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Biomedical subjects

Stephen J Martin

Publications and source records attributed to Stephen J Martin.

13 recordsLinked to original sources
PubMed2005

Learning and discrimination of individual cuticular hydrocarbons by honeybees (Apis mellifera).

In social insect colonies, recognition of nestmates, kinship, caste and reproductive status is crucial both for individuals and for the colony. The recognition cues used are thought to be chemical, with the hydrocarbons found on the cuticle of insects often cited as being particularly important. However, in honeybees (Apis mellifera) the role of cuticular hydrocarbons in nestmate recognition is controversial. Here we use the proboscis extension response (PER) conditioning paradigm to determine how well honeybees learn long-chain linear alkanes and (Z)-alkenes present on the cuticle of worker bees, and also how well they can discriminate between them. We found large differences both in learning and discrimination abilities with the different cuticular hydrocarbons. Thus, the tested hydrocarbons could be classified into those which the bees learnt and discriminated well (mostly alkenes) and those which they did not (alkanes and some alkenes). These well-learnt alkenes may constitute important compounds used as cues in the social recognition processes.

Alkanes↗
PubMed2005

Interrogating rodents regarding their object and spatial memory.

Today, neuroscientists have access to a host of advanced techniques -- ranging from targeted genetic interventions to brain imaging -- that are rapidly providing new insights. Ultimately, however, memory must be inferred from its behavioral read-out. Thus, to fully utilize the advanced technologies available today, we must select the most appropriate behavioral procedures from those currently available, or else devise novel behavioral techniques to meet a specific demand. If we merely use standard tests of memory in a non-optimal way, we risk collecting incomplete information and reaching erroneous conclusions. Relevant to these issues, there have been substantial developments in the methods used to evaluate two of the most frequently studied forms of memory in the rodent -- recognition memory and spatial memory.

Animals↗
PubMed2005

Retrograde amnesia: neither partial nor complete hippocampal lesions in rats result in preferential sparing of remote spatial memory, even after reminding.

Many lesion experiments have provided evidence that the hippocampus plays a time-limited role in memory, consistent with the operation of a systems-level memory consolidation process during which lasting neocortical memory traces become established [see Squire, L. R., Clark, R. E., & Knowlton, B. J. (2001). Retrograde amnesia. Hippocampus 11, 50]. However, large lesions of the hippocampus at different time intervals after acquisition of a watermaze spatial reference memory task have consistently resulted in temporally ungraded retrograde amnesia [Bolhuis, J. J., Stewart, C. A., Forrest, E. M. (1994). Retrograde amnesia and memory reactivation in rats with ibotenate lesions to the hippocampus or subiculum. Quarterly Journal of Experimental Psychology 47B, 129; Mumby, D. G., Astur, R. S., Weisend, M. P., Sutherland, R. J. (1999). Retrograde amnesia and selective damage to the hippocampal formation: memory for places and object discriminations. Behavioural Brain Research 106, 97; Sutherland, R. J., Weisend, M. P., Mumby, D., Astur, R. S., Hanlon, F. M., et al. (2001). Retrograde amnesia after hippocampal damage: recent vs. remote memories in two tasks. Hippocampus 11, 27]. It is possible that spatial memories acquired during such a task remain permanently dependent on the hippocampus, that chance performance may reflect a failure to access memory traces that are initially unexpressed but still present, or that graded retrograde amnesia for spatial information might only be observed following partial hippocampal lesions. This study examined the retrograde memory impairments of rats that received either partial or complete lesions of the hippocampus either 1-2 days, or 6 weeks after training in a watermaze reference memory task. Memory retention was assessed using a novel 'reminding' procedure consisting of a series of rewarded probe trials, allowing the measurement of both free recall and memory reactivation. Rats with complete hippocampal lesions exhibited stable, temporally ungraded retrograde amnesia, and could not be reminded of the correct location. Partially lesioned rats could be reminded of a recently learned platform location, but no recovery of remote memory was observed. These results offer no support for hippocampus-dependent consolidation of allocentric spatial information, and suggest that the hippocampus can play a long-lasting role in spatial memory. The nature of this role--in the storage, retrieval, or expression of memory--is discussed.

Amnesia, Retrograde↗
PubMed2004

Forgetting, reminding, and remembering: the retrieval of lost spatial memory.

Retrograde amnesia can occur after brain damage because this disrupts sites of storage, interrupts memory consolidation, or interferes with memory retrieval. While the retrieval failure account has been considered in several animal studies, recent work has focused mainly on memory consolidation, and the neural mechanisms responsible for reactivating memory from stored traces remain poorly understood. We now describe a new retrieval phenomenon in which rats' memory for a spatial location in a watermaze was first weakened by partial lesions of the hippocampus to a level at which it could not be detected. The animals were then reminded by the provision of incomplete and potentially misleading information-an escape platform in a novel location. Paradoxically, both incorrect and correct place information reactivated dormant memory traces equally, such that the previously trained spatial memory was now expressed. It was also established that the reminding procedure could not itself generate new learning in either the original environment, or in a new training situation. The key finding is the development of a protocol that definitively distinguishes reminding from new place learning and thereby reveals that a failure of memory during watermaze testing can arise, at least in part, from a disruption of memory retrieval.

Amnesia, Retrograde↗
PubMed2004

Conservation of Bio synthetic pheromone pathways in honeybees Apis.

Social insects use complex chemical communication systems to govern many aspects of their life. We studied chemical changes in Dufour's gland secretions associated with ovary development in several genotypes of honeybees. We found that C28-C38 esters were associated only with cavity nesting honeybee queens, while the alcohol eicosenol was associated only with their non-laying workers. In contrast, both egg-laying anarchistic workers and all parasitic Cape workers from queenright colonies showed the typical queen pattern (i.e. esters present and eicosenol absent), while egg-laying wild-type and anarchistic workers in queenless colonies showed an intermediate pattern, producing both esters and eicosenol but at intermediate levels. Furthermore, neither esters nor eicosenol were found in aerial nesting honeybee species. Both esters and eicosenol are biosynthetically similar compounds since both are recognizable products of fatty acid biosynthesis. Therefore, we propose that in honeybees the biosynthesis of esters and eicosenol in the Dufour's gland is caste-regulated and this pathway has been conserved over evolutionary time.

Animals↗
PubMed2004

A model for the quartz crystal microbalance frequency response to wetting characteristics of corrugated surfaces.

We consider the effect of surface roughness, and its unique wetting behavior, on the response of a quartz crystal microbalance (QCM) resonator operating in contact with a fluid. The rough surface is modeled as sinusoidally corrugated particular to the case of a fixed relationship between amplitude and periodicity, as would arise from polishing with monodisperse spherical particles. The penetration of fluid into the troughs of the corrugations and the resulting meniscus are determined as a competition between surface tension and compression of the trapped gas. Liquid contained below the corrugation peaks, but above the gas/liquid meniscus, is trapped and behaves as an ideal mass layer, contributing a frequency shift that adds to that arising from liquid entrainment. This model allows QCM responses on rough surfaces to be described as a function of liquid properties and contact angle. This permits responses on hydrophobic surfaces to be understood in terms of incomplete surface wetting.

Journal Article↗
PubMed2003

Comparing data on the reproduction of Varroa destructor.

Varroa destructor reproductive success is considered an important character for determining the resistance of honey bees to this mite parasite. However, most of the published data are not comparable due to the different methods of ascertaining and reporting reproduction. A recently published technique that involves reconstructing mite families in older worker brood gives repeatable and reliable parameters. This methodology was used to compare various categories of reproduction of approximately 1,000 V. destructor females in each of three studies on Africanized bees in Brazil and Mexico and European bees in England. The most objective and useful measure was the determination of the number of viable females per female that had invaded the worker brood in singly infested cells, which was denominated the "effective reproduction rate". Viable females are those that can reach the adult stage and have a mate available. The effective reproduction rate in worker brood was 0.64, 0.73 and 1.01 in Brazil, Mexico and England, respectively. Standardization of reproduction determination techniques would make published data comparable and much more useful.

Animals↗
PubMed2002

SynGAP regulates ERK/MAPK signaling, synaptic plasticity, and learning in the complex with postsynaptic density 95 and NMDA receptor.

At excitatory synapses, the postsynaptic scaffolding protein postsynaptic density 95 (PSD-95) couples NMDA receptors (NMDARs) to the Ras GTPase-activating protein SynGAP. The close association of SynGAP and NMDARs suggests that SynGAP may have an important role in NMDAR-dependent activation of Ras signaling pathways, such as the MAP kinase pathway, and in synaptic plasticity. To explore this issue, we examined long-term potentiation (LTP), p42 MAPK (ERK2) signaling, and spatial learning in mice with a heterozygous null mutation of the SynGAP gene (SynGAP(-/+)). In SynGAP(-/+) mutant mice, the induction of LTP in the hippocampal CA1 region was strongly reduced in the absence of any detectable alteration in basal synaptic transmission and NMDAR-mediated synaptic currents. Although basal levels of activated ERK2 were elevated in hippocampal extracts from SynGAP(-/+) mice, NMDAR stimulation still induced a robust increase in ERK activation in slices from SynGAP(-/+) mice. Thus, although SynGAP may regulate the ERK pathway, its role in LTP most likely involves additional downstream targets. Consistent with this, the amount of potentiation induced by stimulation protocols that induce an ERK-independent form of LTP were also significantly reduced in slices from SynGAP(-/+) mice. An elevation of basal phospho-ERK2 levels and LTP deficits were also observed in SynGAP(-/+)/H-Ras(-)/- double mutants, suggesting that SynGAP may normally regulate Ras isoforms other than H-Ras. A comparison of SynGAP and PSD-95 mutants suggests that PSD-95 couples NMDARs to multiple downstream signaling pathways with very different roles in LTP and learning.

Animals↗
PubMed2002

Reassessing the role of the honeybee (Apis mellifera) Dufour's gland in egg marking.

Dufour's gland secretion may allow worker honeybees to discriminate between queen-laid and worker-laid eggs. To investigate this, we combined the chemical analysis of individually treated eggs with an egg removal bioassay. We partitioned queen Dufour's gland into hydrocarbon and ester fractions. The bioassay showed that worker-laid eggs treated with either whole gland extract, ester fraction or synthetic gland esters were removed more slowly than untreated worker-laid eggs. However, the effect only lasted up to 20 h. Worker-laid eggs treated with the hydrocarbon fraction were removed at the same rate as untreated eggs. The amount of ester which reduced the egg removal rate was far higher than that naturally found on queen-laid or worker-laid eggs, and at natural ester levels no effect was found. Our results indicate that esters or hydrocarbons probably do not function as the signal by which eggs can be discriminated.

Animals↗
PubMed2002

Parasitic Cape honeybee workers, Apis mellifera capensis, evade policing.

Relocation of the Cape honeybee, Apis mellifera capensis, by bee-keepers from southern to northern South Africa in 1990 has caused widespread death of managed African honeybee, A. m. scutellata, colonies. Apis mellifera capensis worker bees are able to lay diploid, female eggs without mating by means of automictic thelytoky (meiosis followed by fusion of two meiotic products to restore egg diploidy), whereas workers of other honeybee subspecies are able to lay only haploid, male eggs. The A. m. capensis workers, which are parasitizing and killing A. m. scutellata colonies in northern South Africa, are the asexual offspring of a single, original worker in which the small amount of genetic variation observed is due to crossing over during meiosis (P. Kryger, personal communication). Here we elucidate two principal mechanisms underlying this parasitism. Parasitic A. m. capensis workers activate their ovaries in host colonies that have a queen present (queenright colonies), and they lay eggs that evade being killed by other workers (worker policing)-the normal fate of worker-laid eggs in colonies with a queen. This unique parasitism by workers is an instance in which a society is unable to control the selfish actions of its members.

Animals↗
PubMed2002

Reproduction of Varroa destructor in worker brood of Africanized honey bees (Apis mellifera).

Reproduction and population growth of Varroa destructor was studied in ten naturally infested, Africanized honey bee (AHB) (Apis mellifera) colonies in Yucatan, Mexico. Between February 1997 and January 1998 monthly records of the amount of pollen, honey, sealed worker and drone brood were recorded. In addition, mite infestation levels of adult bees and worker brood and the fecundity of the mites reproducing in worker cells were determined. The mean number of sealed worker brood cells (10,070 +/- 1,790) remained fairly constant over the experimental period in each colony. However, the presence and amount of sealed drone brood was very variable. One colony had drone brood for 10 months and another for only 1 month. Both the mean infestation level of worker brood (18.1 +/- 8.4%) and adult bees (3.5 +/- 1.3%) remained fairly constant over the study period and did not increase rapidly as is normally observed in European honey bees. In fact, the estimated mean number of mites fell from 3,500 in February 1997 to 2,380 in January 1998. In May 2000 the mean mite population in the study colonies was still only 1,821 mites. The fertility level of mites in this study was much higher (83-96%) than in AHB in Brazil (25-57%). and similar to that found in EHB (76-94%). Mite fertility remained high throughout the entire study and was not influenced by the amount of pollen, honey or worker brood in the colonies.

Animals↗
PubMed2002

Effect of acaricide resistance on reproductive ability of the honey bee mite Varroa destructor.

The reproduction of pyrethroid-resistant Varroa destructor mite, a brood parasite of honey bees, was observed in Weslaco, Texas, and the results compared with known susceptible mite populations from other studies. Seven Apis mellifera colonies that had mite populations resistant to the acaricide Apistan were used. Pyrethroid-resistance was confirmed when only 17% rather than 90% of mites confined in dishes containing Apistan died after 12 h of exposure. The average number of eggs laid by resistant mites invading worker and drone cells was 4.4 and 5.4 respectively. This is similar to the number of eggs laid by susceptible mites in worker (4.4-4.8) or drone (4.7-5.5) cells. Also the average number of fertilised V. destructor female mites produced by resistant mites in worker (1.0) and drone (2.1) cells were similar to the number produced by susceptible mites in worker (0.9) and drone (1.9-2.2) cells. In addition, no major differences between the resistant and susceptible mite populations were observed in either worker or drone cells when six different reproductive categories and offspring mortality rates were compared. Therefore, it appears that there is little or no reproductive fitness cost associated with pyrethroid resistance in V. destructor in Texas.

Animals↗