Alpha2‐adrenergic receptor activation regulates cortical interneuron migration

Monoamines such as serotonin and dopamine have been shown to regulate cortical interneuron migration but very little is known regarding noradrenaline. Similarly to other monoamines, noradrenaline is detected during embryonic cortical development and adrenergic receptors are expressed in transient embryonic zones of the pallium that contain migrating neurons. Evidence of a functional role for the adrenergic system in interneuron migration is lacking. In this study we first investigated the expression pattern of adrenergic receptors in mouse cortical interneuron subtypes preferentially derived from the caudal ganglionic eminences, and found that they expressed different subtypes of adrenergic receptors. To directly monitor the effects of adrenergic receptor stimulation on interneuron migration we used time‐lapse recordings in cortical slices and observed that alpha2 adrenergic receptors (adra2) receptor activation inhibits the migration of cortical interneurons in a concentration‐dependent and reversible manner. Furthermore, we observed that following adra2 activation the directionality of migrating interneurons was significantly modified, suggesting that adra2 stimulation could modulate their responsiveness to guidance cues. Finally the distribution of cortical interneurons was altered in vivo in adra2a/2c‐knockout mice. These results support the general hypothesis that adrenergic dysregulation occurring during embryonic development alters cellular processes involved in the formation of cortical circuits.     

Corticotropin‐releasing factor infusion into nucleus incertus suppresses medial prefrontal cortical activity and hippocampo‐medial prefrontal cortical long‐term potentiation

The medial prefrontal cortex (mPFC) in the rat has been implicated in a variety of cognitive processes, including working memory and expression of fear memory. We investigated the inputs from a brain stem nucleus, the nucleus incertus (NI), to the prelimbic area of the mPFC. This nucleus strongly expresses corticotropin‐releasing factor type 1 (CRF₁) receptors and responds to stress. A retrograde tracer was used to verify connections from the NI to the mPFC. Retrogradely labelled cells in the NI expressed CRF receptors. Electrophysiological manipulation of the NI revealed that stimulation of the NI inhibited spontaneous neuronal firing in the mPFC. Similarly, CRF infusion into the NI, in order to mimic a stressful condition, inhibited neuronal firing and burst firing in the mPFC. The effect of concurrent high‐frequency stimulation of the NI on plasticity in the hippocampo‐prelimbic medial prefrontal cortical (HP‐mPFC) pathway was studied. It was found that electrical stimulation of the NI impaired long‐term potentiation in the HP‐mPFC pathway. Furthermore, CRF infusion into the NI produced similar results. These findings might account for some of the extra‐pituitary functions of CRF and indicate that the NI may play a role in stress‐driven modulation of working memory and possibly other cognitive processes subserved by the mPFC.     

Ethanol and PTZ effects on siRNA‐mediated GABAB1 receptor: Down regulation of intracellular signaling pathway in prenatal rat cortical and hippocampal neurons

GABA_B receptors (R) are widely expressed and distributed in the nervous system, and have been implicated in variety of neurodegenerative and pathophysiological disorders. However, the exact molecular mechanism regarding responsibility of GABA_B1R in downstream signaling pathway is not well understood. The present study was undertaken to explore the downstream signaling and role of GABA_B1R upon acute ethanol and pentylenetetrazol (PTZ) exposure for (20 min) in cortical and hippocampal neuronal cell cultures by using GABA_B1R RNA interference (i) (30 nM, 48 h) at gestational days 17.5. The results showed that GABA_B1R and protein kinase A‐α (PKA) showed decreased expression upon ethanol and PTZ exposure in cortical and hippocampal neurons during transfected and nontransfected conditions, whereas these effects could lead to significant changes in phosphorylation of cAMP‐response element binding protein (p‐CREB) expression where GABA_B1R was knocked down. Furthermore, intracellular Ca⁺² concentrations were also reduced in some groups after transfection with GABA_B1R RNAi. These results showed a critical role of GABA_B1R upon ethanol and PTZ exposure by modulating downstream signaling pathway. Finally, these findings suggested that inhibition of GABA_B1R results in the modulation of PKA, p‐CREB pathway may play a role in long‐term changes in the nervous system, and may be an underlying cause of ethanol's effects. Synapse 64:181–190, 2010. © 2009 Wiley‐Liss, Inc.     

Parvalbumin‐, calbindin‐, and calretinin‐immunoreactive hippocampal interneuron density in autism

Lawrence YA, Kemper TL, Bauman ML, Blatt GJ. Parvalbumin‐, calbindin‐, and calretinin‐immunoreactive hippocampal interneuron density in autism.
Acta Neurol Scand: 2010: 121: 99–108.
© 2009 The Authors Journal compilation © 2009 Blackwell Munksgaard. Background – There has been a long‐standing interest in the possible role of the hippocampus in autism and both postmortem brain and neuroimaging studies have documented varying abnormalities in this limbic system structure. Aims – This study investigates the density of subsets of hippocampal interneurons, immunostained with the calcium binding proteins, calbindin (CB), calretinin (CR) and parvalbumin (PV) to determine whether specific subpopulations of interneurons are impacted in autism. Materials and methods – Unbiased stereological techniques were used to quantify the neuronal density of these immunoreactive subpopulations of gamma‐aminobutyric acid‐ergic (GABAergic) interneurons analyzed in the CA and subicular fields in postmortem brain material obtained from five autistic and five age‐, gender‐ and postmortem interval‐matched control cases. Results – Results indicate a selective increase in the density of CB‐immunoreactive interneurons in the dentate gyrus, an increase in CR‐immunoreactive interneurons in area CA1, and an increase in PV‐immunoreactive interneurons in areas CA1 and CA3 in the hippocampus of individuals with autism when compared with controls. Discussion/conclusions – Although our sample size is small, these findings suggest that GABAergic interneurons may represent a vulnerable target in the brains of individuals with autism, potentially impacting upon their key role in learning and information processing. These preliminary findings further suggest the need for future more expanded studies in a larger number of postmortem brain samples from cases of autism and controls.     

Beta-adrenergic receptors are differentially expressed in distinct interneuron subtypes in the rat hippocampus

Noradrenaline (NA) acting via beta-adrenergic receptors (betaARs) plays an important role in the modulation of memory in the hippocampus. betaARs have been shown to be expressed in principal cells, but their distribution across different interneuron classes is unknown. We have used specific interneuron markers including calcium binding proteins (parvalbumin, calbindin, and calretinin) and neuropeptides (somatostatin, neuropeptide Y, and cholecystokinin) together with either beta1AR or beta2AR to determine the distribution of these receptors in all major subfields of the hippocampus. We found that beta1AR-expressing interneurons were more prevalent in the CA3 and CA1 regions of the hippocampus than in the dentate gyrus, where they were relatively sparse. beta2AR-expressing interneurons were more uniformly distributed between all three regions of the hippocampus. A high proportion of neuropeptide Y-containing interneurons in the dentate gyrus co-expressed beta2AR. beta1AR labeling was common in interneurons expressing somatostatin and parvalbumin in the CA3 and CA1 regions, particularly in the stratum oriens of these regions. beta2AR labeling was more likely to be found than beta1AR labeling in cholecystokinin-expressing interneurons. In contrast, calretinin-containing interneurons were virtually devoid of beta1AR or beta2AR labeling. These regional and interneuron type-specific differences suggest functionally distinct roles for NA in modulating hippocampal activity via activation of betaARs.     

Development of benzodiazepine binding subtypes in three regions of rat brain

An examination of the development of benzodiazepine binding of the high and low affinity triazolopyridizine (TPZ) type was undertaken in rat cortex, hippocampus and cerebellum. Various concentrations of a typical triazolopyridizine, CL-218-872, were used to displace [3H]flunitrazepam from synaptosomal fractions from rats of postnatal ages day 0, 7, 14, 21, 35 and 70. In contrast to the cortex and cerebellum, hippocampus displays high affinity TPZ binding at birth, prior to the periods of dendritic elaboration and synaptogenesis, suggesting that adult proportions of high and low affinity sites are maintained throughout postnatal development. Delayed postnatal development of high affinity TPZ sites is observed in the cerebellum, similar to the postnatal development previously observed in the cortex.     

Orexin‐A increases the firing activity of hippocampal CA1 neurons through orexin‐1 receptors

Orexins including two peptides, orexin‐A and orexin‐B, are produced in the posterior lateral hypothalamus. Much evidence has indicated that central orexinergic systems play numerous functions including energy metabolism, feeding behavior, sleep/wakefulness, and neuroendocrine and sympathetic activation. Morphological studies have shown that the hippocampal CA1 regions receive orexinergic innervation originating from the hypothalamus. Positive orexin‐1 (OX₁) receptors are detected in the CA1 regions. Previous behavioral studies have shown that microinjection of OX₁ receptor antagonist into the hippocampus impairs acquisition and consolidation of spatial memory. However, up to now, little has been known about the direct electrophysiological effects of orexin‐A on hippocampal CA1 neurons. Employing multibarrel single‐unit extracellular recordings, the present study showed that micropressure administration of orexin‐A significantly increased the spontaneous firing rate from 2.96 ± 0.85 to 8.45 ± 1.86 Hz (P < 0.001) in 15 out of the 23 hippocampal CA1 neurons in male rats. Furthermore, application of the specific OX₁ receptor antagonist SB‐334867 alone significantly decreased the firing rate from 4.02 ± 1.08 to 2.11 ± 0.58 Hz in 7 out of the 17 neurons (P < 0.05), suggesting that endogenous orexinergic systems modulate the firing activity of CA1 neurons. Coapplication of SB‐334867 completely blocked orexin‐A–induced excitation of hippocampal CA1 neurons. The PLC pathway may be involved in activation of OX₁ receptor–induced excitation of CA1 neurons. Taken together, the present study's results suggest that orexin‐A produces excitatory effects on hippocampal neurons via OX₁ receptors. © 2016 Wiley Periodicals, Inc.     

Adolescent onset of cortical disinhibition in schizophrenia: insights from animal models

Schizophrenia and related mental disorders are common and devastating conditions for which we have a limited understanding of their origin and mechanisms. Although this apparent lack of progress despite vast research efforts could be due to difficulties in reproducing the disease in animals, animal work is now providing important insight onto possible pathophysiological changes in the brain. Postmortem studies of human brains have provided data indicating altered local inhibitory circuits in the cerebral cortex in schizophrenia and different developmental, pharmacological, and genetic animal models converge in revealing deficits in cortical interneuron function that can be associated with neurophysiological and behavioral alterations resembling aspects of the disease. Schizophrenia pathophysiology has a complex developmental trajectory because overt symptoms become evident during late adolescence despite earlier events contributing to the disease. The late incidence of schizophrenia can be explained by the protracted maturation of brain circuits implicated in the disease, particularly during adolescence. Excitatory and inhibitory processes in cortical circuits are tightly modulated by dopamine (DA), and many aspects of DA function in cortical regions acquire their adult profile during adolescence. This maturation fails to occur or is abnormal in several different rodent models of schizophrenia, yielding a number of functional and behavioral deficits relevant to the disease. Thus, periadolescent changes in cortical inhibitory circuits are a critical developmental stage likely implicated in the transition to schizophrenia. These observations provide the foundation for novel research-based therapeutic approaches and perhaps will even lead to ways to prevent the progression of the disease in predisposed subjects.     

Hippocampal‐prefrontal theta phase synchrony in planning of multi‐step actions based on memory retrieval

Planning of multi‐step actions based on the retrieval of acquired information is essential for efficient foraging. The hippocampus (HPC) and prefrontal cortex (PFC) may play critical roles in this process. However, in rodents, many studies investigating such roles utilized T‐maze tasks that only require one‐step actions (i.e., selection of one of two alternatives), in which memory retrieval and selection of an action based on the retrieval cannot be clearly differentiated. In monkeys, PFC has been suggested to be involved in planning of multi‐step actions; however, the synchrony between HPC and PFC has not been evaluated. To address the combined role of the regions in planning of multi‐step actions, we introduced a task in rats that required three successive nose‐poke responses to three sequentially illuminated nose‐poke holes. During the task, local field potentials (LFP) and spikes from hippocampal CA1 and medial PFC (mPFC) were simultaneously recorded. The position of the first hole indicated whether the following two holes would be presented in a predictable sequence or not. During the first nose‐poke period, phase synchrony of LFPs in the theta range (4–10 Hz) between the regions was not different between predictable and unpredictable trials. However, only in trials of predictable sequences, the magnitude of theta phase synchrony during the first nose‐poke period was negatively correlated with latency of the two‐step ahead nose‐poke response. Our findings point to the HPC‐mPFC theta phase synchrony as a key mechanism underlying planning of multi‐step actions based on memory retrieval rather than the retrieval itself.     

The action of pulse‐modulated GSM radiation increases regional changes in brain activity and c‐Fos expression in cortical and subcortical areas in a rat model of picrotoxin‐induced seizure proneness

The action of the pulse‐modulated GSM radiofrequency of mobile phones has been suggested as a physical phenomenon that might have biological effects on the mammalian central nervous system. In the present study, GSM‐exposed picrotoxin‐pretreated rats showed differences in clinical and EEG signs, and in c‐Fos expression in the brain, with respect to picrotoxin‐treated rats exposed to an equivalent dose of unmodulated radiation. Neither radiation treatment caused tissue heating, so thermal effects can be ruled out. The most marked effects of GSM radiation on c‐Fos expression in picrotoxin‐treated rats were observed in limbic structures, olfactory cortex areas and subcortical areas, the dentate gyrus, and the central lateral nucleus of the thalamic intralaminar nucleus group. Nonpicrotoxin‐treated animals exposed to unmodulated radiation showed the highest levels of neuronal c‐Fos expression in cortical areas. These results suggest a specific effect of the pulse modulation of GSM radiation on brain activity of a picrotoxin‐induced seizure‐proneness rat model and indicate that this mobile‐phone‐type radiation might induce regional changes in previous preexcitability conditions of neuronal activation. © 2008 Wiley‐Liss, Inc.     

Differential connectivity of short‐ vs. long‐range extrinsic and intrinsic cortical inputs to perirhinal neurons

The perirhinal cortex plays a critical role in recognition and associative memory. However, the network properties that support perirhinal contributions to memory are unclear. To shed light on this question, we compared the synaptic articulation of short‐ and long‐range inputs from the perirhinal cortex or temporal neocortex with perirhinal neurons in rats. Iontophoretic injections of the anterograde tracer Phaseolus vulgaris‐leucoagglutinin (PHAL) were performed at different rostrocaudal levels of the ventral temporal neocortex or perirhinal cortex, and electron microscopic observations of anterogradely labeled (PHAL⁺) axon terminals found at perirhinal sites adjacent to or rostrocaudally distant from the injection sites were performed. After neocortical injections, the density of PHAL⁺ axons in the perirhinal cortex decreased steeply with rostrocaudal distance from the injection sites, much more so than following perirhinal injections. Otherwise, similar results were obtained with neocortical and perirhinal injections. In both cases, most (76–86%) PHAL⁺ axon terminals formed asymmetric synapses, typically with spines (type A, 83–89%) and less frequently with dendritic profiles (type B, 11–17%). The remaining terminals formed symmetric synapses with dendritic profiles (type C, 14–23%). Type B and C synapses were 2.4–2.6 times more frequent in short‐ than long‐range connections. The postsynaptic elements in type A–C synapses were identified with immunocytochemistry for CAMKIIα, a marker of glutamatergic cortical neurons. Type A and C terminals contacted CAMKIIα‐positive principal cells, whereas type B synapses contacted presumed inhibitory neurons. Overall, these results suggest that principal perirhinal neurons are subjected to significantly more inhibition from short‐ than from long‐range cortical inputs, an organization that likely impacts perirhinal contributions to memory. J. Comp. Neurol. 521:2538–2550, 2013. © 2013 Wiley Periodicals, Inc.     

Diffusion‐weighted imaging in multiple system atrophy: A comparison between clinical subtypes

Multiple system atrophy can be classified into two main types, a Parkinsonian (MSA‐P) and a cerebellar (MSA‐C) variant based on clinical presentation. We obtained diffusion‐weighted magnetic resonance imaging (DWI) in 9 MSA‐P and 12 MSA‐C patients and 11 controls, and correlated DWI changes with disease duration and severity. We found that Trace (D) values in the entire and anterior putamen were significantly higher in MSA‐P than in MSA‐C patients and controls, whereas Trace (D) values in the cerebellum and middle cerebellar peduncle (MCP) were significantly higher in MSA‐C than in MSA‐P patients and controls. Increased disease duration was significantly correlated with increased Trace (D) values in pons of MSA‐P patients, and in cerebellum and MCP of MSA‐C patients. Both UMSARS and UPDRS motor scores positively correlated with entire and posterior putaminal Trace (D) values in MSA‐P patients. The diffusivity changes parallel phenotypical and pathologic differences between MSA‐P and MSA‐C patients, suggesting that DWI is a feasible tool for in vivo evaluation of neurodegeneration in MSA. Based on our findings, Trace (D) measurements in the putamen and pons in MSA‐P patients and in the cerebellum and MCP in MSA‐C patients could serve as quantitative markers for microstructural damage in the course of disease. © 2008 Movement Disorder Society     

Increased proximal bifurcation of CA1 pyramidal apical dendrites in sema3A mutant mice

Semaphorin‐3A (Sema3A) is an attractive guidance molecule for cortical apical dendrites. To elucidate the role of Sema3A in hippocampal dendritic formation, we examined the Sema3A expression pattern in the perinatal hippocampal formation and analyzed hippocampal dendrites of the brains from young adult sema3A mutant mice. Sema3A protein was predominantly expressed in the hippocampal plate and the inner marginal zone at the initial period of apical dendritic growth. Neuropilin‐1 and plexin‐A, the receptor components for Sema3A, were also localized in the same regions. The Golgi impregnation method revealed that in wildtype mice more than 90% of hippocampal CA1 pyramidal neurons extended a single trunk or apical trunks bifurcated in stratum radiatum. Seven percent of the pyramidal neurons showed proximal bifurcation of apical trunks in stratum pyramidale or at the border of the stratum pyramidale and stratum radiatum. In sema3A mutant mice, proximally bifurcated apical dendrites were increased to 32%, while the single apical dendritic pyramidal neurons were decreased. We designate this phenotype in sema3A mutant mice as “proximal bifurcation.” In the dissociated culture system, approximately half of the hippocampal neurons from wildtype mice resembled pyramidal neurons, which possess a long, thick, and tapered dendrite. In contrast, only 30% of the neurons from sema3A mutants exhibited pyramidal‐like morphology. Proximal bifurcation of CA1 pyramidal neurons was also increased in the mutant mice of p35, an activator of cyclin‐dependent kinase 5 (Cdk5). Thus, Sema3A may facilitate the initial growth of CA1 apical dendrites via the activation of p35/Cdk5, which may in turn signal hippocampal development. J. Comp. Neurol. 516:360–375, 2009. © 2009 Wiley‐Liss, Inc.     

The peri‐microvascular edema in hippocampal CA1 area in a rat model of sepsis

Encephalopathy is a common complication of sepsis. However, little is known about the morphological changes that occur in the brain during sepsis. In this study, fecal peritonitis was induced in Wistar rats, which had been monitored for 4 h before their brains were removed and samples from the CA1 area taken. In addition to higher blood pressure with a decreasing pattern and a significant drop in rectal temperature, an increased heart rate and marked respiratory failure were observed. The tissue was investigated and compared with corresponding hippocampal samples taken from sham‐operated and not operated control groups. Significantly more peri‐microvascular edema was found in the hippocampal CA1 area in the septic group. The percentages of the peri‐microvascular edema were 158.57 ± 3.6%, 122.84 ± 1.5% and 120.24 ± 1.9% in the fecal peritonitis group, sham‐operated and not operated control groups, respectively. The results may suggest that the edema observed around the microvessels may participate in the pathogenesis of the septic encephalopathy probably by causing in the microvascular permeability characteristics.     

Cytoarchitectural,behavioural and neurophysiological dysfunctions in the BCNU‐treated rat model of cortical dysplasia

Cortical dysplasias (CDs) include a spectrum of cerebral lesions resulting from cortical development abnormalities during embryogenesis that lead to cognitive disabilities and epilepsy. The experimental model of CD obtained by means of in utero administration of BCNU (1‐3‐bis‐chloroethyl‐nitrosurea) to pregnant rats on embryonic day 15 mimics the histopathological abnormalities observed in many patients. The aim of this study was to investigate the behavioural, electrophysiological and anatomical profile of BCNU‐treated rats in order to determine whether cortical and hippocampal lesions can directly lead to cognitive dysfunction. The BCNU‐treated rats showed impaired short‐term working memory but intact long‐term aversive memory, whereas their spontaneous motor activity and anxiety‐like response were normal. The histopathological and immunohistochemical analyses, made after behavioural tests, revealed the disrupted integrity of neuronal populations and connecting fibres in hippocampus and prefrontal and entorhinal cortices, which are involved in memory processes. An electrophysiological evaluation of the CA1 region of in vitro hippocampal slices indicated a decrease in the efficiency of excitatory synaptic transmission and impaired paired pulse facilitation, but enhanced long‐term potentiation (LTP) associated with hyperexcitability in BCNU‐treated rats compared with controls. The enhanced LTP, associated with hyperexcitability, may indicate a pathological distortion of long‐term plasticity. These findings suggest that prenatal developmental insults at the time of peak cortical neurogenesis can induce anatomical abnormalities associated with severe impairment of spatial working memory in adult BCNU‐treated rats and may help to clarify the pathophysiological mechanisms of cognitive dysfunction that is often associated with epilepsy in patients with CD.     

In vivo and in vitro studies on putative interneurones in the rat hippocampus: Possible mediators of feed-forward inhibition

Extracellular and intracellular recordings have been made from non-pyramidal neurones in the rat hippocampus in vivo and in vitro. These cells were situated in the stratum pyramidale but were orthodromically activated with a lower threshold than pyramidal neurones in response to stimulation of the Schaffer collateral/commissural afferents. Cells fired earlier than pyramidal neurones in response to suprathreshold stimulation and, in contrast to pyramidal cells, often fired a burst of action potentials. The non-pyramidal neurones also appeared to be orthodromically activated on stimulating the alveus and fired later than antidromically activated pyramidal cells. A very short action potential duration and the ability to fire at high frequencies in response to long depolarizing current pulses also distinguished these neurons from pyramidal cells. It is suggested that these non-pyramidal cells are interneurones which could mediate an early feed-forward activity onto pyramidal cells such as feed-forward inhibition. They may also be recurrently activated and hence could conceivably mediate a recurrent inhibition.