Role of calcium ions in dopamine release induced by sodium cyanide perfusion in rat striatum

Effects of melatonin on KCN-induced neurodegeneration in mice

Melatonin is known to have a neuroprotective effect by preventing epileptic seizures, which are normally induced by cyanide. To demonstrate the neuroprotective function of melatonin, we examined cell death and changes in plasma melatonin level in KCN-treated mice. Neuronal cell death is shown in substantial nigra of KCN-treated groups. In melatonin-treated groups, this cell death decreased in substantia nigra. Plasma melatonin level at 12:00 was significantly decreased to 52.6% after KCN injection as compared to the normal group. In contrast, melatonin level was significantly decreased (74.5%) in KCN + melatonin group. Melatonin level at 24:00 was significantly decreased to 57.0% after KCN injection and also significantly decreased to 81.0% in KCN-melatonin group as compared to the normal group. Results from the present study suggest that melatonin prevents neuronal cell death in KCN-induced brain.

Induced mitochondrial failure in the feline brain: implications for understanding acute post-traumatic metabolic events

OBJECTIVE

Recently, evidence has become available implicating mitochondrial failure as a crucial factor in the pathogenesis of acute brain damage following severe traumatic brain injury (TBI). However, it remains unclear how mitochondrial dysfunction affects cerebral metabolism. Therefore the aim of the study was to evaluate the impact of 'isolated' mitochondrial failure on local cerebral metabolism.

METHODS

Cerebral mitochondrial metabolism was blocked by local microdialysis perfusion with cyanide in seven cats. Local brain tissue oxygen tension (p(tiO(2))), carbon dioxide tension (p(tiCO(2))) and pH, as well as extracellular cerebral fluid, glucose, lactate, pyruvate and glutamate were monitored, using a Neurotrend sensor and microdialysis, respectively. Tissue oxygen consumption was measured in a microrespirometric system, and ultrastructural changes evaluated via electron microscopy.

RESULTS

Brain tissue oxygen tension increased from a baseline of 31+/-9 mmHg to 84+/-30 mmHg after 60 min of cyanide perfusion (P<0.05), concomitant a decrease in oxygen consumption from 14.45+/-3.91 microl/h/mg to 10.83+/-1.74 microl/h/mg (P<0.05). Brain tissue pH was decreased after 60 min of cyanide perfusion (6.83+/-0.16) compared to baseline (7.07+/-0.39) (P<0.05), whereas p(tiCO(2)) did not show significant changes. Lactate massively increased from a baseline of 599+/-270 micromol/l to 2609+/-1188 micromol/l immediately after cyanide perfusion (P<0.05). The lactate:glucose ratio increased from 0.79+/-0.15 before cyanide perfusion to 6.40+/-1.44 at 40 min after cyanide perfusion (P<0.05), while no significant changes in the lactate:pyruvate ratio could be observed. Glutamate increased from a baseline of 11.6+/-7.2 micromol/l to 61.4+/-44.7 micromol/l after cyanide perfusion (P<0.05).

CONCLUSION

The results of this study show that 'isolated' cerebral mitochondrial failure initiates changes in cerebral substrates and biochemistry, which are very similar to most of the changes seen after severe human head injury, except for the early fall in p(tiO(2)), further indicating a crucial involvement of mitochondrial impairment in the development of brain damage after TBI.

Differential susceptibility of brain areas to cyanide involves different modes of cell death

We have demonstrated that cyanide (KCN) induces selective degeneration of dopaminergic neurons in mice and apoptotic cell death in cultured neurons. In the present study the mode of cyanide-induced cell death was determined in the susceptible brain areas. Mice were treated with KCN (6 mg/kg ip) or vehicle (saline) twice daily for 1 to 12 days. After 3 days of KCN treatment, two separate lesions were observed in coronal brain sections. Widespread DNA fragmentation in parietal and suprarhinal regions of the motor cortex was observed by the in situ terminal deoxynucleotide transferase nick-end labeling (TUNEL) technique. Pyknosis and chromatin condensation, morphological hallmarks of apoptotic cells, were observed in TUNEL-positive regions. On the other hand, in the substantia nigra (SN), KCN produced a progressive, bilateral necrotic lesion that was evident by 3 days of treatment. The SN lesion was circumscribed by a prominent ring of glial infiltration, as determined by glial-acidic fibrillary protein (GFAP) immunostaining. The extent of the SN lesion steadily increased with treatment duration, and DNA fragmentation was not observed over the 1- to 12-day period. On the other hand, cortical apoptosis was not associated with necrotic cell loss or astrogliosis. Pretreatment of animals with the antioxidant alpha-phenyl-tert-butyl nitrone (PBN) for 7 days prior to and during 3 days of KCN administration markedly reduced cortical DNA fragmentation whereas the PBN treatment did not influence the SN necrosis or astrocytic gliosis. Except for moderate GFAP immunostaining in corpus callosum, other brain areas were not affected by cyanide. It is concluded that KCN-induced neuronal loss involves selective activation of necrosis or apoptosis in different neuronal populations, and involves divergent mechanisms and sensitivity to antioxidants.

Effects of various dopamine uptake inhibitors on striatal extracellular dopamine levels and behaviours in rats

In vivo central effects of some dopamine uptake inhibitors were evaluated in both brain microdialysis and behavioural studies in rats, and compared with their in vitro affinities to dopamine uptake sites. IC50 values of GBR12909 (1-[2- bis(4-fluorophenyl)methoxy]ethyl]-4-(3- phenylpropyl)piperazine), diclofensine, mazindol, amfonelic acid and nomifensine for inhibiting 1 nM [3H]GBR12935 (1-[2-(diphenylmethoxy)ethyl]-4-(3-phenylpropyl)piperazine) binding to rat striatal membrane were 7.0, 36, 81, 187 and 290 nM, respectively. In the brain microdialysis study, dopamine levels in the striatal dialysates were increased to 16.3- (GBR12909), 14.1- (nomifensine), 4.8- (diclofensine) and 1.9-fold (amfonelic acid) the respective basal levels 40-60 min after i.p. administration (0.1 mmol/kg) and thereafter decreased slowly but remained at the elevated levels for a further 3 h, while mazindol gradually increased dopamine levels though less pronouncedly than others (1.7-fold 200 min after administration). Remarkable and comparable stereotyped behaviours (licking and forepaw treading) were continuously observed at least for 3 h after administration of GBR12909, nomifensine and amfonelic acid, while stereotypies induced by diclofensine and mazindol were moderate and marginal, respectively. In vivo potencies of dopamine uptake inhibitors to increase the extracellular dopamine levels in the striatum tended to correlate with their in vitro affinities to dopamine uptake sites except in the case of nomifensine, and correlated significantly with their potencies to induce stereotyped behaviours except in the case of amfonelic acid. Based on these findings, pharmacological characteristics of these dopamine uptake inhibitors are discussed.

Is there an energy conservation "system" in brain that protects against the consequences of energy depletion?

A poorly understood marked decrease (circa 50% of control) in local cerebral glucose utilization is caused by sublethal doses of NaCN. The decrease is global, occurring in essentially all brain regions and is entirely reversible within hours, leaving no obvious pathology. This event is not unique to NaCN in so far as a strikingly similar pattern of decreased glucose utilization occurs with some other toxins. Nor can it be attributed to a direct action of NaCN since local application by microdialysis to the striatum produces a global depression. These results imply that some widely distributed "system" or substance is involved. We speculate the existence of a "system" possibly related to the reticular activating system that senses a fall in energy production and acts globally to make cells quiescent and thus would give some protection from excitotoxic driven damage.