Effect of oral tryptamines on the gut microbiome of rats-a preliminary study.

Background: Psilocybin and related tryptamines have come into the spotlight in recent years as potential therapeutics for depression. Research on the mechanisms of these effects has historically focused on the direct effects of these drugs on neural processes. However, in addition to such neural effects, alterations in peripheral physiology may also contribute to their therapeutic effects. In particular, substantial support exists for a gut microbiome-mediated pathway for the antidepressant efficacy of other drug classes, but no prior studies have determined the effects of tryptamines on microbiota. Methods: To address this gap, in this preliminary study, male Long Evans rats were treated with varying dosages of oral psilocybin (0.2 or 2 mg/kg), norbaeocystin (0.25 or 2.52 mg/kg), or vehicle and their fecal samples were collected 1 week and 3 weeks after exposure for microbiome analysis using integrated 16S ribosomal DNA sequencing to determine gut microbiome composition. Results: We found that although treatment with neither psilocybin nor norbaeocystin significantly affected overall microbiome diversity, it did cause significant dose- and time-dependent changes in bacterial abundance at the phylum level, including increases in Verrucomicrobia and Actinobacteria, and decreases in Proteobacteria. Conclusion and Implications: These preliminary findings support the idea that psilocybin and other tryptamines may act on the gut microbiome in a dose- and time-dependent manner, potentially identifying a novel peripheral mechanism for their antidepressant activity. The results from this preliminary study also suggest that norbaeocystin may warrant further investigation as a potential antidepressant, given the similarity of its effects to psilocybin.

Visual boundary cues suffice to anchor place and grid cells in virtual reality.

The hippocampal formation contains neurons responsive to an animal's current location and orientation, which together provide the organism with a neural map of space.1,2,3 Spatially tuned neurons rely on external landmark cues and internally generated movement information to estimate position.4,5 An important class of landmark cue are the boundaries delimiting an environment, which can define place cell field position6,7 and stabilize grid cell firing.8 However, the precise nature of the sensory information used to detect boundaries remains unknown. We used 2-dimensional virtual reality (VR)9 to show that visual cues from elevated walls surrounding the environment are both sufficient and necessary to stabilize place and grid cell responses in VR, when only visual and self-motion cues are available. By contrast, flat boundaries formed by the edges of a textured floor did not stabilize place and grid cells, indicating only specific forms of visual boundary stabilize hippocampal spatial firing. Unstable grid cells retain internally coherent, hexagonally arranged firing fields, but these fields "drift" with respect to the virtual environment over periods >5 s. Optic flow from a virtual floor does not slow drift dynamics, emphasizing the importance of boundary-related visual information. Surprisingly, place fields are more stable close to boundaries even with floor and wall cues removed, suggesting invisible boundaries are inferred using the motion of a discrete, separate cue (a beacon signaling reward location). Subsets of place cells show allocentric directional tuning toward the beacon, with strength of tuning correlating with place field stability when boundaries are removed.

Learning to Choose: Behavioral Dynamics Underlying the Initial Acquisition of Decision-Making.

Current theories of decision-making propose that decisions arise through competition between choice options. Computational models of the decision process estimate how quickly information about choice options is integrated and how much information is needed to trigger a choice. Experiments using this approach typically report data from well-trained participants. As such, we do not know how the decision process evolves as a decision-making task is learned for the first time. To address this gap, we used a behavioral design separating learning the value of choice options from learning to make choices. We trained male rats to respond to single visual stimuli with different reward values. Then, we trained them to make choices between pairs of stimuli. Initially, the rats responded more slowly when presented with choices. However, as they gained experience in making choices, this slowing reduced. Response slowing on choice trials persisted throughout the testing period. We found that it was specifically associated with increased exponential variability when the rats chose the higher value stimulus. Additionally, our analysis using drift diffusion modeling revealed that the rats required less information to make choices over time. These reductions in the decision threshold occurred after just a single session of choice learning. These findings provide new insights into the learning process of decision-making tasks. They suggest that the value of choice options and the ability to make choices are learned separately and that experience plays a crucial role in improving decision-making performance.

Disrupting dorsal hippocampus impairs category learning in rats.

Categorization requires a balance of mechanisms that can generalize across common features and discriminate against specific details. A growing literature suggests that the hippocampus may accomplish these mechanisms by using fundamental mechanisms like pattern separation, pattern completion, and memory integration. Here, we assessed the role of the rodent dorsal hippocampus (HPC) in category learning by combining inhibitory DREADDs (Designer Receptors Exclusively Activated by Designer Drugs) and simulations using a neural network model. Using touchscreens, we trained rats to categorize distributions of visual stimuli containing black and white gratings that varied along two continuous dimensions. Inactivating the dorsal HPC impaired category learning and generalization, suggesting that the rodent HPC plays an important role during categorization. Hippocampal inactivation had no effect on a control discrimination task that used identical trial procedures as the categorization tasks, suggesting that the impairments were specific to categorization. Model simulations were conducted with variants of a neural network to assess the impact of selective deficits on category learning. The hippocampal inactivation groups were best explained by a model that injected random noise into the computation that compared the similarity between category stimuli and existing memory representations. This model is akin to a deficit in mechanisms of pattern completion, which retrieves similar memory representations using partial information.

Exploring ketamine's reinforcement, cue-induced reinstatement, and nucleus accumbens cFos activation in male and female long evans rats.

Ketamine (KET), a non-competitive N-methyl-d-aspartate (NMDA) receptor antagonist, has rapid onset of antidepressant effects in Treatment-Resistant Depression patients and repeated infusions are required to sustain its antidepressant properties. However, KET is an addictive drug, and so more preclinical and clinical research is needed to assess the safety of recurring treatments in both sexes. Thus, the aim of this study was to investigate the reinforcing properties of various doses of KET (0-, 0.125-, 0.25-, 0.5 mg/kg/infusion) and assess KET's cue-induced reinstatement and neuronal activation in both sexes of Long Evans rats. Neuronal activation was assessed using the protein expression of the immediate early gene cFos in the nucleus accumbens (Nac), an important brain area implicated in reward, reinforcement and reinstatement to most drug-related cues. Our findings show that KET has reinforcing effects in both male and female rats, albeit exclusively at the highest two doses (0.25 and 0.5 mg/kg/infusion). Furthermore, we noted sex differences, particularly at the highest dose of ketamine, with female rats displaying a higher rate of self-administration. Interestingly, all groups that self-administered KET reinstated to drug-cues. Following drug cue-induced reinstatement test in rats exposed to KET (0.25 mg/kg/infusion) or saline, there was higher cFos protein expression in KET-treated animals compared to saline controls, and higher cFos expression in the core compared to the shell subregions of the Nac. As for reinstatement, there were no notable sex differences reported for cFos expression in the Nac. These findings reveal some sex and dose dependent effects in KET's reinforcing properties and that KET at all doses induced similar reinstatement in both sexes. This study also demonstrated that cues associated with ketamine induce comparable neuronal activation in the Nac of both male and female rats. This work warrants further research into the potential addictive properties of KET, especially when administered at lower doses which are now being used in the clinic for treating various psychopathologies.

Pharmacological manipulations of the dorsomedial and dorsolateral striatum during fear extinction reveal opposing roles in fear renewal.

Systemic manipulations that enhance dopamine (DA) transmission around the time of fear extinction can strengthen fear extinction and reduce conditioned fear relapse. Prior studies investigating the brain regions where DA augments fear extinction focus on targets of mesolimbic and mesocortical DA systems originating in the ventral tegmental area, given the role of these DA neurons in prediction error. The dorsal striatum (DS), a primary target of the nigrostriatal DA system originating in the substantia nigra (SN), is implicated in behaviors beyond its canonical role in movement, such as reward and punishment, goal-directed action, and stimulus-response associations, but whether DS DA contributes to fear extinction is unknown. We have observed that chemogenetic stimulation of SN DA neurons during fear extinction prevents the return of fear in contexts different from the extinction context, a form of relapse called renewal. This effect of SN DA stimulation is mimicked by a DA D1 receptor (D1R) agonist injected into the DS, thus implicating DS DA in fear extinction. Different DS subregions subserve unique functions of the DS, but it is unclear where in the DS D1R agonist acts during fear extinction to reduce renewal. Furthermore, although fear extinction increases neural activity in DS subregions, whether neural activity in DS subregions is causally involved in fear extinction is unknown. To explore the role of DS subregions in fear extinction, adult, male Long-Evans rats received microinjections of either the D1R agonist SKF38393 or a cocktail consisting of GABAA/GABAB receptor agonists muscimol/baclofen selectively into either dorsomedial (DMS) or dorsolateral (DLS) DS subregions immediately prior to fear extinction, and extinction retention and renewal were subsequently assessed drug-free. While increasing D1R signaling in the DMS during fear extinction did not impact fear extinction retention or renewal, DMS inactivation reduced later renewal. In contrast, DLS inactivation had no effect on fear extinction retention or renewal but increasing D1R signaling in the DLS during extinction reduced fear renewal. These data suggest that DMS and DLS activity during fear extinction can have opposing effects on later fear renewal, with the DMS promoting renewal and the DLS opposing renewal. Mechanisms through which the DS could influence the contextual gating of fear extinction are discussed.

Optogenetic Inhibition of the Orbitofrontal Cortex Disrupts Inhibitory Control during Stop-Change Performance in Male Rats.

Historically, the orbitofrontal cortex (OFC) has been implicated in a variety of behaviors ranging from reversal learning and inhibitory control to more complex representations of reward value and task space. While modern interpretations of the OFC's function have focused on a role in outcome evaluation, these cognitive processes often require an organism to inhibit a maladaptive response or strategy. Single-unit recordings from the OFC in rats performing a stop-change task show that the OFC responds strongly to STOP trials. To investigate the role that the OFC plays in stop-change performance, we expressed halorhodopsin (eNpHR3.0) in excitatory neurons in the OFC and tested rats on the stop-change task. Previous work suggests that the OFC differentiates between STOP trials based on trial sequence (i.e., gS trials: STOP trials preceded by a GO vs sS trials: STOP trials preceded by a STOP). We found that yellow light activation of the eNpHR3.0-expressing neurons significantly decreased accuracy only on STOP trials that followed GO trials (gS trials). Further, optogenetic inhibition of the OFC speeded reaction times on error trials. This suggests that the OFC plays a role in inhibitory control processes and that this role needs to be accounted for in modern interpretations of OFC function.

Analysis of hippocampal local field potentials by diffusion mapped delay coordinates.

Spatial navigation through novel spaces and to known goal locations recruits multiple integrated structures in the mammalian brain. Within this extended network, the hippocampus enables formation and retrieval of cognitive spatial maps and contributes to decision making at choice points. Exploration and navigation to known goal locations produce synchronous activity of hippocampal neurons resulting in rhythmic oscillation events in local networks. Power of specific oscillatory frequencies and numbers of these events recorded in local field potentials correlate with distinct cognitive aspects of spatial navigation. Typically, oscillatory power in brain circuits is analyzed with Fourier transforms or short-time Fourier methods, which involve assumptions about the signal that are likely not true and fail to succinctly capture potentially informative features. To avoid such assumptions, we applied a method that combines manifold discovery techniques with dynamical systems theory, namely diffusion maps and Takens' time-delay embedding theory, that avoids limitations seen in traditional methods. This method, called diffusion mapped delay coordinates (DMDC), when applied to hippocampal signals recorded from juvenile rats freely navigating a Y-maze, replicates some outcomes seen with standard approaches and identifies age differences in dynamic states that traditional analyses are unable to detect. Thus, DMDC may serve as a suitable complement to more traditional analyses of LFPs recorded from behaving subjects that may enhance information yield.

Developmental trajectory of social reward motivation from early adolescence into adulthood in female and male Long-Evans rats.

Most studies of adolescent and adult behavior involved one age group of each, whereas the dynamic changes in brain development suggest that there may be behavioral flux in adolescence. In two studies, we investigated developmental changes in social reward motivation in female and male Long-Evans rats from prepuberty to early adulthood in a social operant conditioning task. Given the earlier onset of puberty in females than in males, we predicted the course of social reward development would differ between the sexes. Overall, the pattern of results from both studies suggests that the trajectory of social motivation across adolescence is characterized by upward and downward shifts that do not depend on the sex of the rats. During training, in both studies, the mean number of social gate openings and percentage of social gate openings was higher at P30 (prepubertal, early adolescence) and P50 (late adolescence) than at P40 (mid adolescence) and P70 (adulthood) irrespective of sex. Nevertheless, the specific age comparisons that were significant depended on the study. In both studies, P30 rats had greater levels of social motivation than did adults in accessing a social reward when increased effort was required (progressive ratio tests). In an extinction test, only P30 and P50 rats continued to show more nose-pokes at the previously social gate than at the nonsocial gate, suggesting resistance to extinction. The results highlight the importance of characterizing behavior at several timepoints in adolescence to understand the neural mechanisms, many of which show similar discontinuities as they develop across adolescence.

Inhibition of p70 Ribosomal S6 Kinase (S6K1) Reduces Cortical Blood Flow in a Rat Model of Autism-Tuberous Sclerosis.

The manifestations of tuberous sclerosis complex (TSC) in humans include epilepsy, autism spectrum disorders (ASD) and intellectual disability. Previous studies suggested the linkage of TSC to altered cerebral blood flow and metabolic dysfunction. We previously reported a significant elevation in cerebral blood flow in an animal model of TSC and autism of young Eker rats. Inhibition of the mammalian target of rapamycin (mTOR) by rapamycin could restore normal oxygen consumption and cerebral blood flow. In this study, we investigated whether inhibiting a component of the mTOR signaling pathway, p70 ribosomal S6 kinase (S6K1), would yield comparable effects. Control Long Evans and Eker rats were divided into vehicle and PF-4708671 (S6K1 inhibitor, 75 mg/kg for 1 h) treated groups. Cerebral regional blood flow (14C-iodoantipyrine) was determined in isoflurane anesthetized rats. We found significantly increased basal cortical (+ 32%) and hippocampal (+ 15%) blood flow in the Eker rats. PF-4708671 significantly lowered regional blood flow in the cortex and hippocampus of the Eker rats. PF-4708671 did not significantly lower blood flow in these regions in the control Long Evans rats. Phosphorylation of S6-Ser240/244 and Akt-Ser473 was moderately decreased in Eker rats but only the latter reached statistical significance upon PF-4708671 treatment. Our findings suggest that moderate inhibition of S6K1 with PF-4708671 helps to restore normal cortical blood flow in Eker rats and that this information might have therapeutic potential in tuberous sclerosis complex and autism.

Theta Phase Entrainment of Single-Cell Spiking in Rat Somatosensory Barrel Cortex and Secondary Visual Cortex Is Enhanced during Multisensory Discrimination Behavior.

Phase entrainment of cells by theta oscillations is thought to globally coordinate the activity of cell assemblies across different structures, such as the hippocampus and neocortex. This coordination is likely required for optimal processing of sensory input during recognition and decision-making processes. In quadruple-area ensemble recordings from male rats engaged in a multisensory discrimination task, we investigated phase entrainment of cells by theta oscillations in areas along the corticohippocampal hierarchy: somatosensory barrel cortex (S1BF), secondary visual cortex (V2L), perirhinal cortex (PER), and dorsal hippocampus (dHC). Rats discriminated between two 3D objects presented in tactile-only, visual-only, or both tactile and visual modalities. During task engagement, S1BF, V2L, PER, and dHC LFP signals showed coherent theta-band activity. We found phase entrainment of single-cell spiking activity to locally recorded as well as hippocampal theta activity in S1BF, V2L, PER, and dHC. While phase entrainment of hippocampal spikes to local theta oscillations occurred during sustained epochs of task trials and was nonselective for behavior and modality, somatosensory and visual cortical cells were only phase entrained during stimulus presentation, mainly in their preferred modality (S1BF, tactile; V2L, visual), with subsets of cells selectively phase-entrained during cross-modal stimulus presentation (S1BF: visual; V2L: tactile). This effect could not be explained by modulations of firing rate or theta amplitude. Thus, hippocampal cells are phase entrained during prolonged epochs, while sensory and perirhinal neurons are selectively entrained during sensory stimulus presentation, providing a brief time window for coordination of activity.

Electrophysiological Properties of the Medial Mammillary Bodies across the Sleep-Wake Cycle.

The medial mammillary bodies (MBs) play an important role in the formation of spatial memories; their dense inputs from hippocampal and brainstem regions makes them well placed to integrate movement-related and spatial information, which is then extended to the anterior thalamic nuclei and beyond to the cortex. While the anatomical connectivity of the medial MBs has been well studied, much less is known about their physiological properties, particularly in freely moving animals. We therefore carried out a comprehensive characterization of medial MB electrophysiology across arousal states by concurrently recording from the medial MB and the CA1 field of the hippocampus in male rats. In agreement with previous studies, we found medial MB neurons to have firing rates modulated by running speed and angular head velocity, as well as theta-entrained firing. We extended the characterization of MB neuron electrophysiology in three key ways: (1) we identified a subset of neurons (25%) that exhibit dominant bursting activity; (2) we showed that ∼30% of theta-entrained neurons exhibit robust theta cycle skipping, a firing characteristic that implicates them in a network for prospective coding of position; and (3) a considerable proportion of medial MB units showed sharp-wave ripple (SWR) responsive firing (∼37%). The functional heterogeneity of MB electrophysiology reinforces their role as an integrative node for mnemonic processing and identifies potential roles for the MBs in memory consolidation through propagation of SWR-responsive activity to the anterior thalamus and prospective coding in the form of theta cycle skipping.

Distinct Hippocampal Oscillation Dynamics in Trace Eyeblink Conditioning Task for Retrieval and Consolidation of Associations.

Trace eyeblink conditioning (TEBC) has been widely used to study associative learning in both animals and humans. In this paradigm, conditioned responses (CRs) to conditioned stimuli (CS) serve as a measure for retrieving learned associations between the CS and the unconditioned stimuli (US) within a trial. Memory consolidation, that is, learning over time, can be quantified as an increase in the proportion of CRs across training sessions. However, how hippocampal oscillations differentiate between successful memory retrieval within a session and consolidation across TEBC training sessions remains unknown. To address this question, we recorded local field potentials (LFPs) from the rat dorsal hippocampus during TEBC and investigated hippocampal oscillation dynamics associated with these two functions. We show that transient broadband responses to the CS were correlated with memory consolidation, as indexed by an increase in CRs across TEBC sessions. In contrast, induced alpha (8-10 Hz) and beta (16-20 Hz) band responses were correlated with the successful retrieval of the CS-US association within a session, as indexed by the difference in trials with and without CR.

Reach-to-Grasp and tactile discrimination task: A new task for the study of sensory-motor learning.

Although active touch in rodents arises from the forepaws as well as whiskers, most research on active touch only focuses on whiskers. This results in a paucity of tasks designed to assess the process of active touch with a forepaw. We develop a new experimental task, the Reach-to-Grasp and Tactile Discrimination task (RGTD task), to examine active touch with a forepaw in rodents, particularly changes in processes of active touch during motor skill learning. In the RGTD task, animals are required to (1) extend their forelimb to an object, (2) grasp the object, and (3) manipulate the grasped object with the forelimb. The animals must determine the direction of the manipulation based on active touch sensations arising during the period of the grasping. In experiment 1 of the present study, we showed that rats can learn the RGTD task. In experiment 2, we confirmed that the rats are capable of reversal learning of the RGTD task. The RGTD task shared most of the reaching movements involved with conventional forelimb reaching tasks. From the standpoint of a discrimination task, the RGTD task enables rigorous experimental control, for example by removing bias in the stimulus-response correspondence, and makes it possible to utilize diverse experimental procedures that have been difficult in prior tasks.

Selective plasticity of layer 2/3 inputs onto distal forelimb controlling layer 5 corticospinal neurons with skilled grasp motor training.

Layer 5 neurons of the neocortex receive their principal inputs from layer 2/3 neurons. We seek to identify the nature and extent of the plasticity of these projections with motor learning. Using optogenetic and viral intersectional tools to selectively stimulate distinct neuronal subsets in rat primary motor cortex, we simultaneously record from pairs of corticospinal neurons associated with distinct features of motor output control: distal forelimb vs. proximal forelimb. Activation of Channelrhodopsin2-expressing layer 2/3 afferents onto layer 5 in untrained animals produces greater monosynaptic excitation of neurons controlling the proximal forelimb. Following skilled grasp training, layer 2/3 inputs onto corticospinal neurons controlling the distal forelimb associated with skilled grasping become significantly stronger. Moreover, peak excitatory response amplitude nearly doubles while latency shortens, and excitatory-to-inhibitory latencies become significantly prolonged. These findings demonstrate distinct, highly segregated, and cell-specific plasticity of layer 2/3 projections during skilled grasp motor learning.

Parkinsonism originates in a discrete secondary and dystonia in a primary motor cortical-basal ganglia subcircuit.

Although manifesting contrasting phenotypes, Parkinson's disease and dystonia, the two most common movement disorders, can originate from similar pathophysiology. Previously, we demonstrated that lesioning (silencing) of a discrete dorsal region in the globus pallidus (rodent equivalent to globus pallidus externa) in rats and produced parkinsonism, while lesioning a nearby ventral hotspot-induced dystonia. Presently, we injected fluorescent-tagged multi-synaptic tracers into these pallidal hotspots (n = 36 Long Evans rats) and permitted 4 days for the viruses to travel along restricted connecting pathways and reach the motor cortex before sacrificing the animals. Viral injections in the Parkinson's hotspot fluorescent labeled a circumscribed region in the secondary motor cortex, while injections in the dystonia hotspot labeled within the primary motor cortex. Custom probability mapping and N200 staining affirmed the segregation of the cortical territories for Parkinsonism and dystonia to the secondary and primary motor cortices. Intracortical microstimulation localized territories specifically to their respective rostral and caudal microexcitable zones. Parkinsonian features are thus explained by pathological signaling within a secondary motor subcircuit normally responsible for initiation and scaling of movement, while dystonia is explained by abnormal (and excessive) basal ganglia signaling directed at primary motor corticospinal transmission.

Developmentally Unique Cerebellar Processing Prioritizes Self- over Other-Generated Movements.

Animals must distinguish the sensory consequences of self-generated movements (reafference) from those of other-generated movements (exafference). Only self-generated movements entail the production of motor copies (i.e., corollary discharges), which are compared with reafference in the cerebellum to compute predictive or internal models of movement. Internal models emerge gradually over the first three postnatal weeks in rats through a process that is not yet fully understood. Previously, we demonstrated in postnatal day (P) 8 and P12 rats that precerebellar nuclei convey corollary discharge and reafference to the cerebellum during active (REM) sleep when pups produce limb twitches. Here, recording from a deep cerebellar nucleus (interpositus, IP) in P12 rats of both sexes, we compared reafferent and exafferent responses with twitches and limb stimulations, respectively. As expected, most IP units showed robust responses to twitches. However, in contrast with other sensory structures throughout the brain, relatively few IP units showed exafferent responses. Upon finding that exafferent responses occurred in pups under urethane anesthesia, we hypothesized that urethane inhibits cerebellar cortical cells, thereby disinhibiting exafferent responses in IP. In support of this hypothesis, ablating cortical tissue dorsal to IP mimicked the effects of urethane on exafference. Finally, the results suggest that twitch-related corollary discharge and reafference are conveyed simultaneously and in parallel to cerebellar cortex and IP. Based on these results, we propose that twitches provide opportunities for the nascent cerebellum to integrate somatotopically organized corollary discharge and reafference, thereby enabling the development of closed-loop circuits and, subsequently, internal models.

Infralimbic cortex plays a similar role in the punishment and extinction of instrumental behavior.

Learning to stop responding is a fundamental process in instrumental learning. Animals may learn to stop responding under a variety of conditions that include punishment-where the response earns an aversive stimulus in addition to a reinforcer-and extinction-where a reinforced response now earns nothing at all. Recent research suggests that punishment and extinction may be related manifestations of a common retroactive interference process. In both paradigms, animals learn to stop performing a specific response in a specific context, suggesting direct inhibition of the response by the context. This process may depend on the infralimbic cortex (IL), which has been implicated in a variety of interference-based learning paradigms including extinction and habit learning. Despite the behavioral parallels between extinction and punishment, a corresponding role for IL in punishment has not been identified. Here we report that, in a simple arrangement where either punishment or extinction was conducted in a context that differed from the context in which the behavior was first acquired, IL inactivation reduced response suppression in the inhibitory context, but not responding when it "renewed" in the original context. In a more complex arrangement in which two responses were first trained in different contexts and then extinguished or punished in the opposite one, IL inactivation had no effect. The results advance our understanding of the effects of IL in retroactive interference and the behavioral mechanisms that can produce suppression of a response.

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.

Effects of sensory overstimulation in postpartum rats.

Research in rodents has shown that exposure to excessive early life audiovisual stimulation leads to altered anxiety-like behaviors and cognitive deficits. Since this period of stimulation typically begins prior to weaning, newborn rodents receive sensory overstimulation (SOS) as a litter within their home cage while the dam is present. However, the effects of SOS during the postpartum period remain unexplored. To this end, we adapted an SOS paradigm for use in rats and exposed rat dams and their litters from postpartum days (PD) 10-23. Maternal observations were conducted to determine whether SOS produced changes in positive and/or negative maternal behaviors. Next, we assessed changes in anxiety-like behavior and cognition by testing dams in the elevated zero maze, open field, and novel object recognition tests. To assess potential effects on HPA-axis function, levels of the stress hormone corticosterone (CORT) were measured approximately 1-week after the cessation of SOS exposure. Our results indicate increased nursing and licking in SOS dams compared to controls, although SOS dams also exhibited significant increases in pup dragging. Moreover, SOS dams exhibited reduced self-care behaviors and nest-building compared to control dams. No differences were found for anxiety-like behaviors, object recognition memory, or CORT levels. This study is the first to assess the impact of postpartum SOS exposure in rat dams. Our findings suggest an SOS-induced enhancement in positive caregiving, but limited impact in all other measures.