Steroid hormones, energetic state, and immunocompetence vary across reproductive contexts in a parthenogenetic lizard.

Reproduction is energetically expensive and investing in this life history trait is likely accompanied by significant changes in physiological activity. Investment strategy necessary for achieving reproductive success in reptiles can vary with reproductive form and pattern, potentiating different consequences for competing fitness-related traits such as those key to survival. The goal of this study was to assess if and how energetic state (i.e., energy metabolites) and self-maintenance (i.e., immunocompetence) are hormonally modulated across reproductive contexts in an oviparous, parthenogenetic lizard, the Colorado Checkered Whiptail Aspidoscelis neotesselata. Here blood plasma samples were collected from lizards within the US Army Fort Carson Military Installation near Colorado Springs, CO, USA, during seasons of reproductive activity (i.e., June) and inactivity (i.e., August). Measures of reproductive (i.e., estradiol) and energy-mobilizing (i.e., corticosterone) hormones, energy metabolites (i.e., glucose, triglycerides, and free glycerol), and innate immunity (i.e., bactericidal ability) were compared by season and reproductive stage. Levels of energy metabolites and bactericidal ability were compared to levels of E2 and CORT. Bactericidal ability was also compared to levels of energy metabolites. Corticosterone and glucose levels were lower during the reproductive season while triglyceride levels and bactericidal ability were higher, but both estradiol and free glycerol levels did not differ between seasons. Throughout vitellogenesis, corticosterone and glucose levels as well as bactericidal ability did not differ, but estradiol levels were higher during early and mid-stage and both triglyceride and free glycerol levels were lower during gravidity. Corticosterone levels were negatively associated with circulating triglycerides and bactericidal ability, but were not related to glucose nor free glycerol levels. Estradiol levels were positively associated with free glycerol levels and bactericidal ability, but were not related to glucose nor triglyceride levels. Finally, bactericidal ability was negatively associated with glucose, but positively associated with triglycerides. Differences in energetic state and immunocompetence are thus reflected by shifts in hormone secretion across reproductive investment. These findings provide partial support for the hypothesis that energetic state is differentially regulated by steroid hormones to afford reproduction, potentially at the cost of future survival.

Transcranial Doppler Ultrasound Detection of Microemboli as a Predictor of Cerebral Events in Patients with Symptomatic and Asymptomatic Carotid Disease: A Systematic Review and Meta-Analysis.

OBJECTIVE: Identification of patients who will benefit from carotid endarterectomy is not entirely effective, primarily utilising degree of carotid stenosis. This study aimed at determining if microembolic signals (MES) detected by transcranial Doppler ultrasound (TCD) can provide clinically useful information regarding stroke risk in patients with carotid atherosclerosis. METHODS: A meta-analysis of prospective studies was performed. Three analyses were proposed investigating MES detection as a predictor of: stroke or TIA, stroke alone, and stroke or TIA but with an increased positivity threshold. Subgroup analysis was used to compare pre-operative (symptomatic or asymptomatic) patients and peri- or post-operative patients. RESULTS: Twenty-eight studies reported data regarding both MES status and neurological outcome. Of these, 22 papers reported data on stroke and TIA as an outcome, 19 on stroke alone, and eight on stroke and TIA with increased positivity threshold. At the median pre-test probability of 3.0%, the post-test probabilities of a stroke after a positive and negative TCD were 7.1% (95% CI 5-10.1) and 1.2% (95% CI 0.6-2.5), respectively. In addition, the sensitivities and specificities of each outcome showed that increasing the threshold for positivity to 10 MES per hour would make TCD a more clinically useful tool in peri- and post-operative patients. CONCLUSION: TCD provides clinically useful information about stroke risk for patients with carotid disease and is technically feasible in most patients. However, the generally weak level of evidence constituting this review means definitive recommendations cannot be made.

Human monocyte Arg-Serpin cDNA. Sequence, chromosomal assignment, and homology to plasminogen activator-inhibitor.

An LPS-stimulated, human monocyte cDNA library was screened for stimulation-specific clones. One clone (pcD-1214) contained a 1.9-kb pair insert that hybridized to a 2,000-nucleotide mRNA expressed by peripheral blood monocytes, the histiocytic lymphoma cell line U937, and umbilical cord endothelial cells. The 415-amino-acid precursor polypeptide predicted from the cDNA (46,596 molecular weight) has a putative 22-residue signal peptide and approximately 35% homology with members of the serine protease inhibitor (Serpin) superfamily. On the basis of amino acid homology and alignment of COOH-terminal residues within the Serpin-reactive center, the clone pcD-1214 was identified as coding for an Arg-Serpin. Southern blot analysis of human-mouse somatic cell hybrid DNA locates the Arg-Serpin gene on human chromosome 18. A perfect match between amino acid residues 347-376 in this Arg-Serpin and the published sequence of a 30-residue, tryptic peptide from the COOH-terminus of a monocyte plasminogen activator-inhibitor (PAI-2), strongly suggests that the Arg-Serpin encoded by pcD-1214 is PAI-2.

Multiple biological activities of human recombinant interleukin 1.

Complementary DNA coding for human monocyte interleukin 1 (IL-1), pI 7 form, was expressed in Escherichia coli. During purification, IL-1 activity on murine T cells was associated with the recombinant protein. Homogeneous human recombinant IL-1 (hrIL-1) was tested in several assays to demonstrate the immunological and inflammatory properties attributed to this molecule. hrIL-1 induced proliferative responses in a cloned murine T cell in the presence of suboptimal concentrations of mitogen, whereas no effect was observed with hrIL-1 alone. At concentrations of 0.05 ng/ml, hrIL-1 doubled the response to mitogen (5 X 10(6) half maximal units/mg). Human peripheral blood T cells depleted of adherent cells underwent a blastogenic response and released interleukin 2 in the presence of hrIL-1 and mitogen. hrIL-1 was a potent inflammatory agent by its ability to induce human dermal fibroblast prostaglandin E2 production in vitro and to produce monophasic (endogenous pyrogen) fever when injected into rabbits or endotoxin-resistant mice. These studies establish that the dominant pI 7 form of recombinant human IL-1 possesses immunological and inflammatory properties and acts on the central nervous system to produce fever.

Identification of transcripts encoding a parathyroid hormone-like peptide in messenger RNAs from a variety of human and animal tumors associated with humoral hypercalcemia of malignancy.

The syndrome of humoral hypercalcemia of malignancy (HHM) appears to be mediated in many instances by a parathyroid hormone-like peptide, which has recently been purified, sequenced, and cloned. Using a probe representing the coding region of the human PTH-like peptide, we examined by Northern analysis poly (A)+ RNA from a variety of human and animal tumors associated with HHM. Hybridizing transcripts were identified in mRNA from each of 12 human and each of four animal HHM-associated tumors, with a complex hybridization pattern observed in the human mRNAs and a relatively simple pattern observed in the animal mRNAs. Poly (A)+ RNA prepared from tumors of similar histological types unassociated with HHM failed to hybridize with the probe. Messenger RNA-dependent biological activity from the animal tumors was entirely eliminated in a hybridization-arrest experiment using a complementary oligonucleotide spanning the region of homology between human PTH and the PTH-like peptide. These findings indicate that the PTH-like peptide is associated with the syndrome of HHM in a wide spectrum of tumor types from a variety of mammalian species and that the PTH-like sequence in the proximal amino terminus of the peptide is highly conserved.

Monocyte expression of the human prointerleukin 1 beta gene (IL1B) is dependent on promoter sequences which bind the hematopoietic transcription factor Spi-1/PU.1.

Interleukin-1 beta (IL-1 beta) is produced primarily by stimulated monocytes, suggesting that the IL1B gene, which codes for this protein, depends upon at least one cell-type-specific factor. Our previous characterization of the IL1B promoter indicated that the region between -131 and +12 is sufficient to direct cell-type-specific expression of a reporter gene (F. Shirakawa, K. Saito, C.A. Bonagura, D.L. Galson, M.J. Fenton, A.C. Webb, and P. E. Auron, Mol. Cell. Biol. 13:1332-1344, 1993). We now show that a sequence located between positions -50 and -39 of the IL1B promoter binds the tissue-restricted Ets domain transcription factor Spi-1/PU.1 (Spi-1). Mutation of this site abrogates binding of this factor and reduces the ability of the IL1B promoter to function in macrophages. A second Spi-1 binding site located between positions -115 and -97 also is required for maximal IL1B promoter activity in the presence of the proximal Spi-1 binding site. In addition, an activation domain-deficient Spi-1 expression vector acts as a dominant-negative inhibitor of reporter gene expression in a monocyte cell line. Finally, the IL1B promoter, which is inactive in Spi-1-deficient HeLa cells, is activated in these cells by cotransfection with a Spi-1 expression vector. Thus, the cell-type-specific expression of the IL1B promoter appears to be dependent on the binding of Spi-1.

A novel STAT-like factor mediates lipopolysaccharide, interleukin 1 (IL-1), and IL-6 signaling and recognizes a gamma interferon activation site-like element in the IL1B gene.

Binding of many cytokines to their cognate receptors immediately activates Jak tyrosine kinases and their substrates, STAT (signal transducers and activators of transcription) DNA-binding proteins. The DNA binding targets of STATs are sequence elements related to the archetypal gamma interferon activation site, GAS. However, association of interleukin 1 (IL-1) with Jak-STAT signaling has remained unresolved. We now report an element termed LILRE (lipopolysaccharide [LPS] and IL-1-responsive element) in the human prointerleukin 1beta gene (IL1B) which can be immediately induced by either lipopolysaccharide (LPS) or IL-1 protein to bind a tyrosine-phosphorylated protein. This LPS- and IL-1-induced factor (LIL factor) is recognized by an antibody raised against the N terminus of Stat1, but not by those specific for either the C terminus of Stat1 or any other GAS-binding STAT. Phosphotyrosine (P-Tyr) specifically inhibits formation of the LIL factor-DNA complex, suggesting the importance of P-Tyr for the DNA-binding activity, as has been found for all STAT dimers. Analysis of DNA-binding specificity demonstrates that the LIL factor possesses a novel GAS-like binding activity that contrasts with those of other STATs in a requirement for a G residue at position 8 (TTCCTGAGA). Further investigation has revealed that IL-6, but neither IL-4 nor gamma interferon, activates the LIL factor. Thus, the existence of such a STAT-like factor (LIL-Stat) relates the LPS and IL-1 signaling pathway to other cytokine receptor signaling pathways via the activation of STATs. Moreover, the unique DNA-binding specificity and antigenicity of this factor suggest that LPS, IL-1, and IL-6 may use a common signaling pathway.

Identification of a competitive translation determinant in the 3' untranslated region of alfalfa mosaic virus coat protein mRNA.

We report that the competitive translational activity of alfalfa mosaic virus coat protein mRNA (CP RNA), a nonadenylated mRNA, is determined in part by the 3' untranslated region (UTR). Competitive translation was characterized both in vitro, with cotranslation assays, and in vivo, with microinjected Xenopus laevis oocytes. In wheat germ extracts, coat protein synthesis was constant when a fixed amount of full-length CP RNA was cotranslated with increasing concentrations of competitor globin mRNA. However, translation of CP RNA lacking the 3' UTR decreased significantly under competitive conditions. RNA stabilities were equivalent. In X. laevis oocytes, which are translationally saturated and are an inherently competitive translational environment, full-length CP RNA assembled into large polysomes and coat protein synthesis was readily detectable. Alternatively, CP RNA lacking the 3' UTR sedimented as small polysomes, and little coat protein was detected. Again, RNA stabilities were equivalent. Site-directed mutagenesis was used to localize RNA sequences or structures required for competitive translation. Since the CP RNA 3' UTR has an unusually large number of AUG nucleotide triplets, two AUG-containing sites were altered in full-length RNA prior to oocyte injections. Nucleotide substitutions at the sequence GAUG, 20 nucleotides downstream of the coat protein termination codon, specifically reduced full-length CP RNA translation, while similar substitutions at the next AUG triplet had little effect on translation. The competitive influence of the 3' UTR could be explained by RNA-protein interactions that affect translation initiation or by ribosome reinitiation at downstream AUG codons, which would increase the number of ribosomes committed to coat protein synthesis.

Transcription factors NF-IL6 and CREB recognize a common essential site in the human prointerleukin 1 beta gene.

A site located between -2782 and -2729 of the human prointerleukin-1 beta (IL1B) gene functions as a strong lipopolysaccharide (LPS)-responsive enhancer independent of the previously identified enhancer located between -2896 and -2846 (F. Shirakawa, K. Saito, C.A. Bonagura, D.L. Galson, M. J. Fenton, A. C. Webb, and P. E. Auron, Mol. Cell. Biol. 13:1332-1344, 1993). Although these two enhancers appear to function cooperatively in the native sequence context, they function independently as LPS-responsive elements upon removal of an interposed silencer sequence. The new enhancer is not induced by dibutyryl cyclic AMP (dbcAMP) alone but is superinduced by costimulation with LPS-dbcAMP. This pattern of induction depends upon the nature of the sequence, a composite NF-IL6-cAMP response element (CRE) binding site. This pseudosymmetrical sequence is shown to contrast with a classical symmetric CRE which responds to dbcAMP but not LPS. DNA binding studies using in vivo nuclear extract, recombinant proteins, and specific antibodies show that LPS induces the formation of two different complexes at the enhancer: (i) an NF-IL6-CREB heterodimer and (ii) a heterodimer consisting of NF-IL6 and a non-CREB, CRE-binding protein. Cotransfection studies using NF-IL6 and CREB expression vectors show that NF-IL6 transactivates the enhancer in the presence of LPS, whereas CREB acts either positively or negatively, depending upon its cAMP-regulated phosphorylation state. Our data demonstrate that the newly identified enhancer is a specialized LPS-responsive sequence which can be modulated by cAMP as a result of the involvement of NF-IL6-CRE-binding protein heterodimers.

The human prointerleukin 1 beta gene requires DNA sequences both proximal and distal to the transcription start site for tissue-specific induction.

In these studies, we have identified DNA sequences and specific protein interactions necessary for transcriptional regulation of the human prointerleukin 1 beta (proIL-1 beta) gene. A cell-type-independent lipopolysaccharide (LPS)-responsive enhancer element located between -3757 and -2729 bp upstream from the transcription start site (cap site) consisted of at least six discrete subregions which were essential to the maximal induction by LPS in transfected monocytes. The enhancer also appeared to mediate phorbol myristate acetate induction in monocytes and IL-1 responsiveness in fibroblasts. Deletion and base substitution mutations along with DNA binding studies demonstrated that the enhancer contained a minimum of three functional protein binding sequences, two of which appeared to be important for gene induction. One of the essential proteins which bound to the enhancer was similar or identical to members of the C/EBP family of transcription factors required for both IL-1- and LPS-specific induction of the IL-6 gene (i.e., the NF-IL6 proteins). When ligated to the proIL-1 beta cap site-proximal region (located between -131 to +12), both the proIL-1 beta and the simian virus 40 enhancer elements functioned more efficiently in monocytes than in HeLa cells, which are not normally competent for IL-1 beta expression. When ligated to the murine c-fos promoter, however, the proIL-1 beta enhancer was inducible in phorbol myristate acetate-stimulated HeLa cells, suggesting the existence of a proIL-1 beta promoter-proximal requirement for tissue specificity.

Cytomegalovirus IE2 protein stimulates interleukin 1beta gene transcription via tethering to Spi-1/PU.1.

Potent induction of the gene coding for human prointerleukin 1beta (il1b) normally requires a far-upstream inducible enhancer in addition to a minimal promoter located between positions -131 and +12. The transcription factor Spi-1 (also called PU.1) is necessary for expression and binds to the minimal promoter, thus providing an essential transcription activation domain (TAD). In contrast, infection by human cytomegalovirus (HCMV) can strongly activate il1b via the expression of immediate early (IE) viral proteins and eliminates the requirement for the upstream enhancer. Spi-1 has been circumstantially implicated as a host factor in this process. We report here the molecular basis for the direct involvement of Spi-1 in HCMV activation of il1b. Transfection of Spi-1-deficient HeLa cells demonstrated both the requirement of Spi-1 for IE activity and the need for a shorter promoter (-59 to +12) than that required in the absence of IE proteins. Furthermore, in contrast to normal, enhancer-dependent il1b expression, which absolutely requires both the Spi-1 winged helix-turn-helix (wHTH) DNA-binding domain and the majority of the Spi-1 TAD, il1b expression in the presence of IE proteins does not require the Spi-1 TAD, which plays a synergistic role. In addition, we demonstrate that a single IE protein, IE2, is critical for the induction of il1b. Protein-protein interaction experiments revealed that the wing motif within the Spi-1 wHTH domain directly recruits IE2. In turn, IE2 physically associates with the Spi-1 wing and requires the integrity of at least one region of IE2. Functional analysis demonstrates that both this region and a carboxy-terminal acidic TAD are required for IE2 function. Therefore, we propose a protein-tethered transactivation mechanism in which the il1b promoter-bound Spi-1 wHTH tethers IE2, which provides a TAD, resulting in the transactivation of il1b.

The functional importance of a cap site-proximal region of the human prointerleukin 1 beta gene is defined by viral protein trans-activation.

Prointerleukin 1 beta (IL-1 beta) is a cytokine that mediates a broad range of biological activities. Genomic sequences that regulate IL-1 beta transcription include both inducible regulatory elements located more than 2,700 bp upstream of the transcriptional start site (cap site) and proximal elements located near the TATA box of this gene. In this study, we focused on the identification and characterization of trans-acting nuclear regulatory proteins that bind to the cap site-proximal region of the human IL-1 beta gene. We identified a protein, termed NFIL-1 beta A (NF beta A), that binds to a highly conserved 12-bp DNA sequence (-49 to -38) located upstream of the TATA box motif in both the human and murine IL-1 beta genes. The IL-1 alpha gene, which lacks a TATA motif, does not possess an NF beta A-binding sequence within the promoter region, suggesting that NF beta A may selectively regulate IL-1 beta expression. Using electrophoretic mobility shift assays, we identified several distinct DNA-protein complexes that are expressed in a cell-type-specific manner. In monocytic cell lines, the relative abundance of these complexes varies rapidly following stimulation of the cells with phorbol esters or lipopolysaccharide. UV cross-linking analysis identified two distinct DNA-binding polypeptides that comprise distinct complexes. The functional role of NF beta A was assessed in transient transfection assays. These data indicate that NF beta A is required for both basal and inducible promoter activity in monocytic cells. Furthermore, the human cytomegalovirus immediate-early 1 gene product requires the presence of NF beta A in order to trans-activate the proximal IL-1 beta promoter in a monocytic cell line. We propose that NF beta A is a factor that mediates either direct or indirect activation by the immediate-early 1 gene product. The proximity of this essential factor to the TATA motif suggests a possible role in transcriptional initiation.

Microinjected Xenopus oocytes secrete mature, biologically active parathyroid hormone.

Xenopus oocytes have been shown to faithfully translate, process, and secrete a number of secretory proteins after the injection of heterologous mRNAs. The oocyte has the capacity to perform a variety of posttranslational protein modifications but has been reported to be incapable of carrying out certain two-step cleavages which proceed via propeptide intermediates. We examined the ability of the oocyte to process preproPTH after the injection of parathyroid mRNA. Microinjected oocytes secreted material which could be detected in a sensitive cytochemical bioassay for PTH. This activity paralleled that of the PTH standard in the assay and was entirely eliminated by a competitive inhibitor of PTH binding, by preincubation with an anti-PTH antiserum, and by coinjecting oocytes with an oligonucleotide mixture complementary to PTH sequences. Immunoprecipitable proPTH and PTH were present in oocyte homogenates, but oocyte-conditioned medium contained only mature PTH(1-84). We conclude that the Xenopus oocyte is capable of accurately processing preproPTH to the mature secretory form of the peptide.

Messenger ribonucleic acid from tumors associated with humoral hypercalcemia of malignancy directs the synthesis of a secretory parathyroid hormone-like peptide.

Previous studies have provided evidence that tumors associated with humoral hypercalcemia of malignancy produce a factor that shares certain biological properties with, but is not, native PTH. In the present study, media from Xenopus oocytes microinjected with polyadenylated RNA prepared from three human or animal tumors associated with humoral hypercalcemia of malignancy are shown to have activity in the cytochemical bioassay for PTH. This activity parallels that of the PTH standard in the assay and is completely inhibited by the PTH analog [Nle8,Nle18,Tyr34]bovine PTH-(3-34)NH2. Media from oocytes injected with mRNA from control tumors contain no such activity. The mRNA encoding this activity in one of the animal tumors has been enriched approximately 10-fold by preparative polyacrylamide gel electrophoresis. These results demonstrate that tumors associated with humoral hypercalcemia of malignancy have the capacity for directing the synthesis of a secretory protein that fulfills certain criteria for being the humoral mediator in question. These techniques may provide the basis for molecular cloning of this factor.

The effects of arginine-8 vasopressin on the cerebral cortex of rats anaesthetised with urethane.

The effects of arginine-8 vasopressin (AVP) on the spontaneous electrical activity of the cerebral cortex were investigated in rats anaesthetised with urethane. Direct application of a relatively large concentration of AVP (0.5-2.0 mU AVP/microliter; 1.25-5.00 ng AVP/microliter) to the pial surface of a small area of the parietal cortex produced a complete cessation of spontaneous neural activity, which was often preceded by a short-lasting increase in frequency of discharge. There was also a decline in the number of large waves in the local electrocorticogram. These changes occurred after 1-4 min. A slow recovery began 10-30 min later, but was sometimes still incomplete after more than an hour. Only the first application of AVP produced the local effects described above. A second application, 2 hr later, was without effect. Direct application to a small area of one hemisphere did not alter the electrical activity of the contralateral cortex. Smaller concentrations of AVP (0.005-0.200 mU AVP/microliter; 12.5 pg-0.5 ng AVP/microliter) were variable in their actions. Occasionally, no effect at all was seen, while sometimes the cells stopped firing completely. However, the most usual consequence was a reduction in discharge frequency, the magnitude of which appeared to be related to the concentration of AVP applied. A second application of a small concentration of AVP usually failed to reduce the rate of spontaneous discharge.

Use of the polymerase chain reaction for screening and evaluation of recombinant baculovirus clones.

We report the application of the PCR for screening and high-resolution characterization of recombinant baculovirus clones. Starting with less than 10 nanograms of viral DNA, it is possible to 1) demonstrate that the DNA sequence to be expressed has not been deleted or rearranged during the co-transfection or homologous recombination events, 2) test for the presence of wild-type virus in the isolate and 3) generate amplified DNA that can be used for nucleotide sequence analysis or high-resolution restriction analysis. The method is based upon PCR of genomic viral DNA prepared from primary amplified stocks of extracellular virus using a small-scale procedure. The approach has special relevance for definitive characterization of recombinant virus used to express point mutant proteins and for characterization of recombinant virus generated through use of mixed oligonucleotides or random mutagenesis.

The effects of age and visual experience on potentiation of responses in slices from the chick forebrain.

A single coronal slice, containing the intermediate part of the medial hyperstriatum ventrale (IMHV) was cut from the left forebrain of a series of domestic chicks and maintained in vitro. Records were made of field responses evoked in the IMHV by local electrical stimuli. Two 1-min periods of 5 Hz stimulation, separated by 10 min, were used in attempts to induce persistent potentiation of the responses (PPR) to test stimulation at 0.1 Hz. In dark-hatched chicks the probability of producing PPR is much higher in slices from chicks aged 2-5 days post-hatch than in those from either younger or older birds. As an independent measure of plasticity in dark-hatched chicks, the probability of eliciting unit responses to repeated stimulation of remote sites in the slice at 3.3 Hz was analysed. This probability was greater in slices from chicks aged 2-5 days than in those from either younger or older birds. In light-hatched chicks the probability of inducing PPR is significantly higher during the first day post-hatch, than in dark-hatched chicks of this age. The probability of producing PPR in slices from light-hatched chicks aged 2-3 days is less than that in slices from either younger or older birds. It is clear that both the age and past experience of the domestic chick affect the neurophysiological properties of slices of brain, tested in vitro.

Potentiation of synaptic responses in slices from the chick forebrain.

Coronal slices, containing part of the medial hyperstriatum ventrale (MHV), were cut from the left forebrains of domestic chicks and maintained in vitro. Records were made of the field responses evoked in the MHV by local electrical stimuli provided at 0.1 Hz. Two 1 min periods of stimulation at 5 Hz, separated by 10 min, were used in attempts to induce a persistent increase in the size of the postsynaptic response to test stimulation at 0.1 Hz. This procedure produced a potentiation which usually lasted longer than 2 h. The probability of inducing this persistent potentiation of the response (PPR) is not distributed evenly over the whole anteroposterior length of the MHV but is higher in slices that also contain the septo-mesencephalic tract ventrally. These are the slices that contain the intermediate part of the medial hyperstriatum ventrale (IMHV); an area that is essential for early behavioural learning. At this level PPR is not confined to the IMHV. It can also be produced in the lateral neostriatum in response to similar local stimulation at 5 Hz. No PPR was observed in either the caudal ectostriatum, or the paleostriatum.

Morphological correlates of persistent potentiation in the chick brain slice.

In an in-vitro slice preparation of the chick brain it is possible to induce persistent potentiation of responses to single electrical stimuli by giving two bursts of 300 stimuli at 5 Hz separated by ten minutes of control stimulation at 0.1 Hz. We investigated the morphological correlates of this potentiation in a group of 2 day old chicks using quantitative electron microscopical techniques. It was found that in slices which showed a clearly potentiated response there was a significant increase in the size of the postsynaptic densities of synapses on spines in the left hyperstriatum ventrale (IMHV). No such increases were seen in a control group nor in slices which failed to potentiate. These results provide further evidence for the lability of synapses in the IMHV.

Noradrenaline and potentiation in the chick brain slice.

The role of the noradrenergic system as a modulator of neurotransmission in the chick forebrain was investigated in brain slices containing the medial hyperstriatum ventrale, an area known to be involved in learning and memory. The alpha 2-agonist clonidine (20 microM) decreased the post-synaptic response to local stimulation at 0.1 Hz, while activation of beta 2 receptors increased this response. Induction of persistent potentiation following stimulation at 5 Hz was blocked by drugs (20 microM ICI 118,551; 20 microM propranolol) which showed preferential antagonistic activity at the beta 2 receptor but not by the beta 1-preferential antagonist timolol. This effect may be due to an interaction with the NMDA receptor system.