Transmitter release patterns of noradrenergic, dopaminergic and cholinergic axons in rabbit brain slices during short pulse trains, and the operation of presynaptic autoreceptors.
Slices of rabbit brain were field-stimulated either by single electrical pulses or by trains of 4 or 8 pulses at 1 or 100 Hz in order to study transmitter release patterns and the autoinhibition of transmitter release. The slices were preincubated with 3H-noradrenaline (cortex), 3H-dopamine (caudate nucleus) or 3H-choline (caudate nucleus). Slices preincubated with 3H-noradrenaline were superfused with medium containing desipramine 1 mumol/l. The overflow of tritium elicited by single pulses amounted to 0.19% of the tritium content of the tissue. The overflow elicited by 4 pulses/1 Hz was similar, whereas that elicited by 4 pulses/100 Hz was 5.1-fold higher. Yohimbine 10-1000 nmol/l increased up to 2.5-fold the overflow evoked by 4 pulses/1 Hz but did not change the overflow evoked by single pulses or 4 pulses/100 Hz. - Slices preincubated with 3H-dopamine were superfused with medium containing nomifensine 1 mumol/l. The overflow of tritium elicited by single pulses was 0.39% of the tritium content of the tissue. The overflow elicited by 4 pulses/1 Hz was 1.3-fold and the overflow elicited by 4 pulses/100 Hz 1.4-fold higher. Domperidone 1-100 nmol/l and sulpiride 10-1000 nmol/l increased up to 2.4-fold the overflow evoked by 4 pulses/1 Hz but increased only slightly the overflow evoked by single pulses or 4 pulses/100 Hz. - Slices preincubated with 3H-choline were superfused either with physostigmine-free medium or with medium containing physostigmine 1 mumol/l. In physostigmine-free medium, atropine did not increase the evoked overflow of tritium at any stimulation condition. In physostigmine-containing medium, the overflow elicited by single pulses was 0.18% of the tritium content of the tissue. The overflow elicited by 8 pulses/1 Hz was 2.0-fold and the overflow elicited by 8 pulses/100 Hz 2.2-fold higher. Atropine 2-200 nmol/l increased up to 2.4-fold the overflow evoked by 8 pulses/1 Hz but increased only slightly the overflow evoked by single pulses or 8 pulses/100 Hz. In physostigmine-free medium, sulpiride 10-1000 nmol/l did not change the single-pulse-evoked overflow of tritium in the absence but increased it in the presence of nomifensine 1 mumol/l. Single pulses elicit a large release of 3H-noradrenaline, 3H-dopamine and 3H-acetylcholine under the conditions of these experiments. Release elicited by single pulses is not subject to autoinhibition except for a small inhibition by spontaneously released transmitter in the case of dopaminergic and cholinergic axons.(ABSTRACT TRUNCATED AT 400 WORDS)
Mayer
A
A
Pharmakologisches Institut der Universität, Freiburg i. Br., Federal Republic of Germany.
Limberger
N
N
Starke
K
K
D000109:Acetylcholine / Q000378:metabolism; D000818:Animals; D001369:Axons / Q000378:metabolism*; D001923:Brain Chemistry; D004298:Dopamine / Q000502:physiology*; D004558:Electric Stimulation; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D018377:Neurotransmitter Agents / Q000378:metabolism*; D009638:Norepinephrine / Q000502:physiology*; D010275:Parasympathetic Nervous System / Q000378:metabolism*; D010277:Parasympathomimetics / Q000494:pharmacology; D011817:Rabbits; D017981:Receptors, Neurotransmitter / Q000378:metabolism
D018377:Neurotransmitter Agents; D010277:Parasympathomimetics; D017981:Receptors, Neurotransmitter; D000109:Acetylcholine; D004298:Dopamine; D009638:Norepinephrine