Neurokinin1 - cholinergic receptor mechanisms in the medial Septum-Dorsal hippocampus axis mediates experimental neuropathic pain.

The neurokinin-1 receptors (NK1Rs) in the forebrain medial septum (MS) region are localized exclusively on cholinergic neurons that partly project to the hippocampus and the cingulate cortex (Cg), regions implicated in nociception. In the present study, we explored the hypothesis that neurotransmission at septal NK1R and hippocampal cholinergic mechanisms mediate experimental neuropathic pain in the rodent chronic constriction injury model (CCI). Our investigations showed that intraseptal microinjection of substance P (SP) in rat evoked a peripheral hypersensitivity (PH)-like response in uninjured animals that was attenuated by systemic atropine sulphate, a muscarinic-cholinergic receptor antagonist. Conversely, pre-emptive destruction of septal cholinergic neurons attenuated the development of PH in the CCI model that also prevented the expression of cellular markers of nociception in the spinal cord and the forebrain. Likewise, anti-nociception was evoked on intraseptal microinjection of L-733,060, an antagonist at NK1Rs, and on bilateral or unilateral microinjection of the cholinergic receptor antagonists, atropine or mecamylamine, into the different regions of the dorsal hippocampus (dH) or on bilateral microinjection into the Cg. Interestingly, the effect of L-733,060 was accompanied with a widespread decreased in levels of CCI-induced nociceptive cellular markers in forebrain that was not secondary to behaviour, suggesting an active modulation of nociceptive processing by transmission at NK1R in the medial septum. The preceding suggest that the development and maintenance of neuropathic nociception is facilitated by septal NK1R-dH cholinergic mechanisms which co-ordinately affect nociceptive processing in the dH and the Cg. Additionally, the data points to a potential strategy for pain modulation that combines anticholinergics and anti-NKRs.

Optogenetic silencing of medial septal GABAergic neurons disrupts grid cell spatial and temporal coding in the medial entorhinal cortex.

The hippocampus and medial entorhinal cortex (MEC) form a cognitive map that facilitates spatial navigation. As part of this map, MEC grid cells fire in a repeating hexagonal pattern across an environment. This grid pattern relies on inputs from the medial septum (MS). The MS, and specifically GABAergic neurons, are essential for theta rhythm oscillations in the entorhinal-hippocampal network; however, the role of this population in grid cell function is unclear. To investigate this, we use optogenetics to inhibit MS-GABAergic neurons and observe that MS-GABAergic inhibition disrupts grid cell spatial periodicity. Grid cell spatial periodicity is disrupted during both optogenetic inhibition periods and short inter-stimulus intervals. In contrast, longer inter-stimulus intervals allow for the recovery of grid cell spatial firing. In addition, grid cell phase precession is also disrupted. These findings highlight the critical role of MS-GABAergic neurons in maintaining grid cell spatial and temporal coding in the MEC.

Regulation of Hippocamposeptal Synaptic Transmission by GABABRs Is Altered in 5XFAD Mice in a Sex- and Age-Dependent Manner.

Hippocamposeptal (HS) neurons send GABAergic projections from the hippocampus to the medial septum/diagonal band of Broca (MS/DBB) as part of a reciprocal loop that is critical for memory. HS neurons are proposed to be particularly sensitive to the deleterious effects of pathological exposure to amyloid-ß (Aß), as would occur during Alzheimer's disease (AD). However, it is not known how HS GABA release in the MS/DBB is altered during the progression of AD. To target HS neurons in a mouse model of AD, we crossed SST-Cre mice to 5XFAD mice and performed stereotaxic injections of Cre-dependent AAV containing mCherry/channelrhodopsin-2 (ChR2) into the hippocampus of offspring at 4, 6, 9, and 12 months. We used optogenetics to selectively stimulate HS terminals while performing whole-cell patch-clamp recordings from MS/DBB neurons in slices. There was a transient reduction in HS-inhibitory postsynaptic current (IPSC) amplitude in female 5XFAD mice at 6 months, but no difference in males at any age, and no difference in paired-pulse ratio in either sex at any age. When bath applying the GABABR agonist, baclofen, we found a larger decrease in HS-IPSC amplitude in 5XFAD females at 9 months and 5XFAD males at 12 months. In 12-month-old 5XFAD females, response to baclofen was significantly reduced. These data suggest that there is a transient increase in responsiveness to GABABR activation in 5XFAD mice that occurs earlier in females than in males. These sex-specific changes to HS function are likely to impact the relay of information between the hippocampus and MS/DBB.

Frequency-dependent seizure-suppressing effects of optogenetic activation of septal inhibitory cells in mesial temporal lobe epilepsy.

Mesial temporal lobe epilepsy (MTLE) is characterized by recurring focal seizures that arise from limbic areas and are often refractory to pharmacological interventions. We have reported that optogenetic stimulation of PV-positive cells in the medial septum at 0.5 Hz exerts seizure-suppressive effects. Therefore, we compared here these results with those obtained by optogenetic stimulation of medial septum PV-positive neurons at 8 Hz in male PV-ChR2 mice (P60-P100) undergoing an initial, pilocarpine-induced status epilepticus (SE). Optogenetic stimulation (5 min ON, 10 min OFF) was performed from day 8 to day 12 after SE at a frequency of 8 Hz (n = 6 animals) or 0.5 Hz (n = 8 animals). Surprisingly, in both groups, no effects were observed on the occurrence of interictal spikes and interictal high frequency oscillations (HFOs). However, 0.5 Hz stimulation induced a significant decrease of seizure occurrence (p < 0.05). Such anti-ictogenic effect was not observed in the 8 Hz protocol that instead triggered seizures (p < 0.05); these seizures were significantly longer under optogenetic stimulation compared to when optogenetic stimulation was not implemented (p < 0.05). Analysis of ictal HFOs revealed that in the 0.5 Hz group, but not in the 8 Hz group, seizures occurring under optogenetic stimulation were associated with significantly lower rates of fast ripples compared to when optogenetic stimulation was not performed (p < 0.05). Our results indicate that activation of GABAergic PV-positive neurons in the medial septum exerts seizure-suppressing effects that are frequency-dependent and associated with low rates of fast ripples. Optogenetic activation of medial septum PV-positive neurons at 0.5 Hz is efficient in blocking seizures in the pilocarpine model of MTLE, an effect that did not occur with 8 Hz stimulation.

A regulatory role of the medial septum in the chloroquine-induced acute itch through local GABAergic system and GABAergic pathway to the anterior cingulate cortex.

Itch, a common somatic sensation, serves as a crucial protective system. Recent studies have unraveled the neural mechanisms of itch at peripheral, spinal cord as well as cerebral levels. However, a comprehensive understanding of the central mechanism governing itch transmission and regulation remains elusive. Here, we report the role of the medial septum (MS), an integral component of the basal forebrain, in modulating the acute itch processing. The increases in c-Fos+ neurons and calcium signals within the MS during acute itch processing were observed. Pharmacogenetic activation manipulation of global MS neurons suppressed the scratching behaviors induced by chloroquine or compound 48/80. Microinjection of GABA into the MS or pharmacogenetic inhibition of non-GABAergic neurons markedly suppressed chloroquine-induced scratching behaviors. Pharmacogenetic activation of the MS-ACC GABAergic pathway attenuated chloroquine-induced acute itch. Hence, our findings reveal that MS has a regulatory role in the chloroquine-induced acute itch through local increased GABA to inhibit non-GABAergic neurons and the activation of MS-ACC GABAergic pathway.

Alterations in hippocampal cholinergic dynamics following CRF infusions into the medial septum of male and female rats.

Corticoptropin releasing factor (CRF) is implicated in stress-related physiological and behavioral changes. The septohippocampal pathway regulates hippocampal-dependent mnemonic processes, which are affected in stress-related disorders, and given the abundance of CRF receptors in the medial septum (MS), this pathway is influenced by CRF. Moreover, there are sex differences in the MS sensitivity to CRF and its impact on hippocampal function. However, the mechanisms underlying these associations remain elusive. In the present study, we utilized an in vivo biosensor-based electrochemistry approach to examine the impact of MS CRF infusions on hippocampal cholinergic signaling dynamics in male and female rats. Our results show increased amplitudes of depolarization-evoked phasic cholinergic signals in the hippocampus following MS infusion of CRF at the 3 ng dose as compared to the infusion involving artificial cerebrospinal fluid (aCSF). Moreover, a trend for a sex × infusion interaction indicated larger cholinergic transients in females. On the contrary, intraseptal infusion of a physiologically high dose (100 ng) of CRF produced a subsequent reduction in phasic cholinergic transients in both males and females. The assessment of tonic cholinergic activity over 30 min post-infusion revealed no changes at the 3 ng CRF dose in either sex, but a significant infusion × sex interaction indicated a reduction in females at the 100 ng dose of CRF as compared to the aCSF. Taken together, our results show differential, dose-dependent modulatory effects of MS CRF on the dynamics of phasic and tonic modes of cholinergic signaling in the hippocampus of male and female rats. These cholinergic signaling modes are critical for memory encoding and maintaining arousal states, and may underlie sex differences in cognitive vulnerability to stress and stress-related psychiatric disorders.

Selective Medial Septum Lesions in Healthy Rats Induce Longitudinal Changes in Microstructure of Limbic Regions, Behavioral Alterations, and Increased Susceptibility to Status Epilepticus.

Septo-hippocampal pathway, crucial for physiological functions and involved in epilepsy. Clinical monitoring during epileptogenesis is complicated. We aim to evaluate tissue changes after lesioning the medial septum (MS) of normal rats and assess how the depletion of specific neuronal populations alters the animals' behavior and susceptibility to establishing a pilocarpine-induced status epilepticus. Male Sprague-Dawley rats were injected into the MS with vehicle or saporins (to deplete GABAergic or cholinergic neurons; n = 16 per group). Thirty-two animals were used for diffusion tensor imaging (DTI); scanned before surgery and 14 and 49 days post-injection. Fractional anisotropy and apparent diffusion coefficient were evaluated in the fimbria, dorsal hippocampus, ventral hippocampus, dorso-medial thalamus, and amygdala. Between scans 2 and 3, animals were submitted to diverse behavioral tasks. Stainings were used to analyze tissue alterations. Twenty-four different animals received pilocarpine to evaluate the latency and severity of the status epilepticus 2 weeks after surgery. Additionally, eight different animals were only used to evaluate the neuronal damage inflicted on the MS 1 week after the molecular surgery. Progressive changes in DTI parameters in both white and gray matter structures of the four evaluated groups were observed. Behaviorally, the GAT1-saporin injection impacted spatial memory formation, while 192-IgG-saporin triggered anxiety-like behaviors. Histologically, the GABAergic toxin also induced aberrant mossy fiber sprouting, tissue damage, and neuronal death. Regarding the pilocarpine-induced status epilepticus, this agent provoked an increased mortality rate. Selective septo-hippocampal modulation impacts the integrity of limbic regions crucial for certain behavioral skills and could represent a precursor for epilepsy development.

Up-regulation of GPR139 in the medial septum ameliorates cognitive impairment in two mouse models of Alzheimer's disease.

G-protein coupled receptors (GPCRs) constitute the largest class of cell surface receptors and present prominent drug targets. GPR139 is an orphan GPCR detected in the septum of the brain. However, its roles in cognition are still unclear. Here we first established a mouse model of cognitive impairment by a single intracerebroventricular injection of aggregated amyloid-beta peptide 1-42 (Aß1-42). RNA-sequencing data analysis showed that Aß1-42 induced a significant decrease of GPR139 mRNA in the basal forebrain. Using GPR139 agonist JNJ-63533054 and behavioral tests, we found that GPR139 activation in the brain ameliorated Aß1-42-induced cognitive impairment. Using western blot, TUNEL apoptosis and Golgi staining assays, we showed that GPR139 activation alleviated Aß1-42-induced apoptosis and synaptotoxicity in the basal forebrain rather than prefrontal cortex and hippocampus. The further study identified that GPR139 was widely expressed in cholinergic neurons of the medial septum (MS). Using the overexpression virus and transgenic animal model, we showed that up-regulation of GPR139 in MS cholinergic neurons ameliorated cognitive impairment, apoptosis and synaptotoxicity in APP/PS1 transgenic mice. These findings reveal that GPR139 of MS cholinergic neurons could be a critical node in cognition and potentially provides insight into the pathogenesis of Alzheimer's disease.

Interaction of acetylcholine and oxytocin neuromodulation in the hippocampus.

A postulated role of subcortical neuromodulators is to control brain states. Mechanisms by which different neuromodulators compete or cooperate at various temporal scales remain an open question. We investigated the interaction of acetylcholine (ACh) and oxytocin (OXT) at slow and fast timescales during various brain states. Although these neuromodulators fluctuated in parallel during NREM packets, transitions from NREM to REM were characterized by a surge of ACh but a continued decrease of OXT. OXT signaling lagged behind ACh. High ACh was correlated with population synchrony and gamma oscillations during active waking, whereas minimum ACh predicts sharp-wave ripples (SPW-Rs). Optogenetic control of ACh and OXT neurons confirmed the active role of these neuromodulators in the observed correlations. Synchronous hippocampal activity consistently reduced OXT activity, whereas inactivation of the lateral septum-hypothalamus path attenuated this effect. Our findings demonstrate how cooperative actions of these neuromodulators allow target circuits to perform specific functions.

A dynamical computational model of theta generation in hippocampal circuits to study theta-gamma oscillations during neurostimulation.

Neurostimulation of the hippocampal formation has shown promising results for modulating memory but the underlying mechanisms remain unclear. In particular, the effects on hippocampal theta-nested gamma oscillations and theta phase reset, which are both crucial for memory processes, are unknown. Moreover, these effects cannot be investigated using current computational models, which consider theta oscillations with a fixed amplitude and phase velocity. Here, we developed a novel computational model that includes the medial septum, represented as a set of abstract Kuramoto oscillators producing a dynamical theta rhythm with phase reset, and the hippocampal formation, composed of biophysically realistic neurons and able to generate theta-nested gamma oscillations under theta drive. We showed that, for theta inputs just below the threshold to induce self-sustained theta-nested gamma oscillations, a single stimulation pulse could switch the network behavior from non-oscillatory to a state producing sustained oscillations. Next, we demonstrated that, for a weaker theta input, pulse train stimulation at the theta frequency could transiently restore seemingly physiological oscillations. Importantly, the presence of phase reset influenced whether these two effects depended on the phase at which stimulation onset was delivered, which has practical implications for designing neurostimulation protocols that are triggered by the phase of ongoing theta oscillations. This novel model opens new avenues for studying the effects of neurostimulation on the hippocampal formation. Furthermore, our hybrid approach that combines different levels of abstraction could be extended in future work to other neural circuits that produce dynamical brain rhythms.

Basal forebrain cholinergic systems as circuits through which traumatic stress disrupts emotional memory regulation.

Contextual and spatial systems facilitate changes in emotional memory regulation brought on by traumatic stress. Cholinergic basal forebrain (chBF) neurons provide input to contextual/spatial systems and although chBF neurons are important for emotional memory, it is unknown how they contribute to the traumatic stress effects on emotional memory. Clusters of chBF neurons that project to the prefrontal cortex (PFC) modulate fear conditioned suppression and passive avoidance, while clusters of chBF neurons that project to the hippocampus (Hipp) and PFC (i.e. cholinergic medial septum and diagonal bands of Broca (chMS/DBB neurons) are critical for fear extinction. Interestingly, neither Hipp nor PFC projecting chMS/DBB neurons are critical for fear extinction. The retrosplenial cortex (RSC) is a contextual/spatial memory system that receives input from chMS/DBB neurons, but whether this chMS/DBB-RSC circuit facilitates traumatic stress effects on emotional memory remain unexplored. Traumatic stress leads to neuroinflammation and the buildup of reactive oxygen species. These two molecular processes may converge to disrupt chBF circuits enhancing the impact of traumatic stress on emotional memory.

A septal-ventral tegmental area circuit drives exploratory behavior.

To survive, animals need to balance their exploratory drive with their need for safety. Subcortical circuits play an important role in initiating and modulating movement based on external demands and the internal state of the animal; however, how motivation and onset of locomotion are regulated remain largely unresolved. Here, we show that a glutamatergic pathway from the medial septum and diagonal band of Broca (MSDB) to the ventral tegmental area (VTA) controls exploratory locomotor behavior in mice. Using a self-supervised machine learning approach, we found an overrepresentation of exploratory actions, such as sniffing, whisking, and rearing, when this projection is optogenetically activated. Mechanistically, this role relies on glutamatergic MSDB projections that monosynaptically target a subset of both glutamatergic and dopaminergic VTA neurons. Taken together, we identified a glutamatergic basal forebrain to midbrain circuit that initiates locomotor activity and contributes to the expression of exploration-associated behavior.

Accelerated neurodegeneration of basal forebrain cholinergic neurons in HIV-1 gp120 transgenic mice: Critical role of the p75 neurotrophin receptor.

Human Immunodeficiency Virus-1 (HIV) infection of the brain induces HIV-associated neurocognitive disorders (HAND). The set of molecular events employed by HIV to drive cognitive impairments in people living with HIV are diverse and remain not completely understood. We have shown that the HIV envelope protein gp120 promotes loss of synapses and decreases performance on cognitive tasks through the p75 neurotrophin receptor (p75NTR). This receptor is abundant on cholinergic neurons of the basal forebrain and contributes to cognitive impairment in various neurological disorders. In this study, we examined cholinergic neurons of gp120 transgenic (gp120tg) mice for signs of degeneration. We observed that the number of choline acetyltransferase-expressing cells is decreased in old (12-14-month-old) gp120tg mice when compared to age matched wild type. In the same animals, we observed an increase in the levels of pro-nerve growth factor, a ligand of p75NTR, as well as a disruption of consolidation of extinction of conditioned fear, a behavior regulated by cholinergic neurons of the basal forebrain. Both biochemical and behavioral outcomes of gp120tg mice were rescued by the deletion of the p75NTR gene, strongly supporting the role that this receptor plays in the neurotoxic effects of gp120. These data indicate that future p75NTR-directed pharmacotherapies could provide an adjunct therapy against synaptic simplification caused by HIV.

Cholinergic modulation of rearing in rats performing a spatial memory task.

Spatial memory encoding depends in part on cholinergic modulation. How acetylcholine supports spatial memory encoding is not well understood. Prior studies indicate that acetylcholine release is correlated with exploration, including epochs of rearing onto hind legs. Here, to test whether elevated cholinergic tone increases the probability of rearing, we tracked rearing frequency and duration while optogenetically modulating the activity of choline acetyltransferase containing (i.e., acetylcholine producing) neurons of the medial septum in rats performing a spatial working memory task (n = 17 rats). The cholinergic neurons were optogenetically inhibited using halorhodopsin for the duration that rats occupied two of the four open arms during the study phase of an 8-arm radial arm maze win-shift task. Comparing rats' behaviour in the two arm types showed that rearing frequency was not changed, but the average duration of rearing epochs became significantly longer. This effect on rearing was observed during optogenetic inhibition but not during sham inhibition or in rats that received infusions of a fluorescent reporter virus (i.e., without halorhodopsin; n = 6 rats). Optogenetic inhibition of cholinergic neurons during the pretrial waiting phase had no significant effect on rearing, indicating a context-specificity of the observed effects. These results are significant in that they indicate that cholinergic neuron activity in the medial septum is correlated with rearing not because it motivates an exploratory state but because it contributes to the processing of information acquired while rearing.

Orexinergic lateral hypothalamus (LH) projections to medial septum (MS) modulate ethanol-induced sedation in male and female mice and binge-like ethanol drinking in male mice only.

Orexin in both the lateral hypothalamus (LH) and medial septum (MS) is involved in sleep- and consciousness-related conditions. Since orexin modulates the intoxicating as well as rewarding effects of ethanol, this study focused on the role of orexin-projecting neurons from the LH to the MS, and this neurocircuit's role in mediating the sedative effects of alcohol. Drinking-in-the-Dark (DID) behavior was also assessed as a measure of the role of the LH-MS pathway in modulating binge-like ethanol intake, with a particular focus on sex differences in both behavioral paradigms. Male and female Hcrt-ires-cre mice received cannulation in the MS, while the LH was injected bilaterally with cre-dependent excitatory (Gq) Designer Receptor Exclusively Activated by Designer Drug (DREADD), inhibitory (Gi) DREADD or control virus. All subjects received a 3.75 g/kg dose of 20 % ethanol intraperitoneally and the sedative effect was assessed by the loss of righting reflex (LORR). After behavioral testing, brains were used for c-Fos immunohistochemistry analyses. A separate cohort of mice was used for a 2-week DID protocol using excitatory (Gq) DREADD and control virus. Gq DREADD-induced activation of the orexin neurocircuitry from the LH to the MS significantly reduced sedation time in both female and male mice. Furthermore, CNO treatment failed to alter ethanol sedation times in both animals expressing Gi DREADDs and control virus. There were no significant differences in blood ethanol concentrations (BECs) in any experimental group, suggesting that changes in sedation were not due to treatment-induced alterations of ethanol metabolism. Interestingly, in the DID study, only male mice decreased their ethanol consumption when Gq DREADDs were activated. These results provide novel evidence on the role played by this orexinergic LH to MS circuit on the sedative effects of ethanol and ethanol consumption in a sex-dependent manner. Thus, the MS should be considered further as a novel sexually dimorphic target.

Pontine parabrachial nucleus-basal forebrain circuitry regulating cortical and hippocampal arousal.

INTRODUCTION: The basal forebrain (BF) and the medial septum (MS) respectively drive neuronal activity of cerebral cortex and hippocampus (HPC) in sleep-wake cycle. Our previous studies of lesions and neuronal circuit tracing have shown that the pontine parabrachial nucleus (PB) projections to the BF and MS may be a key circuit for cortical and HPC arousal. AIMS: This study aims to demonstrate that PB projections to the BF and MS activate the cerebral cortex and HPC. RESULTS: By using chemogenetic stimulation of the BF, the PB-BF and the PB-MS pathway combined with electroencephalogram (EEG) Fast Fourier Transformation (FFT) analysis in rats, we demonstrated that chemogenetic stimulation of the BF or PB neurons projecting to the BF activated the cerebral cortex while chemogenetic stimulation of the MS or PB neurons projecting to the MS activated HPC activity, in sleep and wake state. These stimulations did not significantly alter sleep-wake amounts. CONCLUSIONS: Our results support that PB projections to the BF and MS specifically regulating cortical and HPC activity.

Stimulation of the muscarinic receptor M4 regulates neural precursor cell proliferation and promotes adult hippocampal neurogenesis.

Cholinergic signaling plays a crucial role in the regulation of adult hippocampal neurogenesis; however, the mechanisms by which acetylcholine mediates neurogenic effects are not completely understood. Here, we report the expression of muscarinic acetylcholine receptor subtype M4 (M4 mAChR) on a subpopulation of neural precursor cells (NPCs) in the adult mouse hippocampus, and demonstrate that its pharmacological stimulation promotes their proliferation, thereby enhancing the production of new neurons in vivo. Using a targeted ablation approach, we also show that medial septum (MS) and the diagonal band of Broca (DBB) cholinergic neurons support both the survival and morphological maturation of adult-born neurons in the mouse hippocampus. Although the systemic administration of an M4-selective allosteric potentiator fails to fully rescue the MS/DBB cholinergic lesion-induced decrease in hippocampal neurogenesis, it further exacerbates the impairment in the morphological maturation of adult-born neurons. Collectively, these findings reveal stage-specific roles of M4 mAChRs in regulating adult hippocampal neurogenesis, uncoupling their positive role in enhancing the production of new neurons from the M4-induced inhibition of their morphological maturation, at least in the context of cholinergic signaling dysfunction.

Investigating the Co-administration of Ghrelin and Nicotine Into the Medial Septum and Its Influencing on Morphine Amnestic Effect.

Introduction: Evidence indicates that medial septum nicotinic receptors regulate cognitive processes. Ghrelin is a gut hormone that regulates energy homeostasis. Ghrelin is also produced in the brain and is involved in cognitive function. This study aims to evaluate the effects of medial septal administration of ghrelin on the amnestic effect of morphine in rats. In addition, the possible relationship between the medial septal ghrelin and acetylcholine nicotinic receptors on the amnestic effect of morphine is evaluated. Methods: The rats were implanted at the medial septum area and were microinjected with ghrelin and nicotinic receptor agents. The step-through type inhibitory avoidance apparatus was used for memory retrieval assessment. Results: The results showed that the administration of morphine after the training phase impaired memory consolidation. Post-training intra-septal injection of the same doses of either ghrelin or nicotine did not change memory performance; however, their co-application with morphine (significant dose: 7.5 mg/kg subcutaneous injection) increased the step-through latency and improved memory consolidation. Moreover, post-training co-application of low doses of the two agonists could not affect morphine-induced memory impairment. Conclusion: These results indicated no interaction between medial septal ghrelin and nicotinic receptors on the amnestic effect of morphine in rats. Highlights: Post-training morphine administration impaired memory performance.Intra-septal injection of ghrelin or nicotine alone did not affect memory performance.Co-application of either ghrelin or nicotine with morphine improved memory.Co-application of the two agents could not affect morphine-induced memory impairment. Plain Language Summary: Morphine abuse has been associated with memory disturbance. Ghrelin is a gastrointestinal hormone known as hunger hormone. It also affects cognitive performance via binding ghrelin receptors in central nervous system. On the other hand, the medial septum nicotinic receptors improve memory-associated behavior. Hence, we hypothesized that septal ghrelin receptors could affect the effect of nicotine on morphine-induced memory deficit. We examined this hypothesis in avoidance memory task. We found that subcutaneous administration of morphine inhibited avoidance memory. The effect of morphine was blocked by intra-medial septum injection of nicotine or ghrelin. However, co-infusion of ghrelin with nicotine into the medial septum area had no effect on morphine amnesia. Overall, the study results suggest no interaction between ghrelin and cholinergic nicotinic receptors in morphine amnesia.

Maternal choline supplementation protects against age-associated cholinergic and GABAergic basal forebrain neuron degeneration in the Ts65Dn mouse model of Down syndrome and Alzheimer's disease.

Down syndrome (DS) is a genetic disorder caused by triplication of human chromosome 21. In addition to intellectual disability, DS is defined by a premature aging phenotype and Alzheimer's disease (AD) neuropathology, including septohippocampal circuit vulnerability and degeneration of basal forebrain cholinergic neurons (BFCNs). The Ts65Dn mouse model recapitulates key aspects of DS/AD pathology, namely age-associated atrophy of BFCNs and cognitive decline in septohippocampal-dependent behavioral tasks. We investigated whether maternal choline supplementation (MCS), a well-tolerated treatment modality, protects vulnerable BFCNs from age- and genotype-associated degeneration in trisomic offspring. We also examined the effect of trisomy, and MCS, on GABAergic basal forebrain parvalbumin neurons (BFPNs), an unexplored neuronal population in this DS model. Unbiased stereological analyses of choline acetyltransferase (ChAT)-immunoreactive BFCNs and parvalbumin-immunoreactive BFPNs were conducted using confocal z-stacks of the medial septal nucleus and the vertical limb of the diagonal band (MSN/VDB) in Ts65Dn mice and disomic (2N) littermates at 3-4 and 10-12 months of age. MCS trisomic offspring displayed significant increases in ChAT-immunoreactive neuron number and density compared to unsupplemented counterparts, as well as increases in the area of the MSN/VDB occupied by ChAT-immunoreactive neuropil. MCS also rescued BFPN number and density in Ts65Dn offspring, a novel rescue of a non-cholinergic cell population. Furthermore, MCS prevented age-associated loss of BFCNs and MSN/VDB regional area in 2N offspring, indicating genotype-independent neuroprotective benefits. These findings demonstrate MCS provides neuroprotection of vulnerable BFCNs and non-cholinergic septohippocampal BFPNs, indicating this modality has translational value as an early life therapy for DS, as well as extending benefits to the aging population at large.

Cholinergic modulation of rearing in rats performing a spatial memory task.

Spatial memory encoding depends in part on cholinergic modulation. How acetylcholine supports spatial memory encoding is not well understood. Prior studies indicate that acetylcholine release is correlated with exploration, including epochs of rearing onto hind legs. Here, to test whether elevated cholinergic tone increases the probability of rearing, we tracked rearing frequency and duration while optogenetically modulating the activity of choline acetyltransferase containing (i.e., acetylcholine producing) neurons of the medial septum in rats performing a spatial working memory task (n = 17 rats). The cholinergic neurons were optogenetically inhibited using halorhodopsin for the duration that rats occupied two of the four open arms during the study phase of an 8-arm radial arm maze win-shift task. Comparing rats' behavior in the two arm types showed that rearing frequency was not changed but the average duration of rearing epochs became significantly longer. This effect on rearing was observed during optogenetic inhibition but not during sham inhibition or in rats that received infusions of a fluorescent reporter virus (i.e., without halorhodopsin; n = 6 rats). Optogenetic inhibition of cholinergic neurons during the pre-trial waiting phase had no significant effect on rearing, indicating a context-specificity of the observed effects. These results are significant in that they indicate that cholinergic neuron activity in the medial septum is correlated with rearing not because it motivates an exploratory state but because it contributes to the processing of information acquired while rearing.