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Genetically modified mice lacking the glutamate receptor A (GluR-A) subunit of the AMPA receptor (GluR-[A.sup.-/-] mice) display normal spatial reference memory but impaired spatial working memory (SWM). This study tested whether the SWM impairment in these mice could be explained by a greater sensitivity to within-session proactive interference. The SWM performance of GluR-[A.sup.-/-] and wild-type mice was assessed during nonmatching-to-place testing under conditions in which potential proactive interference from previous trials was reduced or eliminated. SWM was impaired in GluR-[A.sup.-/-] mice, both during testing with pseudotrial-unique arm presentations on the radial maze and when conducting each trial on a different 3-arm maze, each in a novel testing room. Experimentally naive GluR-[A.sup.-/-] mice also exhibited chance performance during a single trial of spontaneous alternation. This 1-trial spatial memory deficit was present irrespective of the delay between the sample information and the response choice (0 or 45 min) and the length of the sample phase (0.5 or 5 min). These results imply that the SWM deficit in GluR-[A.sup.-/-] mice is not due to increased susceptibility to proactive interference. Keywords: AMPA receptors, LTP, hippocampus, spatial memory, mice

Four related experiments studied operant performance of mice on differential reinforcement of low rates of responding (DRL) paradigms. Experiment 1 showed that excitotoxic hippocampal lesions impaired performance of a 10-s DRL schedule (DRL-10). Experiments 2 and 3 showed that GluR-A AMPA receptor subunit knockout mice, which are deficient in CA3-CA1 long-term potentiation (LTP), were markedly impaired at 15 s (DRL-15), but less impaired at DRL-10. Experiment 4 compared DRL-15 performance in mice from the 2 strains from which the GluR-A colony was derived and showed that they did not differ. The results show that GluR-A-containing AMPA receptors are required for normal performance on hippocampus-dependent, nonspatial working memory tasks, consistent with a role for GluR-A in the temporal encoding (what happened when) of nonspatial information. Keywords: AMPA receptors, LTP, hippocampus, DRL, nonspatial

Previous studies have demonstrated a spatial working memory deficit in glutamate receptor (GluR)-A (GluR1) AMPA receptor subunit knockout mice. The present study evaluated male and female wild-type and GluR-[A.sup.-/-] mice on a test battery that assessed sensorimotor, affective, and cognitive behaviors. Results revealed a behavioral phenotype more extensive than previously described. GluR-[A.sup.-/-] mice were hyperactive, displayed a subtle lack of motor coordination, and were generally more anxious than wild-type controls. In addition, they showed a deficit in spontaneous alternation, consistent with previous reports of a role for GluR-A-dependent plasticity in hippocampus-dependent, spatial working memory. Although changes in motor coordination or anxiety cannot explain the dissociations already reported within the spatial memory domain, it is clear that they could significantly affect interpretation of results obtained in other kinds of behavioral tasks.

Acquisition and reversal of a spatial discrimination were assessed in an appetitive, elevated plus-maze task in 4 groups of mice: knockout mice lacking the AMPA receptor subunit GluR-A (GluR1), wild-type controls, mice with cytotoxic hippocampal lesions, and controls that had undergone sham surgery. In agreement with previous studies using tasks such as the water maze, GluR-[A.sup.-/-] mice were unimpaired during acquisition of the spatial discrimination task, whereas performance in the hippocampal group remained at chance levels. In contrast to their performance during acquisition, the GluR-[A.sup.-/-] mice displayed a mild deficit during reversal of the spatial discrimination and were profoundly impaired during discrete trial, rewarded-alternation testing on the elevated T maze. The latter result suggests a short-term, flexible spatial working memory impairment in GluR-[A.sup.-/-] mice, which might also underlie their mild deficit during spatial reversal.

Cloned human dopamine D2 receptor cDNA was isolated from a pituitary cDNA library and found to encode an additional 29 amino acid residues in the predicted intracellular domain between transmembrane regions 5 and 6 relative to a previously described rat brain D2 receptor. Results from polymerase chain reactions as well as in situ hybridization revealed that mRNA encoding both receptor forms is present in pituitary and brain of both rat and man. The larger form was predominant in these tissues and, as shown in the rat, expressed by dopaminergic and dopaminoceptive neurons. Analysis of the human gene showed that the additional peptide sequence is encoded by a separate exon. Hence, the two receptor forms are generated by differential splicing possibly to permit coupling to different G proteins. Both receptors expressed in cultured mammalian cells bind [3H]spiperone with high affinity and inhibit adenylyl cyclase, as expected of the D2 receptor subtype.

The relationship between platelet‐derived growth factor (PDGF) and the proto‐oncogene c‐sis has been determined by amino acid sequence analysis of PDGF and nucleotide sequence analysis of c‐sis genomic clones. The nucleotide sequences of five regions of the human c‐sis gene which are homologous to sequences of the transforming region (v‐sis) of simian sarcoma virus (SSV) were determined. By alignment of the c‐sis and v‐sis nucleotide sequences the predicted amino acid sequence of a polypeptide homologous to the putative transforming protein p28sis of SSV was deduced. Both predicted sequences use the same termination codon and additional coding sequences may lie 5′ to the homologous regions. Amino acid sequence analysis of the PDGF B chain shows identity to the amino acid sequence predicted from the c‐sis sequences over 109 amino acid residues. Polymorphism may exist at two amino acid residues. These results suggest that c‐sis encodes a polypeptide precursor of the B chain. A partial amino acid sequence of the PDGF A chain is also described. This chain is 60% homologous to the B chain and cannot be encoded by that part of c‐sis which has been sequenced but could be encoded by sequences which lie 5′ to the five regions of v‐sis homology in c‐sis, or at a separate locus.

This report describes the cloning of a full length cDNA encoding PKBS, a protein of approximately 17 kDa associated with peripheral-type benzodiazepine binding sites. Cyanogen bromide digestion of purified PKBS yielded several peptide fragments which were subjected to gas-phase sequencing. Based on these partial amino acid sequences, oligonucleotide probes were used to screen a rat adrenal cDNA library. Several hybridizing clones were isolated which were found to contain overlapping sequences. The longest cDNA spanned 781 base pairs and specified an open reading frame of 169 amino acids which matched all of the peptide sequences. Northern analysis with this PKBS cDNA probe in different rat tissues revealed one RNA species of approximately 850 nucleotides exhibiting relative abundances qualitatively comparable with the densities of peripheral-type benzodiazepine binding sites in each tissue. The PKBS cDNA was cloned into an eukaryotic expression vector placing it under transcriptional control of the β-globin promoter and SV40 enhancer. Transfection of the transformed human kidney 293 cell line with this recombinant vector resulted in stoichiometric increases of about 900 fmol/mg of protein in binding capacities for Ro5-4864 (4′-chlorodiazepam) and PK 11195, two peripheral-type benzodiazepine ligands. These increases were accounted for by the expression of binding sites with approximate dissociation constants of 5 nMfor PK 11195 and 8 nMfor Ro5-4864, thereby distinguishing the expressed binding sites as being characteristic of the receptor from rat origin rather than of the host human-derived cell line. The rank order of potency of different ligands to compete against [3H]Ro5-4864 binding in the transfected cells was PK 11195 > Ro5-4864 > diazepam > protoporphyrin IX > clonazepam, consistent with the specificity characteristic of rat peripheral-type benzodiazepine binding sites. These studies suggest that PKBS comprises binding domains for benzodiazepines and isoquinoline carboxamides and hence is apparently responsible for the manifestation of peripheral-type benzodiazepine recognition sites.