Stimulus-induced dissociation of neuronal firing rates and local field potential gamma power and its relationship to the resonance blood oxygen level-dependent signal in macaque primary visual cortex.

The functional magnetic resonance imaging (fMRI) blood oxygenation level-dependent (BOLD) signal is regularly used to assign neuronal activity to cognitive function. Recent analyses have shown that the local field potential (LFP) gamma power is a better predictor of the fMRI BOLD signal than spiking activity. However, LFP gamma power and spiking activity are usually correlated, clouding the analysis of the neural basis of the BOLD signal. We show that changes in LFP gamma power and spiking activity in the primary visual cortex (V1) of the awake primate can be dissociated by using grating and plaid pattern stimuli, which differentially engage surround suppression and cross-orientation inhibition/facilitation within and between cortical columns. Grating presentation yielded substantial V1 LFP gamma frequency oscillations and significant multi-unit activity. Plaid pattern presentation significantly reduced the LFP gamma power while increasing population multi-unit activity. The fMRI BOLD activity followed the LFP gamma power changes, not the multi-unit activity. Inference of neuronal activity from the fMRI BOLD signal thus requires detailed a priori knowledge of how different stimuli or tasks activate the cortical network.

Endoscopic closure of large colonic perforations using an over-the-scope clip: a randomized controlled porcine study.

BACKGROUND AND STUDY AIMS: Perforation of the colon is considered to be one of the most serious complications of flexible endoscopy. The over-the-scope clip system (OTSC) has previously been shown to close small colonic perforations effectively. The aim of this randomized controlled porcine study was to compare acute closure strengths between the novel 11-mm over-the-scope-clip and surgical closure for large colonic perforations. MATERIAL AND METHODS: In 24 anesthetized domestic pigs, an 18-mm sigmoid perforation was created endoscopically using a needle knife and dilating balloon. The animals were randomly assigned to undergo either open surgical repair (n = 12) or endoscopic closure using the OTSC system (n = 12). Pressurized leak tests were performed during necropsy. RESULTS: Mean time to perform the incision in the sigmoid colon and obtain peritoneal access was 5.5 minutes (range 3-12; SD +/- 2.5). Mean time for endoscopic closure was 6.8 minutes (range 3-14; SD +/- 3). At necropsy, all OTSC and surgical closures demonstrated complete sealing of colotomy sites. In one case peritoneum and in a second case adjacent small intestine were found incorporated into the OTSC closure. No other complications occurred. Pressurized leak tests revealed a mean burst pressure of 62.8 mmHg (range 18-112; SD 35.7) for OTSC closures and 67.4 mmHg (range 30-90; SD 19) for sutured closure. No significant differences in burst pressures were noted between the OTSC closures and surgical repair. CONCLUSION: Closure of acute perforations using the OTSC system is comparable to surgical closure in a nonsurvival porcine model.

Comparison of spatial integration and surround suppression characteristics in spiking activity and the local field potential in macaque V1.

Neurons in primary visual cortex exhibit well documented centre-surround receptive field organization, whereby the centre is dominated by excitatory influences and the surround is generally dominated by inhibitory influences. These effects have largely been established by measuring the output of neurons, i.e. their spiking activity. How excitation and inhibition are reflected in the local field potential (LFP) is little understood. As this can bear on the interpretation of human fMRI BOLD data and on our understanding of the mechanisms of local field potential oscillations, we measured spatial integration and centre-surround properties in single- and multiunit recordings of V1 in the awake fixating macaque monkey, and compared these to spectral power in different frequency bands of simultaneously recorded LFPs. We quantified centre-surround organization by determining the size of the summation and suppression area in spiking activity as well as in different frequency bands of the LFP, with the main focus on the gamma band. Gratings extending beyond the summation area usually inhibited spiking activity while the LFP gamma-band activity increased monotonically for all grating sizes. This increase was maximal for stimuli infringing upon the near classical receptive field surround, where suppression started to dominate spiking activity. Thus, suppressive influences in primary cortex can be inferred from spiking activity, but they also seem to affect specific features of gamma-band LFP activity.

Acetylcholine contributes through muscarinic receptors to attentional modulation in V1.

Attention exerts a strong influence over neuronal processing in cortical areas. It selectively increases firing rates and affects tuning properties, including changing receptive field locations and sizes. Although these effects are well studied, their cellular mechanisms are poorly understood. To study the cellular mechanisms, we combined iontophoretic pharmacological analysis of cholinergic receptors with single cell recordings in V1 while rhesus macaque monkeys (Macaca mulatta) performed a task that demanded top-down spatial attention. Attending to the receptive field of the V1 neuron under study caused an increase in firing rates. Here we show that this attentional modulation was enhanced by low doses of acetylcholine. Furthermore, applying the muscarinic antagonist scopolamine reduced attentional modulation, whereas the nicotinic antagonist mecamylamine had no systematic effect. These results demonstrate that muscarinic cholinergic mechanisms play a central part in mediating the effects of attention in V1.

A novel electrode-pipette design for simultaneous recording of extracellular spikes and iontophoretic drug application in awake behaving monkeys.

We developed a novel design of an electrode-pipette combination (EPC) which allows access to brain structures in awake behaving primates without the need for guide tubes or to mechanically open the dura prior to electrode insertion. The EPC consists of an etched tungsten in glass electrode flanked by two pipettes which allow for local and highly controlled iontophoretic administration of neuroactive substances. These EPCs have excellent single cell isolation properties and are sturdy enough to penetrate the primate dura for up to 8 weeks following either a craniotomy or a dura scrape (i.e. even after substantial built up of fibrous scar tissue). We show that the EPCs can be used to selectively manipulate the cholinergic system in primate V1 during passive fixation and while animals perform an attentionally demanding task.

Sex pheromone of the oleander scale, Aspidiotus nerii: structural characterization and absolute configuration of an unusual functionalized cyclobutane.

The sex pheromone emitted by the female oleander scale, Aspidiotus nerii (Homoptera, Diaspididae), has been isolated and characterized as (1R, 2S)-cis-2-isopropenyl-1-(4'-methyl-4'-penten-1'-yl)cyclobutaneethanol acetate by using advanced MS and NMR spectroscopic methods, as well as a variety of microderivatization sequences. The structure has been confirmed by stereo- and enantioselective synthesis of the four possible stereoisomers. The absolute configuration has been determined by comparison of the activity of the cis (1S,2R) and (1R, 2S) enantiomers with that exhibited by the natural material in greenhouse bioassays and field tests. The structure of this sesquiterpenoid pheromone is new in the coccids and in the pheromone field in general.

Synthesis and identification of a third component of the San Jose scale sex pheromone.

Two components of the San Jose scale sex pheromone had previously been identified as 7-methyl-3-methylene-7-octen-1-yl propanoate (I) and (Z)-3,7-dimethyl-2,7-octadien-1-yl propanoate (II). An isomer and various homologs have subsequently been synthesized and tested in a greenhouse bioassay. TheE isomer of II (XI) was found to be attractive to male scales. This compound has now been isolated and identified from airborne extracts of virgin female scales. The composition of the natural pheromone was 48.5%, 46.7%, and 4.8% of I, II, and XI, respectively. In field tests in California and New York, synthetic XI was found to be attractive to male scales alone and in combination with I and II, but there was no obvious increase in trap catch when the synthetic isomers were present in the same ratio as in the natural blend.