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Many C57BL/6J inbred mice were tested for paw preference. In unbiased worlds, approximately 10 percent exhibited lateral preferences inconsistent with the world bias, and males were more strongly lateralized. Influences of world bias appear to be superimposed upon an already laterally dichotomized population. Initial left-right sense, it is posited, arises as an outcome of a seemingly random process.

The behavioral effects of repeated methylphenidate (MPH) treatment were assessed in young rats. In 4 experiments, rats (starting at Postnatal Day 10 or 16) were pretreated on 5 consecutive days with saline or MPH (2.5-20.0 mg/kg i.p.). Sensitization was assessed after 1 or 7 abstinence days, with rats receiving a test day challenge injection of either a low dose of MPH (2.5 mg/kg) or the same dose of MPH as given during pretreatment. Results show that a test day injection of 2.5 mg/kg MPH produced a sensitized locomotor response in rats pretreated with 2.5-20.0 mg/kg MPH. This MPH-induced locomotor sensitization was evident only after 1 abstinence day. Various pretreatment doses of MPH (5, 10, 15, or 20 mg/kg) were capable of sensitizing the stereotyped sniffing of young rats, but only rats pretreated and tested with the highest dose (20 mg/kg) of MPH showed an augmented stereotyped sniffing response that was still robust after 7 abstinence days. Results indicate that young rats are capable of exhibiting sensitization after an extended abstinence period, which contrasts with previous research suggesting that psychostimulant treatment does not produce long-term sensitization in young rats.

Objectives To study the effects of levodopa and walking speed on gait variability in individuals with Parkinson's disease (PD). Methods Thirty-three individuals with PD were studied. Their mean age was 70.61 ± 9.23 yr. The average time since diagnosis was 9.65 ± 5.80 yr years. Gait variability was studied while “OFF” and “ON” dopaminergic medication when the subjects walked at their usual and fastest speeds. Results Variability of step time, double support time, stride length and stride velocity decreased significantly (p = .037; p = .037; p = .022; p = .043, respectively) after dopaminergic treatment. When subjects increased walking speed, the variability of stride length and stride velocity decreased significantly (p = .038 and p = .004, respectively) both while “OFF” and “ON” levodopa. Increasing walking speed did not change the variability of step time and double support time regardless of medication status. Conclusions Levodopa decreased gait variability in persons with PD. Stride length and stride velocity variability appeared to be speed dependent parameters, whereas, the variability of step time and double support time appeared to be speed independent measures. Levodopa had positive effects on gait stability in PD.

Normal Wechsler Adult Intelligence Scale (WAIS)-IV performance relative to average normative scores alone can be an oversimplification as this fails to recognize disparate subtest heterogeneity that occurs with increasing age. The purpose of the present study is to characterize the patterns of raw score change and associated variability on WAIS-IV subtests across age groupings. Raw WAIS-IV subtest means and standard deviations for each age group were tabulated from the WAIS-IV normative manual along with the coefficient of variation (CV), a measure of score dispersion calculated by dividing the standard deviation by the mean and multiplying by 100. The CV further informs the magnitude of variability represented by each standard deviation. Raw mean scores predictably decreased across age groups. Increased variability was noted in Perceptual Reasoning and Processing Speed Index subtests, as Block Design, Matrix Reasoning, Picture Completion, Symbol Search, and Coding had CV percentage increases ranging from 56% to 98%. In contrast, Working Memory and Verbal Comprehension subtests were more homogeneous with Digit Span, Comprehension, Information, and Similarities percentage of the mean increases ranging from 32% to 43%. Little change in the CV was noted on Cancellation, Arithmetic, Letter/Number Sequencing, Figure Weights, Visual Puzzles, and Vocabulary subtests (<14%). A thorough understanding of age-related subtest variability will help to identify test limitations as well as further our understanding of cognitive domains which remain relatively steady versus those which steadily decline.

Mice of some inbred strains, such as 21-dayold DBA/2J mice, have generalized convulsions when exposed to intense auditory stimulation. Analysis of susceptibility to audiogenic seizures in BXD recombinant inbred strains has demonstrated the influence of at least three loci. One locus, Asp-], is located on chromosome 12 between Ah and D12Nyul; another locus, Asp-2, is on chromosome 4, tightly linked to b.Here we report evidence that Asp-2 is located within an 8-centimorgan segment distal to b and that Asp-3 is linked to Mtv-1 on chromosome 7. We also present evidence that these three loci account for most of the heritable variation in susceptibility to audiogenic seizures in crosses of DBA/2J and C57BL/6J mice and that susceptibility to audiogenic seizures is influenced by genomic imprinting. Thus, genomic imprinting may complicate linkage and mapping studies and should be considered in analyses of complex modes of inheritance.Convulsive seizures can be induced in experimental animals by intense auditory stimuli (1, 2). Susceptibility to audiogenic seizures (AS) varies widely between inbred strains of mice (2,3). The genetic basis for the difference in susceptibility to AS between DBA and C57BL mice has been studied several times since the strain difference was discovered by Hall (1). The typical AS consists of wild running followed by a clonic seizure and then a tonic seizure that is usually fatal, unless the mouse is resuscitated (1, 2, 4). DBA/2J (D2) mice are susceptible from 14 to 42 days of age with peak sensitivity at 21 days (5), whereas C57BL/6J (B6) mice are resistant to intense auditory stimuli. Variation in AS susceptibility has been attributed to a single locus (6-8), two loci (9, 10), and multifactorial (or polygenic) modes of inheritance (11)(12)(13)(14). The differing conclusions of these investigators can be attributed to many causes, including the use of different DBA and C57BL sublines, mice of different ages, and different experimental protocols (4, 15, 16).Testing of the BXD series of recombinant inbred (RI) strains and F1 hybrids from crosses between BXD RI strains and D2 revealed that at least three loci are involved in the genetic variation in AS susceptibility in crosses between D2 and B6 mice (14). Two of these loci have already been given chromosomal assignments. Asp-] (audiogenic seizure prone-1, formerly Ias) is tightly linked to the Ah locus on chromosome 12 (13,14,17), and Asp-2 (formerly asp) is located on chromosome 4 (7, 8), tightly linked to b (brown) (14).Here we report the mapping of Asp-3 by a reevaluation of published data (8,13,14,(17)(18)(19) in the light of advances in our understanding of the mode of inheritance of susceptibility to AS in crosses of D2 and B6 mice. We also report the results of reciprocal backcrosses that confirm the conclusions of the genetic dissection. MATERIALS AND METHODSThe data from two multipoint crosses reported by Collins (8) were recompiled and reexamined in an attempt to place Asp-2 on the linkage map (see Tables 1 and 2). In the firs...

Significant genetic differences were demonstrated in the rate of avoidance conditioning among offspring from all 25 mating combinations of 5 highly inbred mouse strains. Hybrids of C3H parents learned fastest, while those of A/JAX parents learned slowest. Most hybrids learned better than either parent. Evidence that differential influences of the early maternal environment affected the rate of learning was not supported.