15 research outputs found
Projections from Gudden's tegmental nuclei to the mammillary body region in the cynomolgus monkey (Macaca fascicularis)
No full textGudden's tegmental nuclei provide major inputs to the rodent mammillary bodies, where they are thought to be important for learning and navigation. Comparable projections have yet to be described in the primate brain, where part of the problem has been in effectively delineating these nuclei. Immunohistochemical staining of tissue from a series of macaque monkeys (Macaca mulatta) showed that cells in the region of both the ventral and dorsal tegmental nuclei selectively stain for parvalbumin, thus helping to reveal these nuclei. These same tegmental nuclei were not selectively revealed when tissue was stained for SMI32, acetylcholinesterase, calbindin, or calretinin. In a parallel study, horseradish peroxidase was injected into the mammillary bodies of five cynomolgus monkeys (Macaca fascicularis). Retrogradely labeled neurons were consistently found in the three subdivisions of the ventral tegmental nucleus of Gudden, which are located immediately below, within, and above the medial longitudinal fasciculus. Further projections to the mammillary body region arose from cells in the anterior tegmental nucleus, which appears to be a rostral continuation of the infrafascicular part of the ventral tegmental nucleus. In the dorsal tegmental nucleus of Gudden, labeled cells were most evident when the tracer injection was more laterally placed in the mammillary bodies, consistent with a projection to the lateral mammillary nucleus. The present study not only demonstrates that the primate mammillary bodies receive parallel inputs from the dorsal and ventral tegmental nuclei of Gudden, but also helps to confirm the extent of these poorly distinguished nuclei in the monkey brain
Theta synchronization in the limbic system: The role of Gudden’s tegmental nuclei
No full textrhythm Theta rhythm is most prominent in the hippocampus but has also been recorded in other cortical and limbic structures and can play an important role in functional coupling of widely separated structures responsible for different components of the memory building process. Here we demonstrate in the rat that neuronal activity exhibiting strong state-dependent synchrony with rhythmic hippocampal electroencephalogram is present also at the brainstem level, speci®cally in the relatively small tegmental nuclei of Gudden intimately connected with the limbic forebrain. We found that during theta states, either occurring spontaneously or triggered by sensory stimulation in the urethane anaesthetized rat, all neurons in the anterior and ventral tegmental nuclei exhibited a consistent switch from irregular discharges to rhythmic bursts. The switch between these patterns closely matched the analogous transformations in the hippocampal EEG, but the level of synchrony between the two signals varied depending on the level of theta activation. During sensory stimulation, when theta is faster and more regular, the rhythmic bursts in the tegmentum showed extremely high coherence (up to 0.96) with hippocampal ®eld potentials. During spontaneous theta, the average coherence was lower but still highly signi®cant (0.62). Gudden's nuclei are reciprocally connected to the mammillary body complex (MB) occupying a strategic position at the gateway of hippocampofugal connections organized in the Papez circuit. Thus, coupling between the MB-Gudden circuit and the hippocampus and consequently the neuronal traf®c through the Papez circuit and hence the assembly of limbic structures connected to the hippocampus may vary according to the activity in these speci®c brainstem nuclei
Electric Stimulation of Recombination Luminescence in a Rigid Organic Solution (a Gudden—Pohl Effect)
No full textTime to put the mammillothalamic pathway into context
No full textThe medial diencephalon, in particular the mammillary bodies and anterior thalamic nuclei, has long been linked to memory and amnesia. The mammillary bodies provide a dense input into the anterior thalamic nuclei, via the mammillothalamic tract. Lesions of the mammillary bodies, mammillothalamic tract and anterior thalamic nuclei all produce severe impairments in temporal and contextual memory, in both animal models and in patients, yet it is uncertain why these regions are critical. Mounting evidence from electrophysiological and neural imaging studies suggests that mammillothalamic projections exercise considerable distal influence over thalamo-cortical and hippocampo-cortical interactions. Here, we outline how damage to the mammillary body-anterior thalamic axis, in both patients and animal models, disrupts behavioural performance on tasks that relate to contextual (“where”) and temporal (“when”) processing. Focusing on the medial mammillary nuclei as a possible ‘theta-generator’ (through their interconnections with the ventral tegmental nucleus of Gudden) we discuss how the mammillary body-anterior thalamic pathway may contribute to the mechanisms via which the hippocampus and neocortex encode representations of experience
Focus on focus: lack of coherence between systemic and microvascular indices of oedema formation
No full text
Focus on focus: Lack of coherence between systemic and microvascular indices of oedema formation
No full textBackground: Fluid therapy remains a cornerstone of therapy in shock states. However, fluid overloading ultimately results in oedema formation which is related to excess morbidity and mortality. Handheld microscopes are now frequently used to study the sublingual microcirculation. As a corollary, these devices measure focal distance, or surface to capillary distance. Physiologically, this could represent a microvascular index of oedema formation and could have the potential to guide fluid therapy. This potential tool should be investigated, especially given the frequently reported lack of coherence between systemic and microvascular parameters in the critically ill. Therefore, we set out to assess the correlation between microvascular focal distance and systemic indices of oedema formation, specifically fluid balance and weight gain. Methods: Following ex vivo testing of focal distance measurement reliability, we conducted a prospective observational cohort study in patients admitted to the intensive care unit of our university teaching hospital. We determined surface to capillary distance using sidestream dark field (SDF) and incident dark field (IDF) imaging by assessing the focal distance point or object distance range at which a sharp recording could be made. Measurements were performed in post-cardiac surgery patients and in patients following emergency admission at two time points separated by at least several hours. Data on fluid balance, weight and weight gain were collected simultaneously. Results: Sixty patients were included. The focal setting, focus point for SDF and the object distance range for IDF did not differ significantly between time points. Focus was not correlated with difference in fluid balance or weight gain. Conclusions: There is a lack of coherence between surface to capillary distance as determined by SDF or IDF imaging and fluid balance or weight gain. Thus, focal distance as a microvascular index of oedema formation cannot currently be used as a proxy for systemic indices of oedema formation. However, given the lack of coherence, further research should determine whether focal distance may provide better guidance for fluid therapy than traditional markers of overzealous fluid administration
No evidence for distinguishing bacterial from viral acute rhinosinusitis using symptom duration and purulent rhinorrhea: a systematic review of the evidence base
No full textOBJECTIVE: To evaluate the diagnostic value of symptom duration and purulent rhinorrhea in adults suspected of having acute bacterial rhinosinusitis. DATA SOURCES: PubMed, EMBASE, and the Cochrane Library. REVIEW METHODS: We performed a comprehensive systematic search on March 28, 2013. We included studies on the diagnostic value of duration of symptoms and purulent rhinorrhea in patients suspected of having acute bacterial rhinosinusitis. We assessed study design of included articles for directness of evidence and risk of bias. We extracted prevalence and positive and negative predictive values. RESULTS: Of 4173 unique publications, we included 1 study with high directness of evidence and moderate risk of bias. The prior probability of bacterial rhinosinusitis was 0.29 (95% confidence interval [CI], 0.24-0.35); we could not extract posterior probabilities. Odds ratios (95% CI) from univariate analysis were 1.03 (0.78-1.36) for duration of symptoms and 2.69 (1.39-5.18) for colored discharge on the floor of the nasal cavity. CONCLUSION AND RECOMMENDATION: We included 1 study with moderate risk of bias, reporting data in such a manner that we could not assess the value of symptom duration and purulent rhinorrhea in adults suspected of having acute bacterial rhinosinusitis. Recommendations to distinguish between a viral and a bacterial source based on purulent rhinorrhea are not supported by evidence, and the decision to prescribe antibiotic treatment should not depend on its presence. Based on judgment driven by theory and subsidiary evidence of a greater likelihood of bacterial rhinosinusitis after 10 days, antibiotic therapy may seem a reasonable empirical option
Episodic-like event recollection in the rat: E-maze task, memory retention accuracy and the role of the fornix.
No full textEpisodic memory was proposed to be a memory system unique to human (Tulving, 1972, 2002), until Clayton and Dickinson (1998) presented evidence form their study of the scrub jays that animals were capable of recalling episodic-like past events. To date the evidence of episodic-like memory was demonstrated in avian behaviour but not in the non- human mammals. Therefore, this thesis set out to establish a similar "what" "where" "which" episodic-like memory model in rats. Research findings showed that rats can learn a behavioural task encompassing information about specific objects, placed in a given location at a particular time in the recent past, which is evidence of episodic-like recall. Furthermore, rats were capable of retaining the newly attained episodes for at least 15 minutes and performed the episodic-like test with a decreased degree of accuracy subsequent to sustaining bilateral fornix section. Hence these tests of episodic-like memory in the rat provided evidence that the capability of the non-human memory has potential for further research, proving useful in the general understanding of the episodic memory system
