Toshimichi Hata

Intracranial self-stimulation enhances neurogenesis in hippocampus of adult mice and rats.

Running is known to promote neurogenesis. Besides being exercise, it results in a reward, and both of these factors might contribute to running-induced neurogenesis. However, little attention has been paid to how reward and exercise relate to neurogenesis. The present study is an attempt to determine whether a reward, in the form of intracranial self-stimulation (ICSS), influences neurogenesis in the hippocampus of adult rodents. We used bromodeoxyuridine labeling to quantify newly generated cells in mice and rats that experienced ICSS for 1 h per day for 3 days. ICSS increased the number of 5-bromodeoxyuridine (Brdu)-labeled cells in the hippocampal dentate gyrus (DG) of both species. The effect, when examined at 1 day, 1 week, and 4 weeks post-ICSS, was predominantly present in the side ipsilateral to the stimulation, although it was distributed to the contralateral side. We also found in rats that, 4 weeks after Brdu injection, surviving newborn cells in the hippocampal DG of the ICSS animals co-localized with a mature neuron marker, neuronal nuclei (NeuN), and these surviving cells in rats were double-labeled with Fos, a marker of neuronal activation, after the rats had been trained to perform a spatial task. The results demonstrate that ICSS can increase newborn neurons in the hippocampal DG that endure into maturity.

Hippocampal acetylcholine efflux increases during negative patterning and elemental discrimination in rats.

The purpose of this paper is to examine whether hippocampal acetylcholine (ACh) efflux increases during negative patterning (NP) discrimination tasks. For these tasks, a rats response was rewarded when either a single stimulus A (tone) or stimulus B (light) was presented, but was not rewarded when the compound stimulus AB (tone+light) was presented to the NP group of rats. An elemental discrimination (E) task was given to another group (E group). In the E group, the rats response was rewarded when one of two stimuli (e.g., tone) was presented, but not rewarded when the other stimulus (e.g., light) was presented. After reaching a learning criterion, a guide cannula was implanted into dorsal hippocampus under anesthesia. In test sessions, rats were given the same task as before the guide cannula implantation, and ACh efflux was measured. Hippocampal ACh efflux increased during both NP and E tasks. In addition, the magnitude of increase was higher in the NP group than in the E group. Thus, over all our results demonstrate that task difficulty is a critical factor that relates to the difference in ACh efflux in the hippocampus.

Intra-ventral tegmental area or intracerebroventricular orexin-A increases the intra-cranial self-stimulation threshold via activation of the corticotropin-releasing factor system in rats.

Although orexin‐A peptide was recently found to inhibit the brain reward system, the exact neural substrates for this phenomenon remain unclear. The aim of the present study was to investigate the role of orexin neurons in intra‐cranial self‐stimulation behavior and to clarify the pathways through which orexin‐A inhibits the brain reward system. Immunohistochemical examination using Fos, a neuronal activation marker, revealed that the percentage of activated orexin cells was very low in the lateral hypothalamus even in the hemisphere ipsilateral to self‐stimulation, suggesting that orexin neurons play only a small part, if any, in performing intra‐cranial self‐stimulation behavior. Intra‐ventral tegmental area administration of orexin‐A (1.0 nmol) significantly increased the intra‐cranial self‐stimulation threshold. Furthermore, the threshold‐increasing effects of intra‐ventral tegmental area or intracerebroventricular orexin‐A were inhibited by administration of the nonspecific corticotropin‐releasing factor receptor antagonist, d‐Phe‐CRF12–41 (20 μg). Following intra‐ventral tegmental area infusion of orexin‐A, the percentage of cells double‐labeled with corticotropin‐releasing factor and Fos antibodies increased in the central nucleus of the amygdala but not in the bed nucleus of the stria terminalis, and brain microdialysis analyses indicated that dopamine efflux in both the central nucleus of the amygdala and bed nucleus of the stria terminalis were enhanced. Taken together, the present findings suggest that intra‐ventral tegmental area or intracerebroventricular administration of orexin‐A exerts its threshold‐increasing effect via subsequent activation of the corticotropin‐releasing factor system.

Post-acquisition hippocampal NMDA receptor blockade sustains retention of spatial reference memory in Morris water maze

Several studies have demonstrated that the hippocampal N-methyl-D-aspartate type glutamate receptors (NMDARs) are necessary for the acquisition but not the retention of spatial reference memory. In contrast, a few studies have shown that post-acquisition repetitive intraperitoneal injections of an NMDAR antagonist facilitate the retention of spatial reference memory in a radial maze task. In the present study, we investigated the role of hippocampal NMDARs in the retention of spatial reference memories in Morris water maze. In Experiment 1, 24 h after training (4 trials/day for 4 days), D-AP5 was chronically infused into the hippocampus of rats for 5 days. In the subsequent probe test (seven days after training), we found that rats infused with D-AP5 spent a significantly longer time in the target quadrant compared to chance level, whereas rats in the control group did not. In Experiment 2, D-AP5 was infused into the hippocampus 1 (immediate) or 7 (delayed) days after the training session. In the probe test, following the retention interval of 13 days, immediate infusion facilitated the performance in a manner similar to Experiment 1, whereas the delayed infusion did not. These findings suggest that hippocampal NMDARs play an important role in the deterioration of spatial reference memory.

Glutamate - a forgotten target for interval timing.

Since the early 1980s, dopamine and acetylcholine have received much interest in research on the neural substrates of interval timing (e.g., Meck, 1983, 1996; Meck and Church, 1987; Cheng et al., 2007a,b). The information-processing component of scalar expectancy theory (SET) formed the theoretical basis for many of these pharmacological studies (Gibbon et al., 1984). Alternative theories, including the Behavioral Theory of timing (Killeen and Fetterman, 1988), the Learning-to-Time model (Machado, 1997), the Multiple-Time-Scale model (Staddon and Higa, 1999), and the Striatal Beat Frequency (SBF) model (Matell and Meck, 2004) have been proposed for overcoming some of the deficiencies of SET. Evaluation of the similarities and differences of these models has been undertaken elsewhere (Matell and Meck, 2000). From a neuroscientific perspective, however, the SBF model is the most appealing, because it is the only model that deals with the specific neural substrates of interval timing. The SBF model was developed to elucidate the role of glutamate (Glu), a forgotten target for the neural substrate of interval timing, emphasizing the role of cortico-striatal Glu on behavior. However, few studies have focused on the role of Glu in the temporal control of behavior in the seconds-to-minutes range (Cheng et al., 2006; Bhave et al., 2008). This article seeks to identify important points to consider when examining the role of Glu in interval timing guided by the SBF model. In psychopharmacological studies, a direct injection of drugs such as Glu receptor antagonists into the dorsal striatum is preferable to systemic injection, because the model assumes that the cortical Glu input to the medium spiny neurons (MSNs) in the dorsal striatum, in which neural plasticity occurs, is important for “coincidence detection” underlying duration discrimination. Pioneering work by Miller et al. (2006) revealed that the NMDA receptor antagonist MK-801 increased the peak time and variance of the response rate function in the peak-interval procedure. Unfortunately, this study did not conclusively demonstrate the importance of the Glu in the dorsal striatum, because the drug was injected systemically. In future studies, the role(s) of two distinct types of ion channel Glu receptors (AMPA and NMDA) should be examined in two distinct phases; acquisition (memory formation for specific target durations) and performance (accuracy and precision of timing behavior following acquisition). Glu synapses predominantly act through AMPA-type receptors to produce fast synaptic excitation (i.e., normal synaptic transmission). However, striatal long-term potentiation (LTP), a representative form of neural plasticity, requires activation of NMDA-type Glu receptors (Lovinger, 2010). Therefore, the role of AMPA and NMDA receptors may differ between the acquisition and performance phases of interval timing. Not only ion channel-type receptors, but also the role of metabotropic Glu receptors 1 and 5 should be clarified during the acquisition phase, because these receptors are thought to be important for neural plasticity among MSNs (Surmeier et al., 2007; Lopez de Maturana and Sanchez-Pernaute, 2010). In order to examine drug effects on memory formation for target durations, we propose the adoption of a “time-shift paradigm.” In this paradigm, once the discrimination for the first required target duration (e.g., 20 s) is acquired in, for example, the peak-interval procedure, the required target duration is then changed (e.g., to 40 s), and behavioral training is continued (second phase). The drug effect is examined during the formation of memory for the target duration in the second phase. This “time-shift paradigm” can dissociate the effects of the drug on the formation of the memory for the target duration from the effect on other processes (e.g., learning task rules, which may be included in the first stage of learning). Recently, Hohn et al. (2010) adopted a version of the “time-shift paradigm” in delayed classical conditioning and immunohistochemical analysis against Arc protein was used to test whether a change in the CS–US interval (resulting in a new memory formation for duration) triggers plasticity in the dorsal striatum. In a similar fashion, the “time-shift paradigm” provides a powerful tool for isolating the role of Glu in the formation of memory for target durations. Recently, we examined the effect of intraperitoneal injection of a non-competitive NMDA receptor antagonist, MK-801, on the formation of the memory for the target duration in a “time-shift paradigm” version of peak-interval procedure. Contrary to our expectations, the peak time in MK-801 group was immediately shifted in the earliest sessions of the second phase (unpublished observation). A previous study (Miller et al., 2006) reported that systemic injection of MK-801 immediately increased the peak time, which can mask the possible effects of MK-801 on memory formation in our study. The effect of intra-dorsal striatum injection of drugs should be examined in the “time-shift paradigm” in future studies. Taken together, the role of Glu in interval timing will be clarified more precisely by considering the above three points: injection routes, receptor subtypes, and learning phases.

Medial prefrontal cortex and precision of temporal discrimination: a lesion, microinjection, and microdialysis study

In this paper, we examined the role of the medial prefrontal cortex in temporal discrimination in three experiments using rats. Experiment 1 attempted to dissociate the roles of the medial precentral (PrCm) area from the prelimbic and infralimbic (PL-IL) area in temporal discrimination using fixed-interval (FI) schedule. The gradient of response rate distribution became more moderate by a lesion of the PrCm, but not by a lesion of the PL-IL. In experiment 2, the efflux of acetylcholine (ACh) in the PrCm area during temporal discrimination tasks was compared to that during non-temporal discrimination tasks. ACh efflux was not different between these two tasks. In experiment 3, microinjection of the anticholinergic drug scopolamine (10 microg) into the PrCm area made the gradient of response rate distribution moderate. These findings suggest that reduced activity of the ACh system within the PrCm area impairs the precision of temporal discrimination, even though enhancement of this system is not indispensable for performing temporal discrimination.

Post-acquisition hippocampal blockade of the NMDA receptor subunit GluN2A but not GluN2B sustains spatial reference memory retention

HighlightsPost‐acquisition infusion of NVP‐AAM077 suppresses spatial memory decay.Post‐acquisition infusion of Ro 25‐6981 does not suppress spatial memory decay.The NMDAR subunit GluN2A, but not GluN2B, is important for spatial memory deterioration. ABSTRACT While it has been shown that the blockade of N‐methyl‐d‐aspartate type glutamate receptors (NMDARs) impairs memory acquisition, recent studies have reported that the post‐acquisition administration of NMDAR antagonists suppresses spatial memory decay. These findings suggest that NMDARs are important not only for the acquisition of new memories but also for the decay of previously acquired memories. The present study investigated the contributions of specific NMDAR subunits to spatial memory decay using NVP‐AAM077 (NVP), an NMDAR antagonist that preferentially binds to GluN2A subunits, and the selective GluN2B blocker Ro 25‐6981 (Ro). Following Morris water maze training (four trials/day for four days), nvp and/or Ro were subchronically infused into the rat hippocampus for five days. Seven days after training, NVP‐treated rats and NVP/Ro‐treated rats explored the target area significantly more than the control and Ro‐treated rats. These results demonstrate that post‐acquisition treatment with NVP, but not Ro, suppresses the forgetting of previously acquired spatial memories. The NVP‐treated rats more persistently explored the target area in the second test, which was conducted one day after the first, while the NVP/Ro‐treated rats did not, which suggest that Ro treatment downregulates memory retention. In conclusion, the present results indicate that the NMDAR GluN2A and GluN2B subunits contribute to spatial memory deterioration and maintenance, respectively.

Basolateral amygdala inactivation eliminates fear-induced underestimation of time in a temporal bisection task

&NA; We examined interval timing – time perception in the seconds‐to‐minutes range – of the fear‐inducing stimulus and the role of the amygdala in this phenomenon. Rats were initially trained to perform a temporal bisection task, in which their responses to levers A and B were reinforced following 2‐s and 8‐s tones, respectively. After acquisition, the rats were also presented with tones of intermediate durations and pressed one of the two levers to indicate whether the tone duration was closer to 2 or 8 s. Subsequently, the rats underwent differential fear conditioning, in which one frequency tone (conditioned stimulus; CS+) was paired with an electric foot shock, whereas another frequency tone (CS−) was presented alone. The rats were then infused with artificial cerebrospinal fluid (aCSF) or the GABAA agonist muscimol into the bilateral basolateral amygdala (BLA) before performing the bisection task with CS+ and CS−. In rats infused with aCSF, the psychophysical function shifted rightward in CS+ relative to that in CS−. Moreover, the point of subjective equality of the CS+ was higher than that of CS−, suggesting that the duration of the fear −CS was perceived as shorter than that of the neutral CS. However, muscimol infusion into the BLA abolished this difference, suggesting that BLA inactivation suppresses the effect of the fear −CS. Our results demonstrate that normal BLA activity is essential for fear‐induced underestimation of time. HighlightsThe duration of the fear‐CS was underestimated relative to the neutral CS.Amygdala inactivation eliminated fear‐induced underestimation of time.The amygdala may be crucial for fear‐induced modulation of time perception.

Insular cortex inactivation generalizes fear-induced underestimation of interval timing in a temporal bisection task

HighlightsDuration of a fear cue was underestimated relative to a neutral cue.Insular cortex inactivation generalized underestimation of time to the neutral cue.Insular cortex inactivation had no effect on interval timing per se.The insular cortex seems to be involved in fear modulation of interval timing. ABSTRACT In this study, we investigated: (1) the effect of fear on interval timing—time perception in the seconds‐to‐minutes range—and (2) the role of the insular cortex in the modulation of this effect. Rats were first trained on a temporal bisection task in which their response to a lever A was reinforced following a 2.00‐s tone, whereas their response to a lever B was reinforced following an 8.00‐s tone. After acquisition, the rats were also presented with intermediate‐duration tones and pressed one of two levers to indicate whether tone duration was closer to 2.00 or 8.00s. Subsequently, the rats underwent differential fear conditioning in which one pitch tone (conditioned stimulus; CS+) was paired with an electric foot shock, while the other pitch tone (CS−) was presented alone. Either artificial cerebrospinal fluid (aCSF) or the GABAA agonist muscimol was then infused into the rats’ bilateral insular cortex before the animals were tested on the bisection task using the CS+and CS− tones. We found that in the rats infused with aCSF, the point of subjective equality (PSE) of the CS+ was higher than that for CS−, suggesting that the duration for CS+ was perceived to be shorter than that of CS−. However, muscimol eliminated the difference in PSE between CS+ and CS− by generalizing of the effect from CS+to the CS−. Taken together, our results show that normal activity in the insular cortex is involved in fear‐induced modulation of interval timing.

Increase in ICSS threshold with orexin A is blocked by an antagonism of CRF receptor

we investigated the effects of bilateral intra-accumbal administration of AM251, a CB1 receptor antagonist, on the expression of ineffective dose of morphineinduced conditioned place preference (CPP) in morphine-sensitized rats. Bilateral intra-accumbal administration of AM251 (25 and 125 ng/0.5 l per side) on the test day 5 min before the test decreased the expression of morphine-induced CPP in morphine-sensitized animals which had received effective dose of morphine (5 mg/kg) for 3 and 5 days free of opioids (sensitization period). The results indicated that CB1 receptor within the nucleus accumbens is involved in the expression of morphine-induced CPP in sensitized rats.