Superior Colliculus Research Articles

Longitudinal In Vivo Imaging of Retinal Cells with Tailored Adeno-Associated Virus Serotypes via Confocal Scanning Laser Ophthalmoscopy.

The dynamic nature of retinal cellular processes necessitates advancements in gene delivery and live monitoring techniques to enhance the understanding and treatment of ocular diseases. This study introduces an optimized adeno-associated virus (AAV) approach, utilizing specific serotypes and promoters to achieve optimal transfection efficiency in targeted retinal cells, including retinal ganglion cells (RGCs) and Müller glia. Leveraging the precision of confocal scanning laser ophthalmoscopy (CSLO), this work presents a non-invasive method for in vivo imaging that captures the longitudinal expression of AAV-mediated green fluorescent protein (GFP). This approach eliminates the need for terminal procedures, preserving the continuity of observation and the well-being of the subject. Furthermore, the GFP signal can be traced in AAV-infected RGCs along the visual pathway to the superior colliculus (SC) and lateral geniculate nucleus (LGN), enabling the potential for direct visual pathway mapping. These findings provide a detailed protocol and demonstrate the application of this powerful tool for real-time studies of retinal cell behavior, disease pathogenesis, and the efficacy of gene therapy interventions, offering valuable insights into the living retina and its connections.

Neuroprotective Effects of Astragalus Polysaccharide on Retina Cells and Ganglion Cell Projection in NMDA-Induced Retinal Injury.

Astragalus polysaccharide (APS), a water-soluble heteropolysaccharide, possesses immunomodulatory, anti-inflammatory, and cardioprotective properties. This study investigates the neuroprotective potential of APS in a model of N-Methyl-d-aspartic acid (NMDA)-induced retinal neurodegeneration, aiming to explore its potential as a treatment for retinal degenerative diseases. Retinal function was evaluated using electroretinography (ERG), optomotor reflex (OMR), and flash visual evoked potentials (FVEP). Retinal inflammatory responses were examined through immunohistochemistry, western blotting (WB), and quantitative reverse transcription PCR (qRT-PCR). To assess the integrity of visual projections, an intravitreal injection of adeno-associated virus (AAV) was employed to trace the projections of retinal ganglion cells (RGCs) to the visual centers. APS treatment conferred protection to retinal cells, as indicated by ERG and OMR assessments. And APS intervention mitigated NMDA-induced apoptosis, evidenced by a decrease in TUNEL-positive cells. Furthermore, APS treatment attenuated the NMDA-induced reduction in RGC projections to the visual centers, including the superior colliculus and lateral geniculate nucleus, as demonstrated by AAV tracing. Our findings reveal that APS shields the retina from NMDA-induced damage by inhibiting the NF-κB signaling pathway and reduces the detrimental effects of NMDA on RGC projections to the visual centers. These findings propose APS as a potential novel therapeutic agent for the treatment of retinal diseases.

Ndufs4 knockout mice with isolated complex I deficiency engage a futile adaptive brain response

Paediatric Leigh syndrome (LS) is an early-onset and fatal neurodegenerative disorder lacking treatment options. LS is frequently caused by mutations in the NDUFS4 gene, encoding an accessory subunit of mitochondrial complex I (CI), the first complex of the oxidative phosphorylation (OXPHOS) system. Whole-body Ndufs4 knockout (KO) mice (WB-KO mice) are widely used to study isolated CI deficiency, LS pathology and interventions. These animals develop a brain-specific phenotype via an incompletely understood pathomechanism. Here we performed a quantitative analysis of the sub-brain proteome in six-weeks old WB-KO mice vs. wildtype mice. Brain regions comprised of a brain slice (BrSl), cerebellum (CB), cerebral cortex (CC), hippocampus (HC), inferior colliculus (IC), and superior colliculus (SC). Proteome analysis demonstrated similarities between CC/HC, and between IC/SC, whereas BrSl and CB differed from these two groups and each other. All brain regions displayed greatly reduced levels of two CI structural subunits (NDUFS4, NDUFA12) and an increased level of the CI assembly factor NDUFAF2. The level of CI-Q module subunits was significantly more reduced in IC/SC than in BrSl/CB/CC/HC, whereas other OXPHOS complex levels were not reduced. Gene ontology and pathway analysis demonstrated specific and common proteome changes between brain regions.Across brain regions, upregulation of cold-shock-associated proteins, mitochondrial fatty acid (FA) oxidation and synthesis (mtFAS) were the most prominent. FA-related pathways were predominantly upregulated in CB and HC. Based upon these results, we argue that stimulation of these pathways is futile and pro-pathological and discuss alternative strategies for therapeutic intervention in LS. SignificanceThe Ndufs4 knockout mouse model is currently the most relevant and most widely used animal model to study the brain-linked pathophysiology of human Leigh Syndrome (LS) and intervention strategies. We demonstrate that the Ndufs4 knockout brain engages futile and pro-pathological responses. These responses explain both negative and positive outcomes of intervention studies in Leigh Syndrome mice and patients, thereby guiding novel intervention opportunities.

Saccades to both vision and touch are modified following adaptation but cross-modal transfers are asymmetrical.

Adaptation of reactive saccades (RS), made toward the sudden appearance of stimuli in our environment, is a plastic mechanism thought to occur at the motor level of saccade generation. As saccadic oculomotor commands integrate multisensory information in the parietal cortex and superior colliculus, adaptation of RS should occur not only toward visual but also tactile targets. In addition, saccadic adaptation in one modality (vision or touch) should transfer cross-modally. To test these predictions, we used the double-step target paradigm to adapt rightward saccades made at two different eccentricities toward the participants' index and middle fingers, identified either visually (experiment 1) or tactually (experiment 2). In each experiment, the rate of adaptation induced for the adapted modality and the rate of adaptation transfer to the nonadapted modality were compared with that measured in a control (no adaptation) session. Results revealed that touch-triggered RS can be adapted as well as visually triggered ones. Moreover, the transfer pattern was asymmetric: visual saccadic adaptation transferred fully to tactile saccades, whereas tactile saccadic adaptation, despite full generalization to nonadapted fingers, transferred only partially to visual saccades. These findings disclose that in the case of tactile saccades, adaptation can be elicited in the absence of postsaccadic visual feedback. In addition, the asymmetric adaptation transfer across sensory modalities suggests that the adaptation locus for tactile saccades may occur in part upstream of the final motor pathway common to all saccades. These findings bring new insights both on the functional loci(us) and on the error signals of RS adaptation. NEW & NOTEWORTHY The present study revealed that, as predicted from a large literature, adaptation of visual reactive saccades transfers to tactile saccades of the same as well as neighboring amplitudes. Furthermore, in a modified double-step target paradigm, tactile saccades exposed to repeated errors adapt with a similar rate and spatial generalization as visual saccades, but this adaptation only slightly transfers to visual saccades. These findings bring new information on saccadic adaptation processes.

Age-dependent deficits of auditory brainstem responses in juvenile Neurexin1α knockout rats.

Abnormal sensory processing is core to neuropsychiatric and neurodevelopmental disorders, such as schizophrenia and autism spectrum disorders. Developing efficient therapies requires understanding the basic sensory pathways and identifying circuit abnormalities during early development. Auditory brainstem responses (ABRs) are well-established biomarkers for auditory processing on the brainstem level. Beyond their advantage of being easily applicable in clinics (given their non-invasive nature), ABRs have high reproducibility in rodents and translate well to humans (e.g. wave identity), despite species differences (e.g. wave features). We hypothesized that ABRs would reveal sensory abnormalities in neurodevelopmental models with construct validity, such as Neurexin1α knockout (Nrxn1α KO) rats during their development. In a previous study, adult Nrxn1α KO rats showed altered cortical auditory-evoked potentials and impaired prediction error to auditory stimuli (Janz in Transl Psychiat, 12:455, 2022 ). This study used ABR measurements to assess brainstem physiology during auditory processing in Nrxn1α KO rats and their wild-type littermates. Therefore, we followed the development trajectories of ABRs from the age of 3weeks to 12weeks longitudinally. We found that juvenile Nrxn1α KO rats (3weeks of age) show altered ABRs, which normalized during further development. This alteration was confined to increased latency in waves II, III, and IV of the ABRs, suggesting impaired auditory processing on the level of the superior olivary complex and inferior colliculus. In conclusion, our results suggest that early but transient deficits in the processing of auditory information on the level of the brainstem are present in Nrxn1α KO rats, which may contribute to later cortical auditory processing deficits observed in adulthood. Our study emphasizes the value of ABRs as a functional readout of auditory brainstem circuit function with potential value as a translational biomarker.

Monosynaptic inputs to ventral tegmental area glutamate and GABA co-transmitting neurons.

A unique population of ventral tegmental area (VTA) neurons co-transmits glutamate and GABA. However, the circuit inputs to VTA VGluT2+VGaT+ neurons are unknown, limiting our understanding of their functional capabilities. By coupling monosynaptic rabies tracing with intersectional genetic targeting in male and female mice, we found that VTA VGluT2+VGaT+ neurons received diverse brain-wide inputs. The largest numbers of monosynaptic inputs to VTA VGluT2+VGaT+ neurons were from superior colliculus, lateral hypothalamus, midbrain reticular nucleus, and periaqueductal gray, whereas the densest inputs relative to brain region volume were from dorsal raphe nucleus, lateral habenula, and ventral tegmental area. Based on these and prior data, we hypothesized that lateral hypothalamus and superior colliculus inputs were glutamatergic neurons. Optical activation of glutamatergic lateral hypothalamus neurons activated VTA VGluT2+VGaT+ neurons regardless of stimulation frequency and resulted in flee-like ambulatory behavior. In contrast, optical activation of glutamatergic superior colliculus neurons activated VTA VGluT2+VGaT+ neurons for a brief period of time at high stimulation frequency and resulted in head rotation and arrested ambulatory behavior (freezing). Stimulation of glutamatergic lateral hypothalamus neurons, but not glutamatergic superior colliculus neurons, was associated with VTA VGluT2+VGaT+ footshock-induced activity. In addition, inhibition of lateral hypothalamus glutamatergic neurons disrupted VTA VGluT2+VGaT+ tailshock-induced activity. We interpret these results such that inputs to VTA VGluT2+VGaT+ neurons may integrate diverse signals related to the detection and processing of motivationally-salient outcomes.Significance Statement VTA glutamate neurons have roles in motivated behavior and unique neurotransmission capabilities. A specific VTA glutamate neuron subtype, those that co-transmit glutamate and GABA, have unique outcome signaling properties compared to other VTA cell-types. However, the circuits that regulate these neurons are unclear. We identified the whole-brain inputs to VTA glutamate and GABA co-transmitting neurons. We also identify two distinct glutamatergic inputs that activate VTA glutamate and GABA co-transmitting neurons and result in different behavioral repertoires suggestive of threat processing. Together, these results provide novel insights into the circuit and cell-type specific influences on VTA glutamate and GABA co-transmitting neuronal activity as integrators of motivationally salient outcomes.

The neural circuit of Superior colliculus to ventral tegmental area modulates visual cue associated with rewarding behavior in optical intracranial Self-Stimulation in mice

Visual system is the most important system of animal to cognize the information in outside world, and reward-related visual cues are the key factors in the consolidation and retrieval of reward memory. However, the neural circuit mechanism is still unclear. Superior Colliculus (SC) receive direct input from the retina and belong to the earliest stages of visual processing. Recent studies identified a specific pathway from SC to ventral tegmental area (VTA) that underlie specific innate behaviors, eg. flight or freezing, approach behaviors and so on. In present research, we investigated that inhibition of SC to VTA circuit with chemogenetics suppressed light cue-associated reward-seeking behaviors, while activation of the SC-VTA circuit with chemogenetic technology triggered the reward-seeking behaviors in optical intracranial self-stimulation for VTA DA neurons (oICSS) in mice. These findings suggest that neural circuit of SC-VTA mediates the retrieval of reward memory associated with visual cues, which will provide a new field for revealing the neural mechanism of pathological memory such as addiction.

Neural substrates for saccadic modulation of visual representations in mouse superior colliculus.

How do sensory systems account for stimuli generated by natural behavior? We addressed this question by examining how an ethologically relevant class of saccades modulates visual representations in the mouse superior colliculus (SC), a key region for sensorimotor integration. We quantified saccadic modulation by recording SC responses to visual probes presented at stochastic saccade-probe latencies. Saccades significantly impacted population representations of the probes, with early enhancement that began prior to saccades and pronounced suppression for several hundred milliseconds following saccades, independent of units' visual response properties or directional tuning. To determine the cause of saccadic modulation, we presented fictive saccades that simulated the visual experience during saccades without motor output. Some units exhibited similar modulation by fictive and real saccades, suggesting a sensory-driven origin of saccadic modulation, while others had dissimilar modulation, indicating a motor contribution. These findings advance our understanding of the neural basis of natural visual coding.

Primate superior colliculus is causally engaged in abstract higher-order cognition.

The superior colliculus is an evolutionarily conserved midbrain region that is thought to mediate spatial orienting, including saccadic eye movements and covert spatial attention. Here, we reveal a role for the superior colliculus in higher-order cognition, independent of its role in spatial orienting. We trained rhesus macaques to perform an abstract visual categorization task that involved neither instructed eye movements nor differences in covert attention. We compared neural activity in the superior colliculus and the posterior parietal cortex, a region previously shown to causally contribute to abstract category decisions. The superior colliculus exhibits robust encoding of learned visual categories, which is stronger than in the posterior parietal cortex and arises at a similar latency in the two areas. Moreover, inactivation of the superior colliculus markedly impaired animals' category decisions. These results demonstrate that the primate superior colliculus mediates abstract, higher-order cognitive processes that have traditionally been attributed to the neocortex.

GABAergic Retinal Ganglion Cells Projecting to the Superior Colliculus Mediate the Looming-Evoked Flight Response.

The looming stimulus-evoked flight response to approaching predators is a defensive behavior in most animals. However, how looming stimuli are detected in the retina and transmitted to the brain remains unclear. Here, we report that a group of GABAergic retinal ganglion cells (RGCs) projecting to the superior colliculus (SC) transmit looming signals from the retina to the brain, mediating the looming-evoked flight behavior by releasing GABA. GAD2-Cre and vGAT-Cre transgenic mice were used in combination with Cre-activated anterograde or retrograde tracer viruses to map the inputs to specific GABAergic RGC circuits. Optogenetic technology was used to assess the function of SC-projecting GABAergic RGCs (scpgRGCs) in the SC. FDIO-DTA (Flp-dependent Double-Floxed Inverted Open reading frame-Diphtheria toxin) combined with the FLP (Florfenicol, Lincomycin & Prednisolone) approach was used to ablate or silence scpgRGCs. In the mouse retina, GABAergic RGCs project to different brain areas, including the SC. ScpgRGCs are monosynaptically connected to parvalbumin-positive SC neurons known to be required for the looming-evoked flight response. Optogenetic activation of scpgRGCs triggers GABA-mediated inhibition in SC neurons. Ablation or silencing of scpgRGCs compromises looming-evoked flight responses without affecting image-forming functions. Our study reveals that scpgRGCs control the looming-evoked flight response by regulating SC neurons via GABA, providing novel insight into the regulation of innate defensive behaviors.

Face-related activity in superior colliculus and temporal cortex of primates

Face-related activity in superior colliculus and temporal cortex of primates

Mixed Selectivity for Target Selection Biases in the Superior Colliculus

Mixed Selectivity for Target Selection Biases in the Superior Colliculus

Selectivity for binocular disparity in the primate superior colliculus may not be directly inherited from V1

Selectivity for binocular disparity in the primate superior colliculus may not be directly inherited from V1

Saccadic decision making based on uncertain auditory cues in monkey superior colliculus

Saccadic decision making based on uncertain auditory cues in monkey superior colliculus

Visual responses to local vs. full-field textures in the primate superior colliculus

Visual responses to local vs. full-field textures in the primate superior colliculus

Probing correlates of saccadic suppression in the primate superior colliculus and primary visual cortex using simulated and real saccades

Probing correlates of saccadic suppression in the primate superior colliculus and primary visual cortex using simulated and real saccades

Electrophysiological properties of neurons in the visual sensory layers of the superior colliculus in early postnatal mice

Objective: To investigate the action potential firing patterns of neurons in the visual sensory layers of the superior colliculus in early postnatal mice and the electrophysiological characteristics of neurons with different firing patterns. Methods: This experimental study utilized whole-cell patch-clamp recordings performed on neurons in the visual sensory layers of the superior colliculus using brain slices from 57 healthy male C57BL/6J mice aged 14 to 20 days (weighing 5.0 to 8.9 g) using brain slices. In current-clamp mode, action potential characteristics were analyzed based on the first action potential generated by depolarizing current, and the firing patterns of neurons were recorded using step depolarizing currents. Neuronal firing patterns were analyzed using hierarchical clustering, and the active electrical properties of neurons with different firing patterns were compared. Results: A total of 135 neurons from the visual sensory layers of the superior colliculus were successfully recorded. Cluster analysis of the neuronal firing patterns identified three types of firing patterns: tonic firing (97, 72%), phasic firing (26, 19%), and single firing (12, 9%). The number of action potentials for each firing pattern was 13.30±7.38, 3.73±3.61, and 0.83±0.39, respectively, with significant differences (P<0.001). There was no significant difference in the membrane potential response to step currents among the three firing pattern types (P>0.05). The action potential amplitudes were (60.45±12.22), (53.67±13.20), and (44.04± 12.92) mV, and the afterhyperpolarization amplitudes were (13.45±13.79), (12.02±13.11), and (20.75±2.85) mV, respectively. The maximum rising slopes were (171.29±77.46), (130.14±61.83), and (78.89±37.08) V/s, and the maximum falling slopes were (-76.33±33.61), (-68.17±31.65), and (-47.97±13.92) V/s, respectively, with all differences being statistically significant (all P<0.05). There were no significant differences in the resting membrane potential, action potential threshold, half-width, and afterhyperpolarization duration among the three firing pattern types (all P>0.05). Conclusions: In the early postnatal mice, neurons in the visual sensory layers of the superior colliculus exhibit three distinct firing patterns: tonic, phasic, and single firing. These firing pattern types show significant differences in action potential amplitude, afterhyperpolarization amplitude, maximum rising slopes, and maximum falling slopes.

Retinal Input to Macaque Superior Colliculus Derives from Branching Axons Projecting to the Lateral Geniculate Nucleus.

The superior colliculus receives a direct projection from retinal ganglion cells. In primates, it remains unknown if the same ganglion cells also supply the lateral geniculate nucleus. To address this issue, a double-label experiment was performed in 2 male macaques. The animals fixated a target while injection sites were scouted in the superior colliculus by recording and stimulating with a tetrode. Once suitable sites were identified, cholera toxin - subunit B Alexa Fluor 488 was injected via an adjacent micropipette. In a subsequent acute experiment, cholera toxin subunit B - Alexa Fluor 555 was injected into the lateral geniculate nucleus at matching retinotopic locations. After a brief survival period, ganglion cells were examined in retinal flatmounts. The percentage of double-labeled cells varied locally, depending on the relative efficiency of retrograde transport by each tracer and the precision of retinotopic overlap of injection sites in each target nucleus. In counting boxes with extensive overlap, 76-98% of ganglion cells projecting to the superior colliculus were double-labeled. Cells projecting to the superior colliculus constituted 4.0 - 6.7% of the labeled ganglion cell population. In one particularly large zone, there were 5,746 cells labeled only by CTB-AF555, 561cells double-labeled by CTB-AF555 and CTB-AF488, but no cell labeled only by CTB-AF488. These data indicate that retinal input to the macaque superior colliculus arises from a collateral axonal branch supplied by about 5% of the ganglion cells that project to the lateral geniculate nucleus. Surprisingly, there exist no ganglion cells that project exclusively to the SC.Significance statement The retina contains a multitude of ganglion cell classes, projecting in parallel to different brain targets. The superior colliculus receives retinal input, but its source remains controversial. In two macaques, a green tracer was injected into the superior colliculus and an orange tracer into the lateral geniculate nucleus. When retinotopic overlap was optimal, ganglion cells containing the green tracer were also labeled by the orange tracer. This finding indicates that retinal input to the superior colliculus arises from axon collaterals of ganglion cells that project to the lateral geniculate nucleus, even though these two retinal targets serve utterly different functions. The next challenge is to determine the purpose of this projection and why it is shared.

A flexible high-precision photoacoustic retinal prosthesis.

Retinal degenerative diseases of photoreceptors are a leading cause of blindness with no effective treatment. Retinal prostheses seek to restore sight by stimulating remaining retinal cells. We here present a photoacoustic retinal stimulation technology. We designed a polydimethylsiloxane and carbon-based flexible film that converts near-infrared laser pulses into a localized acoustic field, aiming at high-precision acoustic activation of mechanosensitive retinal cells. This photoacoustic stimulation of wild-type and degenerated ex vivo retinae resulted in robust and localized retinal ganglion cell activation with sub-100-µm resolution in both wild-type and degenerated ex vivo retinae. Our millimeter-size photoacoustic film generated neural activation in vivo along the visual pathway to the superior colliculus, as measured by functional ultrasound imaging when the film was implanted in the rat subretinal space and stimulated by pulsed laser. Biosafety of the film was indicated by absence of short-term adverse effect under optical coherence tomography retinal imaging, while local thermal increase was measured below 1 °C. These findings demonstrate the potential of our photoacoustic stimulation for visual restoration in blind patients with a high spatial precision and a large field of view.

Functional segregation and dynamic integration of the corticotectal descending signal in rat

The superior colliculus (SC) receives inputs from various brain regions in a layer- and radial subregion-specific manner, but whether the SC exhibits subregion-specific dynamics remains unclear. To address this issue, we recorded the spiking activity of single SC neurons while photoactivating cortical areas in awake head-fixed Thy1-ChR2 rats. We classified 309 neurons that responded significantly into 8 clusters according to the response dynamics. Among them, neurons with monophasic excitatory responses (7–12 ms latency) that returned to baseline within 20 ms were commonly observed in the optic and intermediate gray layers of centromedial and centrolateral SC. In contrast, neurons with complex polyphasic responses were commonly observed in the deep layers of the anterolateral SC. Cross-correlation analysis suggested that the complex pattern could be only partly explained by an internal circuit of the deep gray layer. Our results indicate that medial to centrolateral SC neurons simply relay cortical activity, whereas neurons in the deep layers of the anterolateral SC dynamically integrate inputs from the cortex, SNr, CN, and local circuits. These findings suggest a spatial gradient in SC integration, with a division of labor between simple relay circuits and those integrating complex dynamics.