Central amygdala contributes to stimulus facilitation and pre-stimulus vigilance during cerebellar learning.

Our previous studies found that the central amygdala (CeA) modulates cerebellum-dependent eyeblink conditioning (EBC) using muscimol inactivation. We also found that CeA inactivation decreases cerebellar neuronal activity during the conditional stimulus (CS) from the start of training. Based on these findings, we hypothesized that the CeA facilitates CS input to the cerebellum. The current study tested the CS facilitation hypothesis using optogenetic inhibition with archaerhodopsin (Arch) and excitation with channelrhodopsin (ChR2) of the CeA during EBC in male rats. Optogenetic manipulations were administered during the 400 ms tone CS or during a 400 ms pre-CS period. As predicted by the CS facilitation hypothesis CeA inhibition during the CS impaired EBC and CeA excitation during the CS facilitated EBC. Unexpectedly, CeA inhibition just prior to the CS also impaired EBC, while CeA excitation during the pre-CS pathway did not facilitate EBC. The results suggest that the CeA contributes to CS facilitation and vigilance during the pre-CS period. These putative functions of the CeA may be mediated through separate output pathways from the CeA to the cerebellum.

Knockdown of the Non-canonical Wnt Gene Prickle2 Leads to Cerebellar Purkinje Cell Abnormalities While Cerebellar-Mediated Behaviors Remain Intact.

Autism spectrum disorders (ASD) involve brain wide abnormalities that contribute to a constellation of symptoms including behavioral inflexibility, cognitive dysfunction, learning impairments, altered social interactions, and perceptive time difficulties. Although a single genetic variation does not cause ASD, genetic variations such as one involving a non-canonical Wnt signaling gene, Prickle2, has been found in individuals with ASD. Previous work looking into phenotypes of Prickle2 knock-out (Prickle2-/-) and heterozygous mice (Prickle2-/+) suggest patterns of behavior similar to individuals with ASD including altered social interaction and behavioral inflexibility. Growing evidence implicates the cerebellum in ASD. As Prickle2 is expressed in the cerebellum, this animal model presents a unique opportunity to investigate the cerebellar contribution to autism-like phenotypes. Here, we explore cerebellar structural and physiological abnormalities in animals with Prickle2 knockdown using immunohistochemistry, whole-cell patch clamp electrophysiology, and several cerebellar-associated motor and timing tasks, including interval timing and eyeblink conditioning. Histologically, Prickle2-/- mice have significantly more empty spaces or gaps between Purkinje cells in the posterior lobules and a decreased propensity for Purkinje cells to fire action potentials. These structural cerebellar abnormalities did not impair cerebellar-associated behaviors as eyeblink conditioning and interval timing remained intact. Therefore, although Prickle-/- mice show classic phenotypes of ASD, they do not recapitulate the involvement of the adult cerebellum and may not represent the pathophysiological heterogeneity of the disorder.

Shaking up the silence: consequences of HMGN1 antagonizing PRC2 in the Down syndrome brain.

Intellectual disability is a well-known hallmark of Down Syndrome (DS) that results from the triplication of the critical region of human chromosome 21 (HSA21). Major studies were conducted in recent years to gain an understanding about the contribution of individual triplicated genes to DS-related brain pathology. Global transcriptomic alterations and widespread changes in the establishment of neural lineages, as well as their differentiation and functional maturity, suggest genome-wide chromatin organization alterations in trisomy. High Mobility Group Nucleosome Binding Domain 1 (HMGN1), expressed from HSA21, is a chromatin remodeling protein that facilitates chromatin decompaction and is associated with acetylated lysine 27 on histone H3 (H3K27ac), a mark correlated with active transcription. Recent studies causatively linked overexpression of HMGN1 in trisomy and the development of DS-associated B cell acute lymphoblastic leukemia (B-ALL). HMGN1 has been shown to antagonize the activity of the Polycomb Repressive Complex 2 (PRC2) and prevent the deposition of histone H3 lysine 27 trimethylation mark (H3K27me3), which is associated with transcriptional repression and gene silencing. However, the possible ramifications of the increased levels of HMGN1 through the derepression of PRC2 target genes on brain cell pathology have not gained attention. In this review, we discuss the functional significance of HMGN1 in brain development and summarize accumulating reports about the essential role of PRC2 in the development of the neural system. Mechanistic understanding of how overexpression of HMGN1 may contribute to aberrant brain cell phenotypes in DS, such as altered proliferation of neural progenitors, abnormal cortical architecture, diminished myelination, neurodegeneration, and Alzheimer's disease-related pathology in trisomy 21, will facilitate the development of DS therapeutic approaches targeting chromatin.

The dorsal hippocampus' role in context-based timing in rodents.

To act proactively, we must predict when future events will occur. Individuals generate temporal predictions using cues that indicate an event will happen after a certain duration elapses. Neural models of timing focus on how the brain represents these cue-duration associations. However, these models often overlook the fact that situational factors frequently modulate temporal expectations. For example, in realistic environments, the intervals associated with different cues will often covary due to a common underlying cause. According to the 'common cause hypothesis,' observers anticipate this covariance such that, when one cue's interval changes, temporal expectations for other cues shift in the same direction. Furthermore, as conditions will often differ across environments, the same cue can mean different things in different contexts. Therefore, updates to temporal expectations should be context-specific. Behavioral work supports these predictions, yet their underlying neural mechanisms are unclear. Here, we asked whether the dorsal hippocampus mediates context-based timing, given its broad role in context-conditioning. Specifically, we trained rats with either hippocampal or sham lesions that two cues predicted reward after either a short or long duration elapsed (e.g., tone-8 s/light-16 s). Then, we moved rats to a new context and extended the long cue's interval (e.g., light-32 s). This caused rats to respond later to the short cue, despite never being trained to do so. Importantly, when returned to the initial training context, sham rats shifted back toward both cues' original intervals. In contrast, lesion rats continued to respond at the long cue's newer interval. Surprisingly, they still showed contextual modulation for the short cue, responding earlier like shams. These data suggest the hippocampus only mediates context-based timing if a cue is explicitly paired and/or rewarded across distinct contexts. Furthermore, as lesions did not impact timing measures at baseline or acquisition for the long cue's new interval, our data suggests that the hippocampus only modulates timing when context is relevant.

Theta oscillations in rat infralimbic cortex are associated with the inhibition of cocaine seeking during extinction.

Infralimbic cortical (IL) manipulations indicate that this region mediates extinction learning and suppresses cocaine seeking following cocaine self-administration. However, little work has recorded IL activity during the inhibition of cocaine seeking due to the difficulty of determining precisely when cocaine-seeking behaviour is inhibited within a cocaine-seeking session. The present study used in vivo electrophysiology to examine IL activity across extinction as well as during cocaine self-administration and reinstatement. Sprague-Dawley rats underwent 6-h access cocaine self-administration in which the response lever was available during discrete signalled trials, a procedure which allowed for the comparison between epochs of cocaine seeking versus the inhibition thereof. Subsequently, rats underwent extinction and cocaine-primed reinstatement using the same procedure. Results indicate that theta rhythms (4-10 Hz) dominated IL local-field potential (LFP) activity during all experimental stages. During extinction, theta power fluctuated significantly surrounding the lever press and was lower when rats engaged in cocaine seeking versus when they withheld from doing so. These patterns of oscillatory activity differed from self-administration and reinstatement stages. Single-unit analyses indicate heterogeneity of IL unit responses, supporting the idea that multiple neuronal subpopulations exist within the IL and promote the expression of different and even opposing cocaine-seeking behaviours. Together, these results are consistent with the idea that aggregate synaptic and single-unit activity in the IL represent the engagement of the IL in action monitoring to promote adaptive behaviour in accordance with task contingencies and reveal critical insights into the relationship between IL activity and the inhibition of cocaine seeking.

Amygdala central nucleus modulation of cerebellar learning in female rats.

Previous studies found that inactivation of the central amygdala (CeA) severely impaired acquisition of cerebellum-dependent delay eye-blink conditioning (EBC) in male rats and rabbits. Sex differences in EBC and the effects of stress on EBC have been reported and might be related to sex differences in amygdala modulation of cerebellar learning. The current study examined the effects of CeA inactivation with muscimol on acquisition and retention of EBC in female rats. Like male rats, CeA inactivation in female rats severely impaired EBC acquisition and retention. Comparison of the female data with previously published data from males indicates no substantive sex differences in the effects of CeA inactivation on acquisition or retention of EBC. The results indicate that amygdala modulation of cerebellar learning is not sex-specific. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Amygdala central nucleus modulation of cerebellar learning with a visual conditioned stimulus.

Previous studies found that reversible inactivation of the central amygdala (CeA) severely impairs acquisition and retention of cerebellum-dependent eye-blink conditioning (EBC) with an auditory conditioned stimulus (CS). A monosynaptic pathway between the CeA and basilar pontine nuclei (BPN) may be capable of facilitating cerebellar learning. However, given that the CeA projects to the medial auditory thalamus, a critical part of the auditory CS pathway in EBC, the CeA influence on cerebellar learning could be specific to auditory stimuli. Here we examined the generality of CeA facilitation of EBC acquisition and retention in rats using a visual CS. As in our previous studies using an auditory CS, inactivation of the CeA with muscimol severely impaired acquisition and retention of EBC with a visual CS. Extending training to 15 100-trial sessions resulted in acquisition of EBC, indicating that the CeA plays a modulatory role in cerebellar learning and is not part of the necessary neural circuitry for EBC. Tract-tracing experiments verified that axons from the CeA reach both the BPN and medial auditory thalamus (part of the necessary auditory CS pathway), but were not found in the ventral lateral geniculate (part of the necessary visual CS pathway). The neuroanatomical results suggest that the CeA most likely modulates cerebellar learning through its projection to the BPN. The findings of the current study are consistent with the hypothesis that the CeA modulates cerebellar learning by increasing CS-related sensory input to the cerebellar cortex and interpositus nucleus via the BPN. This increase in CS-related input is thought to constitute an increase in attention to the CS during EBC.

Amygdala Modulation of Cerebellar Learning.

Previous studies showed that amygdala lesions or inactivation slow the acquisition rate of cerebellum-dependent eyeblink conditioning, a type of associative motor learning. The current study was designed to determine the behavioral nature of amygdala-cerebellum interactions, to identify the neural pathways underlying amygdala-cerebellum interactions, and to examine how the amygdala influences cerebellar learning mechanisms in rats. Pharmacological inactivation of the central amygdala (CeA) severely impaired acquisition and retention of eyeblink conditioning, indicating that the amygdala continues to interact with the cerebellum after conditioning is consolidated (Experiment 1). CeA inactivation also substantially reduced stimulus-evoked and learning-related neuronal activity in the cerebellar anterior interpositus nucleus during acquisition and retention of eyeblink conditioning (Experiment 2). A very small proportion of cerebellar neurons responded to the conditioned stimulus (CS) during CeA inactivation. Finally, retrograde and anterograde tracing experiments identified the basilar pontine nucleus at the confluence of outputs from CeA that may support amygdala modulation of CS input to the cerebellum (Experiment 3). Together, these results highlight a role for the CeA in the gating of CS-related input to the cerebellum during motor learning that is maintained even after the conditioned response is well learned. SIGNIFICANCE STATEMENT: The current study is the first to demonstrate that the amygdala modulates sensory-evoked and learning-related neuronal activity within the cerebellum during acquisition and retention of associative learning. The findings suggest a model of amygdala-cerebellum interactions in which the amygdala gates conditioned stimulus inputs to the cerebellum through a direct projection from the medial central nucleus to the basilar pontine nucleus. Amygdala gating of sensory input to the cerebellum may be an attention-like mechanism that facilitates cerebellar learning. In contrast to previous theories of amygdala-cerebellum interactions, the sensory gating hypothesis posits that the gating mechanism continues to be necessary for retrieval of cerebellar memory after learning is well established.

Reevaluating hippocampus-dependent learning in FVB/N mice.

The FVB/N (FVB) mouse has been a popular background strain for constructing transgenic mice. However, behavioral phenotyping of the resultant mice is complicated, due to severe visual impairment in the FVB background strain. Previous studies reported cognitive impairments with the FVB strain, suggesting the background as unsuitable for behavioral analysis. In this study, we compared FVB mice to the well-characterized C57BL/6 (B6) strain in a battery of hippocampus-dependent tasks that had several nonvisual cues. The tasks included: trace eyeblink conditioning, spontaneous alternation in the Y maze, social recognition, trace and contextual fear conditioning, and odor habituation-dishabituation. FVB mice were able to learn all the tasks, often to similar levels as B6 mice. In contrast to previous reports, our data suggest FVB mice are not cognitively deficient with temporal memory tasks, when the tasks do not rely heavily upon vision. Thus, the FVB strain may be used as the genetic background for behavioral phenotyping when nonvisual hippocampal-dependent tasks are utilized.

Association between moxifloxacin ophthalmic solution and fungal infection in patients with corneal ulcers and microbial keratitis.

BACKGROUND: Fungal keratitis is a painful and dangerous fungal infection of the cornea. Recently, use of a contact lens solution with a novel ophthalmic preservative was linked to an increased risk of fungal keratitis. This study investigated whether fungal contamination was present in bottles of a widely used moxifloxacin ophthalmic solution, and whether there was an association between the use of this solution and fungal keratitis in a corneal referral practice. METHODS: Fungal cultures were obtained for 32 moxifloxacin bottles brought in by 32 keratitis patients referred to our cornea practice from June 2003 to March 2006. Demographic and clinical data were also collected for 29 patients with fungal keratitis and 82 patients with bacterial keratitis, referred to our practice for corneal ulcers between June 2003 and April 2006. These two groups were compared with respect to moxifloxacin use and other variables. Logistic regression was carried out to determine whether an association between fungal keratitis and moxifloxacin use was present after taking into account potential confounding variables. RESULTS: Thirteen (41%) of the bottles of moxifloxacin solution grew fungus on culture. Patients with fungal keratitis were nearly twice as likely as patients with bacterial keratitis to report the use of moxifloxacin ophthalmic solution: 41% vs. 22% (P = 0.043). The association between fungal keratitis and moxifloxacin use persisted after taking into account potential confounding variables. CONCLUSIONS: Fungal contamination is present in the moxifloxacin bottles used by some keratitis patients. There appears to be an association between the use of moxifloxacin ophthalmic solution and fungal keratitis.