Effects of acute and chronic morphine on regional rat brain acetylcholine turnover rate

A simplified method to study the acetylcholine (ACh) turnover rate (TR_ACh) in brain parts of drug treated rats has been presented. In striatum and occipital cortex of rats receiving a large dose of morphine (140 μ moles/kg i.p.) or implanted chronically with morphine pellets, the TR_ACh is influenced in a different manner. The single injection of morphine reduced the synthesis of ACh in cortex but not in striatum. Morphine pellets decreased striatal TR_ACh but failed to alter the TR_ACh in occipital cortex. Naloxone reversed both changes of TR_ACh elicited by morphine although it was devoid of any effect of the synthesis of ACh in rat brain parts. We suggest that morphine may prevent the ACh release from neurons as proposed by others, however, this effect in striatum of rats receiving a single dose of morphine is masked by the simultaneous action of morphine on the dopaminergic nigrostriatal pathway which regulates the turnover rate of striatal ACh.     

The effects of acute and chronic morphine treatment and of morphine withdrawal on rat brain in vivo

1. The effects of morphine, nalorphine, acetazolamide, and 10% CO₂ on brain metabolite concentrations of 24h-starved rats were studied. 2. A single dose of morphine (20mg/kg body wt.) caused an increase in brain glucose concentration (42%) and decreased concentrations of lactate (24%), pyruvate (29%), citrate (20%), α-oxoglutarate (16%), malate (14%) and creatine phosphate (10%) after 30min. No changes were found in adenine nucleotide concentrations. 3. The same dose of morphine increased arterial CO₂ from 5.07 to 7.60 kN/m² (38 to 57 Torr), decreased the pH from 7.41 to 7.31 and decreased O₂ from 14.1 to 10.8kN/m² (106 to 81 Torr) at 30min. 4. Rats injected with morphine three times daily (20mg/kg body wt.) for 2 weeks had no changes in brain metabolite concentrations or in blood gases 30min after their last injection. 5. Nalorphine (an antagonist of morphine) caused essentially no changes in brain metabolite concentrations in normal rats. When nalorphine (20mg/kg) was administered to rats previously treated with morphine three times daily for 2 weeks, there was an increase in brain glucose (100%), lactate (23%), pyruvate (18%) and citrate (10%) concentrations. 6. Acetazolamide (an inhibitor of carbonic anhydrase) and 10% CO₂ increased the arterial CO₂ from 4.79 to 6.78kN/m² (36 to 51 Torr) and from 5.32 to 10.8kN/m² (40 to 81 Torr) respectively. 7. Both acetazolamide and 10% CO₂ caused changes in brain metabolite concentrations similar to those for acutely administered morphine. Thus 10% CO₂ caused increased brain glucose concentration (123%) and decreased brain lactate (46%), pyruvate (34%), citrate (26%), α-oxoglutarate (33%), malate (45%) and creatine phosphate (7%) concentrations. No changes in adenine nucleotide concentrations were found. 8. The results indicate that the effect of morphine on brain metabolite concentrations may be accounted for by the increased [CO₂]. 9. These findings constitute a consistent pattern of metabolic changes after acute morphine administration, morphine addiction, and withdrawal from morphine addiction.     

Effects of acute asphyxia on brain energy metabolism in fetal guinea pigs near term.

In a previous study we suggested that--unlike other forms of asphyxia--acute asphyxia caused by arrest of uterine blood flow is accompanied by a fall in oxygen delivery to the fetal brain (Jensen et al., 1987). This may change cerebral energy metabolism by causing an increase in the glycolytic rate. To test this hypothesis we studied the time course of the changes in the levels of high-energy phosphates and glycolytic intermediates in the cerebral cortex of unanaesthetized fetal guinea pigs near term before and after 2 and 4 min of acute asphyxia. During asphyxia there was a progressive fall of adenosine triphosphate, creatine-phosphate, glucose and fructose-1,6-diphosphate concentrations, whereas adenosine diphosphate, adenosine monophosphate and lactate concentrations increased. Pyruvate concentrations did not change. We conclude that fetal cerebral energy metabolism becomes increasingly anaerobic during acute asphyxia caused by arrest of uterine blood flow, because oxygen delivery to the fetal brain falls.     

Effects of narcotic antagonists on fluid intake in the rat

The fluid intake (sweetened Enfamil) of rats that had been deprived of food and water for 24 hours was measured following the subcutaneous administration of eight narcotic antagonists and agonists and $\text{d}$-amphetamine. Drugs were tested over at least a 30-fold range of doses. Fluid intake was depressed by the highest dose of each drug, but only the narcotic antagonists naloxone, naltrexone and nalorphine produced dose-related decreases in fluid intake that were not associated with gross disturbances of behavior. The anorexigenic activity of these drugs in the rat does not appear to be related to the drugs' narcotic antagonist properties.     

Effects of acute and chronic hypoxia on the locomotion and enzyme of energy metabolism in Chinese shrimp Fenneropenaeus chinensis

ABSTRACT

To characterize the locomotor behaviors and their relation with physiological regulation in Chinese shrimp Fenneropenaeus chinensis, animals were held at approximately 6.0 (normoxia), 4.5, and 3.0 mg L^-1 dissolved oxygen (DO) for 1 day (acute) and 15 days (chronic), after which the swimming and tail-flipping abilities, and the activities of key enzymes involved in anaerobic and aerobic metabolism in hepatopancreas and pleopod and abdominal muscles were determined. Results showed that hepatopancreas was preferentially powered compared with pleopod and abdominal muscles during hypoxia. Physiological differences in muscles resulted in locomotion differences. F. chinensis presented reduced reliance on anaerobic glycolysis to conserve energy during chronic hypoxia at 3.0 mg L^-1 DO, but this physiological regulation reduce the survival of shrimp in the wild due to a reduction in tail-flipping. These findings suggested that when assessing the survival strategy of shrimp during hypoxia, both physiological regulation and behavioral changes should be considered.     

Effects of narcotic antagonists on L-dopa reversal of reserpine-induced catalepsy and blepharoptosis in mice

Reserpine (1 mg/kg, i.p.) induced catalepsy and blepharoptosis in mice which were readily reversed by the administration of L-dopa (300 mg/kg, i.p.). The administration of the pure narcotic antagonists naloxone (10 mg/kg, i.p.) and naltrexone (1 mg/kg, i.p.) significantly potentiated L-dopa reversal of reserpine-induced catalepsy. Lower doses of the narcotic antagonists did not significantly alter this reversal. The L-dopa reversal of blepharoptosis was not significantly altered by either naloxone or naltrexone. These results indicate that while opiate receptors may be involved in L-dopa reversal of catalepsy, they may not have a role in the alteration of blepharoptosis.     

Effects of continuous-wave, pulsed, and sinusoidal-amplitude-modulated microwaves on brain energy metabolism

A comparison of the effects of continuous-wave, sinusoidal-amplitude-modulated, and pulsed square-wave-modulated 591-MHz microwave exposures on brain energy metabolism was made in male Sprague-Dawley rats (175-225 g). Brain NADH fluorescence, adenosine triphosphate (ATP) concentration, and creatine phosphate (CP) concentration were determined as a function of modulation frequency. Brain temperatures of animals were maintained between -0.1 and -0.4 degrees C from the preexposure temperature when subjected to as much as 20 mW/cm2 (average power) CW, pulsed, or sinusoidal-amplitude modulated 591-MHz radiation for 5 min. Sinusoidal-amplitude-modulated exposures at 16-24 Hz showed a trend toward preferential modulation frequency response in inducing an increase in brain NADH fluorescence. The pulse-modulated and sinusoidal-amplitude-modulated (16 Hz) microwaves were not significantly different from CW exposures in inducing increased brain NADH fluorescence and decreased ATP and CP concentrations. When the pulse-modulation frequency was decreased from 500 to 250 pulses per second the average incident power density threshold for inducing an increase in brain NADH fluorescence increased by a factor of 4--ie, from about 0.45 to about 1.85 mW/cm2. Since brain temperature did not increase, the microwave-induced increase in brain NADH and decrease in ATP and CP concentrations was not due to hyperthermia. This suggests a direct interaction mechanism and is consistent with the hypothesis of microwave inhibition of mitochondrial electron transport chain function of ATP production.     

Brain energy metabolism and mitochondrial dysfunction in acute and chronic hepatic encephalopathy

One proposed mechanism for acute and chronic hepatic encephalopathy (HE) is a disturbance in cerebral energy metabolism. It also reviews the current status of this mechanism in both acute and chronic HE, as well as in other hyperammonemic disorders. It also reviews abnormalities in glycolysis, lactate metabolism, citric acid cycle, and oxidative phosphorylation as well as associated energy impairment. Additionally, the role of mitochondrial permeability transition (mPT), a recently established factor in the pathogenesis of HE and hyperammonemia, is emphasized. Energy failure appears to be an important pathogenetic component of both acute and chronic HE and a potential target for therapy.     

Expression changes of hippocampal energy metabolism enzymes contribute to behavioural abnormalities during chronic morphine treatment

Dependence and impairment of learning and memory are two well-established features caused by abused drugs such as opioids. The hippocampus is an important region associated with both drug dependence and learning and memory. However, the molecular events in hippocampus following exposure to abused drugs such as opioids are not well understood. Here we examined the effect of chronic morphine treatment on hippocampal protein expression by proteomic analyses. We found that chronic exposure of mice to morphine for 10 days produced robust morphine withdrawal jumping and memory impairment, and also resulted in a significant downregulation of hippocampal protein levels of three metabolic enzymes, including Fe-S protein 1 of NADH dehydrogenase, dihydrolipoamide acetyltransferase or E2 component of the pyruvate dehydrogenase complex and lactate dehydrogenase 2. Further real-time quantitative PCR analyses confirmed that the levels of the corresponding mRNAs were also remarkably reduced. Consistent with these findings, lower ATP levels and an impaired ability to convert glucose into ATP were also observed in the hippocampus of chronically treated mice. Opioid antagonist naltrexone administrated concomitantly with morphine significantly suppressed morphine withdrawal jumping and reversed the downregulation of these proteins. Acute exposure to morphine also produced robust morphine withdrawal jumping and significant memory impairment, but failed to decrease the expression of these three proteins. Intrahippocampal injection of D-glucose before morphine administration significantly enhanced ATP levels and suppressed morphine withdrawal jumping and memory impairment in acute morphine-treated but not in chronic morphine-treated mice. Intraperitoneal injection of high dose of D-glucose shows a similar effect on morphine-induced withdrawal jumping as the central treatment. Taken together, our results suggest that reduced expression of the three metabolic enzymes in the hippocampus as a result of chronic morphine treatment contributes to the development of drug-induced symptoms such as morphine withdrawal jumping and memory impairment.     

Effects of chronic weight perturbation on energy homeostasis and brain structure in mice

Maintenance of reduced body weight in lean and obese human subjects results in the persistent decrease in energy expenditure below what can be accounted for by changes in body mass and composition. Genetic and developmental factors may determine a central nervous system (CNS)-mediated minimum threshold of somatic energy stores below which behavioral and metabolic compensations for weight loss are invoked. A critical question is whether this threshold can be altered by environmental influences and by what mechanisms such alterations might be achieved. We examined the bioenergetic, behavioral, and CNS structural responses to weight reduction of diet-induced obese (DIO) and never-obese (CON) C57BL/6J male mice. We found that weight-reduced (WR) DIO-WR and CON-WR animals showed reductions in energy expenditure, adjusted for body mass and composition, comparable (-10-15%) to those seen in human subjects. The proportion of excitatory synapses on arcuate nucleus proopiomelanocortin neurons was decreased by ～50% in both DIO-WR and CON-WR mice. These data suggest that prolonged maintenance of an elevated body weight (fat) alters energy homeostatic systems to defend a higher level of body fat. The synaptic changes could provide a neural substrate for the disproportionate decline in energy expenditure in weight-reduced individuals. This response to chronic weight elevation may also occur in humans. The mouse model described here could help to identify the molecular/cellular mechanisms underlying both the defense mechanisms against sustained weight loss and the upward resetting of those mechanisms following sustained weight gain.     

The effects of NMDA receptor antagonists on acute morphine antinociception in mice

Summary.  Antagonists of the N-methyl-d-aspartate (NMDA) receptor complex inhibit the development of tolerance to antinociceptive effects of morphine and upon acute administration, influence morphine antinociceptive activity. The analysis of numerous studies investigating acute interaction between NMDA receptor antagonists and morphine in mice indicate a variety of procedural differences and reveal that these compounds may potentiate, attenuate and produce no effect on morphine antinociception. The conditions responsible for such conflicting experimental outcome of acute interaction remain unclear. It appears that the effects of NMDA receptor antagonists on morphine tolerance are not causally related to their acute effects on morphine antinociception. Received July 6, 2001 Accepted August 6, 2001 Published online August 9, 2002     

Effects of acute and chronic treatment elicited by lamotrigine on behavior, energy metabolism, neurotrophins and signaling cascades in rats

The present study was aimed to investigate the behavioral and molecular effects of lamotrigine. To this aim, Wistar rats were treated with lamotrigine (10 and 20 mg/kg) or imipramine (30 mg/kg) acutely and chronically. The behavior was assessed using forced swimming test. Brain-derived neurotrophic factor (BDNF), nerve growth factor (NGF), Proteina Kinase B (PKB, AKT), glycogen synthase kinase 3 (GSK-3) and B-cell lymphoma 2 (Bcl-2) levels, citrate synthase, creatine kinase and mitochondrial chain (I, II, II-III and IV) activities were assessed in the brain. The results showed that both treatments reduced the immobility time. The BDNF were increased in the prefrontal after acute treatment with lamotrigine (20 mg/kg), and the BDNF and NGF were increased in the prefrontal after chronic treatment with lamotrigine in all doses. The AKT increased and Bcl-2 and GSK-3 decreased after both treatments in all brain areas. The citrate synthase and creatine kinase increased in the amygdala after acute treatment with imipramine. Chronic treatment with imipramine and lamotrigine (10 mg/kg) increased the creatine kinase in the hippocampus. The complex I was reduced and the complex II, II-III and IV were increased, but related with treatment and brain area. In conclusion, lamotrigine exerted antidepressant-like, which can be attributed to its effects on pathways related to depression, such as neurotrophins, metabolism energy and signaling cascade.     

The effects of narcotic analgesics and narcotic antagonists on ganglionic transmission in the rat.

The effects of narcotic analgesics, narcotic-antagonist analgesics and narcotic antagonists on ganglionic transmission in the superior cervical ganglia of the rat were studied $\text{in}$$\text{vivo}$ and $\text{in}$$\text{vitro}$. $\text{In}$$\text{vivo}$ administration of morphine, meperidine, methadone, pentazocine or naltrexone blocked ganglionic transmission. Levorphanol, cyclazocine, nalorphine and naloxone had no effect on ganglionic transmission in this procedure. $\text{In}$$\text{vitro}$ studies confirmed the $\text{in}$$\text{vivo}$ results with the exception of levorphanol, cyclazocine and nalorphine, which were also found to block ganglionic transmission $\text{in}$$\text{vitro}$. In both preparations, naloxone did not antagonize the effect of morphine, suggesting that the effects of morphine and the other opiates were nonspecific. Similar potency of $\text{d}$- and $\text{l}$-isomers of pentazocine and cyclazocine support this conclusion. The observation that naltrexone blocked ganglionic transmission, but the other pure narcotic antagonist, naloxone, was inactive is somewhat unique to this test procedure and possibly significant.     

Alterations in brain metabolism induced by chronic morphine treatment: NMR studies in rat CNS

High-resolution (500 MHz) multiresonance/multinuclear proton (¹H) nuclear magnetic resonance (NMR) spectroscopy was used to detect metabolic changes and cellular injury in the rat brain stem and spinal cord following chronic morphine treatment. Compensatory changes were observed in glycine, glutamate, and inositols in the brain stem, but not the spinal cord, of chronic morphine-treated rats. In spinal cord, increases were detected in lactate and N-acetyl-aspartate (NAA), suggesting that there is anaerobic glycolysis, plasma membrane damage, and altered pH preferentially in the spinal cord of chronic morphine-treated rats.     

Human brain glycogen content and metabolism: implications on its role in brain energy metabolism

The adult brain relies on glucose for its energy needs and stores it in the form of glycogen, primarily in astrocytes. Animal and culture studies indicate that brain glycogen may support neuronal function when the glucose supply from the blood is inadequate and/or during neuronal activation. However, the concentration of glycogen and rates of its metabolism in the human brain are unknown. We used in vivo localized 13C-NMR spectroscopy to measure glycogen content and turnover in the human brain. Nine healthy volunteers received intravenous infusions of [1-(13)C]glucose for durations ranging from 6 to 50 h, and brain glycogen labeling and washout were measured in the occipital lobe for up to 84 h. The labeling kinetics suggest that turnover is the main mechanism of label incorporation into brain glycogen. Upon fitting a model of glycogen metabolism to the time courses of newly synthesized glycogen, human brain glycogen content was estimated at approximately 3.5 micromol/g, i.e., three- to fourfold higher than free glucose at euglycemia. Turnover of bulk brain glycogen occurred at a rate of 0.16 micromol.g-1.h-1, implying that complete turnover requires 3-5 days. Twenty minutes of visual stimulation (n=5) did not result in detectable glycogen utilization in the visual cortex, as judged from similar [13C]glycogen levels before and after stimulation. We conclude that the brain stores a substantial amount of glycogen relative to free glucose and metabolizes this store very slowly under normal physiology.     

Microwave effects on energy metabolism of rat brain

Rat brain was exposed to 591-MHz, continuous-wave (CW) microwaves at 13.8 or 5.0 mW/cm² to determine the effect on nicotinamide adenine dinucleotide, reduced (NADH), adenosine triphosphate (ATP) and creatine phosphate (CP) levels. On initiation of the in vivo microwave exposures, fluorimetrically determined NADH rapidly increased to a maximum of 4.0%–12.5% above pre-exposure control levels at one-half minute, then decreased slowly to 2% above control at three minutes, finally increasing slowly to 5% above control level at five minutes. ATP and CP assays were performed on sham- and microwave-exposed brain at each exposure time. At 13.8 mW/cm², brain CP level was decreased an average of 39.4%, 41.1%, 18.2%, 13.1%, and 36.4% of control at exposure points one-half, one, two three, and five minutes, respectively, and brain ATP concentration was decreased an average of 25.2%, 15.2%, 17.8%, 7.4%, and 11.2% of control at the corresponding exposure periods. ATP and CP levels of rat brain exposed to 591-MHz cw microwaves at 5 mW/cm² for one-half and one minute were decreased significantly below control levels at these exposure times, but were not significantly different from the 13.8 mW/cm² exposures. For all exposures, rectal temperature remained constant. Heat loss through the skull aperture caused brain temperature to decrease during the five-minute exposures. This decrease was the same in magnitude for experimental and control subjects. Changes in NADH, ATP, and CP levels during microwave exposure cannot be attributed to general tissue hyperthermia. The data support the hypothesis that microwave exposure inhibits mitochondrial electron transport chain function, which results in decreased ATP and CP levels in brain.