Biomedical subjects

Juan Carlos Tapia

Publications and source records attributed to Juan Carlos Tapia.

4 recordsLinked to original sources

PubMed2004

Gamma protocadherins are required for synaptic development in the spinal cord.

Fifty-eight cadherin-related protocadherin (Pcdh) genes are tandemly arrayed in three clusters (alpha, beta, and gamma) on mouse chromosome 18. The large number of clustered Pcdh family members, their presence at synapses, and the known binding specificities of other cadherin superfamily members all suggest that these Pcdhs play roles in specifying synaptic connectivity. Consistent with this idea, mice lacking all 22 genes of the Pcdh-gamma cluster have decreased numbers of spinal cord synapses and are nearly immobile. Interpretation of this phenotype was complicated, however, by the fact that Pcdh-gamma loss also led to apoptosis of many spinal interneurons. Here, we used two methods to circumvent apoptosis and neurodegeneration in Pcdh-gamma mutant mice. First, we analyzed mutants lacking both Pcdh-gamma proteins and the proapoptotic protein Bax. Second, we generated a hypomorphic allele of Pcdh-gamma in which apoptosis was minimal. In both cases, spinal interneurons were preserved but the mice bore dramatically decreased numbers of spinal cord synapses and exhibited profound neurological defects. Moreover, synaptic function was compromised in neurons cultured from the hypomorphs. These results provide evidence for a direct role of gamma-Pcdhs in synaptic development and establish genetic tools for elucidating their contribution to synaptic specificity.

Animals↗

PubMed2004

Lethal impairment of cholinergic neurotransmission in hemicholinium-3-sensitive choline transporter knockout mice.

Presynaptic acetylcholine (ACh) synthesis and release is thought to be sustained by a hemicholinium-3-sensitive choline transporter (CHT). We disrupted the murine CHT gene and examined CHT-/- and +/- animals for evidence of impaired cholinergic neurotransmission. Although morphologically normal at birth, CHT-/- mice become immobile, breathe irregularly, appear cyanotic, and die within an hour. Hemicholinium-3-sensitive choline uptake and subsequent ACh synthesis are specifically lost in CHT-/- mouse brains. Moreover, we observe a time-dependent loss of spontaneous and evoked responses at CHT-/- neuromuscular junctions. Consistent with deficits in synaptic ACh availability, we also observe developmental alterations in neuromuscular junction morphology reminiscent of changes in mutants lacking ACh synthesis. Adult CHT+/- mice overcome reductions in CHT protein levels and sustain choline uptake activity at wild-type levels through posttranslational mechanisms. Our results demonstrate that CHT is an essential and regulated presynaptic component of cholinergic signaling and indicate that CHT warrants consideration as a candidate gene for disorders characterized by cholinergic hypofunction.

Acetylcholine↗

PubMed2003

Developmental-dependent action of microtubule depolymerization on the function and structure of synaptic glycine receptor clusters in spinal neurons.

Microtubules have been proposed to interact with gephyrin/glycine receptors (GlyRs) in synaptic aggregates. However, the consequence of microtubule disruption on the structure of postsynaptic GlyR/gephyrin clusters is controversial and possible alterations in function are largely unknown. In this study, we have examined the physiological and morphological properties of GlyR/gephyrin clusters after colchicine treatment in cultured spinal neurons during development. In immature neurons (5-7 DIV), disruption of microtubules resulted in a 33 +/- 4% decrease in the peak amplitude and a 72 +/- 15% reduction in the frequency of spontaneous glycinergic miniature postsynaptic currents (mIPSCs) recorded in whole cell mode. However, similar colchicine treatments resulted in smaller effects on 10-12 DIV neurons and no effect on mature neurons (15-17 DIV). The decrease in glycinergic mIPSC amplitude and frequency reflects postsynaptic actions of colchicine, since postsynaptic stabilization of microtubules with GTP prevented both actions and similar reductions in mIPSC frequency were obtained by modifying the Cl(-) driving force to obtain parallel reductions in mIPSC amplitude. Confocal microscopy revealed that colchicine reduced the average length and immunofluorescence intensity of synaptic gephyrin/GlyR clusters in immature (approximately 30%) and intermediate (approximately 15%) neurons, but not in mature clusters. Thus the structural and functional changes of postsynaptic gephyrin/GlyR clusters after colchicine treatment were tightly correlated. Finally, RT-PCR, kinetic analysis and picrotoxin blockade of glycinergic mIPSCs indicated a reorganization of the postsynaptic region from containing both alpha2beta and alpha1beta GlyRs in immature neurons to only alpha1beta GlyRs in mature neurons. Microtubule disruption preferentially affected postsynaptic sites containing alpha2beta-containing synaptic receptors.

Animals↗

PubMed2003

Lung computed tomography during a lung recruitment maneuver in patients with acute lung injury.

OBJECTIVE: To assess the acute effect of a lung recruitment maneuver (LRM) on lung morphology in patients with acute lung injury (ALI) or acute respiratory distress syndrome (ARDS). PATIENTS: Ten patients with ALI/ARDS on mechanical ventilation. DESIGN: Prospective clinical study. SETTING: Computed tomography (CT) scan facility in a teaching hospital. INTERVENTIONS: An LRM performed by stepwise increases in positive end-expiratory pressure (PEEP) of up to 30-40 cm H(2)O. Lung basal CT sections were taken at end-expiration (patients 1 to 5), and at end-expiration and end-inspiration (patients 6 to 10). Arterial blood gases and static compliance (C(st)) were measured before, during and after the LRM. MEASUREMENTS AND MAIN RESULTS: Poorly aerated and non-aerated tissue at PEEP 10 cm H(2)O accounted for 60.0+/-29.1% of lung parenchyma, while only 1.1+/-1.8% was hyperinflated. Increasing PEEP to 20 and 30 cm H(2)O, compared to PEEP 10 cm H(2)O, decreased poorly aerated and non-aerated tissue by 16.2+/-28.0% and 33.4+/-13.8%, respectively ( p<0.05). This was associated with an increase in PaO(2) and a decrease in total static compliance. Inspiration increased alveolar recruitment at all PEEP levels. Hyperinflated tissue increased up to 2.9+/-4.0% with PEEP 30 cm H(2)O, and to a lesser degree with inspiration. No barotrauma or severe hypotension occurred. CONCLUSIONS: Lung recruitment maneuvers improve oxygenation by expanding collapsed alveoli without inducing too much hyperinflation in ALI/ARDS patients. An LRM during the CT scan gives morphologic and functional information that could be useful in setting ventilatory parameters.

Adult↗