Riordan, A. J. | bioRxiv Science

bioRxiv2018

Collicular circuits for flexible sensorimotor routing

Historically, cognitive processing has been thought to rely on cortical areas such as prefrontal cortex (PFC), with the outputs of these areas modulating activity in lower, putatively simpler spatiomotor regions, such as the midbrain superior colliculus (SC). Using a rat task in which subjects switch rapidly between task contexts that demand changes in sensorimotor mappings, we report a surprising role for the SC in non-spatial cognitive processes. Before spatial response choices could be formed, neurons in SC encoded task context more strongly than neurons in PFC, and bilateral SC silencing impaired behavioral performance. Once spatial choices could begin to be formed, SC neurons encoded the choice faster than PFC, while bilateral SC silencing no longer impaired choices. A set of dynamical models of the SC replicates our findings. Our results challenge cortically-focused views of cognition, and suggest that ostensibly spatiomotor structures can play central roles in non-spatiomotor cognitive processes.

neuroscience↗

bioRxiv2017

Estradiol and luteinizing hormone reverse memory loss in phencyclidine model of schizophrenia: Evidence for hippocampal GABA action

The cognitive symptoms of schizophrenia are poorly understood and difficult to treat. Estrogens may mitigate these symptoms via unknown mechanisms. To examine these mechanisms, we tested whether increasing estradiol (E) or decreasing luteinizing hormone (LH) could rescue declarative memory in a phencyclidine (PCP) model of schizophrenia. We then assessed whether changes in cortical or hippocampal GABA may underlie these effects. Female rats were ovariectomized and injected subchronically with PCP. To modulate E and LH, animals received hormone capsules or Antide injections. Short-term episodic memory was assessed using the novel object recognition task. Brain expression of GAD67 was analyzed via western blot, and parvalbumin-containing cells were counted using immunohistochemistry. Some rats received hippocampal infusions of a GABAA agonist, GABAA antagonist, or GAD inhibitor before behavioral testing. We found that PCP reduced hippocampal GAD67 and abolished object recognition. Antide restored hippocampal GAD67 and rescued recognition memory in PCP-treated animals. Estradiol reversed PCPs amnesic effect but failed to restore hippocampal GAD67. PCP did not cause significant differences in number of parvalbumin-expressing cells or cortical expression of GAD67. Hippocampal infusions of a GABAA agonist restored memory in PCP-treated rats. Blocking hippocampal GAD or GABAA receptors in ovx animals reproduced memory loss similar to PCP and inhibited estradiols memory rescue in PCP-treated animals. In summary, decreasing LH or increasing E can reverse memory loss in a PCP model of schizophrenia. Alterations in hippocampal GABA may contribute to both PCPs effects on declarative memory and the hormones ability to reverse them.

neuroscience↗