Biomedical subjects

Christian G Reich

Publications and source records attributed to Christian G Reich.

4 recordsLinked to original sources

PubMed2005

Endocannabinoid signaling dynamics probed with optical tools.

Intercellular signaling dynamics critically influence the functional roles that the signals can play. Small lipids are synthesized and released from neurons, acting as intercellular signals in regulating neurotransmitter release, modulating ion channels on target cells, and modifying synaptic plasticity. The repertoire of biological effects of lipids such as endocannabinoids (eCBs) is rapidly expanding, yet lipid signaling dynamics have not been studied. The eCB system constitutes a powerful tool for bioassaying the dynamics of lipid signaling. The eCBs are synthesized in, and released from, postsynaptic somatodendritic domains that are readily accessible to whole-cell patch electrodes. The dramatic effects of these lipid signals are detected electrophysiologically as CB1-dependent alterations in conventional synaptic transmission, which therefore serve as a sensitive reporter of eCB actions. We used electrophysiological recording, photolytic release of caged glutamate and a newly developed caged AEA (anandamide), together with rapid [Ca2+]i measurements, to investigate the dynamics of retrograde eCB signaling between CA1 pyramidal cells and GABAergic synapses in rat hippocampus in vitro. We show that, at 22 degrees C, eCB synthesis and release must occur within 75-190 ms after the initiating stimulus, almost an order of magnitude faster than previously thought. At 37 degrees C, the time could be < 50 ms. Activation of CB1 and downstream processes constitute a significant fraction of the total delay and are identified as major rate-limiting steps in retrograde signaling. Our findings imply that lipid messenger dynamics are comparable with those of metabotropic neurotransmitters and can modulate neuronal interactions on a similarly fast time scale.

Animals↗

PubMed2005

Regulation of IPSP theta rhythm by muscarinic receptors and endocannabinoids in hippocampus.

Theta rhythms are behaviorally relevant electrical oscillations in the mammalian brain, particularly the hippocampus. In many cases, theta oscillations are shaped by inhibitory postsynaptic potentials (IPSPs) that are driven by glutamatergic and/or cholinergic inputs. Here we show that hippocampal theta rhythm IPSPs induced in the CA1 region by muscarinic acetylcholine receptors independent of all glutamate receptors can be briefly interrupted by action potential-induced, retrograde endocannabinoid release. Theta IPSPs can be recorded in CA1 pyramidal cell somata surgically isolated from CA3, subiculum, and even from their own apical dendrites. These results suggest that perisomatic-targeting interneurons whose output is subject to inhibition by endocannabinoids are the likely source of theta IPSPs. Interneurons having these properties include the cholecystokinin-containing cells. Simultaneous recordings from pyramidal cell pairs reveal synchronous theta-frequency IPSPs in neighboring pyramidal cells, suggesting that these IPSPs may help entrain or modulate small groups of pyramidal cells.

Action Potentials↗

PubMed2004

Novel form of LTD induced by transient, partial inhibition of the Na,K-pump in rat hippocampal CA1 cells.

We tested the hypothesis that transient, partial inhibition of the Na,K-pumps could produce lasting effects on synaptic efficacy in brain tissue by applying a low concentration of the ouabain analogue, dihydroouabain (DHO), to hippocampal slices for 15 min and studying the effects on field excitatory postsynaptic potentials (fEPSPs). DHO caused a suppression of fEPSPs during the application period, but this recovered only partially, to approximately 80% of control levels, after washout lasting as long as 2 h. The lasting suppression had several properties in common with low-frequency stimulation induced long-term depression (LFS-LTD), including an ability to depotentiate long-term potentiated responses. However, DHO-LTD was insensitive to blockade of N-methyl-d-aspartate or mGlu receptors or to inhibitors of protein kinase C or p38 MAP kinase. DHO-LTD did not co-occlude with LFS-LTD and therefore appears to represent a novel form of LTD. Interestingly, DHO-LTD could be prevented by pretreating slices with iberiotoxin, the selective blocker of large, Ca(2+)-dependent K+ channels ("big K," BK channels), although this toxin did not affect basal fEPSPs. Certain pathological conditions, including hypoxia and ischemia, are associated with a decrease in Na,K-pump activity and hence DHO-LTD may serve as a model for the effects on neuronal function in these conditions.

Animals↗

PubMed2003

Dynamic coding of taste stimuli in the brainstem: effects of brief pulses of taste stimuli on subsequent taste responses.

Recent studies have suggested that the response profiles of taste-responsive cells in the brainstem may be modulated by inhibitory interactions, potentially originating from activity in peripheral taste nerves. This idea was explored by testing the hypothesis that brief (100 msec) pulses of taste stimuli would alter the responses to subsequently presented tastants in the nucleus of the solitary tract (NTS) of urethane-anesthetized rats. Pulses of taste stimuli, called prepulses, were followed by a 3 sec presentation of the same or different taste stimulus. The prepulse-stimulus interval was either 1 or 5 sec, during which the tongue was rinsed with distilled water. Taste stimuli consisted of 0.1 m NaCl, 0.5 m sucrose, 0.01 m quinine HCl, and 0.01 m HCl. Taste prepulses suppressed (or enhanced) subsequent taste responses in 30 of 49 (61%) units when the prepulse-stimulus interval was 1 sec but were ineffective when this interval was 5 sec. Most commonly, NaCl or HCl prepulses attenuated the response to quinine. Control experiments showed that these effects were not attributable to adaptation, mixture effects, or response variability. In 19 (39%) of the units tested, effects of prepulses were large enough to change the order of effectiveness of the taste stimuli. Taste responses in these cells were "dynamically tuned" in that the magnitude of response was a function of the taste stimulus that immediately preceded it. Dynamic tuning may be the result of inhibitory interactions within the NTS; cells that show dynamic tuning may have a unique function in taste coding.

Action Potentials↗