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PubMed1984

Specific retrograde transport of nerve growth factor (NGF) from neocortex to nucleus basalis in the rat.

[125I]labeled NGF injected in very small quantities into the frontal or dorsal anterior occipital cortex of adult rats, was specifically taken up and transported retrogradely to large, presumably cholinergic neurons in the nucleus basalis region (lateral preoptic nucleus, anterior lateral hypothalamic nucleus, substantia innominata, ventral globus pallidus and internal capsule), as revealed by light microscopic autoradiography. Cells projecting to the injection site in the frontal cortex were localized ipsilaterally in the more caudal parts of the nucleus basalis region, whereas cells projecting to the dorsal anterior occipital cortex could be found throughout the entire extent of the nucleus basalis and also in the vertical and horizontal limb of the nucleus of the diagonal band of Broca. Other nuclei known to project to the cortex (locus coeruleus, substantia nigra, nucleus raphe, thalamus) were consistently found to be unlabeled. In contrast to [125I]NGF, injection of [125I]cytochrome C failed to label any cell bodies in the basal forebrain nuclei by retrograde transport. This high selectivity for uptake and retrograde transport of NGF indicates the presence of membrane receptors for NGF or a closely related molecule on these cholinergic neurons of the basal forebrain innervating the cerebral cortex.

Animals↗
PubMed1985

Behavioural effects in the rat after acute unilateral intranigral infusions of N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine.

N-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induced a dose-dependent contralateral circling in the rat when infused unilaterally into the central region of the pars reticulata of the substantia nigra. This action of MPTP seems to be nigral dopamine-mediated since rotation was potentiated by intranigral amphetamine (50 micrograms unilaterally) and blocked by haloperidol (5 micrograms bilaterally) as well as by picrotoxin (5 micrograms bilaterally) and by unilateral lesions of the internal capsule. MPTP was not effective in inducing rotation in rats with unilateral 6-hydroxydopamine lesions of the median forebrain bundle in contrast to intranigral apomorphine which produced robust turning. The data suggest that MPTP may not act as a dopamine receptor agonist but induce rotation by other mechanisms, for example, by enhancing the accumulation of dopamine release from dendrites in the pars reticulata.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1986

The identification of some sources of afferent input to the rat nucleus basalis magnocellularis by retrograde transport of horseradish peroxidase.

Neurons of the nucleus basalis magnocellularis (NBm) of the rat are contained within the ventromedial globus pallidus and adjacent internal capsule. Horseradish peroxidase injection limited to the ventromedial globus pallidus result in sparse neuronal labeling in a variety of brainstem, thalamic and hypothalamic nuclei, and the basal nuclei identified after NBm injections. Thus, these contiguous regions have comparable subcortical inputs. By contrast, only NBm injections yielded a large number of labeled neurons in layer V of NBm cholinergic neurons. in addition to the reciprocity observed between NBm and frontal cortex, the ventral tegmental area and NBm likewise appear to be reciprocally connected.

Afferent Pathways↗
PubMed1986

Postsynaptic potentials evoked in spiny neostriatal projection neurons by stimulation of ipsilateral and contralateral neocortex.

Postsynaptic potentials were evoked in neostriatal neurons by stimulation of the ipsilateral and contralateral medial agranular frontal cortical field (AGm) in the rat. This cortical region is known to project bilaterally to the dorsal lateral head of the caudate-putamen of rats. Ipsilateral stimulation of AGm should excite all types of corticostriatal neurons projecting to neostriatal neurons in the corresponding area in neostriatum, while stimulation of the same cortical area on the side contralateral to the recording should evoke synaptic potentials from a more restricted subpopulation of crossed corticostriatal neurons. Neostriatal neuronal responses were recorded intracellularly and spiny projection neurons identified by intracellular staining with horseradish peroxidase. The initial EPSP response to contralateral stimulation was similar to that evoked from the ipsilateral side, except for the absence of a relatively small short latency component responsible for the earliest part of the response to ipsilateral cortical stimulation. Comparison with previous findings indicated that this earliest EPSP component was due to activation of fast-conducting descending cortical efferents with collateral projections exclusively to the ipsilateral neostriatum. Stimulation of contralateral neostriatum evoked responses identical to those obtained using stimulation of contralateral neocortex. Analyses of these responses indicated that both EPSPs arise from activation of the same population of fibers. Stimulation of the contralateral internal capsule just caudal to neostriatum was not effective in evoking the EPSP. Chronic hemidecortication did not change the shape of the EPSP evoked from the intact contralateral side, but reduced its amplitude by approximately one half. These observations indicate that contralaterally projecting corticostriatal neurons in the rat project bilaterally in neostriatum, have axonal branches to the contralateral cerebral cortex as well as neostriatum, and converge onto neostriatal neurons that also receive input from the corresponding cortical region on the ipsilateral side.

Animals↗
PubMed1987

Spinal monoamine mediation of stimulation-produced antinociception from the lateral hypothalamus.

Stimulation-produced antinociception can be evoked from a wide variety of sites in the brain, including the lateral hypothalamus (LH). The present study, in rats lightly anesthetized with pentobarbital, examined descending inhibition of the nociceptive tail flick (TF) reflex produced by focal electrical stimulation in the LH and the neurotransmitter(s), at the level of the lumbar enlargement, mediating the inhibition. Systematic tracking studies demonstrated that stimulation in the diencephalon dorsal to the hypothalamus did not reliably inhibit the TF reflex. Inhibition of the TF reflex was produced, however, throughout the hypothalamus at intensities of stimulation typically between 50 and 200 microA. The area requiring low intensities of stimulation (50-100 microA) to inhibit the TF reflex was a diffuse region of the LH, inferior to the mammillothalamic tract and internal capsule, medial to the supraoptic decussation and including the medial forebrain bundle. Microinjections of S-glutamate (100 mM, 0.5 microliter) in the LH did not inhibit the TF reflex, suggesting that activation of fibers of passage by stimulation was responsible for inhibition of the TF reflex produced from the LH. The intrathecal administration of pharmacologic antagonists (15-30 micrograms; naloxone, methysergide, phentolamine, prazosin or yohimbine) revealed that the alpha-adrenoceptor antagonists phentolamine and yohimbine produced the greatest increases in stimulation thresholds in the LH for inhibition of the TF reflex (83.7% and 89.8%, respectively). The intrathecal administration of methysergide produced a lesser, but statistically significant 11% increase in the stimulation threshold for inhibition of the TF reflex. These results indicate that spinal alpha 2-adrenoceptors primarily mediate the descending inhibition of the TF reflex produced by electrical stimulation in the LH.

Adrenergic alpha-Antagonists↗
PubMed1987

Transplantation of oligodendrocytes in the newborn mouse brain: extension of myelination by transplanted cells. Anatomical study.

The shiverer model allows for the immunocytochemical staining of the patches of myelin formed by transplanted oligodendrocytes from a normal newborn mouse. Fragments of the olfactory bulb were transplanted into various parts of the brain to place the myelinating cells in different anatomical conditions. Whole brains were horizontally sectioned in order to study the full pattern of migration and myelination of the grafted oligodendrocytes. Transplanted oligodendrocytes were capable of short and long distance migration before their differentiation. Long distance migration occurred in the caudal as well as in the rostral direction and into the contralateral part of the brain through the commissures. The patches of immunoreactive myelin were mainly found in the large myelinated bundles: corpus callosum, internal capsule, fimbria-fornix, medial lemniscus, cerebellar peduncles and spinal cord funiculi. Some sites of migration indicate that oligodendrocytes followed at least two different axonal pathways successively. The thalamic area which contained numerous patches could be a place where oligodendrocytes switch from one fasciculus to another.

Animals↗
PubMed1987

Effect of intravenous heroin and naloxone on regional cerebral blood flow in the conscious rat.

Regional cerebral blood flow (RCBF) was measured with the [14C]iodoantipyrine technique and quantitative autoradiography in awake, restrained rats shortly after intravenous injection of heroin, naloxone or naloxone before heroin. The RCBF observed in these animals was compared to those obtained in similarly treated, saline-injected rats. In an identically treated series of animals, no significant change in arterial blood gases, pH or bicarbonate was seen following any of the drug treatments at the equivalent time RCBF was determined. Blood flow increased an average 36% in 37 of the 40 areas measured 1 min after heroin injection. Significant increases were found in 21 areas including visual and piriform cortex, basal ganglia, diencephalon, limbic system, midbrain tegmentum, superior colliculus, periaqueductal gray, internal capsule and fornix. These elevations in blood flow were reversed in rats receiving heroin following naloxone pretreatment. RCBF decreased in 35 areas (mean = -12%) 4 min after naloxone injection; a 40% decrease in blood flow to entorhinal cortex was significant. These results suggest that opiate receptor stimulation by heroin increases functional activity within selected brain areas, and this effect is not limited to regions with dense populations of opiate receptors.

Animals↗
PubMed1987

Electrical membrane properties of rat subthalamic neurons in an in vitro slice preparation.

The electrical membrane properties of subthalamic (STH) neurons and their response characteristics to stimulation of the internal capsule (IC) were studied in an in vitro slice preparation. Most STH neurons recorded exhibited spontaneous repetitive firing. The input resistance of STH neurons was 146 +/- 48 M omega and showed both an anomalous and a delayed rectification when the membrane was hyperpolarized or depolarized by current injections. In neurons with the membrane potential less negative than 65 mV, depolarizing current pulses generated repetitive firing with the maximum frequency of up to 500 Hz. Two types of tetrodotoxin (TTX)-resistant cobalt-sensitive potentials, slow depolarizing potential and slow action potential, were observed in STH neurons. The slow depolarizing potential had a long duration (over 500 ms in some cases) and was able to trigger repetitive firing. The slow action potential had a duration of about 30 ms and triggered a burst of firing. The slow action potential was seen only when the neurons were hyperpolarized to more negative than 65 mV by a current injection. Electrical stimulation of IC evoked monosynaptic inhibitory postsynaptic potentials (IPSPs) in most of the neurons examined. The polarity of IPSPs was reversed in the depolarizing direction by intracellular injection of Cl-. Bath application of bicuculline markedly suppressed IPSPs and unmasked monosynaptic excitatory postsynaptic potentials (EPSPs). The EPSP was able to trigger a slow depolarization with repetitive firing or a slow action potential with burst of firing when the neuron was hyperpolarized by a continuous current injection. The results demonstrated that STH neurons in an in vitro preparation have spontaneous discharges, high input resistance, capability to generate high-frequency firing, and Ca potentials. The pattern of responses of STH neurons to synaptic inputs is dependent on their membrane potentials.

Action Potentials↗
PubMed1988

Autoradiographic visualization in rat brain of receptors for omega-conotoxin GVIA, a newly discovered calcium antagonist.

Putative N-type voltage-sensitive calcium channels were localized autoradiographically in thaw-mounted rat brain slices using [125I]omega-conotoxin GVIA as a ligand. Density of the toxin binding sites were highly heterogeneous throughout the brain. The highest density of the binding sites was observed in the glomerular layer of the olfactory bulb, cerebral cortex, molecular layer of the hippocampus, amygdaloid complex, reticular part of the substantia nigra, molecular layer of the cerebellar cortex, and nucleus of the solitary tract. White matter tract regions such as the internal capsule, corpus callosum, fimbria of the hippocampus, fornix, and fasciculus retroflexus showed an extremely low density.

Animals↗
PubMed1988

Excitability properties of medial forebrain bundle axons of A9 and A10 dopamine cells.

A9 and A10 units identified as dopaminergic were recorded with extracellular micropipettes. The units were antidromically activated by electrical stimulation at the level of the preoptic area. The absolute refractory periods ranged from 1.2 to 2.5 ms. During the 2-8 ms of the relative refractory period, conduction was slower than normal by up to 1.5 ms. The time constant, C, of the strength-duration curve ranged from 0.4 to 0.6 ms. The current (I)-distance (D) relationship, tested by moving the stimulating electrode past the axon, was approximately parabolic (I = K D exp 2), with the constant of the equation, K, ranging from 900 to 2000 microA/mm exp 2, for 0.5 ms pulses. This relationship allows calculation of the radius of the field of dopamine axon excitation at any current. These high K values show that axons of dopamine cells cannot be activated unless high current densities are delivered, even when electrodes are placed near the axons. These data allow determination of the extent to which dopamine axons can be the directly activated substrates for behaviors, such as self-stimulation and circling, which are evoked by electrical stimulation of the medial forebrain bundle or internal capsule.

Action Potentials↗
PubMed1989

Autoradiographic visualization of a calcium channel antagonist, [125I]omega-conotoxin GVIA, binding site in the brains of normal and cerebellar mutant mice (pcd and weaver).

An in vitro autoradiographic technique has been used to localize [125I]omega-conotoxin GVIA binding sites in the brains of normal and cerebellar mutant mice. In the brains of normal mice, the highest densities of binding sites were observed at glomeruli of the olfactory bulb, cerebral cortex, caudate nucleus-putamen, hippocampus, and the nucleus of the solitary tract. Moderate densities of the silver grains occurred on the granular layer of the olfactory bulb, the molecular layer of the dentate gyrus, the molecular layer of the cerebellum, and the cochlear nucleus. No specific binding appeared in the white matter or the deep nucleus of the cerebellum, the corpus callosum, the internal capsule and the external plexiform layer of the olfactory bulb. Autoradiographic studies of the cerebella of Purkinje cell degeneration (pcd) mice showed that the distribution of binding sites on the molecular layer of the cerebellum are not affected by the degeneration of Purkinje cells. However, only background levels of the silver grains occurred on the cerebella of agranular weaver mutant mice, suggesting that the receptors for omega-conotoxin GVIA in the cerebellum are predominantly distributed on the parallel fibers of granule cells.

Animals↗
PubMed1990

Cerebral glucose utilization during diazepam withdrawal in rats.

The diazepam withdrawal syndrome in rats was characterized behaviorally by an increase in spontaneous motor activity, slight body tremor and a lack of convulsions. The 2-deoxyglucose (2-DG) technique was used to measure quantitatively cerebral glucose utilization during diazepam withdrawal and revealed changes in glucose utilization in 30% of the 54 structures evaluated. Areas of increased glucose utilization included medial geniculate, inferior colliculus, visual cortex, mammillary body, dorsal hippocampus, cerebellar flocculus, and zona reticulata and globus pallidus, olfactory cortex, nucleus accumbens and internal capsule. There was no single or consistent relationship between reported benzodiazepine receptor densities and glucose utilization.

Animals↗
PubMed1990

Effects of hypoxia-ischemia and seizures on neuronal and glial-like c-fos protein levels in the infant rat.

Unilateral carotid ligation in immature rats, followed by 2 h of hypoxia led to ischemic cell change from 2 h after the insult, on the ligated side of the brain. There was a time-dependent induction of immunoreactive c-fos protein in neurones but not glia or ependyma on the non-ligated side of the brain. Induction only occurred in rats that had seizures post hypoxia-ischemia. In the ligated hemisphere c-fos protein was induced in glial-like cells in the corpus callosum, fornix/fimbria and internal capsule and in ependymal cells lining the lateral ventricle starting from 2 h after hypoxia but subsiding by 3 days. No neuronal c-fos induction was seen in areas showing neuronal damage. MK-801 or carbamazepine, which prevented hypoxia-ischemia-induced seizures, also prevented c-fos induction in the non-ligated hemisphere while MK-801 was associated with increased c-fos induction in hippocampal neurones from the ligated side, as well as in glial-like and ependymal cells. These results suggest several processes are involved following the hypoxic-ischemic insult. Firstly, severe hypoxia-ischemia is associated with a reduction in neuronal c-fos protein levels, probably as a result of neuronal failure and death. Secondly, post hypoxic seizures cause c-fos induction in surviving neurones. Thirdly, glial-like from regions in which there is neural loss also exhibit induction of c-fos, which may be important for their subsequent proliferation or for the production of growth factors.

Animals↗
PubMed1992

Localization of the ras-like rab3A protein in the adult rat brain.

Rab3A is a small GTP-binding synaptic vesicle protein, shown to dissociate from synaptic vesicle membranes upon depolarization-induced exocytosis. Using an antiserum raised against rab3A, we found that the antigen was localized to the neuropil of specific brain regions, but was not present in major fiber tracts or most cell bodies. For example, the neuropil of several thalamic nuclei (i.e., dorsal lateral geniculate nucleus, lateral posterior nucleus, ventroposterior nucleus), cerebral cortex, upper layers of the superior colliculus and matrix zones of the neostriatum, were strongly immunoreactive, while the anterior commissure, corpus callosum, optic tract and internal capsule were devoid of staining. The hippocampus, regions of cerebral cortex and the cerebellum exhibited striking laminar distributions of rab3A immunoreactivity. In the hippocampus, dark staining was observed in the stratum oriens, stratum radiatum and molecular layer of the dentate gyrus, while the pyramidal, stratum lacunosum moleculare and dentate granule layers were not stained. In cerebellum the molecular layer and to a lesser extent, the underlying granule cell layer showed enhanced immunoreactivity. Seven days after excitotoxic lesions of the cerebral cortex, rab3A immunoreactivity was diminished in the mirror locus in the contralateral cortical hemisphere and in certain thalamic nuclei ipsilateral to the injection site. These results show that rab3A is localized to a number of specific regions. Its absence from other areas suggests that this synaptic vesicle protein is not universal to all neuronal terminals and pathways. In addition, our lesion studies indicate that for some brain regions, much of the antigen originates in cortical neurons and is distributed within specific axonal projections.

Animals↗
PubMed1995

Organization of the basal forebrain in the cat: localization of L-enkephalin, substance P, and choline acetyltransferase immunoreactivity.

The present study uses immunocytochemical techniques to determine whether cholinergic basal forebrain neurons in the cat are in a position to receive a homogeneous pattern of inputs, or if specific immunocytochemically defined afferent systems are localized to only selected regions of the basal forebrain. Monoclonal antibodies against choline acetyltransferase (ChAT) were used to identify the location of putative cholinergic neurons which are known to project to the cerebral cortex. In addition, polyclonal antibodies against substance P (SP) or enkephalin (Enk) were used on either adjacent or on the same histological sections reacted for ChAT to identify the neuropeptide plexuses that provide input to the basal forebrain. ChAT-immunoreactive (ChAT-IR) perikarya were located throughout the vertical limb, genu and horizontal limb of the diagonal band of Broca. ChAT-IR neurons also were located within the substantia innominata (SI), within the peripallidal zone around the globus pallidus, and were intercalated within the internal capsule. Enk-IR and SP-IR were used to determine the distribution of putative peptidergic terminals within the basal forebrain. Extensive Enk-IR and SP-IR terminal label was localized within the globus pallidus and the surrounding peripallidal zones, as well as within the SI, whereas the components of the diagonal band of Broca demonstrated negligible Enk-IR and SP-IR label. These data predict that the subdivisions of the cholinergic basal forebrain in the cat do not share a uniform afferent system, and only selective portions of this cholinergic system are in an anatomical position to receive a major direct input from the identified subcortical peptidergic afferents. The segregation of afferents has important consequences in the selective control of cortical function by the cholinergic basalocortical pathway.

Animals↗
PubMed1995

Impulse-dependent and tetrodotoxin-sensitive release of GABA in the rat's substantia nigra measured by microdialysis.

gamma-Aminobutyric acid (GABA) release in the rat substantia nigra pars reticulata (SNR) was studied by microdialysis coupled with high-performance liquid chromatography and fluorimetric detection. Electrical stimulation of striatonigral axons in the internal capsule (IC) increased nigral GABA release in conscious and halothane-anaesthetized rats. This was prevented by intranigral infusion of tetrodotoxin (TTX) while basal GABA release was unaffected. Calcium-free, cobalt-containing (2 mM CoCl2) artificial cerebrospinal fluid reduced basal GABA overflow but not that evoked with high K+ (100 mM). Extracellular levels of glutamate (GLU) and taurine (TAU) were not modified by IC stimulation, TTX or 0 Ca2+ although high K+ promoted GABA and TAU release but not that of GLU. These data demonstrate an impulse-and sodium-dependent release of GABA from nigral afferent neurones which contribute little to the extracellular concentration of GABA under steady-state conditions.

Animals↗
PubMed1995

The fate of human glial cells following transplantation in normal rodents and rodent models of neurodegenerative disease.

Investigations on xenografting in the brain have previously focused on the anatomical and functional integration of the transplanted neurons. More recently, astrocytes are being implicated as having complex functions following transplantation, and are being investigated to determine their role(s) in transplantation. The present study was undertaken to investigate the migration of human astrocytes following transplantation of thalamic, striatal, and mesencephalic tissue into the rodent striatum. Human donor fetuses (9-16 weeks in gestation) obtained through elective and spontaneous abortions were utilized in this study. Following transplantation, donor astrocytes were labeled with an antiserum directed against human glial fibrillary acidic protein. Our results demonstrate that astrocytic elements from all three tissue types are capable of incorporating into the host brain, and have a tendency to follow white matter tracts (such as the corpus callosum, internal capsule, and fiber bundles in the striatum). Human astrocytes, originating from the striatum and thalamus exhibited extensive migration, while migration was more limited in animals with ventral mesencephalon transplants. Ventral mesencephalon transplanted animal demonstrated positive astrocytes within the transplant, with processes (very few cell bodies) extending into white matter of adjacent host striatum. Astrocytes demonstrating immature morphology were observed with all transplant types, but were most prevalent in the striatal transplanted animals. The extent of astrocyte migration and the morphologies observed in this study reflect regional differences of the developing human brain. These results confirm and extend previous investigations on glial cell migration following transplantation in the brain.

Animals↗
PubMed1996

Conditionally immortalized neural progenitor cell lines integrate and differentiate after grafting to the adult rat striatum. A combined autoradiographic and electron microscopic study.

Neural progenitor cell lines, generated by conditional immortalization from the embryonic CNS, have previously been shown to survive and integrate after transplantation to the adult brain. The present study was designed to investigate the in vivo differentiation and morphological features of grafted neural progenitors using combined autoradiography and transmission electron microscopy of two temperature-sensitive neural progenitor cell lines, HiB5 and ST14A, labeled with 3H-thymidine prior to grafting. Two weeks after transplantation to the striatum the cells were found dispersed over an area extending about 1.5 mm from the injection site. Labeled cells located within the myelinated fiber bundles of the internal capsule were closely associated with myelinated axons and presented profiles similar to oligodendrocytes, while most of the grafted cells in the grey matter had morphological features of astroglia. Some labeled cells occurred also in close association with small blood vessels, morphologically resembling host pericytes. The results show that the immortalized neural progenitors can differentiate into mature glial cells, including astrocytes, oligodendrocytes and pericytes, after implantation into the adult striatum. The ability of the cells to become fully integrated with the resident glial population suggests that they will be highly useful as vehicles for intracerebral transgene expression in ex vivo gene transfer.

Animals↗