Peripheral chemoreflex activation with potassium cyanide (KCN) in awake rats or in the working heart-brainstem preparation (WHBP) produces: (a) a sympathoexcitatory/pressor response; (b) bradycardia; and (c) an increase in the frequency of breathing. Our main aim was to evaluate neurotransmitters involved in mediating the sympathoexcitatory component of the chemoreflex within the nucleus tractus solitarii (NTS). In previous studies in conscious rats, the reflex bradycardia, but not the pressor response, was reduced by antagonism of either ionotropic glutamate or purinergic P2 receptors within the NTS. In the present study we evaluated a possible dual role of both P2 and NMDA receptors in the NTS for processing the sympathoexcitatory component (pressor response) of the chemoreflex in awake rats as well as in the WHBP. Simultaneous blockade of ionotropic glutamate receptors and P2 receptors by sequential microinjections of kynurenic acid (KYN, 2 nmol (50 nl) −1 ) and pyridoxalphosphate-6-azophenyl-2 ,4 -disulphonate (PPADS, 0.25 nmol (50 nl) −1 ) into the commissural NTS in awake rats produced a significant reduction in both the pressor (+38 ± 3 versus +8 ± 3 mmHg) and bradycardic responses (−172 ± 18 versus −16 ± 13 beats min −1 ; n = 13), but no significant changes in the tachypnoea measured using plethysmography (270 ± 30 versus 240 ± 21 cycles min −1 , n = 7) following chemoreflex activation in awake rats. Control microinjections of saline produced no significant changes in these reflex responses. In WHBP, microinjection of KYN (2 nmol (20 nl) −1 ) and PPADS (1.6 nmol (20 nl) −1 ) into the commissural NTS attenuated significantly both the increase in thoracic sympathetic activity (+52 ± 2% versus +17 ± 1%) and the bradycardic response (−151 ± 17 versus −21 ± 3 beats min −1 ) but produced no significant changes in the increase of the frequency of phrenic nerve discharge (+0.24 ± 0.02 versus +0.20 ± 0.02 Hz). The data indicate that combined microinjections of PPADS and KYN into the commissural NTS in both awake rats and the WHBP are required to produce a significant reduction in the sympathoexcitatory response (pressor response) to peripheral chemoreflex activation. We conclude that glutamatergic and purinergic mechanisms are part of the complex neurotransmission system of the sympathoexcitatory component of the chemoreflex at the level of the commissural NTS. There is both anatomical and functional evidence that the peripheral chemoreceptor afferents make their first synapses in the nucleus tractus solitarii (NTS) terminating mainly in the commissural NTS (Donoghue et al.

No abstract

There has been a growing interest in the use of bioabsorbable polymers in interference screws for knee ligament reconstruction surgeries. This interest is driven by virtue of the relevant properties exhibited by these polymers. Among such essential properties include excellent biocompatibility and bioabsorption, good integration between graft/bone, in addition to the ease they offer when it comes to surgical revision. This article seeks to report the results obtained from the study aimed at the development of a bioabsorbable interference screw produced by the injection molding process with two distinct polymeric materials: PLDL poly(L,DL-Lactic acid) and a composite PLDL + 30 wt% TCP (β-tricalcium phosphate). Finite element analysis (FEA) was used for the development of the screw design. The mechanical strength of the screws was evaluated, where the maximum torque to break was found to surpass the insertion torque by 136% in PLDL material and by 190% in PLDL+TCP. The mean values of pullout force obtained for PLDL and PLDL+TCP were 1635 N and 809 N, respectively. An in vitro degradation test performed over a period of 180 days helped to assess the mechanical behavior during degradation and facilitated the comparison of the screws based on specific application requirements. The composite material (PLDL +TCP) exhibited a faster degradation process, with 88% loss of mechanical resistance following 180 days of degradation compared with 55% observed in the PLDL material. The results show that the addition of bioactive ceramic TCP contributed toward raising the initial mechanical resistance and acceleration during the process of degradation.