Teaching Diagnostic Reasoning to Medical Students: a four-step approach.

Diagnosis is fundamental to clinical medicine, and diagnostic errors are a serious public health problem. However, there is little consensus regarding the best approach to teaching diagnostic reasoning in medical schools. One approach ("pattern recognition") uses learned associations between patient symptoms and signs and human disorders to help experienced clinicians solve problems rapidly and efficiently.

Combined computational and experimental approaches to understanding the Ca(2+) regulatory network in neurons.

Ca(2+) is a ubiquitous signaling ion that regulates a variety of neuronal functions by binding to and altering the state of effector proteins. Spatial relationships and temporal dynamics of Ca(2+) elevations determine many cellular responses of neurons to chemical and electrical stimulation. There is a wealth of information regarding the properties and distribution of Ca(2+) channels, pumps, exchangers, and buffers that participate in Ca(2+) regulation.

Enhanced synaptic inhibition disrupts the efferent code of cerebellar Purkinje neurons in leaner Cav2.1 Ca 2+ channel mutant mice.

Cerebellar Purkinje cells (PCs) encode afferent information in the rate and temporal structure of their spike trains. Both spontaneous firing in these neurons and its modulation by synaptic inputs depend on Ca(2+) current carried by Ca(v)2.1 (P/Q) type channels.

Impact of the leaner P/Q-type Ca2+ channel mutation on excitatory synaptic transmission in cerebellar Purkinje cells.

Loss-of-function mutations in the gene encoding P/Q-type Ca(2+) channels cause cerebellar ataxia in mice and humans, but the underlying mechanism(s) are unknown. These Ca(2+) channels play important roles in regulating both synaptic transmission and intrinsic membrane properties, and defects in either could contribute to ataxia. Our previous work described changes in intrinsic properties and excitability of cerebellar Purkinje cells (PCs) resulting from the leaner mutation, which is known to reduce whole-cell Ca(2+) currents in PCs and cause severe ataxia.

The leaner P/Q-type calcium channel mutation renders cerebellar Purkinje neurons hyper-excitable and eliminates Ca2+-Na+ spike bursts.

The leaner mouse mutation of the Cacna1a gene leads to a reduction in P-type Ca2+ current, the dominant Ca2+ current in Purkinje cells (PCs). Here, we compare the electro-responsiveness and structure of PCs from age-matched leaner and wild-type (WT) mice in pharmacological isolation from synaptic inputs in cerebellar slices. We report that compared with WT, leaner PCs exhibit lower current threshold for Na+ spike firing, larger subthreshold membrane depolarization, rapid adaptation followed by complete block of Na+ spikes upon strong depolarization, and fail to generate Ca2+-Na+ spike bursts.

Calcium dynamics: analyzing the Ca2+ regulatory network in intact cells.

Calcium signaling is critical for all cells. As a free ion (Ca(2+)), calcium links many physiological stimuli to their intracellular effectors by interacting with binding proteins whose occupancy determines the cellular effect of stimulation. Because binding site occupancy depends on the history of Ca(2+) concentration ([Ca(2+)]), Ca(2+) dynamics are critical.

Depolarization-induced calcium responses in sympathetic neurons: relative contributions from Ca2+ entry, extrusion, ER/mitochondrial Ca2+ uptake and release, and Ca2+ buffering.

Many models have been developed to account for stimulus-evoked [Ca(2+)] responses, but few address how responses elicited in specific cell types are defined by the Ca(2+) transport and buffering systems that operate in the same cells. In this study, we extend previous modeling studies by linking the time course of stimulus-evoked [Ca(2+)] responses to the underlying Ca(2+) transport and buffering systems. Depolarization-evoked [Ca(2+)](i) responses were studied in sympathetic neurons under voltage clamp, asking how response kinetics are defined by the Ca(2+) handling systems expressed in these cells.

The amplitude distribution of release events through a fusion pore.

Neurotransmitters, hormones, or dyes may be released from vesicles via a fusion pore, rather than by full fusion of the vesicle with the plasma membrane. If the lifetime of the fusion pore is comparable to the time required for the substance to exit the vesicle, only a fraction of the total vesicle content may be released during a single pore opening. Assuming 1), fusion pore lifetimes are exponentially distributed (tauP), as expected for simple single channel openings, and 2), vesicle contents are lost through the fusion pore with an exponential time course (tauD), we derive an analytical expression for the probability density function of the fraction of vesicle content released (F): dP/dF=A (1-F)(A-1), where A=tauD/tauP.

Differential regulation of ER Ca2+ uptake and release rates accounts for multiple modes of Ca2+-induced Ca2+ release.

The ER is a central element in Ca(2+) signaling, both as a modulator of cytoplasmic Ca(2+) concentration ([Ca(2+)](i)) and as a locus of Ca(2+)-regulated events. During surface membrane depolarization in excitable cells, the ER may either accumulate or release net Ca(2+), but the conditions of stimulation that determine which form of net Ca(2+) transport occurs are not well understood. The direction of net ER Ca(2+) transport depends on the relative rates of Ca(2+) uptake and release via distinct pathways that are differentially regulated by Ca(2+), so we investigated these rates and their sensitivity to Ca(2+) using sympathetic neurons as model cells.