Primary and secondary neural networks of auditory prepulse inhibition: a functional magnetic resonance imaging study of sensorimotor gating of the human acoustic startle response

Feedforward inhibition deficits have been consistently demonstrated in a range of neuropsychiatric conditions using prepulse inhibition (PPI) of the acoustic startle eye-blink reflex when assessing sensorimotor gating. While PPI can be recorded in acutely decerebrated rats, behavioural, pharmacological and psychophysiological studies suggest the involvement of a complex neural network extending from brainstem nuclei to higher order cortical areas. The current functional magnetic resonance imaging study investigated the neural network underlying PPI and its association with electromyographically (EMG) recorded PPI of the acoustic startle eye-blink reflex in 16 healthy volunteers. A sparse imaging design was employed to model signal changes in blood oxygenation level-dependent (BOLD) responses to acoustic startle probes that were preceded by a prepulse at 120 ms or 480 ms stimulus onset asynchrony or without prepulse. Sensorimotor gating was EMG confirmed for the 120-ms prepulse condition, while startle responses in the 480-ms prepulse condition did not differ from startle alone. Multiple regression analysis of BOLD contrasts identified activation in pons, thalamus, caudate nuclei, left angular gyrus and bilaterally in anterior cingulate, associated with EMGrecorded sensorimotor gating. Planned contrasts confirmed increased pons activation for startle alone vs 120-ms prepulse condition, while increased anterior superior frontal gyrus activation was confirmed for the reverse contrast. Our findings are consistent with a primary pontine circuitry of sensorimotor gating that interconnects with inferior parietal, superior temporal, frontal and prefrontal cortices via thalamus and striatum. PPI processes in the prefrontal, frontal and superior temporal cortex were functionally distinct from sensorimotor gating.

GABAergic inhibition in the fear conditioning circuit of the lateral amygdala is potentiated by dopamine D1 agonists

Auditory fear conditioning is dependent on auditory signaling from the medial geniculate (MGm) and the auditory cortex (TE3) to principal neurons of the lateral amygdala (LA). Local circuit GABAergic interneurons are known to inhibit LA principal neurons via fast and slow IPSP's. Stimulation of MGm and TE3 produces excitatory post-synaptic potentials in both LA principal and interneurons, followed by inhibitory post-synaptic potentials. Manipulations of D1 receptors in the lateral and basal amygdala modulate the retrieval of learned association between an auditory CS and foot shock. Here we examined the effects of D1 agonists on GABAergic IPSP's evoked by stimulation of MGm and TE3 afferents in vitro. Whole cell patch recordings were made from principal neurons of the LA, at room temperature, in coronal brain slices using standard methods. Stimulating electrodes were placed on the fiber tracts medial to the LA and at the external capsule/layer VI border dorsal to the LA to activate (0.1-0.2mA) MGm and TE3 afferents respectively. Neurons were held at -55.0 mV by positive current injection to measure the amplitude of the fast IPSP. Changes in input resistance and membrane potential were measured in the absence of current injection. Stimulation of MGm or TE3 afferents produced EPSP's in the majority of principal neurons and in some an EPSP/IPSP sequence. Stimulation of MGm afferents produced IPSP's with amplitudes of -2.30 ± 0.53 mV and stimulation of TE3 afferents produced IPSP's with amplitudes of -1.98 ± 1.26 mV. Bath application of 20μM SKF38393 increased IPSP amplitudes to -5.94 ± 1.62 mV (MGm, n=3) and-5.46 ± 0.31 mV (TE3, n=3). Maximal effect occurred <10mins. A small increase in resting membrane potential and decrease in input resistance were observed. These data suggest that DA modulates both the auditory thalamic and auditory cortical inputs to the LA fear conditioning circuit via local GABAergic circuits. Supported by NIMH Grants 00956, 46516, and 58911.

Human cortical processing of colour and pattern

Investigated human visual processing of simple two-colour patterns using a delayed match to sample paradigm with positron emission tomography (PET). This study is unique in that the authors specifically designed the visual stimuli to be the same for both pattern and colour recognition with all patterns being abstract shapes not easily verbally coded composed of two-colour combinations. The authors did this to explore those brain regions required for both colour and pattern processing and to separate those areas of activation required for one or the other. 10 right-handed male volunteers aged 18–35 yrs were recruited. The authors found that both tasks activated similar occipital regions, the major difference being more extensive activation in pattern recognition. A right-sided network that involved the inferior parietal lobule, the head of the caudate nucleus, and the pulvinar nucleus of the thalamus was common to both paradigms. Pattern recognition also activated the left temporal pole and right lateral orbital gyrus, whereas colour recognition activated the left fusiform gyrus and several right frontal regions.

Inhibition of myeloperoxidase-mediated hypochlorous acid production by nitroxides

Tissue damage resulting from the extracellular production of HOCl (hypochlorous acid) by the MPO (myeloperoxidase)-hydrogen peroxide-chloride system of activated phagocytes is implicated as a key event in the progression of a number of human inflammatory diseases. Consequently, there is considerable interest in the development of therapeutically useful MPO inhibitors. Nitroxides are well established antioxidant compounds of low toxicity that can attenuate oxidative damage in animal models of inflammatory disease. They are believed to exert protective effects principally by acting as superoxide dismutase mimetics or radical scavengers. However, we show here that nitroxides can also potently inhibit MPO-mediated HOCl production, with the nitroxide 4-aminoTEMPO inhibiting HOCl production by MPO and by neutrophils with IC50 values of approx. 1 and 6 μM respectively. Structure–activity relationships were determined for a range of aliphatic and aromatic nitroxides, and inhibition of oxidative damage to two biologically-important protein targets (albumin and perlecan) are demonstrated. Inhibition was shown to involve one-electron oxidation of the nitroxides by the compound I form of MPO and accumulation of compound II. Haem destruction was also observed with some nitroxides. Inhibition of neutrophil HOCl production by nitroxides was antagonized by neutrophil-derived superoxide, with this attributed to superoxide-mediated reduction of compound II. This effect was marginal with 4-aminoTEMPO, probably due to the efficient superoxide dismutase-mimetic activity of this nitroxide. Overall, these data indicate that nitroxides have considerable promise as therapeutic agents for the inhibition of MPO-mediated damage in inflammatory diseases.

Effect of poly(acrylic acid) end-group functionality on inhibition of calcium oxalate crystal growth

A number of series of poly(acrylic acids) (PAA) of differing end-groups and molecular weights prepared using atom transfer radical polymerization were used as inhibitors for the crystallization of calcium oxalate at 23 and 80°C. As measured by turbidimetry and conductivity and as expected from previous reports, all PAA series were most effective for inhibition of crystallization at molecular weights of 1500–4000. However, the extent of inhibition was in general strongly dependent on the hydrophobicity and molecular weight of the end-group. These results may be explicable in terms of adsorption/desorption of PAA to growth sites on crystallites. The overall effectiveness of the series didn't follow a simple trend with end-group hydrophobicity, suggesting self-assembly behavior or a balance between adsorption and desorption rates to crystallite surfaces may be critical in the mechanism of inhibition of calcium oxalate crystallization.

In vivo knockdown of the androgen receptor results in growth inhibition and regression of well-established, castration-resistant prostate tumours

Purpose: Progression to the castration-resistant state is the incurable and lethal end stage of prostate cancer, and there is strong evidence that androgen receptor (AR) still plays a central role in this process. We hypothesize that knocking down AR will have a major effect on inhibiting growth of castration-resistant tumors. Experimental Design: Castration-resistant C4-2 human prostate cancer cells stably expressing a tetracycline-inducible AR-targeted short hairpin RNA (shRNA) were generated to directly test the effects of AR knockdown in C4-2 human prostate cancer cells and tumors. Results:In vitro expression of AR shRNA resulted in decreased levels of AR mRNA and protein, decreased expression of prostate-specific antigen (PSA), reduced activation of the PSA-luciferase reporter, and growth inhibition of C4-2 cells. Gene microarray analyses revealed that AR knockdown under hormone-deprived conditions resulted in activation of genes involved in apoptosis, cell cycle regulation, protein synthesis, and tumorigenesis. To ensure that tumors were truly castration-resistant in vivo, inducible AR shRNA expressing C4-2 tumors were grown in castrated mice to an average volume of 450 mm3. In all of the animals, serum PSA decreased, and in 50% of them, there was complete tumor regression and disappearance of serum PSA. Conclusions: Whereas castration is ineffective in castration-resistant prostate tumors, knockdown of AR can decrease serum PSA, inhibit tumor growth, and frequently cause tumor regression. This study is the first direct evidence that knockdown of AR is a viable therapeutic strategy for treatment of prostate tumors that have already progressed to the castration-resistant state.

Ovine cortical osteoblasts outperform bone marrow cells in an ectopic bone assay

Reviewing the available literature, one could conclude that marrow-derived mesenchymal stem cells (BMSCs) are the ‘gold standard’ source for bone tissue engineering applications, due to their multilineage differentiation potential and easy accessibility. However, comprehensive studies comparing their osteogenic potential with bone-derived osteoblasts (OBs) to justify the preferred application of BMSCs based on performance are few. To address these shortfalls, in the present study, ovine BMSCs and OBs seeded onto scaffolds were characterized in vitro and transplanted subcutaneously into NOD/SCID mice in combination with and without recombinant human bone morphogenetic protein 7 (rhBMP-7). It was hypothesized that cell origin, ossification type and degree of vascularization and ossification depends on the nature and commitment of transplanted cells and stimulating growth factors, such as rhBMP-7. After retrieval, specimens were analysed by biomechanical testing, µCT analysis, scanning electron microscopy/energy-dispersive X-ray spectroscopy and histo- and immunohistochemistry for osteocalcin, type II collagen and BrdU. The results showed a high degree of cell survival and proliferation ectopically, resulting in active contribution to endochondral osteogenesis. When compared to BMSCs, OBs showed a higher degree of bone deposition while OB-derived bone was of higher maturation. Stimulation with rhBMP-7 increased the rate of bone synthesis for both BMSCs and OBs, additionally promoting neovascularization and osteoclast activity. These results suggest that the origin and commitment of transplanted cells highly influence the type and degree of ossification, that rhBMP-7 represents a powerful adjuvant for bone tissue-engineering applications, and that mature bone is an adequate alternative cell source for bone tissue-engineering applications.

Inhibition of integrative cartilage repair by proteoglycan 4 in synovial fluid

To determine the effects of the articular cartilage surface, as well as synovial fluid (SF) and its components, specifically proteoglycan 4 (PRG4) and hyaluronic acid (HA), on integrative cartilage repair in vitro. Methods. Blocks of calf articular cartilage were harvested, some with the articular surface intact and others without. Some of the latter types of blocks were pretreated with trypsin, and then with bovine serum albumin, SF, PRG4, or HA. Immunolocalization of PRG4 on cartilage surfaces was performed after treatment. Pairs of similarly treated cartilage blocks were incubated in partial apposition for 2 weeks in medium supplemented with serum and 3 H-proline. Following culture, mechanical integration between apposed cartilage blocks was assessed by measuring adhesive strength, and protein biosynthesis and deposition were determined by incorporated 3 H-proline. Results. Samples with articular surfaces in apposition exhibited little integrative repair compared with samples with cut surfaces in apposition. PRG4 was immunolocalized at the articular cartilage surface, but not in deeper, cut surfaces (without treatment). Cartilage samples treated with trypsin and then with SF or PRG4 exhibited an inhibition of integrative repair and positive immunostaining for PRG4 at treated surfaces compared with normal cut cartilage samples, while samples treated with HA exhibited neither inhibited integrative repair nor PRG4 at the tissue surfaces. Deposition of newly synthesized protein was relatively similar under conditions in which integration differed significantly. Conclusion. These results support the concept that PRG4 in SF, which normally contributes to cartilage lubrication, can inhibit integrative cartilage repair. This has the desirable effect of preventing fusion of apposing surfaces of articulating cartilage, but has the undesirable effect of inhibiting integrative repair.