Houri Hintiryan

Cyto- and chemoarchitecture of the hypothalamic paraventricular nucleus in the C57BL/6J male mouse: A study of immunostaining and multiple fluorescent tract tracing

The paraventricular nucleus of the hypothalamus (PVH) plays a critical role in the regulation of autonomic, neuroendocrine, and behavioral activities. This understanding has come from extensive characterization of the PVH in rats, and for this mammalian species we now have a robust model of basic PVH neuroanatomy and function. However, in mice, whose use as a model research animal has burgeoned with the increasing sophistication of tools for genetic manipulation, a comparable level of PVH characterization has not been achieved. To address this, we employed a variety of fluorescent tract tracing and immunostaining techniques in several different combinations to determine the neuronal connections and cyto‐ and chemoarchitecture of the PVH in the commonly used C57BL/6J male mouse. Our findings reveal a distinct organization in the mouse PVH that is substantially different from the PVH of male rats. The differences are particularly evident with respect to the spatial relations of two principal neuroendocrine divisions (magnocellular and parvicellular) and three descending preautonomic populations in the PVH. We discuss these data in relation to what is known about PVH function and provide the work as a resource for further studies of the neuronal architecture and function of the mouse PVH. J. Comp. Neurol., 2012.

The mouse cortico-striatal projectome

Different cortical areas are organized into distinct intracortical subnetworks. The manner in which descending pathways from the entire cortex interact subcortically as a network remains unclear. We developed an open-access comprehensive mesoscale mouse cortico-striatal projectome: a detailed connectivity projection map from the entire cerebral cortex to the dorsal striatum or caudoputamen (CP) in rodents. On the basis of these projections, we used new computational neuroanatomical tools to identify 29 distinct functional striatal domains. Furthermore, we characterized different cortico-striatal networks and how they reconfigure across the rostral–caudal extent of the CP. The workflow was also applied to select cortico-striatal connections in two different mouse models of disconnection syndromes to demonstrate its utility for characterizing circuitry-specific connectopathies. Together, our results provide the structural basis for studying the functional diversity of the dorsal striatum and disruptions of cortico-basal ganglia networks across a broad range of disorders.

Comprehensive connectivity of the mouse main olfactory bulb: analysis and online digital atlas

We introduce the first open resource for mouse olfactory connectivity data produced as part of the Mouse Connectome Project (MCP) at UCLA. The MCP aims to assemble a whole-brain connectivity atlas for the C57Bl/6J mouse using a double coinjection tracing method. Each coinjection consists of one anterograde and one retrograde tracer, which affords the advantage of simultaneously identifying efferent and afferent pathways and directly identifying reciprocal connectivity of injection sites. The systematic application of double coinjections potentially reveals interaction stations between injections and allows for the study of connectivity at the network level. To facilitate use of the data, raw images are made publicly accessible through our online interactive visualization tool, the iConnectome, where users can view and annotate the high-resolution, multi-fluorescent connectivity data (www.MouseConnectome.org). Systematic double coinjections were made into different regions of the main olfactory bulb (MOB) and data from 18 MOB cases (~72 pathways; 36 efferent/36 afferent) currently are available to view in iConnectome within their corresponding atlas level and their own bright-field cytoarchitectural background. Additional MOB injections and injections of the accessory olfactory bulb (AOB), anterior olfactory nucleus (AON), and other olfactory cortical areas gradually will be made available. Analysis of connections from different regions of the MOB revealed a novel, topographically arranged MOB projection roadmap, demonstrated disparate MOB connectivity with anterior versus posterior piriform cortical area (PIR), and exposed some novel aspects of well-established cortical olfactory projections.

BAMS2 workspace: A comprehensive and versatile neuroinformatic platform for collating and processing neuroanatomical connections

We describe a novel neuroinformatic platform, the BAMS2 Workspace (http://brancusi1.usc.edu), designed for storing and processing information on gray matter region axonal connections. This de novo constructed module allows registered users to collate their data directly by using a simple and versatile visual interface. It also allows construction and analysis of sets of connections associated with gray matter region nomenclatures from any designated species. The Workspace includes a set of tools allowing the display of data in matrix and networks formats and the uploading of processed information in visual, PDF, CSV, and Excel formats. Finally, the Workspace can be accessed anonymously by third‐party systems to create individualized connectivity networks. All features of the BAMS2 Workspace are described in detail and are demonstrated with connectivity reports collated in BAMS and associated with the rat sensory‐motor cortex, medial frontal cortex, and amygdalar regions. J. Comp. Neurol. 522:3160–3176, 2014.

Dissociating the Conditioning and the Anorectic Effects of Estradiol in Female Rats

The present series of experiments challenges the ability of the hormone estradiol to act as an unconditioned stimulus in the conditioned taste avoidance (CTA) learning paradigm. We hypothesize that reductions in sucrose consumption observed after pairing it with estradiol are not indicative of associative learning, but due to the unconditioned expression of estradiols anorectic effects during the time of CTA assessment. Three experiments in which a sucrose solution was paired with estradiol were conducted to test this hypothesis. Experiment 1 demonstrated that female rats expressed a reduction in post-pairing sucrose consumption even though the anorectic effects of estradiol had subsided. Experiment 2 showed that although a low dose of estradiol produced anorexia, it did not elicit post-pairing reductions in sucrose consumption. Experiment 3 revealed that contingent pairing was a requirement for post-pairing reduction in sucrose consumption even when testing was done at a time when anorexia is expressed. These findings demonstrate the dissociability of the conditioning and anorectic effects of estradiol, providing evidence against the hypothesis. The results are discussed in terms of independent neural mechanisms underlying the disparate behaviors.

Intraoral cheek fistulae: a refined technique

Taste reactivity testing (TRT), which entails infusing a solution into the oral cavity of subjects, is used across a wide range of studies. For laboratories inexperienced in the conventional technique of implanting cheek fistulae, the surgery can be problematic for both the subjects and the experimenter. We have proposed a refined method for fistulae implantation that is less invasive, thereby reducing the pain and distress of the animals. Using this refined technique, we were able to replicate the findings of previous TRT studies, namely that a high dose of lithium chloride produces an increase in aversive and a decrease in ingestive orofacial and somatic responses. Using indices of health, we demonstrate that unlike animals with the conventional method of fistulae implantation, subjects that receive the refined technique regain their pre-surgery body weights rapidly and show no physical signs of discomfort. Additional advantages of the refined technique are discussed.

The role of histamine in estradiol-induced conditioned consumption reductions.

Conditioned consumption reductions (CCRs) develop toward novel taste stimuli as a consequence of associating those tastes with certain physiological changes. Few studies have focused on the neurochemical basis of this learned behavior. The purpose of these experiments was to reexamine the role of histamine in CCRs elicited by estradiol. Previous studies have suggested that histamine mediates CCRs induced by radiation, centrifugal rotation, and estradiol. However, because the animals were trained in a drug state, but tested in a nondrug state, it is possible that state-dependent learning confounded the results of these studies. The following series of experiments was performed to test this possibility for estradiol-induced CCRs. Implementing our own methodologies in Experiment 1, we demonstrated that an estradiol-induced CCR was blocked by treatment with the histamine 1 receptor blocker, chlorpheniramine maleate, before sucrose consumption during acquisition. In Experiment 2, identical states were maintained during acquisition and extinction by administering chlorpheniramine prior to sucrose exposure during both phases. The results indicated that chlorpheniramine blocked the estradiol-induced CCR. However, circumventing state-dependency in Experiment 3 by administering chlorpheniramine following exposure to sucrose during acquisition augmented the estradiol CCR. Taken together, the results of these experiments suggest that the ability of chlorpheniramine to abolish estradiol-induced CCRs is not due to state-dependency or to the antihistaminergic properties of chlorpheniramine. It is proposed that the results of all of the experiments can be accounted for by the aversive properties of chlorpheniramine.

Integration of gene expression and brain-wide connectivity reveals the multiscale organization of mouse hippocampal networks

Understanding the organization of the hippocampus is fundamental to understanding brain function related to learning, memory, emotions, and diseases such as Alzheimer’s disease. Physiological studies in humans and rodents have suggested that there is both structural and functional heterogeneity along the longitudinal axis of the hippocampus. However, the recent discovery of discrete gene expression domains in the mouse hippocampus has provided the opportunity to re-evaluate hippocampal connectivity. To integrate mouse hippocampal gene expression and connectivity, we mapped the distribution of distinct gene expression patterns in mouse hippocampus and subiculum to create the Hippocampus Gene Expression Atlas (HGEA). Notably, previously unknown subiculum gene expression patterns revealed a hidden laminar organization. Guided by the HGEA, we constructed the most detailed hippocampal connectome available using Mouse Connectome Project (http://www.mouseconnectome.org) tract tracing data. Our results define the hippocampus’ multiscale network organization and elucidate each subnetwork’s unique brain-wide connectivity patterns.Bienkowski et al. have created a new subregional atlas of the mouse hippocampus that integrates gene expression with anatomical connectivity to reveal the multiscale organization of the hippocampus and its connections throughout the brain.