Postnatal Development Of Electrophysiological Properties Research Articles

Spinal motoneuron firing properties mature from rostral to caudal during postnatal development of the mouse.

Key points Many mammals are born with immature motor systems that develop through a critical period of postnatal development.In rodents, postnatal maturation of movement occurs from rostral to caudal, correlating with maturation of descending supraspinal and local spinal circuits.We asked whether development of fundamental electrophysiological properties of spinal motoneurons follows the same rostro‐caudal sequence.We show that in both regions, repetitive firing parameters increase and excitability decreases with development; however, these characteristics mature earlier in cervical motoneurons.We suggest that in addition to autonomous mechanisms, motoneuron development depends on activity resulting from their circuit milieu. Altricial mammals are born with immature nervous systems comprised of circuits that do not yet have the neuronal properties and connectivity required to produce future behaviours. During the critical period of postnatal development, neuronal properties are tuned to participate in functional circuits. In rodents, cervical motoneurons are born prior to lumbar motoneurons, and spinal cord development follows a sequential rostro‐caudal pattern. Here we asked whether birth order is reflected in the postnatal development of electrophysiological properties. We show that motoneurons of both regions have similar properties at birth and follow the same developmental profile, with maximal firing increasing and excitability decreasing into the third postnatal week. However, these maturative processes occur in cervical motoneurons prior to lumbar motoneurons, correlating with the maturation of premotor descending and local spinal systems. These results suggest that motoneuron properties do not mature by cell autonomous mechanisms alone, but also depend on developing premotor circuits.

Adult‐like action potential properties and abundant GABAergic synaptic responses in amygdala neurons from newborn marmosets

The amygdala plays an important role in the processing of emotional events. This information processing is altered by development, but little is known about the development of electrophysiological properties of neurons in the amygdala. We studied the postnatal development of electrophysiological properties of neurons in the basolateral amygdala (BLA) of the common marmoset (Callithrix jacchus). Whole-cell patch-clamp recordings were obtained from BLA pyramidal neurons in brain slices prepared from developing and adult marmosets, and electrophysiological properties known to change during development in rats were analysed. Two passive electrical properties of the neuronal membrane - the input resistance (R(in)) and the membrane time constant () - significantly decreased with postnatal development. In contrast, the action potential only showed a slight decrease in duration during the first month of life, whereas the amplitude did not change after birth. Passive electrical properties and action potentials in neurons of 4-week-old marmosets were similar to those in neurons of 4-year-old marmosets. The development of the action potential duration was not correlated with the development of R(in) or , whereas the development of R(in) and was correlated with each other. Abundant spontaneous and noradrenaline-induced GABAergic currents were present immediately after birth and did not change during postnatal development. These results suggest that newborn infant marmoset BLA pyramidal neurons possess relatively mature action potentials and receive vigorous GABAergic synaptic inputs, and that they acquire adult-like electrophysiological properties by the fourth week of life.

Postnatal development of electrophysiological properties of principal neurons in the rat basolateral amygdala.

The basolateral amygdala (BLA) is critically involved in the pathophysiology of psychiatric disorders, which often emerge during brain development. Several studies have characterized postnatal changes to the morphology and biochemistry of BLA neurons, and many more have identified sensitive periods of emotional maturation. However, it is impossible to determine how BLA development contributes to emotional development or the aetiology of psychiatric disorders because no study has characterized the physiological maturation of BLA neurons. We addressed this critical knowledge gap for the first time using whole-cell patch clamp recording in rat BLA principal neurons to measure electrophysiological properties at postnatal day (P)7, P10, P14, P21, P28 and after P35. We show that intrinsic properties of these neurons undergo significant transitions before P21 and reach maturity around P28. Specifically, we observed significant reductions in input resistance and membrane time constant of nearly 10-and 4-fold, respectively, from P7 to P28. The frequency selectivity of these neurons to input also changed significantly, with peak resonance frequency increasing from 1.0 Hz at P7 to 5.7 Hz at P28. In the same period, maximal firing frequency significantly increased and doublets and triplets of action potentials emerged. Concomitantly, individual action potentials became significantly faster, firing threshold hyperpolarized 6.7 mV, the medium AHP became faster and shallower, and a fast AHP emerged. These results demonstrate neurons of the BLA undergo vast change throughout postnatal development, and studies of emotional development and treatments for juvenile psychiatric disorders should consider the dynamic physiology of the immature BLA.

Postnatal development of membrane properties of layer I neurons in rat neocortex

Using whole-cell patch-clamp techniques in brain slices, we studied the postnatal development of electrophysiological properties of rat neocortical layer I neurons during the first three weeks of postnatal life. Neurons, including Cajal-Retzius cells, were visualized under Nomarski optics before recording. In the first postnatal week, all layer I neurons, including Cajal-Retzius cells, had low resting membrane potentials (-40 to -55 mV), high input resistances (1-5 G omega), and long membrane time constants (80-130 msec). Action potentials (APs) of layer I neurons early in postnatal development were lower in amplitude and longer in duration. The threshold for APs also was more depolarized than in older neurons. A medium after-hyperpolarization already was present at postnatal day 0 (PN0), but fast afterhyperpolarizations were not seen until PN10. At all postnatal ages, layer I neurons were capable of repetitive firing, displayed little or no frequency adaptation, and did not display slow afterhyperpolarizations. Early in development, layer I neurons had a prominent hyperpolarization-activation depolarizing sag that decreased with age. These results suggest that the membrane properties of rat neocortical layer I neurons mature rapidly during the first two postnatal weeks. Cajal-Retzius cells had electrical properties similar to other layer I neurons and did not show an earlier maturation of membrane properties.

Post-natal development of electrophysiological properties of rat cerebral cortical pyramidal neurones.

1. The post-natal development of the electrophysiological properties of cortical layer V pyramidal neurons was investigated with intracellular recordings from rat sensorimotor cortical slices, in vitro. 2. At all ages post-natally (post-natal day 1 to day 36; P1-P36) neurons were capable of generating a train of Na+-dependent action potentials in response to intracellular injection of sufficient depolarizing current. During the second and third week post-natally, these action potentials changed substantially, becoming faster in both their rising and falling phases, shorter in duration, and larger in amplitude. 3. Both mature (greater than P21) and immature (P2-P4) cortical neurones could generate Ca2+-dependent action potentials only if a substantial portion of K+ conductances were blocked. The maximum rate of rise of Ca2+ spikes also increased with age. 4. The apparent input resistance, specific membrane resistance, and membrane time constant all decreased with age from P1 to P30. Immature neurones had I-V relationships that were substantially more linear than those of adult cells, although rectification was often present in both the hyperpolarizing and depolarizing range. Inward rectification in the depolarizing range was Na+ dependent and was substantially larger in mature versus immature neurones. 5. Single, or trains of, action potentials in immature neurones were followed by short duration (10-50 ms) and long duration (1-5 s) after-hyperpolarizations (a.h.p.s) respectively. The duration of the latter appeared to decrease with age. The presence of large a.h.p.s indicates that Ca2+ entry occurs during the action potential of immature, as well as mature, neurones. 6. Responses to intracellular injection of depolarizing current pulses indicated that immature neurones have frequency versus injected current (f-I) relationships which are in general less steep than those for adult neurones and more limited in terms of the range of firing frequencies. 7. Our results are consistent with the hypothesis that there is a considerable increase in the density of voltage-dependent ionic channels underlying the electro-responsiveness of cortical pyramidal neurones during post-natal development.