Mechanisms and Treatment of Pain-Depressed Behavior in Male and Female Mice

One of the largest discrepancies between preclinical and clinical assessment of pain and analgesia is the type of behavioral endpoint used. Although most preclinical research has historically focused on drug effectiveness to block reflexive withdrawal behaviors stimulated by a noxious stimulus, increasing evidence shows that drug-induced restoration of pain-depressed behaviors provides increased clinical translation with decreased susceptibility to false-positives. Accordingly, the first portion of this dissertation designed a behavioral battery that featured pain-depressed behaviors as well as more conventional pain-stimulated behaviors for testing candidate analgesics in male and female mice. The main findings are as follows. (1) Intraperitoneal injection of dilute lactic acid (IP acid) served as an effective visceral chemical noxious stimulus to produce concentration-dependent stimulation of two behaviors (stretching and facial grimace; pain-stimulated behaviors) and depression of two behaviors (rearing and nesting; pain-depressed behaviors). (2) Pharmacological characterization with two positive control analgesics (ketoprofen, oxycodone) and two active negative controls (diazepam, amphetamine) validated a strategy for distinguishing analgesics from nonanalgesics by profiling drug effects in this battery of complementary pain-stimulated and pain-depressed behaviors along with two additional pain-independent behaviors (nesting and locomotor activity in the absence of the IP acid noxious stimulus). (3) A National Institutes of Health mandate for consideration of Sex as a Biological Variable (SABV) was published at the start of this dissertation research. Accordingly, we developed an experimental design for considering SABV when sex differences are not the principle independent variable, with emphases on exploratory power analyses (effect size, power, predicted N) and segregation of data by sex to allow transparent analysis of SABV and help guide future study designs. The second portion of this dissertation applied this behavioral battery and SABV data-analysis strategy to evaluate a spectrum of endocannabinoid (eCB) catabolic enzyme inhibitors ranging in selectivity for the eCB catabolic enzymes monoacylglycerol lipase (MAGL) and fatty acid amide hydrolase (FAAH), which have received increasing interest for development of candidate analgesics. The main findings are as follows: (1) antinociceptive effectiveness decreased as MAGL-selectivity decreased, with the most MAGL-selective inhibitor MJN110 producing the most effective antinociceptive profile, (2) time course and antagonism studies for MJN110 showed a long duration of antinociceptive action (40min – 6hrs), mediation by CB1R but not CB2­R, a tendency for greater effects in females, and (3) repeated administration of MJN110 produced partial but sustained attenuation of IP acid-induced depression of nesting, with segregation of data by sex demonstrating sustained but weak antinociception in males and variable effects following repeated dosing in females. Overall, these data provide a framework for predicting the analgesic potential of test drugs in preclinical pain models in male and female mice, and suggest that MJN110 may have only partial effectiveness as a candidate analgesic for treatment of visceral episodic pain

Semantic Associations between Signs and Numerical Categories in the Prefrontal Cortex

The utilization of symbols such as words and numbers as mental tools endows humans with unrivalled cognitive flexibility. In the number domain, a fundamental first step for the acquisition of numerical symbols is the semantic association of signs with cardinalities. We explored the primitives of such a semantic mapping process by recording single-cell activity in the monkey prefrontal and parietal cortices, brain structures critically involved in numerical cognition. Monkeys were trained to associate visual shapes with varying numbers of items in a matching task. After this long-term learning process, we found that the responses of many prefrontal neurons to the visual shapes reflected the associated numerical value in a behaviorally relevant way. In contrast, such association neurons were rarely found in the parietal lobe. These findings suggest a cardinal role of the prefrontal cortex in establishing semantic associations between signs and abstract categories, a cognitive precursor that may ultimately give rise to symbolic thinking in linguistic humans

Productivity changes across the mid-Pleistocene climate transition

We use benthic foraminiferal accumulation rates as a proxy for productivity changes during the mid-Pleistocene climate transition (MPT) (~1.2 Ma to 0.4 Ma). Our data are chosen to test the hypothesis that longer-term cooling and the onset of 100 kyr cyclicity are linked to atmospheric CO2 draw-down associated with an increase in primary productivity. To this end, we have constructed records from a global array of seven sites spanning major ocean basins and representing different hydrographic regimes (e.g., high and low latitudes, upwelling versus the deep western warm pools). We compare our data to published productivity proxy records from each site to identify limitations and uncertainties in the reconstructions. Results indicate that there is evidence for productivity increases during the onset of the MPT (1.2–1.0 Ma), but the changes are not globally synchronous and likely reflect regional hydrographic variability. On the orbital scale, productivity maxima tend to occur more closely related to glacial than interglacial intervals overall, but the relationships are not consistent. High interglacial productivity characterizes low latitude sites some of the time. In the obliquity band, high interglacial productivity in the eastern equatorial Pacific coincides with low interglacial productivity in the Southern Ocean, supporting a high to low latitude link via intermediate water circulation distribution of nutrients. On the regional scale, our records contribute new evidence for changes in Northern Hemisphere frontal systems during the MPT and for a close link between surface ocean production of organic matter and consumption on the ocean floor in the western tropical Atlantic. Pyrite counts at the two Southern Ocean sites provide supporting evidence for sluggish thermohaline overturn during the mid-point of the MPT at ~900 ka. Taken together, our records do not show a globally synchronous productivity signal that would support the biological pump as a driver for potential CO2-induced climate cooling during the MPT. Instead, we document complex regional variations in the carbon cycle, reflecting a combination of both biological and physical processes both on the longer as well as on the orbital time-scale

Light-dark cycles in opal-rich sediments near the Plio-Pleistocene boundary, DSDP Site 532, Walvis Ridge continental terrace

Samples taken at 10 cm intervals from DSDP Core 532B-17 contain variations in carbonate, opal, organic carbon, and terrigenous components that correlate with light-dark cycles in sediment color. The core site, at 1300 m water depth, is well above the CCD, yet the color variations appear to result largely from cyclical fluctuations in carbonate dissolution, which was greater during glacial periods. Higher concentrations of organic carbon and of terrigenous sediment components correlate with enhanced carbonate dissolution, but opal concentrations inversely correlate and suggest that biological productivity at this site diminished during glacial periods. A complicated glacial-interglacial picture emerges from the data. In interglacial times, upwelling associated with the Benguela Current produced abundant opaline material, organic matter was fairly well preserved, and carbonate was only moderately dissolved. In glacial times, the upwelling core shifted as sea level fell and winds intensified. Productivity in the waters over Site 532 decreased, but lateral supply of oxidizable organic matter enhanced carbonate dissolution, giving rise to light-dark cycles in these sediments.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26049/1/0000122.pd

Carbonate crash and biogenic bloom in the late Miocene: Evidence from ODP Sites 1085, 1086, and 1087 in the Cape Basin, southeast Atlantic Ocean

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95125/1/palo1086.pd

Gamma-Rhythmic Gain Modulation

Cognition requires the dynamic modulation of effective connectivity, i.e., the modulation of the postsynaptic neuronal response to a given input. If postsynaptic neurons are rhythmically active, this might entail rhythmic gain modulation, such that inputs synchronized to phases of high gain benefit from enhanced effective connectivity. We show that visually induced gamma-band activity in awake macaque area V4 rhythmically modulates responses to unpredictable stimulus events. This modulation exceeded a simple additive superposition of a constant response onto ongoing gamma-rhythmic firing, demonstrating the modulation of multiplicative gain. Gamma phases leading to strongest neuronal responses also led to shortest behavioral reaction times, suggesting functional relevance of the effect. Furthermore, we find that constant optogenetic stimulation of anesthetized cat area 21a produces gamma-band activity entailing a similar gain modulation. As the gamma rhythm in area 21a did not spread backward to area 17, this suggests that postsynaptic gamma is sufficient for gain modulation

Molecular and Cellular Approaches for Diversifying and Extending Optogenetics

Optogenetic technologies employ light to control biological processes within targeted cells in vivo with high temporal precision. Here, we show that application of molecular trafficking principles can expand the optogenetic repertoire along several long-sought dimensions. Subcellular and transcellular trafficking strategies now permit (1) optical regulation at the far-red/infrared border and extension of optogenetic control across the entire visible spectrum, (2) increased potency of optical inhibition without increased light power requirement (nanoampere-scale chloride-mediated photocurrents that maintain the light sensitivity and reversible, step-like kinetic stability of earlier tools), and (3) generalizable strategies for targeting cells based not only on genetic identity, but also on morphology and tissue topology, to allow versatile targeting when promoters are not known or in genetically intractable organisms. Together, these results illustrate use of cell-biological principles to enable expansion of the versatile fast optogenetic technologies suitable for intact-systems biology and behavior

Cholinergic Interneurons Control Local Circuit Activity and Cocaine Conditioning

Cholinergic neurons are widespread, and pharmacological modulation of acetylcholine receptors affects numerous brain processes, but such modulation entails side effects due to limitations in specificity for receptor type and target cell. As a result, causal roles of cholinergic neurons in circuits have been unclear. We integrated optogenetics, freely moving mammalian behavior, in vivo electrophysiology, and slice physiology to probe the cholinergic interneurons of the nucleus accumbens by direct excitation or inhibition. Despite representing less than 1% of local neurons, these cholinergic cells have dominant control roles, exerting powerful modulation of circuit activity. Furthermore, these neurons could be activated by cocaine, and silencing this drug-induced activity during cocaine exposure (despite the fact that the manipulation of the cholinergic interneurons was not aversive by itself) blocked cocaine conditioning in freely moving mammals

Biogeochemical changes within the Benguela Current upwelling system during the Matuyama Diatom Maximum: Nitrogen isotope evidence from Ocean Drilling Program Sites 1082 and 1084

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95071/1/palo944.pd