Cytonuclear discordance, reticulation and cryptic diversity in one of North America's most common frogs.

Complicated phylogenetic histories benefit from diverse sources of inference. Pseudacris crucifer (spring peeper) spans most of eastern North America and comprises six mtDNA lineages that form multiple contact zones. The putative Miocene or early Pliocene origins of the oldest lineages within Pseudacris crucifer imply sufficient time for species-level divergence. To understand why this species appears unified while congeners have radiated, we analyze and compare male advertisement calls, mitochondrial, and nuclear markers and speak to the complex processes that have potentially influenced its contemporary patterns. We find extensive geographic and topological mitonuclear discordance, with three nuclear lineages containing 6 more-structured mtDNA lineages, and nuclear introgression at some contact zones. Male advertisement call differentiation is incongruent with the genetic structure as only one lineage appears differentiated. Occupying the Interior Highlands of the central United States, this Western lineage also has the most concordant mitochondrial and nuclear geographic patterns. Based on our findings we suggest that the antiquity of common ancestors was not as important as the maintenance of allopatry in the divergence in P. crucifer genetic lineages. We use multiple lines of evidence to generate hypotheses of isolation, reticulation, and discordance within this species and to expand our understanding of the early stages of speciation.

Contact zone dynamics during early stages of speciation in a chorus frog (Pseudacris crucifer).

Characterizing the genetic and behavioural consequences of contact between previously geographically isolated lineages provides insights into the mechanisms underlying diversification and ultimately speciation. The spring peeper (Pseudacris crucifer) is a widespread Nearctic chorus frog with six divergent mitochondrial DNA (mtDNA) lineages, many of which came into secondary contact during the Holocene. We examined genetics, morphology, advertisement calls and female preference for two lineages that began diverging in allopatry in the Pliocene and now overlap in southwestern Ontario, Canada. We found non-coincident clines in mtDNA and nuclear DNA, mirroring directionality of premating isolation barriers. We also found divergence in a range of traits between these two lineages, displacement in male call attributes and female preference for calls of their natal lineage in sympatry. Hybrids were morphologically distinct from both parental lineages, but hybrid male calls were acoustically intermediate. Female hybrids showed asymmetrical preference for Eastern male calls. These results considered together provide evidence of either unidirectional hybridization or selection against hybrids, potentially implying reproductive character displacement. Our work demonstrates the utility of integrated, multi-character approaches to understanding the processes of divergence and the nature of speciation.

Critically ill children in non-paediatric intensive care units: a survey, review and proposal for practice.

Despite strong arguments in favour of centralising care of critically ill children to paediatric intensive care units, around 2000 children per year are cared for in non-paediatric intensive care units in Australia and New Zealand. This paper reports a survey of consultants from 13 such units that admitted over 50 children in 2002 and 2003, to find out what factors affect the decision to keep critically ill children locally or transfer them to a paediatric intensive care unit and what infrastructure existed to support local care of these children. The results of this survey form the basis for a proposal to improve care of critically ill children in the non-paediatric intensive care units. The four key elements of this proposal are: the use of protocols, routine consultation with the regional paediatric intensive care unit, the use of telemedicine, and enhancing skills and experience of local staff Evidence supporting these measures as well as the evidence for centralising care of critically ill children is reviewed.

Previous exposure to VTA amphetamine enhances cocaine self-administration under a progressive ratio schedule in a D1 dopamine receptor dependent manner.

The effect of previous exposure to amphetamine (AMPH) in the ventral tegmental area (VTA) on the subsequent self-administration of cocaine was assessed. Rats in different groups were pre-exposed to three injections into the VTA of either saline (0.5 microl/side) or AMPH (2.5 microg/0.5 microl/side). Injections were given once every third day. Starting 7-10 days after the last pre-exposure injection, rats were trained to self-administer cocaine (0.3 mg/kg/infusion) under fixed ratio 1 and 2 (FR1 and FR2) schedules and then tested under a progressive ratio (PR) schedule of reinforcement for six consecutive days. No differences between groups were observed during self-administration training under the FR schedules of reinforcement. However, when tested under the PR schedule, VTA AMPH pre-exposed rats worked more and, as a result, obtained more infusions of cocaine than saline pre-exposed rats. Rats in a separate group pre-exposed to VTA AMPH but co-infused with the D(1)-like dopamine (DA) receptor antagonist SCH23390 (0.25 microg/0.5 microl/side) did not show enhanced cocaine self-administration. These rats, as well as others pre-exposed to VTA SCH23390 alone showed levels of cocaine self-administration similar to saline pre-exposed rats. Thus, in a manner paralleling the sensitization of AMPH-induced locomotion and nucleus accumbens DA overflow, previous exposure to AMPH in the VTA leads to enhanced intravenous self-administration of cocaine and activation of D(1) DA receptors in this site during pre-exposure is necessary for the production of this effect.

Locomotor response to novelty predicts a rat's propensity to self-administer nicotine.

RATIONALE: A positive correlation between responding to novelty and propensity to subsequently self-administer a drug has been reported for opioids and psychomotor stimulants but remains to be investigated for nicotine. OBJECTIVE: The possibility that locomotor responding to novelty can predict a rat's propensity to self-administer nicotine was therefore assessed. METHODS: Rats' locomotor response to a novel environment was assessed, and animals were subsequently tested for their self-administration of nicotine. RESULTS: Significant positive correlations were obtained between responding to novelty and acquisition of nicotine self-administration over 12 days of testing under fixed-ratio schedules as well as subsequent responding for the drug under a progressive-ratio (PR) schedule of reinforcement. When designated as high (HR) or low (LR) responders based on whether their locomotor responses on the novelty screen were above or below the median activity level of the subject sample, HR animals, compared with LR rats, acquired nicotine self-administration more readily and worked more to obtain the drug when tested under the PR schedule. CONCLUSION: These findings are consistent with those obtained with other drugs and suggest that locomotor responding to a novel environment can be used to predict a rat's propensity to self-administer nicotine.

Previous exposure to amphetamine enhances the subsequent locomotor response to a D1 dopamine receptor agonist when glutamate reuptake is inhibited.

The role of nucleus accumbens (NAcc) glutamate (GLU) and D(1) dopamine (DA) receptor activation in the expression of locomotor sensitization to amphetamine (AMPH) was investigated in rats. Rats were preexposed to either AMPH or saline, and 2 weeks later their locomotion was assessed after a microinjection into the NAcc of the selective glutamate reuptake blocker l-trans-pyrrolidine-2,4-dicarboxylic acid (PDC) (10 nmol per side), the D(1)-like DA receptor agonists SKF82958 (2.4 nmol per side) and SKF38393 (3.1 nmol per side), the D(2)-like DA receptor agonist quinelorane (3.1 nmol per side), or AMPH (6.8 nmol per side). All compounds other than quinelorane increased locomotion when infused into the NAcc. Only AMPH, however, produced enhanced locomotion in AMPH relative to saline-preexposed rats. When additional rats were tested after NAcc infusions of PDC together with either SKF82958 or quinelorane, enhanced locomotion was observed in AMPH relative to saline-preexposed rats after NAcc PDC + SKF82958. These results suggest that in the NAcc, increased GLU neurotransmission and activation of D(1) DA receptors, neither of which is by itself sufficient, together contribute to the expression of locomotor sensitization by AMPH. They stress, with other findings, the importance of GLU-DA interactions in the NAcc not only in the generation of acute stimulant drug effects but in sensitized responding to these drugs as well.