Kainic acid lesions decrease striatal dopamine receptors and 1,4-dihydropyridine sites

Iminodipropionitrile-induced dyskinesia in mice: striatal calcium channel changes and sensitivity to calcium channel antagonists

Administration of 3,3'-iminodipropionitrile (IDPN) (1 g/kg, i.p. for 3 days) in mice leads to the development of a characteristic syndrome consisting of lateral and vertical head and neck movements, hyperactivity, random circling, increased locomotor activity, and increased startle response. Nifedipine, verapamil, and diltiazem (10 mg/kg) inhibited significantly the symptoms of IDPN-induced dyskinesia. However, there was no change in the affinity (KD) or the density of PN 200-110 binding sites (Bmax) in whole brains of IDPN-treated mice. Similarly, the K(+)-depolarization-dependent Ca2+ uptake in synaptosomes from whole brain, cortex, or striatum was not altered following IDPN treatment. However, IDPN caused a significant increase in the Bmax value (from 157 +/- 7 fmol/mg to 237 +/- 31 fmol/mg in control and treated groups, respectively) of PN 200-110 binding to the striatum without change of KD value (38 +/- 4.7 pM versus 33 +/- 1.6 pM). IDPN also caused a slight but significant decrease in the KD value (from 68 +/- 10.1 pM to 45 +/- 4.5 pM in control and treated groups, respectively), without significant change of Bmax value (563 +/- 51 fmol/mg versus 485 +/- 41 fmol/mg) of PN 200-110 binding to the cortex. IDPN did not alter omega-conotoxin binding in whole brain, striatum, or cortex. The behavioral effects of chronic IDPN treatment as inhibited by L-type calcium channel antagonists and this may be associated with the observed increase in striatal L-type calcium channels.

Striatal dopamine in motor activation and reward-mediated learning: steps towards a unifying model

On the basis of behavioural evidence, dopamine is found to be involved in two higher-level functions of the brain: reward-mediated learning and motor activation. In these functions dopamine appears to mediate synaptic enhancement in the corticostriatal pathway. However, in electrophysiological studies, dopamine is often reported to inhibit corticostriatal transmission. These two effects of dopamine seem incompatible. The existence of separate populations of dopamine receptors, differentially modulating cholinergic and glutamatergic synapses, suggests a possible resolution to this paradox. The synaptic enhancement which occurs in reward-mediated learning may also be involved in dopamine-mediated motor activation. The logical form of reward-mediated learning imposes constraints on which mechanisms can be considered possible. Dopamine D1 receptors may mediate enhancement of corticostriatal synapses. On the other hand, dopamine D2 receptors on cholinergic terminals may mediate indirect, inhibitory effects of dopamine on striatal neurons.