Acetylcholine determination of microdialysates of fetal neocortex grafts that induce recovery of learning

Opposing Roles of Cholinergic and GABAergic Activity in the Insular Cortex and Nucleus Basalis Magnocellularis during Novel Recognition and Familiar Taste Memory Retrieval

Acetylcholine (ACh) is thought to facilitate cortical plasticity during memory formation and its release is regulated by the nucleus basalis magnocellularis (NBM). Questions remain regarding which neuronal circuits and neurotransmitters trigger activation or suppression of cortical cholinergic activity. During novel, but not familiar, taste consumption, there is a significant increase in ACh release in the insular cortex (IC), a highly relevant structure for taste learning. Here, we evaluate how GABA inhibition modulates cholinergic transmission and its involvement during taste novelty processing and familiar taste memory retrieval. Using saccharin as a taste stimulus in a taste preference paradigm, we examined the effects of injecting the GABAA receptor agonist muscimol or the GABAA receptor antagonist bicuculline into the IC or NBM during learning or retrieval of an appetitive taste memory on taste preference in male Sprague Dawley rats. GABAA receptor agonism and antagonism had opposite effects on cortical ACh levels in novel taste presentation versus familiar taste recognition and ACh levels were associated with the propensity to acquire or retrieve a taste memory. These results indicate that the pattern of cortical cholinergic and GABAergic neuroactivity during novel taste exposure is the opposite of that which occurs during familiar taste recognition and these differing neurotransmitter system states may enable different behavioral consequences. Divergences in ACh and GABA levels may produce differential alterations in excitatory and inhibitory neural processes within the cortex during acquisition and retrieval.

SIGNIFICANCE STATEMENT

During learning and recall, several brain structures act together. This work demonstrates interactions between cortical cholinergic and GABAergic systems during taste learning and memory retrieval. We found that the neuroactivity pattern during novel taste exposure is opposite that which occurs during familiar taste recognition. GABAA receptors must be inactive during novel tasting to enable new memory formation, but must be active and inhibiting acetylcholine release in the cortex to allow memory retrieval. These findings indicate that GABA inhibition modulates cholinergic transmission and that cholinergic-GABAergic system interactions are important during the transition from novel to familiar memory.

Histaminergic modulation of cholinergic release from the nucleus basalis magnocellularis into insular cortex during taste aversive memory formation

The ability of acetylcholine (ACh) to alter specific functional properties of the cortex endows the cholinergic system with an important modulatory role in memory formation. For example, an increase in ACh release occurs during novel stimulus processing, indicating that ACh activity is critical during early stages of memory processing. During novel taste presentation, there is an increase in ACh release in the insular cortex (IC), a major structure for taste memory recognition. There is extensive evidence implicating the cholinergic efferents of the nucleus basalis magnocellularis (NBM) in cortical activity changes during learning processes, and new evidence suggests that the histaminergic system may interact with the cholinergic system in important ways. However, there is little information as to whether changes in cholinergic activity in the IC are modulated during taste memory formation. Therefore, in the present study, we evaluated the influence of two histamine receptor subtypes, H1 in the NBM and H3 in the IC, on ACh release in the IC during conditioned taste aversion (CTA). Injection of the H3 receptor agonist R-α-methylhistamine (RAMH) into the IC or of the H1 receptor antagonist pyrilamine into the NBM during CTA training impaired subsequent CTA memory, and simultaneously resulted in a reduction of ACh release in the IC. This study demonstrated that basal and cortical cholinergic pathways are finely tuned by histaminergic activity during CTA, since dual actions of histamine receptor subtypes on ACh modulation release each have a significant impact during taste memory formation.

Biologic Transplantation and Neurotrophin-Induced Neuroplasticity After Traumatic Brain Injury

OBJECTIVE

In this review, we analyze progress in the treatment of traumatic brain injury with neurotrophins, growth factors and cell and tissue neurotransplantation. The primary objective of these therapies is to reduce neurologic deficits associated with the trauma by inducing neuroplasticity. These therapies are restorative and not necessarily neuroprotective.

MAIN OUTCOME MEASURES

An extensive literature on administration of neurotrophics factors and cell and tissue cerebral transplantation is reviewed. The effects of these therapeutic approaches on brain biochemical, molecular, cellular, and tissue responses are summarized.

CONCLUSION

The cumulative data indicate that cell therapy shows substantial promise in the treatment of neural injury.

Effects of conditioned food aversions on nutritional behavior in humans

Conditioned food aversion (CFA) and taste aversion (CTA) are widely occurring phenomena mediating rejection of solids or liquids, the ingestion of which has induced the onset of post-ingestional malaise. It is a powerful and durable imprint learning that may influence food choice and intake in all animals, including humans. For ethical reasons, CTA has been extensively investigated in a wide variety of laboratory animal's species but only incidentally in humans. Nevertheless, convincing evidence has been provided that CFA and CTA learning are possible in a wide range of human subjects. The results in humans may have some limitations in accuracy since data are sparse, sometimes indirect, and poorly controlled. There is only limited information on the extent of CFA in the elderly since most studies have employed questionnaire and/or interview methods on young people (i.e. college students). The present review evaluates the literature derived both from laboratory animals and humans. In the first instance, the salient features of food and taste aversion learning and the neural mechanisms involved in this learning behavior will be examined. Then, the problems encountered when trying to assess the role of learned food and taste aversions in the nutritional status of healthy as well as sick young or elderly people will be considered. In particular, the importance of CFA on the nutritional status of cancer patients and treatment of alcoholism will be examined. It is concluded that the data are compelling enough to warrant further research and, some indications and recommendations are suggested.