AAV-mediated delivery of optogenetic constructs to the macaque brain triggers humoral immune responses

Gene delivery to the primate central nervous system via recombinant adeno-associated viral vectors (AAV) allows neurophysiologists to control and observe neural activity precisely. A current limitation of this approach is variability in vector transduction efficiency. Low levels of transduction can foil experimental manipulations, prompting vector readministration. The ability to make multiple vector injections into the same animal, even in cases where successful vector transduction has already been achieved, is also desirable. However, vector readministration has consequences for humoral immunity and gene delivery that depend on vector dosage and route of administration in complex ways. As part of optogenetic experiments in rhesus monkeys, we analyzed blood sera collected before and after AAV injections into the brain and quantified neutralizing antibodies to AAV using an in vitro assay. We found that injections of AAV1 and AAV9 vectors elevated neutralizing antibody titers consistently. These immune responses were specific to the serotype injected and were long lasting. These results demonstrate that optogenetic manipulations in monkeys trigger immune responses to AAV capsids, suggesting that vector readministration may have a higher likelihood of success by avoiding serotypes injected previously

AAV-mediated delivery of optogenetic constructs to the macaque brain triggers humoral immune responses

Gene delivery to the primate central nervous system via recombinant adeno-associated viral vectors (AAV) allows neurophysiologists to control and observe neural activity precisely. A current limitation of this approach is variability in vector transduction efficiency. Low levels of transduction can foil experimental manipulations, prompting vector readministration. The ability to make multiple vector injections into the same animal, even in cases where successful vector transduction has already been achieved, is also desirable. However, vector readministration has consequences for humoral immunity and gene delivery that depend on vector dosage and route of administration in complex ways. As part of optogenetic experiments in rhesus monkeys, we analyzed blood sera collected before and after AAV injections into the brain and quantified neutralizing antibodies to AAV using an in vitro assay. We found that injections of AAV1 and AAV9 vectors elevated neutralizing antibody titers consistently. These immune responses were specific to the serotype injected and were long lasting. These results demonstrate that optogenetic manipulations in monkeys trigger immune responses to AAV capsids, suggesting that vector readministration may have a higher likelihood of success by avoiding serotypes injected previously

Focal optogenetic suppression in macaque area MT biases direction discrimination and decision confidence, but only transiently

Insights from causal manipulations of brain activity depend on targeting the spatial and temporal scales most relevant for behavior. Using a sensitive perceptual decision task in monkeys, we examined the effects of rapid, reversible inactivation on a spatial scale previously achieved only with electrical microstimulation. Inactivating groups of similarly tuned neurons in area MT produced systematic effects on choice and confidence. Behavioral effects were attenuated over the course of each session, suggesting compensatory adjustments in the downstream readout of MT over tens of minutes. Compensation also occurred on a sub-second time scale: behavior was largely unaffected when the visual stimulus (and concurrent suppression) lasted longer than 350 ms. These trends were similar for choice and confidence, consistent with the idea of a common mechanism underlying both measures. The findings demonstrate the utility of hyperpolarizing opsins for linking neural population activity at fine spatial and temporal scales to cognitive functions in primates

Neuronal and behavioral responses to visual form

To support perception and guide behavior, the visual system must extract form information from retinal images. Form cues vary in their complexity and spatial extent. Human and macaque observers can detect forms that are defined by differences in texture. These cues are useful for segmenting figures from their backgrounds, and may also contribute to object identification. In the first experiment, I measured the development of behavioral sensitivity to texture-defined form in macaques. Infants could discriminate texture orientation as early as 6 weeks. Peak sensitivity continued to improve up to 40 weeks, reaching half of adult levels by 10–17 weeks. Surprisingly, texture sensitivity matured earlier than basic spatial acuity, and much earlier than global form sensitivity. Thus, different aspects of form vision develop over different rates, with local form mechanisms such as those implicated in texture processing maturing earlier than global form mechanisms. In the second experiment, I measured neuronal responses to texture-defined form in macaque visual area V2. Most cells responded best to texture patterns containing orientations that matched their preferences for luminance gratings. In some, these responses were modulated by aspects of the texture-defined form, either by its orientation or motion direction. Only a few cells preferred texture patterns whose orientations could not be predicted from their grating tuning, and thus showed true selectivity for the texture-defined form. Consistent with human imaging studies, these results suggest that signals related to texture-defined form in primates are found mainly in areas downstream of V2. In the third experiment, I identified V1 neurons projecting to V2 by antidromic electrical stimulation, and characterized their visual response properties. Projection neurons included both simple and complex cells. Most were tuned for orientation but not for direction, and were suppressed by large stimuli. In addition, most showed significant binocular phase interactions, and were better driven by luminance-modulated than chromatically-modulated stimuli. Thus, the heterogeneity of V1 inputs to V2 contributes to the diverse neuronal response types found there. These results provide a foundation for future work on how V1 inputs contribute to V2 receptive fields, particularly in the context of form vision