Kazuto Kobayashi

SUMMARY: Prior experience allows selective learning by filtering out redundant cues, as exemplified by blocking, in which prior learning about one cue prevents a novel but redundant cue from being learned during subsequent compound conditioning. Top-down cortico-cortical pathways have been implicated in sensory filtering, but whether, how, and when they contribute to blocking remain unknown. Here we establish a head-fixed blocking paradigm in mice in which prior auditory cue-reward learning prevents a redundant somatosensory cue-reward association during subsequent compound conditioning. We found that a projection from anterior cingulate cortex (ACC) to primary somatosensory cortex (S1) facilitates blocking. Prior auditory learning establishes ACC-driven inhibitory control over S1 via parvalbumin neurons, before explicit somatosensory experience, thereby suppressing burst responses to the somatosensory cue, limiting network plasticity, and promoting blocking. These findings propose a proactive cortical filter that preconfigures inhibitory sensory bias to constrain future learning about redundant cues. Graphical

Immunotoxin (ITX)-mediated cell targeting enables selective elimination of neuronal types of interest from a complex neural network. In this technology, human interleukin-2 receptor α-subunit or CD25 (hCD25) is expressed in specific cell types in transgenic rodents, and then the animals are treated with a recombinant ITX composed of monoclonal antibody variable regions for hCD25 fused to a Pseudomonas exotoxin fragment (PE38), resulting in the ablation of hCD25-expressing cells. However, there is a critical issue on the cross-reactivity of the recombinant ITX for endogenous CD25 in non-human primates (NHPs), leading to off-target effects. Here we generated a mouse CD25 (mCD25)-specific recombinant ITX, termed anti-mCD25-PE38, based on variable regions of a rabbit monoclonal antibody that specifically reacts to mCD25, but not to hCD25. Anti-mCD25-PE38 showed high-affinity binding to mCD25 and cytotoxic activity toward mCD25-expressing cells. Injection of anti-mCD25-PE38 into the ventral midbrain of common marmosets, in which the mCD25 transgene was expressed in dopamine neurons by a lentiviral vector for retrograde gene transfer, induced a significant loss of midbrain dopamine neurons. Therefore, anti-mCD25-PE38 provides a useful strategy for selective targeting of neuronal types to study the behavioral and neurological functions of these neurons in the NHP brain.

Lentiviral (LV) vectors derived from human immunodeficiency virus type 1 (HIV-1) mediate efficient gene transfer into various cell types, including neuronal, glial, and neural stem cells in the central nervous system. The HIV-1-based LV vectors commonly used are self-inactivating and pseudotyped with a variety of viral envelope glycoproteins. Pseudotyping with vesicular stomatitis virus glycoprotein (VSV-G) confers broad tropism to wide variety of cells and enhances vector stability of the vectors. Pseudotyping with other glycoproteins alters the tropism. In particular, the use of rabies virus glycoprotein (RV-G) or fusion glycoproteins (FuGs) consisting of VSV-G and RV-G segments increases the efficiency of retrograde gene delivery into neuronal cells. The LV vector strategy provides useful approaches to genetic manipulation of specific neural pathways for elucidating the structure and function of neural circuits, and also to genome-wide screening of key molecules and gene regulatory elements in development and survival of the nervous system. Such a strategy also provides a powerful tool for clinical applications aimed at gene therapy for neurological and neurodegenerative diseases as well as central nervous system tumors.

Previous studies revealed critical involvement of the striatum in adapting to the environment by actions that anticipate rewards from experiences as a policy. However, it remains unclear how current policy is evaluated to explore more advantageous alternatives. Here, we show that during policy-based sequential actions in a rat reversal task, the dorsomedial striatum plays an essential role in pathway-specific manner. Recording and optical manipulation of the indirect pathway showed that late-onset activity following unrewarded suboptimal action represents a lowered valuation of the current action policy and a heightened bias to try the suboptimal action. The early-onset activity complementarily mediated policy-based suppression of unrewarded action. These results demonstrate the indirect pathway’s role in monitoring unreliability of current action policy and probing alternative one. This study extends conventional understanding of consequence-guided persistence with reward-oriented action policy and provides key insights regarding how the dorsomedial striatum enables proactive and flexible adaptation to environmental changes.

The striatum, the central hub of cortico-basal ganglia loops, contains functionally heterogeneous subregions distinguished by the topographic patterns of structural connectivity. These subregions mediate various processes of procedural learning. However, it remains unclear when and how striatal subregions engage in the acquisition of sensory stimulus-based decision-making. A neuroimaging of regional brain activity shows that the anterior dorsolateral striatum (aDLS) and posterior ventrolateral striatum (pVLS) in rats are activated in a different temporal pattern during the acquisition phase of auditory discrimination. Chronic and transient pharmacologic manipulations show that the aDLS promotes the behavioral strategy driven by the stimulus-response association while suppressing that by the response-outcome association, and that the pVLS contributes to forming and maintaining the stimulus-response strategy. Electrophysiological recording indicates that subpopulations of aDLS neurons predominantly represent the outcome of specific behaviors at the initial period of discrimination learning, and that pVLS subpopulations encode the beginning and ending of each behavior according to the progress of learning. In addition, other subpopulations of striatal neurons indicate sustained activation after obtaining reward with distinct patterns reflecting the stimulus-response associations. Our findings demonstrate that aDLS and pVLS neurons integrate the new learning of auditory discrimination in spatiotemporally and functionally different manners.

Maternal behaviors, which are crucial for the survival of mammalian infants, require the coordinated operation of multiple brain regions to process infant cues, make decisions, and execute motor plans. Although these processes likely demand higher cognitive functions, the prefrontal areas that regulate limbic parental programs remains poorly understood. Here, we show that the orbitofrontal cortex (OFC) excitatory projection neurons promote alloparental caregiving behaviors in female mice. By chronic microendoscopy, we observed robust yet adaptable representations of pup-directed anticipatory and motor-related activities within the OFC. Some of these plastic responses were significantly overlapped with those related to nonsocial reward signals. The inactivation of OFC output reduced the phasic activities of midbrain dopamine (DA) neurons specifically tied to pup retrieval and impaired the modulation of DA release to the ventral striatum during the acquisition of alloparental behaviors. These findings suggest that the OFC transiently boosts DA activity during the acquisition phase, thereby facilitating the manifestation of alloparental behaviors.

Understanding the structural and the functional organization of neural circuits in the brain is a fundamental goal of neuroscience. Lentiviral vectors for retrograde gene transfer transduce neurons through the entry from synaptic terminals and enable tracing and manipulation of neuronal populations of interests based on the synaptic connections. The highly efficient and neuron-specific retrograde gene transfer (NeuRet) vectors are derived from the pseudotyping of human immunodeficiency virus type 1-based vectors with fusion envelope glycoproteins. Viral RNA genome is reverse-transcribed and synthesized DNA is integrated into the host genomes, allowing stable and long-term expression of transgenes. Dorsal striatum, the input layer of the basal ganglia, integrates signals from various brain regions, including cerebral cortex, thalamus, and ventral midbrain, and plays a critical role in motor control, learning, and decision-making. Consequently, understanding the input and the output connectivity of the dorsal striatum is fundamental to revealing how circuits within the basal ganglia contribute to physiological and behavioral functions, and its impairments are related to neurological disorders. This paper outlines the procedures for injecting a NeuRet vector carrying a green fluorescent protein gene into the sub-regions of dorsal striatum in rats, followed by immunohistochemistry to detect the transgene expression in the brain.

The striatum, the central hub of cortico-basal ganglia loops, contains functionally heterogeneous subregions distinguished by the topographic patterns of structural connectivity. These subregions mediate various processes of procedural learning. However, it remains unclear when and how striatal subregions engage in the acquisition of sensory stimulus-based decision-making. A neuroimaging of regional brain activity shows that the anterior dorsolateral striatum (aDLS) and posterior ventrolateral striatum (pVLS) in rats are activated in a different temporal pattern during the acquisition phase of auditory discrimination. Chronic and transient pharmacologic manipulations show that the aDLS promotes the behavioral strategy driven by the stimulus- response association while suppressing that by the response-outcome association, and that the pVLS contributes to forming and maintaining the stimulus-response strategy. Electrophysiological recording indicates that subpopulations of aDLS neurons predominantly represent the outcome of specific behaviors at the initial period of discrimination learning, and that pVLS subpopulations encode the beginning and ending of each behavior according to the progress of learning. In addition, other subpopulations of striatal neurons indicate sustained activation after obtaining reward with distinct patterns reflecting the stimulus-response associations. Our findings demonstrate that aDLS and pVLS neurons integrate the new learning of auditory discrimination in spatiotemporally and functionally different manners.

Placebo analgesia is caused by inactive treatment, implicating endogenous brain function involvement. However, the neurobiological basis remains unclear. In this study, we found that μ-opioid signals in the medial prefrontal cortex (mPFC) activate the descending pain inhibitory system to initiate placebo analgesia in neuropathic pain rats. Chemogenetic manipulation demonstrated that specific activation of μ-opioid receptor–positive (MOR ⁺ ) neurons in the mPFC or suppression of the mPFC–ventrolateral periaqueductal gray (vlPAG) circuit inhibited placebo analgesia in rats. MOR ⁺ neurons in the mPFC are monosynaptically connected and directly inhibit layer V pyramidal neurons that project to the vlPAG via GABA _A receptors. Thus, intrinsic opioid signaling in the mPFC disinhibits excitatory outflow to the vlPAG by suppressing MOR ⁺ neurons, leading to descending pain inhibitory system activation that initiates placebo analgesia. Our results shed light on the fundamental neurobiological mechanism of the placebo effect that maximizes therapeutic efficacy and reduces adverse drug effects in medical practice.