Schizophrenia Animal Modeling with Epidermal Growth Factor and Its Homologs: Their Connections to the Inflammatory Pathway and the Dopamine System.

Epidermal growth factor (EGF) and its homologs, such as neuregulins, bind to ErbB (Her) receptor kinases and regulate glial differentiation and dopaminergic/GABAergic maturation in the brain and are therefore implicated in schizophrenia neuropathology involving these cell abnormalities. In this review, we summarize the biological activities of the EGF family and its neuropathologic association with schizophrenia, mainly overviewing our previous model studies and the related articles. Transgenic mice as well as the rat/monkey models established by perinatal challenges of EGF or its homologs consistently exhibit various behavioral endophenotypes relevant to schizophrenia. In particular, post-pubertal elevation in baseline dopaminergic activity may illustrate the abnormal behaviors relevant to positive and negative symptoms as well as to the timing of this behavioral onset. With the given molecular interaction and transactivation of ErbB receptor kinases with Toll-like receptors (TLRs), EGF/ErbB signals are recruited by viral infection and inflammatory diseases such as COVID-19-mediated pneumonia and poxvirus-mediated fibroma and implicated in the immune-inflammatory hypothesis of schizophrenia. Finally, we also discuss the interaction of clozapine with ErbB receptor kinases as well as new antipsychotic development targeting these receptors.

Rapid development of motion-streak coding in the mouse visual cortex.

Despite its importance, the development of higher visual areas (HVAs) at the cellular resolution remains largely unknown. Here, we conducted 2-photon calcium imaging of mouse HVAs lateromedial (LM) and anterolateral (AL) and V1 to observe developmental changes in visual response properties. HVA neurons showed selectivity for orientations and directions similar to V1 neurons at eye opening, which became sharper in the following weeks. Neurons in all areas over all developmental stages tended to respond selectively to dots moving along an axis perpendicular to their preferred orientation at slow speeds, suggesting a certain level of conventional motion coding already at eye opening. In contrast, at high speeds, many neurons responded to dots moving along the axis parallel to the preferred orientation in older animals but rarely after eye opening, indicating a lack of motion-streak coding in the earlier stage. Together, our results uncover the development of visual properties in HVAs.

Motion Streak Neurons in the Mouse Visual Cortex.

Motion streaks are smeared representation of fast-moving objects due to temporal integration. Here, we test for motion streak signals in mice with two-photon calcium imaging. For small dots moving at low speeds, neurons in primary visual cortex (V1) encode the component motion, with preferred direction along the axis perpendicular to their preferred orientation. At high speeds, V1 neurons prefer the direction along the axis parallel to their preferred orientation, as expected for encoding motion streaks. Whereas some V1 neurons (∼20%) display a switch of preferred motion axis with increasing speed, others (>40%) respond specifically to high speeds at the parallel axis. Motion streak neurons are also seen in higher visual lateromedial (LM), anterolateral (AL), and rostrolateral (RL) areas, but with higher transition speeds, and many still prefer the perpendicular axis even with fast motion. Our results thus indicate that diverse motion encoding exists in mouse visual cortex, with intriguing differences among visual areas.

Feedback inhibition derived from the posterior parietal cortex regulates the neural properties of the mouse visual cortex.

Feedback regulation from the higher association areas is thought to control the primary sensory cortex, contribute to the cortical processing of sensory information, and work for higher cognitive functions such as multimodal integration and attentional control. However, little is known about the underlying neural mechanisms. Here, we show that the posterior parietal cortex (PPC) persistently inhibits the activity of the primary visual cortex (V1) in mice. Activation of the PPC causes the suppression of visual responses in V1 and induces the short-term depression, which is specific to visual stimuli. In contrast, pharmacological inactivation of the PPC or disconnection of cortical pathways from the PPC to V1 results in an effect of transient enhancement of visual responses in V1. Two-photon calcium imaging demonstrated that the cortical disconnection caused V1 excitatory neurons an enhancement of visual responses and a reduction of orientation selectivity index (OSI). These results show that the PPC regulates the response properties of V1 excitatory neurons. Our findings reveal one of the functions of the PPC, which may contribute to higher brain functions in mice.

Impaired clustered protocadherin-α leads to aggregated retinogeniculate terminals and impaired visual acuity in mice.

Clustered protocadherins (cPcdhs) comprising cPcdh-α, -ß, and -γ, encode a large family of cadherin-like cell-adhesion molecules specific to neurons. Impairment of cPcdh-α results in abnormal neuronal projection patterns in specific brain areas. To elucidate the role of cPcdh-α in retinogeniculate projections, we investigated the morphological patterns of retinogeniculate terminals in the lateral geniculate (LG) nucleus of mice with impaired cPcdh-α. We found huge aggregated retinogeniculate terminals in the dorsal LG nucleus, whereas no such aggregated terminals derived from the retina were observed in the olivary pretectal nucleus and the ventral LG nucleus. These aggregated terminals appeared between P10 and P14, just before eye opening and at the beginning of the refinement stage of the retinogeniculate projections. Reduced visual acuity was observed in adult mice with impaired cPcdh-α, whereas the orientation selectivity and direction selectivity of neurons in the primary visual cortex were apparently normal. These findings suggest that cPcdh-α is required for adequate spacing of retinogeniculate projections, which may be essential for normal development of visual acuity.

The extrageniculate visual pathway generates distinct response properties in the higher visual areas of mice.

BACKGROUND: Visual information conveyed through the extrageniculate visual pathway, which runs from the retina via the superior colliculus (SC) and the lateral posterior nucleus (LPN) of the thalamus to the higher visual cortex, plays a critical role in the visual capabilities of many mammalian species. However, its functional role in the higher visual cortex remains unclear. Here, we observed visual cortical area activity in anesthetized mice to evaluate the role of the extrageniculate pathway on their specialized visual properties. RESULTS: The preferred stimulus velocities of neurons in the higher visual areas (lateromedial [LM], anterolateral [AL], anteromedial [AM], and rostrolateral [RL] areas) were measured using flavoprotein fluorescence imaging and two-photon calcium imaging and were higher than those in the primary visual cortex (V1). Further, the velocity-tuning properties of the higher visual areas were different from each other. The response activities in these areas decreased after V1 ablation; however, the visual properties' differences were preserved. After SC destruction, these preferences for high velocities disappeared, and their tuning profiles became similar to that of the V1, whereas the tuning profile of the V1 remained relatively normal. Neural tracer experiments revealed that each of these higher visual areas connected with specific subregions of the LPN. CONCLUSIONS: The preservation of visual property differences among the higher visual areas following V1 lesions and their loss following SC lesions indicate that pathways from the SC through the thalamus to higher cortical areas are sufficient to support these differences.

Visual map shifts based on whisker-guided cues in the young mouse visual cortex.

Mice navigate nearby space using their vision and whiskers, and young mice learn to integrate these heterogeneous inputs in perceptual space. We found that cortical responses were depressed in the primary visual cortex of young mice after wearing a monocular prism. This depression was uniformly observed in the primary visual cortex and was eliminated by whisker trimming or lesions in the posterior parietal cortex. Compensatory visual map shifts of responses elicited via the eye that had worn the prism were also observed. As a result, cortical responses elicited via each eye were clearly separated when a visual stimulus was placed in front of the mice. A comparison of response areas before and after prism wearing indicated that the map shifts were produced by depression with spatial eccentricity. Visual map shifts based on whisker-guided cues may serve as a model for investigating the cellular and molecular mechanisms underlying higher sensory integration in the mammalian brain.

Auditory cortical areas activated by slow frequency-modulated sounds in mice.

Species-specific vocalizations in mice have frequency-modulated (FM) components slower than the lower limit of FM direction selectivity in the core region of the mouse auditory cortex. To identify cortical areas selective to slow frequency modulation, we investigated tonal responses in the mouse auditory cortex using transcranial flavoprotein fluorescence imaging. For differentiating responses to frequency modulation from those to stimuli at constant frequencies, we focused on transient fluorescence changes after direction reversal of temporally repeated and superimposed FM sweeps. We found that the ultrasonic field (UF) in the belt cortical region selectively responded to the direction reversal. The dorsoposterior field (DP) also responded weakly to the reversal. Regarding the responses in UF, no apparent tonotopic map was found, and the right UF responses were significantly larger in amplitude than the left UF responses. The half-max latency in responses to FM sweeps was shorter in UF compared with that in the primary auditory cortex (A1) or anterior auditory field (AAF). Tracer injection experiments in the functionally identified UF and DP confirmed that these two areas receive afferent inputs from the dorsal part of the medial geniculate nucleus (MG). Calcium imaging of UF neurons stained with fura-2 were performed using a two-photon microscope, and the presence of UF neurons that were selective to both direction and direction reversal of slow frequency modulation was demonstrated. These results strongly suggest a role for UF, and possibly DP, as cortical areas specialized for processing slow frequency modulation in mice.

Transcranial flavoprotein fluorescence imaging of mouse cortical activity and plasticity.

Endogenous fluorescence signals derived from mitochondria reflect activity-dependent changes in brain metabolism and may be exploited in functional brain imaging. Endogenous flavoprotein fluorescence imaging in mice is especially important because many genetically manipulated strains of mice are available and the transparent skull of mice allows transcranial fluorescence imaging of cortical activities. In the primary sensory areas of mice, cortical activities and experience-dependent plasticity have been investigated using transcranial fluorescence imaging. Furthermore, differential imaging, based on stimulus specificity of cortical areas, distinguished activities in higher visual areas around the primary visual cortex from those in primary visual cortex. The combination of transcranial fluorescence imaging with the suppression of cortical activities using photobleaching of flavoproteins is expected to aid in elucidating the roles of sensory cortices including higher areas in mice.

Roles of nitric oxide as a vasodilator in neurovascular coupling of mouse somatosensory cortex.

Neural activities trigger regional vasodilation in the brain. Diffusible messengers such as nitric oxide (NO) and prostanoids are considered to work as vasodilators in neurovascular coupling. However, their roles are still controversial. In the present study, cortical images of neural activities and vasodilation were recorded through the intact skull of C57BL/6 mice anesthetized with urethane. Flavoprotein fluorescence responses elicited by vibratory hindpaw stimulation were followed by darkening of arteriole images reflecting vasodilation in the somatosensory cortex. Vasodilation was also observed in light reflection images at the wavelength of 570 nm in the same mice. We perfused the surface of the cortex under the skull with 100 microM N(G)-nitro-l-arginine (l-NA), an inhibitor of NO synthase (NOS), and 10 microM indomethacin, an inhibitor of cyclooxygenase (COX). These drugs suppressed vasodilation without changing flavoprotein fluorescence responses. A mixture of l-NA and indomethacin almost completely eliminated vasodilation. In mice lacking neuronal NOS (nNOS), activity-dependent vasodilation was significantly suppressed compared with that in littermate control mice, while that in mice lacking cytosolic phospholipase A2 alpha (cPLA2alpha) was unchanged. These results indicate that NO works as a vasodilator in neurovascular coupling of the mouse somatosensory cortex.

Enduring critical period plasticity visualized by transcranial flavoprotein imaging in mouse primary visual cortex.

Experience-dependent plasticity in the visual cortex was investigated using transcranial flavoprotein fluorescence imaging in mice anesthetized with urethane. On- and off-responses in the primary visual cortex were elicited by visual stimuli. Fluorescence responses and field potentials elicited by grating patterns decreased similarly as contrasts of visual stimuli were reduced. Fluorescence responses also decreased as spatial frequency of grating stimuli increased. Compared with intrinsic signal imaging in the same mice, fluorescence imaging showed faster responses with approximately 10 times larger signal changes. Retinotopic maps in the primary visual cortex and area LM were constructed using fluorescence imaging. After monocular deprivation (MD) of 4 d starting from postnatal day 28 (P28), deprived eye responses were suppressed compared with nondeprived eye responses in the binocular zone but not in the monocular zone. Imaging faithfully recapitulated a critical period for plasticity with maximal effects of MD observed around P28 and not in adulthood even under urethane anesthesia. Visual responses were compared before and after MD in the same mice, in which the skull was covered with clear acrylic dental resin. Deprived eye responses decreased after MD, whereas nondeprived eye responses increased. Effects of MD during a critical period were tested 2 weeks after reopening of the deprived eye. Significant ocular dominance plasticity was observed in responses elicited by moving grating patterns, but no long-lasting effect was found in visual responses elicited by light-emitting diode light stimuli. The present results indicate that transcranial flavoprotein fluorescence imaging is a powerful tool for investigating experience-dependent plasticity in the mouse visual cortex.

Strain-dependent behavioral alterations induced by peripheral interleukin-1 challenge in neonatal mice.

Interleukin-1 (IL-1) is implicated in the pathogenesis of various psychiatric diseases. Peripheral administration of IL-1alpha to neonatal rats induces cognitive and behavioral abnormalities and, therefore, the IL-1alpha-treated animals might serve as a schizophrenia model. The present study assessed genetic influences on IL-1alpha-triggered behavioral impairments, using four different strains of neonatal mice, C3H/He, DBA/2, C57BL/6, and ddY. Neonatal treatments with IL-1alpha differentially altered adult behavioral/cognitive traits in a strain-dependent manner. IL-1alpha treatment decreased prepulse inhibition in DBA/2 and C57BL/6 mice but not in C3H/He and ddY. The treatment increased locomotor activity and startle responses in DBA/2 mice and, conversely, decreased startle responses in C3H/He mice. Behavioral alterations were most remarkable in DBA/2 mice but undetectable in ddY mice. The magnitudes of IL-1alpha actions differed between the brain and periphery and were influenced by mouse genetic background. The IL-1-triggered acute signaling, Ikappa-B degradation, was significant in the frontal cortex of DBA/2 mice and in the hypothalamus of C3H/He mice. An increase in brain p38 MAP kinase phosphorylation was also most marked in the DBA/2 strain. In contrast, subchronic influences of IL-1alpha injections failed to illustrate the strain-dependent behavioral alterations. The peripheral effects of IL-1alpha did not match the strain-dependency of the behavioral alterations, either. Acceleration of tooth eruption and eyelid opening as well as attenuation of weight gain was most marked in C3H/He mice and the induction of serum amyloid protein was the largest in ddY mice. Thus, the peripheral effects of IL-1alpha in DBA/2 mice were relatively inferior to those in the other strains. The present animal study suggests that, in early postnatal development, circulating IL-1alpha trigger brain cytokine signaling and produce distinct influences on later neurobehavioral traits, both depending on genetic background.

Distinct influences of neonatal epidermal growth factor challenge on adult neurobehavioral traits in four mouse strains.

Epidermal growth factor (EGF) receptor (ErbB1) signals regulate dopaminergic development and function and are implicated in schizophrenia. We evaluated genetic effects on neurobehavioral changes induced by neonatal EGF administration, using four mouse strains. Subcutaneous EGF administration increased phosphorylation of brain ErbB1 in all strains, although DBA/2 and C57BL/6 mice had lower basal phosphorylation. Neonatal EGF treatment differentially influenced physical and behavioral/cognitive development, depending on mouse strain. Prepulse inhibition was decreased in DBA/2 and C57BL/6 mice but not C3H/He and ddY mice. Locomotor activity was accelerated in DBA/2 mice, but reduced in ddY mice. EGF treatment enhanced fear-learning performance with a tone cue in DBA/2 mice, but decreased performance with tone and context cues in C3H/He and ddY mice, respectively. The strain-dependent behavioral sensitivity was correlated with basal ErbB1 phosphorylation. Genetic components regulating brain ErbB1 signaling strongly influence the direction and strength of behavioral responses stemming from the neonatal neurotrophic perturbation.

Perinatal inflammatory cytokine challenge results in distinct neurobehavioral alterations in rats: implication in psychiatric disorders of developmental origin.

Maternal stress, viral infection, and obstetric complications, which trigger cytokine signaling, are hypothesized to be involved in schizophrenia and its related disorders. The etiologic contribution of individual cytokines to such psychiatric disorders, however, remains to be evaluated. To estimate the impact of peripheral cytokine challenge on neurobehavioral development, we examined effects of four proinflammatory cytokines on rat neonates and their later behavioral performance. Sublethal doses of interleukin-1 alpha, interleukin-2, interleukin-6, or interferon-gamma were subcutaneously administered to rat pups for 9 days. These animals displayed alterations in physical development, including lower weight gain and/or accelerated eyelid opening. In addition, behavioral abnormalities related to fear/anxiety levels and sensorimotor gating emerged at different developmental stages, depending on the cytokine species administered. During juvenile stages, neonatal interleukin-2 treatment increased exploratory locomotor activity, whereas other cytokine treatments did not. At the post-puberty stage, however, the interleukin-2-induced abnormal motor activity became undetectable, whereas interleukin-1 alpha-treated rats developed abnormalities in startle response, prepulse inhibition (PPI), and social interaction. Subchronic treatment of an anti-psychotic drug, clozapine, ameliorated the impairment of prepulse inhibition without altering startle responses. These animal experiments illustrate that, during early postnatal development, inflammatory cytokine challenge in the periphery can induce future psycho-behavioral and/or cognitive impairments with various latencies, although the pathologic mechanisms underlying these abnormalities remain to be determined.