Stem cells from the adult human brain develop into functional neurons in culture

Recent research communications indicate that the adult human brain contains undifferentiated, multipotent precursors or neural stem cells. It is not known, however, whether these cells can develop into fully functional neurons. We cultured cells from the adult human ventricular wall as neurospheres and passed them at the individual cell level to secondary neurospheres. Following dissociation and plating, the cells developed the antigen profile of the three main cell types in the brain (GFAP, astrocytes; O2, oligodendrocytes; and beta-III-tubulin/NeuN, neurons). More importantly, the cells developed the electrophysiological profiles of neurons and glia. Over a period of 3 weeks, neuron-like cells went through the same phases as neurons do during development in vivo, including up-regulation of inward Na+ -currents, drop in input resistance, shortening of the action potential, and hyperpolarization of the cell membrane. The cells developed overshooting action potentials with a mature configuration. Recordings in voltage-clamp mode displayed both the fast inactivating TTX-sensitive sodium current (INa) underlying the rising phase of the action potential and the two potassium currents terminating the action potential in mature neurons (IA and IK, sensitive to 4-AP and TEA, respectively). We have thus demonstrated that the human ventricular wall contains multipotent cells that can differentiate into functionally mature neurons.     

A critical period for enhanced synaptic plasticity in newly generated neurons of the adult brain

Active adult neurogenesis occurs in discrete brain regions of all mammals and is widely regarded as a neuronal replacement mechanism. Whether adult-born neurons make unique contributions to brain functions is largely unknown. Here we systematically characterized synaptic plasticity of retrovirally labeled adult-born dentate granule cells at different stages during their neuronal maturation. We identified a critical period between 1 and 1.5 months of the cell age when adult-born neurons exhibit enhanced long-term potentiation with increased potentiation amplitude and decreased induction threshold. Furthermore, such enhanced plasticity in adult-born neurons depends on developmentally regulated synaptic expression of NR2B-containing NMDA receptors. Our study demonstrates that adult-born neurons exhibit the same classic critical period plasticity as neurons in the developing nervous system. The transient nature of such enhanced plasticity may provide a fundamental mechanism allowing adult-born neurons within the critical period to serve as major mediators of experience-induced plasticity while maintaining stability of the mature circuitry.     

3H-diazepam binding to brain synaptic membranes during the development of generalized epileptic activity

The development of bemegride-induced generalized epileptic activity in rats was shown to reduce the constant (CB). of specific 3H-diazepam binding with synaptic membranes from 0.23 nM-1 to 0.15 nM-1 and to increase the maximum number of membrane binding sites (Bmax) from 410 fmol/mg protein to 550 fmol/mg protein. It is assumed that the changes of benzodiazepine receptor properties are due to alteration in physico-chemical characteristics of synaptic membrane lipids resulting from the activation of lipid peroxidation.     

Effect of nitrite on the excitability of brain neurons in helix

Incubation of the Helix brain in sodium nitrite (SN) decreased the firing threshold of silent neurones, increased firing rate and a response to stimulation, activated excitatory synaptic inputs of the neurones under study. The effects were stable but reversible. Rapid responses to the SN application were only shown for spontaneously active neurones. The SN effects were accompanied by a depolarisation and an increase in the input resistance. Inhibitor of the NO synthase exerted opposite effects to the NO donors and SN. A possible role of the NO and hypoxia in the SN effects, is discussed.     

Transport Ca-ATPase activity of brain synaptic membranes in rats with korazol-induced epileptic activity

Changes in the activity of transport Ca-ATPase in osmotically disrupted synaptosomes were studied in corazol-induced generalized epileptic activity (EA) monitored by electrocorticogram. The enzyme activity was found to be unchanged at the beginning of the latent period, but significantly diminished towards the end of the latent period and further reduced at the peak of EA. After ET was no longer observed the enzyme activity returned to normal. The activity of transport Ca-ATPase in synaptic junction fraction was found to be 3 times higher than in osmotically disrupted synaptosomes. A possible role of the inactivation of membrane Ca pump in synaptic brain structures is discussed in relation to pathological hyperactivity of neurons.     

The common properties of neurogenesis in the adult brain: from invertebrates to vertebrates

Until recently, it was believed that adult brains were unable to generate any new neurons. However, it is now commonly known that stem cells remain in the adult central nervous system and that adult vertebrates as well as adult invertebrates are currently adding new neurons in some specialized structures of their central nervous system. In vertebrates, the subventricular zone and the dentate gyrus of the hippocampus are the sites of neuronal precursor proliferation. In some insects, persistent neurogenesis occurs in the mushroom bodies, which are brain structures involved in learning and memory and considered as functional analogues of the hippocampus. In both vertebrates and invertebrates, secondary neurogenesis (including neuroblast proliferation and neuron differentiation) appears to be regulated by hormones, transmitters, growth factors and environmental cues. The functional implications of adult neurogenesis have not yet been clearly demonstrated and comparative study of the various model systems could contribute to better understand this phenomenon. Here, we review and discuss the common characteristics of adult neurogenesis in the various animal models studied so far.     

M-channels modulate the intrinsic excitability and synaptic responses of layer 2/3 pyramidal neurons in auditory cortex

Neurons in the auditory cortex are believed to utilize temporal patterns of neural activity to accurately process auditory information but the intrinsic neuronal mechanism underlying the control of auditory neural activity is not known. The slowly activating, persistent K⁺ channel, also called M-channel that belongs to the Kv7 family, is already known to be important in regulating subthreshold neural excitability and synaptic summation in neocortical and hippocampal pyramidal neurons. However, its functional role in the primary auditory cortex (A1) has never been characterized. In this study, we investigated the roles of M-channels on neuronal excitability, short-term plasticity, and synaptic summation of A1 layer 2/3 regular spiking pyramidal neurons with whole-cell current-clamp recordings in vitro. We found that blocking M-channels with a selective M-channel blocker, XE991, significantly increased neural excitability of A1 layer 2/3 pyramidal neurons. Furthermore, M-channels controled synaptic responses of intralaminar-evoked excitatory postsynaptic potentials (EPSPs); XE991 significantly increased EPSP amplitude, decreased the rate of short-term depression, and increased the synaptic summation. These results suggest that M-channels are involved in controlling spike output patterns and synaptic responses of A1 layer 2/3 pyramidal neurons, which would have important implications in auditory information processing.     

Young and excitable: the function of new neurons in the adult mammalian brain

Adult neurogenesis occurs in most species and is regulated by a wide variety of environmental and pharmacological challenges. The functional integration of neurons generated in the adult was first demonstrated in songbirds more than two decades ago. In the adult mammalian brain, neurons are continuously generated in two structures, the olfactory bulb and the hippocampus. Current evidence suggests that adult-born immature neurons have distinct electrophysiological properties from old neurons, and proposed roles in a variety of functions including olfaction, learning and mood regulation.     

成年蜜蜂脑神经细胞的培养和电生理特征

为了研究杀虫剂等对蜜蜂毒性作用的神经机制,需在体外建立成年蜜蜂脑神经细胞的分离培养和电生理记录技术并研究其正常电生理特征,而对成年蜜蜂脑神经细胞的分离培养和电生理特性的研究报道甚少。我们采用酶解和机械吹打相结合的方法获得了数量较多且活力较好的成年意大利蜜蜂Apis mellifera脑神经细胞,并用全细胞膜片钳技术研究了成年意大利蜜蜂脑神经细胞对电流和电压刺激的反应,获得了成年意蜂脑神经细胞的基本电生理特征以及钠电流和钾电流的特性。全细胞电流钳的记录结果表明,在体外培养条件下,细胞无自发放电发生,注射电流后仅引起细胞单次放电,引起细胞放电的阈电流平均为60.8±63 pA; 细胞动作电位产生的阈电位平均为−27.4±2.3 mV。用全细胞电压钳记录了神经细胞的钠电流和钾电流。钠电流的分离是在电压刺激下通过阻断钾通道和钙通道实现。细胞的内向钠电流在指令电压为−40～−30 mV左右激活,−10 mV达峰值,钠通道的稳态失活电压V_1/2为−58.4 mV; 外向钾电流成份至少包括较小的快速失活钾电流和和较大的缓慢失活钾电流（占总钾电流的80%）,其半激活膜电位V_1/2为3.86 mV,无明显的稳态失活。结果提示缓慢失活钾电流的特征可能是细胞单次放电的机制之一。     

Activity-dependent morphological synaptic plasticity in an adult neurosecretory system: magnocellular oxytocin neurons of the hypothalamus.

Oxytocin and vasopressin neurons, located in the supraoptic and paraventricular nuclei of the hypothalamus, send their axons to the neurohypophysis where the neurohormones are released directly into the general circulation. Hormone release depends on the electrical activity of the neurons, which in turn is regulated by different afferent inputs. During conditions that enhance oxytocin secretion (parturition, lactation, and dehydration), these afferents undergo morphological remodelling which results in an increased number of synapses contacting oxytocin neurons. The synaptic changes are reversible with cessation of stimulation. Using quantitative analyses on immunolabelled preparations, we have established that this morphological synaptic plasticity affects both inhibitory and excitatory afferent inputs to oxytocin neurons. This review describes such synaptic modifications, their functional significance, and the cellular mechanisms that may be responsible.     

Intrinsic and synaptic properties of neurons in the vocal-control nucleus lMAN from in vitro slice preparations of juvenile and adult zebra finches

A common theme of diverse neural systems is that circuits that are important for initial acquisition of learning do not necessarily serve as a substrate for the long-term storage of that memory. The neural basis of vocal learning in songbirds provides an example of this phenomenon, since a circuit that is necessary for vocal production during initial stages of vocal development apparently plays no subsequent role in controlling learned vocalizations. This striking functional change suggests the possibility of marked physiological changes in synaptic transmission within this circuit. We therefore examined intrinsic and synaptic properties of neurons in the cortical nucleus lMAN (lateral magnocellular nucleus of the anterior neostriatum), which forms part of this developmentally regulated circuit, in an in vitro preparation of the zebra finch forebrain. Although both functional and morphological characteristics of these neurons change substantially during vocal development, we did not observe widespread, substantive changes in the electrophysiological characteristics of juvenile versus adult lMAN neurons examined in vitro. Overall, both the intrinsic properties and synaptic responses of lMAN neurons were similar in slices from juvenile birds (at ages when lesions of lMAN disrupt vocal production) and in slices from adult birds (when lMAN lesions have no effect on song production). However, one intrinsic property that did vary between juvenile and adult cells was spike duration, which was longer in juvenile cells, suggesting the potential for activation of second-messenger cascades and/or enhanced synaptic transmission onto target cells of lMAN neurons. The pattern of synaptic response observed in both juvenile and adult cells suggests that lMAN projection neurons receive direct excitatory afferent inputs, as well as disynaptic inhibitory inputs from interneurons within lMAN. Activation of inhibitory interneurons rapidly curtails the excitatory response seen in projection neurons. This inhibition was abolished by bicuculline, indicating that the inhibitory interneurons normally exert their postsynaptic response via GABA_A receptors on projection neurons. The inhibitory response could also be blocked by CNQX (6-cyano-7-nitroquinoxaline-2,3-dione), suggesting that the activation of inhibitory interneurons within lMAN may be governed primarily by AMPA receptors. © 1998 John Wiley & Sons, Inc. J Neurobiol 37: 642–658, 1998     

Heterogenous properties of dentate granule neurons in the adult rat

Postnatal neurogenesis contributes substantially to the neuronal population of the adult dentate gyrus. We report here that the neurons located in the deep aspects of the granule cell layer, near the proliferative zone, have different properties from those located in the superficial layers. The former group of neurons, tentatively designated as young, can be readily identified in a standard hippocampal slice preparation by morphological, immunohistochemical, and electrophysiological criteria. Electrophysiological recordings and imaging with Lucifer yellow from these neurons in the standard hippocampal slice preparation showed one or two main dendrites and conically shaped branches possessing varicose protrusions. These features are in agreement with the appearance of the same population of young neurons immunopositive for TOAD-64, a marker for immature neurons. In disinhibited slices, these putative young neurons are distinguished from the mature neurons, located in the superficial granule cell layer, by showing paired pulse facilitation and having a lower threshold for induction of long-term potentiation. The putative young neurons are completely unaffected by GABA(A) inhibition and always display robust long-term potentiation. In contrast, the mature neurons never produce long-term potentiation when the GABA(A) inhibition is intact. We propose that the heterogeneity of the functional properties of the granule neurons is related to the ongoing neurogenesis in the adult animals.     

Disrupted-In-Schizophrenia 1 regulates integration of newly generated neurons in the adult brain

Adult neurogenesis occurs throughout life in discrete regions of the adult mammalian brain. Little is known about the mechanism governing the sequential developmental process that leads to integration of new neurons from adult neural stem cells into the existing circuitry. Here, we investigated roles of Disrupted-In-Schizophrenia 1 (DISC1), a schizophrenia susceptibility gene, in adult hippocampal neurogenesis. Unexpectedly, downregulation of DISC1 leads to accelerated neuronal integration, resulting in aberrant morphological development and mispositioning of new dentate granule cells in a cell-autonomous fashion. Functionally, newborn neurons with DISC1 knockdown exhibit enhanced excitability and accelerated dendritic development and synapse formation. Furthermore, DISC1 cooperates with its binding partner NDEL1 in regulating adult neurogenesis. Taken together, our study identifies DISC1 as a key regulator that orchestrates the tempo of functional neuronal integration in the adult brain and demonstrates essential roles of a susceptibility gene for major mental illness in neuronal development, including adult neurogenesis.     

Music and emotions in the brain: familiarity matters

The importance of music in our daily life has given rise to an increased number of studies addressing the brain regions involved in its appreciation. Some of these studies controlled only for the familiarity of the stimuli, while others relied on pleasantness ratings, and others still on musical preferences. With a listening test and a functional magnetic resonance imaging (fMRI) experiment, we wished to clarify the role of familiarity in the brain correlates of music appreciation by controlling, in the same study, for both familiarity and musical preferences. First, we conducted a listening test, in which participants rated the familiarity and liking of song excerpts from the pop/rock repertoire, allowing us to select a personalized set of stimuli per subject. Then, we used a passive listening paradigm in fMRI to study music appreciation in a naturalistic condition with increased ecological value. Brain activation data revealed that broad emotion-related limbic and paralimbic regions as well as the reward circuitry were significantly more active for familiar relative to unfamiliar music. Smaller regions in the cingulate cortex and frontal lobe, including the motor cortex and Broca's area, were found to be more active in response to liked music when compared to disliked one. Hence, familiarity seems to be a crucial factor in making the listeners emotionally engaged with music, as revealed by fMRI data.     

Multicomponent synaptic potentials in rubrospinal neurons of cat brain evoked by corticofugal impulses

The compound nature of EPSP occurring in response to stimulation of the sensorimotor area of the cerebral cortex and the association area of the parietal cortex was shown during acute experiments on cats anesthetized by pentobarbital using an intracellular recording technique. The monosynaptic nature of the two first components of EPSP produced by corticofugal impulses spreading at the average rate of 18.5 and 7.5 msec, respectively, was established. It is postulated that these EPSP components are produced by activating the slow conducting pyramidal and corticorubral neurons. In a portion of rubrospinal neurons the first component of EPSP produced by corticofugal impulses was marked by a fast-rising phase and reflected electrophysiological activation of axosomatic synapses. Findings are discussed with regard to mechanisms reorganizing cortical synaptic inputs to the red nucleus neurons.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 17, No. 5, pp. 665–672, September–October, 1985.     

Regeneration of functional synaptic connections between widely separated neurons in the adult mammalian central nervous system

The responses to light of retinal ganglion cells with regenerated axons can be recorded from axons teased from peripheral nerve grafts replacing the optic nerve of the adult rat or hamster. These responses resemble those of normal retinal ganglion cells but can no longer be observed several months after grafting, concomitant with ongoing loss of the population of axotomized retinal ganglion cells. Synapses formed with neurons in the superior colliculus by retinal ganglion cell axons regenerated through peripheral nerve grafts mediate both excitatory and inhibitory responses. These experiments demonstrate that when provided with an appropriate milieu for elongation, neurons indigenous to the adult mammalian central nervous system can make functional reconnections with distant targets within the nervous system.     

成年斑胸草雀在体HVC-RA突触传递的电生理特性

鸣禽高级发声中枢（high vocal center,HVC）至弓状皮质栎核（robust nucleus ofthe arcopallium,RA）的突触传递是鸣唱运动通路中的关键部分.本文运用在体场电位电生理记录的方法,研究了成年雄性斑胸草雀（Taeniopygia guttata）HVC-RA突触的电生理特性.实验结果显示,刺激HVC,在RA内所记录到的诱发场电位幅度较小.配对脉冲检测发现,HVC-RA突触传递具有明显的配对脉冲易化特性.当以强直刺激作用于HVC,RA内诱发场电位随即显著减小,并在15 min内逐渐恢复,表明HVC-RA突触传递在强直刺激过后出现了短时抑制.该通路的突触传递特性可能与其在发声控制中的作用有关.以上的实验结果为进一步研究发声运动过程中的突触可塑性提供了资料.