Dysfunctional hippocampal-prefrontal network underlies a multidimensional neuropsychiatric phenotype following early-life seizure.

Brain disturbances during development can have a lasting impact on neural function and behavior. Seizures during this critical period are linked to significant long-term consequences such as neurodevelopmental disorders, cognitive impairments, and psychiatric symptoms, resulting in a complex spectrum of multimorbidity. The hippocampus-prefrontal cortex (HPC-PFC) circuit emerges as a potential common link between such disorders. However, the mechanisms underlying these outcomes and how they relate to specific behavioral alterations are unclear. We hypothesized that specific dysfunctions of hippocampal-cortical communication due to early-life seizure would be associated with distinct behavioral alterations observed in adulthood. Here, we performed a multilevel study to investigate behavioral, electrophysiological, histopathological, and neurochemical long-term consequences of early-life Status epilepticus in male rats. We show that adult animals submitted to early-life seizure (ELS) present working memory impairments and sensorimotor disturbances, such as hyperlocomotion, poor sensorimotor gating, and sensitivity to psychostimulants despite not exhibiting neuronal loss. Surprisingly, cognitive deficits were linked to an aberrant increase in the HPC-PFC long-term potentiation (LTP) in a U-shaped manner, while sensorimotor alterations were associated with heightened neuroinflammation, as verified by glial fibrillary acidic protein (GFAP) expression, and altered dopamine neurotransmission. Furthermore, ELS rats displayed impaired HPC-PFC theta-gamma coordination and an abnormal brain state during active behavior resembling rapid eye movement (REM) sleep oscillatory dynamics. Our results point to impaired HPC-PFC functional connectivity as a possible pathophysiological mechanism by which ELS can cause cognitive deficits and psychiatric-like manifestations even without neuronal loss, bearing translational implications for understanding the spectrum of multidimensional developmental disorders linked to early-life seizures.

Prediction of Learned Resistance or Helplessness by Hippocampal-Prefrontal Cortical Network Activity during Stress.

The perception of control over a stressful experience may determine its impacts and generate resistance against future stressors. Although the medial prefrontal cortex (PFC) and the hippocampus (HPC) are implicated in the encoding of stressor controllability, the neural dynamics underlying this process are unknown. Here, we recorded HPC and PFC neural activities in male rats during the exposure to controllable, uncontrollable, or no shocks and investigated electrophysiological predictors of escape performance upon exposure to subsequent uncontrollable shocks. We were able to accurately discriminate stressed from nonstressed animals and predict resistant (R) or helpless (H) individuals based on hippocampal-cortical oscillatory dynamics. Remarkably, R animals exhibited an increase in theta power during CS, while H exhibited a decrease. Furthermore, R exhibited higher HPC to PFC θ synchronization during stress. Notably, HPC-PFC θ connectivity in the initial stress exposure showed strong correlations with escape performance evaluated days later. R rats also showed stronger θ coupling to both γ oscillations and neuronal firing in the PFC. Finally, we found that these distinct features of network dynamics collectively formed a pattern that accurately predicted learned resistance and was lacking in H individuals. Our findings suggest that hippocampal-prefrontal network θ activity supports cognitive mechanisms of stress coping, whose impairment may underlie vulnerability to stress-related disorders.SIGNIFICANCE STATEMENT The appraisal of adversities as controllable or uncontrollable is key in determining resilience or risk for stress-related disorders. Here, we performed the first electrophysiological investigation during controllable or uncontrollable stress. Pharmacological studies showed that the prefrontal cortex (PFC) and the hippocampus (HPC) encode stressor controllability, and here we identified the neural activity underlying this process. This "neural signature of stressor controllability" accurately predicted resistance to future stressors and was characterized by increased HPC-PFC oscillatory activity in the θ frequency (4-10 Hz). Our findings suggest a new role of frontal θ oscillations in adaptive stress coping, integrating its emotional and cognitive functions. We also endorse the potential of this biomarker to guide neurophysiologically-informed and rhythm-based stimulation therapies for depression.

Selective post-training time window for memory consolidation interference of cannabidiol into the prefrontal cortex: Reduced dopaminergic modulation and immediate gene expression in limbic circuits.

The prefrontal cortex (PFC), amygdala and hippocampus display a coordinated activity during acquisition of associative fear memories. Evidence indicates that PFC engagement in aversive memory formation does not progress linearly as previously thought. Instead, it seems to be recruited at specific time windows after memory acquisition, which has implications for the treatment of post-traumatic stress disorders. Cannabidiol (CBD), the major non-psychotomimetic phytocannabinoid of the Cannabis sativa plant, is known to modulate contextual fear memory acquisition in rodents. However, it is still not clear how CBD interferes with PFC-dependent processes during post-training memory consolidation. Here, we tested whether intra-PFC infusions of CBD immediately after or 5h following contextual fear conditioning was able to interfere with memory consolidation. Neurochemical and cellular correlates of the CBD treatment were evaluated by the quantification of extracellular levels of dopamine (DA), serotonin, and their metabolites in the PFC and by measuring the cellular expression of activity-dependent transcription factors in cortical and limbic regions. Our results indicate that bilateral intra-PFC CBD infusion impaired contextual fear memory consolidation when applied 5h after conditioning, but had no effect when applied immediately after it. This effect was associated with a reduction in DA turnover in the PFC following retrieval 5days after training. We also observed that post-conditioning infusion of CBD reduced c-fos and zif-268 protein expression in the hippocampus, PFC, and thalamus. Our findings support that CBD interferes with contextual fear memory consolidation by reducing PFC influence on cortico-limbic circuits.

Animal models of epilepsy: use and limitations.

Epilepsy is a chronic neurological condition characterized by recurrent seizures that affects millions of people worldwide. Comprehension of the complex mechanisms underlying epileptogenesis and seizure generation in temporal lobe epilepsy and other forms of epilepsy cannot be fully acquired in clinical studies with humans. As a result, the use of appropriate animal models is essential. Some of these models replicate the natural history of symptomatic focal epilepsy with an initial epileptogenic insult, which is followed by an apparent latent period and by a subsequent period of chronic spontaneous seizures. Seizures are a combination of electrical and behavioral events that are able to induce chemical, molecular, and anatomic alterations. In this review, we summarize the most frequently used models of chronic epilepsy and models of acute seizures induced by chemoconvulsants, traumatic brain injury, and electrical or sound stimuli. Genetic models of absence seizures and models of seizures and status epilepticus in the immature brain were also examined. Major uses and limitations were highlighted, and neuropathological, behavioral, and neurophysiological similarities and differences between the model and the human equivalent were considered. The quest for seizure mechanisms can provide insights into overall brain functions and consciousness, and animal models of epilepsy will continue to promote the progress of both epilepsy and neurophysiology research.

NMDA receptor blockade impairs the muscarinic conversion of sub-threshold transient depression into long-lasting LTD in the hippocampus-prefrontal cortex pathway in vivo: correlation with γ oscillations.

Cholinergic fibers from the brainstem and basal forebrain innervate the medial prefrontal cortex (mPFC) modulating neuronal activity and synaptic plasticity responses to hippocampal inputs. Here, we investigated the muscarinic and glutamatergic modulation of long-term depression (LTD) in the intact projections from CA1 to mPFC in vivo. Cortical-evoked responses were recorded in urethane-anesthetized rats for 30 min during baseline and 4 h following LTD. In order to test the potentiating effects of pilocarpine (PILO), independent groups of rats received either a microinjection of PILO (40 nmol; i.c.v.) or vehicle, immediately before or 20 min after a sub-threshold LTD protocol (600 pulses, 1 Hz; LFS600). Other groups received either an infusion of the selective NMDA receptor antagonist (AP7; 10 nmol; intra-mPFC) or vehicle, 10 min prior to PILO preceding LFS600, or prior to a supra-threshold LTD protocol (900 pulses, 1 Hz; LFS900). Our results show that PILO converts a transient cortical depression induced by LFS600 into a robust LTD, stable for at least 4 h. When applied after LFS600, PILO does not change either mPFC basal neurotransmission or late LTD. Our data also indicate that NMDA receptor pre-activation is essential to the muscarinic enhancement of mPFC synaptic depression, since AP7 microinjection into the mPFC blocked the conversion of transient depression into long-lasting LTD produced by PILO. In addition, AP7 effectively blocked the long-lasting LTD induced by LFS900. Therefore, our findings suggest that the glutamatergic co-activation of prefrontal neurons is important for the effects of PILO on mPFC synaptic depression, which could play an important role in the control of executive and emotional functions.

Psychiatric comorbidities in temporal lobe epilepsy: possible relationships between psychotic disorders and involvement of limbic circuits / Comorbidades psiquiátricas na epilepsia do lobo temporal: possíveis relações entre desordens psicóticas e comprometimento de circuitos límbicos

OBJECTIVE: Mounting evidence suggests that the limbic system is pathologically involved in cases of psychiatric comorbidities in temporal lobe epilepsy (TLE) patients. Our objective was to develop a conceptual framework describing how neuropathological and connectivity changes might contribute to the development of psychosis and to the potential neurobiological mechanisms that cause schizophrenia-like psychosis in TLE patients. METHODS: In this review, clinical and neuropathological findings, especially brain circuitry of the limbic system, were examined together to enhance our understanding of the association between TLE and psychosis. Finally, the importance of animal models in epilepsy and psychiatric disorders was discussed. CONCLUSIONS: TLE and psychiatric symptoms coexist more frequently than chance would predict. Damage and deregulation among critical anatomical regions, such as the hippocampus, amygdala, thalamus, and the temporal, frontal and cingulate cortices, might predispose TLE brains to psychosis. Studies of the effects of kindling and injection of neuroactive substances on behavior and electrophysiological patterns may offer a model of how limbic seizures in humans increase the vulnerability of TLE patients to psychiatric symptoms.

OBJETIVO: Existem cada vez mais evidências de que o sistema límbico está envolvido na patologia das comorbidades psiquiátricas em pacientes com epilepsia do lobo temporal (ELT). Nosso objetivo foi elaborar um desenho conceitual descrevendo como aspectos neuropatológicos e de conectividade podem contribuir para o desenvolvimento de psicose em pacientes com ELT. MÉTODOS: Nesta revisão, achados clínicos e neuropatológicos, e especialmente os aspectos da circuitaria límbica, foram examinados em conjunto para auxiliar nossa compreensão sobre a associação entre ELT e psicose. Achados em modelos animais de epilepsia e esquizofrenia também foram levados em consideração. CONCLUSÕES: ELT e comorbidades psiquiátricas coexistem com maior frequência que o predito pela associação ao acaso. Dano e desregulação entre estruturas anatômicas críticas, como hipocampo, amígdala, tálamo, e córtices temporal, frontal e cingulado podem predispor o cérebro com ELT à psicose. Estudos sobre efeitos comportamentais e eletrofisiológicos do abrasamento elétrico e injeções de substâncias neuroativas em modelos animais podem oferecer pistas sobre como crises límbicas em humanos aumentam a vulnerabilidade de pacientes com ELT a sintomas psiquiátricos.

Muscarinic and nicotinic modulation of thalamo-prefrontal cortex synaptic plasticity [corrected] in vivo.

The mediodorsal nucleus of the thalamus (MD) is a rich source of afferents to the medial prefrontal cortex (mPFC). Dysfunctions in the thalamo-prefrontal connections can impair networks implicated in working memory, some of which are affected in Alzheimer disease and schizophrenia. Considering the importance of the cholinergic system to cortical functioning, our study aimed to investigate the effects of global cholinergic activation of the brain on MD-mPFC synaptic plasticity by measuring the dynamics of long-term potentiation (LTP) and depression (LTD) in vivo. Therefore, rats received intraventricular injections either of the muscarinic agonist pilocarpine (PILO; 40 nmol/µL), the nicotinic agonist nicotine (NIC; 320 nmol/µL), or vehicle. The injections were administered prior to either thalamic high-frequency (HFS) or low-frequency stimulation (LFS). Test pulses were applied to MD for 30 min during baseline and 240 min after HFS or LFS, while field postsynaptic potentials were recorded in the mPFC. The transient oscillatory effects of PILO and NIC were monitored through recording of thalamic and cortical local field potentials. Our results show that HFS did not affect mPFC responses in vehicle-injected rats, but induced a delayed-onset LTP with distinct effects when applied following PILO or NIC. Conversely, LFS induced a stable LTD in control subjects, but was unable to induce LTD when applied after PILO or NIC. Taken together, our findings show distinct modulatory effects of each cholinergic brain activation on MD-mPFC plasticity following HFS and LFS. The LTP-inducing action and long-lasting suppression of cortical LTD induced by PILO and NIC might implicate differential modulation of thalamo-prefrontal functions under low and high input drive.

Psychiatric comorbidities in temporal lobe epilepsy: possible relationships between psychotic disorders and involvement of limbic circuits.

OBJECTIVE: Mounting evidence suggests that the limbic system is pathologically involved in cases of psychiatric comorbidities in temporal lobe epilepsy (TLE) patients. Our objective was to develop a conceptual framework describing how neuropathological and connectivity changes might contribute to the development of psychosis and to the potential neurobiological mechanisms that cause schizophrenia-like psychosis in TLE patients. METHODS: In this review, clinical and neuropathological findings, especially brain circuitry of the limbic system, were examined together to enhance our understanding of the association between TLE and psychosis. Finally, the importance of animal models in epilepsy and psychiatric disorders was discussed. CONCLUSIONS: TLE and psychiatric symptoms coexist more frequently than chance would predict. Damage and deregulation among critical anatomical regions, such as the hippocampus, amygdala, thalamus, and the temporal, frontal and cingulate cortices, might predispose TLE brains to psychosis. Studies of the effects of kindling and injection of neuroactive substances on behavior and electrophysiological patterns may offer a model of how limbic seizures in humans increase the vulnerability of TLE patients to psychiatric symptoms.

Serial conditional discrimination and temporal bisection in rats selectively lesioned in the dentate gyrus.

In positive serial conditional discrimination, animals respond during a target stimulus when it is preceded by a feature stimulus, but they do not respond when the same target stimulus is presented alone. Moreover, the feature and target stimuli are separated from each other by an empty interval. The present work aimed to investigate if two durations (4 or 16s) of the same feature stimulus (light) could modulate the operant responses of rats to different levers (A and B) during a 5-s target stimulus (tone). In the present study, lever A was associated with the 4-s light, and lever B was associated with the 16-s light. A 5-s empty interval was included between the light and the tone. In the same training procedure, the rats were also presented with the 5-s tone without the preceding light stimuli. In these trials, the responses were not reinforced. We evaluated the hippocampal involvement of these behavioral processes by selectively lesioning the dentate gyrus with colchicine. Once trained, the rats were submitted to a test using probe trials without reinforcement. They were presented with intermediate durations of the feature stimulus (light) to obtain a temporal bisection curve recorded during the exposure to the target stimuli. The rats from both groups learned to respond with high rates during tones preceded by light and with low rates during tones presented alone, which indicated acquisition of the serial conditional discrimination. The rats were able to discriminate between the 4- and 16-s lights by correctly choosing lever A or B. In the test, the temporal bisection curves from both experimental groups showed a bisection point at the arithmetic mean between 4 and 16s. Such processes were not impaired by the dentate gyrus lesion. Thus, our results showed that different durations of a feature stimulus could result in conditional properties. However, this processing did not appear to depend on the dentate gyrus alone.

Estimação temporal de ratos com lesão hipocampal em discriminação condicional operante / Temporal estimation of rats with hippocampal lesion in operant conditional discrimination

O desempenho de ratos com lesão no giro denteado do hipocampo foi avaliado durante tarefa operante de discriminação condicional com manipulação da duração do estímulo-característica. Foram usados 16 ratos privados de água: oito lesados no giro denteado com microinjeções de colchicina e oito controle-operados. Os ratos foram submetidos a treino de discriminação condicional positiva (práticas L15 seta img border=0 width=32 height=32 src="../img/revistas/rip/v41n3/3a08f1.jpg">T5+ e T5-) e negativa (L5 seta img border=0 width=32 height=32 src="../img/revistas/rip/v41n3/3a08f1.jpg">R15- e R15+), sendo L estímulo-característica luz branca, T (tom puro) e R (ruído branco) estímulos-alvo, 5 e 15 durações em segundos, seta (seta img border=0 width=32 height=32 src="../img/revistas/rip/v41n3/3a08f1.jpg">) intervalo vazio de 5 s e + e - presença e ausência de reforçamento, respectivamente. O teste empregou práticas de extinção, com durações de L de 15, 13, 11, 9, 7 e 5 s. Os dados mostraram aquisição da discriminação condicional positiva e negativa, sem diferenças entre o grupo experimental e o controle. Diferentes durações de um estímulo podem adquirir propriedades condicionais. Contudo, o processamento da duração do estímulo-característica parece não depender somente do giro denteado do hipocampo.

The performance of rats with hippocampus´ dentate gyrus lesion was evaluated during an operant conditional discrimination task with manipulation of the duration of the feature-stimulus. Sixteen rats under water deprivation were used: eight lesioned in the dentate gyrus by colchicine microinjections and eight sham-operated. The rats were submitted to a conditional discrimination training with feature-positive practices (L15 arrow img border=0 width=32 height=32 src="../img/revistas/rip/v41n3/3a08f1.jpg">T5+ and T5-) and feature-negative practices (L5 arrow img border=0 width=32 height=32 src="../img/revistas/rip/v41n3/3a08f1.jpg">R15- and R15+), where L is feature-stimulus white light, T (pure tone) and R (white noise) are target-stimuli, 5 and 15 are durations in seconds, arrow (arrow img border=0 width=32 height=32 src="../img/revistas/rip/v41n3/3a08f1.jpg">) is a 5 s empty interval and + and - are presence and absence of reinforcement, respectively. In the test, practices in extinction were used, with L durations of 15, 13, 11, 9, 7 and 5 s. The data indicated acquisition of positive and negative conditional discrimination, without differences between the experimental group and the control group. Different durations of a stimulus can acquire conditional properties. However, the feature-stimulus duration processing apparently do not depends on the hippocampus´ dentate gyrus alone.

Estimação temporal de ratos com lesão hipocampal em discriminação condicional operante / Temporal estimation of rats with hippocampal lesion in operant conditional discrimination

O desempenho de ratos com lesão no giro denteado do hipocampo foi avaliado durante tarefa operante de discriminação condicional com manipulação da duração do estímulo-característica. Foram usados 16 ratos privados de água: oito lesados no giro denteado com microinjeções de colchicina e oito controle-operados. Os ratos foram submetidos a treino de discriminação condicional positiva (práticas L15 T5+ e T5-) e negativa (L5 R15- e R15+), sendo L estímulo-característica luz branca, T (tom puro) e R (ruído branco) estímulos-alvo, 5 e 15 durações em segundos, seta intervalo vazio de 5 s e + e - presença e ausência de reforçamento, respectivamente. O teste empregou práticas de extinção, com durações de L de 15, 13, 11, 9, 7 e 5 s. Os dados mostraram aquisição da discriminação condicional positiva e negativa, sem diferenças entre o grupo experimental e o controle. Diferentes durações de um estímulo podem adquirir propriedades condicionais. Contudo, o processamento da duração do estímulo-característica parece não depender somente do giro denteado do hipocampo.(AU)

The performance of rats with hippocampus´ dentate gyrus lesion was evaluated during an operant conditional discrimination task with manipulation of the duration of the feature-stimulus. Sixteen rats under water deprivation were used: eight lesioned in the dentate gyrus by colchicine microinjections and eight sham-operated. The rats were submitted to a conditional discrimination training with feature-positive practices (L15 T5+ and T5-) and feature-negative practices (L5 R15- and R15+), where L is feature-stimulus white light, T (pure tone) and R (white noise) are target-stimuli, 5 and 15 are durations in seconds, arrow is a 5 s empty interval and + and - are presence and absence of reinforcement, respectively. In the test, practices in extinction were used, with L durations of 15, 13, 11, 9, 7 and 5 s. The data indicated acquisition of positive and negative conditional discrimination, without differences between the experimental group and the control group. Different durations of a stimulus can acquire conditional properties. However, the feature-stimulus duration processing apparently do not depends on the hippocampus´ dentate gyrus alone.(AU)