Substance P in the ascending cholinergic reticular system

The neocortex receives a major cholinergic innervation from magnocellular neurones in the basal forebrain. However, an ascending cholinergic reticular system has also been postulated to arise from acetylcholinesterase (AChE)-containing neurones in the midbrain and pontine tegmentum. Lesions of this region decrease both AChE and choline acetyltransferase (ChAT) in various forebrain areas, and recent immunohistochemical studies have identified a group of ChAT-containing cell bodies in the midbrain reticular formation and dorsolateral pontine tegmentum. Here we have combined retrograde tracing with ChAT immunohistochemistry to demonstrate that this tegmental cholinergic cell group also directly innervates the cerebral cortex. Other immunohistochemical studies have indicated that the neuropeptide substance P is also present in certain cells in the laterodorsal tegmentum, and these too appear to project to the forebrain. We have therefore performed immunohistochemistry for both ChAT and substance P and have discovered that a subpopulation of the ascending cholinergic reticular neurones contains substance P. Thus, peptide-cholinergic coexistence, previously noted in peripheral neurones, also occurs in the brain.     

游泳训练及环境应激对大鼠中脑酪氨酸羟化酶与纹状体多巴胺含量的影响

50只SD雄性成年大鼠分别接受不同时间的水应激、一次性力竭游泳运动和长期游泳耐力训练,用免疫印迹法检测中脑TH含量,以荧光发光分析法检测纹状体DA含量。结果显示：长期游泳训练与安静状态的大鼠和一次性力竭游泳大鼠相比中脑TH含量有升高的趋势,但以上变化并没有显著性差异;而一次性力竭游泳运动使得大鼠纹状体DA含量高与安静组,长期游泳耐力训练引起了大鼠纹状体DA含量显著性升高;处于一次性水环境与长期水环境的大鼠中脑TH与纹状体DA含量无显著性差异;长期耐力游泳训练大鼠中脑TH和纹状体DA含量显著性高于处于水环境的大鼠。提示：一次性力竭游泳运动抑制了中脑TH活性,而长期游泳耐力训练有助于提高大鼠中脑TH含量,增加纹状体DA的释放量,提高中枢兴奋性,从而能够改善中枢机能,延迟中枢疲劳的发生时间;水环境会抑制大鼠中脑TH含量,从而使机体处于中枢抑制状态,建议在建立大鼠游泳训练模型中,应增列水环境对照组,从而增强实验的可比性与真实性。     

Phorbol esters block a voltage-sensitive chloride current in hippocampal pyramidal cells

The importance of second-messenger systems in controlling the excitability of neurones and other cells, through modulation of voltage- and calcium-dependent ionic conductances, has become increasingly clear. Cyclic AMP, acting via protein kinase A, has been identified as the second messenger for several neurotransmitters, and recent studies have suggested that activation of protein kinase C may have similar modulatory actions on neurones. Calcium and potassium currents have so far been shown to be the major ionic conductances modified by kinase activation. We now report that hippocampal pyramidal cells contain a previously undescribed voltage-dependent chloride current which is active at resting potential and is turned off either by membrane depolarization or by activation of protein kinase C by phorbol esters. We propose that this current may reside predominantly in the cell's dendritic membrane and thereby may regulate dendritic excitability.     

Dopamine neurons derived from human ES cells efficiently engraft in animal models of Parkinson's disease

Human pluripotent stem cells (PSCs) are a promising source of cells for applications in regenerative medicine. Directed differentiation of PSCs into specialized cells such as spinal motoneurons or midbrain dopamine (DA) neurons has been achieved. However, the effective use of PSCs for cell therapy has lagged behind. Whereas mouse PSC-derived DA neurons have shown efficacy in models of Parkinson's disease, DA neurons from human PSCs generally show poor in vivo performance. There are also considerable safety concerns for PSCs related to their potential for teratoma formation or neural overgrowth. Here we present a novel floor-plate-based strategy for the derivation of human DA neurons that efficiently engraft in vivo, suggesting that past failures were due to incomplete specification rather than a specific vulnerability of the cells. Midbrain floor-plate precursors are derived from PSCs 11 days after exposure to small molecule activators of sonic hedgehog (SHH) and canonical WNT signalling. Engraftable midbrain DA neurons are obtained by day 25 and can be maintained in vitro for several months. Extensive molecular profiling, biochemical and electrophysiological data define developmental progression and confirm identity of PSC-derived midbrain DA neurons. In vivo survival and function is demonstrated in Parkinson's disease models using three host species. Long-term engraftment in 6-hydroxy-dopamine-lesioned mice and rats demonstrates robust survival of midbrain DA neurons derived from human embryonic stem (ES) cells, complete restoration of amphetamine-induced rotation behaviour and improvements in tests of forelimb use and akinesia. Finally, scalability is demonstrated by transplantation into parkinsonian monkeys. Excellent DA neuron survival, function and lack of neural overgrowth in the three animal models indicate promise for the development of cell-based therapies in Parkinson's disease.     

P物质对大鼠星状神经节细胞的影响

应用细胞内生物电记录方法，观察神经肽Ｐ物质（ＳＰ）对大鼠星状神经节能细胞的影响，用灌流或用加压向细胞周围施加ＳＰ可使部分细胞发生膜除极反应，用低钙或用含河豚毒素克氏液灌流神经节，并不影响ＳＰ引起的除极反应的幅度和时程。ＳＰ引起除极反应的同时常伴有膜电阻增大，当膜电位增大时，除极化反应幅度变小，反转电位为－８０ｍＶ至－１００ｍＶ，研究表明，ＳＰ对部分星状神经节细胞具有直接兴奋作用，并且ＳＰ对细胞膜的     

Nicotine reinforcement and cognition restored by targeted expression of nicotinic receptors

Worldwide, 100 million people are expected to die this century from the consequences of nicotine addiction, but nicotine is also known to enhance cognitive performance. Identifying the molecular mechanisms involved in nicotine reinforcement and cognition is a priority and requires the development of new in vivo experimental paradigms. The ventral tegmental area (VTA) of the midbrain is thought to mediate the reinforcement properties of many drugs of abuse. Here we specifically re-expressed the beta2-subunit of the nicotinic acetylcholine receptor (nAChR) by stereotaxically injecting a lentiviral vector into the VTA of mice carrying beta2-subunit deletions. We demonstrate the efficient re-expression of electrophysiologically responsive, ligand-binding nicotinic acetylcholine receptors in dopamine-containing neurons of the VTA, together with the recovery of nicotine-elicited dopamine release and nicotine self-administration. We also quantified exploratory behaviours of the mice, and showed that beta2-subunit re-expression restored slow exploratory behaviour (a measure of cognitive function) to wild-type levels, but did not affect fast navigation behaviour. We thus demonstrate the sufficient role of the VTA in both nicotine reinforcement and endogenous cholinergic regulation of cognitive functions.     

Dopaminergic stimulation of prolactin release

Prolactin (PRL) secretion from anterior pituitary is believed to be under tonic inhibitory control of dopamine (DA) released from the tubero-infundibular dopaminergic neurones into the hypophysial portal blood. Inhibition of PRL release by DA seems to be mediated by sereospecific DA receptors located in PRL cells. Apomorphine and various ergot alkaloids such as bromocryptine mimic the inhibitory effect of DA both in vivo and in vitro, presumably by a direct agonist action on these 'inhibitory' receptors. We now report that PRL secretion in primary cultures of rat pituitary cells can be stimulated by DA when concentrations a thousand times lower than those required for inhibition are used. Secretion rates above basal release can also be induced by apomorphine and bromocryptine when the 'inhibitory' receptors are blocked with certain DA receptor antagonists.     

Evidence that substance P is a neurotransmitter in the myenteric plexus

Substance P (SP) is an undecapeptide originally isolated from the gut and since shown to occur within neurones in several parts of the peripheral and central nervous systems. Immunohistochemical studies indicate an exceedingly dense network of SP-containing nerves within the myenteric plexus of the guinea pig ileum. These nerves are intrinsic to the gut wall and can release SP to contract the longitudinal muscle layer. We have previously shown that SP directly depolarizes myenteric neurones and that this depolarization has a time course and ionic mechanism similar to the slow excitatory postsynaptic potential (e.p.s.p.) which can be produced by electrical stimulation of presynaptic nerves within the myenteric ganglia. We wondered whether SP might mediate this slow synaptic potential. We report here that the SP depolarization and the slow e.p.s.p. are reversibly depressed by chymotrypsin, an enzyme which degrades SP, although the responses to acetylcholine, serotonin and an unknown hyperpolarizing transmitter are unaffected. The results provide direct evidence that a peptide can mediate chemical transmission between neurones in the mammalian nervous system.     

Dopaminergic D-3 binding sites are not presynaptic autoreceptors

Postsynaptic dopamine (DA) receptors have been classified biochemically and pharmacologically into two types: D-1 receptors mediate adenylate cyclase stimulation, demonstrating micromolar affinity for DA and butyrophenone antagonists; D-2 receptors mediate adenylate cyclase inhibition, demonstrating nanomolar affinity for DA and butyrophenone antagonists. D-1 receptors are labelled by 3H-thioxanthene antagonists, while D-2 receptors are labelled by both 3H-agonists and all 3H-antagonists. A third class of dopaminergic binding site, termed D-3, represents high-affinity 3H-agonist binding sites demonstrating low, micromolar, affinity for butyrophenones. In the rat striatum, D-3 sites were decreased 50% by 6-hydroxydopamine (6-OHDA) lesions of the nigrostriatal DA pathway, suggesting that such D-3 binding labels presynaptic DA autoreceptors on nigrostriatal terminals. However, nigrostriatal denervation produces a concomitant depletion of striatal DA. Here we demonstrate that a reserpine-induced depletion of DA produces a decrease in D-3 binding comparable to that seen with nigrostriatal denervation, independent of presynaptic terminal degeneration. This loss in binding, or that caused by 6-OHDA lesions, is recovered by preincubating the striatal membranes with DA or with the supernatant from control striatal membrane preparations. We therefore suggest that the loss of D-3 binding following 6-OHDA lesions results from the depletion of endogenous DA rather than the degeneration of terminals and their putatively associated autoreceptors.     

Repeated cocaine exposure in vivo facilitates LTP induction in midbrain dopamine neurons

Drugs of abuse are known to cause persistent modification of neural circuits, leading to addictive behaviours. Changes in synaptic plasticity in dopamine neurons of the ventral tegmental area (VTA) may contribute to circuit modification induced by many drugs of abuse, including cocaine. Here we report that, following repeated exposure to cocaine in vivo, excitatory synapses to rat VTA dopamine neurons become highly susceptible to the induction of long-term potentiation (LTP) by correlated pre- and postsynaptic activity. This facilitated LTP induction is caused by cocaine-induced reduction of GABA(A) (gamma-aminobutyric acid) receptor-mediated inhibition of these dopamine neurons. In midbrain slices from rats treated with saline or a single dose of cocaine, LTP could not be induced in VTA dopamine neurons unless GABA-mediated inhibition was reduced by bicuculline or picrotoxin. However, LTP became readily inducible in slices from rats treated repeatedly with cocaine; this LTP induction was prevented by enhancing GABA-mediated inhibition using diazepam. Furthermore, repeated cocaine exposure reduced the amplitude of GABA-mediated synaptic currents and increased the probability of spike initiation in VTA dopamine neurons. This cocaine-induced enhancement of synaptic plasticity in the VTA may be important for the formation of drug-associated memory.     

Somatostatin immunoreactivity in neuritic plaques of Alzheimer's patients

Senile dementia of the Alzheimer's type can be diagnosed with certainty only by examining neurofibrillary tangles and neuritic plaques under the microscope. Recently, it has been suggested that the condition is linked to specific neurotransmitter systems, with a decline of cortical acetylcholine, choline acetyltransferase, cholinergic neurones projecting to the cortex, cortical noradrenaline content, locus coeruleus neurones and cortical somatostatic content. Using immunocytochemical methods, we here report that somatostatin-immunoreactive processes are present in neuritic plaques in human Alzheimer's specimens. These data, as well as other reports of non-cholinergic changes, strongly imply that Alzheimer's disease cannot be linked exclusively to cortical cholinergic elements, as proposed previously. Rather, our data on plaque and somatostatin co-localization and distribution patterns suggest that Alzheimer's neuropathology may involve primarily the loss of selective cortical neurones that are targets of the implicated transmitter systems and that plaque formation may result from the degeneration of presynaptic and postsynaptic neurites of large projection neurones in layers III and V. Given the neurochemically heterogeneous input to these cells, it is not surprising that several neurotransmitter systems, one of which is somatostatin, are implicated in the pathology of Alzheimer's disease.     

Nerve growth factor is a mitogen for cultured chromaffin cells

Nerve growth factor (NGF) is essential for the survival and differentiation of a number of neural crest derivatives, including sympathetic and sensory neurones. While early studies suggested that NGF might also have a mitogenic effect on these neurones, subsequent work has favoured the interpretation that NGF promotes cell survival or differentiation rather than proliferation. We have addressed the issue of a mitogenic effect of NGF using adrenal chromaffin cells, which are endocrine cells derived from the neural crest, and are closely related to sympathetic neurones. Adrenal chromaffin cells respond to NGF in vitro by expressing neuronal traits. We now report that NGF elicits a mitotic response in cultured chromaffin cells from young rats, and that this response is blocked by an antiserum to 2.5S NGF. The chromaffin cells that divided in response to NGF can subsequently become neuronal in the continued presence of NGF.     

稀土钝钒剂对钒污染催化剂活性与再生性能的影响

考察了稀土钝钒剂（其活性组分为Ｌａ２Ｏ３）对钒污染的ＲＨＺ－３００裂化催化剂的裂化活性、生焦及再生性能的影响。研究结果表明,随着钝钒剂中活性组分Ｌａ２Ｏ３负载量的增加,催化剂的裂解活性也增加,但负载量有一个最佳值。同时,随着钝钒剂加入量的增加,催化剂的裂解活性增加,其加入量也有一个最佳值。稀土钝钒剂能明显地抑制钒污染的ＲＨＺ－３００催化剂的生焦。对催化剂的烧焦反应行为及热重动力学研究表明,稀土钝钒剂的加入能明显地降低烧焦反应的活化能和烧焦温度,并有助于催化剂的低温再生。     

Positron emission tomography after MPTP: observations relating to the cause of Parkinson's disease

The dopa analogue 6-fluorodopa (6-FD) used with positron emission tomography (PET) allows in vivo visualization of dopamine and its metabolites in nigrostriatal nerve endings. We have now found abnormal 6-FD scans in four subjects exposed to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). None had parkinsonism. The results suggest subclinical damage to the nigrostriatal pathway. This is the first direct evidence that dopaminergic impairment can exist without clinical deficits. Here we discuss this finding in the context of the hypothesis that Parkinson's disease may stem from clinically silent damage to the substantia nigra, followed by slow attrition of neurones in this region because of its particular vulnerability to cell loss as a normal consequence of ageing.     

ATP excites a subpopulation of rat dorsal horn neurones

The peripheral receptive properties and central projections of different classes of dorsal root ganglion neurones are well characterized. Much less is known about the transmitters used by these neurones. Excitatory amino acids have been proposed as sensory transmitters but the sensitivity of virtually all central neurones to those compounds has made it difficult to assess their precise role in sensory transmission. Several neuropeptides have been localized within discrete subclasses of primary sensory neurones that project to the superficial dorsal horn of the spinal cord and may be afferent transmitters. However, only about one-third of spinal sensory neurones have been shown to contain neuropeptides. We have recently described the presence of a 5'-nucleotide hydrolysing acid phosphatase in a separate subpopulation of dorsal root ganglion neurones that project to the superficial dorsal horn. This enzyme also appears in certain autonomic and endocrine cells that contain high concentrations of releasable nucleotides in their storage granules. It is possible that the presence of this enzyme in sensory neurones is also associated with a releasable pool of nucleotides. Holton and Holton have provided evidence that ATP is released from the peripheral terminals of unmyelinated sensory fibres and have suggested that release of ATP might also occur from central sensory terminals. To investigate the possibility that nucleotides act as central sensory transmitters we have examined their actions on rat dorsal horn and dorsal root ganglion neurones maintained in dissociated cell culture. We report here a selective and potent excitation of subpopulations of both neuronal types by ATP.     

Bipolar cells in the mudpuppy retina use an excitatory amino acid neurotransmitter

The bipolar cells of the vertebrate retina are the principal neuronal elements which transmit photoreceptor activity from the outer to the inner retina. An important function of the bipolars is to segregate photoreceptor input into independent ON and OFF channels which are subserved, respectively, by the depolarizing and hyperpolarizing bipolar subtypes. Ultrastructural and physiological observations suggest that chemical neurotransmission is the predominant means of bipolar input to the inner retina. Both ON and OFF bipolars apparently release excitatory transmitters. Histological studies with cytotoxic agents and physiological studies indicate that third-order neurones have excitatory amino acid receptors. In ON-OFF amacrine and ganglion cells, which receive input from both bipolars, ON and OFF excitation have a similar ionic basis, suggesting that the same transmitter may be released by both types of bipolars. We have now found that (+/-)cis-2,3-piperidine dicarboxylic acid (PDA), a new excitatory amino acid antagonist, blocks bipolar input to the inner retina and thus suggests that an excitatory amino acid is a bipolar cell transmitter.     

Multiple classes of glutamate receptor on depolarizing bipolar cells in retina

Multiple subtypes of excitatory amino acid receptor have been found on individual dissociated neurones. These findings were obtained from cells without intact synaptic connections, so the functional roles for such receptor subtypes are unknown. We have recorded intracellular responses from depolarizing bipolar cells (DBC) that receive direct synaptic input from two distinct populations of neurones: rods and cones. We report here that 2-amino-4-phosphonobutyrate (APB), a glutamate analogue, reveals two subtypes of glutamate receptors on DBCs. APB acts on the same receptor that mediates synaptic transmission from rods but has no action on the second subtype of glutamate receptor. These results show that the rod and cone inputs to DBCs are mediated by pharmacologically distinct receptors and that subtypes of glutamate receptor existing on single neurones can subserve separate, functionally defined synaptic inputs.     

Increase of corticotropin-releasing factor staining in rat paraventricular nucleus neurones by depletion of hypothalamic adrenaline

In response to stress, adrenocorticotropic hormone (ACTH) is released by corticotrophs in the anterior pituitary under the control of several central and peripheral factors including corticotropin-releasing factor (CRF), which was recently isolated from the brain and sequenced. Immunocytochemical studies have shown that most of the CRF-containing cell bodies that project to the median eminence are present in the hypothalamic paraventricular nucleus (PVN). A dense PNMT(phenylethanolamine-N-methyltransferase)-containing fibre network was also observed in the same region--PNMT is the final enzyme in the biosynthesis of adrenaline and has been demonstrated in the brain. In the present study we found an association of adrenergic nerve fibres and CRF neurones by immunohistochemistry using antisera to PNMT and CRF. To examine the functional significance of the adrenergic projection to the PVN, we blocked the synthesis of adrenaline using a specific inhibitor of PNMT. The depletion of adrenaline resulted in an increase in CRF immunoreactivity. The present results suggest that, as well as catecholamines which regulate ACTH release at the anterior pituitary level via a beta 2-adrenergic receptor mechanism, central catecholamines (mainly adrenaline) also affect ACTH release through their action on CRF cells. Peripheral catecholamines seem to have a direct stimulatory effect on the pituitary corticotroph cells, whereas the present findings suggest that central adrenaline-containing neurones have an inhibitory role in the physiological response to stress.     

Synaptic potentiation onto habenula neurons in the learned helplessness model of depression

The cellular basis of depressive disorders is poorly understood. Recent studies in monkeys indicate that neurons in the lateral habenula (LHb), a nucleus that mediates communication between forebrain and midbrain structures, can increase their activity when an animal fails to receive an expected positive reward or receives a stimulus that predicts aversive conditions (that is, disappointment or anticipation of a negative outcome). LHb neurons project to, and modulate, dopamine-rich regions, such as the ventral tegmental area (VTA), that control reward-seeking behaviour and participate in depressive disorders. Here we show that in two learned helplessness models of depression, excitatory synapses onto LHb neurons projecting to the VTA are potentiated. Synaptic potentiation correlates with an animal's helplessness behaviour and is due to an enhanced presynaptic release probability. Depleting transmitter release by repeated electrical stimulation of LHb afferents, using a protocol that can be effective for patients who are depressed, markedly suppresses synaptic drive onto VTA-projecting LHb neurons in brain slices and can significantly reduce learned helplessness behaviour in rats. Our results indicate that increased presynaptic action onto LHb neurons contributes to the rodent learned helplessness model of depression.