The ontogenetic origins of mirror neurons: evidence from 'tool-use' and 'audiovisual' mirror neurons

Since their discovery, mirror neurons-units in the macaque brain that discharge both during action observation and execution-have attracted considerable interest. Whether mirror neurons are an innate endowment or acquire their sensorimotor matching properties ontogenetically has been the subject of intense debate. It is widely believed that these units are an innate trait; that we are born with a set of mature mirror neurons because their matching properties conveyed upon our ancestors an evolutionary advantage. However, an alternative view is that mirror neurons acquire their matching properties during ontogeny, through correlated experience of observing and performing actions. The present article re-examines frequently overlooked neurophysiological reports of 'tool-use' and 'audiovisual' mirror neurons within the context of this debate. It is argued that these findings represent compelling evidence that mirror neurons are a product of sensorimotor experience, and not an innate endowment.     

Synaptic properties of layer VI inverted pyramidal cells in the rodent somatosensory cortex

The properties of specific cortical cell types enable greater understanding of how cortical microcircuits process and transmit sensory, motor, and cognitive information. Previous reports have characterized the intrinsic properties of the inverted pyramidal cell (IPC) where the most prominent dendrite is orientated towards the cortical white matter. Using whole cell patch clamp recordings from rat and mouse somatosensory cortex in conjunction with electric microstimulation of the white matter we characterized the synaptic inputs onto IPCs and the more common upright pyramidal cell (UPC) in the infragranular layers. Both classes of pyramidal cells received monosynaptic glutamatergic input following white matter stimulation, but varied on a number of parameters. Most prominently, UPCs displayed higher amplitude responses and showed greater rates of depression compared to IPCs. These data reinforce the view that IPCs are a separate functional class of cortical neuron.     

Control of luteinizing hormone-releasing hormone pulse generation in nonhuman primates

Summary 1. The pulsatile release of luteinizing hormone-releasing hormone (LHRH) is critical for reproductive function. However, the exact mechanism of LHRH pulse generation is unclear. The purpose of this article is to review the current knowledge on LHRH pulse generation and to discuss a series of studies in our laboratory.2. Using push-pull perfusion in the stalk-median eminence of the rhesus monkey several important facts have been revealed. There is evidence indicating that LHRH neurons themselves have endogenous pulse-generating mechanisms but that the pulsatility of LHRH release is also modulated by input from neuropeptide Y (NPY) and norepinephrine (NE) neurons. The release of NPY and NE is pulsatile, with their pulses preceding or occurring simultaneously with LHRH pulses, and the neuroligands NPY and NE and their agonists stimulate LHRH pulses, while the antagonists of the ligands suppress LHRH pulses.3. The pulsatile release of LHRH increases during the estrogen-induced LH surge as well as the progesterone-induced LH surge. These increases are partly due to the stimulatory effects of estrogen and progesterone on NPY neurons.4. An increase in pulsatile LHRH release occurs at the onset of puberty. This pubertal increase in LHRH release appears to be due to the removal of tonic inhibition from aminobutyric acid (GABA) neurons and a subsequent increase in the inputs of NPY and NE neurons to LHRH neurons.5. There are indications that additional neuromodulators are involved in the control of the LHRH pulse generation and that glia may play a role in coordinating pulses of the release of LHRH and neuromodulators.6. It is concluded that the mechanism generating LHRH pulses appears to comprise highly complex cellular elements in the hypothalamus. The study of neuronal and nonneuronal elements of LHRH pulse generation may serve as a model to study the oscillatory behavior of neurosecretion.     

Ontogeny of Neurochemical Markers for Noradrenergic, GABAergic and Cholinergic Neurons in Neocortex Lesioned with Methylazoxymethanol Acetate

Abstract: Methylazoxymethanol acetate (MAM), a potent, rapidly eliminated nucleic acid alkylating agent, produces microencephaly in rat pups when injected into their dams on day 15 of gestation. In the adult microencephalic rats, neuronal loss is largely confined to telencephalic structures, such as the superficial neocortical laminae, whose neuroepithelial progenitor cells were undergoing vigorous replication during the chemical exposure. Histological examination of the forebrain 2 days after injection revealed early selective damage to the ventricular geminal zone with relative sparing of cortical plate neurons generated on earlier days. The degree of specificity of MAM's action on neurochemically defined neuronal populations was examined by measuring presynaptic markers for GABAergic, noradrenergic and cholinergic neurons in atrophic lateral cortex from 20 days gestation to adulthood. Although treatment reduced GABAergic markers (GABA, its synthetic enzyme and synaptosomal uptake process) in proportion to loss of cortex mass (-67%), the maturational pattern for remaining GABAergic neurons was virtually normal. Although the maturational sequence of noradrenergic markers was similar to control, the concentration of endogenous norepinephrine, [³H]norepinephrine uptake and tyrosine hydroxylase specific activity were two- to fourfold higher than control at each time. However, total noradrenergic markers per cortex section were nearly identical to control throughout development, indicating that development of the noradrenergic axonal arbor in neocortex was insensitive to loss of neurons in the terminal field. Maturation of cholinergic markers (endogenous acetylcholine, its synthetic enzyme and [³H]choline uptake) in the atrophic cortex was biphasic: concentrations were similar to control values for the first 12 postnatal days, but gradually rose to levels twofold higher than control. These results indicate that neurochemical alterations observed in cortex from prenatally MAM-treated rats are primarily the result of early selective elimination of neuronal subpopulations. Fetal MAM exposure appeared to have minimal effects on biochemical differentiation of neurons remaining intact in the atrophic cortex. MAM appears to be a useful toxin for producing selective loss of neuronal groups based on their time of generation in the fetus.     

Laser microirradiation of cerebellar neurons in culture

Electrophysiological and ultrastructural effects of focused laser radiation on neurons from neonatal rat cerebellum in tissue culture are reported. Action potentials were elicited by an extracellular current pulse train. The stimulator voltage required for half-maximum response frequency was measured as a function of the energy delivered by a single laser pulse. Above a “threshold” laser energy, the cell response to stimulation became negligible for all stimulator voltages. Electron micrographs of cells revealed that the mitochondria are preferentially damaged at an energy comparable to the electrophysiological threshold. The damaged mitochondria showed swollen matrix space and disrupted cristae membranes. Higher laser energies resulted in damage to other cytoplasmic structures. The results are consistent with a model that assumes that light interaction with the nerve cells proceeds by local heating of the mitochondria and nearby structures and leads to an increased conductance of the membrane to some ionic species.     

Neurochemical Studies of the Mesolimbic Dopaminergic Pathway: Somatodendritic Mechanisms and GABAergic Neurones in the Rat Ventral Tegmentum

Abstract: The rat ventral tegmentum (containing dendrites and somata of mesolimbic neurones) contained 1.3 μg/g of dopamine, which was reduced to 40% of the control level by reserpine. Slices of ventral tegmentum were able to accumulate and release (elevated potassium or protoveratrine A) exogenous [³H]dopamine. In parallel studies the uptake mechanism in ventral tegmentum was shown to be virtually identical to the nerve terminal uptake of [³H]dopamine by slices of nucleus accumbens. The release of [³H]dopamine was indistinguishable from that observed in substantia nigra, where there is substantial evidence for dendritic mechanisms. Basal adenylate cyclase activity was present, but dopamine-stimulated activity was not detected. A high GABA concentration (7.7 μmol/g) was present in ventral tegmentum, in conjunction with an uptake and a release mechanism for [³H]GABA. GABA and muscimol elicited a small, reproducible efflux of [³H]dopamine, but an interaction between dopamine and [³H]GABA efflux was not observed. The results are in accord with transmitter roles for dopamine and GABA in the somatoden-dritic area of mesolimbic dopaminergic neurons.     

脑室注射5-羟色胺对大鼠丘脑束旁核痛兴奋和痛抑制神经元电活动的调制作用

本实验利用两根微电极同时记录大鼠丘脑束旁核两个痛兴奋、两个痛抑制或一个痛兴奋和一个痛抑制神经元的放电,观察脑室注射5-羟色胺后对两个神经元同时电活动的影响。结果表明,当脑内5-羟色胺含量增加时,丘脑束旁核两个神经元同时电活动的变化主要有如下三个方面:1.两个痛兴奋神经元的电活动均受抑制,诱发放电频率减少,潜伏期延长。2.两个痛抑制神经元抑制均解除,诱发抑制时程均缩短。3.一个痛兴奋神经元电活动受抑制的同时,另一个痛抑制神经元的电活动加强。以上结果提示,在痛和镇痛过程中,痛兴奋和痛抑制神经元的作用是协同进行的。     

Diverse mechanisms for assembly of branchiomeric nerves

The formation of branchiomeric nerves (cranial nerves V, VII, IX and X) from their sensory, motor and glial components is poorly understood. The current model for cranial nerve formation is based on the Vth nerve, in which sensory afferents are formed first and must enter the hindbrain in order for the motor efferents to exit. Using transgenic zebrafish lines to discriminate between motor neurons, sensory neurons and peripheral glia, we show that this model does not apply to the remaining three branchiomeric nerves. For these nerves, the motor efferents form prior to the sensory afferents, and their pathfinding show no dependence on sensory axons, as ablation of cranial sensory neurons by ngn1 knockdown had no effect. In contrast, the sensory limbs of the IXth and Xth nerves (but not the Vth or VIIth) were misrouted in gli1 mutants, which lack hindbrain bmn, suggesting that the motor efferents are crucial for appropriate sensory axon projection in some branchiomeric nerves. For all four nerves, peripheral glia were the intermediate component added and had a critical role in nerve integrity but not in axon guidance, as foxd3 null mutants lacking peripheral glia exhibited defasciculation of gVII, gIX, and gX axons. The bmn efferents were unaffected in these mutants. These data demonstrate that multiple mechanisms underlie formation of the four branchiomeric nerves. For the Vth, sensory axons initiate nerve formation, for the VIIth the sensory and motor limbs are independent, and for the IXth/Xth the motor axons initiate formation. In all cases the glia are patterned by the initiating set of axons and are needed to maintain axon fasciculation. These results reveal that coordinated interactions between the three neural cell types in branchiomeric nerves differ according to their axial position.     

Immunocytochemical localization of somatostatin and vasotocin in the brain of the Pacific hagfish,Eptatretus stouti

Summary The brain of the Pacific hagfish, Eptatretus stouti, was studied immunocytochemically using antisera against somatostatin (SRIH), arginine vasopressin (AVP), and adrenocorticotropic hormone (ACTH). SRIH-immunoreactive perikarya were distributed bilaterally in the postoptic nucleus and in the hypothalamic nucleus. Although several short, stained fibers were observed in the vicinity of the perikarya, SRIH-immunoreactivity was not found in the neurohypophysis, nor in other parts of the brain. On the other hand, presumed arginine vasotocin (AVT) perikarya were distributed in an arc-shaped region extending from the posterior part of the preoptic nucleus to the anterior-most end of the hypothalamic nucleus and projected their fibers to the neurohypophysis. Most presumptive AVT perikarya were located close to the paired prehypophysial arteries near the anterior end of the postoptic nucleus. In the neurohypophysis, abundant presumptive AVT-fibers terminated in the posterior dorsal wall, although some fibers terminated in the anterior dorsal wall and only a few fiber endings were found in the ventral wall. No ACTH-positive cells were detected in the hagfish brain or in the pituitary gland.Supported from a grant from the National Science Foundation PCM 8141393     

Phosphorylation and dephosphorylation of distinct isoforms of the heavy neurofilament protein NF-H

Summary 1. Previous immunohistochemical studies led to the suggestion that distinctly phosphorylated neurofilament isoforms exist in different types of neurons. We have recently examined this hypothesis by direct biochemical experiments, which revealed that the heavy neurofilament protein NF-H of bovine ventral root cholinergic neurons is more acidic and markedly more phosphorylated than that of bovine dorsal root neurons.2. In the present study we employed this system to study the degree to which distinctly phosphorylated NF-H isoforms differ in the extents to which they can be phosphorylated and dephosphorylatedin vitro. This was performed utilizing alkaline phosphatase and protein kinase PK40^ERK, which is specific to serines of Lys-Ser-Pro (KSP) repeats. The results obtained reveal that:3. The more extensively phosphorylated ventral root NF-H is dephosphorylated more rapidly than dorsal root NF-H.4. Ventral root NF-H and dorsal root NF-H in their native form are both poor substrates of PK40^ERK.5. Following dephosphorylation, ventral root and dorsal root NF-H are phosphorylated extensively and differentially by this kinase. Under these conditions, PK40^ERK catalyzes the incorporation of, respectively, 4.2±1.3 and 2.8±0.6 mol of phosphate per molecule of ventral root NF-H and dorsal root NF-H. The ratio of phosphates incorporated into ventral root NF-H to those incorporated into dorsal root NF-H is 1.46±0.17.6. These findings support the hypothesis that different classes of neurons contain distinctly phosphorylated neurofilaments and show that ventral root and dorsal root neurons are a useful model system for studying the distinct characteristics of neurofilament phosphorylation in different types of neurons.     

A comprehensive study on long‐term injury to nigral dopaminergic neurons following intracerebroventricular injection of lipopolysaccharide in rats

Parkinson's disease (PD) is characterized by selective and progressive degeneration of dopaminergic neurons in the substantia nigra (SN). Lipopolysaccharide (LPS) can induce chronic inflammation and has been widely used to study the pathogenesis of PD. In this study, a single intracerebroventricular injection of LPS was used to induce neurotoxic effects on dopaminergic neurons in Sprague–Dawley rats. The long‐term neurotoxic effects of LPS were evaluated at different time points. Microglia were activated in the hippocampus and striatum at 4 weeks, and in the SN at 24 weeks. Astrocytes were activated in the hippocampus and nigrostriatal system at 2 and 24 weeks. The expression of brain‐derived neurotrophic factor in the SN increased at 4 weeks and decreased after 12 weeks, and tyrosine hydroxylase‐positive neurons in the SN were shown to have an atrophic appearance, with cell loss evident after 24 weeks. Phospho‐α‐synuclein expression, a reflection of parkinsonian pathogenesis, increased at 12 weeks, and peaked at 24 weeks. Abnormal motor behavior appeared at 16 weeks and lasted up to 48 weeks. These results indicate that microglia are activated for several months after a single, low dose injection of LPS, which eventually results in progressive and selective damage to dopaminergic neurons in the SN.     

Respiration in Primary Cultured Cerebellar Granule Neurons and Cerebral Cortical Neurons

Respiration was measured polarographically in primary cultures enriched with cerebellar granule neurons or cerebral cortical neurons. The basal respiratory rate, measured on the sixth day after culturing, was 12.00 natom equiv. O/mg protein/min for the cortical neurons and 12.70 natom equiv. O/mg protein/min for the granule neurons. Maximal stimulation by 2,4-dinitrophenol produced a 20-40% increase over the basal rate for both neuronal types. Oligomycin inhibited neuronal basal respiration by 45%. These respiratory rates in neurons from primary culture are markedly lower than those measured in astrocytes grown under similar conditions.     

Cerebrospinal fluid-contacting neurons in the regenerating spinal cord of lizards and amphibians are likely mechanoreceptors

During spinal cord (SC) regeneration in the tail of amphibians and lizards, small neurons in contact with the central canal and cerebrospinal fluid (CSF) are formed. The present review summarizes previous and recent studies that have characterized most of these neurons as cerebrospinal fluid-contacting neurons (CSFCNs), especially in the regenerating caudal SC of lizards. CSFCNs form tufts of stereocilia immersed in the CSF, secrete exosomes, and are often in contact with a secreted protein-rod indicated as Reissner fiber. Ultrastructural, autoradiographic, immunohistochemical, and behavioral studies strongly indicate that most of these cells are mechanoreceptors that differentiate from ependymal cells within 20–30 days after SC amputation. Numerous CSFCNs are gamma amino-butyric acid (GABA)-ergic, uptake amino acids, receive few synaptic boutons, and contain neurofilaments, fibroblast growth factor (FGFs), and other signaling proteins, the latter likely secreted into the central canal. Similar neurons are formed in the SC of the tuatara (Sphenodon puctatus), anurans, and urodeles during tail regeneration. In lizard, most of their projection remains in the SC close to the regenerated tail, but they form synapses with neurons that receive descending nerves from the brainstem, including vestibular nuclei. CSFCNs, aside a possible neurosecretory activity, might sense liquor movements for maintenance of balance, a role that is supported from recent studies on other caudate vertebrates. The regeneration of these cells also in the nervous system of other vertebrates remains unknown.     

Neural circuit mechanisms linking courtship and reward in Drosophila males

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Immunocytochemical localization of vasotocin and mesotocin in the hypothalamus of lacertilian reptiles

Summary The hypothalamic magnocellular neurosecretory system of lizards was studied with the unlabeled antibody peroxidase-antiperoxidase complex (PAP) technique at the light microscopic level. It was shown that vasotocin and mesotocin are synthesized in separate neurons. The vasotocinergic as well as the mesotocinergic perikarya are of different sizes. Both cell types occur in close juxtaposition, but without a distinct pattern of distribution. The external zone of the lacertilian median eminence contains numerous immunoreactive vasotocinergic fibers and only few immunoreactive mesotocinergic fibers. The general organization of the hypothalamic magnocellular neurosecretory system of lizards, as revealed by immunocytochemistry, is essentially similar to that revealed with unspecific staining methods.This investigation was supported by a grant from the Belgian Nationaal Fonds voor Geneeskundig Wetenschappelijk Onderzoek     

乙酰胆碱对大鼠丘脑束旁核痛兴奋和痛抑制神经元放电的影响

本实验观察了脑室注射乙酰胆碱(ACh)对丘脑束旁核(Pf)痛兴奋神经元(PEN)和痛抑制神经元(PIN)电活动的影响,并与吗啡的作用进行了比较。结果表明,脑内ACh增加可使PEN放电潜伏期延长,频率降低,持续时程缩短;可使PIN的完全抑制时程缩短。腹腔注射吗啡与ACh的作用相似。M胆碱受体阻断剂阿托品能阻断ACh对PEN和PIN的作用,但不影响吗啡对PEN和PIN的作用。说明吗啡镇痛不是通过胆碱能转递而实现的。     

Immunocytochemical investigation of the hypothalamo-neurohypophysial system in birds

Summary The results of an immunohistochemical investigation of the hypothalamo-neurohypophysial system in several species of birds have shown that: (1) mesotocin and vasotocin are synthesized in separate neurons; (2) in all species investigated the distribution of mesotocinergic and vasotocinergic perikarya follows a common pattern; (3) the external zone of the avian anterior median eminence contains exclusively vasotocinergic nerve fibers, originating in supraoptic and ventral paraventricular regions; (4) the distribution of immunoreactive elements in the neural lobe shows a definite species-dependent pattern.     

Tangential migration of glutamatergic neurons and cortical patterning during development: Lessons from Cajal‐Retzius cells

Tangential migration is a mode of cell movement, which in the developing cerebral cortex, is defined by displacement parallel to the ventricular surface and orthogonal to the radial glial fibers. This mode of long‐range migration is a strategy by which distinct neuronal classes generated from spatially and molecularly distinct origins can integrate to form appropriate neural circuits within the cortical plate. While it was previously believed that only GABAergic cortical interneurons migrate tangentially from their origins in the subpallial ganglionic eminences to integrate in the cortical plate, it is now known that transient populations of glutamatergic neurons also adopt this mode of migration. These include Cajal‐Retzius cells (CRs), subplate neurons (SPs), and cortical plate transient neurons (CPTs), which have crucial roles in orchestrating the radial and tangential development of the embryonic cerebral cortex in a noncell‐autonomous manner. While CRs have been extensively studied, it is only in the last decade that the molecular mechanisms governing their tangential migration have begun to be elucidated. To date, the mechanisms of SPs and CPTs tangential migration remain unknown. We therefore review the known signaling pathways, which regulate parameters of CRs migration including their motility, contact‐redistribution and adhesion to the pial surface, and discuss this in the context of how CR migration may regulate their signaling activity in a spatial and temporal manner. © 2015 Wiley Periodicals, Inc. Develop Neurobiol 76: 847–881, 2016