An aromatic L-amino acid decarboxylase inhibitor blocks L-dopa-induced air-stepping in neonatal rats

Rat pups suspended in air and administered L-DOPA engage in a locomotor behavior termed air-stepping. The role of L-DOPA itself was investigated by administering several doses of an aromatic L-amino acid decarboxylase inhibitor, NSD 1015, prior to 100 mg/kg L-DOPA to 5-day-old rats. NSD 1015 dose-dependently increased the latency to onset and decreased the duration of L-DOPA-induced air-stepping. Thus L-DOPA induces air-stepping only after its conversion to dopamine and/or noradrenaline.

Potentiation of the dorsal immobility response following intrastriatal injections of enkephalins

The effects of bilateral intrastriatal injections (1.0 microgram/side) of leucine5- and methionine5-enkephalins and their related nonopiate fragments upon three measures of immobility over a time course were investigated. Both leucine5-enkephalin and des-Tyr1-leucine-enkephalin potentiated the duration of the dorsal immobility response (DIR) 15 min postinjection and over a 1-h time course. On the other hand, methionine5-enkephalin and des-Tyr1-methionine-enkephalin potentiated the duration of the DIR at 5 and 15 min. These enkephalins and their fragments had no effect upon vertical cling and bar catalepsy. In a second study, an SC injection of 4 mg/kg naloxone 15 min prior to the central injections blocked the potentiation of the DIR effects of the enkephalins.

Rotation and postural deviation elicited by microinjections of dopamine into medial and lateral regions of dorsal striatum

Unilateral microinjections of DA (25 micrograms/0.25 microliter) into several medial to lateral regions of the dorsal striatum of female rats produced both contralateral postural deviation and rotation. However, injections of DA into the medial striatum were more effective in producing rotation than postural deviation, whereas the opposite was the case for lateral striatal injections.

Effects of intrastriatal and intracortical scopolamine on behavior in rats

The anticholinergic drug scopolamine (20 micrograms, 30 micrograms, 40 micrograms) or its vehicle was injected unilaterally into the dorsal anterior striatum or overlying rostral neocortex in rats in order to examine the role of each region in contralateral postural deviation and stereotyped rearing. Scopolamine-induced contralateral deviation was observed in all subjects with striatal injections (p less than 0.01), and was of the same magnitude at all dose levels. Intracortical scopolamine did not induce contralateral deviation. However, stereotyped rearing was elicited from both the striatum and neocortex (p less than 0.01) at the two highest dose levels of scopolamine. Thus the mechanisms for contralateral deviation and stereotyped rearing differ both with respect to brain region and drug sensitivity.

Estradiol suppresses then enhances intracaudate dopamine-induced contralateral deviation

The effects of estradiol on the amount of contralateral postural deviation elicited by unilateral intracaudate injection of dopamine (DA) were tested 2 days and 6 days after hormone treatment. DA (25 micrograms/0.25 microliter) or a control vehicle solution (VH, 0.25 microliter) was injected unilaterally into the dorsal anterior caudate-putamen of intact male rats and postural deviation was measured. Then, rats were given estradiol benzoate (EB, 50 micrograms/100 g body wt per 0.05 ml) or the vehicle, peanut oil (OIL, 0.05 ml/100 g body wt) once. At 2 days and 6 days after EB or OIL treatment, the rats were again administered DA or VH intrastriatally and the amount of contralateral postural deviation was measured. At 2 days after EB treatment the response to intrastriatal DA was significantly decreased, but by 6 days it was significantly increased; OIL had no effect. Thus, the behavioral effects of estrogen are time-dependent and may affect the postsynaptic response to DA in the striatum.