A Cross-Sectional Study of Bone Nanomechanics in Hip Fracture and Aging.

Bone mechanics is well understood at every length scale except the nano-level. We aimed to investigate the relationship between bone nanoscale and tissue-level mechanics experimentally. We tested two hypotheses: (1) nanoscale strains were lower in hip fracture patients versus controls, and (2) nanoscale mineral and fibril strains were inversely correlated with aging and fracture. A cross-sectional sample of trabecular bone sections was prepared from the proximal femora of two human donor groups (aged 44-94 years): an aging non-fracture control group (n = 17) and a hip-fracture group (n = 20). Tissue, fibril, and mineral strain were measured simultaneously using synchrotron X-ray diffraction during tensile load to failure, then compared between groups using unpaired t-tests and correlated with age using Pearson's correlation. Controls exhibited significantly greater peak tissue, mineral, and fibril strains than the hip fracture (all p < 0.05). Age was associated with a decrease in peak tissue (p = 0.099) and mineral (p = 0.004) strain, but not fibril strain (p = 0.260). Overall, hip fracture and aging were associated with changes in the nanoscale strain that are reflected at the tissue level. Data must be interpreted within the limitations of the observational cross-sectional study design, so we propose two new hypotheses on the importance of nanomechanics. (1) Hip fracture risk is increased by low tissue strain, which can be caused by low collagen or mineral strain. (2) Age-related loss of tissue strain is dependent on the loss of mineral but not fibril strain. Novel insights into bone nano- and tissue-level mechanics could provide a platform for the development of bone health diagnostics and interventions based on failure mechanisms from the nanoscale up.

Nanoscale mechanisms in age-related hip-fractures.

Nanoscale mineralized collagen fibrils may be important determinants of whole-bone mechanical properties and contribute to the risk of age-related fractures. In a cross-sectional study nano- and tissue-level mechanics were compared across trabecular sections from the proximal femora of three groups (n = 10 each): ageing non-fractured donors (Controls); untreated fracture patients (Fx-Untreated); bisphosphonate-treated fracture patients (Fx-BisTreated). Collagen fibril, mineral and tissue mechanics were measured using synchrotron X-Ray diffraction of bone sections under load. Mechanical data were compared across groups, and tissue-level data were regressed against nano. Compared to controls fracture patients exhibited significantly lower critical tissue strain, max strain and normalized strength, with lower peak fibril and mineral strain. Bisphosphonate-treated exhibited the lowest properties. In all three groups, peak mineral strain coincided with maximum tissue strength (i.e. ultimate stress), whilst peak fibril strain occurred afterwards (i.e. higher tissue strain). Tissue strain and strength were positively and strongly correlated with peak fibril and mineral strains. Age-related fractures were associated with lower peak fibril and mineral strain irrespective of treatment. Indicating earlier mineral disengagement and the subsequent onset of fibril sliding is one of the key mechanisms leading to fracture. Treatments for fragility should target collagen-mineral interactions to restore nano-scale strain to that of healthy bone.

Spatially offset Raman spectroscopy for photon migration studies in bones with different mineralization levels.

The ability of Spatially Offset Raman Spectroscopy (SORS) to obtain chemically specific information from below the sample surface makes it a promising technique for non-invasive in vivo diagnosis of bone conditions by sampling bone through the skin. The depth below a surface interrogated by SORS depends on the system's optical properties and is difficult to estimate for complex bone material. This paper uses 830 nm laser excitation to investigate the influence of bone mineralization on photon migration properties in deer antler cortex, equine metacarpal cortex and whale tympanic bulla. Thin slices form each type of bone (thickness: 0.6-1.0 mm) were cut and put together on top of each other forming stacks with a total thickness of 4.1-4.7 mm. A 0.38 mm thin slice of polytetrafluoroethylene (PTFE) served as a test material for Raman signal recovery and was placed in between the individual bone slices within the stack. At SORS offsets of 8.0-9.5 mm Raman bands of materials not present in healthy bone (e.g. PTFE as an example) can be recovered through 4.4-4.7 mm of cortical bone tissue, depending on mineralization level and porosity. These findings significantly increase our understanding of SORS analysis through bones of different composition and provide information that is vital to determine the value of SORS as a medical diagnostic technique. The data serve to define which SORS offset is best deployed for the non-invasive detection of chemically specific markers associated with infection, degeneration and disease or cancer within bone.

Is the Collagen Primed for Mineralization in Specific Regions of the Turkey Tendon? An Investigation of the Protein-Mineral Interface Using Raman Spectroscopy.

The tendons in the turkey leg have specific well-defined areas which become mineralized as the animal ages and they are a thoroughly characterized model system for studying the mineralization process of bone. In this study, nondestructive Raman spectroscopic analysis was used to explore the hypothesis that regions of the turkey tendon that are associated with mineralization exhibit distinct and observable chemical modifications of the collagen prior to the onset of mineralization. The Raman spectroscopy features associated with mineralization were identified by probing (on the micrometer scale) the transition zone between mineralized and nonmineralized regions of turkey leg tendons. These features were then measured in whole tendons and identified in regions of tendon which are destined to become rapidly mineralized around 14 weeks of age. The data show there is a site-specific difference in collagen prior to the deposition of mineral, specifically the amide III band at 1270 cm(-1) increases as the collagen becomes more ordered (increased amide III:amide I ratio) in regions that become mineralized compared to collagen destined to remain nonmineralized. If this mechanism were present in materials of different mineral fraction (and thus material properties), it could provide a target for controlling mineralization in metabolic bone disease.

Age-related changes in insula cortical thickness and impulsivity: significance for emotional development and decision-making.

Insula function has been associated with emotional regulation, adjusting to changing outcomes under risk, reward and loss anticipation, discounting of future rewards, and self-rated impulsivity. The role of the insula in these processes may be fundamentally related to prospective thinking, a trait that increases with age. There is evidence that insular cortical thickness shows age related decreases that parallel age related increases in future orientation and planning. We tested the hypothesis that nonplanning decreases with age and that insula thickness is related to both age and nonplanning impulsivity. Fifty-nine male and female participants, ranging in age from 10 to 22 years old, underwent structural magnetic resonance imaging (MRI) procedures and were assessed using the Barratt Impulsiveness Scale (BIS). We observed that anterior insula thickness and nonplanning impulsivity show an inverse relationship with age and that there is a significant positive linear relationship between anterior insula thickness and nonplanning.

Temporal associations for spatial events: the role of the dentate gyrus.

Previous research suggests that the dorsal dentate gyrus (DG) hippocampal subregion mediates spatial processing functions. However, a novel role for the DG in temporal processing for spatial information has begun to emerge based on the development of a computational model of neurogenesis. According to this model, adult born granule cells in the DG contribute to a temporal associative integration process for events presented closer in time. Currently, there is a paucity of behavioral evidence to support the temporal integration theory. Therefore, we developed a novel behavioral paradigm to investigate the role of the dDG in temporal integration for proximal and distal spatial events. Male Long-Evans rats were randomly assigned to a control group or to receive bilateral intracranial infusions of colchicine into the dDG. Following recovery from surgery, each rat was tested on a cued-recall of sequence paradigm. In this task, animals were allowed to explore identical objects placed in designated spatial locations on a cheeseboard maze across 2 days (e.g., Day 1: A and B; Day 2: C and D). One week later, animals were given a brief cue (A or C) followed by a preference test between spatial location B and D. Control animals had a significant preference for the spatial location previously paired with the cue (the temporal associate) whereas dDG lesioned animals failed to show a preference. These findings suggest that selective colchicine-induced dDG lesions are capable of disrupting the formation of temporal associations between spatial events presented close in time.

The role of the dentate gyrus in the formation of contextual representations.

The hippocampus is involved in encoding and integrating contextual information. Recently, it has been suggested that the dorsal dentate gyrus (dDG) hippocampal subregion may mediate the formation of contextual representations of the spatial environment through a conjunctive encoding process whereby incoming multimodal information is integrated into a single higher-order representation. Despite anatomical evidence in support of this claim, behavioral evidence is limited. Therefore, a contextual associative learning paradigm was used to determine whether the dDG supports the formation of integrated contextual representations. Male Long-Evans rats were randomly assigned as controls or to receive bilateral intracranial infusions of colchicine into the dDG. Following recovery from surgery, each rat was tested on an appetitive task that required animals to form an association between a cue (odor) and a context to receive a food reward. Each rat received 10 trials per day and was tested for 10 consecutive days. Upon completion of testing, animals were tested on an additional two-choice olfactory and contextual discrimination task. The testing order was counterbalanced across animals. Results showed that control animals successfully acquired the contextual associative learning task for olfactory stimuli as indicated by improved performance across the 10 testing days. In contrast, animals with dDG lesions were impaired in the ability to acquire the odor-context associations. Results from follow-up odor and context discrimination tests indicated that both groups acquired the discriminations at similar rates. Therefore, it is unlikely that deficits in performance on the contextual associative learning task were due to an inability to discriminate between odors or contexts. The present findings provide further support for DG involvement in the formation of conjunctive contextual representations.

Abnormal striatal circuitry and intensified novelty seeking among adolescents who abuse methamphetamine and cannabis.

It has been hypothesized that changes in striatal-mediated dopamine modulation during adolescence may increase the risk for initiating substance abuse as a result of its fundamental role in arbitrating reward sensitivity and motivation during learning and decision making. However, substance abuse during adolescence may also significantly modify striatal structure and function and concomitantly alter reward sensitivity and action control while this brain region is undergoing remodeling. In the present investigation, to assess the relationship of methamphetamine (Meth) or Meth and cannabis (CA) abuse to regional striatal morphology, we acquired structural magnetic resonance images, using a 3T Siemens Trio scanner, from three groups of adolescents composed of healthy controls (n = 10), Meth abusers (n = 9) and combined Meth and CA abusers (Meth+CA, n = 8). We also assessed novelty seeking using the novelty seeking subscale of Cloninger's Tridimensional Character Inventory. The results indicate that adolescent Meth+CA abusers have increased regional striatal volume and show intensified novelty seeking in contrast to the controls. The degree of Meth exposure was also positively correlated with regional striatal volume and novelty seeking in both the Meth and Meth+CA users. These preliminary findings support theories that propose a role for the striatum in adolescent substance abuse and further indicate that novelty seeking may be related to the initiation of, or sustained, drug use.

Selective lesions of the dentate gyrus produce disruptions in place learning for adjacent spatial locations.

The hippocampus (HPP) plays a known role in learning novel spatial information. More specifically, the dentate gyrus (DG) hippocampal subregion is thought to support pattern separation, a mechanism for encoding and separating spatially similar events into distinct representations. Several studies have shown that lesions of the dorsal DG (dDG) in rodents result in inefficient spatial pattern separation for working memory; however, it is unclear whether selective dDG lesions disrupt spatial pattern separation for reference memory. Therefore, the current study investigated the role of the dDG in pattern separation using a spatial reference memory paradigm to determine whether the dDG is necessary for acquiring spatial discriminations for adjacent locations. Male Long-Evans rats were randomly assigned to receive bilateral intracranial infusions of colchicine or saline (control) into the dDG. Following recovery from surgery, each rat was pseudo-randomly assigned to an adjacent arm or separate arm condition and subsequently tested on a place-learning task using an eight-arm radial maze. Rats were trained to discriminate between a rewarded arm and a nonrewarded arm that were either adjacent to one another or separated by a distance of two arm positions. Each rat received 10 trials per day and was tested until the animal reached a criterion of nine correct choices out of 10 consecutive trials across 2 consecutive days of testing. Both groups acquired spatial discriminations for the separate condition at similar rates. However, in the adjacent condition, dDG lesioned animals required significantly more trials to reach the learning criterion than controls. The results suggest that dDG lesions decrease efficiency in pattern separation resulting in impairments in the adjacent condition involving greater overlap among the distal cues. Conversely, in the separate condition, there was less overlap among distal cues during encoding and less need for pattern separation. These findings provide further support for a critical role for the dDG in spatial pattern separation by demonstrating the importance of a processing mechanism that is capable of reducing interference among overlapping spatial inputs across a variety of memory demands.

Hippocampal-prefrontal dynamics in spatial working memory: interactions and independent parallel processing.

Memory processes may be independent, compete, operate in parallel, or interact. In accordance with this view, behavioral studies suggest that the hippocampus (HPC) and prefrontal cortex (PFC) may act as an integrated circuit during performance of tasks that require working memory over longer delays, whereas during short delays the HPC and PFC may operate in parallel or have completely dissociable functions. In the present investigation we tested rats in a spatial delayed non-match to sample working memory task using short and long time delays to evaluate the hypothesis that intermediate CA1 region of the HPC (iCA1) and medial PFC (mPFC) interact and operate in parallel under different temporal working memory constraints. In order to assess the functional role of these structures, we used an inactivation strategy in which each subject received bilateral chronic cannula implantation of the iCA1 and mPFC, allowing us to perform bilateral, contralateral, ipsilateral, and combined bilateral inactivation of structures and structure pairs within each subject. This novel approach allowed us to test for circuit-level systems interactions, as well as independent parallel processing, while we simultaneously parametrically manipulated the temporal dimension of the task. The current results suggest that, at longer delays, iCA1 and mPFC interact to coordinate retrospective and prospective memory processes in anticipation of obtaining a remote goal, whereas at short delays either structure may independently represent spatial information sufficient to successfully complete the task.

An analysis of rat prefrontal cortex in mediating executive function.

While it is acknowledged that species specific differences are an implicit condition of comparative studies, rodent models of prefrontal function serve a significant role in the acquisition of converging evidence on prefrontal function across levels of analysis and research techniques. The purpose of the present review is to examine whether the prefrontal cortex (PFC) in rats supports a variety of processes associated with executive function including working memory, temporal processing, planning (prospective coding), flexibility, rule learning, and decision making. Therefore, in this review we examined changes associated with working memory processes for spatial locations, visual objects, odors, tastes, and response domains or attributes, temporal processes including temporal order, sequence learning, prospective coding, behavioral flexibility associated with reversal learning and set shifting, paired associate learning, and decision making based on effort, time discounting, and uncertainty following damage to the PFC in rats. In addition, potential parallel processes of executive function in monkeys and humans based on several theories of subregional differentiation within the PFC will be presented. Specifically, theories based on domain or attribute specificity (Goldman-Rakic, 1996), level of processing (Petrides, 1996), rule learning based on complexity (Wise, Murray, & Gerfen, 1996), executive functions based on connectivity with other brain regions associated with top-down control (Miller & Cohen, 2001), are presented and applied to PFC function in rats with the aim of understanding subregional specificity in the rat PFC. The data suggest that there is subregional specificity within the PFC of rats, monkey and humans and there are parallel cognitive functions of the different subregions of the PFC in rats, monkeys and humans.

Neuroimaging correlates of traumatic brain injury and suicidal behavior.

INTRODUCTION: There is an urgent need to define the neurobiological and cognitive underpinnings of suicidal ideation and behavior in veterans with traumatic brain injury (TBI). Separate studies implicate frontal white matter systems in the pathophysiology of TBI, suicidality, and impulsivity. We examined the relationship between the integrity of major frontal white matter (WM) systems on measures of impulsivity and suicidality in veterans with TBI. METHODS: Fifteen male veterans with TBI and 17 matched healthy controls (HC) received clinical ratings, measures of impulsivity and MRI scans on a 3T magnet. Diffusion tensor imaging (DTI) data for the genu and cingulum were analyzed using Freesurfer and FSL. Correlations were performed for fractional anisotropy (FA) (DTI) values and measures of suicidality and impulsivity for veterans with TBI. RESULTS: Significantly decreased in FA values in the left cingulum (P = 0.02), and left (P = 0.02) and total genu (P = 0.01) were observed in the TBI group relative to controls. Measures of impulsivity were significantly greater for the TBI group and total and right cingulum FA positively correlated with current suicidal ideation and measures of impulsivity (P <0.03). CONCLUSION: These data demonstrate a significant reduction in FA in frontal WM tracts in veterans with mild TBI that was associated with both impulsivity and suicidality. These findings may reflect a neurobiological vulnerability to suicidal risk related to white matter microstructure.

Prefrontal and hippocampal contributions to encoding and retrieval of spatial memory.

The prefrontal cortex is thought to be critical for goal-directed action and the hippocampus is known to be importantly involved in spatial memory. Several studies have been suggestive of a role for the orbitofrontal cortex (OFC) in spatial navigation. However, the medial prefrontal cortex (mPFC) receives projections directly from the intermediate CA1 (iCA1) region of hippocampus and this link may be critical for spatial navigation. The purpose of the present investigation was to test the performance of rats receiving bilateral or disconnection infusions of lidocaine into OFC, mPFC, or iCA1 to determine the contribution of these structures to encoding and retrieval of spatial memory using the Hebb-Williams maze. A total of 92 male Long-Evans rats received chronic bilateral, contralateral, or ipsilateral implantation of cannulas into OFC, mPFC, or iCA1. Prior to testing on day 1 or day 2, subjects received central infusions of saline or lidocaine. The number of errors committed on the first five trials compared to the second five trials of day 1 was used to determine encoding, whereas retrieval was determined by comparing the second five trials of day 1 with the first five trials of day 2. The present findings suggest that mPFC and iCA1 are necessary and interact during encoding and retrieval; however, the OFC does not appear to be essential for either process. While the nature of the interaction between mPFC and iCA1 during encoding and retrieval is unclear, it may be supported by the integration of goals and spatial cues or strategy switching.

Altered frontal cortical volume and decision making in adolescent cannabis users.

Anticipating future outcomes is central to decision making and a failure to consider long-term consequences may lead to impulsive choices. Adolescence is a vulnerable period during which underdeveloped prefrontal cortical systems may contribute to poor judgment, impulsive choices, and substance abuse. Conversely, substance abuse during this period may alter neural systems involved in decision making and lead to greater impulsivity. Although a broad neural network which supports decision making undergoes extensive change during adolescent development, one region that may be critical is the medial prefrontal cortex. Altered functional integrity of this region may be specifically related to reward perception, substance abuse, and dependence. In the present investigation, we acquired structural magnetic resonance images (MRI), using a 3T Siemens Trio scanner, from 18 cannabis abusing adolescents (CA; 2 female and 16 male subjects; mean age, 17.7 years; range 16-19 years), and 18 healthy controls (HC; 6 female and 12 male subjects; mean age, 17.2 years; range 16-19 years). In order to measure medial orbital prefrontal cortex (moPFC) morphology related to substance abuse and impulsivity, semi-automated cortical reconstruction and volumetric segmentation of MRIs was performed with FreeSurfer. Impulsivity was evaluated with the Barratt Impulsiveness Scale (BIS). Our results indicate that cannabis abusing adolescents have decreased right moPFC volume compared to controls, p = 0.01, d = 0.92, CI(0.95) = 0.21, 1.59. Cannabis abusing adolescents also show decreased future orientation, as indexed by the BIS non-planning subscale, when compared to controls, p = 0.01, d = 0.89, CI(0.95) = 0.23, 1.55. Moreover, total moPFC volume was positively correlated with age of first use r (18) = 0.49, p < 0.03, suggesting that alterations in this region may be related to initiation of cannabis use or that early initiation may lead to reduced moPFC volume.

Interactions between the prefrontal cortex and amygdala during delay discounting and reversal.

Interactions between the prefrontal cortex and amygdala are thought to be critical for reward anticipation. Alterations in reward anticipation that lead to an inability to wait for rewards or a diminished capacity to change behavior when doing so would be optimal are often termed impulsivity and compulsivity, respectively. Distinct regions of the prefrontal cortex may support decreased impulsivity through self-control and decreased compulsivity through flexibility. However, both self-control and flexibility appear to involve the amygdala. Using a delay discounting paradigm, the current investigation found that inactivation and disconnection of the medial prefrontal cortex and basolateral amygdala led rats to become more impulsive by affecting preference for smaller immediate over larger delayed rewards. Conversely, inactivation and disconnection of the orbitofrontal cortex and amygdala led rats to become more compulsive as demonstrated by an inability to flexibly reverse stimulus-reward relationships in an odor reversal task. The current findings support a double dissociation between orbitofrontal cortex-amygdala interactions for odor reversal and medial prefrontal cortex-amygdala interactions for delay discounting.

Post-training lesions of the medial prefrontal cortex interfere with subsequent performance of trace eyeblink conditioning.

Rabbits were trained on trace eyeblink (EB) conditioning until they reached a criterion of 10 consecutive EB conditioned responses (CRs). Electrolytic lesions were made in the medial prefrontal cortex (mPFC) centered on the prelimbic area (Brodmann's area 32), at five different intervals after training. These included immediately, 24 h, 1 and 2 weeks, and 1 month after training. Separate groups of animals received sham lesions at these same intervals after training. After a 2 week postoperative recovery period, all animals were retested for 3 d on trace conditioning, using the same parameters used during preoperative training. Mean EB conditioning performance deficits occurred in the animals with mPFC lesions compared with sham-lesioned animals on the first day of retesting in all five groups. However, by the second or third day of retesting, the rabbits with lesions were performing at a level that was comparable with that of sham animals. Rabbits that received more posterolateral lesions of the neocortex did not, however, show postoperative conditioning deficits. A comparison of percentage EB CRs of animals with postoperative training with that of animals that received mPFC lesions before training suggests that the mPFC post-training lesions produce damage to a retrieval process and not to a storage site or an acquisition process.

Medial prefrontal lesions and Pavlovian eyeblink and heart rate conditioning: effects of partial reinforcement on delay and trace conditioning in rabbits (Oryctolagus cuniculus).

Effects of continuous (100%) versus partial (25%) reinforcement were studied on Pavlovian delay and trace eyeblink conditioning in rabbits (Oryctolagus cuniculus) with either lesions to the medial prefrontal cortex (mPFC) or sham lesions. Concomitant heart rate changes evoked by the conditioned stimulus were also assessed. Partial reinforcement retarded eyeblink conditioning in both the trace and delay paradigm, but this impairment was greater during trace conditioning and in rabbits with mPFC lesions. Accompanying conditioned stimulus-evoked heart rate slowing was attenuated under all conditions by the mPFC lesions, although this result was not always statistically significant.

Heart rate changes accompanying jaw movement Pavlovian conditioning in rabbits: concomitant blood pressure adjustments and effects of peripheral autonomic blockade.

Two experiments were conducted to ascertain the cardiovascular accompaniments of differential Pavlovian jaw movement (JM) conditioning. The first examined the blood pressure (BP) changes that accompany the tachycardiac conditioned responses (CRs) associated with JM conditioning. The BP response in all instances consisted of a depressor response that was greater to the reinforced CS+ than CS-, although the magnitude of the CR was quite small. The second experiment determined the effects of peripheral autonomic antagonists on the cardiac accelerations associated with JM conditioning. It was found that the peripheral vagal antagonist methyl scopolamine completely abolished responses to both CS+ and CS-, whereas atenolol, a beta adrenergic antagonist, augmented the response, compared to saline control injections. The JM responses were also affected by the autonomic blockades, with minimal responding occurring in the scopolamine group but slightly more JM CRs in the atenolol group, compared to saline control animals. These results suggest that the major cardiovascular response to an appetitive stimulus, which evokes JM conditioning, consists of cardiac accelerations with the BP depressor responses playing a minimal, if any, role. Moreover, these conditioned cardiac increases appear to be due solely to the release of vagal inhibition.

Medial prefrontal cortex and pavlovian conditioning: trace versus delay conditioning.

Pavlovian eyeblink (EB) conditioning was studied in both trace and delay paradigms in rabbits (Oryctolagus cuniculus) with either medial prefrontal cortex (mPFC) lesions or sham lesions. mPFC lesions of prelimbic cortex (Brodmann's Area 32) retarded EB conditioning in the trace but not the delay paradigm. However, this effect was significant only when the conditioned stimulus (CS) was 500 rather than 100 ms in duration. Lesions of the anterior cingulate cortex (Area 24) did not affect EB conditioning in a trace paradigm. Accompanying CS-evoked heart rate slowing was attenuated under all conditions by the mPFC lesions, although this result was not always statistically significant.