Dorsal-Ventral Differences in Modulation of Synaptic Transmission in the Hippocampus

Distinct Ventral Hippocampus Network Properties in Dissociated Cultures

Extensive research has been focused in the past century on structural, physiological, and molecular attributes of the hippocampus. This interest was created by the unique involvement of the hippocampus in cognitive and affective functions of the brain. Functional analysis revealed that the hippocampus has divergent properties along its axial dimension to the extent that the dorsal sector (dorsal hippocampus, DH) has different connections with the rest of the brain than those of the ventral sector (VH). Still, longitudinal pathways connect the DH with the VH and dampen the functional differences between the sectors. To be able to identify the intrinsic functional difference between the DH and VH, we produced dissociated monolayer cultures from prenatal DH and VH and examined their properties at 10-20 days after plating by imaging the spontaneous activity of the network using Fluo-2 AM, a calcium indicator. Surprisingly, while DH and VH sectors produced dissociated cultures with similar morphological attributes, VH cultures were more active spontaneously than DH cultures. Furthermore, when stimulated to produce action potentials, VH neurons triggered network bursts in postsynaptic neurons more often than DH cultures. Finally, in both DH and VH cultures, electrical stimulation of single cells produced network bursts in response to a burst of action potentials rather than to single spikes. These experiments indicate that even in dissociated cultures, neurons of the VH are more excitable and sensitive to electrical stimulation than DH; hence, they are more likely to generate network bursts and epileptic seizures, as suggested for in vivo brains.

Ablated Sonic Hedgehog Signaling in the Dentate Gyrus of the Dorsal and Ventral Hippocampus Impairs Hippocampal-Dependent Memory Tasks and Emotion in a Rat Model of Depression

Specific memory processes and emotional aberrations in depression can be attributed to the different dorsal-ventral regions of the hippocampus. However, the molecular mechanisms underlying the differential functions of the dorsal hippocampus (dHip) and ventral hippocampus (vHip) remain unclear. As Sonic Hedgehog (Shh) is involved in the dorsal-ventral patterning of the neural tube and its signaling is dysregulated by chronic unpredictable mild stress (CUMS), we investigated its role in influencing the differential functions of the dHip and vHip. Here, CUMS downregulated the expression of Shh signaling markers, including Shh and its downstream effectors GLI family zinc finger 12 (Gli1/2), Patched (Ptch), and smoothened (Smo), in both the dHip and vHip of rats, though more so in the vHip. Additionally, Shh knockdown in the dorsal or ventral dentate gyrus (DG) resulted in restrained neurogenic activity in newborn neurons, especially in immature neurons through decreased expression of Shh signaling markers. Furthermore, Shh knockdown in the DG of the dHip led to memory impairment by inhibiting experience-dependent activation of immature neurons, whereas its knockdown in the DG of the vHip led to an emotional handicap by delaying the maturation of immature neurons. Finally, Shh knockdown in either the dDG or vDG of hippocampus abolished the corresponding cognitive enhancement and emotional recovery of fluoxetine. In conclusion, Shh is essential to maintain the functional heterogeneity of dHip and vHip in depressed rat, which was mainly mediating by local changes of dependent activation and maturity of immature neurons, respectively.

Region-Related Differences in Short-Term Synaptic Plasticity and Synaptotagmin-7 in the Male and Female Hippocampus of a Rat Model of Fragile X Syndrome

Fragile X syndrome (FXS) is an intellectual developmental disorder characterized, inter alia, by deficits in the short-term processing of neural information, such as sensory processing and working memory. The primary cause of FXS is the loss of fragile X messenger ribonucleoprotein (FMRP), which is profoundly involved in synaptic function and plasticity. Short-term synaptic plasticity (STSP) may play important roles in functions that are affected by FXS. Recent evidence points to the crucial involvement of the presynaptic calcium sensor synaptotagmin-7 (Syt-7) in STSP. However, how the loss of FMRP affects STSP and Syt-7 have been insufficiently studied. Furthermore, males and females are affected differently by FXS, but the underlying mechanisms remain elusive. The aim of the present study was to investigate possible changes in STSP and the expression of Syt-7 in the dorsal (DH) and ventral (VH) hippocampus of adult males and females in a Fmr1-knockout (KO) rat model of FXS. We found that the paired-pulse ratio (PPR) and frequency facilitation/depression (FF/D), two forms of STSP, as well as the expression of Syt-7, are normal in adult KO males, but the PPR is increased in the ventral hippocampus of KO females (6.4 ± 3.7 vs. 18.3 ± 4.2 at 25 ms in wild type (WT) and KO, respectively). Furthermore, we found no gender-related differences, but did find robust region-dependent difference in the STSP (e.g., the PPR at 50 ms: 50.0 ± 5.5 vs. 17.6 ± 2.9 in DH and VH of WT male rats; 53.1 ± 3.6 vs. 19.3 ± 4.6 in DH and VH of WT female rats; 48.1 ± 2.3 vs. 19.1 ± 3.3 in DH and VH of KO male rats; and 51.2 ± 3.3 vs. 24.7 ± 4.3 in DH and VH of KO female rats). AMPA receptors are similarly expressed in the two hippocampal segments of the two genotypes and in both genders. Also, basal excitatory synaptic transmission is higher in males compared to females. Interestingly, we found more than a twofold higher level of Syt-7, not synaptotagmin-1, in the dorsal compared to the ventral hippocampus in the males of both genotypes (0.43 ± 0.1 vs. 0.16 ± 0.02 in DH and VH of WT male rats, and 0.6 ± 0.13 vs. 0.23 ± 0.04 in DH and VH of KO male rats) and in the WT females (0.97 ± 0.23 vs. 0.31 ± 0.09 in DH and VH). These results point to the susceptibility of the female ventral hippocampus to FMRP loss. Importantly, the different levels of Syt-7, which parallel the higher score of the dorsal vs. ventral hippocampus on synaptic facilitation, suggest that Syt-7 may play a pivotal role in defining the striking differences in STSP along the long axis of the hippocampus.

Perinatal compromise affects development, form, and function of the hippocampus part two; preclinical studies

The hippocampus is a vital brain structure deep in the medial temporal lobe that mediates a range of functions encompassing emotional regulation, learning, memory, and cognition. Hippocampal development is exquisitely sensitive to perturbations and adverse conditions during pregnancy and at birth, including preterm birth, fetal growth restriction (FGR), acute hypoxic-ischaemic encephalopathy (HIE), and intrauterine inflammation. Disruptions to hippocampal development due to these conditions can have long-lasting functional impacts. Here, we discuss a range of preclinical models of prematurity and FGR and conditions that induce hypoxia and inflammation, which have been critical in elucidating the underlying mechanisms and cellular and subcellular structures implicated in hippocampal dysfunction. Finally, we discuss potential therapeutic targets to reduce the burden of these perinatal insults on the developing hippocampus. IMPACT: The review explores the preclinical literature examining the association between pregnancy and birth complications, and hippocampal form and function. The developmental processes and cellular mechanisms that are disrupted within the hippocampus following perinatal compromise are described, and potential therapeutic targets are discussed.

Muscarinic Modulation of Synaptic Transmission and Short-Term Plasticity in the Dorsal and Ventral Hippocampus

Muscarinic neurotransmission is fundamentally involved in supporting several brain functions by modulating flow of information in brain neural circuits including the hippocampus which displays a remarkable functional segregation along its longitudinal axis. However, how muscarinic neuromodulation contributes to the functional segregation along the hippocampus remains unclear. In this study we show that the nonselective muscarinic receptor agonist carbachol similarly suppresses basal synaptic transmission in the dorsal and ventral CA1 hippocampal field, in a concentration-depended manner. Furthermore, using a ten-pulse stimulation train of varying frequency we found that carbachol changes the frequency filtering properties more in ventral than dorsal hippocampus by facilitating synaptic inputs at a wide range of input frequencies in the ventral compared with dorsal hippocampus. Using the M2 receptor antagonist gallamine and the M4 receptor antagonist tropicamide, we found that M2 receptors are involved in controlling basal synaptic transmission and short-term synaptic plasticity (STSP) in the ventral but not the dorsal hippocampus, while M4 receptors participate in modulating basal synaptic transmission and STSP in both segments of the hippocampus. These results were corroborated by the higher protein expression levels of M2 receptors in the ventral compared with dorsal hippocampus. We conclude that muscarinic transmission modulates excitatory synaptic transmission and short-term synaptic plasticity along the entire rat hippocampus by acting through M4 receptors and recruiting M2 receptors only in the ventral hippocampus. Furthermore, M4 receptors appear to exert a permissive role on the actions of M2 receptors on STSP in the ventral hippocampus. This dorsoventral differentiation of muscarinic modulation is expected to have important implications in information processing along the endogenous hippocampal circuitry.

Voluntary running wheel exercise induces cognitive improvement post traumatic brain injury in mouse model through redressing aberrant excitation regulated by voltage-gated sodium channels 1.1, 1.3, and 1.6

Traumatic brain injury (TBI) leads to disturbed brain discharge rhythm, elevated excitability, anxiety-like behaviors, and decreased learning and memory capabilities. Cognitive dysfunctions severely affect the quality of life and prognosis of TBI patients, requiring effective rehabilitation treatment. Evidence indicates that moderate exercise after brain injury decreases TBI-induced cognitive decline. However, the underlying mechanism remains unelucidated. Our results demonstrate that TBI causes cognitive impairment behavior abnormalities and overexpression of Nav1.1, Nav1.3 and Nav1.6 proteins inside the hippocampus of mice models. Three weeks of voluntary running wheel (RW) exercise treatments before or/and post-injury effectively redressed the aberrant changes caused by TBI. Additionally, a 10% exercise-conditioned medium helped recover cell viability, neuronal sodium current and expressions of Nav1.1, Nav1.3 and Nav1.6 proteins across cultured neurons after injury. Therefore, the results validate the neuroprotection induced by voluntary RW exercise treatment before or/and post-TBI. The RW exercise-induced improvement in cognitive behaviors and neuronal excitability could be associated with correcting the Nav1.1, Nav1.3, and Nav1.6 expression levels. The current study proves that voluntary exercise is an effective treatment strategy against TBI. The study also highlights novel potential targets for rehabilitating TBI, including the Navs proteins.

Comparing the synaptic potentiation in schaffer collateral-CA1 synapses in dorsal and intermediate regions of the hippocampus in normal and kindled rats

There is growing evidence that the hippocampus comprises diverse neural circuits that exhibit longitudinal variation in their properties, however, the intermediate region of the hippocampus has received comparatively little attention. Therefore, this study was designed to compared short- and long-term synaptic plasticity between the dorsal and intermediate regions of the hippocampus in normal and PTZ-kindled rats. Short-term plasticity was assessed by measuring the ratio of field excitatory postsynaptic potentials' (fEPSPs) slope in response to paired-pulse stimulation at three different inter-pulse intervals (20, 80, and 160 ms), while long-term plasticity was assessed using primed burst stimulation (PBS). The results showed that the basal synaptic strength differed between the dorsal and intermediate regions of the hippocampus in both control and kindled rats. In the control group, paired-pulse stimulation of Schaffer collaterals resulted in a significantly lower fEPSP slope in the intermediate part of the hippocampus compared to the dorsal region. Additionally, the magnitude of long-term potentiation (LTP) was significantly lower in the intermediate part of the hippocampus compared to the dorsal region. In PTZ-kindled rats, both short-term facilitation and long-term potentiation were impaired in both regions of the hippocampus. Interestingly, there was no significant difference in synaptic plasticity between the dorsal and intermediate regions in PTZ-kindled rats, despite impairments in both regions. This suggests that seizures eliminate the regional difference between the dorsal and intermediate parts of the hippocampus, resulting in similar electrophysiological activity in both regions in kindled animals. Future studies should consider this when investigating the responses of the dorsal and intermediate regions of the hippocampus following PTZ kindling.

Pathway specific interventions reveal the multiple roles of ventral hippocampus projections in cognitive functions

Since the 1950s study of Scoville and Milner on the case H.M., the hippocampus has attracted neuroscientists' attention. The hippocampus has been traditionally divided into dorsal and ventral parts, each of which projects to different brain structures and mediates various functions. Despite a predominant interest in its dorsal part in animal models, especially regarding episodic-like and spatial cognition, recent data highlight the role of the ventral hippocampus (vHPC), as the main hippocampal output, in cognitive processes. Here, we review recent studies conducted in rodents that have used advanced in vivo functional techniques to specifically monitor and manipulate vHPC efferent pathways and delineate the roles of these specific projections in learning and memory processes. Results highlight that vHPC projections to basal amygdala are implicated in emotional memory, to nucleus accumbens in social memory and instrumental actions and to prefrontal cortex in all the above as well as in object-based memory. Some of these hippocampal projections also modulate feeding and anxiety-like behaviours providing further evidence that the "one pathway-one function" view is outdated and future directions are proposed to better understand the role of hippocampal pathways and shed further light on its connectivity and function.

Tonic activin signaling shapes cellular and synaptic properties of CA1 neurons mainly in dorsal hippocampus

Dorsal and ventral hippocampus serve different functions in cognition and affective behavior, but the underpinnings of this diversity at the cellular and synaptic level are not well understood. We found that the basal level of activin A, a member of the TGF-β family, which regulates hippocampal circuits in a behaviorally relevant fashion, is much higher in dorsal than in ventral hippocampus. Using transgenic mice with a forebrain-specific disruption of activin receptor signaling, we identified the pronounced dorsal-ventral gradient of activin A as a major factor determining the distinct neurophysiologic signatures of dorsal and ventral hippocampus, ranging from pyramidal cell firing, tuning of frequency-dependent synaptic facilitation, to long-term potentiation (LTP), long-term depression (LTD), and de-potentiation. Thus, the strong activin A tone in dorsal hippocampus appears crucial to establish cellular and synaptic phenotypes that are tailored specifically to the respective network operations in dorsal and ventral hippocampus.

Alteration of hippocampal CA2 plasticity and social memory in adult rats impacted by juvenile stress

The hippocampal CA2 region has received greater attention in recent years due to its fundamental role in social memory and hippocampus-dependent memory processing. Unlike entorhinal cortical inputs, the Schaffer collateral inputs to CA2 do not support activity-dependent long-term potentiation (LTP), which serves as the basis for long-term memories. This LTP-resistant zone also expresses genes that restrict plasticity. With the aim of exploring social interaction and sociability in rats that were subjected to juvenile stress, we addressed questions about how the neural circuitry is altered and its effects on social behavior. Although there was induction of LTP in both Schaffer collateral and entorhinal cortical pathways in juvenile-stressed rats, LTP declined in both pathways after 2-3 h. Moreover, exogenous bath application of substance P, a neuropeptide that resulted in slow onset long-lasting potentiation in control animals while it failed to induce LTP in juvenile-stressed rats. Our study reveals that juvenile-stressed rats show behavioral and cellular abnormalities with a long-lasting impact in adulthood.

Microglial diversity along the hippocampal longitudinal axis impacts synaptic plasticity in adult male mice under homeostatic conditions

The hippocampus is a plastic brain area that shows functional segregation along its longitudinal axis, reflected by a higher level of long-term potentiation (LTP) in the CA1 region of the dorsal hippocampus (DH) compared to the ventral hippocampus (VH), but the mechanisms underlying this difference remain elusive. Numerous studies have highlighted the importance of microglia-neuronal communication in modulating synaptic transmission and hippocampal plasticity, although its role in physiological contexts is still largely unknown. We characterized in depth the features of microglia in the two hippocampal poles and investigated their contribution to CA1 plasticity under physiological conditions. We unveiled the influence of microglia in differentially modulating the amplitude of LTP in the DH and VH, showing that minocycline or PLX5622 treatment reduced LTP amplitude in the DH, while increasing it in the VH. This was recapitulated in Cx3cr1 knockout mice, indicating that microglia have a key role in setting the conditions for plasticity processes in a region-specific manner, and that the CX3CL1-CX3CR1 pathway is a key element in determining the basal level of CA1 LTP in the two regions. The observed LTP differences at the two poles were associated with transcriptional changes in the expression of genes encoding for Il-1, Tnf-α, Il-6, and Bdnf, essential players of neuronal plasticity. Furthermore, microglia in the CA1 SR region showed an increase in soma and a more extensive arborization, an increased prevalence of immature lysosomes accompanied by an elevation in mRNA expression of phagocytic markers Mertk and Cd68 and a surge in the expression of microglial outward K⁺ currents in the VH compared to DH, suggesting a distinct basal phenotypic state of microglia across the two hippocampal poles. Overall, we characterized the molecular, morphological, ultrastructural, and functional profile of microglia at the two poles, suggesting that modifications in hippocampal subregions related to different microglial statuses can contribute to dissect the phenotypical aspects of many diseases in which microglia are known to be involved.

Septotemporal variation in modulation of synaptic transmission, paired-pulse ratio and frequency facilitation/depression by adenosine and GABAB receptors in the rat hippocampus

Short-term synaptic plasticity represents a fundamental mechanism in neural information processing and is regulated by neuromodulators. Here, using field recordings from the CA1 region of adult rat hippocampal slices, we show that excitatory synaptic transmission is suppressed by strong but not moderate activation of adenosine A₁ receptors by 2-Chloro-N⁶-cyclopentyladenosine (CCPA) more in the dorsal than the ventral hippocampus; in contrast, both mild and strong activation of GABA_B receptors by baclofen (1 μM, 10 μM) suppress synaptic transmission more in the ventral than the dorsal hippocampus. Using a 10-pulse stimulation train of variable frequency, we found that CCPA modulates short-term synaptic plasticity independently of the suppression of synaptic transmission in both segments of the hippocampus and at stimulation frequencies greater than 10 Hz. However, specifically regarding the paired-pulse ratio (PPR) and frequency facilitation/depression (FF/D) we found significant drug action before but not after adjusting conditioning responses to control levels. Activation of GABA_BRs by baclofen suppressed synaptic transmission more in the ventral than the dorsal hippocampus. Furthermore, relatively high (10 μM) but not low (1 μM) baclofen concentration enhanced both PPR and FF in both hippocampal segments at stimulation frequencies greater than 1 Hz, independently of the suppression of synaptic transmission by baclofen. These results show that A₁Rs and GABA_BRs control synaptic transmission more effectively in the dorsal and the ventral hippocampus, respectively, and suggest that these receptors modulate PPR and FF/D at different frequency bands of afferent input, in both segments of the hippocampus.

The Sedentary Lifestyle and Masticatory Dysfunction: Time to Review the Contribution to Age-Associated Cognitive Decline and Astrocyte Morphotypes in the Dentate Gyrus

As aging and cognitive decline progresses, the impact of a sedentary lifestyle on the appearance of environment-dependent cellular morphologies in the brain becomes more apparent. Sedentary living is also associated with poor oral health, which is known to correlate with the rate of cognitive decline. Here, we will review the evidence for the interplay between mastication and environmental enrichment and assess the impact of each on the structure of the brain. In previous studies, we explored the relationship between behavior and the morphological features of dentate gyrus glial fibrillary acidic protein (GFAP)-positive astrocytes during aging in contrasting environments and in the context of induced masticatory dysfunction. Hierarchical cluster and discriminant analysis of GFAP-positive astrocytes from the dentate gyrus molecular layer revealed that the proportion of AST1 (astrocyte arbors with greater complexity phenotype) and AST2 (lower complexity) are differentially affected by environment, aging and masticatory dysfunction, but the relationship is not straightforward. Here we re-evaluated our previous reconstructions by comparing dorsal and ventral astrocyte morphologies in the dentate gyrus, and we found that morphological complexity was the variable that contributed most to cluster formation across the experimental groups. In general, reducing masticatory activity increases astrocyte morphological complexity, and the effect is most marked in the ventral dentate gyrus, whereas the effect of environment was more marked in the dorsal dentate gyrus. All morphotypes retained their basic structural organization in intact tissue, suggesting that they are subtypes with a non-proliferative astrocyte profile. In summary, the increased complexity of astrocytes in situations where neuronal loss and behavioral deficits are present is counterintuitive, but highlights the need to better understand the role of the astrocyte in these conditions.

Caffeine Functions by Inhibiting Dorsal and Ventral Hippocampal Adenosine 2A Receptors to Modulate Memory and Anxiety, Respectively

As a nonspecific antagonist of the adenosine A_2A receptor (A_2AR), caffeine enhances learning and improves memory impairment. Simultaneously, the consumption of caffeine correlates with a feeling of anxiety. The hippocampus is functionally differentiated along its dorsal/ventral axis and plays a crucial role both in memory and anxiety. Whether caffeine exerts its regulation by inhibiting A_2ARs in different subregions of the hippocampus is still unknown. In the present study, we found that after chronic intake of drinking water containing caffeine (1 g/L, 3 weeks), mice exhibited aggravated anxiety-like behavior and enhanced memory function. Tissue-specific, functional disruption of dorsal hippocampal A_2ARs by the CRE-LoxP system prevented the memory-enhancing effect of caffeine, while selective disruption of ventral hippocampal A_2ARs blocked the impact of caffeine on anxiety. These results, together with the enhanced memory of dorsal hippocampus A_2AR knockout mice and greater anxiety-like behavior of ventral hippocampus A_2AR knockout mice without caffeine, indicates a dissociation between the roles of ventral and dorsal hippocampal A_2A receptors in caffeine’s effects on anxiety-like and memory-related behavioral measures, respectively. Furthermore, optogenetic activation of dorsal or ventral hippocampal A_2ARs reversed the behavioral alterations caused by drinking caffeine, leading to impaired memory or decreased anxiety-like behaviors, respectively. Taken together, our findings suggest that the memory- and anxiety-enhancing effects of caffeine are related to the differential effects of inhibiting A_2ARs in the dorsal and ventral hippocampus, respectively.

Extracranial 125I Seed Implantation Allows Non-invasive Stereotactic Radioablation of Hippocampal Adult Neurogenesis in Guinea Pigs

Adult hippocampal neurogenesis (AHN) is important for multiple cognitive functions. We sort to establish a minimal or non-invasive radiation approach to ablate AHN using guinea pigs as an animal model. ¹²⁵I seeds with different radiation dosages (1.0, 0.8, 0.6, 0.3 mCi) were implanted unilaterally between the scalp and skull above the temporal lobe for 30 and 60 days, with the radiation effect on proliferating cells, immature neurons, and mature neurons in the hippocampal formation determined by assessment of immunolabeled (+) cells for Ki67, doublecortin (DCX), and neuron-specific nuclear antigen (NeuN), as well as Nissl stain cells. Spatially, the ablation effect of radiation occurred across the entire rostrocaudal and largely the dorsoventral dimensions of the hippocampus, evidenced by a loss of DCX⁺ cells in the subgranular zone (SGZ) of dentate gyrus (DG) in the ipsilateral relative to contralateral hemispheres in reference to the ¹²⁵I seed implant. Quantitatively, Ki67⁺ and DCX⁺ cells at the SGZ in the dorsal hippocampus were reduced in all dosage groups at the two surviving time points, more significant in the ipsilateral than contralateral sides, relative to sham controls. NeuN⁺ neurons and Nissl-stained cells were reduced in the granule cell layer of DG and the stratum pyramidale of CA1 in the groups with 0.6-mCi radiation for 60 days and 1.0 mCi for 30 and 60 days. Minimal cranial trauma was observed in the groups with 0.3– 1.0-mCi radiation at 60 days. These results suggest that extracranial radiation with ¹²⁵I seed implantation can be used to deplete HAN in a radioactivity-, duration-, and space-controllable manner, with a “non-invasive” stereotactic ablation achievable by using ¹²⁵I seeds with relatively low radioactivity dosages.

Ih, GIRK, and KCNQ/Kv7 channels differently modulate sharp wave - ripples in the dorsal and ventral hippocampus

Sharp waves and ripples (SPW-Rs) are endogenous transient patterns of hippocampus local network activity implicated in several functions including memory consolidation, and they are diversified between the dorsal and the ventral hippocampus. Ion channels in the neuronal membrane play important roles in cell and local network function. In this study, using transverse slices and field potential recordings from the CA1 field of rat hippocampus we show that GIRK and KCNQ2/3 potassium channels play a higher role in modulating SPW-Rs in the dorsal hippocampus, while I_h and other KCNQ (presumably KCNQ5) channels, contribute to shaping SPW-R activity more in the ventral than in dorsal hippocampus. Specifically, blockade of I_h channels by ZD 7288 reduced the rate of occurrence of SPW-Rs and increased the generation of SPW-Rs in the form of clusters in both hippocampal segments, while enhanced the amplitude of SPW-Rs only in the ventral hippocampus. Most effects of ZD 7288 appeared to be independent of NMDA receptors' activity. However, the effects of blockade of NMDA receptors depended on the functional state of I_h channels in both hippocampal segments. Blockade of GIRK channels by Tertiapin-Q increased the rate of occurrence of SPW-Rs only in the dorsal hippocampus and the probability of clusters in both segments of the hippocampus. Blockade of KCNQ2/3 channels by XE 991 increased the rate of occurrence of SPW-Rs and the probability of clusters in the dorsal hippocampus, and only reduced the clustered generation of SPW-Rs in the ventral hippocampus. The blocker of KCNQ1/2 channels, that also enhances KCNQ5 channels, UCL 2077, increased the probability of clusters and the power of the ripple oscillation in the ventral hippocampus only. These results suggest that GIRK, KCNQ and I_h channels represent a key mechanism for modulation of SPW-R activity which act differently in the dorsal and ventral hippocampus, fundamentally supporting functional diversification along the dorsal-ventral axis of the hippocampus.