Pharmacological investigations on electrically-induced changes of cyclic nucleotides in guinea-pig brain slices

cGMP: a second messenger for acetylcholine in the brain?

Already 30 years ago, it became apparent that there exists a relationship between acetylcholine and cGMP in the brain. Acetylcholine plays a role in a great number of processes in the brain, however, the role of cGMP in these processes is not known. A review of the data shows that, although the connection between NO-mediated cGMP synthesis and acetylcholine is firmly established, the complexities of the heterosynaptic pathways and the oligosynaptic structures involved preclude a clear definition of the role of cGMP in the functioning of acetylcholine presently.

Influence of Ca2+ channel modulators on [3H]purine release from rat cultured glial cells

[3H]Purine release from rat striatum astrocyte cultures was studied at 14 days in vitro (DIV). Superfusion of cultures with a Ca(2+)-free medium + 0.5 mM ethylene glycol-bis(beta-aminoethylether)N,N,N',N'-tetracetic acid (EGTA) reduced the electrically evoked [3H]purine release. Nimodipine only at the concentration of 10 microM modified [3H]purine outflow whereas 0.1 microM omega-conotoxin and 0.03-0.1 microM nitrendipine reduced the evoked one. Superfusion of cultures with 0.1 microM omega-conotoxin + 0.1 microM nitrendipine antagonized the evoked [3H]purine release similarly to each drug given alone. Neither nitrendipine nor omega-conotoxin influenced the uptake of 45Ca2+ by the cultures. The treatment of cells with the Ca2+ agonist Bay K 8644 did not affect [3H]purine release or the 45Ca2+ uptake. The drug did not either alter [Ca2+]i, evaluated by loading the cells with 3 microM Fura-2/AM. 10-30 microM 3,4,5-trimethoxybenzoic acid 8-(diethylamino)octyl ester (TMB-8), a blocker of intracellular Ca2+ discharge, significantly reduced the evoked [3H]purine release. On the other hand, 2 microM thapsigargin, an inhibitor of the ion store Ca2+ ATPase, was able to increase either the culture [3H]purine release or the [Ca2+]i. Together, the findings indicate that voltage-sensitive calcium channels (VSCCs) of the neuronal N and L-types are not involved in the modulation of [3H]purine release from rat cultured astrocytes whereas Ca2+ coming from intracytoplasmic stores seems to play a prevailing role. Moreover, agents which block VSCC, seem to be able to affect [3H]purine outflow with mechanisms other than VSCC gating.

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.