Comparison of the connectivity of the posterior intralaminar thalamic nucleus and peripeduncular nucleus in rats and mice.

The posterior intralaminar thalamic nucleus (PIL) and peripeduncular nucleus (PP) are two adjoining structures located medioventral to the medial geniculate nucleus. The PIL-PP region plays important roles in auditory fear conditioning and in social, maternal and sexual behaviors. Previous studies often lumped the PIL and PP into single entity, and therefore it is not known if they have common and/or different brain-wide connections. In this study, we investigate brain-wide efferent and afferent projections of the PIL and PP using reliable anterograde and retrograde tracing methods. Both PIL and PP project strongly to lateral, medial and anterior basomedial amygdaloid nuclei, posteroventral striatum (putamen and external globus pallidus), amygdalostriatal transition area, zona incerta, superior and inferior colliculi, and the ectorhinal cortex. However, the PP rather than the PIL send stronger projections to the hypothalamic regions such as preoptic area/nucleus, anterior hypothalamic nucleus, and ventromedial nucleus of hypothalamus. As for the afferent projections, both PIL and PP receive multimodal information from auditory (inferior colliculus, superior olivary nucleus, nucleus of lateral lemniscus, and association auditory cortex), visual (superior colliculus and ectorhinal cortex), somatosensory (gracile and cuneate nuclei), motor (external globus pallidus), and limbic (central amygdaloid nucleus, hypothalamus, and insular cortex) structures. However, the PP rather than PIL receives strong projections from the visual related structures parabigeminal nucleus and ventral lateral geniculate nucleus. Additional results from Cre-dependent viral tracing in mice have also confirmed the main results in rats. Together, the findings in this study would provide new insights into the neural circuits and functional correlation of the PIL and PP.

Possible rodent equivalent of the posterior cingulate cortex (area 23) interconnects with multimodal cortical and subcortical regions.

Posterior cingulate cortex (area 23, A23) in human and monkeys is a critical component of the default mode network and is involved in many diseases such as Alzheimer's disease, autism, depression, attention deficit hyperactivity disorder and schizophrenia. However, A23 has not yet identified in rodents, and this makes modeling related circuits and diseases in rodents very difficult. Using a comparative approach, molecular markers and unique connectional patterns this study has uncovered the location and extent of possible rodent equivalent (A23~) of the primate A23. A23 ~ but not adjoining areas in the rodents displays strong reciprocal connections with anteromedial thalamic nucleus. Rodent A23 ~ reciprocally connects with the medial pulvinar and claustrum as well as with anterior cingulate, granular retrosplenial, medial orbitofrontal, postrhinal, and visual and auditory association cortices. Rodent A23 ~ projects to dorsal striatum, ventral lateral geniculate nucleus, zona incerta, pretectal nucleus, superior colliculus, periaqueductal gray, and brainstem. All these findings support the versatility of A23 in the integration and modulation of multimodal sensory information underlying spatial processing, episodic memory, self-reflection, attention, value assessment and many adaptive behaviors. Additionally, this study also suggests that the rodents could be used to model monkey and human A23 in future structural, functional, pathological, and neuromodulation studies.

The effects of bilateral prostriata lesions on spatial learning and memory in the rat.

Area prostriata is the primary limbic structure for rapid response to the visual stimuli in the far peripheral visual field. Recent studies have revealed that the prostriata receives inputs not only from the visual and auditory cortices but also from many structures critical for spatial processing and navigation. To gain insight into the functions of the prostriata in spatial learning and memory the present study examines the effects of bilateral lesions of the prostriata on motor ability, exploratory interest and spatial learning and memory using the open field, elevated plus-maze and Morris water maze tests. Our results show that the spatial learning and memory abilities of the rats with bilateral prostriata lesions are significantly reduced compared to the control and sham groups. In addition, the lesion rats are found to be less interested in space exploration and more anxious while the exercise capacity of the rats is not affected based on the first two behavioral tests. These findings suggest that the prostriata plays important roles in spatial learning and memory and may be involved in anxiety as well.