An estimate of the flavour singlet contributions to the hyperfine splitting in charmonium

We explore the splitting between flavour singlet and non-singlet mesons in charmonium. This has implications for the hyperfine splitting in charmonium

Retinal tyrosine hydroxylase: comparison of short-term and long-term stimulation by light

No abstract availabl

Differentiation of dopaminergic and noradrenergic neurons in rat spinal cord

Norepinephrine (NE), dopamine (DM) and 3-methoxy-4-hydroxyphenylacetic acid (HVA) content have been measured in different parts of rat spinal cord and cerebellum by a gas chromatographic-mass spectrometric method. In cerebellum, which does not contain dopaminergic neurons, the ratio of NE to DA content was 47, whereas in parts of the spinal cord this ratio varied between 11 and 19. In the cord after desipramine (25 mg/kg, i.p.) plus 6-hydroxydopamine (6-HDA, 100 \u3bcg intracisternally), there was a significant depletion of DM but not of NE. Conversely, after benztropine (25 mg/kg, i.p.) plus 6-HDA there was a significant depletion of NE but not of DM. Chlorpromazine (10 mg/kg, i.p.) or clozapine (25 mg/kg, i.p.) caused a significant increase in spinal cord HVA concentration 1 h after treatment. Evidence is presented which suggests that the increased HVA measured in the cord did not originate in the brain. After electrolytic lesion of the locus coeruleus there was a significant reduction of NE but not of DM. Spinal cord DM and NE were depleted by reserpine in a dose-dependent manner, the threshold dose for DM depletion being less than that for NE depletion. Seven days after cord transection at T10 spinal cord DM was significantly reduced in the lumbar region. These results suggest that dopaminergic neurons exist in rat spinal cord independently of noradrenergic neurons and that the DM is likely to be present in the terminals of descending axons

Retinal tyrosine hydroxylase: comparison of short-term and long-term stimulation by light

Dopamine (DA) is a putative neurotransmitter within some retinal amacrine neurons. Exposure of rats to light for either 15 min or 96 hr increases retinal tyrosine hydroxylase activity. Concomitant with the increase of enzyme activity is a 4-fold increase of DA formation. The molecular mechanism for the increased enzyme activity for the two exposures to light is apparently different. Short-term exposure to light decreases the K(m) but not the V(max) of the enzyme for the pteridine cofactor, while 96 hr of exposure to light increases the V(max) for tyrosine but has no significant effect on the K(m) for tyrosine or cofactor. Enzyme activity of rats exposed to 15 min of light decreases to the level found in 96 hr dark-adapted rats within 30 min of darkness, while more than 6 hr of darkness are required after 96 hr of light exposure. These studies are consistent with the hypothesis that retinal DA formation is modulated by different molecular mechanisms depending on the duration of exposure of light. Short-term exposure to light activates tyrosine hydroxylase while long-term exposure to light results in the formation of more active molecules of enzyme

Activation of the nigrostriatal dopaminergic pathway by injection of cholera enterotoxin into the substantia nigra

Twenty-four hours after unilateral injection of cholera enterotoxin into the rat substantia nigra there is an increase, in the striatum on the injected side, of basal adenylate cyclase activity, 3,4-dihydroxyphenylacetic acid, and 3-methoxy-4-hydroxyphenylacetic acid. Moreover, there is an increase of motor activity, and rats tend to circle contralateral to the side of the injection. Injection of cholera enterotoxin into brain nuclei may be a useful procedure for pharmacologically activating selected neuronal systems of brain and for studying the pharmacology of drugs that are suspected of interacting with these systems

Incorporation of 18O2 into brain serotonin in vivo as a procedure for estimating turnover: a feasibility study in animals

Serotonin (5HT) containing 180 instead of 160 was found in brain after exposing rats to an atmosphere of 1802. The 180 incorporation appeared linear with time and 22% of the 5HT in striatum contained 180 after one hour of exposure. 180 entered 5HT by enzymatic reaction rather than by isotope exchange as treatment with p-chlorophenylalanine, to block tryptophan hydroxylase, prevented incorporation, while more 180-5HT than normal was found in brain after treatment with pargyline, to block monoamine oxidase. Our studies suggest that the incorporation of 1802 into brain 5HT might be a feasible approach for evaluating 5HT turnover in animals and with some modification might be applied in man

Light stimulates tyrosine hydroxylase activity and dopamine synthesis in retinal amacrine neurons

Retinal dopamine-containing amacrine neurons are rapidly activated by light, as shown by an increase in the rate of dopamine formation in vivo and a concomitant increase in the activity of tyrosine hydroxylase, measured in vitro with a subsaturating concentration of pteridine cofactor. Activation of tyrosine hydroxylase also occurs when isolated eyes from rats killed in the dark are exposed to a strobe light. Studies of amacrine neurons should provide basic data about the biochemical processing of visual information, as well as the physiological presynaptic regulatory mechanisms of dopamine-containing neurons