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Most mammals rely on chemosensory cues for individual recognition, which is essential to many aspects of social behavior, such as maternal bonding, mate recognition, and inbreeding avoidance. Both volatile molecules and nonvolatile peptides secreted by individual conspecifics are detected by olfactory sensory neurons in the olfactory epithelium and the vomeronasal organ. The pertinent cues used for individual recognition remain largely unidentified. Here we show that nonformylated, but not N-formylated, mitochondrially encoded peptides—that is, the nine N-terminal amino acids of NADH dehydrogenases 1 and 2—can be used to convey strain-specific information among individual mice. We demonstrate that these nonformylated peptides are sufficient to induce a strain-selective pregnancy block. We also observed that the pregnancy block by an unfamiliar peptide derived from a male of a different strain was prevented by a memory formed at the time of mating with that male. Our findings also demonstrate that pregnancy-blocking chemosignals in the urine are maternally inherited, as evidenced by the production of reciprocal sons from two inbred strains and our test of their urine’s ability to block pregnancy. We propose that this link between polymorphic mitochondrial peptides and individual recognition provides the molecular means to communicate an individual’s maternal lineage and strain.

The formation of mate recognition memory in mice is associated with neural changes at the reciprocal dendrodendritic synapses between glutamatergic mitral cell (MC) projection neurons and GABAergic granule cell (GC) interneurons in the accessory olfactory bulb (AOB). Although noradrenaline (NA) plays a critical role in the formation of the memory, the mechanism by which it exerts this effect remains unclear. Here we used extracellular field potential and whole-cell patch-clamp recordings to assess the actions of bath-applied NA (10 µM) on the glutamatergic transmission and its plasticity at the MC-to-GC synapse in the AOB. Stimulation (400 stimuli) of MC axons at 10 Hz but not at 100 Hz effectively induced N-methyl-d-aspartate (NMDA) receptor-dependent long-term potentiation (LTP), which exhibited reversibility. NA paired with subthreshold 10-Hz stimulation (200 stimuli) facilitated the induction of NMDA receptor-dependent LTP via the activation of α2-adrenergic receptors (ARs). We next examined how NA, acting at α2-ARs, facilitates LTP induction. In terms of acute actions, NA suppressed GC excitatory postsynaptic current (EPSC) responses to single pulse stimulation of MC axons by reducing glutamate release from MCs via G-protein coupled inhibition of calcium channels. Consequently, NA reduced recurrent inhibition of MCs, resulting in the enhancement of evoked EPSCs and spike fidelity in GCs during the 10-Hz stimulation used to induce LTP. These results suggest that NA, acting at α2-ARs, facilitates the induction of NMDA receptor-dependent LTP at the MC-to-GC synapse by shifting its threshold through disinhibition of MCs.

Background. We have observed changes in body reactions during cooking, which is one of the treatment modalities used in occupational therapy. The perception of food-related odors during cooking may have behavioral effects on human activities through the activation of appetitive motivation. Objectives. We investigated whether odor components contained in seasonings could facilitate the human motor system and the specificity of this effect. Methods. The subjects were 72 healthy adults, randomly assigned to a water exposure group, a phenylethyl alcohol (PEA, pleasant rose-like odor) exposure group, and a Japanese soy sauce (Koikuchi Shoyu) exposure group (n=24 each). The subjects’ olfactory sense was stimulated by their sniffing of three different test tubes containing 5 ml of water, PEA, or Japanese soy sauce for 20 sec while they were seated. The modified Functional Reach Test (mFRT), which mimics a functional activity that is required in daily living and assesses a reliable measure of sitting balance, was performed prior to and immediately after the sniffing. Results. Sniffing the soy sauce increased the subjects’ mFRT scores. This facilitation effect was odorant-specific and was absent when the subjects were presented with water or PEA. Conclusions. Cooking interventions are aimed at improving tool-handling skills such as using knives and chopsticks. The results indicate that treatment interventions using odors of seasonings would be effective for improving subjects’ physical functions.

[Purpose] To examine the ability of young and elderly individuals to control the timing and force of periodic sequential foot tapping. [Subjects and Methods] Participants were 10 young (age, 22.1 ± 4.3 years) and 10 elderly individuals (74.8 ± 6.7 years) who were healthy and active. The foot tapping task consisted of practice (stimulus-synchronized tapping with visual feedback) and recall trials (self-paced tapping without visual feedback), periodically performed in this order, at 500-, 1,000-, and 2,000-ms target interstimulus-onset intervals, with a target force of 20% maximum voluntary contraction of the ankle plantar-flexor muscle. [Results] The coefficients of variation of force and intertap interval, used for quantifying the steadiness of the trials, were significantly greater in the elderly than in the young individuals. At the 500-ms interstimulus-onset interval, age-related effects were observed on the normalized mean absolute error of force, which was used to quantify the accuracy of the trials. The coefficients of variation of intertap interval for elderly individuals were significantly greater in the practice than in the recall trials at the 500- and 1,000-ms interstimulus-onset intervals. [Conclusion] The elderly individuals exhibited greater force and timing variability than the young individuals and showed impaired visuomotor processing during foot tapping sequences.

The formation of mate recognition memory in mice is associated with neural changes at the reciprocal dendrodendritic synapses between glutamatergic mitral cell (MC) projection neurons and GABAergic granule cell (GC) interneurons in the accessory olfactory bulb (AOB). Although noradrenaline (NA) plays a critical role in the formation of the memory, the mechanism by which it exerts this effect remains unclear. Here we used extracellular field potential and whole-cell patch-clamp recordings to assess the actions of bath-applied NA (10 µM) on the glutamatergic transmission and its plasticity at the MC-to-GC synapse in the AOB. Stimulation (400 stimuli) of MC axons at 10 Hz but not at 100 Hz effectively induced N-methyl-d-aspartate (NMDA) receptor-dependent long-term potentiation (LTP), which exhibited reversibility. NA paired with subthreshold 10-Hz stimulation (200 stimuli) facilitated the induction of NMDA receptor-dependent LTP via the activation of α2-adrenergic receptors (ARs). We next examined how NA, acting at α2-ARs, facilitates LTP induction. In terms of acute actions, NA suppressed GC excitatory postsynaptic current (EPSC) responses to single pulse stimulation of MC axons by reducing glutamate release from MCs via G-protein coupled inhibition of calcium channels. Consequently, NA reduced recurrent inhibition of MCs, resulting in the enhancement of evoked EPSCs and spike fidelity in GCs during the 10-Hz stimulation used to induce LTP. These results suggest that NA, acting at α2-ARs, facilitates the induction of NMDA receptor-dependent LTP at the MC-to-GC synapse by shifting its threshold through disinhibition of MCs.

Cholinergic modulation of spontaneous GABAergic currents (mIPSC) was studied using whole-cell patch methods in mouse accessory olfactory bulb slices. Carbachol (above 100 microM) administration produced an increase in the mIPSC frequency in mitral cells, but did not affect the responses of mitral cells to GABA. The carbachol effect persisted in the presence of combined ionotropic and metabotropic glutamatergic receptor antagonists. The carbachol effect was reduced by the muscarinic receptor type-1 and -4 (M1 and M4) antagonist pirenzepine (10 microM), but not by the M2 and M4 antagonist himbacine (10 microM). The KCNQ/Kv7 potassium channel openers retigabine (80 microM) and diclofenac (300 microM) blocked the carbachol action, while the KCNQ potassium channel blocker XE-911 (20 microM) increased the mIPSC frequency. XE-911's action persisted in the presence of glutamate receptor blockers. In the presence of carbachol, mIPSCs were abolished by Ni (200 microM), while being insensitive to the calcium channel blocker nimodipine (30 microM), suggesting a role for R-type calcium channels in the GABA release. These results suggest that carbachol closed KCNQ channels by stimulating M1 receptors on granule cell dendrites, and the resulting depolarized and unstable membrane promoted calcium influx, thus increasing the GABA release. The possible role of acetylcholine in facilitating formation of a pheromone memory in mice is also discussed.

Propylene glycol (PG) is commonly used as a solvent for odorous chemicals employed in studies of the olfactory system because PG has been considered to be odorless for humans and other animals. However, if laboratory rats can detect the vapor of PG and if exposure to this influences behaviors, such effects might confound data obtained from experiments exposing conscious rats to odorants dissolved in PG. Therefore, we examined this issue using differences in the acoustic startle reflex (ASR) as an index. We also conducted a habituation/dishabituation test to assess the ability of rats to detect the vapor of PG. In addition, we observed Ca(2+) responses of vomeronasal neurons (VNs) in rats exposed to PG using the confocal Ca(2+)-imaging approach. Pure PG vapor significantly enhanced the ASR at a dose of 1 x 10(-4) M, which was much lower than the dose for efficiently detecting. In Ca(2+) imaging, VNs were activated by PG at a dose of 1 x 10(-4) M or lower. These results suggest that PG vapor acts as an aversive stimulus to rats at very low doses, even lower than those required for its detection, indicating that we should consider such effect of PG when it is employed as a solvent for odorants in studies using conscious rats. In addition, our study suggests that some non-pheromonal volatile odorants might affect animal behaviors via the vomeronasal system.

When female mice are mated, they form a memory to the pheromonal signal of their male partner. Several lines of evidence indicate that the neural changes underlying this memory occur in the accessory olfactory bulb (AOB) at the first stage of the vomeronasal system. The formation of this memory depends on the mating-induced release of noradrenaline in the AOB. In addition to noradrenaline, the neuropeptide oxytocin (OT) is also released within the central nervous system during mating. Because OT has been implicated in social memory and its receptors are expressed in the AOB, we hypothesized that OT might promote the strength of synaptic transmission from mitral to granule cells in the AOB. To test this hypothesis, we analyzed the lateral olfactory tract-evoked field potential that represents the granule cell response to mitral cell activation and its plasticity in parasagittal slices of the AOB. Of the 10-, 20-, 50-, and 100-Hz stimulations tested, the 100-Hz stimulation was optimal for inducing long-term potentiation (LTP). OT paired with 100-Hz stimulation that only produced short-term potentiation enhanced LTP induction in a dose-dependent manner. OT-paired LTP was blocked by both the selective OT antagonist desGly-NH 2 ,d(CH 2 ) 5 [Tyr(Me) 2 ,Thr 4 ]-ornithine vasotocin and the N -methyl- d -aspartate (NMDA) receptor antagonist dl -2-amino-5-phosphonovaleric acid. These results indicate that OT can function as a gate to modulate the establishment of NMDA receptor-dependent LTP at the mitral-to-granule cell synapse in the AOB.

An electrophysiological study was performed with mice lacking complexin II, a presynaptic protein. The long-term potentiation (LTP) by high-frequency stimulation, recorded in the hippocampal CA1 area, was decreased in complexin II-lacking mice (CPXII KO mice). The overall postsynaptic currents elicited by low frequency stimulation on the Schaffer collateral/commissural fibers in the hippocampal CA1 pyramidal cells were not different between wild-type and mutant mice. Excitatory postsynaptic currents (EPSCs) recorded in the presence of 50 microM bicuculline and inhibitory postsynaptic currents (IPSCs) recorded in the presence of 50 microM AP-5 (DL-2-amino-5-phosphonopentanoic acid) + 30 microM CNQX (6-cyano-7-nitroquinoxaline-2,3-dione) were also identical between wild-types and mutants. Furthermore, the EPSCs following repetitive stimulation (10 Hz) in CPXII KO mice did not show any difference with wild-types. These findings suggest that complexin II does not play a crucial role in ordinary neural transmission, short-term synaptic plasticity or synaptic transmission during high-frequency repetitive stimulation. Therefore, the protein is thought to be involved in the LTP process following tetanic stimulation, including the induction and/or maintenance of the LTP.

Attachment to an abusive caregiver has wide phylogenetic representation, suggesting that animal models are useful in understanding the neural basis underlying this phenomenon and subsequent behavioral outcomes. We previously developed a rat model, in which we use classical conditioning to parallel learning processes evoked during secure attachment (odor-stroke, with stroke mimicking tactile stimulation from the caregiver) or attachment despite adversity (odor-shock, with shock mimicking maltreatment). Here we extend this model to mice. We conditioned infant mice (postnatal day (PN) 7–9 or 13–14) with presentations of peppermint odor and either stroking or shock. We used 14C 2-deoxyglucose (2-DG) to assess olfactory bulb and amygdala metabolic changes following learning. PN7-9 mice learned to prefer an odor following either odor-stroke or shock conditioning, whereas odor-shock conditioning at PN13-14 resulted in aversion/fear learning. 2-DG data indicated enhanced bulbar activity in PN7-9 preference learning, whereas significant amygdala activity was present following aversion learning at PN13-14. Overall, the mouse results parallel behavioral and neural results in the rat model of attachment, and provide the foundation for the use of transgenic and knockout models to assess the impact of both genetic (biological vulnerabilities) and environmental factors (abusive) on attachment-related behaviors and behavioral development.

When female mice are mated, they form a memory to the pheromonal signal of their male partner. The neural mechanisms underlying this memory involve changes at the reciprocal dendrodendritic synapses between glutamatergic mitral cells and gamma-aminobutyric acid (GABA)-ergic granule cells in the accessory olfactory bulb (AOB). Blockade of GABA(A) receptors in the AOB leads to the formation of an olfactory memory. In an attempt to disrupt memory formation at mating, we used local infusions of the GABA(A) receptor agonist muscimol into the AOB during the critical period for memory formation. Muscimol across a wide range of doses (1-1000 pmol) did not prevent memory formation. The resistance of this memory to GABA(A) receptor activation may reflect the complexity of synaptic microcircuits in the AOB.

Mice have an olfactory (pheromone) recognition memory located at the first relay in the sensory system. It is acquired with one-trial learning, contingent upon norepinephrine activation at mating, and lasts for several weeks. The mechanism involves Hebbian (association-dependent) changes in synaptic efficacy at dendrodendritic synapses in the accessory olfactory bulb. As a result of this memory, males made familiar by mating are recognized by the females, thereby mitigating pregnancy block. Such a memory function is biologically important to the female, as it is required to sustain pregnancy in the presence of her stud male's odors.

One context of olfactory learning that has been investigated in some detail concerns the memory, established at mating, and formed by the female mouse to the odours (pheromones) of the mating male. This olfactory memory is vital for mitigating pregnancy block that might otherwise be induced by his pheromones (Keverne and Rosser, 1986). Pheromones from an unfamiliar male, for which no memory has been formed, activate the vomeronasal system with their receptors in the vomeronasal organ, thereby initiating a neuroendocrine reflex that suppresses prolactin secretion from the pituitary (Keverne, 1983). The removal of luteotrophic support results in a fall in progesterone levels and a return to oestrus. Therefore, it has been hypothesized that the pheromonal memory functions as a gate to suppress or modulate the specific pheromonal signal (Brennan et al., 1990; Kaba and Nakanishi, 1995; Brennan and Keverne, 1997; Brennan, 2001). The pheromonal memory is acquired with one trial learning, depends upon mating and lasts for several weeks (Keverne and de la Riva, 1982; Kaba et al., 1988). The neural changes underlying memory formation occur in the accessory olfactory bulb (AOB), the first relay in the vomeronasal system, independently of the main olfactory system and the hippocampus (Brennan et al., 1990; Kaba and Nakanishi, 1995; Brennan and Keverne, 1997). Microcircuits in the AOB include the prominent reciprocal dendrodendritic synapse between mitral cells, a single class of projection neurons and granule cell interneurons. Glutamate released from mitral cell dendrites activates the dendrites of granule cells, which in turn mediate GABAergic dendrodendritic inhibition back onto mitral cell dendrites (Jia et al., 1999; Taniguchi and Kaba, 2001). This feedback inhibition at the reciprocal synapses regulates mitral cell activity (Jia et al., 1999; Taniguchi and Kaba, 2001). The formation of the pheromonal memory requires the association of the pheromonal and the mating signals in the AOB. The mating signal is conveyed by noradrenergic projections from the locus coeruleus. Artificial vaginocervical stimulation (Rosser and Keverne, 1985) or mating (Brennan et al., 1995) promotes the release of noradrenaline (NA) in the AOB. Blockade of α-adrenergic receptors in the AOB immediately after mating prevents the formation of the pheromonal memory (Kaba and Keverne, 1988), as does removal of noradrenergic innervation of the AOB prior to mating (Rosser and Keverne, 1985). Furthermore, memory formation is associated with neurochemical and morphological changes at the mitral–granule cell reciprocal synapses (Brennan et al., 1995; Matsuoka et al., 1997, 2004). Despite advances such as these, however, an important void in our knowledge of electrophysiological aspects has remained: a longlasting increase in synaptic strength, known as long-term potentiation (LTP), has been little investigated. Moreover, the cellular and synaptic mechanisms underlying noradrenergic modulation of pheromonal learning are also unknown. To address these questions, we have carried out a series of experiments in AOB slices. Induction of LTP at the mitral-to-granule cell synapse in the AOB

Field potentials evoked in the accessory olfactory bulb (AOB) of the mouse by a vomeronasal organ (VNO) volley were analyzed with current source-density (CSD) techniques. The potentials were recorded with an electrode oriented in the direction perpendicular to the laminae of the centre of the AOB in five tracks of equal spatial lattice for identical coordinates. There were little or no differences in the amplitude or time course of the potentials at equal depth among the five tracks. The CSD profile from a one-dimensional CSD analysis corresponded closely with that of a three-dimensional CSD analysis of a central track in the AOB. Furthermore, VNO-evoked field potentials were recorded in the AOB external plexiform layer while an electrode was being moved in the direction parallel to this layer. The potentials recorded at adjacent points were nearly identical and hence the related one-dimensional CSD calculations revealed no net currents along this layer. These results indicate that a one-dimensional CSD analysis is applicable to the mouse AOB.

Female mice form an olfactory memory of male pheromones at mating; exposure to the pheromones of a strange male after that mating will block pregnancy. The formation of this memory is mediated by the accessory olfactory system, in which an increase in norepinephrine after mating reduces inhibitory transmission of gamma-aminobutyric acid from the granule cells to the mitral cells. This study shows that the activation of mGluR2, a metabotropic glutamate receptor that suppresses the gamma-aminobutyric acid inhibition of the mitral cells, permits the formation of a specific olfactory memory without the occurrence of mating by infusion of mGluR2 agonists into the female's accessory olfactory bulb. This memory faithfully reflects the memory formed at mating.

In virgin rats, odour cues from pups are aversive and maternal behaviour is not elicited until this aversion is overcome. Oxytecin as a neurohypophyseai peptide has long been recognized for its effects on labour and milk ejection. This traditional view of oxytocin has been extended to include a network of nonpituitary projections. Oxytocin fibres, arising principally from parvocellular neurons in the hypothalamic paraventricular nucleus (PVN), have been found in limbic and autonomic centres. The close proximity of many oxytocin fibres to the cerebroventricular system has also been found. Vaginocervical stimulation releases oxytocin, which further promotes uterine contraction, an event which is associated with a dramatic increase in maternal responsiveness. Intracerebroventricular (ICV) infusions of oxytocin induce the rapid activation of maternal behaviour in non-parturient rats; oxytocin is increased in the olfactory bulb of sheep during parturition. These findings raise the possibility that oxytocin decreases olfactory processing in the olfactory bulb, thereby permitting parturient rats to approach their pups. We examined the effects of electrical stimulation of the PVN (0.5-1.0 mA, 100 Hz, 10-20 pulses) on the spontaneous firing of mitral and granule cells in the main olfactory bulb in urethane-anaesthetized female rats. Of mitrai cells tested, 80% showed inhibitory responses to PVN stimulation, with latencies ranging from 2 to 150 s. In contrast, 74% of granule cells tested showed excitatory responses to PVN stimulation, with latencies ranging from 2 to 145 s. Both the inhibitory and excitatory responses were blocked by local infusions of [d(CHs)s,Tyr(Me)2]-ornitine-vasotocin (10 pmol), an oxytocin antagonist, into the olfactory bulb. Mitral and

Twenty neurons in the subfornical organ (SFO) were antidromically activated by electrical stimulation of the hypothalamic supraoptic nucleus (SON) in the rat. Electrical stimulation of the lateral hypothalamic area (LHA) excited the activity of 12 identified units, but did not affect that of the remaining units. The excitatory responses to LHA stimulation were blocked by microiontophoretically applied saralasin (Sar), an angiotensin II (AII) antagonist. These results suggest that the LHA has an excitatory influence on the activity of SFO neurons projecting to the SON and that the influence may be mediated by AII receptors.

Fifteen neurons in the subfornical organ (SFO) were antidromically activated by electrical stimulation of the supraoptic nucleus (SON) of the hypothalamus in urethane-anesthetized rats. Microiontophoretically (MIPh) applied angiotensin II (AII) excited the activity of all identified SFO neurons and the effect of AII was blocked by MIPh-applied saralasin (Sar), an AII antagonist. Intravenously administered AII excited the activity of most (n=13) of these identified SFO neurons and this exciting effect by intravenous AII was also blocked by MIPh-applied Sar.

Noradrenaline (NA), but not clonidine applied microiontophoretically, inhibited the firing of neurons in the rat A1 noradrenergic region, whereas intravenous clonidine dose-dependently inhibited their firing (ED50 = 18.3 micrograms/kg). The NA-induced inhibition was blocked by the beta-antagonist timolol, but not by the alpha-antagonists phentolamine or piperoxane. These results suggest that neurons in the A1 region possess beta-adrenoceptors rather than alpha-adrenoceptors near their cell bodies, and that systemically administered clonidine acts indirectly on these cells.