Biology subjects

Vann, S. D.

Publications and source records attributed to Vann, S. D..

3 recordsLinked to original sources

bioRxiv2023

Impairments in the early consolidation of spatial memories via group II mGluR agonism in the mammillary bodies

mGluR2 receptors are widely expressed in limbic brain regions associated with memory, including the hippocampal formation, retrosplenial and frontal cortices, as well as subcortical regions including the mammillary bodies. mGluR2/3 agonists have been proposed as potential therapeutics for neurological and psychiatric disorders, however, there is still little known about the role of these receptors in cognitive processes, including memory consolidation. To address this, we assessed the effect of the mGluR2/3 agonist, eglumetad, on spatial memory consolidation in both mice and rats. Using the novel place preference paradigm, we found that post-sample injections of eglumetad impaired subsequent spatial discrimination when tested 6 hours later. Using the immediate early gene c-fos as a marker of neural activity, we showed that eglumetad injections reduced activity in a network of limbic brain regions including the hippocampus and mammillary bodies. To determine whether the systemic effects could be replicated with more targeted manipulations, we performed post-sample infusions of the mGluR2/3 agonist 2R,4R-APDC into the mammillary bodies. This impaired novelty discrimination on a place preference task and an object-in-place task, again highlighting the role of mGluR2/3 transmission in memory consolidation and demonstrating the crucial involvement of the mammillary bodies in post-encoding processing of spatial information.

animal behavior and cognition↗

bioRxiv2023

Electrophysiological properties of the medial mammillary bodies across the sleep-wake cycle

The medial mammillary bodies (MB) play an important role in the formation of spatial memories. Dense anatomical connectivity with hippocampal, brainstem, and thalamic structures, positions them as a focal point for the integration of movement-related and spatial information that is extended to the anterior thalamic nuclei and beyond to cortex. While their anatomical connectivity has been well-studied, much less is known about the physiological properties of the medial MBs, 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 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 show 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; 3) A considerable proportion of medial MB units show 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. Significance StatementWhile the medial mammillary bodies (MBs) are important for memory, it is still not clear how they support memory formation. Through conjoint medial MB and hippocampal recordings across different arousal states we identified a population of medial MB units with diverse and often conjunctive physiological properties, including theta-entrained cells, cells modulated by running speed and angular head velocity, complex bursting, theta cycle skipping activity, and hippocampal sharp-wave ripple-responsive firing. These properties likely support a role for the medial MBs in mnemonic processing, enabling the integration of separate sensory streams and the propagation of information to the thalamus.

neuroscience↗

bioRxiv2018

Striking reduction in neurons and glial cells in anterior thalamic nuclei of older patients with Down’s syndrome

The anterior thalamic nuclei are important for spatial and episodic memory; however, there is surprisingly little information about how these nuclei are affected in many conditions that present with memory impairments, including Downs syndrome. To assess the status of the anterior thalamic nuclei in Downs syndrome we quantified neurons and glial cells in the brains from four older patients with this condition. There was a striking reduction in the volume of the anterior thalamic nuclei and this appeared to reflect the loss of approximately 70% of neurons. The number of glial cells was also reduced but to a lesser degree than neurons. The anterior thalamic nuclei appear to be particularly sensitive to effects of aging in Downs syndrome and the pathology in this region likely contributes to the memory impairments observed. These findings re-affirm the importance of assessing the status of the anterior thalamic nuclei in conditions where memory impairments have been principally assigned to pathology in the medial temporal lobe.

neuroscience↗