Effects of cholinergic agonists on regional brain energy metabolism in the scopolamine-treated rat.

The effects of scopolamine, physostigmine, RS86 and U-80816B on regional energy metabolism were studied in rodents by means of the 2-deoxyglucose autoradiographic technique. Scopolamine depressed metabolism in an area of cerebral cortex, focused around the parietal region. Rats treated with cholinergic direct agonists (U-80816B, RS86) as well as with the indirect agonist (physostigmine) all showed decreases in cortical energy metabolism, similar to scopolamine. They also induced an increase in thalamic metabolism. When these drugs were given in conjunction with scopolamine, metabolism tended to change in the opposite direction from the values obtained with the drug alone. These results suggest that there are complex interactions between pre- and post-synaptic muscarinic receptors. Additionally, nicotinic receptors could also be involved in some of the effects of physostigmine.     

Haloperidol in large doses reduces the cataleptic response and increases noradrenaline metabolism in the brain of the rat

The neurochemical basis for the clinical observation that some patients receiving a large dose of haloperidol exhibit no extrapyramidal side effects was investigated in rats. Haloperidol at doses of 1, 2.5, 5, 7.5 and 10 mg/kg (i.p.) caused a dose-dependent decrease in the duration of catalepsy. Haloperidol at a dose of 10 mg/kg induced catalepsy lasting for only 20% of that obtained with 1 mg/kg. Haloperidol decreased the content of noradrenaline in the frontal cortex and thalamus in a dose-dependent manner, while the content of 3-methoxy-4-hydroxyphenylglycol (MHPG) showed a dose-dependent increase in the same areas of the brain. Thus, there was an inverse relationship between the duration of catalepsy and the ratio of 3-methoxy-4-hydroxyphenylglycol to noradrenaline in the frontal cortex or thalamus. The concomitant administration of 20 mg/kg of phenoxybenzamine with 10 mg/kg of haloperidol induced a long-lasting catalepsy. The result may indicate that the increased metabolism of noradrenaline by large doses of haloperidol was not secondary to the blocking of dopaminergic receptors. In contrast, haloperidol caused a dose-dependent decrease in the content of homovanillic acid and 3,4-dihydroxyphenylacetic acid in the striatum and mesolimbic area. These results indicate that noradrenergic hyperfunction in the frontal cortex or thalamus induced by large doses of haloperidol may reduce the cataleptogenic effect of the drug via indirect stimulation of a dopaminoceptive neuron in the striatum or mesolimbic area.     

Changes in limb tone produced by regional injections of opiates into rat brain

Summary A mechanical apparatus was used to measure the resistance of the hindlegs to flexion in conscious rats. Systemically-administered morphine (7.5–12.5 mg/kg) caused increased muscle tone in the limbs. In rats with intracerebral cannulae, intrastriatal morphine (5–15 g) had no effect on limb tone, whereas an increase in limb tone was induced by morphine (1–30 g) in the globus pallidus. A strong and sustained increase in limb tone developed when morphine (0.2–2.5 g) and the mu opiate receptor agonist DAGO (1.5–2.5 g) were administered into the periaqueductal gray region of the midbrain, whereas the delta opiate receptor agonist DADLE (2.5–8 g) was ineffective. The increased limb tone induced by opiates may be generated by mu-type receptors in at least two areas of brain. Send offprint requests to P. Slater at the above address     

Alterations in glucose metabolism by cyclosporine in rat brain slices link to oxidative stress: interactions with mTOR inhibitors

Co-administration of the calcineurin inhibitor cyclosporine and the mTOR inhibitors sirolimus or everolimus increases the efficacy of immunosuppression after organ transplantation. However, clinical studies showed enhancement of cyclosporine toxicity. To characterize the biochemical mechanisms involved, we assessed the time-dependent effects of cyclosporine in combination with mTOR inhibitors on energy production (ex vivo (31)P-MRS), glucose metabolism (ex vivo (13)C-MRS), and reactive oxygen species (ROS) formation (using the fluorescent agent 2',7'-dichlorofluorescein diacetate) in perfused rat brain slices. Cyclosporine alone inhibited energy production (ATP: 75+/-9%), the Krebs cycle (4-(13)C-glutamate from 1-(13)C-glucose: 61+/-27%), and oxidative phosphorylation (NAD(+): 62+/-25%) after 4 h of perfusion. After 10 h, activation of anaerobic glycolysis (3-(13)C-lactate: 140+/-17%) compensated for inhibition of mitochondrial energy production and lowered the intracellular pH. ROS formation was increased after 4 h (285+/-55% of untreated control), but not after 10 h. mTOR inhibitors alone inhibited lactate production. When combined with cyclosporine, sirolimus enhanced cyclosporine-induced inhibition of energy metabolism (ATP: 64+/-9%) and ROS formation (367+/-46%). Most importantly, sirolimus inhibited cytosolic glycolysis and therefore compensation for cyclosporine-induced ATP reduction after 10 h. In contrast to sirolimus, everolimus antagonized cyclosporine-induced inhibition of mitochondrial energy metabolism (ATP: 91+/-7%) and ROS formation (170+/-49%). The antioxidant tocopherol antagonized all cyclosporine effects on cell metabolism. Cyclosporine time-dependently inhibited mitochondrial metabolism and increased ROS, followed by compensation involving anaerobic glycolysis. Everolimus antagonized cyclosporine-induced mitochondrial dysfunction, whereas sirolimus inhibited compensatory anaerobic glycolysis, thus enhancing cyclosporine's negative effects. ROS play the key role in mediating the negative effects of cyclosporine on cell energy metabolism.     

Modification of rat brain 5-hydroxytryptamine metabolism by sublethal doses of organophosphate agents

The early and late effects of sublethal doses of two organophosphate agents (paraoxon and soman) on 5-hydroxytryptamine (5-HT) metabolism were investigated in several rat brain areas. Parallel determinations of acetylcholinesterase (AcChE) inhibition were performed. An increase in 5-HT level was observed during the first phase of soman intoxication and a rise in 5-hydroxyindol acetic acid (5-HIAA) appeared in the early and late effects of both anticholinesterase agents with a predominant action in the striatum. These data suggested that paraoxon and soman induce a long-lasting increase in 5-HT turnover. This action cannot be related neither to the AcChE inhibition nor to the acetylcholine level.     

Presynaptic dopamine receptors in the pithed rat: characterization with apomorphine and comparison with central dopamine autoreceptors

Apomorphine, a dopamine agonist with high affinity for presynaptic dopamine receptors, caused dose-dependent inhibition (10-300 micrograms/kg intravenously) of the stimulation-induced increase in diastolic blood pressure in the pithed rat. This effect of apomorphine could be antagonized with (-)-sulpiride or haloperidol but not with yohimbine or atropine, indicating the involvement of inhibitory dopamine receptors. The alpha-1-adrenoceptor mediated pressor response to phenylephrine (5 micrograms/kg intravenously) was not significantly attenuated by apomorphine. The sensitivity of peripheral presynaptic dopamine receptors was then studied in the cardiovascular system of rats treated subchronically with haloperidol (2 mg/kg, twice daily intraperitoneally for 10 days). The inhibition of sympathetic vasoconstrictor responses exerted by apomorphine was found to be enhanced after subchronic haloperidol treatment suggesting the development of presynaptic dopamine receptor supersensitivity in the periphery. In addition, the previously reported supersensitivity of central dopamine autoreceptors to low doses of apomorphine could be confirmed in behavioural experiments.     

Influence of therapeutic and toxic doses of neuroleptics and antidepressants on energy metabolism of the isolated perfused rat brain

Summary The isolated perfused rat brain was used for a comparative study of the effects of promazine, imipramine, monodesmethyl promazine and desipramine on cerebral energy metabolism. After perfusion for 30 min or 1 h the brain levels of the following substrates and metabolites were estimated: P-creatine, creatine, ATP, ADP, AMP, glycogen, glucose, glucose-6-P, fructose diphosphate, dihydroxyacetone-P, pyruvate, lactate, -ketoglutarate, and ammonia. Drug concentrations of 5·10^–6 M and 10^–5 M in the perfusion medium caused a significant decrease of glucose-6-P alone. When the drug concentration was raised to a toxic range (10^–4 M), reflected in the EEG by the pattern of secondary discharges, an accumulation of P-creatine and glucose and a decrease of glycogen, glucose-6-P and ammonia occurred; the lactate/pyruvate ratios remained unchanged. As there were no qualitative differences between the effects of the investigated neuroleptics and antidepressants on cerebral metabolism, these effects might be unspecific and not correlated with the pharmacological action of the drugs.Presented in part at the spring meeting of the Deutsche Pharmakologische Gesellschaft, Mainz 1973 (Stock et al.).     

Polychlorinated biphenyls produce regional alterations of dopamine metabolism in rat brain

Adult male rats were gavaged with a mixture of polychlorinated biphenyls (PCBs; Aroclors 1254 and 1260) at either 500 or 1000 mg/kg body weight. Concentrations of dopamine (DA) and its major metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), were determined in caudate nucleus and lateral olfactory tract on postgavage Days 1, 3, 7 and 14. DA and DOPAC concentrations in caudate decreased after exposure to PCBs, as did HVA/DA ratios. DA concentrations in the lateral olfactory tract were unaffected, although DOPAC/DA ratios decreased. These results demonstrate that the mature mammalian nervous system is sensitive to a brief exposure to PCBs and that regional differences exist in the neurochemical sequelae of exposure to PCBs.     

Influence of SCH 23390, a DA1-receptor antagonist, on the behavioural responsiveness to small and large doses of apomorphine in rats

SCH 23390 (SCH), a DA1-receptor antagonist, did not influence the decrease in locomotor activity elicited by a dose of apomorphine (20 micrograms/kg) believed to stimulate DA autoreceptors in rats. Conversely, SCH antagonized the effects on locomotion and the stereotyped behaviour elicited by a dose of apomorphine (1 mg/kg) which stimulates postsynaptic DA receptors. These results showing that the behavioural effects produced by small and large doses of apomorphine are differently affected by SCH, further confirm that DA autoreceptors can be pharmacologically distinguished from postsynaptic DA receptors.     

Effect of progesterone on regional 5-hydroxytryptamine metabolism in the rat brain

The influence of progesterone upon 5-hydroxytryptamine (5-HT) metabolism in the rat brain was investigated in view of a possible connection with premenstrual tension and postpartum depression. A progesterone dose, resulting in a plasma level which was still in a physiological range, increased 5-HT turnover in septum, hypothalamus and raphe. A higher unphysiological dose, besides producing a further increase of 5-HT turnover, also resulted in a decrease of 5-hydroxyindoleacetic acid (5-HIAA) levels which was most pronounced in the septum. Neither of the two doses showed a clearcut influence on 5-HT concentrations in any of the investigated brain areas.     

Physostigmine, tacrine and metrifonate: the effect of multiple doses on acetylcholine metabolism in rat brain

The effects of two consecutive intramuscular doses of three cholinesterase inhibitors (physostigmine, tetrahydroaminoacridine and metrifonate) were compared in rats. The results revealed major differences in biochemical effects on the brain of the rat including the extent and duration of inhibition of cholinesterase, inhibition of release of acetylcholine and increase in levels of acetylcholine. Side effects were also markedly different in the time of appearance, duration and severity. These results suggest that there are significant differences in the mechanisms of action of various cholinesterase inhibitors. Since all three cholinesterase inhibitors are currently used in the experimental treatment of Alzheimer's disease, these findings have potential implications for the symptomatic therapy of these patients.     

The influence of early postnatal treatment with haloperidol on the effects induced by small and large doses of apomorphine on locomotion of adult rats

Chronic administration of haloperidol (0.5 mg/kg, s.c.) during early postnatal life did not modify the effects produced by a small dose of apomorphine (0.02 mg/kg, s.c.) on the locomotor activity of adult rats; conversely, the reduction of locomotion induced by a large dose of apomorphine (1 mg/kg, s.c.) was much more kared in haloperidol-pretreated rat than in saline-pretreated ones.The differentail ontogeny of dopamine auto- and postsynaptic receptors could be partly responsible for the different influence of postnatal treatment with haloperidol on the responsiveness of the adult to small and large doses of apomorphine.     

The effects of lesions produced by 5,7-dihydroxytryptamine on 5-hydroxytryptamine-mediated behaviour induced by amphetamine in large doses in the rat

The role of 5-hydroxytryptamine (5-HT)-containing terminals in the spinal cord and basal ganglia in behavioural responses induced by amphetamine in large doses have been investigated using the neurotoxin for 5-HT, 5,7-dihydroxytryptamine (5,7-DHT). The effects of pretreatment with 5,7-DHT were also examined using the 5-HT agonist, 5-methoxy-N,N-dimethyltryptamine (5-MeODMT). d-Amphetamine (25 mg/kg) induced several classical 5-HT-dependent behavioural responses (head weaving, forepaw treading, hind limb abduction, “wet dog” shakes, Straub tail), together with some classical dopamine (DA)-dependent behaviour and backward locomotion which requires both transmitters. Pretreatment with 5,7-DHT, given into the striatum significantly decreased “wet dog” shakes and virtually abolished backward walking. Pretreatment with 5,7-DHT in the nucleus accumbens or substantia nigra did not significantly alter behaviour. Pretreatment with 5,7-DHT intraspinally did not significantly alter behaviour induced by amphetamine, although a decrease of Straub tail just failed to reach significance (P = 0.056). Similar pretreatment in rats given 5-MeODMT (8 mg/kg) significantly enhanced both Straub tail and tremor but did not alter the other behavioural responses induced by this drug (limb abduction, forepaw treading, head weaving). The results in general suggest that behavioural responses induced by 5-HT can be classified into 3 groups (a) those requiring striatal 5-HT (“wet dog” shakes and backward locomotion), (b) those requiring spinal 5-HT (Straub tail, tremor) and (c) those requiring neither spinal nor striatal 5-HT (hind limb abduction, head weaving and forepaw treading).     

The hypomotility elicited by small doses of apomorphine seems exclusively mediated by dopaminergic systems in the nucleus accumbens

The reduction of motor activity elicited in rats by a subcutaneous injection of a small dose of apomorphine was reversed by pretreatment of the nucleus accumbens with haloperidol (10 pg), sulpiride (10 pg) or desenkephalin-gamma-endorphin (DE gamma E) (100 pg or 10 ng). These doses of the compounds did not change motor activity in placebo-treated rats. Pretreatment of the nucleus caudatus with the same neuroleptics or DE gamma E did not diminish the effect of subcutaneously administered low doses of apomorphine. A small dose of apomorphine decreased motor activity when it was injected directly into the nucleus accumbens. This effect was dose dependently antagonized by subcutaneous pretreatment with DE gamma E. It is suggested that the hypoactivity elicited by small doses of apomorphine is exclusively mediated by dopaminergic systems in the nucleus accumbens.     

Effects of subchronic haloperidol and sulpiride on regional brain dopamine metabolism in the rat

The DOPAC/dopamine and HVA/dopamine ratios in extracted whole tissue were determined to obtain an index of dopaminergic activity in various rat brain regions 24 h following 10 days' treatment with haloperidol (0.5 and 2 mg/kg) or sulpiride (10 and 100 mg/kg). Both neuroleptics caused a reduction in the metabolite/amine ratio in nucl. accumbens but not frontal cortex or substantia nigra. Haloperidol, but not sulpiride significantly reduced the HVA/dopamine ratio in striatum. A region-specific action of neuroleptics on brain dopamine neurons is discussed.     

Catecholamine synthesis in rat brain after axotomy: Interaction between apomorphine and haloperidol

Summary Axotomy of the ascending monoaminergic fibers by means of a complete cerebral hemitransection stimulated the formation of dopa during 30 min after inhibition of the aromatic amino acid decarboxylase with 3-hydroxybenzylhydrazine HCl, 100 mg/kg i.p., in c. striatum and the dopamine-rich part of the limbic system. Apomorphine, 0.5 mg/kg i.p., antagonized the accumulation of dopa not only on the intact but also on the lesioned side. Haloperidol, 2 mg/kg i.p., stimulated dopa accumulation on the intact side but could not further stimulate the increase in dopa caused by transection. When both drugs were given together, the inhibitory effect of apomorphine was fully counteracted by haloperidol on both sides. In the predominantly noradrenaline-innervated occipito-temporal cortex dopa formation was slightly higher on the lesioned than on the intact side and was not markedly influenced by apomorphine.In the rest of the hemispheres the apomorphine-induced decrease in dopa formation was more pronounced on the intact than on the lesioned side and was fully antagonized by haloperidol.The dopamine concentration was slightly higher in the lesioned c. striatum as compared to the intact side irrespective of the drugs administered. In c. striatum and the limbic system haloperidol caused a decrease in dopamine on the intact side which was not antagonized by additional treatment with apomorphine.Hemitransection caused a decrease in noradrenaline especially in the hemisphere portion. Neither apomorphine nor haloperidol or both drugs in combination changed the latter effect.In general, the tyrosine concentration tended to be higher on the lesioned than on the intact side in all brain structures investigated.The data support the view that a local receptor-mediated feedback mechanism exists which is controlling dopamine synthesis even in the absence of impulse flow.