Non-neuronal Elements Research Articles

Neuropharmacology of anxiolytic drugs: A selected review of the field

The review begins by outlining some of the animal models of anxiety that have been used to evaluate anxiolytic activity. Whereas acute screening tests such as antagonism of chemically induced convulsions and foot shock-induced aggression in mice have proved to be useful in the selection of compounds chemically related to known anxiolytics, more sophisticated animal models of anxiety (e.g., the various conflict models) appear to be required if the essential features of human anxiety are to be simulated in the laboratory. The review summarizes our experience with such a model and also critically assesses the value of “open-field” induced stress in rats as a model of anxiety that is relatively simple but which enables the investigator to try to find biochemical correlates of anxiolytic action. Using the open-field' model, we have examined the effects of a number of anxiolytics (diazepam, clobazam, and nicotinamide, the putative endogenous ligand of benzodiazepine receptors) on behaviour and neurotransmitter function in different regions of the rat brain. Evidence is presented that anxiolytics act primarily by facilitating gamma-aminobutyric (GABA)-ergic transmission in limbic regions of the brain. The review concludes by outlining some of the mechanisms whereby both the 1,5- and 1,4-benzodiazepines may exert their effects at the cellular level. Whereas there is substantial experimental evidence suggesting that GABA-ergic activity is facilitated by the anxiolytic displacing a specific protein (GABA-modulin) from some of the GABA-receptor sites, thereby facilitating chloride transport into the neurons (hyperpolarization), the distribution of the benzodiazepine receptors on nonneuronal elements (glia) suggests that these drugs have more complex actions than is generally stated. Furthermore, the interactions between the benzodiazepines, GABA, and the enkephalins in subcortical regions of the brain suggest that the pharmacological profile of these drugs cannot be explained only in terms of a facilitation of GABA-ergic transmission.

Effects of phenytoin on [ 3H]diazepam binding in dissociated primary cortical cell culture

The effects of chronic exposure of primary dissociated cerebral cortical cells in culture to the anticonvulsant drug phenytoin have been investigated using benzodiazepine binding techniques. By separating benzodiazepine binding into pharmacologically distinct subtypes, the data indicate that clonazepam-displaceable benzodiazepine binding (associated primarily with neuronal membranes) is significantly decreased by exposure to therapeutic and toxic doses of phenytoin while R05-4864-displaceable benzodiazepine binding (associated principally with non-neuronal elements) is enhanced. The ratio of clonazepam-displaceable to R05-4864-displaceable benzodiazepine binding appears to be the most sensitive indicator for these changes.

Cholinergic neuronotrophic factors: VI. Age-dependent requirements by chick embryo ciliary ganglionic neurons

During development, ciliary ganglionic neurons become postmitotic and extend neurites in apparent independence of the presence of their future intraocular innervation targets. After reaching their peripheral innervation territory, however, these neurons become target dependent and about half of them die. We have previously reported that chick embryo intraocular target tissues contain a ciliary neuronotrophic factor (CNTF), which can be extracted and partially purified in a soluble form and which ensures near-total survival of 8-day chick embryo ciliary ganglionic neurons in monolayer cultures. In this study we have dissociated and cultured ciliary ganglia from embryonic Day (ED) 5 through 14, and examined dependence and responsiveness of their neurons to exogenously added CNTF. Two cell classes (dark and bright) could be distinguished by phase microscopy and differentially counted in cell dissociates from ED7–14, but not in ED5–6 ones. Dark cell number per ganglion increased from 6000 to 78,000 over this developmental time period. In contrast, bright cells (putative neurons) declined from a maximum of about 10,000 to 6000, suggesting a correlation with the expected neuronal cell death in vivo. Dissociated cells from ED5–14 ganglia were seeded on a polyornithine substratum coated with neurite promoting factor, cultured for 24 hr with or without added CNTF, and numerically examined for survival and neuritic development. Cultures from ED7–14 ganglia showed two cell categories: (i) flat nonneuronal elements dramatically increased in number with ganglionic age (thereby correlating with the increasing number of dark cells in the dissociates) and (ii) large, bright cells (often displaying neurite outgrowth) decreased in number in parallel with bright cell number in the dissociate. The survival of these neuronal elements was strictly dependent on exogenously added CNTF between ED7 and 10, but became progressively independent with older ages. ED14 neurons (fully capable of surviving for 24 hr without added CNTF) continued to require CNTF for neurite extension, thus displaying retained sensitivity to this factor. Although the ED5–6 cultures contained well-recognizable flat cells, the dominant category comprised cells with variable morphology, practically all of which exhibited neurite-like processes. Both the survival and neurite extension of these cells, which we tentatively interpret as immature neurons were independent of the presence of added CNTF.

Morphological studies on neuroglia. II. Response of glial cells to kainic acid-induced lesions.

The cellular response of non-neuronal elements of the pyramidal cell layer of the rat hippocampus, especially the area CA3, was observed electron microscopically following destruction of this formation by means of intraventricular administration of kainic acid (KA). The neuroglial cell types responding to the KA-induced lesion included astrocytes and the "microglia-like reactive cells". In addition, numerous brain macrophages appeared in the damaged area CA3. Oligodendrocytes and pericytes revealed no morphological changes. Swollen astrocytes were seen in the KA-induced lesion during the early stage. Glial filaments gradually developed in the soma and cell processes of these cells. Brain macrophages were seen in the KA-induced lesion during the early stage; they gradually decreased in number with time. Numerous small cells displaying a dark nucleus appeared in the damaged area CA3 during the first two days after the KA-administration, and gradually increased in number. During the later stage this cell type could hardly be distinguished from the intrinsic microglial cells. It is open to discussion whether this cell type originates from the intrinsic microglial cells or from the hematogenic monocytes; therefore it is designated as "microglia-like reactive cell" in the present study.

3H]Diazepam binding in mammalian central nervous system: a pharmacological characterization

Two types of benzodiazepine binding sites for [3H]diazepam in mammalian central nervous tissue were identified using selective in vitro tissue culture and in situ kainic acid lesion techniques. These two binding sites were pharmacologically distinguished by differential displacement of the [3H]diazepam radioligand using the centrally active benzodiazepine, clonazepam, and the centrally inactive benzodiazepine, RO5-4864. Clonazepam-displaceable binding sites were found to be located principally on neuronal membranes, while RO5-4864-displaceable binding sites were found to be located on non-neuronal elements. These pharmacological distinctions can be used to characterize the predominant cell types which bind benzodiazepines in nervous tissue. It is suggested that one quantitative measure of different cell populations is the ratio of clonazepam- to RO5-4864-displaceable [3H]diazepam binding within a single neuronal tissue simple.

A scanning electron microscope study of the in vitro development of dissociated hippocampal cells

Cultures of dissociated hippocampal neurons from 18-day-old rat fetuses were examined by scanning electron microscopy after periods between one hour and 20 days following plating on a poly-L-lysine coated substrate. Cell attachment was virtually complete within one hour after plating, and at that stage many cells could be seen which had started to extend processes with broad growth cones. By four hours in culture, process formation was well advanced and some cells had already assumed a pyramidal configuration. After 16 hours in culture, numerous contacts were seen between neighboring growth cones, and this frequently led to fasciculation of the interacting fibers. During the next three weeks the cell bodies enlarged considerably and rounded-up, and two distinct types of processes became evident: large, rapidly tapering dendrite-like processes and finer, essentially uniform-diametered processes that resemble axons. In most of the older cultures a dense plexus of processes was formed, and many of the finer processes appeared to have "bouton-like" swellings as they traversed the upper surfaces of the neuronal perikarya. Non-neuronal elements, which comprised only about 5% of the cells initially plated, rapidly proliferated in our cultures and within three to six days formed a confluent monolayer beneath the neurons.

Neurotransmitter receptor localizations: Brain lesion induced alterations in benzodiazepine, GABA, β-adrenergic and histamine H 1-receptor binding

Selective neuronal lesions have been utilized in efforts to localize binding sites in rat brain for β-adrenergic, γ-aminobutyric acid (GABA), histamine H 1 and benzodiazepine receptors. The various receptors respond differentially to lesions both in extent of change and in time course. After kainate lesions in the corpus striatum, benzodiazepine receptors are depleted up to 45% at 45–78 days but are unaffected after 7 days. By contrast striatal GABA receptors are increased at 7 days but depleted at later times. Thus both striatal benzodiazepine and GABA receptors appear to be associated at least in part with intrinsic neurons. In the cerebellum both benzodiazepine and GABA receptors are reduced in kainate treated rats and in Nervous mice, mutants which lack Purkinje cells. The most pronounced dissimilarity between benzodiazepine and GABA receptors occurs in Weaver mice, which selectively lack granule cells and display a 60% reduction in GABA receptors but a 40% augmentation in benzodiazepine receptors. A major portion of cerebellar GABA receptors, therefore, appear to be localized to granule cells. Striatal β-adrenergic receptors are reduced following intrastriatal kainate injections but are unaffected by cerebral cortex ablation, suggesting an association with intrinsic neurons but not with axon terminals of the corticostriate pathway. While intraventricular injections of 6-hydroxydopamine enhance [ 3H]dihydroalprenolol binding to β-adrenergic receptors in the cerebral cortex and hippocampus, such binding is not augmented in the corpus striatum, brain stem, midbrain or thalamus-hypothalamus by this treatment. Moreover, medial forebrain bundle lesions, which destroy ascending adrenergic neurons, fail to alter cerebral cortical or striatal β-adrenergic receptors. Thus denervation-elicited increase in β-adrenergic receptors vary with brain region and the type of denervating lesion. Histamine H 1-receptors are the most resistant of all to neuronal lesions. In the corpus striatum [ 3H]mepyramine binding is unaffected by cerebral cortex ablation, nigral injections of 6-hydroxydopamine or brain stem hemisection. In the hippocampus, medial forebrain bundle lesions, intrahippocampal kainate injection, and fimbria and fornix transection largely fail to alter [ 3H]mepyramine binding. Accordingly, a major portion of these receptors may be associated with nonneuronal elements such as glia or blood vessels.

Scanning electron microscopic studies of the surface morphology of the vomeronasal epithelium and olfactory epithelium of garter snakes.

Fixed vomeronasal and olfactory epithelia from normal adult garter snakes were microdissected, fractured, and examined with a scanning electron microscope. The method permits a detailed comparative study of the structural organization and morphological characteristics of the constituent cells of the vomeronasal and olfactory epithelia. Despite similarities in the nomenclature of the constituent cells in both epithelia, significant differences exist in their surface morphology. A unique columnar structure composed of non-neuronal elements is present in the vomeronasal epithelium. These columns house the bioplar neurons and undifferentiated cells. Such a columnar organization is absent in the olfactory epithelium. In vomeronasal epithelium the bipolar neurons possess microvillous terminals at their dendritic tips, while the dendritic tips of the bipolar neurons of the olfactory epithelium possess cilia. Vomeronasal supporting cells are covered with microvilli, while olfactory supporting cells are covered with cytoplasmic protuberances in addition to the microvilli. In the vomeronasal epithelium the pear-shaped neurons have a grossly smooth surface and are organized into clusters, while in the olfactory epithelium the elliptical bipolar neurons are spinous, aligned side-by-side and interdigitate. The basal (undifferentiated) cell layer in the vomeronasal epithelium has a high packing density and is composed of several layers of irregularly shaped cells. In the olfactory epithelium the basal cell layer is loosely organized and composed of a single layer of oval cells. This information on the three-dimensional cell structure of both epithelia provides a basis for experimental observations on changes in morphology of the bipolar neurons during genesis, development, maturation, degeneration, and regeneration in postnatal, adult animals.

Cobalt mapping of the nervous system: evidence that cobalt can cross a neuronal membrane.

Exposing intact nerves of Aplysia to exogenous CoCl2 was sufficient to fill neurons by axonal iontophoresis. There were no significant differences between filling intact nerves and nerves whose ends had been cut. Nonneuronal elements were not filled appreciably. These results show that Co2+ can cross intact axonal membranes and suggest that in tracing neuronal pathways Co2+ may not remain confined to neurons whose interiors are directly exposed to it.

Selective survival of neurons from chick embryo sensory ganglionic dissociates utilizing serum-free supplemented medium

Dissociated embryonic chick dorsal root ganglionic cells were plated on collagen-coated tissue culture dishes in Eagle's basal medium containing 10% fetal calf serum (FCS). After 48 h, which allowed adequate cell attachment, the cultures were washed with serum-free medium and then received fresh medium supplemented with 10% FCS or serum-free defined medium (N1), which was supplemented with insulin, transferrin, progesterone, putrescine and selenium. In addition, both media required the addition of Nerve Growth Factor (NGF). N1 medium selectively maintained the neurons and did not support proliferation or even survival of almost all non-neuronal elements (fibroblasts and Schwann cells). Survival of neurons in N1 was initially as good and eventually better than in serum-containing medium. After 6 days in N1 the cultures consisted almost entirely of neurons (>95%), which had smaller cell bodies but more extensive process formation than in serum-supplemented medium. The omission of any one of the supplements resulted in a reduction of neuron survival. The ability to generate cultures of pure neurons in a serum-free defined medium may be useful for studying ( i) the role of specific hormones and growth factors normally supplied by serum in the maintenance of neurons and ( ii) biochemical parameters of neurons in the absence of the substantial background due to non-neuronal elements.

Intrahippocampal injections of ibotenic acid provide histological evidence for a neurotoxic mechanism different from kainic acid

Stereotaxic injections of ibotenic acid (IBO) and kainic acid (KA) into either the dorsal hippocampus or the lateral cerebroventricle were performed in order to determine the relative potencies of the drugs and the vulnerability of different hippocampal cell types to their neurotoxic action. IBO was found to be approximately five times less potent than KA in causing degeneration of hippocampal neuronal cell bodies. Unlike KA (0.5 and 1.0 μg), IBO (5.0 μg) caused few signs of intrahippocampal bleeding or necrosis of non-neuronal elements. Pyramidal cells of the CA3 and CA4 regions were the most sensitive and dentate granule cells the least sensitive to KA. In contrasts, IBO caused degeneration of granule cells and CA3/CA4 pyramids to an equal extent.

Immunohistochemical demonstration of catechol-O-methyltransferase in mammalian brain

Catechol-O-methyltransferase (COMT)(EC 2.1.1.6) was localized using fluorescence immunohistochemistry in rat liver and kidney and in rat, chinchilla, and bovine brains. In the brain, specific fluorescence was visable only in non-neuronal cellular elements in all three species. Ventricular ependymal cells and cells of the choroid plexuses exhibited the greatest intensity of immunofluorescence. Glial immunofluorescence appeared prominently in large myelinated fiber tracts. Interfascicular and perineuronal satellite oligodendrocytes as well as fibrous astrocytes were immunoreactive, though myelin itself did not exhibit a positive reaction. Bergmann glial cells in the cerebellum also stained brightly for COMT. Although this study indicates that the predominant localization of COMT is non-neuronal, it is important to note that the presence of small quantities of this enzyme in neurons cannot be excluded. The patterns of localization observed in the non-neuronal elements suggest that this enzyme may function as a barrier to free diffusion of catechol compounds within the central nervous system.

On the presence of extraneuronal catecholamine in the iris of the rat: A scanning microfluorimetric study

Formaldehyde-induced fluorescence (FIF) of noradrenalin (NA) was studied in histochemical preparations of the rat iris. With the aid of a two-dimensional microfluorimetric scanning method, quantitative information was obtained from neuronal and non-neuronal elements selectively. Spectral analysis and fluorimetric studies showed the existence of extraneuronal NA in the iris of untreated rats. Surgical and pharmacological (reserpine, amphetamine, imipramine, nialamide) manipulation of sympathetic neurotransmission-induced changes in extraneuronal fluorescence, which did not parallel changes in fluorescence of neuronal elements. A positive relationship was found between changes in extraneuronal fluorescence and the postsynaptic effect (pupil diameter). We hypothesize that extraneuronal catecholamine (CA) fluorescence is a histochemical parameter for synaptic neurotransmission.

The culture of chick embryo dorsal root ganglionic cells on polylysine-coated plastic

Polylysine-coated culture surfaces are strongly adhesive for neural cells, restrict locomotion on nonneuronal elements, but do not inhibit neurite elongation. In the present study, culture dishes were pre-treated with poly-D-lysine (PDL) at various concentrations, seed with dissociates from 8-day chick embryo dorsal root ganglia, and incubated under conditions that normally support both neuronal survival and nonneuronal proliferation. Pretreatment with low (0.1 mg/ml) PDL concentrations had no effect on neuronal survival and neuritic growth, but entirely prevented an increase in ganglionic nonneurons, yielding a numericallly stable culture greatly enriched in neurons. Higher PDL concentrations caused increasing losses in both cell classes. The 50% levels of cell loss were achieved at about the same PDL dose, but earlier for neurons that nonneurons and still with no impairment of neuritic growth from the surviving neurons. A procedure was developed to compare acid-soluble and acid-precipitable accumulation of radioactivity under 1-hr pulses of [3H]uridine, which was applicable even to poorly attached cells. The cytotoxic effects of higher PDL pretreatments was revealed as early as 6 hr after seeding by 2- to 4-fold lower radioaccumulation. The data are discussed in terms of possible regulations of cell permeability and metabolism by adhesive interactions between cells and their substratum, or other cells.

An electron microscopic analysis of abnormal ependymal cell proliferation and envelopment of sprouting axons following spinal cord transection in the rat.

Transection of the spinal cord in a series of Long Evans hooded rats results in a rapid degeneration of elements of the neuropil and white matter adjacent to the lesion site, and in the appearance of a wide variety of reactive cellular elements which ingest necrotic debris and produce a connective tissue matrix in the defect left by the lesion. Included among the non-neuronal elements found within the lesion zone and adjacent spinal cord segments cranial to the lesion were large clusters of ependymal cells displaced from their normal location. This aberrant proliferation produces extensive cords and nests of ependymal cells some of which maintain contiguity with those elements lining the central canal while other clusters were found several 100 μm distant in the gray matter. Rosettes with distinct lumina often occurred in such cellular aggregates and were similar in arrangement to those patterns displayed by primitive neuroepithelial cells following experimental manipulation (Watterson, 1965). Electron microscopy revealed typical oval euchromatin nuclei with a pale cytoplasm containing concentrations of filaments. Examination of rosette lumina revealed normal apical specializations including cilia with basal bodies, microvilli, and numerous zonulae adherentes Intracytoplasmic vacuole formation with abnormal microvilli and cilia were reminiscent of patterns described in certain ependymomas (Fu et al., 1974). During the period between 15–45 days following injury, axons sprout into the scar matrix and along the adjacent, eroded cord segments. Those fibers which became apposed to the aberrant ependymal cells were enveloped by them and a typical “mesaxon” was formed. With increasing postoperative periods until 90 dpo, groups of 3–8 fibers could be found enclosed within a single cell.

Changes in the distribution of non-neuronal elements in rat median eminence and in anterior pituitary hormone secretion after activation of tuberoinfundibular dopamine neurones by brain stimulation or nicotine

In order to investigate the possibility of acute functional changes in non-neuronal elements (mainly tanycytes) of the median eminence, the proportion of portal capillary surface covered by such elements was measured by quantitative electron microscopy in ovariectomized, oestrogen-progesterone-pretreated rats. In some of these animals, the functional state of the tuberoinfundibular dopamine (DA) neurones was assessed by histochemical microfluorimetry. Serum concentrations of luteinizing hormone (LH), growth hormone (GH) and prolactin were determined by radioimmunoassay. Two different types of treatment, i.e. systemic administration of nicotine (1 mg/kg, s.c.) or electrical stimulation in the medial amygdaloid nucleus, markedly reduced the percentage of capillary surface covered by non-neuronal profiles within 20 and 15 min, respectively. At the same time, the tuberoinfundibular DA system responded by an increase in cellular fluorescence intensity, reflecting neuronal activation. Medial preoptic stimulation had basically the same effect but with more variability in the change in capillary coverage by tanycytes. The action of nicotine was prevented by pretreatment with the DA receptor blocking agent, pimozide (5 mg/kg), which indicates (1) that a dopaminergic mechanism was involved in the nicotine effect and (2) that the tanycyte response was elicited by DA released from nerve terminals acting at some receptor site. Nicotine also lowered serum levels of GH and prolactin. Pimozide antagonized only the effect on prolactin. While the reaction of DA neurones and capillary coverage by tanycytes were correlated with each other in individual rats, no statistically significant correlation was observed between tanycyte response and hormone levels, so that no conclusions can as yet be drawn as to the neuroendocrine significance of the tanycyte reaction. These results indicate that rapid changes in the proportion or portal capillary surface covered by non-neuronal profiles can be elicited by stimulation of extrahypothalamic brain areas or by activation of cholinergic mechanisms. The tanycyte response appears to be mediated at least in part by the tuberoinfundibular DA neurones.

COMPARATIVE EFFECTS OF HERPES SIMPLEX VIRUS TYPES 1 AND 2 IN ORGANOTYPIC CULTURES OF MOUSE DORSAL ROOT GANGLION

Mature organized cultures of mouse dorsal root ganglion (MDRG) were infected with herpes simplex virus, type 1 (HSV 1) and type 2 (HSV 2). Onset of infectious virus production occurred faster and reached higher levels in HSV 2-infected cultures. Neurons, supporting cells and myelin were affected in both types of infection, but morphological changes occurred significantly earlier and more dramatically with the type 2 infection. The pattern of myelin changes was distinctly different in the two types of infection. Within 20 hours post infection nerve cells infected with HSV 2 developed several types of intranuclear inclusions consisting of membranes and filaments; no such neuronal inclusions were seen with HSV 1 infection. HSV 2 infection showed frequent, large, membranous inclusions in supporting cell nuclei whereas, only rare, small inclusions of this type were seen in supporting cells infected with HSV 1. The observations demonstrate that the two virus types produced different virus replication patterns and different morphologic changes in long term cultures of MDRG. There appears to be a differential response of neurons and non-neuronal elements to the virus in this tissue substrate. Viral latency was not induced in this system by direct inoculation of the virus under the conditions described.

Reactive alterations in non-neuronal elements of the degenerating ventrobasal complex of immature and mature rats. An electron microscopic study.

Sprague-Dawley albino rats ranging in age from neonate to 60 days postnatal (dpn)were subjected to cortical extirpations encompassing the SmI somato-sensory projection fields of neurons in the ventrobasal (VB) complex. Eectron microscopy of this region reveals degenerative changes in VB neurons, the rate and severity of which is inversely proportional to the age of the animal (Matthews et al., 1977). Numerous, distinctive non-neuronal elements, similar to those infiltrating the perivascular space of some vessels in the area, rapidly accumulate within the zone of degeneration in animals lesioned between 0 and 9 dpn. These display dense, heterochromatin nuclei, concentrations of of free ribosomes and rosettes, and pleomorphic dense bodies which become more evident as further reactive transformations accompany the phagocytic incorporation of degenerating neuronal remnants. Other non-neuronal elements exhibit a euchromatin nucleus, bundles of microtubules, and fewer free ribosomes. Such cells are also capable of phagocytosis and production of dense bodies. Both variants are comparable in appearance to the "M" cells of previous reports (Matthews and Kruger, 1973b). Cortical lesions of older animals result in the appearance of "M" cells in VB; however, the population densities observed in the immature VB are not achieved. Conversely, astrocytic hypertrophy, associated with the increased incidence of degenerating boutons in the more mature animal, represents a prominent response to injury which does not occur to a significant extent in younger animals. Morphological criteria for determining the nature of some "M" cells are given for a discussion of their presumptive derivation from various mesodermal progenitors and a brief consideration of other hypothesized origins.

Organotypic development of the organ of Corti in culture.

The preservation and development of the innervation pattern in the organ of Corti have been studied in culture up to 27 days in vitro. The explants were obtained from the newborn mouse. Segments of the cochlear duct dissected together with the appropriate sectors of the spiral ganglion may retain their structural organization for about two weeks. Maturation of some nonneuronal elements which occurs during that time is followed by a subsequent regression of the organ. Only a fraction of the explanted neurons survive. However, the surviving neurons, if connected with the hair cell region, maintain a complex peripheral innervation pattern that contains all the major fibre components which characterize the normal pattern in a young mouse. The peripheral innervation pattern in culture seems largely composed of preserved fibres, that is, of fibres which at the time of explantation have already ramified within the organ of Corti. Nonetheless, there is evidence for growth or maturation, in culture, of at least some peripheral processes of the spiral neurons. Thus, only in older cultures is the innervation of the apical tip established. Likewise, it is only in older explants that the inner spiral bundle becomes prominent. Spiral neurons survive in culture in several modes. Most frequently, the central process is altogether absent and the neuron is effectively a unipolar cell which maintains only the peripheral process. A distinct minority of neurons is bipolar possessing both the peripheral process and a central axon which grows freely, though no central target is present. A neuron may survive also as a unipolar or, rarely, as a bipolar cell with no processes entering the organ of Corti. The observations imply that (1) most or all major fibre systems in the organ of Corti carry components of spiral neuron origin; (2) a small population of spiral neurons innervating a short segment of the organ contributes importantly not only to the radial but also to the spiral innervation of the segment.

Effect of morphine on a depolarising dopamine response

THE structural complexity of nervous tissues and the presence of non-neuronal elements have hindered investigations into the actions of morphine at the cellular level in the vertebrate central nervous system, and contribute to the difficulty of determining whether morphine acts pre- or postsynaptically. Although presynaptic effects of morphine are documented, to our knowledge there has been no demonstration of an effect of morphine on postsynaptic neurotransmitter receptors using intracellular recording techniques.