Behavioral and neurochemical characterization of mice deficient in the phosphodiesterase-1B (PDE1B) enzyme.

PDE1B is a calcium-dependent cyclic nucleotide phosphodiesterase that is highly expressed in the striatum. In order to investigate the physiological role of PDE1B in the central nervous system, PDE1B knockout mice (C57BL/6N background) were assessed in behavioral tests and their brains were assayed for monoamine content. In a variety of well-characterized behavioral tasks, including the elevated plus maze (anxiety-like behavior), forced swim test (depression-like behavior), hot plate (nociception) and two cognition models (passive avoidance and acquisition of conditioned avoidance responding), PDE1B knockout mice performed similarly to wild-type mice. PDE1B knockout mice showed increased baseline exploratory activity when compared to wild-type mice. When challenged with amphetamine (AMPH) and methamphetamine (METH), male and female PDE1B knockout mice showed an exaggerated locomotor response. Male PDE1B knockout mice also showed increased locomotor responses to higher doses of phencyclidine (PCP) and MK-801; however, this effect was not consistently observed in female knockout mice. In the striatum, increased dopamine turnover (DOPAC/DA and HVA/DA ratios) was found in both male and female PDE1B knockout mice. Striatal serotonin (5-HT) levels were also decreased in PDE1B knockout mice, although levels of the metabolite, 5HIAA, were unchanged. The present studies demonstrate increased striatal dopamine turnover in PDE1B knockout mice associated with increased baseline motor activity and an exaggerated locomotor response to dopaminergic stimulants such as methamphetamine and amphetamine. These data further support a role for PDE1B in striatal function.

Phosphodiesterase 1B differentially modulates the effects of methamphetamine on locomotor activity and spatial learning through DARPP32-dependent pathways: evidence from PDE1B-DARPP32 double-knockout mice.

Mice lacking phosphodiesterase 1B (PDE1B) exhibit an exaggerated locomotor response to D-methamphetamine and increased in vitro phosphorylation of DARPP32 (dopamine- and cAMP-regulated phosphoprotein, M r 32 kDa) at Thr34 in striatal brain slices treated with the D1 receptor agonist, SKF81297. These results indicated a possible regulatory role for PDE1B in pathways involving DARPP32. Here, we generated PDE1B x DARPP32 double-knockout (double-KO) mice to test the role of PDE1B in DARPP32-dependent pathways in vivo. Analysis of the response to d-methamphetamine on locomotor activity showed that the hyperactivity experienced by PDE1B mutant mice was blocked in PDE1B-/- x DARPP32-/- double-KO mice, consistent with participation of PDE1B and DARPP32 in the same pathway. Further behavioral testing in the elevated zero-maze revealed that DARPP32-/- mice showed a less anxious phenotype that was nullified in double-mutant mice. In contrast, in the Morris water maze, double-KO mice showed deficits in spatial reversal learning not observed in either single mutant compared with wild-type mice. The data suggest a role for PDE1B in locomotor responses to psychostimulants through modulation of DARPP32-dependent pathways; however, this modulation does not necessarily impact other behaviors, such as anxiety or learning. Instead, the phenotype of double-KOs observed in these latter tasks may be mediated through independent pathways.

Evaluation of neonatal exposure to cocaine on learning, activity, startle, scent marking, immobility, and plasma cocaine concentrations.

Prenatal cocaine treatment produces equivocal effects on spatial learning and memory; however, no data are available on neonatal treatment as a model of human third-trimester exposure. Sprague-Dawley rats were treated on postnatal days (P) 1-10 or 11-20 with cocaine (15 mg/kg x 4 per day at 2-h intervals) or saline (P1-P20) and evaluated as adults in the Morris water maze and on tests of activity, startle, scent marking, swimming immobility, and sequential learning. Neonatal cocaine had no effect on mortality; however, early treatment reduced body weight, whereas later treatment did not. Neonatal cocaine had no effects on exploratory activity, swimming ability, sequential learning, multiday activity rhythms, scent marking, or swimming immobility, but augmented acoustic startle amplitude in the early-treated group. Neonatal cocaine also produced an interaction on spatial learning in which the cocaine early-treated males performed slightly more efficiently than controls. Plasma cocaine concentrations were significantly higher in the early-treated group than the later-treated group despite receiving the same weight-adjusted doses. It was concluded that neonatal cocaine, when administered during a stage of brain development analogous to human third trimester, induces few behavioral effects based on the assessments used in this study.

Genetic differences in spatial learning between Dark Agouti and Sprague-Dawley strains: possible correlation with the CYP2D2 polymorphism in rats treated neonatally with methamphetamine.

Following neonatal exposure to d-methamphetamine, adult rats have previously been shown to exhibit augmented acoustic startle and spatial learning deficits. d-Methamphetamine is structurally similar to several phenylethylamines that are metabolized by CYP2D6. In humans, allelic differences in the CYP2D6 confer the extensive or poor metabolizer phenotype for the more than three dozen drugs that are members of the CYP2D6-mediated 'debrisoquine/sparteine panel.' An analogous genotype exists with the CYP2D2 gene in rats. Female Dark Agouti rats show the poor metabolizer phenotype, whereas Sprague-Dawley rats show the extensive metabolizer phenotype; male Dark Agouti rats are intermediate. We sought to test the possibility that these strains might exhibit altered d-methamphetamine-induced developmental neurotoxicity. Dark Agouti and Sprague-Dawley litters (11-20 days of age) were given d-methamphetamine or vehicle alone subcutaneously twice daily (15 mg/kg). Offspring were assessed as adults (beginning at 50 days of age) on acoustic startle, straight-channel swimming, and spatial learning and memory in a Morris hidden platform maze. Increases in d-methamphetamine-induced acoustic startle were found in both male and female Dark Agouti rats, but not Sprague-Dawley rats. In the Morris maze, d-methamphetamine-induced spatial navigation deficits were found in both strains among males, suggesting some mechanism other than the CYP2D2 polymorphism. In contrast, among females only the d-methamphetamine-treated Dark Agouti rats showed deficits in spatial navigation. The maze deficits in Dark Agouti females, and enhanced acoustic startle in Dark Agouti females and males, support the hypothesis that the CYP2D2 poor metabolizer phenotype confers increased vulnerability to d-methamphetamine-induced developmental neurotoxicity, indicating that the parent drug rather than a CYP2D2-mediated metabolite is responsible for this behavioural defect--which occurs in adults who had been exposed to d-methamphetamine during the neonatal period.

Allofix freeze-dried cortical bone pins as an alternative to synthetic absorbable polymeric pins: a preliminary study in short Z bunionectomies.

The purpose of this study was to evaluate the effectiveness of the 2.4-mm freeze-dried cortical bone pins as a secondary stabilizer in short Z bunionectomies. In addition, MRI studies were performed to evaluate the capacity of the cortical pins to incorporate into the surrounding bone tissue. A literature comparison is also made with the currently available synthetic absorbable pins. The advantages and disadvantages of these pins are discussed and compared with the results of the cortical bone pin study. Fifteen patients were included with a 6-month to 1-year postoperative follow-up. There were no obvious complications resulting from the use of the cortical pin. The pins performed well as a secondary stabilizer and incorporated with the patient's bone as proposed. The author concludes that the 2.4-mm freeze-dried cortical bone pin is a reasonable alternative to synthetic absorbable pins as applied within the parameters of the study.

Genomic structure and chromosome location of the murine PDE1B phosphodiesterase gene.

Cyclic nucleotide phosphodiesterases (PDEs) catalyze the hydrolysis of cAMP and cGMP, thereby participating in regulation of the intracellular concentrations of these second messengers. The PDE1 family is defined by regulation of activity by calcium and calmodulin. We have cloned and characterized the mouse PDE1B gene, which encodes the 63-kDa calcium/calmodulin-dependent PDE (CaM-PDE), an isozyme that is expressed in the CNS in the olfactory tract, dentate gyrus, and striatum and may participate in learning, memory, and regulation of phosphorylation of DARPP-32 in dopaminergic neurons. We screened an I-129/SvJ mouse genomic library and identified exons 2-13 of the PDE1B gene that span 8.4 kb of genomic DNA. Exons range from 67 to 205 nucleotides and introns from 91 to 2250 nucleotides in length. Exon 1 was not present in the 3 kb of genomic DNA 5' to exon 2 in our clones. The mouse PDE1B gene shares many similar or identical exon boundaries as well as considerable sequence identity with the rat PDE4B and PDE4D genes and the Drosophila dunce cAMP-specific PDE gene dnc, suggesting that these genes all arose from a common ancestor. Using fluorescence in situ hybridization, we localized the PDE1B gene to the distal tip of mouse Chromosome (Chr) 15.

CYP2D1 polymorphism in methamphetamine-treated rats: genetic differences in neonatal mortality and effects on spatial learning and acoustic startle.

d-Methamphetamine (MA) is one of more than two dozen drugs included in the cytochrome P450-mediated "debrisoquine oxidation polymorphism" panel. The human gene (CYP2D6) is responsible for the "poor metabolizer" (PM) and "extensive metabolizer" (EM) phenotypes for drugs such as MA; a similar polymorphism (the CYP2D1 gene) exists in rats. Female Black or Dark Agouti rats exhibit the PM phenotype, whereas Sprague-Dawley (SD) rats show the EM trait. We sought to test the possibility that these strains of rats might exhibit altered MA-induced developmental neurotoxicity. Neonatal exposure to MA on days 11-20 has previously been shown to induce spatial learning deficits in Sprague-Dawley rats when tested as adults. Therefore, in the present experiment, on postpartum days 11 through 20, ACI (Black Agouti) and SD progeny were administered 30 mg/kg MA twice daily. MA treatment caused larger increases in mortality in ACI than in SD rats, suggesting that decreased MA metabolism leads to enhanced toxicity and lethality. Female offspring were assessed behaviorally as adults. No differences were observed in acoustic startle or straight swimming channel performance. In the Morris maze, both MA-treated rat strains showed longer latencies to find the hidden platform during acquisition, reinstatement, and shift trials, and spent less time in the target quadrant on probe trials; no strain differences in learning were found. Although these data do not support our hypothesis that MA-induced developmental neurotoxicity might be enhanced in the ACI rat, this interpretation is tempered by the high mortality rate (65%) of MA-treated ACI neonates, suggesting a possible "survivor effect" in this strain.

Neonatal methamphetamine-induced long-term acoustic startle facilitation in rats as a function of prepulse stimulus intensity.

Neonatal exposure to methamphetamine (MA) has previously been shown to induce acoustic startle facilitation when the animals were tested as adults. The present experiment sought to replicate and extend this effect using a lower dose of MA and to determine if the effect varied as a function of prepulse stimulus intensity. Sprague-Dawley CD rat offspring were culled on the day after birth to eight (preferentially retaining females). On days 1-10, progeny were injected SC with either 20 mg/kg of d-MA twice per day (doses spaced at least 8 h apart) or distilled water. On postnatal day 50, offspring were administered 51 acoustic startle trials followed by 36 prepulse trials. Prepulse intensities were 0, 70, 75, 80, 85, or 90 dB. MA progeny showed augmented startle response amplitudes on both paradigms but the effect was most pronounced on the prepulse trials. Prepulse intensity interacted with MA treatment in that significant facilitation in the MA animals occurred on 0 and 70 dB prepulse trials but was only a trend (p < 0.10) on 75, 80, 85, and 90 dB trials. This implies that the effect of MA is most likely upon the basic startle reflex and not upon inhibitory pathways that modify startle reactivity.

Modified Elmslie lateral ankle stabilization procedure.

An alternative to traditional lateral ankle stabilization procedures is presented using freeze-dried fascia lata graft tissue. This procedure is minimally invasive and obviates the complications typically associated with tenodesis procedures. Furthermore, the fascia lata graft is more anatomically similar to ligament tissue, and studies suggest that the architecture is maintained through a neovascularization process.

Long-term learning deficits and changes in unlearned behaviors following in utero exposure to multiple daily doses of cocaine during different exposure periods and maternal plasma cocaine concentrations.

Although the possible behavioral neurotoxic effects of in utero exposure to cocaine have been the subject of numerous experiments, only a limited number of different types of animal models of cocaine exposure, critical periods, or long-term effects of such exposures have been investigated. In the present experiment, the effects of multiple daily SC exposures to cocaine (20 mg/kg/dose x 5 doses per day) were investigated when administered to gravid Sprague-Dawley CD rats on embryonic days E7-12 or E13-18 compared to weight-matched, vehicle injected, pair-fed controls. Effects of exposure were assessed on general development, olfactory orientation behavior, early locomotion, startle reactivity, spontaneous motor activity, and learning on two different tasks (Morris and Cincinnati water mazes). The multiple cocaine dosing regimen produced maternal peak serum concentrations of cocaine 3 times higher than that of a single dose (approximately 1550 vs. approximately 550 ng/mL). Early-exposed cocaine offspring had lower olfactory orientation scores and reduced postweaning rearing and hole-poke motor activity, whereas late-exposed cocaine offspring had increased postweaning locomotor, rearing, and hole-poke activity. On the Morris hidden platform maze, the cocaine early-exposed females had longer latencies on acquisition than controls. On the Cincinnati multiple-T water maze, the early-exposed cocaine females and the late-exposed cocaine males had increased errors, whereas the early-exposed cocaine males had reduced errors. The effects on measures of learning, when taken together, and in light of their being in the early-exposed group, suggest that embryonic cocaine exposure may have subtle effects on cognition in the offspring as adults. Such effects represent a form of neurotoxicity not previously associated with prenatal cocaine exposure.

Times to extinction for small populations of large birds.

A major practical problem in conservation biology is to predict the survival times-"lifetimes"-for small populations under alternative proposed management regimes. Examples in the United States include the 'Alala (Hawaiian Crow; Corvus hawaiiensis) and Northern Spotted Owl (Strix occidentalis caurina). To guide such decisions, we analyze counts of all crow, owl, and hawk species in the most complete available data set: counts of bird breeding pairs on 14 European islands censused for 29-66 consecutive years. The data set yielded 129 records for analysis. We define the population ceiling as the highest number of breeding pairs observed from colonization to extinction, within a consecutive series of counts for a given species on a given island. The resulting distributions of population lifetimes as a function of population size prove to be highly skewed: most small populations disappear quickly, but a few last for a long time. Median (i.e., 50th percentile) lifetimes are calculated as only 1-5 yr for hawk, owl, and crow populations with ceilings of one or two breeding pairs. As expected if demographic accidents are the main cause of extinction for small populations, lifetimes rise by a factor of 3-4 for each additional pair up to three pairs. They rise more slowly thereafter. These observations suggest that lifetimes of the 'Alala (now reduced to about three pairs in the wild), and of populations of Northern Spotted Owl in the smallest forest fragments, will be short unless active management is implemented.