and lateral. Although each part contains neurons with similar Nissl patterns, the subdivisions may be distinguished by the size, shape, and orientation of the cells. The lateral DNLL contains a mixture of DNLL neurons and cells from the sagulum. Afferent connections to DNLL were investigated with anterograde axonal transport techniques. Bilateral inputs to DNLL arise from the anteroventral cochlear nucleus and lateral superior olive, while unilateral inputs are provided by the ipsilateral medial superior olive and the contralateral DNLL. The inputs appear to have a tonotopic organization. Afferent fibers to DNLL form horizontal bands that are continuous both mediolaterally and rostrocaudally. All parts of DNLL do not share the same inputs, and a medial-to-lateral gradient in the labeling of some pathways is evident. To study the efferent connections of DNLL, both retrograde and anterograde axonal transport techniques were used. The DNLL projects to the inferior colliculus and the contralateral DNLL. The topography of these projections suggests that areas of similar tonotopic organization are connected. In the inferior colliculus, the projection is heaviest to the central nucleus and extends to the adjacent dorsal and caudal cortex, the rostral pole nucleus, and the ventrolateral nucleus. Axons from DNLL terminate along the fibrodendritic laminae of the central nucleus as bands that are prominent on the contralateral side, whereas those on the ipsilateral colliculus are more diffuse. The afferent and efferent connections of DNLL constitute a multisynaptic pathway, parallel to the other ascending pathways to the inferior colliculus. The other ascending pathways include the direct pathways from the cochlear nucleus to the inferior colliculus and the indirect pathways via the superior olivary complex. Ascending pathways are discussed as to their relationship to the subdivisions of the inferior colliculus, the laterality of their projections, and their banding patterns in the central nucleus. In contrast to the excitatory pathways to the inferior colliculus, the neurons in DNLL may use GABA as a neurotransmitter. Axons from the DNLL terminate in the inferior colliculus as bands that could have a unique inhibitory function. Thus, the multisynaptic, DNLL pathway may provide feed-forward inhibitory inputs to the inferior colliculus, bilaterally, and to the contralateral DNLL.

Nucleus sagulum: Projections of a lateral tegmental area to the inferior colliculus in the cat

The nucleus sagulum, an area of the midbrain tegmentum, has been considered a component of a lateral tegmental system within the ascending auditory pathway to the thalamus. In this study, connections of the nucleus sagulum within the midbrain were investigated in adult cats. Tracing methods using anterograde and retrograde axonal transport of markers were employed. The nucleus sagulum was identified as a region of principally small neurons (261 +/- 79 micron2) at the margin of the midbrain and neighboring the nuclei of the lateral lemniscus. Injections of tritiated leucine in the nucleus sagulum labeled axons that ended in dense patches within the superficial layers of the caudal portion of the dorsal cortex of the inferior colliculus on the ipsilateral side. Retrograde experiments confirmed this connection. Other axonal projections labeled in the anterograde studies included fibers ending in the dorsomedial nucleus, the superficial layers of the dorsal cortex, and the rostral nucleus of the inferior colliculus with some bilateral distribution. Outside of the inferior colliculus, sagulum injections labeled other axons ending in the ventral intercollicular tegmentum on both sides and in a dorsal and rostral region of the contralateral nucleus sagulum that appeared contiguous with the dorsal nucleus of the lateral lemniscus. The latter region included a population of larger neurons (340-540 micron2) and had different connections with the inferior colliculus. The distribution of axonal labeling after injections in the nucleus sagulum was contrasted with the distribution of projections from several neighboring areas of the lateral tegmentum, including the dorsal nucleus of the lateral lemniscus. None of these areas exhibited connections with the superficial layers of the caudal cortex of the inferior colliculus, which was the major target in the inferior colliculus of the nucleus sagulum. Thus, the results indicated that the nucleus sagulum is distinguished from adjacent regions of the lateral tegmentum by its connectivity. Its association with midbrain auditory pathways is supported by these connections as well as ascending ones to the auditory thalamus.

Mechanics of locomotion and jumping in the horse (Equus): in vivo stress in the tibia and metatarsus

Principal stresses acting in the midshaft cortices of the tibia and metatarsus of the horse were determined from in vivo rosette strain gauge recordings for overground locomotion at different gaits, as well as for jumping and acceleration. Bone stresses were correlated with limb kinematics and ground reaction forces. The results for these two hind limb bones were compared to earlier determinations of locomotor stress in the forelimb radius and metacarpus (Biewener, Thomason &amp; Lanyon, 1983b). Peak stresses generally increased with increasing speed; however, because of greater bending, stresses in the tibia were substantially higher (45%) than in the metatarsus over the range of steady state speeds. Bending of the tibia resulted from significant off‐axis loading by the ground reaction force. In contrast, the metatarsus was loaded in compression due to its close alignment with the ground reaction force. Peak stresses as high as ‐ 53 MPa (caudal cortex) in the tibia and ‐38 MPa (plantar cortex) in the metatarsus acted at a canter. Increased skeletal stress was matched by a corresponding increase in ground reaction force and a decrease in hind limb duty factor. In both bones, peak stresses were significantly greater and differed in their distribution during jumping and acceleration, compared to peak stresses during steady speed locomotion. Maximal values of ‐ 126 MPa (cranial cortex) in the tibia and ‐ 117 MPa (dorsal cortex) in the metatarsus were developed during jumping. These stresses are similar in magnitude to those reported for a range of different sized mammals during strenuous activity and correspond to a safety factor to yield failure of 1.5 to 3. Though generally consistent within an individual bone, the distribution and magnitude of stresses varied about 20% among individuals. This variation was greater for the metatarsus because of its lesser curvature, which diminishes the bone's ability to control for bending in a fixed direction.

Ontogeny of [ 3H]neurotensin binding sites in the rat cerebral cortex: Autoradiographic study

The ontogeny of the neurotensin binding sites in the rat caudal cortex such as the retrosplenial cortex, the visual area containing area 17 and 18, the caudal somatosensory area and temporal area was examined by autoradiography. During the early postnatal period (from birth to day 10), very-high-density [ 3H]neurotensin binding sites were observed in the caudal cortical area, but the number of binding sites decreased markedly with age. On the other hand, the ventral tegmental area and substantia nigra pars compacta had a low density of binding sites at birth, but the density increased until about day 15 and remained even in the adult rat. These findings were confirmed by the biochemical binding analysis.