The direction of apomorphine-induced rotation behavior is dependent on the location of excitotoxin lesions in the rat basal ganglia.

Adult rats received unilateral kainic acid (KA) lesions of the striatum with the anterior/posterior coordinates of the lesion at either 1.5 mm or 0.3 mm anterior to bregma. Four to six weeks after the lesion rats were placed in an open field environment and injected with apomorphine (1 mg/kg, s.c.). Rats receiving the more posterior lesion (0.3 mm) rotated ipsilateral to the lesioned side of the brain. In contrast, the majority of rats receiving the more anterior (1.5 mm) placement of the lesion rotated contralateral to the lesioned side of the brain. Histological analysis of several animals receiving posterior lesions revealed damage to the hippocampus and thalamus that was not seen in the animals receiving anterior lesions. Our results are consistent with the hypothesis that the direction of apomorphine-induced rotation after excitotoxin injection into the rat basal ganglia is dependent on the location of the lesion.

Olfactory bulb DA receptors may be located on terminals of the olfactory nerve.

The glomerular layer of the olfactory bulb contains a substantial population of dopaminergic neurons. We determined the quantity and location of D1 and D2 dopamine receptors which are the presumed targets of these neurons. Binding of the D1 selective ligand [3H]SCH23390 was slightly above background and was distributed through all layers of the bulb except the olfactory nerve layer. In contrast there were relatively high levels of [3H]spiperone binding to D2 DA receptors in the glomerular and olfactory nerve layers. The presence of relatively high concentrations of D2 DA receptors in both the nerve layer and glomerular layer suggests the novel hypothesis that these receptors may be localized on terminals of the olfactory nerve.

Sensitization of rotation behavior in rats with unilateral 6-hydroxydopamine or kainic acid-induced striatal lesions.

Following unilateral 6-hydroxydopamine (6-OHDA) lesions of the substantia nigra or unilateral kainic acid (KA) lesions of the striatum rats displayed rotation behavior in response to apomorphine (0.25 mg/kg SC or 1 mg/kg SC for the 6-OHDA- and KA-lesioned rats respectively). Three to five days following the initial apomorphine challenge rats were challenged under identical conditions with the same dose of apomorphine received previously. Both 6-OHDA- and KA-lesioned rats demonstrated a significant increase in the total number of rotations. Following a subsequent challenge with apomorphine, rats showed further increases in the total number of rotations. With the second and the subsequent apomorphine challenges there were significant increases in the maximal number of rotations, a significant decrease in the time of onset of rotation behavior and in some cases an increase in the duration of the rotation behavior. These increases in rotation behavior following repeated challenges with apomorphine indicate a supersensitivity to dopamine receptor agonists distinct from that elicited by lesions and chronic antagonist treatments. Furthermore, the utility of the rotation behavior model for testing the efficacy of dopaminergic agonists might be compromised if repeated challenges in individual animals are employed.