Dopamine release in the nucleus accumbens is classically linked to associative learning, signaling relationships between predictive cues and outcomes. Yet, dopamine is also strongly modulated by novelty, a nonassociative factor that has received comparatively little attention. Here, we used optical dopamine sensors in awake, behaving male and female mice to define how novelty alters the temporal dynamics of dopamine release during aversive learning. We manipulated novelty in three ways: (1) omitting expected footshocks, (2) introducing novel neutral cues concurrently with shock-predictive stimuli, and (3) presenting novel stimuli in an unpaired fashion within a context. Across all conditions, manipulations robustly increased dopamine release and in some cases altered the directionality of cue-evoked dopamine responses. Notably, these effects extended beyond the immediate stimulus window, altering subsequent responses to both conditioned cues and footshocks. Together, these findings demonstrate that changes...

The medial habenula (MHb) and its main projection target, the interpeduncular nucleus (IPN), play an important role in mood/affect, anxiety, and the aversive experience associated with nicotine withdrawal. Given that MHb axons release glutamate onto IPN neurons, we investigated the expression and functional responses of ionotropic glutamate receptors (iGluRs) in neurons of the rostral IPN (IPR) in male rats. After confirming mRNA expression of Gria1 and Grin1 iGluR subunits in IPR, we employed glutamate uncaging coupled with two-photon imaging and patch-clamp electrophysiology. IPR dendrites, which often contained spine-like protrusions suggestive of synaptic contacts, featured a variety of response profiles following localized glutamate uncaging. Pharmacology experiments confirmed functional α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid and N -methyl-d-aspartate iGluR responses in IPR neuronal somata. Rats were trained to self-administer nicotine or saline during 10 fixed ratio 1 sessions and seven...

Olfaction is the dominant sensory modality in rodents. It can be used to assess behavioral phenomena including stress, learning and memory, and social investigation, and impaired olfaction is implicated in several neurological disorders. Paradigms such as the olfactory habituation/dishabituation (OHD) task can assess olfactory perception, memory, and motivation. However, these tasks require manual stimulus presentation, introducing variability and making them labor-intensive. Olfactometers allow automated stimulus delivery, but the OHD task has not yet been adapted for use with an olfactometer. Additionally, current olfactometer designs require proprietary software or components that are difficult to obtain/fabricate and commercial units are expensive. As a result, these apparatuses have not been widely implemented. Here, we describe the design and assembly of the Odor Delivery Optimization Research System (ODORS), an economical, modular, and open-source olfactometer for use in rodents, and describe a vari...

The “sign-tracking” and “goal-tracking” model of individual variation in associative learning permits the identification of rats with different cue-reactivity and predisposition to addiction-like behaviors. Certainly, compared to “goal-trackers” (GTs), “sign-trackers” (STs) show more susceptibility traits such as increased cue-induced ‘relapse’ of drugs of abuse. Different cue- and reward-evoked patterns of activity in the nucleus accumbens (NAc) have been a hallmark of the ST/GT phenotype. However, it is unknown whether differences in the intrinsic neuronal properties of NAc medium spiny neurons (MSNs) in the core and shell subregions are also a physiological correlate of these phenotypes. We performed whole-cell slice electrophysiology in outbred male rats and found that STs exhibited the lowest excitability in the NAc core, with lower number of action potentials and firing frequency as well as a blunted voltage/current relationship curve in response to hyperpolarized potentials in both the NAc core and ...

People with epilepsy may experience sudden death due to respiratory failure through mechanisms that are currently not well understood. Epilepsy causing mutations are thought to elicit seizures due to altered function of forebrain circuits, yet breathing is controlled largely by the brainstem. To investigate how altered forebrain activity could impact breathing, we examined respiratory and seizure phenotypes in a mouse epilepsy model with a forebrain–specific deletion of the phosphatase and tensin homolog (PTEN) gene (PTEN–cKO). Using chronic diaphragm electromyography (EMG) and cortical electroencephalography (EEG), we monitored PTEN–cKO mice (6 males and 4 females) and control littermates (6 males and 3 females) continuously from pre–seizure onset through end–stage disease. PTEN–cKO mice develop spontaneous seizures that progress in frequency with age, accompanied by gradual changes in respiratory function, even during interictal periods. As seizure burden increases, PTEN-cKO mice experience an increased ...

Accurate electrode implantation in the subthalamic nucleus (STN) of rats is essential for high-quality electrophysiological and neuromodulation studies but remains technically challenging due to the small size and deep location of the STN. Traditional stereotactic methods, relying on bregma or averaged bregma-interaural-based coordinates, often result in misplacement of electrode. Here, we introduce a combined anatomical and functional approach—bregma-interaural and electrophysiology-guided technique (BITE)—designed to enhance targeting accuracy for STN electrode implantation in male Sprague Dawley rats. In this method, anterior-posterior (AP), medial-lateral (ML), and dorsal-ventral (DV) coordinates are initially determined using the average of bregma and interaural references. Electrode depth (DV axis) is fine-tuned based on real-time detection of characteristic STN neuronal firing patterns. If STN featured activity is not observed on the first implantation, additional adjustments in the AP and ML axes a...

Neural signals necessary for gaze holding are produced in the excitatory networks of oculomotor neural integrators including the prepositus hypoglossi nucleus (PHN) and the interstitial nucleus of Cajal (INC). Our previous studies have shown that the activation of the networks can be evaluated by sustained excitatory postsynaptic current (EPSC) responses in vitro, in which a higher EPSC frequency after burst stimulation (100 Hz, 20 trains) than the frequency before the stimulation lasts for >1 s. Both the PHN and the INC receive serotonergic inputs mainly from the dorsal raphe nucleus, and serotonin (5-HT) induces depolarizing responses via 5-HT2 or 5-HT3 receptors and hyperpolarizing responses via 5-HT1A receptors in PHN and INC neurons. However, how 5-HT affects sustained EPSC responses remains unknown. In this study, we investigated the effects of 5-HT on sustained EPSC responses using whole-cell recordings in brainstem slices obtained from rats of either sex. Compared with the control treatment, bath a...

RNA localization to neuronal axons and dendrites provides spatiotemporal control over gene expression to support synapse function. Neuronal messenger RNAs (mRNAs) localize as ribonucleoprotein particles (RNPs), commonly known as RNA granules, the composition of which influences when and where proteins are made. High-throughput sequencing has revealed thousands of mRNAs that localize to the hippocampal neuropil. Whether these mRNAs are spatially organized into common RNA granules or distributed as independent mRNAs for proper delivery to synapses is debated. Here, using highly multiplexed single-molecule fluorescence in situ hybridization (HiPlex smFISH) and colocalization analyses, we investigate the subcellular spatial distribution of 15 synaptic neuropil localized mRNAs in the male and female rodent hippocampus. We observed that these mRNAs are present in the neuropil as heterogeneously sized fluorescent puncta with spatial colocalization patterns that generally scale by neuropil mRNA abundance. Indeed, ...

Mice offer a wealth of opportunities for investigating brain circuits regulating multiple behaviors, largely due to their genetic tractability. Social behaviors are translationally relevant, considering both mice and humans are highly social mammals, and human social behavior disruptions are key symptoms of myriad neuropsychiatric disorders. Stresses related to social experiences are particularly influential in the severity and maintenance of neuropsychiatric disorders like anxiety disorders and trauma and stressor-related disorders. Yet, induction and study of social stress in mice has disproportionately focused on males, influenced heavily by their inherent territorial nature. Social target-instigated stress (i.e., defeat), while ethologically relevant, is quite variable and predominantly specific to males, making rigorous and sex-inclusive studies challenging. In pursuit of a controllable, consistent, high-throughput, and sex-inclusive method for social stress elicitation, we modified a paradigm to trai...

People with epilepsy may experience sudden death due to respiratory failure through mechanisms that are currently not well understood. Epilepsy causing mutations are thought to elicit seizures due to altered function of forebrain circuits, yet breathing is controlled largely by the brainstem. To investigate how altered forebrain activity could impact breathing, we examined respiratory and seizure phenotypes in a mouse epilepsy model with a forebrain-specific deletion of the phosphatase and tensin homolog ( Pten ) gene. Using chronic diaphragm electromyography and cortical electroencephalography, we monitored Pten conditional knock-out (PTEN–cKO) mice (six males and four females) and control littermates (six males and three females) continuously from preseizure onset through end-stage disease. PTEN–cKO mice develop spontaneous seizures that progress in frequency with age, accompanied by gradual changes in respiratory function, even during interictal periods. As seizure burden increases, PTEN–cKO mice experi...