Electrophysiological Properties Of Individual Neurons Research Articles

A neuronal signature of accurate imitative learning in wild-caught songbirds (swamp sparrows, Melospiza georgiana)

In humans and other animals, behavioural variation in learning has been associated with variation in neural features like morphology and myelination. By contrast, it is essentially unknown whether cognitive performance scales with electrophysiological properties of individual neurons. Birdsong learning offers a rich system to investigate this topic as song acquisition is similar to human language learning. Here, we address the interface between behavioural learning and neurophysiology in a cohort of wild-caught, hand-reared songbirds (swamp sparrows, Melospiza georgiana). We report the discovery in the forebrain HVC of sensorimotor ‘bridge’ neurons that simultaneously and selectively represent two critical learning-related schemas: the bird’s own song, and the specific tutor model from which that song was copied. Furthermore, the prevalence and response properties of bridge neurons correlate with learning ability – males that copied tutor songs more accurately had more bridge neurons. Our results are consistent with the hypothesis that accurate imitative learning depends on a successful bridge, within single cortical neurons, between the representation of learning models and their sensorimotor copies. Whether such bridge neurons are a necessary mechanism for accurate learning or an outcome of learning accuracy is unknown at this stage, but can now be addressed in future developmental studies.

Morphological characteristics and electrophysiological properties of CA1 pyramidal neurons in macaque monkeys

Little is known about the morphological characteristics and intrinsic electrophysiological properties of individual neurons in the nonhuman primate hippocampus. We have used intracellular recording and biocytin-labeling techniques in the in vitro hippocampal slice preparation to provide quantitative evaluation of the fundamental morphological and intrinsic electrophysiological characteristics of macaque monkey CA1 pyramidal neurons. These neurons have previously been studied in the rat in our laboratory. Monkey CA1 pyramidal neurons have an average soma volume of 3578μm 3, 4.71 basal dendrites with 53 terminal branches for a dendritic length of about 10,164μm, 1.13 apical dendrites with 47 terminal branches for a dendritic length of about 10,678μm. In comparison, rat CA1 pyramidal neurons have an average soma volume of 2066μm 3, 3.35 basal dendrites with 29 terminal branches for a dendritic length of about 4,586μm, 1.43 apical dendrites with 62 terminal branches for a dendritic length of about 8,838μm. The basic intrinsic electrophysiological properties of CA1 pyramidal cells are similar in monkeys and rats. Monkey CA1 pyramidal neurons have a resting membrane potential of about −62 mV (rat: −62 mV), an input resistance of 35 MΩ (rat: 34–49 MΩ), a rheobase of 0.17 nA (rat: 0.12–0.20 nA) and an action potential amplitude of 83 mV (rat: 71–89 mV). Although morphological differences such as the increased dendritic length may translate into differences in neural processing between primates and rodents, the functional significance of these morphological differences is not yet clear. Quantitative studies of the primate brain are critical in order to extrapolate information derived from rodent studies into better understanding of the normal and pathological function of the human hippocampus.

Functional Effects of Auxiliary β4-Subunit on Rat Large-Conductance Ca 2+-Activated K + Channel

Large-conductance calcium-activated potassium (BK Ca) channels are composed of the pore-forming α-subunit and the auxiliary β-subunits. The β4-subunit is dominantly expressed in the mammalian central nervous system. To understand the physiological roles of the β4-subunit on the BK Ca channel α-subunit (Slo), we isolated a full-length complementary DNA of rat β4-subunit (r β4), expressed heterolgously in Xenopus oocytes, and investigated the detailed functional effects using electrophysiological means. When expressed together with rat Slo (rSlo), r β4 profoundly altered the gating characteristics of the Slo channel. At a given concentration of intracellular Ca 2+, rSlo/r β4 channels were more sensitive to transmembrane voltage changes. The activation and deactivation rates of macroscopic currents were decreased in a Ca 2+-dependent manner. The channel activation by Ca 2+ became more cooperative by the coexpression of r β4. Single-channel recordings showed that the increased Hill coefficient for Ca 2+ was due to the changes in the open probability of the rSlo/r β4 channel. Single BK Ca channels composed of rSlo and r β4 also exhibited slower kinetics for steady-state gating compared with rSlo channels. Dwell times of both open and closed events were significantly increased. Because BK Ca channels are known to modulate neuroexcitability and the expression of the β4-subunit is highly concentrated in certain subregions of brain, the electrophysiological properties of individual neurons should be affected profoundly by the expression of this second subunit.

Dendritic morphology, local circuitry, and intrinsic electrophysiology of principal neurons in the entorhinal cortex of macaque monkeys.

Little is known about the neuroanatomical or electrophysiological properties of individual neurons in the primate entorhinal cortex. We have used intracellular recording and biocytin-labeling techniques in the entorhinal slice preparation from macaque monkeys to investigate the morphology and intrinsic electrophysiology of principal neurons. These neurons have previously been studied most extensively in rats. In monkeys, layer II neurons are usually stellate cells, as in rats, but they occasionally have a pyramidal shape. They tend to discharge trains, not bursts, of action potentials, and some display subthreshold membrane potential oscillations. Layer III neurons are pyramidal, and they do not appear to display membrane potential oscillations. The distribution of dendrites and of axon collaterals suggests that neurons in layers II and III are interconnected by a network of associational fibers. Layer V and VI neurons are pyramidal and tend to discharge trains of action potentials. The distribution of dendrites and axon collaterals suggests that there is an associative network of principal neurons in layers V and VI, and they also project axon collaterals toward superficial layers. Importantly, entorhinal cortical neurons in monkeys appear to exhibit significant differences from those in rats. Morphologically, neurons in monkey entorhinal layers II and III have more primary dendrites, more dendritic branches, and greater total dendritic length than in rats. Electrophysiologically, layer II neurons in monkeys exhibit less sag, and subthreshold oscillations are less robust and slower. Some monkey layer III neurons discharge bursts of action potentials that are not found in rats. The interspecies differences revealed by this study may influence information processing and pathophysiological processes in the primate entorhinal cortex. J. Comp. Neurol. 470:317-329, 2004.

Characterization of subthreshold voltage fluctuations in neuronal membranes.

Synaptic noise due to intense network activity can have a significant impact on the electrophysiological properties of individual neurons. This is the case for the cerebral cortex, where ongoing activity leads to strong barrages of synaptic inputs, which act as the main source of synaptic noise affecting on neuronal dynamics. Here, we characterize the subthreshold behavior of neuronal models in which synaptic noise is represented by either additive or multiplicative noise, described by Ornstein-Uhlenbeck processes. We derive and solve the Fokker-Planck equation for this system, which describes the time evolution of the probability density function for the membrane potential. We obtain an analytic expression for the membrane potential distribution at steady state and compare this expression with the subthreshold activity obtained in Hodgkin-Huxley-type models with stochastic synaptic inputs. The differences between multiplicative and additive noise models suggest that multiplicative noise is adequate to describe the high-conductance states similar to in vivo conditions. Because the steady-state membrane potential distribution is easily obtained experimentally, this approach provides a possible method to estimate the mean and variance of synaptic conductances in real neurons.

Electrophysiological properties of neurons in neonatal rat occipital cortex slices grown in a serum-free medium

The electrophysiological properties of individual neurons within organotypic explants of neonatal rat cortex were examined via intracellular recordings. The explants were grown for two weeks in a serum-free medium. The electrophysiological properties of the neurons within these explants were similar to those reported for both adult cortex in vivo and short-term in vitro slice preparations. The results of the present study show that cortical explants grown under serum-free conditions can serve as a useful model for long-term developmental studies associated with the physiological basis of neural network formation.

Anatomy and electrophysiology of neurons terminating in the corpora allata of the cockroach Diploptera punctata.

Intracellular recording and dye injection were used to study the structure and electrophysiological properties of individual neurons that project to the corpora allata of the cockroach, Diploptera punctata. Neurons in the pars intercerebralis generate long-duration, tetrodotoxin-sensitive action potentials. Dye injection revealed two cell types. One type extends axons to the contralateral nervi corporis cardiaci I, some of which innervate the corpora allata, and another type extends a major axon down each of the circumoesophageal connectives. Neurons in the pars lateralis also generate long-duration action potentials. These neurons extend axons to the ipsilateral nervi corporis cardiaci II, which continue on to terminate in the corpora cardiaca and the corpora allata. Small groups of all the above neuronal types are dye and electrically coupled. Penetration and dye injection into nerve terminals in the corpora allata and corpora cardiaca confirmed the innervation of the corpora allata by neurons located in the pars intercerebralis and pars lateralis and revealed a third class of neurons that have terminals in the corpora allata: intrinsic neurons of the corpora cardiaca.