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M Hadjiconstantinou

Publications and source records attributed to M Hadjiconstantinou.

105 records · Page 6Linked to original sources
PubMed1984

Spinal cord serotonin: a biochemical and immunohistochemical study following transection.

The serotonin (5-HT) content of rat spinal cord was studied following complete cord transection, transverse hemisection and rhizotomy by high pressure liquid chromatography-electrochemical detection (HPLC-EC) chromatography and immunohistochemically with rabbit anti-5-HT antiserum. Spinal cord 5-HT decreased but did not disappear after complete cord transection when studied 5 or 10 days after lesioning. Indeed the indole content 5 or 10 days after section were similar. Below the transection 5-HT-like immunoreactive neuronal elements were present, appeared normal but were significantly reduced compared with control cord. Although neuronal fibers were present after transection, no immunoreactive neuronal cell bodies were observed. The neuronal elements remaining after transection were capable of synthesizing and metabolizing 5-HT as evidenced by elevated 5-HT and decreased 5-hydroxyindoleacetic acid (5-HIAA) after inhibition of monoamine oxidase. Complete cord transection resulted in a fall of 5-HT in the ventral roots suggesting that they contain efferent 5-HT elements that originate above the transection. Rhizotomy plus cord transection did not change cord indole content more than transection alone demonstrating that the indoles that remain in the cord after transection did not originate from peripheral afferent 5-HT neurons. Hemitransection resulted in partial loss of immunoreactive neuronal elements on the cut side, but 5-HT-like immunoreactive nerve fibers were observed crossing within the cord from the intact side by the spinal canal. Analysis of indole content in the hemitransected cord were consistent with crossing of 5-HT fibers within spinal segments. Our studies, taken together with reports by other laboratories, support the notion that significant 5-HT elements remain in the spinal cord after transection. These elements appear normal morphologically and biochemically.

Animals↗
PubMed1984

Catecholamine systems of retina: a model for studying synaptic mechanisms.

The retina contains three catecholamine neurotransmitters: dopamine (DA); norepinephrine (NE); and epinephrine (EPI). DA and EPI appear to be associated with separate amacrine neurons that directly participate in the visual process. NE, in contrast, appears to be associated primarily with the sympathetic nerves that innervate the blood vessels of the retina. We present a synopsis of the anatomy, physiology, biochemistry and pharmacology of these retinal neurons. We also suggest that some diseases usually associated with catecholamines of brain may have their counterpart in retina.

Adenylyl Cyclases↗
PubMed1984

Acetylcholine measurement by high-performance liquid chromatography using an enzyme-loaded postcolumn reactor.

Choline oxidase and cholinesterase were found to retain their activity for 1-2 weeks at room temperature while adsorbed to a commercially available anion-exchange cartridge. These enzymes convert acetylcholine to H2O2. Acetylcholine can be measured in tissue extracts by separation at pH 7 on a polymeric reverse-phase high-performance liquid chromatography column, conversion of acetylcholine to H2O2 on a postcolumn enzyme-loaded anion-exchange cartridge, and electrochemical detection of the H2O2 formed.

Acetylcholine↗
PubMed1984

Immunohistochemical evidence for epinephrine-containing retinal amacrine cells.

The enzyme for the synthesis of epinephrine, phenylethanolamine-N-methyltransferase, has been localized, by an indirect immunofluorescent staining method, to a subpopulation of amacrine cells in the rat retina. The immunoreactive cells are located primarily in the inner nuclear layer and send a single process to the inner plexiform layer. Most of the immunoreactivity is found in the center of the inner plexiform layer. A small percentage of immunoreactive cell bodies were found in the inner plexiform layer and occasionally cells were observed in the ganglion cell layer. These epinephrine-containing amacrine cells are morphologically distinct from the dopamine-containing amacrine cells previously described by formaldehyde fluorescence and we speculate from reports in the literature that epinephrine-containing amacrine cells may play a role in modulating the activity of dopamine-containing amacrine cells.

Animals↗
PubMed1984

Measurement of acetylcholine turnover rate in brain: an adjunct to a simple HPLC method for choline and acetylcholine.

An existing method for measuring acetylcholine (ACh) and choline (Ch) is shown to be useful for measuring the turnover rate of ACh in mouse brain. Methyl-[3H]Ch is injected into mice. They are killed at different times by microwave irradiation and Ch and ACh extracted and separated by reverse-phase HPLC. Ch and ACh are converted to hydrogen peroxide by a post-column enzyme reaction. Hydrogen peroxide, which is directly related to the tissue content of Ch or ACh, is determined electrochemically. The fractions that correspond to the detector response for Ch and ACh are collected for the measurement of radioactivity. In this way specific radioactivities of endogenous Ch and ACh are estimated in the same sample. We used the specific radioactivity values determined by this procedure to estimate the turnover of ACh for striatum, cerebral cortex, and hippocampus of the mouse.

Acetylcholine↗
PubMed1984

An endogenous ligand modulates dopamine-containing neurons of retina via alpha-2 adrenoceptors.

Environmental light induces the activation of dopamine (DA)-containing neurons of rat retina and as a consequence DA turnover increases. The state of DA metabolism is directly related to the content of 3,4-dihydroxyphenylacetic acid in retina. Alpha-2 adrenoceptors are present in the retina and their activation diminishes the retinal content of 3,4-dihydroxyphenylacetic acid of rats placed in the light, but not of rats placed in the dark. When alpha-2 antagonists are administered, they increase retinal DA metabolism of rats in the light as well as of rats in the dark. These results are consistent with the notion that an endogenous agonist fully occupies the alpha-2 receptor in the dark and only partially occupies the receptors in the light. The most likely endogenous agonist for these receptors is epinephrine released from a newly identified population of epinephrine-containing amacrine cells.

Animals↗
PubMed1984

Identification of epinephrine and phenylethanolamine N-methyltransferase activity in rat retina.

Epinephrine (E) and phenylethanolamine N-methyltransferase (PNMT) are endogenous to the rat retina. The retinal enzyme shows substrate specificity and inhibitor sensitivity similar to the PNMT of brain. The E system in the retina may be part of a functional adrenergic system, because amine metabolism of dopamine-containing amacrine cells is inhibited by alpha 2 agonists and stimulated by alpha 2 antagonists.

Aging↗
PubMed1983

Activation of dopamine-containing amacrine cells of retina: light-induced increase of acidic dopamine metabolites.

The acidic metabolites of dopamine, homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic acid (DOPAC), are present in rat retina. DOPAC is the most abundant metabolite. Both metabolites increase in parallel when rats are taken from a dark to a lighted environment. Haloperidol treatment also increases the metabolites in both dark and light while apomorphine decreases both metabolites in dark and light and partially antagonizes the increase induced by haloperidol.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1983

Epinephrine: a potential neurotransmitter in retina.

Dopamine (DA), norepinephrine (NE), and epinephrine (EPI) are present in rat retina. DA is the major catecholamine, whereas NE and EPI represent approximately 5% of the DA content. DA is contained in a subpopulation of amacrine cells and has been the subject of numerous studies. We investigated the origin and properties of NE and EPI in retina. Following superior cervical ganglionectomy, there was a decrease in NE content, but no decrease in EPI or phenylethanolamine-N-methyltransferase (PNMT) activity. PNMT in retina has many of the substrate-specificity and inhibitor-sensitivity characteristics of other tissues. Enzyme activity is enhanced in newborn rats by treatment with dexamethasone. Exposure to a lighted environment increases retinal EPI in normal and superior cervical ganglionectomized rats. EPI content increased for more than 2 h in a lighted environment. We conclude that most of the NE is contained within the sympathetic neurons that innervate the eye from the superior cervical ganglion, whereas EPI is contained in retinal elements that are responsive to photic stimulation.

Animals↗
PubMed1983

Dopamine-containing small intensely fluorescent cells and sympathetic ganglion function.

This article reviews some of the neuropharmacology of the dopamine (DA)-containing small intensely fluorescent cells of sympathetic ganglia. The major metabolite of DA found in the ganglia is 3,4-dihydroxyphenylacetic acid (DOPAC). DOPAC content appears to be a direct reflection of DA synthesis. DA synthesis can be enhanced by muscarinic agonists and diminished by muscarinic antagonists. Neuroleptic drugs stimulate DA synthesis in the ganglion, which suggests that a local negative neuronal feedback loop might operate within the ganglion. There may be a correlation between deficient DA synthesis in spontaneous hypertensive rats and the development of hypertension. It is possible that some of the peripheral side effects of drugs that act on dopaminergic neurons in the brain might originate from the drugs' action on peripheral dopaminergic neuronal systems such as the sympathetic ganglion.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1983

Immunohistochemical localization of bombesin/gastrin-releasing peptide and substance P in primary sensory neurons.

The existence of bombesin/gastrin-releasing peptide-like immunoreactivity (BN-GRP-LI) in rat sensory ganglia and spinal cord was confirmed using immunocytochemistry, gel filtration chromatography, and high performance liquid chromatography combined with radioimmunoassay. Immunohistochemical studies showed that in the spinal sensory ganglia of the rat about 5% of the neurons exhibited BN-GRP-LI, whereas about 20% of the neurons exhibited substance P-like immunoreactivity (SP-LI). The two immunoreactivities were found in different cells, but both were located in small ganglion cells. In the posterior horn of the spinal cord, BN-GRP-LI and SP-LI were located in the superficial layers, and this distribution was different from that of Met5-enkephalin-like immunoreactivity. The results are in agreement with the concept that there is a primary sensory pathway from the sensory ganglia to the spinal cord which contains BN-GRP-LI and that these neurons are separate from those containing substance P. In extracts prepared from spinal ganglia, two molecular weight forms of BN-GRP-LI were found using gel filtration chromatography. The high molecular weight form coeluted with porcine GRP and the low molecular weight form was smaller than bombesin. The low molecular weight BN-GRP-LI extracted from spinal cord was more hydrophilic than bombesin or ranatensin.

Animals↗
PubMed1982

Trans-synaptic modulation via muscarinic receptors of serotonin-containing small intensely fluorescent cells of superior cervical ganglion.

Verhofstad et al. (Verhofstad, A. A. J., H. W. M. Steinbusch, B. Penke J. Varga, and H. W. J. Joosten (1981) Brain Res. 212: 39-49) have reported that serotonin of the rat superior cervical ganglion is contained in a distinct and separate population of small intensely fluorescent (SIF) cells. We provide evidence that the serotonin-containing SIF cells are modulated, in part, by preganglionic cholinergic neurons. For example, administration of the muscarinic agonists carbachol or oxotremorine increases the content of serotonin, and the increase induced by oxotremorine is blocked by atropine. Treatment with atropine alone or decentralization of the ganglion lowers the content of serotonin. From the rate of accumulation of serotonin in the ganglion after the administration of the monoamine oxidase inhibitor pargyline, it appears that the rate of formation of serotonin is increased after oxotremorine treatment. Reserpine, p-chlorophenylalanine, or fluoxetine treatment reduces the content of serotonin in the ganglion, suggesting that the SIF cell system has properties similar to those of serotonergic neurons of the brain. We postulate that the serotonin-containing SIF cells of the rat superior cervical ganglion participate in local circuit modulation of ganglionic transmission by receiving preganglionic information via muscarinic receptors.

3,4-Dihydroxyphenylacetic Acid↗
PubMedDate not supplied

GM1 and NGF synergism on choline acetyltransferase and choline uptake in aged brain.

In the brain of aged rats high affinity choline uptake (HAChU) of the striatum, hippocampus, and frontal cortex is lower than in young rats, while choline acetyltransferase (ChAT) activity is lower in striatum and frontal cortex. Infusion into the lateral cerebral ventricle with nerve growth factor (NGF) enhances the low values of these cholinergic markers in a dose- and region-dependent manner. GM1 ganglioside infused into the lateral ventricle, at a dose that is ineffective alone, together with NGF synergistically enhances the effect of NGF on ChAT and HAChU activities in the brain of aged animals. The pharmacology of this GM1/NGF synergism suggests potentiation of response.

Aging↗
PubMedDate not supplied

Low concentrations of cerebrospinal fluid GABA correlate to a reduced response to phenobarbital therapy in primary canine epilepsy.

In this study, we investigated whether pretreatment cerebrospinal fluid (CSF) neurotransmitter concentrations of gamma-aminobutyric acid (GABA) and glutamate (GLU) were correlated with response to phenobarbital treatment in dogs with primary epilepsy. Eleven untreated dogs, 6 males and 5 females, with a median age of onset of seizures of 3 years (range: 0.5-5 years) were selected for therapy based on progressive or serious seizure patterns. The median interval between the first observed seizure and start of phenobarbital therapy was 485 days (range: 101-1,765 days). All dogs were purebred, with the exception of I male dog. Oral phenobarbital was started at 2.5 mg/kg every 12 hours. Trough serum phenobarbital concentrations were measured at 15, 45, 90, 180, 360, 540, and 720 days after the start of treatment. There was no difference in the mean trough serum concentration or in the mean number of seizures recorded between each time period of phenobarbital measurement over the 2-year evaluation. No correlation was found between CSF GLU, GABA, or GLU: GABA ratio and the total number of seizures recorded before or after initiation of phenobarbital therapy. Lower CSF GABA concentration, however, was correlated with a lower seizure frequency difference (the total number of seizures before phenobarbital therapy minus the total number of seizures after phenobarbital therapy for an identical time period of evaluation) and lower percentage reduction in seizures: ([total number of seizures before phenobarbital therapy minus the total number of seizures after phenobarbital therapy] divided by the total number of seizures before phenobarbital therapy) x 100. There was no correlation between CSF GLU and the seizure frequency difference and percentage reduction in seizures. A negative correlation between the CSF GLU:GABA ratio and seizure frequency difference was found. Thus, dogs with an initial lower CSF GABA concentration before phenobarbital therapy did not respond as well as did dogs with a higher CSF GABA concentration.

Animals↗