evaluation-synaptic-multiplicity-using-whole-cell-patch-clamp

Evaluation of Synaptic Multiplicity Using Whole-cell Patch-clamp Electrophysiology

In the central nervous system, a pair of neurons often form&#160;multiple synaptic contacts and/or functional neurotransmitter release sites (synaptic ...

University of Western Ontario

Inflammation-induced activation of the hypothalamic-pituitary-adrenal (HPA) axis and the ensuing release of anti-inflammatory glucocorticoids are critical for the fine-tuning of the inflammatory response. This immune-induced neuroendocrine response is in large part mediated by prostaglandin E (PGE ), the central actions of which ultimately translate into the excitation of parvocellular neuroendocrine cells (PNCs) in the hypothalamic paraventricular nucleus. However, the neuronal mechanisms by which PGE excites PNCs remain incompletely understood. In the present study, we report that PGE potently depresses GABAergic inhibitory synaptic transmission onto PNCs. Using whole-cell patch clamp recordings obtained from PNCs in ex vivo hypothalamic slices from rats, we found that bath application of PGE (0.01-100 μmol L ) concentration-dependently decreased the amplitude of evoked inhibitory postsynaptic currents (eIPSCs) with maximum effects at 10 μmol L . The PGE -mediated depression of eIPSCs had a rapid onset and was long-lasting, and also was accompanied by an increase in paired pulse ratio. In addition, PGE decreased the frequency but not the amplitude of both spontaneous IPSCs and miniature IPSCs. These results collectively indicate that PGE acts at a presynaptic locus to decrease the probability of GABA release. Using pharmacological approaches, we also demonstrated that the EP3 subtype of the PGE receptor mediated the actions of PGE on GABA synapses. Taken together, our results show that PGE , via actions of presynaptic EP3 receptors, potently depresses GABA release onto PNCs, providing a plausible mechanism for the disinhibition of HPA axis output during inflammation.

Prostaglandin E depresses GABA release onto parvocellular neuroendocrine neurones in the paraventricular nucleus of the hypothalamus via presynaptic receptors.

The stress response-originally described by Hans Selye as "the nonspecific response of the body to any demand made upon it"-is chiefly mediated by the hypothalamic-pituitary-adrenal (HPA) axis and is activated by diverse sensory stimuli that inform threats to homeostasis. The diversity of signals regulating the HPA axis is partly achieved by the complexity of afferent inputs that converge at the apex of the HPA axis: this apex is formed by a group of neurosecretory neurons that synthesize corticotropin-releasing hormone (CRH) in the paraventricular nucleus of the hypothalamus (PVN). The afferent synaptic inputs onto these PVN-CRH neurons originate from a number of brain areas, and PVN-CRH neurons respond to a long list of neurotransmitters/neuropeptides. Considering this complexity, an important question is how these diverse afferent signals independently and/or in concert influence the excitability of PVN-CRH neurons. While many of these inputs directly act on the postsynaptic PVN-CRH neurons for the summation of signals, accumulating data indicates that they also modulate each other's transmission in the PVN. This mode of transmission, termed heterosynaptic modulation, points to mechanisms through which the activity of a specific modulatory input (conveying a specific sensory signal) can up- or down-regulate the efficacy of other afferent synapses (mediating other stress modalities) depending on receptor expression for and spatial proximity to the heterosynaptic signals. Here, we review examples of heterosynaptic modulation in the PVN and discuss its potential role in the regulation of PVN-CRH neurons' excitability and resulting HPA axis activity.

Heterosynaptic modulation in the paraventricular nucleus of the hypothalamus.

The pedunculopontine tegmental nucleus (PPT) and laterodorsal tegmental nucleus (LDT) are heterogeneous brainstem structures that contain cholinergic, glutamatergic, and GABAergic neurons. PPT/LDT neurons are suggested to modulate both cognitive and noncognitive functions, yet the extent to which acetylcholine (ACh) signaling from the PPT/LDT is necessary for normal behavior remains uncertain. We addressed this issue by using a mouse model in which PPT/LDT cholinergic signaling is highly decreased by selective deletion of the vesicular ACh transporter ( VAChT) gene. This approach interferes exclusively with ACh signaling, leaving signaling by other neurotransmitters from PPT/LDT cholinergic neurons intact and sparing other cells. VAChT mutants were examined on different PPT/LDT-associated cognitive domains. Interestingly, VAChT mutants showed no attentional deficits and only minor cognitive flexibility impairments while presenting large deficiencies in both spatial and cued Morris water maze (MWM) tasks. Conversely, working spatial memory determined with the Y-maze and spatial memory measured with the Barnes maze were not affected, suggesting that deficits in MWM were unrelated to spatial memory abnormalities. Supporting this interpretation, VAChT mutants exhibited alterations in anxiety-like behavior and increased corticosterone levels after exposure to the MWM, suggesting altered stress response. Thus, PPT/LDT VAChT-mutant mice present little cognitive impairment per se, yet they exhibit increased susceptibility to stress, which may lead to performance deficits in more stressful conditions.-Janickova, H., Kljakic, O., Rosborough, K., Raulic, S., Matovic, S., Gros, R., Saksida, L. M., Bussey, T. J., Inoue, W., Prado, V. F., Prado, M. A. M. Selective decrease of cholinergic signaling from pedunculopontine and laterodorsal tegmental nuclei has little impact on cognition but markedly increases susceptibility to stress.

Selective decrease of cholinergic signaling from pedunculopontine and laterodorsal tegmental nuclei has little impact on cognition but markedly increases susceptibility to stress.

Wataru Inoue

University of Western Ontario

Evaluation of Synaptic Multiplicity Using Whole-cell Patch-clamp Electrophysiology