Agmatine is an endogenous amine derived from decarboxylation of arginine catalysed by arginine decarboxylase. Agmatine is considered a novel neuromodulator and possesses neuroprotective properties in the central nervous system. The present study examined whether agmatine has neuroprotective effects against repeated restraint stress-induced morphological changes in rat medial prefrontal cortex and hippocampus. Sprague-Dawley rats were subjected to 6 h of restraint stress daily for 21 days. Immunohistochemical staining with β-tubulin III showed that repeated restraint stress caused marked morphological alterations in the medial prefrontal cortex and hippocampus. Stress-induced alterations were prevented by simultaneous treatment with agmatine (50 mg/kg/day, i.p.). Interestingly, endogenous agmatine levels, as measured by high-performance liquid chromatography, in the prefrontal cortex and hippocampus as well as in the striatum and hypothalamus of repeated restraint rats were significantly reduced as compared with the controls. Reduced endogenous agmatine levels in repeated restraint animals were accompanied by a significant increase of arginine decarboxylase protein levels in the same regions. Moreover, administration of exogenous agmatine to restrained rats abolished increases of arginine decarboxylase protein levels. Taken together, these results demonstrate that exogenously administered agmatine has neuroprotective effects against repeated restraint-induced structural changes in the medial prefrontal cortex and hippocampus. These findings indicate that stress-induced reductions in endogenous agmatine levels in the rat brain may play a permissive role in neuronal pathology induced by repeated restraint stress.

Generalized anxiety disorder (GAD) is a prevalent anxiety disorder that is characterized by persistent excessive worrying that is often difficult to control. The pathology of GAD has been associated with abnormal neural activity and functional connectivity. This systematic review has examined the central neural correlates of GAD which are the prefrontal cortex (PFC), the anterior cingulate cortex (ACC) and the amygdala and how activation and functional connectivity in these brain areas differ between patients with GAD and healthy controls. This review also investigated how abnormal functional connectivity and activation in these brain regions relates to worry which is the most prominent psychological symptom in patients with GAD. A systematic review was conducted and seven original functional magnetic resonance imaging (fMRI) studies were included after a literature search on PubMed, Scopus and, Web of Science. The main findings from this review revealed decreased activation in the PFC and ACC and enhanced activation in the amygdala during the viewing of negative stimuli in patients with GAD. Identifying the neural correlates of GAD and how it relates to worry may provide improved treatment in the future such as developing more effective psychotropic drugs or improved psychotherapy. GAD has been associated with lower well-being and life satisfaction and may even be a risk factor for suicidal thoughts. One of the limitations from this review is that several of the included studies recruited patients with comorbidities and for that reason results from these studies cannot be generalized and applied to individuals with GAD.

One major challenge in developmental neuroscience research is the sheer number of choices researchers face when addressing even a single research question. Even once data collection is complete, the journey from raw data to interpretation of findings may depend on numerous decisions. To address this issue, this dissertation explores “multiverse” analysis techniques for following many analytical paths at once in the same dataset. In chapter 1, multiverses are used to examine which analyses of age-related change in amygdala-medial prefrontal cortex circuitry are robust versus sensitive to researcher decisions. Chapter 2 uses multiverse analysis to identify optimal solutions for mitigating breathing-induced artifacts in resting-state functional magnetic resonance imaging data. Chapter 3 uses a variety of model specifications to characterize simultaneous reward learning strategies in youth contingent on both visual task cues and spatial-motor information. Despite varied approaches and goals, each of the three studies highlight the benefits of conducting multiple parallel analyses for both addressing questions in developmental neuroscience and deepening understanding of the methods used to address them.

Early reports of enhanced behavioral reactivity in isolation-reared rats attributed this syndrome to "isolation stress." In the studies reported here, this "isolation stress syndrome" was reliably obtained in adult rats reared from weaning in individual hanging metal cages. Such isolates showed behavioral and adrenocortical symptoms of profound fear during open-field testing, unlike group-housed controls or littermate isolates reared singly in plastic cages. Animals in hanging metal cages are never touched by human caretakers, whereas rats reared in plastic cages are picked up and put in clean cages twice weekly. Handling hanging-cage isolates twice weekly to model the handling associated with cage changes completely protected against this syndrome. Further, there was no hormonal, neurochemical or anatomical evidence of chronic stress even in hanging-cage isolates. Littermates housed in social groupings (three rats per plastic cage) also froze and defecated in the open field at rates comparable to hanging-cage isolates if they were the first animals to be tested from their social group cage. It is probable that odor cues from familiar cagemates in the open field protected socially reared animals tested subsequently from the same cage from this syndrome. It is concluded that isolates are not chronically stressed, and that rearing effects are the result of a complex interaction between prior handling, social experience and test conditions.

Following a cortical injury, neurons in areas near and connected to the site of injury begin to degenerate. The observed neuronal death may contribute to the severity of the observed behavioral impairments. The purpose of the present study was to examine if progesterone, a hormone known for its effectiveness at reducing cerebral edema, could protect against secondary neuronal death and facilitate the acquisition of an avoidance learning task in an ablation model of cortical injury. Rats served as sham controls or received bilateral ablation of the medial prefrontal cortex followed by a 10-day regimen of progesterone (4 mg/kg) or oil vehicle (1 ml/kg) beginning 1 h after cortical lesions. Progesterone-treated lesion rats showed a significant facilitation of avoidance learning compared to oil- treated lesion controls. In addition, progesterone-treated lesion animals did not differ from either progesterone- or oil-treated sham controls in avoidance learning. Anatomical analysis revealed that progesterone treatment decreased the amount of neuronal death seen in the striatum and the mediodorsal nucleus of the thalamus. The findings are consistent with the notion that progesterone is an effective neuroprotective agent and suggest that the hormone can reduce the behavioral impairments associated with frontal cortical ablation injury.

It is well established that low level Pb-exposure is associated with a wide range of cognitive and neurobehavioral dysfunctions in children. In fact, Pb-induced damage occurs preferentially in the prefrontal cerebral cortex, hippocampus and cerebellum - the anatomical sites which are crucial in modulating emotional response, memory and learning. Previously it was also shown that nitric oxide (NO) signaling pathway as well as glutamatergic neurotransmission are both involved in brain development, neurotoxicity and neurodegeneration processes whereas Pb2+ interfere with both. For this reason we investigated the effect of ontogenetic Pb2+ exposure on dopaminergic neurotransmission in the medial prefrontal cortex (mPFC) of rats after amphetamine (AMPH) and/or 7-nitroindazole (7-NI) administration. Furthermore, the possible role of oxidative stress in Pb2+-induced neurotoxicity in prenatally Pb2+-treated rats was explored in the content of hydroxyl radical (HO•) species in mPFC after AMPH and/or 7-NI injection, assessed by HPLC analysis of 2.3-dihydroxybenzoic acid (2.3-DHBA) - spin trap product of salicylate. As shown, the results of this study suggest that Pb2+ exposure during intrauterine life did not substantially affect cortical dopaminergic neurotransmission in adult offspring rats evaluated by means of microdialysis of mPFC and the content of the cortical HO•. It is likely that striatum, nucleus accumbens or other dopamine rich brain areas are more intricately associated with Pb2+ precipitated behavioral, dopamine - dependent impairments observed in mammalians.

In the present study, we examined the possible effect of chronic treatment with glucocorticoids on the morphology of the rat brain and levels of endogenous agmatine and arginine decarboxylase (ADC) protein, the enzyme essential for agmatine synthesis. Seven-day treatment with dexamethasone, at a dose (10 and 50 μg/kg/day) associated to stress effects contributed by glucocorticoids, did not result in obvious morphologic changes in the medial prefrontal cortex and hippocampus, as measured by immunocytochemical staining with β-tubulin III. However, 21-day treatment (50 μg/kg/day) produced noticeable structural changes such as the diminution and disarrangement of dendrites and neurons in these areas. Simultaneous treatment with agmatine (50 mg/kg/day) prevented these morphological changes. Further measurement with HPLC showed that endogenous agmatine levels in the prefrontal cortex and hippocampus were significantly increased after 7-day treatments with dexamethasone in a dose-dependent manner. On the contrary, 21-day treatment with glucocorticoids robustly reduced agmatine levels in these regions. The treatment-caused biphasic alterations of endogenous agmatine levels were also seen in the striatum and hypothalamus. Interestingly, treatment with glucocorticoids resulted in a similar change of ADC protein levels in most brain areas to endogenous agmatine levels: an increase after 7-day treatment versus a reduction after 21-day treatment. These results demonstrated that agmatine has neuroprotective effects against structural alterations caused by glucocorticoids in vivo. The parallel alterations in the endogenous agmatine levels and ADC expression in the brain after treatment with glucocorticoids indicate the possible regulatory effect of these stress hormones on the synthesis and metabolism of agmatine in vivo.

Rationale and objective: Post-traumatic stress disorder (PTSD) and alcohol use disorder (AUD) are disorders of learning and memory that often occur comorbidly. Exposure to trauma-related cues can increase alcohol intake in PTSD patients that are using alcohol to self-medicate. The recurrence of anxiety symptoms with subsequent alcohol use may initiate a destructive cycle where stress and alcohol exposure impair the function of the prefrontal cortex (PFC). While the incidence of these disorders has steadily increased, current therapies and treatments often lack efficacy. Thus, investigation into the underlying neurocircuitry responsible for the establishment and maintenance of these disorders is necessary to develop novel treatment targets. Methods: The present study examined the effects of ethanol exposure on the ability to create new learned associations around previously conditioned fear cues in a rat model. Animals were exposed to fear conditioning followed by chronic intermittent ethanol to translationally model trauma exposure followed by alcohol abuse. Optogenetics was used to inhibit the prelimbic (PrL) or infralimbic (IfL) cortex during fear memory reconsolidation, and fear behaviors were measured during subsequent extinction and spontaneous recovery tests. Results and conclusion Chronic ethanol exposure led to deficits in fear extinction learning and increased freezing during spontaneous recovery, both of which were prevented following inhibition of the PrL, but not the IfL, during memory reconsolidation. These results support the involvement of the PrL in fear learning and memory, and strongly suggest that the PrL could serve as a potential target for the treatment of the learning and memory deficits that occur following exposure to stress and alcohol.

The prefrontal cortices, in particular lateral prefrontal cortex (LPFC) and anterior cingulate cortex (ACC), have been implicated in top-down control of attention switching and behavioral flexibility. These cortices and their networks are disrupted in autism, a condition in which diverse behaviors such as social communication and attention control are dysregulated. However, little is known about the typical development of these cortical areas or the ways in which this process is altered in neurodevelopmental disorders. In order to identify changes that could affect the local processing of signals transmitted by the short-range pathways connecting the ACC and LPFC I assessed developmental changes in the distinct cortical layers, which send and receive different pathways and have unique inhibitory microenvironments that dictate excitatory-inhibitory balance. Normative developmental trends were compared with those seen in individuals with autism to identify changes that may contribute to symptoms of attention dysfunction. Unbiased quantitative methods were used to study overall neuron density, the density of inhibitory neurons labeled by the calcium-binding proteins calbindin (CB), calretinin (CR), and parvalbumin (PV), and the density, size, and trajectory of myelinated axons in the individual cortical layers in children and adults with and without a diagnosis of autism. There was a reduction in neuron density and an increase in the density of myelinated axons in both areas during neurotypical development. Axons in layers 1-3 of LPFC were disorganized in autism, with increased variability in the trajectory of axons in children and a decrease in the proportion of thin axons in adults. These findings were most significant in layer 1, the ultimate feedback-receiving layer in the cortex. While there were no differences in neuron populations between cohorts in children, in adults with autism there was a significant reduction in the density of CR-expressing neurons in LPFC layers 2-6 and a significant increase in the density of PV-expressing neurons in ACC layers 5-6. In autism, these findings suggest that dysregulation of the normal development of axonal networks, seen in children, may induce compensatory developmental changes in cell and axon populations in adults that could be connected to attention dysregulation. / 2021-10-07T00:00:00Z

The visual system is able to form relationships across a variety of timescales. These relationships could allow the temporal continuity of the retinal image and the underlying temporal structure of the world to serve as key cues in invariant object recognition (the ability of the visual system to recognize objects across a variety of angles, distances, and other conditions) as well as other visual processes at longer timescales. To utilize this temporal continuity and temporal structure the visual system needs a continuous temporal signal that spans multiple timescales and a computational mechanism for forming relationships across this temporal signal. Two studies (Chapters 2 and 3) showed evidence for a temporal signal that could be used in vision in the monkey brain. Time cells, neurons that fire at particular time intervals relative to a stimulus, could be a component of this temporal signal. Evidence of time cells was found through analysis of neural recording from monkey HPC and PFC during a memory task that requires the monkey to associate visual stimuli separated by about a second in time. After the first stimulus was presented, large numbers of units in both HPC and PFC fired in sequence. Many units fired only when a particular stimulus was presented at a particular time in the past. The temporal information of time cells might originate in another form of temporal coding: temporal context cells. Temporal context cells are neurons that quickly change in firing rate in response to a stimuli then slowly relax back to a baseline firing rate. Evidence of temporal context cells was found by analyzing the temporal responses of neural recordings from the entorhinal cortex of macaque monkeys as they viewed complex images. Many neurons in the entorhinal cortex were responsive to image onset, showing large deviations from baseline firing shortly after image onset but relaxing back to baseline at different rates. This range of relaxation rates allowed for the time since image onset to be decoded on the scale of seconds. Further, these neurons carried information about image content, suggesting that neurons in the entorhinal cortex carry information not only about when an event took place but also the identity of that event. Taken together, these findings suggest that the primate entorhinal cortex uses a spectrum of time constants to construct a temporal record of the past in support of episodic memory. A computational model was implemented that can construct and use this putative temporal record to form relationships across timescales. This model is supported by empirical results in visual experiments at timescales of saccades, seconds, and tens of seconds. At the saccadic timescale, this association across time could be relevant to forming invariant object representations.