Modulation Of Behavioral State Research Articles

Single-Nucleus Transcriptional Profiling of GAD2-Positive Neurons From Mouse Lateral Habenula Reveals Distinct Expression of Neurotransmission- and Depression-Related Genes

BackgroundGlutamatergic projection neurons of the lateral habenula (LHb) drive behavioral state modulation by regulating the activity of midbrain monoaminergic neurons. Identifying circuit mechanisms that modulate LHb output is of interest for understanding control of motivated behaviors. MethodsA small population of neurons within the medial subnucleus of the mouse LHb express the GABAergic (gamma-aminobutyric acidergic)-synthesizing enzyme GAD2, and they can inhibit nearby LHb projection neurons; however, these neurons lack markers of classic inhibitory interneurons, and they coexpress the vesicular glutamate transporter VGLUT2. To determine the molecular phenotype of these neurons, we genetically tagged the nuclei of GAD2-positive cells and used fluorescence-activated nuclear sorting to isolate and enrich these nuclei for single-nucleus RNA sequencing. ResultsOur data confirm that GAD2+/VGLUT2+ neurons intrinsic to the LHb coexpress markers of both glutamatergic and GABAergic transmission and that they are transcriptionally distinct from either GABAergic interneurons or habenular glutamatergic neurons. We identify gene expression programs within these cells that show sex-specific differences in expression and that are implicated in major depressive disorder, which has been linked to LHb hyperactivity. Finally, we identify the Ntng2 gene encoding the cell adhesion protein netrin-G2 as a marker of LHb GAD2+/VGLUT2+ neurons and a gene product that may contribute to their target projections. ConclusionsThese data show the value of using genetic enrichment of rare cell types for transcriptome studies, and they advance understanding of the molecular composition of a functionally important class of GAD2+ neurons in the LHb.

Effects of a tripartite intervention on biological stress in preterm infants during heel pricks for newborn screening: A randomized controlled trial.

This prospective randomized trial examined the effects of a tripartite intervention (behavioral state modulation + nonnutritive sucking + tucking) on stress from procedural pain during heel pricks. Blood samples for routine screening were collected by heel pricks 48 h after birth (Stage 1) and at ≥37 weeks' gestation (Stage 2); salivary cortisol levels (SCLs) pre-prick (T0) and 20 min post-prick (T1) assessed stress. Preterm infants (n = 64) sampled by convenience at Level III neonatal care units were randomly assigned to the control condition (usual care) or intervention condition (tripartite intervention). Generalized estimating equations examined differences in salivary cortisol between conditions. After adjusting for effects of gestational age, postmenstrual age, and baseline SCLs, (1) at Stage 1, the change in salivary cortisol from T0 to T1 in preterm infants who received the tripartite intervention was, on average, significantly lower by 0.431 units (log scale) than the change in preterm infants who received the control condition (p < 0.001); (2) in the tripartite intervention condition, the difference between the change in mean SCLs from T0 to T1 at Stages 1 and 2 was significantly lower by 0.287 units (log scale), on average than between the change at Stages 1 and 2 in the control condition (p = 0.026). The provision of a tripartite intervention during heel prick significantly decreased the raise of SCLs compared with infants receiving usual care, suggesting lower stress. Clinicians could easily implement the tripartite intervention for heel-stick support; however, replication is needed before recommending its incorporation into routine heel stick and other stressful procedures.

Cannabinoids modulate associative cerebellar learning via alterations in behavioral state.

Cannabinoids are notorious and profound modulators of behavioral state. In the brain, endocannabinoids act via Type 1-cannabinoid receptors (CB1) to modulate synaptic transmission and mediate multiple forms of synaptic plasticity. CB1 knockout (CB1KO) mice display a range of behavioral phenotypes, in particular hypoactivity and various deficits in learning and memory, including cerebellum-dependent delay eyeblink conditioning. Here we find that the apparent effects of CB1 deletion on cerebellar learning are not due to direct effects on CB1-dependent plasticity, but rather, arise as a secondary consequence of altered behavioral state. Hypoactivity of CB1KO mice accounts for their impaired eyeblink conditioning across both animals and trials. Moreover, learning in these mutants is rescued by walking on a motorized treadmill during training. Finally, cerebellar granule-cell-specific CB1KOs exhibit normal eyeblink conditioning, and both global and granule-cell-specific CB1KOs display normal cerebellum-dependent locomotor coordination and learning. These findings highlight the modulation of behavioral state as a powerful independent means through which individual genes contribute to complex behaviors.

Locomotor activity modulates associative learning in mouse cerebellum.

Changes in behavioral state can profoundly influence brain function. Here we show that behavioral state modulates performance in delay eyeblink conditioning, a cerebellum-dependent form of associative learning. Increased locomotor speed in head-fixed mice drove earlier onset of learning and trial-by-trial enhancement of learned responses that were dissociable from changes in arousal and independent of sensory modality. Eyelid responses evoked by optogenetic stimulation of mossy fiber inputs to the cerebellum, but not at sites downstream, were positively modulated by ongoing locomotion. Substituting prolonged, low-intensity optogenetic mossy fiber stimulation for locomotion was sufficient to enhance conditioned responses. Our results suggest that locomotor activity modulates delay eyeblink conditioning through increased activation of the mossy fiber pathway within the cerebellum. Taken together, these results provide evidence for a novel role for behavioral state modulation in associative learning and suggest a potential mechanism through which engaging in movement can improve an individual’s ability to learn.

Behavioral state modulates the ON visual motion pathway of Drosophila

The behavioral state of an animal can dynamically modulate visual processing. In flies, the behavioral state is known to alter the temporal tuning of neurons that carry visual motion information into the central brain. However, where this modulation occurs and how it tunes the properties of this neural circuit are not well understood. Here, we show that the behavioral state alters the baseline activity levels and the temporal tuning of the first directionally selective neuron in the ON motion pathway (T4) as well as its primary input neurons (Mi1, Tm3, Mi4, Mi9). These effects are especially prominent in the inhibitory neuron Mi4, and we show that central octopaminergic neurons provide input to Mi4 and increase its excitability. We further show that octopamine neurons are required for sustained behavioral responses to fast-moving, but not slow-moving, visual stimuli in walking flies. These results indicate that behavioral-state modulation acts directly on the inputs to the directionally selective neurons and supports efficient neural coding of motion stimuli.

Correction:Behavioral-state modulation of inhibition is context-dependent and cell type specific in mouse visual cortex.

How we perceive what we see depends on the context in which we see it, such as what we are doing at the time. For example, we perceive a park landscape differently when we are running through it than when we are sitting on a park bench. Behavior can also alter neuronal responses in the brain. Indeed, the neurons in the part of the brain that receives information related to vision (known as the visual cortex) respond differently to visual stimuli when an animal is moving compared to when the animal is still. However, while some recent studies revealed that specific types of neurons become more or less responsive during movement, others reported the opposite results. One hypothesis that would explain these contradictory findings would be if the way that behavior, in this case movement, affects neuronal responses also depends on the external context in which the movement happens. Now, Pakan et al. have tested this hypothesis by imaging the activity of different types of neurons in the primary visual cortex of mice that were either running on a treadmill or staying still. The experiments were conducted in two different contexts: in total darkness (in which the mice could not see) and in the presence of display screens (which provided the mice with visual stimulation). Pakan et al. confirmed that running does indeed affect the activity of specific neurons in different ways in different contexts. For example, when the mice received visual stimulation, the three main classes of neurons that send inhibitory signals in the visual cortex became more active during running. However, when the mouse ran in the dark, two of these neuron types became more active during running while the third type of neuron was unresponsive. This finding reveals more about the dynamic nature of inhibitory activity that strongly depends on the animal’s behaviour. It also shows how these neurons influence the excitatory neurons in the visual cortex, which send information to the rest of the brain for further processing towards perception. The next step will be to identify what precise mechanism makes these neurons respond differently in unique contexts, and to tease apart how these movement-dependent signals affect the way animals perceive visual stimuli.

Behavioral-state modulation of inhibition is context-dependent and cell type specific in mouse visual cortex.

Cortical responses to sensory stimuli are modulated by behavioral state. In the primary visual cortex (V1), visual responses of pyramidal neurons increase during locomotion. This response gain was suggested to be mediated through inhibitory neurons, resulting in the disinhibition of pyramidal neurons. Using in vivo two-photon calcium imaging in layers 2/3 and 4 in mouse V1, we reveal that locomotion increases the activity of vasoactive intestinal peptide (VIP), somatostatin (SST) and parvalbumin (PV)-positive interneurons during visual stimulation, challenging the disinhibition model. In darkness, while most VIP and PV neurons remained locomotion responsive, SST and excitatory neurons were largely non-responsive. Context-dependent locomotion responses were found in each cell type, with the highest proportion among SST neurons. These findings establish that modulation of neuronal activity by locomotion is context-dependent and contest the generality of a disinhibitory circuit for gain control of sensory responses by behavioral state.

Sleep Facilitates Memory by Blocking Dopamine Neuron-Mediated Forgetting

Early studies from psychology suggest that sleep facilitates memory retention by stopping ongoing retroactive interference caused by mental activity or external sensory stimuli. Neuroscience research with animal models, on the other hand, suggests that sleep facilitates retention by enhancing memory consolidation. Recently, in Drosophila, the ongoing activity of specific dopamine neurons was shown to regulate the forgetting of olfactory memories. Here, we show this ongoing dopaminergic activity is modulated with behavioral state, increasing robustly with locomotor activity and decreasing with rest. Increasing sleep-drive, with either the sleep-promoting agent Gaboxadol or by genetic stimulation of the neural circuit for sleep, decreases ongoing dopaminergic activity, while enhancing memory retention. Conversely, increasing arousal stimulates ongoing dopaminergic activity and accelerates dopaminergic-based forgetting. Therefore, forgetting is regulated by the behavioral state modulation of dopaminergic-based plasticity. Our findings integrate psychological and neuroscience research on sleep and forgetting.

Layer-specific refinement of visual cortex function after eye opening in the awake mouse.

The laminar structure and conserved cellular organization of mouse visual cortex provide a useful model to determine the mechanisms underlying the development of visual system function. However, the normal development of many receptive field properties has not yet been thoroughly quantified, particularly with respect to layer identity and in the absence of anesthesia. Here, we use multisite electrophysiological recording in the awake mouse across an extended period of development, starting at eye opening, to measure receptive field properties and behavioral-state modulation of responsiveness. We find selective responses for orientation, direction, and spatial frequency at eye opening, which are similar across cortical layers. After this initial similarity, we observe layer-specific maturation of orientation selectivity, direction selectivity, and linearity over the following week. Developmental increases in selectivity are most robust and similar between layers 2-4, whereas layers 5 and 6 undergo distinct refinement patterns. Finally, we studied layer-specific behavioral-state modulation of cortical activity and observed a striking reorganization in the effects of running on response gain. During week 1 after eye opening, running increases responsiveness in layers 4 and 5, whereas in adulthood, the effects of running are most pronounced in layer 2/3. Together, these data demonstrate that response selectivity is present in all layers of the primary visual cortex (V1) at eye opening in the awake mouse and identify the features of basic V1 function that are further shaped over this early developmental period in a layer-specific manner.

Adenosine Mediation of Presynaptic Feedback Inhibition of Glutamate Release

Conditions of increased metabolic demand relative to metabolite availability are associated with increased extracellular adenosine in CNS tissue. Synaptic activation of postsynaptic NMDA receptors on neurons of the cholinergic brainstem arousal center can increase sufficient extracellular adenosine to act on presynaptic A1 adenosine receptors (A1ADRs) of glutamate terminals, reducing release from the readily releasable pool. The time course of the adenosine response to an increase in glutamate release is slow (tau > 10 min), consistent with the role of adenosine as a fatigue factor that inhibits the activity of cholinergic arousal centers to reduce arousal.

Wake-Promoting Actions of Medial Basal Forebrain β₂ Receptor Stimulation.

The locus coeruleus-noradrenergic system exerts an activating influence on forebrain neuronal and behavioral activity states, in part, through the actions of noradrenergic beta receptors located within the medial septal (MS) and medial preoptic (MPOA) areas. The current study examined the extent to which beta2 receptors located within these medial basal forebrain regions modulate behavioral state. In this study, the sleep-wake effects of microinfusion of the beta2 agonist, clenbuterol, into the MS and MPOA were examined. Clenbuterol infusion into both MS and MPOA elicited a dose-dependent increase in time spent awake. These observations indicate that medial basal forebrain beta-sub-2 receptors participate in the noradrenergic-dependent modulation of behavioral state.

Organization of hypocretin/orexin efferents to locus coeruleus and basal forebrain arousal‐related structures

Hypocretin/orexin neurons give rise to an extensive projection system, portions of which innervate multiple regions associated with the regulation of behavioral state. These regions include the locus coeruleus, medial septal area, medial preoptic area, and substantia innominata. Evidence indicates that hypocretin modulates behavioral state via actions within each of these terminal fields. To understand better the circuitry underlying hypocretin-dependent modulation of behavioral state, the present study characterized the degree to which there exists: 1) lateralization of hypocretin efferents to basal forebrain and brainstem arousal-related regions, 2) topographic organization of basal forebrain- and brainstem-projecting hypocretin neurons, and 3) collateralization of individual hypocretin neurons to these arousal-related terminal fields. These studies utilized combined immunohistochemical identification of hypocretin neurons with single or double retrograde tracing from the locus coeruleus, medial preoptic area, medial septal area, and substantia innominata. Results indicate that approximately 80% of hypocretin efferents to basal forebrain regions project ipsilaterally, whereas projections to the locus coeruleus are more bilateral (65%). There was a slight preference for basal forebrain-projecting hypocretin neurons to be distributed within the medial half of the hypocretin cell group. In contrast, hypocretin neurons projecting to the locus coeruleus were located primarily within the dorsal half of the hypocretin cell group. Finally, a large proportion of hypocretin neurons appear to project simultaneously to at least two of the examined terminal fields. These latter observations suggest coordinated actions of hypocretin across multiple arousal-related regions.

Additive wake-promoting actions of medial basal forebrain noradrenergic alpha1- and beta-receptor stimulation.

The locus coeruleus-noradrenergic system exerts an activating influence on forebrain neuronal and behavioral activity states, in part through the actions of noradrenergic beta-receptors in the medial septal (MS) and medial preoptic (MPOA) areas. MPOA alpha1-receptors exert similar wake-promoting actions. The current study examines the influence of alpha1-receptors located within MS on sleep-wake state. In addition, the extent to which alpha1- and beta-receptors located within MS and MPOA interact in the modulation of behavioral state was investigated by examining the effects of individual or combined infusion of alpha1- and beta-agonists into these regions. Results show that alpha1-receptors located within MS exert wake-promoting actions. Within both MS and MPOA, additive wake-promoting actions were observed with alpha1- and beta-receptor stimulation, the sum of which contributes to the overall arousal state of the animal.

Contrasting effects of noradrenergic β-receptor blockade within the medial septal area on forebrain electroencephalographic and behavioral activity state in anesthetized and unanesthetized rat

The locus coeruleus-noradrenergic system participates in the modulation of behavioral state. Previous studies demonstrated that β-receptors located within the general region encompassing the medial septum/vertical limb of the diagonal band of Broca (medial septal area) exert arousal-enhancing actions in both anesthetized and unanesthetized animals. These studies also demonstrated that, under conditions of limited locus coeruleus discharge rates, blockade of β-receptors within this region decreased forebrain electroencephalographic indices of arousal. The current studies assess the extent to which medial septal area β-receptors contribute to the maintenance of electroencephalographic and/or behavioral indices of arousal, under conditions associated with elevated locus coeruleus discharge rates. In the halothane-anesthetized rat, bilateral, but not unilateral, blockade of β-receptors within this area prevented forebrain (cortical and hippocampal) electroencephalographic activation elicited by activation of locus coeruleus neurons. Placement of β-antagonist immediately adjacent to the medial septal area had no effect on locus coeruleus-dependent cortical and hippocampal electroencephalographic activation. In contrast, in unanesthetized rat, bilateral pretreatment of the medial septal area did not alter either electroencephalographic or behavioral measures in animals tested in an arousal-enhancing, brightly-lit novel environment, which has been demonstrated to elicit an activation of the locus coeruleus-noradrenergic system. The results obtained in anesthetized animals are consistent with previous studies demonstrating potent modulatory actions of noradrenergic systems on actions of general anesthetics, and suggest that β-receptors may be an appropriate target for pharmacological adjuncts to general anesthetics. In contrast to that observed in anesthetized animals, medial septal β-receptors alone do not contribute significantly to the maintenance of an activated forebrain in unanesthetized animals. It is presumed that actions of other noradrenergic receptors and/or other neurotransmitter systems located within or outside the medial septal area make the arousal-modulating actions of medial septal area β-receptors redundant, in the unanesthetized, alert animal.

Distribution of dopamine beta-hydroxylase-like immunoreactive fibers within the shell subregion of the nucleus accumbens.

The nucleus accumbens (Acb) can be divided into distinct subfields, delineated on the basis of histochemical markers as well as by afferent and efferent projection patterns. The shell subregion has reciprocal relationships with a variety of limbic areas and brainstem autonomic structures, and has been suggested to participate in motivation-related processes, including reward, stress, and arousal. The locus coeruleus (LC)-noradrenergic system has similarly been implicated in the modulation of behavioral state and stress-related processes, and previous studies have demonstrated reciprocal projections between the locus coeruleus and Acb shell. To better understand the anatomical substrate through which LC could influence activity within Acb shell, immunohistochemical methods were used to visualize the extent and the distribution of noradrenergic axons within this structure. Coronal sections of rat brain were processed to visualize immunoreactivity for the norepinephrine synthetic enzyme dopamine beta-hydroxylase (DBH), a specific marker for noradrenergic processes. In some cases, alternate sections were processed for immunohistochemical localization of substance P, in order to delineate core, shell, and pallidal compartments. Moderate-to-dense DBH-like immunoreactivity (DBHir) was found in approximately the caudal half of the shell subregion, particularly in caudalmost (septal pole) and ventral zones. The innervation of the septal pole was contiguous with a dense innervation of the bed nucleus of the stria terminalis. Few immunoreactive fibers were observed in the caudate-putamen, Acb core, or rostral Acb shell. Many DBHir fibers within the shell region were highly arborized with numerous varicosities, features indicative of terminal fields. These observations suggest noradrenergic systems might modulate certain processes associated with stress, behavioral state, or reinforcement via actions within the Acb shell.

Role of adenosine in behavioral state modulation: a microdialysis study in the freely moving cat

There is considerable evidence to suggest that the activity of forebrain and mesopontine cholinergic neurons is intimately involved in electroencephalographic arousal. Furthermore, our previous in vitro investigation suggested that both cholinergic systems are under a powerful tonic inhibitory control by endogenous adenosine. We thus examined the in vivo effect, on electrographically defined behavioral states, of microdialysis perfusion of adenosine into the cholinergic zones of the substantia innominata of the basal forebrain and the laterodorsal tegmental nucleus of freely moving cats. Localized perfusion of adenosine into either the basal forebrain or the laterodorsal tegmental nucleus caused a marked alteration in sleep–wake architecture. Adenosine (300 μM) perfused into either the basal forebrain or laterodorsal tegmental nucleus produced a dramatic decrease in waking, to about 50% of the basal level. Perfusion into the basal forebrain resulted in a significant increase in rapid eye movement sleep, while slow wave sleep was unchanged. In contrast, adenosine perfusion into the laterodorsal tegmental nucleus produced an increase of both slow wave sleep and rapid eye movement sleep, the magnitude of which were proportional to the decrease in waking. Electroencephalographic power spectral analysis showed that adenosine perfusion into the basal forebrain increased the relative power in the delta frequency band, whereas higher frequency bands (theta, alpha, beta and gamma) showed a decrease. These data strongly support the hypothesis that adenosine might play a key role as an endogenous modulator of wakefulness and sleep. The decrease in wakefulness may be directly related to the inhibition of cholinergic neurons of the basal forebrain and the laterodorsal tegmentum. The increase in rapid eye movement sleep is a novel but robust effect whose origin, at present, is uncertain. The observation that local perfusion of adenosine into either the basal forebrain or the laterodorsal tegmental nucleus dramatically decreases wakefulness suggests that these areas might represent a major site of action of the xanthine stimulants (adenosine antagonists) found in coffee and tea.

A Reconceptualization of the Effects of Undernutrition on Children's Biological, Psychosocial, and Behavioral Development and commentaries

A Reconceptualization of the Effects of Undernutrition on Children's Biological, Psychosocial, and Behavioral Development and commentaries

Enhancement of Behavioral and Electroencephalographic Indices of Waking following Stimulation of Noradrenergic β-Receptors within the Medial Septal Region of the Basal Forebrain

Previous studies in halothane-anesthetized rat documented potent electroencephalographic (EEG) modulatory actions of the locus coeruleus (LC) noradrenergic system, with LC neuronal activity causally related to the maintenance of EEG activity patterns associated with enhanced arousal/alertness. Recent studies, also in halothane-anesthetized rat, demonstrated that the region of the basal forebrain encompassing the medial septum/vertical limb of the diagonal band of Broca (MS) is a site at which noradrenergic efferents act to influence EEG state via actions at beta-receptors. These and other observations are consistent with the hypothesis that the LC noradrenergic system participates in the modulation of behavioral state. However, the degree to which this system modulates EEG state in the absence of anesthesia and to what extent such actions are accompanied by behavioral modulatory actions remain to be determined. The current studies examined whether small infusions of isoproterenol (ISO), a beta-adrenergic agonist, into MS alter behavioral, EEG, and electromyographic (EMG) measures of sleep and waking in the resting, undisturbed rat. These infusions resulted in a significant increase in time spent awake, defined by both behavioral and EEG/EMG measures, and in the nearly complete suppression of REM sleep. EEG/EMG responses either coincided with or preceded behavioral responses by 10-320 sec. The pattern of behavioral responses observed following MS-ISO infusions was qualitatively similar to that associated with normal waking. Infusions of vehicle into MS or ISO into sites adjacent to MS did not elicit consistent alterations in behavioral state. These results suggest that the LC noradrenergic system exerts potent behavioral and EEG-activating effects via actions of norepinephrine at beta-receptors located within MS.

Locus coeruleus activation induces perforant path-evoked population spike potentiation in the dentate gyrus of awake rat

In vitro norepinephrine (NE) induces both short- and long-term beta-receptor-mediated potentiation of the perforant path-evoked population spike in the dentate gyrus. NE or locus coeruleus (LC) activation in vivo also produces a beta-receptor dependent potentiation of population spike amplitude in anesthetized rat. Studies of behavioral state modulation of population spike amplitude in awake rats, and in rats depleted of NE, however, have led to the hypothesis that LC-NE activation should act to suppress or reduce population spike amplitude in the dentate gyrus of unanesthetized rat. Using glutamate activation of LC in awake unrestrained rats (n = 12), the present study provides evidence that LC activation in the awake rat does not reduce, but potentiates, population spike amplitude. The potentiation effect was long-lasting (> 25 min) in 50% of the experiments. In addition glutamate ejections in the third lobe of cerebellar rostral vermis produced potentiation of population spike amplitude (n = 3) and population excitatory postsynaptic potential slope. Ejections at sites outside the LC and rostral vermis were ineffective (n = 5). Behavioral effects of glutamate ejection did not predict the occurrence of potentiation. These data support the hypothesis that phasic activation of LC cells is likely to induce short-term, and possibly long-term, potentiation of dentate gyrus throughput in alert animals.

Prenatal protein malnutrition alters behavioral state modulation of inhibition and facilitation in the dentate gyrus

We have examined the effects of prenatal protein malnutrition on interneuronally mediated inhibition and facilitation in the dentate gyrus of the rat using the paired-pulse technique. Field potentials were recorded in the dentate gyrus in response to paired stimuli delivered to the perforant path. The paired-pulse index (PPI) was used as a measure of the net short-term facilitation or interneuronally mediated inhibition effective at the time of the paired-pulse test and was computed by dividing the amplitude of the second population spike (p2) by the amplitude of the first population spike (p1). PPIs were classified according to p1 in order to compare PPIs between behavioral states and dietary treatments since population spike amplitudes in the dentate gyrus vary in relation to behavioral state. Testing was performed during 4 behavioral states: slow-wave sleep (SWS), paradoxical sleep (REM), immobile waking (IW) and exploratory locomotion (AW) using interpulse intervals (IPI) from 20 to 400 ms. The magnitude and duration of interneuronally mediated inhibition was significantly increased in prenatal protein malnourished animals when compared with controls. Paired-pulse tests performed using an IPI of 20 ms under the high p1 ( p1> median) condition showed significantly smaller PPIs in prenatal protein malnourished rats regardless of behavioral state. For IPIs greater than 20 ms PPIs were consistently smaller in prenatal protein malnourished rats during SWS and IW. These data indicate that both the magnitude and duration of interneuronally mediated inhibition are increased in prenatally malnourished rats. No consistent diet-related differences were found during AW and REM using IPIs greater than 20 ms because interneuronally mediated inhibition was relatively suppressed during these behavioral states for both dietary groups. There was no consistent behavioral state modulation of paired-pulse facilitation ( IPI = 40 to 80 ms) or late inhibition (IPI = 400 ms) in either diet group. In addition, a new relation between PPI and IPI was found under the low p1 ( p1> median) condition. During AW the PPIs observed using IPIs of 40 and 50 ms were smaller than those observed using IPIs of 30 and 60 ms. This depression interrupts what is generally considered the “facilitatory” phase of paired-pulse response and may indicate an interaction between perforant path stimulation and hippocampal theta rhythm which is masked when p1 amplitude is high. Possible reasons for increased interneuronally mediated inhibition in the dentate gyrus of prenatally malnourished rats are 1. 1) increased excitability of GABAergic interneurons. 2. 2) reduced capacity for GABA reuptake. 3. 3) altered activity of extrahippocampal modulatory inputs to GABAergic interneurons. Such alterations may also help to explain why prenatally protein malnourished animals demonstrate both resistance to kindling and failure to maintain LTP.