Influence of N-allyl-normetazocine on acetylcholine release from brain slices: involvement of muscarinic receptors.

The effects of (+/-)N-allyl-normetazocine on the release of acetylcholine from different areas of guinea-pig and rat brain were investigated. 1. The drug did not modify the electrically (2 Hz) evoked tritium efflux from guinea-pig cerebral cortex, thalamus and caudate nucleus slices, preloaded with 3H-choline 0.1 mumol/l and superfused with Krebs solution containing hemicholinium-3 10 mumol/l. 2. (+/-)N-allyl-normetazocine 10 mumol/l enhanced the evoked 3H efflux from guinea-pig brain slices superfused with Krebs solution containing physostigmine 30 mumol/l or oxotremorine 0.3-1 mumol/l; the effect was naloxone-insensitive and was abolished by atropine 0.15 mumol/l, but not by pirenzepine 1 mumol/l. 3. (+/-)N-allyl-normetazocine 5 mumol/l enhanced the electrically evoked release of endogenous acetylcholine as well, in a naloxone-insensitive way. 4. Both (+/-) and (+)N-allyl-normetazocine were without effect on 3H efflux from rat caudate nucleus slices electrically stimulated at 0.2 Hz frequency, after preloading with 3H-choline and during superfusion with hemicholinium-3. 5. The results are discussed in view of the antimuscarinic properties of the drug.

Different approaches to study acetylcholine release: endogenous ACh versus tritium efflux.

Superfused slices of guinea-pig cerebral cortex (CC), caudate nucleus (CN) and thalamus (Th) were used to compare i) the resting and electrically-evoked release of endogenous acetylcholine (ACh) in the presence of physostigmine (Phys) and ii) the resting and electrically-evoked tritium efflux (after preloading with 3H choline) in the absence or in the presence of Phys and hemicholinium (HC-3). In addition, the effect of GABA, morphine and their antagonists on both effluxes was investigated. By matching the ACh and tritium outflow on a molar basis, an average ratio of 100: 2-4 was found. When expressed as a percentage of tissue content, the ACh release at 2 Hz (2 min) was 4.1 in CN, 0.92 in CC and 0.44 in Th. Lower percent values in the same rank order, were found for tritium outflow with Phys. Thus, CN has the highest secretory activity. Tritium evoked outflow in the presence of Phys was nearly halved in comparison with the normal values (without Phys). Therefore, the autoreceptor-mediated negative feed-back seems to be similar in the three areas. Tritium evoked outflow in the presence of HC-3 was more than doubled in Th (less so in CC and CN) in comparison with the normal values. A second stimulation at 2 Hz (2 min) gave rise to the same outflow in Th while an evident fall in radiolabel efflux was found in CN. Therefore the blockade of high affinity choline uptake plays a different role in Th and CN.(ABSTRACT TRUNCATED AT 250 WORDS)

[Effect of morphine on dopamine and 5-HT content of the caudate nucleus in the guinea pig]. / Effetto della morfina sul contenuto di dopamina e 5-HT in fettine di nucleo caudato di cavia.

The effect of Morphine (3 x 10(-6) - 3 x 10(-5)) on tissue Dopamine and 5-hydroxytryptamine content was studied in superfused slices of guniea-pig caudate nucleus kept at rest or stimulated for 30 min at 5 Hz. The caudatal slices submitted to electrical stimulation for 30 min showed a significant reduction in their 5-hydroxytryptamine and Dopamine content. Morphine did not modify the amines content of the slices kept at rest but counteracted the depletion caused by electrical stimulation. The opioid was dose-dependent and antagonized by Naloxone 1 x 10(-5) M.

The effect of morphine on monoamine release and content in guinea-pig brain slices.

The effect of morphine on the efflux of (3H) monoamines as well as the endogenous monoamine contents in electrically stimulated brain slices was investigated. Only at a concentration at high as 30 microM did the drug reduce the tritium efflux and counteracted the monoamine depletion caused by prolonged electrical stimulation. This effect was antagonized by Naloxone 10 microM. Besides the good agreement between the two methods used to evaluate drug effects the discrepancy between morphine concentrations active on the neurosecretory process and those effective in the whole animal is stressed. The opioids may act in vivo either by modulating the firing rate of the monaminergic neurons or by affecting other related neuronal pools.

Effect of morphine on acetylcholine content of electrically stimulated brain slices.

Acetylcholine (ACh) levels were measured in guinea-pig thalamic and caudatal slices kept at rest or electrically stimulated for different times (2-30 min.). The decrease of ACh content caused by electrical pulses at 1 Hz and 2 Hz in caudate nucleus and thalamus slices, respectively, was directly related to the time of stimulation. The depletion was potentiated by HC-3 10 microM. In this condition the relationship between ACh content and time of stimulation was shifted to the left. In the presence of HC-3, Morphine (Mo) 30 microM did not affect the ACh levels of thalamic and caudatal slices kept at rest. The opioid, on the contrary, reduced the depletion of ACh caused by 10 min stimulation. Naloxone (Nx) 10 microM antagonized the opioid effect in caudate nucleus, while it increased the stimulus-induced ACh depletion in the thalamus treated with Morphine 30 microM. In conclusion, the electrically-stimulated brain tissue perfused with HC-3 may be a suitable tool to study drug effects on ACh depletion. This may offer an indirect, mirror-like evaluation of ACh apparent turnover and release. The results obtained with Mo and Nx support this statement.

Effect of gamma-aminobutyric acid on cyclic nucleotides content of guinea-pig cerebral cortex slices.

The effect of GABA and related drugs on 3'5' cAMP and 3'5' cGMP was investigated in slices of guinea-pig cerebral cortex, kept at rest or electrically stimulated. GABA 1 X 10(-4) - 1 X 10(-3) M raised the cAMP basal levels, bud reduced its increase due to electrical stimulation. These effects were antagonized by picrotoxin 1.6 X 10(-5) M. On the contrary, endogenous GABA did not influence cAMP and cGMP content. In fact, neither ethanolamine-O-sulphate 2 X 10(-3) M nor picrotoxin 1.6 X 10(-5) M affected the normal nucleotide values at all. Higher picrotoxin concentrations (3.2 - 8 X 10(-5) M), however, increased both cyclic nucleotides. Phentolamine counteracted the actions of both GABA 1 X 10(-4) M and picrotoxin 8 X 10(-5) M: therefore, the observed increase in cyclic nucleotides were due to norepinephrine release. Tetrodotoxin antagonized GABA but not picrotoxin metabolic effects. Thus it is suggested that the exogenous amino acid released norepinephrine through a sodium-dependent process, while picrotoxin released the monoamine directly from its storage sites. Clearly, attention must be paid when putative transmitters or their antagonists are added at high concentrations to isolated tissue to study the effect of endogenous compounds.