Amphetamine-induced circling behavior in rats: effects of unilateral microinjections of GABA and GABA-related drugs into substantia nigra

Differences in amphetamine and morphine sensitivity in lateralized and non-lateralized rats: locomotor activity and drug self-administration

Morphine and d-amphetamine were tested for their effects on locomotor activity and for their propensities to be intravenously self-administered in rats that had been screened for their tendencies to rotate (turn in circles) spontaneously at night; noctural rotation was used as a behavioral index of asymmetry in the dopaminergic nigrostriatal system. Lateralized (rotating) rats were more sensitive to the locomotor stimulant effects of d-amphetamine than non-lateralized (non-rotating) rats. The stimulant effects of low doses of morphine were also greater in lateralized rats, whereas the depressant effects of high doses of morphine were greater in non-lateralized rats. Lateralized rats self-administered more d-amphetamine than non-lateralized rats whereas non-lateralized rats self-administered more morphine than lateralized rats. The data indicate that the degree of lateralization in some brain pathways is a source of interindividual variation in drug sensitivity--this may in part be responsible for the individual tendencies of humans to selectively abuse particular types of drugs.

Interactions between dopamine and gamma-aminobutyrate in the substantia nigra: implications for the striatonigral output hypothesis

Experiments employing a rodent circling model were conducted to test the predictive capacity of the theory which states that striatonigral gamma-aminobutyrate neurones transmit striatal information influencing the animal's locomotion and orientation. In agreement with this proposal, blocking nerve conduction in one substantia nigra with procaine, or nigral gamma-aminobutyrate receptors with bicuculline administered stereotaxically, frequently forced rats to move ipsiversively to systemic apomorphine, as though the treatment had impaired striatonigral transmission on that side of the brain. Attempts to reverse the direction of apomorphine circling by stimulating gamma-aminobutyrate receptors with muscimol, by facilitating the amino acid's action with flurazepam, or by increasing its synaptic concentration either with a breakdown inhibitor (ethanolamine O-sulphate or 4-amino-hex-5-enoic acid) or an uptake blocker (cis-1,3-aminocyclohexane carboxylic acid) in one nigra, proved unsuccessful. In fact, ethanolamine O-sulphate, flurazepam and muscimol all gave the appearance of hindering rather than enhancing the passage of striatal-derived motor information through the nigra. Broadly speaking, these drugs gave predictable behavioral responses from the ventromedial thalamus, suggesting they were acting in accordance with known mechanisms. The anomalous behaviour with ethanolamine O-sulphate may be attributed to its elevating gamma-aminobutyrate levels in other brain areas, since similar ipsiversive rotations occurred if gamma-aminobutyrate catabolism was prevented at a wide variety of extranigral sites. A simple explanation for the paradoxical ipsiversive behaviours produced by intranigral flurazepam or muscimol in combination with systemic or intracerebral injection of dopamine agonists, is that they act via presynaptic receptors to inhibit the release of endogenous gamma-aminobutyrate and thereby impede striatonigral outflow ipsilaterally.

Involvement of dopamine in circling responses to muscimol depends on intranigral site of injection

The intensity, direction and dopamine dependence of circling behaviour were determined following stereotaxic injections of 40 ng muscimol (in 0.2 microliter over 3 min) into different regions of the rat's substantia nigra (SN). Weak, haloperidol-sensitive ipsilateral postural or locomotor asymmetries were invariably obtained from the rostral SN zona compacta (SNC), whilst robust contraversive rotational behaviour was always initiated from the SN zona reticulata (SNR) and caudal SNC. This was most rapid from the central SNR and was markedly attenuated by i.p. pretreatment with haloperidol (0.1 mg/kg) or pimozide (0.25 mg/kg), or by week-old 6-OHDA lesions of the nigrostriatal dopamine (DA) tract. Turning was significantly weaker from the lateral and ventral areas of the SNR, where it was not susceptible to DAergic blockade. Lower circling rates were also obtained if the SNR injections were made rapidly (in 30 sec), in a large volume (0.5 microliter) or at a supramaximal dose level (400 ng), possibly due to increased spread of the drug to remote neurones having an opposite effect on directional behaviour, or to exaggerated stereotypy. The variable action of muscimol at multiple sites in the SN is suggested to account for the earlier conflicting data in the literature.

Conditioned suppression of behavior: its reversal by intra raphe microinjection of chlordiazepoxide and GABA

Chlordiazepoxide and GABA (5 X 10(-5) M; 0.2 microliters) applied into the nucleus raphe dorsalis significantly reduced behavioral suppression induced in rats by a 10-min presentation of a signal previously associated with the punishment of lever pressing for food. As compared to saline control rats, this reduction was of the same order of magnitude as that obtained after intraperitoneal administration of chlordiazepoxide (8 mg X kg-1). Chlordiazepoxide or GABA (5 X 10(-5) M) failed to alter response maintained under non-aversive conditions. These data suggest the involvement of GABAergic neurons of the raphe dorsalis in the 'disinhibitory' effects of benzodiazepines.

Oxolinic acid and diazepam: their reciprocal antagonism in rodents

The stimulant effects of oxolinic acid were investigated in rats and mice. This drug, given orally, consistantly induced, in doses ranging from 16 to 256 mg.kg-1, locomotor stimulation and stereotyped behavior. These effects were antagonized by pimozide (1 mg.kg-1), alpha-methyltyrosine (64 mg.kg-1) or reserpine (4 mg.kg-1, 24 h before testing) pretreatment, suggesting a facilitatory role of oxolinic acid on catecholaminergic processes. Diazepam (4-16 mg.kg-1) reduced the stimulant effects induced by oxolinic acid but not those induced by amphetamine; oxolinic acid (8 mg.kg-1) markedly reduced the antipunishment effect elicited in rats by diazepam (2 mg.kg-1). Since benzodiazepines have been reported to enhance GABA functioning, these data suggest that oxolinic acid may impair GABA transmission. However, neither muscimol (0.5-1 mg.kg-1) or gamma-acetylenic-GABA (16-64 mg.kg-1) selectively reduced the stimulant effects elicited by oxolinic acid. Therefore, the possible facilitation exerted by this drug on catecholaminergic systems may not derive from the release of an inhibitory GABAergic control.