Changes in neurotransmitter parameters in the brain induced by L-cysteine injections in the young rat.

A single subcutaneous injection of L-cysteine (1.2 mg/g body wt.) to 4-day-old rats leads to atrophy of the brains examined 27-31 days later. The brains could be separated into two groups (type 1 and 2) on account of the degree of atrophy. Type-1 lesion, with a brain weight reduction of 20%, was dominated by a severe reduction in high-affinity uptake of L-glutamate in CNS regions receiving corticofugal fibers such as thalamus and striatum. Glutamate decarboxylase was only reduced in cortical structures. In type-2 lesion, with a severe brain atrophy of about 50%, high-affinity glutamate uptake was further reduced and there was a more pronounced reduction in glutamate decarboxylase activity in several brain regions. Cholinergic neurons were less affected by the lesion and the levels of choline acetyltransferase showed a relative increase in brain regions which partly compensated for their reduction in size.

Effects of organophosphates on presynaptic events in the vascularly perfused phrenic nerve-hemidiaphragm preparation from the rat.

A vascularly perfused phrenic nerve-hemidiaphragm preparation from the rat was developed to study effects of physostigmine and some organophosphate inhibitors on the synthesis and release of endogenous and deuterium-labelled (choline--D9) acetylcholine (ACh) as well as the presynaptic uptake of choline. Choline and ACh were determined by combined gas chromatography/mass spectrometry. Without stimulation the endogenous levels of ACh were 320 pmole/hemidiaphragm for unlabelled and less than 1 pmole/hemidiaphragm of deuterium-labelled ACh. After stimulation at 15 Hz for 1 hr, 460 pmole/hemidiaphragm of unlabelled and 15 pmole/hemidiaphragm of deuterium-labelled ACh were found. Without stimulation the release of unlabelled ACh was 6 pmole/min/hemidiaphragm and for deuterium-labelled 0.2 pmole/min/hemidiaphragm. Evoked release (15 Hz, 1 hr) was 22 pmole/min/hemidiaphragm for unlabelled and 1.8 pmole/min/hemidiaphragm for deuterium labelled ACh. During stimulation and treatment with high concentrations (10(-5)-10(-4) M) of soman, DFP and Vx the level of unlabelled endogenous ACh increased, but the level of deuterium labelled ACh decreased in the diaphragm. During stimulation and treatment with these inhibitors the release of both unlabelled and labelled ACh decreased. During treatment with high concentrations (10(-5)-10(-4) M) of sarin and physostigmine there were no changes in endogenous levels or release of unlabelled or deuterium labelled ACh. The different effects of cholinesterase inhibitors are probably linked to the synthesis and release mechanism of ACh rather than to the choline uptake mechanism.

Determination of succinyldicholine in different tissue samples from guinea pigs after injection of a single intravenous dose.

The distribution and postmortem stability of succinyldicholine in different tissues and urine from guinea-pigs has been studied. Succinyldicholine was extracted from tissue homogenates and urine samples from animals sacrificed by intravenous injections of succinyldicholine hydrochloride (40 mg/kg). The bis-quaternary ammonium compound was demethylated and the tertiary amine was analysed by gas chromatography/mass spectrometry. The concentrations found in muscle, kidney and urine were often low; in muscle below 5 pmol/g, in kidney from 5 to 1500 pmol/g and in urine from 5 to 650 pmol/ml. The eye proved to be the best tissue sample, with a rather high and constant concentration (280 +/- 36 pmol/g) of succinyldicholine. The postmortem stability was studied by storing the bodies at 4 degrees C. After 6 days storage the drug concentrations in the eyes started to decline. Four weeks after death it was not possible to detect any succinyldicholine in this tissue.

Systemic injection of kainic acid: effect on neurotransmitter markers in piriform cortex, amygdaloid complex and hippocampus and protection by cortical lesioning and anticonvulsants.

Systemic injection of kainic acid (12 mg/kg) in rats induces a well established pattern of neuronal lesions in different brain regions. These lesions are accompanied by changes in neurotransmitter markers. In the piriform cortex and amygdaloid complex, the kainic acid lesion was accompanied by a reduction in the high affinity uptake of glutamate and in the activities of glutamate decarboxylase and choline acetyltransferase, whereas in the hippocampus there was a reduction in the high affinity uptake of glutamate and in glutamate decarboxylase activity. Hemidecortication, hemitransection, a caudal knife cut in the cortex, or treatment with diazepam, all protected against the effects of kainic acid in the piriform cortex and amygdaloid complex but not in the hippocampus. Diphenylhydantoin had no effect on the neurotoxicity of kainic acid. The results indicate that the neurotoxic effects of kainic acid in the piriform cortex and amygdala are dependent on an intact cortical structure, probably due to a dependence on specific excitatory circuitry. The neurons involved may be glutamergic/aspartergic.

Kainic acid neurotoxicity; effect of systemic injection on neurotransmitter markers in different brain regions.

Systemic injection of kainic acid (12 mg/kg) induces necrosis and neuronal degeneration in several brain regions. The most pronounced effects were observed in the piriform cortex, amygdaloid complex, hippocampus and septum. A good correlation between morphological changes and changes in some neurotransmitter markers was observed in these 4 areas. High affinity uptake of L-glutamate, as well as glutamate decarboxylase and choline acetyltransferase activities were reduced in the piriform cortex and amygdaloid complex whereas in the hippocampus and septum only the first two markers were reduced. No morphological changes or decrease in any of these neurotransmitter markers were observed in striatum or globus pallidus. A pronounced neuronal degeneration could be demonstrated in lateral thalamus and geniculate body, but this degeneration was not accompanied by any decrease in the transmitter markers tested.

Increased resting and evoked release of transmitter following repetitive electrical tetanization in hippocampus: a biochemical correlate to long-lasting synaptic potentiation.

In vitro stimulation of two axonal branches from hippocampal CA3 pyramids, the CA1 afferent Schaffer collaterals and the CA3 efferents to septum through fimbria, released D-[3H]aspartate as a measure for endogenous L-glutamate. Following bursts of repetitive electrical stimuli to the Schaffer collaterals, a long-lasting and significantly increased resting efflux, as well as an increased stimulus evoked release of D-aspartate, appeared. No such persistent increase in D-aspartate efflux was recorded from the septal terminals. We propose that increased transmitter liberation may account for long-term synaptic potentiation in hippocampus.

Morphological changes in rat brain induced by L-cysteine injection in newborn animals.

A single subcutaneous injection of L-cysteine (1.2 mg/g body weight) to rats 4 days after birth was followed by atrophy of the brain which was well developed 27--32 days after the injection. It was apparent that the lesioned animals could be divided into two groups (type 1 and 2) on account of the degree of brain atrophy. In type 1, which was observed in 80% of the animals, the body weight was unchanged, but the total brain weight was reduced by about 20%. The brain structures most affected were cerebral cortex, hippocampus and thalamus, each having a 30--40% reduction in wet weight. The atrophy of the posterior part of cortex was particularly pronounced in this type of lesion. In type 2 lesion, which appeared in 10% of the survivors, the atrophy was much more severe. There was a 50% reduction in wet weight of brain and in body weight. The most prominent finding was the atrophy of the whole cortex and the hippocampus which were reduced by 80 and 60% of wet weights respectively. In this type of lesion significant morphological changes were observed in several brain regions such as caudato-putamen, thalamus, pons, medulla oblongata, spinal cord and cerebellum.

Differential release of D-[3H]aspartate and [14C]gamma-aminobutyric acid following activation of commissural fibres in a longitudinal slice preparation of guinea pig hippocampus.

Low-stimulus frequencies released both D-[3H]aspartate and [14C]GABA in double labelling experiments after activation of the commissural fibres to stratum oriens in hippocampal slices. The stimulus-dependent release of [14C]GABA was highest at low stimulus frequencies (10 Hz) whereas at higher stimulus frequencies (30--50 Hz) it was almost abolished. All stimulus frequencies used released D-[3H]aspartate. The results indicate that activation of the commissural fibres in stratum oriens, using low stimulus frequencies, activates pyramidal cells which stimulate inhibitory neurones releasing GABA as a transmitter.

Dopaminergic control of the septal-hippocampal cholinergic pathway.

Apomorphine given subcutaneously is known to decrease the turnover rate of acetylcholine (TR(ACh) in the hippocampus. Blockade of dopaminergic receptors by intraseptal haloperidol or destruction of dopaminergic terminals by intraseptal 6-hydroxydopamine results in an increase in TR(ACh) in the hippocampus. Specific destruction of the dopaminergic neurons projecting to the septum by the injection of 6-hydroxydopamine into the A10 mesencephalic cell group also results in an increased TR(ACh) in the hippocampus. None of the above treatments affects TR(ACh) in the cortex. Thus, it appears that dopaminergic neurons exert a tonic inhibitory effect on the ACh metabolism of the septal-hippocampal pathway, but do not affect that of cholinergic neurons projecting from the septum to the cortex. It can be inferred that this decrease in the rate of metabolism may be associated with a regulation of the rate of neuronal firing.

Modulation of ACh turnover in the septal-hippocampal pathway by electrical stimulation and lesioning.

The septal-hippocampal cholinergic pathway of the rat was either electrically stimulated or lesioned in order to study whether or not acetylcholine turnover rate (TRACh) changes with the activity of the cholinergic neurons. Appropriate electrical stimulation of the septum selectively increased the TRACh in the hippocampus in nonanesthetized and in barbiturate-treated animals. The ACh content of the hippocampus increased by approximately 30% 1 h after fimbria lesions, but decreased by about 80% 9 days after fimbria lesions. Acute fimbria lesions decreased the TRACh in the lesioned side by approximately 85%, but the TRACh in the intact side and in the cortex was unchanged. The same was true in rats with chronic fimbria lesions. In conclusion, the hippocampal TRACh increases or decreases proportionally to the activity of the cholinergic neurons; therefore the measurement of this parameter is of particular value in understanding how postynaptic cholinergic neurons are modulated by putative neurotransmitter released from afferent nerve terminals.