Chemogenetics Reveal an Anterior Cingulate-Thalamic Pathway for Attending to Task-Relevant Information.

In a changing environment, organisms need to decide when to select items that resemble previously rewarded stimuli and when it is best to switch to other stimulus types. Here, we used chemogenetic techniques to provide causal evidence that activity in the rodent anterior cingulate cortex and its efferents to the anterior thalamic nuclei modulate the ability to attend to reliable predictors of important outcomes. Rats completed an attentional set-shifting paradigm that first measures the ability to master serial discriminations involving a constant stimulus dimension that reliably predicts reinforcement (intradimensional-shift), followed by the ability to shift attention to a previously irrelevant class of stimuli when reinforcement contingencies change (extradimensional-shift). Chemogenetic disruption of the anterior cingulate cortex (Experiment 1) as well as selective disruption of anterior cingulate efferents to the anterior thalamic nuclei (Experiment 2) impaired intradimensional learning but facilitated 2 sets of extradimensional-shifts. This pattern of results signals the loss of a corticothalamic system for cognitive control that preferentially processes stimuli resembling those previously associated with reward. Previous studies highlight a separate medial prefrontal system that promotes the converse pattern, that is, switching to hitherto inconsistent predictors of reward when contingencies change. Competition between these 2 systems regulates cognitive flexibility and choice.

Anterior thalamic NMDA-induced damage impairs extrapolation relying on serial stimulus patterns, in rats.

Extrapolation of serial stimulus patterns seems to depend upon identification and application of patterns relating sequences of stimuli stored in memory, thus allowing prediction of pending events never experienced before. There have been proposals that such a "generator of predictions system" would include the subiculum, mammillary bodies, anteroventral thalamus and cingulate cortex (e.g., Gray, 1982). The anteroventral thalamus (AVT) seems to be in a strategic position, both hodologically and experimentally, to allow testing of this hypothesis. This study investigated the effect of NMDA-induced damage to the anteroventral thalamus [part of the anterodorsal (AD) thalamus was also damaged in some animals], following stereotaxic minute topic microinjections, on the ability of male Wistar rats to extrapolate relying on serial stimulus patterns. Corresponding sham-operated controls received phosphate-saline buffer microinjections at the same stereotaxic coordinates. The subjects were trained to run through a straight alleyway along 31 sessions, one session per day, to get rewarded. Each session included four successive trials. Subjects exposed to the monotonic serial pattern received 14, 7, 3, 1 sunflower seeds along trials. Subjects exposed to the non-monotonic serial pattern received 14, 3, 7, 1 sunflower seeds. On the 32nd testing session, a fifth trial, never experienced before, was included immediately after the fourth trial. Sham-operated control subjects exposed to the monotonic serial pattern were expected to exhibit longer running times, since the content of their prediction in the fifth trial should be "less than 1 sunflower seeds". In contrast, control subjects exposed to the non-monotonic serial pattern were expected to exhibit shorter running times, since the content of their prediction would be "more than 1 sunflower seeds". Confirming these predictions, control subjects exposed to the monotonic serial pattern exhibited longer running times as compared to both, their own running times in previous trials within the same session and control subjects exposed to the non-monotonic schedule, thus indicating the occurrence of extrapolation. In contrast, AVT/AD lesioned subjects exposed to the monotonic schedule did not exhibit this increase in running times on the fifth trial, indicating lack of extrapolation. These results indicate that extrapolation relying on serial stimulus patterns is disrupted following extensive NMDA-induced damage to AVT and part of the AD. This represents the first consistent demonstration that the anterior thalamic nuclei are required for extrapolation of serial stimulus patterns and generation of predictions.

The Role of Hippocampal Neurogenesis in ANT-DBS for LiCl-Pilocarpine-Induced Epileptic Rats.

PURPOSE: Abnormal neurogenesis in the hippocampus after status epilepticus (SE) has been suggested as a key pathogeny of temporal lobe epilepsy. This study aimed to investigate the effect of deep brain stimulation of the anterior thalamic nucleus (ANT-DBS) on hippocampal neurogenesis in LiCl-pilocarpine-induced epileptic rats and to analyze its relationship with postoperative spontaneous recurrent seizures (SRS) and anxiety. METHOD: SE was induced by a systemic LiCl-pilocarpine injection in adult male rats. Rats in the DBS group underwent ANT-DBS immediately after successful SE induction. SRS was only recorded during the chronic stage. An elevated plus maze was used to evaluate the level of anxiety in rats 7, 28, and 60 days after SE onset. After the elevated plus-maze experiment, rats were sacrificed under anesthesia in order to evaluate hippocampal neurogenesis. Doublecortin (DCX) was used as a marker for neurogenesis. RESULTS: During the chronic stage, SRS in rats in the DBS group were significantly decreased. The level of anxiety was increased significantly in rats in the DBS group 28 days after SE, while no significant differences in anxiety levels were found 7 and 60 days after SE. The number of DCX-positive cells in the hippocampus was significantly increased 7 days after SE and was significantly decreased 60 days after SE in all rats in which SE was induced. However, the number of DCX-positive cells in the DBS group was significantly lower than that in the other groups 28 days after SE. CONCLUSIONS: ANT-DBS may suppress SRS and increase the postoperative anxiety of epileptic rats by influencing hippocampal neurogenesis.

Mediodorsal but not anterior thalamic nuclei lesions impair acquisition of a conditional discrimination task.

The limbic thalamus is a heterogeneous structure with distinctive cortical connectivity. A recent review suggests that the mediodorsal thalamic nucleus (MD), unlike the anterior thalamic nuclei (ATN), may be involved in selecting relevant information in tasks relying on executive functions. We compared the effects of excitotoxic lesions of the MD or the ATN on the acquisition of a simple conditional discrimination in rats. When required to choose from two levers according to auditory or visual cues, ATN rats and sham-lesioned rats performed to the same levels and displayed similar acquisition curves. Under the same conditions, MD rats' acquisition of the task was markedly delayed. This group nevertheless attained nearly normal performances after more extensive training. Furthermore, all rats learned reversal of the original discrimination at the same rate. These results highlight functional specialization within the limbic thalamus and support the notion that MD contributes to the identification of relevant dimensions in conditional tasks during the initial stages of acquisition.

GABAergic neurons of anterior thalamic reticular nucleus regulate states of consciousness in propofol- and isoflurane-mediated general anesthesia.

BACKGROUND: The thalamus system plays critical roles in the regulation of reversible unconsciousness induced by general anesthetics, especially the arousal stage of general anesthesia (GA). But the function of thalamus in GA-induced loss of consciousness (LOC) is little known. The thalamic reticular nucleus (TRN) is the only GABAergic neurons-composed nucleus in the thalamus, which is composed of parvalbumin (PV) and somatostatin (SST)-expressing GABAergic neurons. The anterior sector of TRN (aTRN) is indicated to participate in the induction of anesthesia, but the roles remain unclear. This study aimed to reveal the role of the aTRN in propofol and isoflurane anesthesia. METHODS: We first set up c-Fos straining to monitor the activity variation of aTRNPV and aTRNSST neurons during propofol and isoflurane anesthesia. Subsequently, optogenetic tools were utilized to activate aTRNPV and aTRNSST neurons to elucidate the roles of aTRNPV and aTRNSST neurons in propofol and isoflurane anesthesia. Electroencephalogram (EEG) recordings and behavioral tests were recorded and analyzed. Lastly, chemogenetic activation of the aTRNPV neurons was applied to confirm the function of the aTRN neurons in propofol and isoflurane anesthesia. RESULTS: c-Fos straining showed that both aTRNPV and aTRNSST neurons are activated during the LOC period of propofol and isoflurane anesthesia. Optogenetic activation of aTRNPV and aTRNSST neurons promoted isoflurane induction and delayed the recovery of consciousness (ROC) after propofol and isoflurane anesthesia, meanwhile chemogenetic activation of the aTRNPV neurons displayed the similar effects. Moreover, optogenetic and chemogenetic activation of the aTRN neurons resulted in the accumulated burst suppression ratio (BSR) during propofol and isoflurane GA, although they represented different effects on the power distribution of EEG frequency. CONCLUSION: Our findings reveal that the aTRN GABAergic neurons play a critical role in promoting the induction of propofol- and isoflurane-mediated GA.

Directional responding of C57BL/6J mice in the Morris water maze is influenced by visual and vestibular cues and is dependent on the anterior thalamic nuclei.

Recent findings indicate that rats navigate in spatial tasks such as the Morris water maze (MWM) using a local cue-based reference frame rather than a distal cue-based reference frame. Specifically, rats swim in a particular direction to a location relative to pool-based cues, rather than to an absolute location defined by room-based cues. Neural mechanisms supporting this bias in rodents for relative responding in spatial tasks are not yet understood. Anterior thalamic neurons discharge according to the current directional heading of the animal. The contribution of head direction (HD) cell activity to navigation has been difficult to elucidate. We found that male C57BL/6J mice trained for 4 or 7 d in the MWM exhibited an overwhelming preference for swimming in a direction relative to pool-based cues over absolute responding during a platform-less probe test. Rotation of extramaze cues caused a corresponding rotation of the direction mice swam during the probe test, suggesting that both pool- and room-based reference frames guide platform search. However, disorienting the mice before the probe test disturbed relative responding. Therefore, relative responding is guided by both internal and external cue sources. Selective inactivation of anterior thalamic nuclei (ATN) by microinfusion of muscimol or fluorophore-conjugated muscimol caused a near complete shift in preference from relative to absolute responding. Interestingly, inactivation of the dorsal CA1 region of the hippocampus did not affect relative responding. These data suggest that ATN, and HD cells therein, may guide relative responding in the MWM, a task considered by most to reflect hippocampal processing.

Regulation of Kiss1 and dynorphin gene expression in the murine brain by classical and nonclassical estrogen receptor pathways.

Kisspeptin is a product of the Kiss1 gene and is expressed in the forebrain. Neurons that express Kiss1 play a crucial role in the regulation of pituitary luteinizing hormone secretion and reproduction. These neurons are the direct targets for the action of estradiol-17beta (E(2)), which acts via the estrogen receptor alpha isoform (ER alpha) to regulate Kiss1 expression. In the arcuate nucleus (Arc), where the dynorphin gene (Dyn) is expressed in Kiss1 neurons, E(2) inhibits the expression of Kiss1 mRNA. However, E(2) induces the expression of Kiss1 in the anteroventral periventricular nucleus (AVPV). The mechanism for differential regulation of Kiss1 in the Arc and AVPV by E(2) is unknown. ER alpha signals through multiple pathways, which can be categorized as either classical, involving the estrogen response element (ERE), or nonclassical, involving ERE-independent mechanisms. To elucidate the molecular basis for the action of E(2) on Kiss1 and Dyn expression, we studied the effects of E(2) on Kiss1 and Dyn mRNAs in the brains of mice bearing targeted alterations in the ER alpha signaling pathways. We found that stimulation of Kiss1 expression by E(2) in the AVPV and inhibition of Dyn in the Arc required an ERE-dependent pathway, whereas the inhibition of Kiss1 expression by E(2) in the Arc involved ERE-independent mechanisms. Thus, distinct ER alpha signaling pathways can differentially regulate the expression of identical genes across different brain regions, and E(2) can act within the same neuron through divergent ER alpha signaling pathways to regulate different neurotransmitter genes.

Dissociable contributions of mediodorsal and anterior thalamic nuclei in visual attentional performance: A comparison using nicotinic and muscarinic cholinergic receptor antagonists.

BACKGROUND: Thalamic subregions mediate various cognitive functions, including attention, inhibitory response control and decision making. Such neuronal activity is modulated by cholinergic thalamic afferents and deterioration of such modulatory signaling has been theorised to contribute to cognitive decline in neurodegenerative disorders. However, the thalamic subnuclei and cholinergic receptors involved in cognitive functioning remain largely unknown. AIMS: We investigated whether muscarinic or nicotinic receptors in the mediodorsal thalamus and anterior thalamus contribute to rats' performance in the five-choice serial reaction time task, which measures sustained visual attention and impulsive action. METHODS: Male Long-Evans rats were trained in the five-choice serial reaction time task then surgically implanted with guide cannulae targeting either the mediodorsal thalamus or anterior thalamus. Reversible inactivation of either the mediodorsal thalamus or anterior thalamus were achieved with infusions of the γ-aminobutyric acid-ergic agonists muscimol and baclofen prior to behavioural assessment. To investigate cholinergic mechanisms, we also assessed the behavioural effects of locally administered nicotinic (mecamylamine) and muscarinic (scopolamine) receptor antagonists. RESULTS: Reversible inactivation of the mediodorsal thalamus severely impaired discriminative accuracy and response speed and increased omissions. Inactivation of the anterior thalamus produced less profound effects, with impaired accuracy at the highest dose. In contrast, blocking cholinergic transmission in these regions did not significantly affect five-choice serial reaction time task performance. CONCLUSIONS/INTERPRETATIONS: These findings show the mediodorsal thalamus plays a key role in visuospatial attentional performance that is independent of local cholinergic neurotransmission.

Injection of muscimol, a GABAa agonist into the anterior thalamic nucleus, suppresses hippocampal neurogenesis in amygdala-kindled rats.

The relationship between neurogenesis and epilepsy remains to be solved so far, although aberrant electric circuit recognized in epilepsy might be involved in neurogenesis. In this study, neurogenesis and the proliferation of astrocytes in the subgranular zone of the hippocampus were explored using unilateral amygdala-kindled rats with or without muscimol, a gamma-aminobutyric acid a (GABAa) agonist injection into the bilateral anterior thalamic nuclei (AN). Muscimol injection significantly ameliorated the behavioral scores of epilepsy without any significant alteration on the electroencephalography recorded at the stimulated basolateral amygdala, thus suggesting that muscimol injection might affect the secondary generalization, but not the initial discharge itself. The number of bromodeoxyuridine (BrdU), BrdU/doublecortin and BrdU/glial fibrillary acidic protein-positive cells in the subgranular zone of kindled animals increased markedly. Muscimol injection significantly suppressed neurogenesis, but not the proliferation of astrocyte, in the subgranular zone of the non-stimulated side, probably through the suppression of secondary generalization via AN. The results might indicate the underlying relationships between neurogenesis and epilepsy, that epileptic propagation in unilateral amygdala-kindled rats might go through AN into the contralateral side with subsequent neurogenesis, although further studies need to clarify the hypothesis.

Neuro-behavioral effects after systemic administration of MK-801 and disinhibition of the anterior thalamic nucleus in rats: Potential relevance in schizophrenia.

Non-competitive N-methyl-d-aspartate receptor (NMDA-R) antagonists have been suggested to evoke psychotomimetic-like behaviors by selectively targeting GABAergic elements in cortical and thalamic circuits. In previous studies, we had reported the involvement of the reticular and anterior thalamic nuclei (ATN) in the MK-801-evoked hyperactivity and other motor alterations. Consistent with the possibility that these responses were mediated by thalamic disinhibition, we examined the participation of cortical and hippocampal areas innervated by ATN in the responses elicited by the systemic administration of MK-801 (0.2 mg/kg) and compared them to the effects produced by the microinjection of a subconvulsive dose of bicuculline (GABAA receptor antagonist) in the ATN. We used the expression of Fos related antigen 2 (Fra-2) as a neuronal activity marker in the ATN and its projection areas such as hippocampus (HPC), retrosplenial cortex (RS), entorhinal cortex (EC) and medial prefrontal cortex (mPFC). Dorsal (caudate-putamen, CPu) and ventral striatum (nucleus accumbens, core and shell, NAc,co and NAc,sh) were also studied. Behavioral and brain activation results suggest a partial overlap after the effect of MK-801 administration and ATN disinhibition. MK-801 and ATN disinhibition increases locomotor activity and disorganized movements, while ATN disinhibition also reduces rearing behavior. A significant increase in Fra-2 immunoreactivity (Fra-2-IR) in the ATN, mPFC (prelimbic area, PrL) and NAc,sh was observed after MK-801, while a different pattern of Fra-2-IR was detected following ATN disinhibition (e.g., increase in DG and NAc,sh, and decrease in PrL cortex). Overall, our data may contribute to the understanding of dysfunctional neural circuits involved in schizophrenia.

Combined blockade of serotonergic and muscarinic transmission disrupts the anterior thalamic head direction signal.

Head direction (HD) cells have been speculated to be part of a network mediating navigational behavior. Previous work has shown that combined administration of serotonergic and muscarinic antagonists eliminates hippocampal theta activity and produces navigational deficits more severe than blockade of either neurotransmitter system alone. The authors sought to assess this effect on the directional characteristics of HD cells. HD cells were recorded from the anterior dorsal thalamus of Long-Evans rats before and after administration of the serotonergic antagonist methiothepin, the muscarinic antagonist scopolamine, both drugs, or saline. Combined drug administration produced HD cells with preferred directions that drifted within recording sessions. In addition, cells showed shifts in the preferred directions at the start of a session relative to the position of the major landmarks, suggesting that combined drug administration led to deficits in landmark control of the HD system. Single drug exposures to methiothepin or scopolamine did not noticeably affect the directional characteristics of HD cells. This finding that navigation-impairing drugs can disrupt the HD signal provides further evidence that this network plays an important role in navigational behavior.

Morphology and synaptic organization of non-dopaminergic nigral projections to the medio dorsal thalamic nucleus of the rat, a study by anterograde transport of PHA-L.

BACKGROUND: Mediodorsal (MD) thalamic nucleus, which is considered to take place between extra pyramidal and limbic feedback circuit, receives projective fibers from ventrolateral neurons of reticular part of substantia nigra (SNr). In order to better understand the influence and chemical reaction of these fibers upon MD nucleus, the morphology and synaptology of them were examined in the present study. METHODS: Phaseolous vulgaris-leucoagglutin (PHA-L) was injected into substantia nigra pars reticulate. After 3-4 days, the sections of SNr injection site and MD nucleus were prepared. Then, we examined organization, morphology and, synaptology of PHA-L labeled SNr fibers that go to caudal and lateral part of MD thalamic nucleus. RESULTS: At the electron microscopic level, the SNr terminals made synapses predominantly with the medium to small dendrites and far less frequently with soma and large dendrites. These terminals were packed with polymorphic synaptic vesicles and formed symmetrical synapses; furthermore, it has been already recognized that cortico straital fibers from sensory-motor cortex go to region of the SNr that give rise to the nigrothalamic fibers. CONCLUSION: This data suggest that upon the synaptic organization, morphology and chemical nature of GABAergic, SNr fibers may have different inhibitory influence on MD neurons regulating the thalamic output from MD to cerebral cortex in the control of limbic and extra pyramidal feedback system.

Anterior thalamic nuclei, but not retrosplenial cortex, lesions abolish latent inhibition in rats.

The present study examined the effects of excitotoxic lesions in 2 closely related structures, the anterior thalamic nuclei and the retrosplenial cortex, on latent inhibition. Latent inhibition occurs when nonreinforced preexposure to a stimulus retards the subsequent acquisition of conditioned responding to that stimulus. Latent inhibition was assessed in a within-subject procedure with auditory stimuli and food reinforcement. As expected, sham-operated animals were slower to acquire conditioned responding to a stimulus that had previously been experienced without consequence, relative to a non-preexposed stimulus. This latent inhibition effect was absent in rats with excitotoxic lesions in the anterior thalamic nuclei, as these animals conditioned to both stimuli at equivalent rates. The retrosplenial lesions appeared to spare latent inhibition, as these animals displayed a robust stimulus preexposure effect. The demonstration here that anterior thalamic nuclei lesions abolish latent inhibition is consistent with emerging evidence of the importance of these thalamic nuclei for attentional control. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Differential role of the anterior and intralaminar/lateral thalamic nuclei in systems consolidation and reconsolidation.

The anterior thalamic nuclei (ATN) and the intralaminar/lateral thalamic nuclei (ILN/LT) play different roles in memory processes. The ATN are believed to be part of an extended hippocampal system, and the ILN/LT have strong connections with the medial prefrontal cortex. It was shown that the ILN/LT are involved in systems consolidation. However, whether they are necessary for memory retrieval as well remains unclear. We, therefore, used c-Fos immunohistochemistry and reversible inactivations to investigate the role of the ATN and ILN/LT in recent and remote contextual fear memory retrieval in rats. The results confirm a differential role of the ATN and ILN/LT in systems consolidation, showing the involvement of the ATN in recent but not remote memory retrieval. This study also pinpoints which specific nuclei are involved in retrieval: the anterodorsal nucleus for recent memories, and the lateral mediodorsal nucleus for remote memories. Lastly, we also show that the ATN are not involved in reconsolidation. Together, the results suggest that these nuclei provide critical feedback for successful memory retrieval and systems consolidation.

Beyond spatial memory: the anterior thalamus and memory for the temporal order of a sequence of odor cues.

Influential recent proposals state that the anterior thalamic (AT) nuclei constitute key components of an "extended hippocampal system." This idea is, however, based on lesion studies that used spatial memory tasks and there has been no evidence that AT lesions cause deficits in any hippocampal-dependent nonspatial tasks. The present study investigated the role of the AT nuclei in nonspatial memory for a sequence of events based on the temporal order of a list of odors, because this task has recently been shown to depend on the integrity of the hippocampal formation. After preoperative training, rats with excitotoxic lesions of the AT nuclei showed a severe and selective postoperative impairment when required to remember the order of pseudorandom sequences of six odors. The rats with AT lesions were able instead to learn two new tasks that required recognition memory and the identification of the prior occurrence of events independent of their order. These results strongly matched those described after hippocampal lesions and provide the first unequivocal evidence of a detrimental effect of an AT lesion on a nonspatial hippocampal-dependent memory task.

The effect of pharmacological inactivation of the mammillary body and anterior thalamic nuclei on hippocampal theta rhythm in urethane-anesthetized rats.

The mammillary body (MB) and the anterior thalamic nuclei (ATN) are closely related structures, which take part in learning and memory processes. However, the exact role of these structures has remained unclear. In both structures neurons firing according to hippocampal theta rhythm have been found, mainly in the medial mammillary nucleus (MM) and anteroventral thalamic nucleus (AV). These neurons are driven by descending projections from the hippocampal formation and are thought to convey theta rhythm back to the hippocampus (HP). We argue that the MB-ATN axis not only relays theta signal, but may also modulate it. To examine it, we performed a pharmacological inactivation of the MM and AV by local infusion of procaine, and measured changes in theta activity in selected structures of the extended hippocampal system in urethane-anesthetized rats. The inactivation of the MM resulted in decrease in EEG power in the HP and AV, the most evidently in the lower theta frequency bands, i.e. 3-5Hz in the HP (down to 9.2% in 3- to 4-Hz band and 37.6% in 4- to 5-Hz band, in comparison to the power in the control conditions) and 3-4Hz in the AV (down to 24.9%). After the AV inactivation, hippocampal EEG power decreased in theta frequency bands of 3-8Hz (down to 61.6% in 6- to 7-Hz band and 69.4% in 7- to 8-Hz band). Our results suggest that the role of the MB-ATN axis in regulating theta rhythm signaling may be much more important than has been speculated so far.

A role for the anteromedial thalamic nucleus in the acquisition of contextual fear memory to predatory threats.

Previous studies from our group have shown that cytotoxic lesions in the ventral portion of the anteromedial thalamic nucleus (AMv), one of the main targets of the hypothalamic predator-responsive circuit, strongly impairs contextual fear responses to an environment previously associated with a predator. The AMv is in a position to convey information to cortico-hippocampal-amygdalar circuits involved in the processing of fear memory. However, it remains to be determined whether the nucleus is involved in the acquisition or subsequent expression of contextual fear. In the present investigation, we addressed this question by inactivating the rat AMv with muscimol either prior to cat exposure or prior to exposure to the cat-related context. Accordingly, AMv pharmacological inactivation prior to cat exposure did not interfere with innate fear responses, but it drastically reduced contextual conditioning to the predator-associated environment. On the other hand, AMv inactivation prior to exposure to the environment associated with the predator threat did not affect contextual fear responses. The behavioral results were further supported by the demonstration that AMv inactivation prior to cat exposure also blocked the activation of sites critically involved in the expression of anti-predatory contextual defensive responses (i.e., the dorsal premammillary nucleus and the dorsolateral periaqueductal gray) in animals exposed to the predator-associated context. The AMv projections were also examined, and the results of this investigation outline important paths that can influence hippocampal circuitry and raise new ideas for anterior thalamic-hippocampal paths involved in emotional learning.

Impaired spatial working memory after anterior thalamic lesions: recovery with cerebrolysin and enrichment.

Lesions to the anterior thalamic nuclei (ATN) in rats produce robust spatial memory deficits that reflect their influence as part of an extended hippocampal system. Recovery of spatial working memory after ATN lesions was examined using a 30-day administration of the neurotrophin cerebrolysin and/or an enriched housing environment. As expected, ATN lesions in standard-housed rats given saline produced severely impaired reinforced spatial alternation when compared to standard-housed rats with sham lesions. Both cerebrolysin and enrichment substantially improved this working memory deficit, including accuracy on trials that required attention to distal cues for successful performance. The combination of cerebrolysin and enrichment was more effective than either treatment alone when the delay between successive runs in a trial was increased to 40 s. Compared to the intact rats, ATN lesions in standard-housed groups produced substantial reduction in c-Fos expression in the retrosplenial cortex, which remained low after cerebrolysin and enrichment treatments. Evidence that multiple treatment strategies restore some memory functions in the current lesion model reinforces the prospect for treatments in human diencephalic amnesia.

Spatial working memory and the brainstem cholinergic innervation to the anterior thalamus.

The anteroventral thalamic nucleus (AV) has a role in spatial memory, but the influence of the prominent brainstem cholinergic projection to this region is unknown. Here, spatial memory in a 12-arm radial maze was examined after 0.15 microl bilateral AV infusions of scopolamine. In part one, rats visited six arms singly (the phase 1 arms) and, after a 10 min delay, were allowed free choice to both phase 1 arms and the remaining six baited arms (phase 2 arms). Scopolamine (10 microg) administered during the delay increased errors to both phase 1 and phase 2 arms, whereas PBS infusions increased phase 1 arm errors only. The PBS effect was the result of inserting the internal cannulas alone and not the infusion. The same dose of scopolamine (10 microg) infused before maze testing (part two: no phase 1 arms, no delay) also impaired spatial memory over and above the effects of both PBS and no-infusion, which did not differ markedly. Part two also showed that choice latency and choice strategies were unaffected by PBS and scopolamine. Cannulation and infusion procedures in both parts one and two did not produce any negative carryover effects across multiple control (no internal cannula) sessions, and a trypan blue manipulation indicated that infusions were restricted to the AV region. This study provides the first direct evidence that the brainstem cholinergic innervation to the limbic thalamus influences learning and memory, which may have important implications for human neurological conditions such as alcohol-related disorders and schizophrenia.

Ethanol-induced neuronal apoptosis in vivo requires BAX in the developing mouse brain.

A single episode of ethanol intoxication triggers widespread apoptotic neurodegeneration in the infant rat or mouse brain. The cell death process occurs over a 6-16 h period following ethanol administration, is accompanied by a robust display of caspase-3 enzyme activation, and meets ultrastructural criteria for apoptosis. Two apoptotic pathways (intrinsic and extrinsic) have been described, either of which may culminate in the activation of caspase-3. The intrinsic pathway is regulated by Bax and Bcl-XL and involves Bax-induced mitochondrial dysfunction and release of cytochrome c as antecedent events leading to caspase-3 activation. Activation of caspase-8 is a key event preceding caspase-3 activation in the extrinsic pathway. In the present study, following ethanol administration to infant mice, we found no change in activated caspase-8, which suggests that the extrinsic pathway is not involved in ethanol-induced apoptosis. We also found that ethanol triggers robust caspase-3 activation and apoptotic neurodegeneration in C57BL/6 wildtype mice, but induces neither phenomenon in homozygous Bax-deficient mice. Therefore, it appears that ethanol-induced neuroapoptosis is an intrinsic pathway-mediated phenomenon involving Bax-induced disruption of mitochondrial membranes and cytochrome c release as early events leading to caspase-3 activation.