Quantitative immunogold evidence that glutamate is a neurotransmitter in afferent synaptic terminals within the isthmo-optic nucleus of the pigeon centrifugal visual system

A quantitative electron microscopic analysis of glutamate (GLU) immunoreactivity using the post-embedding immunogold technique was carried out within the isthmo-optic nucleus (ION) of the pigeon centrifugal visual system (CVS). Measurements were performed in each of eight different categories of axon terminals, including those that were GABA-immunoreactive (-ir), considered representing control profiles and identified using a single or double-label immunocytochemical procedure. The results demonstrated that the glutamate immunogold particle densities for both mitochondrial and vesicular pools and for total surface area of bouton profiles were significantly higher in P1a, P1b and P2b terminals and not significantly different in P4 and P5 terminals compared to those recorded in control GABA-ir terminals (P2a, P2c, P3). Moreover, the values measured in GLU-ir positive profiles were all significantly higher than in either P4 or P5 terminals. The results suggest that tectal neurons, which provide the main input to the ION cells, are either inhibitory GABA-ir possibly associated with P2c and/or P3 terminals or excitatory GLU-ir via P1a, P1b and P2b terminals. Such differential effects of tectal afferents may be the basis for the modulation of centrifugal activity and consequently of end target retinal ganglion cell responses. The data are relevant to hypotheses implicating the avian CVS in mechanisms of selective enhancement of visual attention to either novel or meaningful stimuli within the visual field.     

Immunocytochemical evidence for an afferent GABAergic neurotransmission in the guinea pig vestibular system.

To implicate gamma-aminobutyric acid (GABA) as an afferent neurotransmitter (AN), the localization of GABA synthesizing and degradation enzymes; L-glutamate decarboxylase (GAD) and GABA transaminase (GABA-T) was investigated by light and electron microscopy immunocytochemistry in guinea pig vestibular cristae and ganglion cells (GC). GAD-like immunoreactivity was exclusively confined to the sensory hair cell (HC) cytoplasm, suggesting that GAD synthesizes GABA in the HC. GABA-T like immunoreactivity was found within HC, nerve calyces, nerve fibers, and GC, suggesting its participation in terminating transmitter action. These results demonstrate the existence of a GABAergic system in the guinea pig vestibule and strongly support GABA as a vestibular AN.     

Effects of capsaicin treatment on immunoglobulin secretion in the rat: further evidence for involvement of tachykinin-containing afferent nerves.

Neonatal capsaicin treatment has previously been shown to diminish the primary antibody response of adult rats to the subcutaneously administered T-dependent antigen, sheep red blood cells, as measured using a modification of the Cunningham plaque-forming cell assay technique. We have now studied the kinetics of this response in adult normal, neonatally capsaicin-pretreated and neonatally capsaicin-pretreated substance P-infused rats, and examined the effects of the tachykinin antagonist Spantide, on the plaque-forming cell response. Capsaicin pretreatment did not affect the antigen-specific plaque-forming cell response over the first 4 days following antigen injection. At days 5, 6 and 7 of the response, there was a statistically significant decrease in the number of plaque-forming cells secreting antigen-specific IgM, an effect not observed in capsaicin-pretreated rats which were given a subcutaneous infusion of substance P at the time of antigen injection. The tachykinin antagonist Spantide inhibited the plaque-forming cell response in normal rats after in vivo infusion at the time of antigen injection by more than 70%. This effect of Spantide was dose dependent, occurred with maximal effect at 10 microM, and appeared to be independent of any histamine-mediated action. The results of this study provide further evidence for a receptor-mediated immunomodulatory role of tachykinin-containing primary afferent nerves.     

A molecular recognizing system of serotonin in rat fetal axonal growth cones: uptake and high affinity binding.

Axonal growth cone particles (AGCP) isolated from prenatal and postnatal rat brain had different high-affinity 5-HT uptake characteristics. In postnatal AGCP the uptake behaves as in the adult rat brain, while in the prenatal AGCP the uptake characteristics seem to be in a transitional stage. Also in prenatal AGCP we observed specific, high-affinity 5-HT binding sites. These results support the idea of an important role for 5-HT during axogenesis.     

Sympathetic denervation and chronic serotonin uptake blockade by fluoxetine do not affect pineal gland 5-hydroxyindole acetic acid: evidence that oxidative deamination of pineal serotonin is a property of the pinealocyte

Summary This investigation tested the hypothesis that oxidative deamination of 5HT in the pineal gland occurs primarily in cellular compartments other than the pinealocyte (i.e., noradrenergic nerve terminals and glia). Following sympathetic denervation of the pineal gland by bilateral superior cervical sympathectomy, pineal levels of 5HT and its oxidative metabolite, 5HIAA, were measured by HPLC from samples collected at six time points over the 24 h photoperiod. The role of glia in 5HT deamination was further examined by chronic treatment with the 5HT uptake blocker, fluoxetine (10 mg/kg). Sympathectomy abolished the circadian rhythms of both 5HT and 5HIAA, but had no statistically significant effect on the ratio of 5HIAA/5HT compared to shamoperated and intact controls over the 24 h period. Pineal daytime levels of both 5HT and 5HIAA were unaffected by fluoxetine treatment. These findings indicate that the pinealocyte is an important cellular compartment for 5HT oxidative metabolism.     

Vago-aortic nerves stimulation and REM sleep: evidence for a REM-triggering and a REM-maintenance factor.

There is abundant evidence that in non-anoxic brain tissue the blood flow is controlled mainly by the functional activity of the neurons. This enables the use of regional blood flow measurements for the localization and quantitation of events in the human brain which correlate to normal and abnormal mental activity. Measurements of regional cerebral blood flow (rCBF) by means of the ¹³³Xe clearance technique have demonstrated that the activity distribution in the normal resting brain shows a typical ‘landscape’, with the highest activities in the premotor and frontal regions and the lowest in temporal and parietal ones. The resting pattern is readily changed by voluntary motor activity which gives a rolandic-postrolandic activity peak and by sensory stimulation which activates rolandic and prerolandic structures especially. Speech and reading activate the upper, anterior and posterior speech cortices, as well as the face, tongue and mouth area. Problem solving also activates premotor and frontal regions especially and, if visual activity is involved, the occipital pole is also activated. These normal patterns confirm by and large well known aspects of the functional anatomy of the human dominant hemisphere.Brain lesions may alter the functional landscape of the dominant hemisphere profoundly. Most brain lesions cause a decrease of the general flow level and focal lesions give focal reductions which may be pronounced. A number of clinical correlations have been demonstrated between rCBF abnormalities and focal brain lesions caused by cerebrovascular disorders, brain trauma, brain tumors, epilepsy, and infectious disorders. In many such disorders, the above mentioned activation patterns are abnormal or absent, a fact often to be expected from the clinical symptomatology.Finally, it has been found in patients with organic dementia that the flow level of the brain is reduced grossly in proportion to the intellectual deficit and, furthermore, that subsymptoms of the dementia correlate with regional flow abnormalities. Chronic schizophrenia also shows abnormalities of the rCBF landscape in spite of the fact that such patients retain a normal level of total mean cerebral blood flow and oxygen uptake. There appears to be a specific maldistribution of flow (function) in chronic schizophrenia with a low activity in frontal regions and high activity in postcentral ones. This pattern is possibly related to the perceptual and behavioral deficits which characterize this disorder.The present review supports the notion that the rCBF technique may be used with advantage to localize and to quantify cerebral events which are related to normal and abnormal mental activity.     

Low leukocyte glutamate dehydrogenase activity does not correlate with a particular type of multiple system atrophy.

Leucocyte glutamate dehydrogenase (GDH) activity was measured in 26 normal control subjects, 20 patients with multiple system atrophy presenting features of either olivopontocerebellar atrophy or striatonigral degeneration and in a heterogenous group of 15 patients with spinocerebellar degenerations. A broad range of GDH activity was found in all three groups. Low activity failed to correlate with a specific clinical entity. Patients followed to post-mortem examination to date have demonstrated histological features of at least three distinct morbid entities. It is concluded, contrary to earlier reports including the authors', that low leukocyte GDH activity does not identify a particular type of multiple system atrophy.     

Peripheral nerves in shiverer----dystrophic mouse chimeras: evidence that a non-Schwann cell component is required for axon ensheathment in vivo

Peripheral nerves in dystrophic mice express multiple axon ensheathment abnormalities. If an intrinsic deficiency expressed within the Schwann cells themselves were to account for this neuropathy, then such cells, existing in a chimera preparation, would be expected to express the same ensheathment abnormalities, whereas a coexisting population of non-dystrophic Schwann cells should not be similarly affected. The genotype of myelinated Schwann cells in shiverer----dystrophic chimera was established with immunocytochemical techniques. Shiverer myelin lacks the P1 component of myelin basic protein (MBP), whereas dystrophic myelin appears to contain normal levels of MBP. No correlation between the ensheathment characteristics of the chimera spinal roots and the genotype of the local Schwann cell population was found; both dystrophic Schwann cell populations expressing normalized ensheathment characteristics and shiverer Schwann cells failing to respond to the local presence of naked axons were observed. These results require that a defective extra Schwann cell component is involved in the pathogenesis of the dystrophic neuropathy. Moreover, the normal realization of that component appears to be a necessary prerequisite for shiverer Schwann cells to achieve full ensheathment competence. Although a definitive identification of the cell type(s) that expresses the dy gene locus has not been achieved in this chimera preparation, the observations are consistent with defective endoneurial fibroblast function.     

8-Chloro-cyclic adenosine monophosphate, a novel cyclic AMP analog that inhibits human glioma cell growth in concentrations that do not induce differentiation.

Cyclic AMP is supposed to play a role in cell growth and differentiation via activation of protein kinase A. The cAMP signal transduction pathway may therefore be used as a target for the development of anticancer drugs. We compared the effects of 8ClcAMP, a newly developed cAMP analog, to the effects of more commonly used cAMP analogs on the morphology and the proliferation of three human glioma cell lines. 8ClcAMP was the most potent growth inhibitor, exhibiting an IC50 of approximately 10 microM and inducing growth arrest in all three glioma cell lines at a concentration of 100 microM. The cAMP analogs 8CPTcAMP, dibutyryl cAMP, and 8BrcAMP were much less potent. If used in concentrations that induce growth arrest, both 8CPTcAMP and IBMX, but not 8ClcAMP, induced morphological differentiation of the glioma cells. Apparently, the growth-inhibiting effect of 8ClcAMP is not paralleled by its ability to induce morphological differentiation. The explanation for this phenomenon may be that 8ClcAMP does not exert its growth-inhibiting effect via activation of cAMP-dependent protein kinase. Two alternative mechanisms of action are discussed. Since 100 microM 8ClcAMP retarded the growth of normal rat astrocytes only to a marginal extent, without cytotoxic effects, it is concluded that 8ClcAMP may offer interesting perspectives in the treatment of malignant glioma.     

Neuroanatomical evidence for a putative autocrine/paracrine signaling system involving nicotinic acetylcholine receptors, purinergic receptors, and nitric oxide synthase in the airways

Nicotine in tobacco smoke is thought to stimulate sensory nerve fibers by receptors that are located on airway epithelial cells and on terminal branches of C-fiber afferents, but the exact neurochemical substrate that mediates the sensory effects of nicotine associated with cigarette smoking is not clear. ATP and nitric oxide (NO) have both been implicated in lung responsiveness to airborne chemicals such as nicotine. However, the neuroanatomical and functional relationships between nicotinic acetylcholine receptors (nAChRs), purinergic signaling, and NO are not known, and the main source of NO in the airways is not clear. In the present study, we performed RT-PCR to confirm the presence of mRNA for all three isoforms of nitric oxide synthase (NOS), neuronal (n-NOS), endothelial (e-NOS), and inducible (i-NOS), in the lung. Sequential double labeling was performed to assess the site of expression of the different NOS isoforms with respect to nAChRs and purinergic receptors (P2X3R) of the intrapulmonary airways. RT-PCR confirmed the presence of n-NOS, e-NOS, and i-NOS in the lung, and immunohistochemical studies verified their expression by epithelial cells at all levels of the intrapulmonary airways, including the terminal and respiratory bronchioles. Sequential double labeling demonstrated coexpression of n-NOS and/or i-NOS with nAChR- and P2X3R-expressing cells. These neuroanatomical findings suggest that bronchial epithelial cells may be a primary source of NO in the intrapulmonary airways and that the production and release of NO may be regulated by an autocrine/paracrine signaling system involving nAChRs and P2X3Rs.     

Evidence that Abeta42 plasma levels in presenilin-1 mutation carriers do not allow for prediction of their clinical phenotype.

Mutations in the presenilin 1 (PSEN1) gene are an important cause of autosomal dominant Alzheimer's disease (AD). Both in vitro and in vivo experiments showed that PSEN1 mutations increase secretion of amyloid beta42 (Abeta42), the longer and more fibrillogenic isoform of Abeta. We measured secreted Abeta42 in plasma of patients, presymptomatic mutation carriers, and escapees of two extended Belgian early-onset AD families, AD/A and AD/B, with a similar severe phenotype in terms of onset age (mean 35 years), duration of the disease (mean 6.5 years), and pathology. Both families segregate a different missense mutation in PSEN1 located in different parts of the protein: I143T in family AD/A and G384A in family AD/B. A significant increase in Abeta42 concentrations was observed in plasma of mutation carriers in family AD/B, but not in family AD/A. A differential effect of the two PSEN1 mutations on Abeta42 secretion was also detected in conditioned medium of stably transfected HEK293 cells. Both mutations increased Abeta42 secretion significantly; however, the increase was highest for G384A (5.5-fold over wild-type PSEN1), the largest effect observed for missense PSEN1 mutations to date. Although the Abeta42 concentrations measured in vivo and in vitro did not correlate with onset age, a positive correlation was obtained with age in the presymptomatic mutation carriers and a negative correlation with duration of disease in the patients. Our data obtained for PSEN1 mutation carriers suggest that measuring Abeta42 concentrations in plasma will be informative as a diagnostic marker in a limited number of cases.     

Neurons depend on astrocytes in a coculture system for protection from glutamate toxicity.

Glutamate can be toxic to neurons although it is a neurotransmitter. Regulation of extracellular glutamate levels is essential for prevention of glutamate neurotoxicity. Astrocytes play a major role in clearance of glutamate released by neurons. A coculture system combining cerebellar cells and astrocytes was employed to investigate the astrocytic control of glutamate toxicity. Coculture of astrocytes with cerebellar neurons enhanced uptake of glutamate by astrocytes. Inhibition of glutamate uptake in a coculture system led to death of cerebellar cells. This toxicity could be inhibited by MK801. However, in the presence of the glutamate uptake inhibitor, there was no increase in glutamate in the cultures compared to when the neurons were not cocultured. This indicated that neurons become more susceptible to glutamate toxicity in the presence of astrocytes and thus become dependent on astrocytes for prevention of glutamate toxicity. Astrocytes treated with conditioned medium from cerebellar cells did not show an increase in glutamate uptake but medium from astrocytes exposed to neuron conditioned medium was toxic to cerebellar cells. This toxicity was due to glutamate present in the medium. This suggests that a soluble factor released by neurons signals to astrocytes that neurons are present and stimulates a signal back to neurons which causes an increased sensitivity to glutamate toxicity.     

Patterns of cell and fiber vulnerability in the mesostriatal system of the mutant mouse weaver. II. High affinity uptake sites for dopamine

Weaver (gene symbol wv) is an autosomal recessive mutation in the mouse that causes the death of neurons in the cerebellum and of dopamine-containing neurons in the mid-brain. In the accompanying paper and in previous reports, the selective nature of the deficit produced by the gene in the dopamine-containing systems has been described after analysis of the patterns of the residual innervation in the striatum and the patterns of cell death in the midbrain. In the present report, we describe deficits in the terminals of the mesostriatal system occurring prior to a detectable dopamine deficiency in the striatum and prior to the onset of cell death in the mesencephalic dopamine-containing neurons during development. We have also found deficits in the remaining terminals of the adult weaver's striatum after the weaver pattern of innervation has been permanently established. Axonal terminals in the caudoputamen are impaired in weaver mice at postnatal day 7, before the onset of dopamine depletion in the caudoputamen and cell death in the midbrain. The impairment was revealed by a markedly deficient high-affinity uptake for 3H-dopamine by synaptosomes prepared from the caudoputamen. Throughout the remainder of development and in adulthood, the extent of the deficit in 3H-dopamine uptake was always greater than that for dopamine content. No striatal region was completely spared the effects of the gene. In the nucleus accumbens of the weavers, where dopamine content is normal, 3H-dopamine uptake was reduced by 35% in the synaptosomal preparations. In the olfactory tubercle, dopamine levels were reduced by 44% but 3H-dopamine uptake was reduced by 60%.(ABSTRACT TRUNCATED AT 250 WORDS)     

Electromyographic evidence of a multiple motor system: implications for apraxia.

Geschwind (1975) postulated that a multiple motor system accounts for a discrepancy in apraxias in response to commands for truncal and limb movements. Kuypers (1968) provided experimental evidence of a multiple motor system in primates. We present evidence of this multiple motor system in the form of Fourier-transformed electromyographic data in humans of the predominantly short duration motor units for discrete control in hand musculature and the predominantly longer duration motor units in the truncal musculature. Furthermore, the right and left erector spinae muscles had different Fourier-transformed electromyographic data which, in our opinion, represent the medial motor system used by apraxias.     

Chlamydia pneumoniae antibodies and high lipoprotein(a) levels do not predict ischemic cerebral infarctions. Results from a nested case-control study in Northern Sweden.

BACKGROUND AND PURPOSE: An association between high lipoprotein(a) [Lp(a)] levels and positive Chlamydia pneumoniae IgG titers in coronary artery disease has been described. The possibility of predicting ischemic stroke by measurements of plasma Lp(a) and C pneumoniae antibodies was investigated. METHODS: This incident case-control study included 101 case subjects (cases) who had suffered ischemic cerebral infarctions and 201 matched control subjects (controls). The study population was nested within the V?sterbotten Intervention Program or the WHO MONICA project. Plasma samples were measured for C pneumoniae-specific IgG and IgA antibodies and Lp(a). RESULTS: A significantly higher mean Lp(a) level was found in female cases than in female controls. However, plasma Lp(a) was unable to predict ischemic cerebral infarctions in either women or men. The proportion of individuals with positive C pneumoniae-specific IgG or IgA titers did not differ between cases and controls. Antibody titers were unable to predict a future stroke. The proportion of individuals with a positive C pneumoniae IgG titer in combination with a high Lp(a) level did not differ significantly between cases and controls. CONCLUSIONS: These data suggest that there is no association between baseline plasma Lp(a) levels, presence of C pneumoniae antibodies, and future ischemic cerebral infarctions. Furthermore, no evidence of an interactive effect between high Lp(a) levels and C pneumoniae IgG titers was found. However, selection bias and a recent C pneumoniae epidemic may have influenced the results.     

Statistical evidence that a child can create a combinatorial linguistic system without external linguistic input: Implications for language evolution

Can a child who is not exposed to a model for language nevertheless construct a communication system characterized by combinatorial structure? We know that deaf children whose hearing losses prevent them from acquiring spoken language, and whose hearing parents have not exposed them to sign language, use gestures, called homesigns, to communicate. In this study, we call upon a new formal analysis that characterizes the statistical profile of grammatical rules and, when applied to child language data, finds that young children’s language is consistent with a productive grammar rather than rote memorization of specific word combinations in caregiver speech. We apply this formal analysis to homesign, and find that homesign can also be characterized as having productive grammar. Our findings thus provide evidence that a child can create a combinatorial linguistic system without external linguistic input, and offer unique insight into how the capacity of language evolved as part of human biology.