Biomedical subjects

A R Ferguson

Publications and source records attributed to A R Ferguson.

15 recordsLinked to original sources

PubMed2006

Nociceptive plasticity inhibits adaptive learning in the spinal cord.

Spinal plasticity is known to play a role in central neurogenic pain. Over the last 100 years researchers have found that the spinal cord is also capable of supporting other forms of plasticity including several forms of learning. To study instrumental (response-outcome) learning in the spinal cord, we use a preparation in which spinally transected rats are given shock to the hind leg when the leg is extended. The spinal cord rapidly learns to hold the leg in a flexed position when given this controllable shock. However, if shock is independent of leg position (uncontrollable shock), subjects fail to learn. Uncontrollable shock also impairs future learning. As little as 6 min of uncontrollable shock to either the leg or the tail generates a learning deficit that lasts up to 48 h. Recent data suggest links between the learning deficit and the sensitization of pain circuits associated with inflammation or injury (central sensitization). Here, we explored whether central sensitization and the spinal learning deficit share pharmacological and behavioral features. Central sensitization enhances reactivity to mechanical stimulation (allodynia) and depends on the N-methyl-d-aspartate receptor (NMDAR). The uncontrollable shock stimulus that generates a learning deficit produced a tactile allodynia (Exp. 1) and administration of the NMDAR antagonist MK-801 blocked induction of the learning deficit (Exp. 2). Finally, a treatment known to induce central sensitization, intradermal carrageenan, produced a spinal learning deficit (Exp. 3). The findings suggest that the induction of central sensitization inhibits selective response modifications.

Analysis of Variance↗

PubMed2005

Nuclear DNA variation, chromosome numbers and polyploidy in the endemic and indigenous grass flora of New Zealand.

BACKGROUND AND AIMS: Little information is available on DNA C-values for the New Zealand flora. Nearly 85 % of the named species of the native vascular flora are endemic, including 157 species of Poaceae, the second most species-rich plant family in New Zealand. Few C-values have been published for New Zealand native grasses, and chromosome numbers have previously been reported for fewer than half of the species. The aim of this research was to determine C-values and chromosome numbers for most of the endemic and indigenous Poaceae from New Zealand. SCOPE: To analyse DNA C-values from 155 species and chromosome numbers from 55 species of the endemic and indigenous grass flora of New Zealand. KEY RESULTS: The new C-values increase significantly the number of such measurements for Poaceae worldwide. New chromosome numbers were determined from 55 species. Variation in C-value and percentage polyploidy were analysed in relation to plant distribution. No clear relationship could be demonstrated between these variables. CONCLUSIONS: A wide range of C-values was found in the New Zealand endemic and indigenous grasses. This variation can be related to the phylogenetic position of the genera, plants in the BOP (Bambusoideae, Oryzoideae, Pooideae) clade in general having higher C-values than those in the PACC (Panicoideae, Arundinoideae, Chloridoideae + Centothecoideae) clade. Within genera, polyploids typically have smaller genome sizes (C-value divided by ploidy level) than diploids and there is commonly a progressive decrease with increasing ploidy level. The high frequency of polyploidy in the New Zealand grasses was confirmed by our additional counts, with only approximately 10 % being diploid. No clear relationship between C-value, polyploidy and rarity was evident.

Cell Nucleus↗

PubMed2005

IgM accelerates affinity maturation.

Secreted IgM is a potent adjuvant that concentrates antigen into secondary lymphoid organs and initiates antibody responses, germinal centre formation and is crucial in resolving infections. The current studies investigated the influence of specific IgM on both the quantity and quality of antibody produced in response to T-dependent and T-independent antigens. The addition of IgM to either antigen had no significant effect on the titre or duration of antibody responses. However, the presence of specific IgM led to accelerated affinity maturation when mice were challenged with low doses of IgM-containing immune complexes (IgM-IC) of T-dependent antigens compared with antigen alone. Interestingly, the administration of higher concentrations of IgM-IC increased follicular deposition of antigen but did not result in accelerated affinity maturation or in higher antibody affinities. The administration of IgM complexed with T-independent antigens had no effect on antibody titre, duration or affinity maturation, despite increased antigen deposition in lymphoid follicles. Together, these results demonstrate that IgM accelerates affinity maturation in immune responses to T-dependent antigens and implies an antigen optimum exists for the generation of high affinity antibodies. The data also suggest IgM plays an important role in the induction of CD4 T cells, facilitating germinal centre formation and function.

Animals↗

PubMed2004

Monitoring recovery after injury: procedures for deriving the optimal test window.

Researchers studying the impact of treatments designed to facilitate recovery after neural injury face competing demands. On the one hand, because treatment effects often emerge slowly over days, and because researchers seek evidence of stable long-term effects, it is common practice to observe experimental subjects for many weeks after treatment. On the other hand, the cost of performing studies and the need to evaluate a multitude of alternative treatment procedures requires optimal efficiency, pushing researchers towards shorter test procedures. With these issues in mind, researchers have appeared to derive a test window based on previously published methodologies and inspection of their recovery curves, with testing terminated after the recovery curve reaches asymptote (approaches a slope of 0). An alternative procedure is introduced here that evaluates the stability of the data set over time. Using correlational techniques, researchers can determine whether (1) testing should be continued for additional days; or (2) equivalent statistical power can be achieved in fewer days. This provides a rational decision rule to help researchers balance competing demands. Applying these techniques to a procedure that evaluates the impact of acute treatments on recovery from spinal cord injury, it is shown that equal statistical power can be achieved in half the time, greatly increasing the efficiency with which alternative treatments can be evaluated.

Animals↗

PubMed2001

Pain and negative affect: evidence the inverse benzodiazepine agonist DMCM inhibits pain and learning in rats.

RATIONALE: The anxiogenic DMCM, an inverse benzodiazepine agonist, was used to explore the relationship between negative affective states and pain. Past work suggests that the outcome obtained may depend on both the intensity of the affective state and the way in which pain is inferred. OBJECTIVES: The present study was designed to test the impact of relatively low doses of DMCM on multiple measures of pain reactivity and learning. METHODS: In experiment 1, systemic injections of 0.00, 0.015, 0.06, and 0.25 mg/kg DMCM were administered before vocalization and tail movements were assessed in response to a gradually incremented shock and radiant heat stimulus. Experiment 2 tested the effects of DMCM on Pavlovian conditioning. DMCM-treated subjects experienced a context paired with an aversive unconditioned stimulus (US) and conditioned freezing was assessed the next day. RESULTS: Experiment 1 showed that DMCM inhibits both a spinal nociceptive reflex (tail-flick to heat) and a supraspinal measure of pain (vocalization to shock). Because these inhibitory effects could reflect a disruption in motor function, experiment 2 employed a remote test based on Pavlovian conditioning. A moderate dose of DMCM undermined learning, implying that the drug decreased the affective impact of the aversive US. CONCLUSIONS: DMCM induces hypoalgesia on a wide range of assays. Furthermore, pharmacologically inducing a negative affective state blocks Pavlovian fear conditioning. It is suggested that DMCM induces a state of panic and that this state inhibits pain.

Affect↗

PubMed2001

Shock-induced hyperalgesia: IV. Generality.

Brief-moderate shock (3, 0.75 s, 1.0 mA) has opposite effects on different measures of pain, inducing antinociception on the tail-flick test while lowering vocalization thresholds to shock and heat (hyperalgesia) and enhancing fear conditioned by a gridshock unconditioned stimulus (US). This study examined the generality of shock-induced hyperalgesia under a range of conditions and explored parallels to sensitized startle. Reduced vocalization thresholds to shock and antinociception emerged at a similar shock intensity. Severe shocks (3, 25 s, 1.0 mA or 3, 2 s, 3.0 mA) lowered vocalization threshold to shock but increased vocalization and motor thresholds to heat and undermined fear conditioned by a gridshock or a startling tone US. All shock schedules facilitated startle, but only brief-moderate shock inflated fear conditioning. The findings suggest that brief-moderate shock enhances the affective impact of aversive stimuli, whereas severe shocks attenuate pain.

Affect↗

PubMed1994

Effects of positive and negative music on performance of a karate drill.

Although athletes frequently report using music while training or before an event, laboratory studies have not detected a beneficial effect, so the influence of positive and negative music on performance of a selected karate drill was investigated in this double-blind study using 14 volunteers from two Shotokan karate schools. Each subject performed a preselected drill three times following positive and negative music and white noise in a random order. Performance of the drill was rated on a 7-item, 5-point scale by 2 rates. Differences among conditions were assessed via a with-in-subject t test for paired scores. The subjects' self-evaluation of their performance was also examined. Enhancement of performance for both types of music over white noise was significant.

Adolescent↗

PubMed1974