Excitatory and inhibitory effects of dopamine on synaptic transmission in the rat olfactory cortex slice

A study has been undertaken of the effects of dopamine on excitatory transmission at the lateral olfactory tract (LOT)-superficial pyramidal cell synapse of the rat olfactory cortex slice by measuring the effects of bath-applied dopamine on the amplitudes and latencies of the surface field potentials evoked on submaximal LOT stimulation in a total of 32 preparations. In 7 (22%) slices, dopamine had no detectable effects on transmission. In the remaining preparations, dopamine (1-250 microM) depressed transmission in a concentration-dependent manner. This action was unaffected by nadolol (10 microM), phentolamine (10 microM) and picrotoxin (25 microM) but was antagonized by chlorpromazine (10 microM) and trifluoperazine (0.2 and 0.5 microM) and mimicked by bromocriptine (0.01-5 microM) and apomorphine (0.25-25 microM). Investigation of the effects of dopamine on stimulus input-evoked potential output relationships indicated that the inhibitory effect of dopamine on transmission was mediated by a reduction in pyramidal cell excitability. In 6 slices (24% of those sensitive to dopamine) low dopamine concentrations (0.1-1 microM) facilitated transmission at the LOT-superficial pyramidal cell synapse. This excitatory effect was antagonized by nadolol and phentolamine (10 microM) and also by 100 microM 2-amino-5-phosphonovalerate (an antagonist of excitatory amino acid receptors of the N-methyl-D-aspartate type) but was unaffected by chlorpromazine (10 microM) and trifluoperazine (0.2 and 0.5 microM). By a comparison with the effects of noradrenaline on transmission, it is concluded that the excitatory effects of dopamine are mediated either indirectly by the release of noradrenaline or by a direct interaction of dopamine with adrenoceptors.(ABSTRACT TRUNCATED AT 250 WORDS)