cAMP signaling affects age-associated deterioration of pacemaker beating interval dynamics.

Sinoatrial node (SAN) beating interval variability (BIV) and the average beating interval (BI) are regulated by a coupled-clock system, driven by Ca-calmodulin activated adenylyl cyclase, cAMP, and downstream PKA signaling. Reduced responsiveness of the BI and BIV to submaximal, [X], β-adrenergic receptor (β-AR) stimulation, and phosphodiesterase inhibition (PDEI) have been documented in aged SAN tissue, whereas the maximal responses, [X], do not differ by age. To determine whether age-associated dysfunction in cAMP signaling leads to altered responsiveness of BI and BIV, we measured cAMP levels and BI in adult (2-4 months n = 27) and aged (22-26 months n = 25) C57/BL6 mouse SAN tissue in control and in response to β-AR or PDEI at X and [X].

Changes in cAMP signaling are associated with age-related downregulation of spontaneously beating atrial tissue energetic indices.

The prevalence of atria-related diseases increases exponentially with age and is associated with ATP supply-to-demand imbalances. Because evidence suggests that cAMP regulates ATP supply-to-demand, we explored aged-associated alterations in atrial ATP supply-to-demand balance and its correlation with cAMP levels. Right atrial tissues driven by spontaneous sinoatrial node impulses were isolated from aged (22-26 months) and adult (3-4 months) C57/BL6 mice.

Induced neuro-vascular interactions robustly enhance functional attributes of engineered neural implants.

Engineered neural implants have a myriad of potential basic science and clinical neural repair applications. Although there are implants that are currently undergoing their first clinical investigations, optimizing their long-term viability and efficacy remain an open challenge. Functional implants with pre-vascularization of various engineered tissues have proven to enhance post-implantation host integration, and well-known synergistic neural-vascular interplays suggest that this strategy could also be promising for neural tissue engineering.

Holographic fiber bundle system for patterned optogenetic activation of large-scale neuronal networks.

Optogenetic perturbation has become a fundamental tool in controlling activity in neurons. Used to control activity in cell cultures, slice preparations, anesthetized and awake behaving animals, optical control of cell-type specific activity enables the interrogation of complex systems. A remaining challenge in developing optical control tools is the ability to produce defined light patterns such that power-efficient, precise control of neuronal populations is obtained.

All-optical bidirectional neural interfacing using hybrid multiphoton holographic optogenetic stimulation.

Our understanding of neural information processing could potentially be advanced by combining flexible three-dimensional (3-D) neuroimaging and stimulation. Recent developments in optogenetics suggest that neurophotonic approaches are in principle highly suited for noncontact stimulation of network activity patterns. In particular, two-photon holographic optical neural stimulation (2P-HONS) has emerged as a leading approach for multisite 3-D excitation, and combining it with temporal focusing (TF) further enables axially confined yet spatially extended light patterns.

Hybrid multiphoton volumetric functional imaging of large-scale bioengineered neuronal networks.

Planar neural networks and interfaces serve as versatile in vitro models of central nervous system physiology, but adaptations of related methods to three dimensions (3D) have met with limited success. Here, we demonstrate for the first time volumetric functional imaging in a bioengineered neural tissue growing in a transparent hydrogel with cortical cellular and synaptic densities, by introducing complementary new developments in nonlinear microscopy and neural tissue engineering. Our system uses a novel hybrid multiphoton microscope design combining a 3D scanning-line temporal-focusing subsystem and a conventional laser-scanning multiphoton microscope to provide functional and structural volumetric imaging capabilities: dense microscopic 3D sampling at tens of volumes per second of structures with mm-scale dimensions containing a network of over 1,000 developing cells with complex spontaneous activity patterns.

Holographically patterned activation using photo-absorber induced neural-thermal stimulation.

Objective: Patterned photo-stimulation offers a promising path towards the effective control of distributed neuronal circuits. Here, we demonstrate the feasibility and governing principles of spatiotemporally patterned microscopic photo-absorber induced neural-thermal stimulation (PAINTS) based on light absorption by exogenous extracellular photo-absorbers.

Approach: We projected holographic light patterns from a green continuous-wave (CW) or an IR femtosecond laser onto exogenous photo-absorbing particles dispersed in the vicinity of cultured rat cortical cells.

Holographic optogenetic stimulation of patterned neuronal activity for vision restoration.

When natural photoreception is disrupted, as in outer-retinal degenerative diseases, artificial stimulation of surviving nerve cells offers a potential strategy for bypassing compromised neural circuits. Recently, light-sensitive proteins that photosensitize quiescent neurons have generated unprecedented opportunities for optogenetic neuronal control, inspiring early development of optical retinal prostheses. Selectively exciting large neural populations are essential for eliciting meaningful perceptions in the brain.

Learning-induced enhancement of feedback inhibitory synaptic transmission.

Olfactory-discrimination learning results with a series of intrinsic and excitatory synaptic modifications in piriform cortex pyramidal neurons. Here we show that such learning results with long-lasting enhancement of inhibitory synaptic transmission onto proximal dendrites of these pyramidal neurons. Such enhancement is mediated by a strong hyperpolarizing shift in the reversal potential of fast inhibitory postsynaptic potentials (fIPSPs).

Learning-induced modulation of SK channels-mediated effect on synaptic transmission.

Although small conductance (SK)-mediated calcium-dependent potassium currents are usually mostly thought to modulate neuronal adaptation by suppressing repetitive spike firing, recent evidence suggests that these channels also modulate synaptic transmission. SK2 channels were shown to be activated in dendritic spines following calcium entry via N-methyl-d-aspartate (NMDA) receptor. Such activation of potassium currents terminates the NMDA-dependent postsynaptic potential (PSP).

A novel role for extracellular signal-regulated kinase in maintaining long-term memory-relevant excitability changes.

Pyramidal neurons in the piriform cortex from olfactory-discrimination-trained rats show enhanced intrinsic neuronal excitability that lasts for several days after learning. Such enhanced intrinsic excitability is mediated by long-term reduction in the postburst afterhyperpolarization (AHP), which is generated by repetitive spike firing. AHP reduction is attributable to decreased conductance of a calcium-dependent potassium current, the sI(AHP).

Learning-induced reversal of the effect of noradrenalin on the postburst AHP.

Pyramidal neurons in the piriform cortex from olfactory-discrimination-trained rats have reduced postburst afterhyperpolarization (AHP), for 3 days after learning, and are thus more excitable during this period. Such AHP reduction is caused by decreased conductance of one or more of the calcium-dependent potassium currents, I(AHP) and sI(AHP), that mediate the medium and slow AHPs. In this study, we examined which potassium current is reduced by learning and how the effect of noradrenalin (NE) on neuronal excitability is modified by such reduction.

Learning-induced long-term synaptic modifications in the olfactory cortex.

The idea that memory is manifested at the cellular level by enhancement of synaptic connections between simultaneously activated neurons has been suggested half a century ago by Hebb, and is widely accepted since. Much effort is done to describe such enhancement and reveal the underlying mechanisms. Learning-induced synaptic modifications were studied in the last decade with in-vitro brain slices preparations.

A molecular mechanism for stabilization of learning-induced synaptic modifications.

Olfaction is a principal sensory modality in rodents, and rats quickly learn to discriminate between odors and to associate odor with reward. Here we show that such olfactory discrimination (OD) learning consists of two phases with distinct cellular mechanisms: an initial NMDAR-sensitive phase in which the animals acquire a successful behavioral strategy (rule learning), followed by an NMDAR-insensitive phase in which the animals learn to distinguish between individual odors (pair learning). Rule learning regulates the composition of synaptic NMDARs in the piriform cortex, resulting in receptors with a higher complement of the NR2a subunit protein relative to NR2b.

Learning-induced reduction in post-burst after-hyperpolarization (AHP) is mediated by activation of PKC.

We studied the role of protein kinase C (PKC) and protein kinase A (PKA) in mediating learning-related long lasting reduction of the post-burst after-hyperpolarization (AHP) in cortical pyramidal neurons. We have shown previously that pyramidal neurons in the rat piriform (olfactory) cortex from trained (TR) rats have reduced post-burst AHP for 3 days after odour-discrimination learning, and that this reduction is due to decreased conductance of calcium-dependent potassium current. In the present study, we examined whether this long-lasting reduction in AHP is mediated by second messenger systems.