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Three full-length cDNA clones encoding the guinea pig A1 adenosine receptor have been isolated by polymerase chain reaction (PCR) and low-stringency hybridization screening of a guinea pig brain cDNA library. These three cDNAs, though differing in their 5' untranslated regions, contain the same open reading frame encoding a 326 amino acid residue protein with seven hydrophobic [alpha]-helices long enough to form the transmembrane domains, suggesting that it belongs to the G protein-coupled receptor superfamily. This protein is highly homologous to the A1 adenosine receptors previously cloned from other species. Pharmacological characterization of this receptor transiently expressed in mammalian cells demonstrates that, despite its high homology to A1 adenosine receptors of other species, the guinea pig A1 adenosine receptor displays a unique pharmacological profile: high affinity for the A1-selective antagonist CPX, yet very low affinity for some A1-selective agonists such as CCPA, CHA and R-PIA. Northern blotting for different guinea pig tissues and in situ hybridization for guinea pig brain sections reveal an abundant and broad distribution of mRNA of this A1 subtype receptor in the brain.

The present study examined the comparative distribution of 5-HT1A receptor mRNA and 5-HT1A receptors in rat brain using a combination of in situ hybridisation histochemistry and in vitro receptor autoradiography. 5-HT1A mRNA was visualised using a 910 bp cRNA probe synthesised from a BalI-PvuII fragment of the rat 5-HT1A reetor gene, while 5-HT1A receptors were labelled with the 5-HT1A-selective ligand 8-OH-DPAT. In general terms, there was a complementary distribution of cells expressing 5-HT1A receptor mRNA and 5-HT1A receptor sites. High levels of both 5-HT1A mRNA and 5-HT1A receptors were evident in the hippocampal formation (CA1, CA3, dentate gyrus), entorhinal cortex, and raphe nuclei and lower levels in neocortex and thalamus. Although 5-HT1A mRNA was not expressed in any regions which did not also exhibit 5-HT1A receptors, within both the diagonal band and the medial septal nucleus mRNA levels were proportionately higher than 5-HT1A receptor levels, possibly reflecting receptor transport or a heterogeneity in 5-HT1A receptor turnover mechanisms. 5-HT1A receptor mRNA and 5-HT1A binding sites were undetectable in caudate/putamen and cerebellar regions. The present data indicate the synthesis of 5-HT1A receptors both in raphe serotonergic cells and anatomically specific serotonergic projection areas, further supporting both a presynaptic autoregulatory and postsynaptic modulatory role for this receptor in serotonergic transmission.

Neurotransmitter receptor sites have been examined in both human postmortem tissue and a lesioned polysynaptic pathway in rat brain using quantitative ligand binding autoradiography. Human Postmortem Studies The putative involvement of glutamatergic mechanisms in the pathophysiology of Alzheimer's disease (A. D. ) was investigated by determining the distribution and density of Na+ -dependent glutamate uptake sites and glutamate receptor subtypes; kainate, quisqualate and N-methyl-D-aspartate (NMDA), in adjacent sections of frontal, temporal and cerebellar cortex from six patients with A. D. and six age-matched controls. The number of senile plaques in each region was determined in adjacent sections to those used for receptor autoradiography. Binding of [3H]-D-aspartate to Na+-dependent uptake sites was reduced by approximately 40% throughout A. D. frontal cortex relative to controls, indicating a general loss of glutamatergic presynaptic terminals. [3H]-Kainate binding was significantly increased by approximately 70% in deep layers of A. D. frontal cortex compared to controls, but unaltered in superficial laminae. Scatchard analysis of this response indicated an increase in kainate receptor numbers with no change in receptor affinity. [3H]-Kainate binding and senile plaque numbers were positively correlated (r=0.914) in deep layers of A. D. frontal cortex, but unrelated in superficial laminae (r=0.089). There was a small reduction (25%) in NMDA-sensitive [3H]-glutamate binding only in superficial layers of A. D. frontal cortex relative to controls, although [3H]-glutamate binding in A. D. subjects was unrelated to senile plaque numbers in these cortical layers (r=0.104). Quisqualate receptors, as assessed by [3H]-a-amino-3-hydroxy-5-methylisoxazole-4-propionic acid ([3H]-AMPA) binding were unaltered in A. D. frontal cortex compared to controls. There was no significant alteration in any glutamate binding sites in A. D. temporal cortex relative to control brains, des