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The ability of hippocampal slices to accumulate quisqualate by an active uptake process was investigated. All amino acid concentrations were measured by HPLC. Incubation of hippocampal slices for 4 min with 16 microM quisqualate at 25 degrees C led to measurable amounts of quisqualate within supernatant layers derived from slice homogenates. However, estimated tissue:original medium ratios of quisqualate were only 0.6. Addition of 100 microM ouabain did not alter the slice content of quisqualate but did promote marked elevations in the contents of aspartate and glutamate in the bathing medium. Quisqualate contents of the slices were approximately halved by ice-cold incubations or by inclusion of an excitatory amino acid receptor antagonist during the incubation. It is suggested that hippocampal slices do not actively accumulate this concentration of quisqualate and that at least part of the observed quisqualate in supernatant layers from slice homogenates is due to binding to extracellular amino acid receptors.

The present study assessed the role of postsynaptic dopamine (DA) receptors in mediating the actions of focal injections of the classical antipsychotic drug, haloperidol, on DA metabolism in the rat amygdala (AMYG) and caudate-putamen (CP) using a high-performance liquid chromatographic assay. One hour after unilateral injection of haloperidol into either site, significant elevations of the DA metabolite, homovanillic acid, were observed in both ipsilateral (+33%) and contralateral (+81%) hemispheres of the CP and in the ipsilateral (+107%) and contralateral AMYG (+121%). Such increased DA metabolism persisted in these regions if focal injections of muscimol (intended to eliminate transmission in postsynaptic output neurones) had been made into either brain area immediately prior to the focal haloperidol injection. It is argued that neurones lying postsynaptic to DA terminals in both the AMYG and CP are unnecessary for the ability of haloperidol to increase DA metabolism in these regions.

The GABA system was studied in different regions of the rat's brain following inhibition of brain GABA catabolism with intracisternal ethanolamine-O-sulphate or intraperitoneal aminooxyacetic acid. Both treatments lowered GABA aminotransferase and glutamate decarboxylase activities to similar extents in equivalent nuclei on either side of the brain. However, GABA contents were elevates to a consistently higher level in the right-hand substantia nigra, superior colliculus and nucleus accumbens, and in the left-hand ventral tegmentum, ventromedial thalamus and caudate nucleus, with no bilateral asymmetry evident in globus pallidus. These findings are discussed with reference to possible inherent inequalities in the functional states similar GABA systems on opposite sides of the brain.

Lesioning the rat's substantia nigra (SN) with kainic acid (0.8 microgram) or by electrocoagulation (1 mA for 6 sec) significantly lowered GABA and glutamate decarboxylase levels at the treatment site, but not in the nucleus tegmenti pedunculopontinus (PPN), suggesting nigro-PPN fibres do not synthesize or store GABA. Stereotaxic injection of one PPN with muscimol (40 ng), picrotoxin (40 ng) or tetanus toxin (30 mouse LD50 doses) had little or no effect on the animals' behaviour; kainate caused ipsilateral body flexion, sporadic ipsiversive circling and contraversive barrel-rolling. These behavioural abnormalities disappeared after 7 days when histology confirmed virtually complete loss of PPN perikarya, intense gliosis and some demyelination of passing axons. Impairing PPN transmission with kainate (chronically) or muscimol (acutely) caused weak apomorphine-induced contraversive rotation, but did not modify the robust nigral muscimol-evoked contraversive asymmetry. While we do not exclude a role of PPN in motor control, these data suggest that nigro-PPN neurones are neither GABAergic nor mediators of central dopaminergic function.

Dopamine (DA) utilisation (expressed as homovanillic acid:DA) was compared in the medial prefrontal cortex (FCx), the agranular insular cortex (AgCx), the caudate-putamen (medial, CPM and lateral, CPL divisions) and the nucleus accumbens (NAc). DA utilisation in these regions decreased in the order AgCx greater than FCx greater than CPM, CPL, NAc, whilst the concentration of DA decreased in the reverse order. Thus, although fewer DA neurones appear to innervate AgCx compared with FCx, the rate of DA utilisation/release is much greater in AgCx. It is suggested that this apparently more marked activity in DA neurones innervating AgCx may reflect a relative lack of autoreceptor control.

Certain sulphur-containing amino acids are putative excitatory transmitters in the mammalian central nervous system. The quantification and a partial regional analysis of these compounds in the rat brain is presented. Our findings show that (S)-(+)-homocysteate, determined for the first time, is the most concentrated of those sulphonic and sulphinic amino acids assayed here.