Behavioral training-induced c-Fos expression in the rat nucleus basalis of Meynert during aging

Stress alters asenapine-induced Fos expression in the Meynert's nucleus: response of adjacent hypocretin and melanin-concentrating hormone neurons in rat

OBJECTIVE

Asenapine (ASE), an atypical antipsychotic drug used in the treatment of schizophrenia, induces Fos expression in forebrain. Effect of ASE on activity of basal nucleus of Meynert (NBM) cells, a part of the striatal-cortical circuits, was studied. We were also interested to reveal whether a chronic unpredictable variable mild stress (CMS) preconditioning might affect the ASE impact.

METHODS

Rats were divided into as follows: controls-vehicle, controls-ASE, stressed-vehicle and stressed-ASE groups. CMS included restrain, social isolation, crowding, swimming and cold applied for 21 days. On the 22nd day, rats were subcutaneously injected with ASE (0.3 mg/kg) or vehicle (saline 300 μl/rat), 90 min prior euthanizing. After transcardial fixation, brains were cut into 30 μm thick coronal sections. Fos protein presence, as indicator of cell activity, was detected by ABC immunohistochemistry. Hypocretin (Hcrt) and melanin-concentrating hormone (MCH) containing cells were visualized with fluorescent dyes.

RESULTS

ASE induced significant increase in Fos expression in NBM in both controls and CMS preconditioned rats in comparison with the related vehicle-treated controls. CMS preconditioning, however, significantly lowered the Fos response to ASE in NBM. From Hrct and MCH cells, only Hcrt ones displayed Fos presence in response to ASE.

DISCUSSION

This study demonstrates for the first time that ASE may target a special group of cells occupying NBM, which effect can be modulated by CMS preconditioning. This finding extends a view that ASE impact may extend beyond the classical forebrain target areas common for the action of all antipsychotics and might be helpful in the identification of sites and side effects of its therapeutic actions.

NMDA NR2A and NR2B receptors in the rostral anterior cingulate cortex contribute to pain-related aversion in male rats

NMDA receptors, which are implicated in pain processing, are highly expressed in forebrain areas including the anterior cingulate cortex (ACC). The ACC has been implicated in the affective response to noxious stimuli. Using a combination of immunohistochemical staining, Western blot, electrophysiological recording and formalin-induced conditioned place avoidance (F-CPA) rat behavioral model that directly reflects the affective component of pain, the present study examined formalin nociceptive conditioning-induced changes in the expressions of NMDA receptor subunits NR1, NR2A, and NR2B in the rostral ACC (rACC) and its possible functional significance. We found that unilateral intraplantar (i.pl.) injection of dilute formalin with or without contextual conditioning exposure markedly increased the expressions of NMDA receptor subunits NR2A and NR2B but not of NR1 in the bilateral rACC. NMDA-evoked currents in rACC neurons were significantly greater in formalin-injected rats than in naïve or normal saline-injected rats. Selectively blocking either NR2A or NR2B subunit in the rACC abolished the acquisition of F-CPA and formalin nociceptive conditioning-induced Fos expression, but it did not affect formalin acute nociceptive behaviors and non-nociceptive fear stimulus-induced CPA. These results suggest that both NMDA receptor subunits NR2A and NR2B in the rACC are critically involved in pain-related aversion. Thus, a new strategy targeted at NMDA NR2A or NR2B subunit might be raised for the prevention of pain-related emotional disturbance.

'When an old rat smells a cat': A decline in defense-related, but not accessory olfactory, Fos expression in aged rats

Comparisons were made between young (3-6 months) and aged (20-30 months) Wistar rats on locomotor activity, emergence, social interaction and cat odor avoidance. Aged rats were less active and spent less time in the open field during the emergence test than younger rats. Older rats also showed fewer contacts with a novel conspecific in the social interaction test, although total duration of interaction did not differ. There were very few behavioral differences between male and female rats. Older rats were less reactive than younger rats in a test of cat odor avoidance. However, they expressed similar amounts of cat odor-induced Fos in the posterior accessory olfactory bulb, a critical region for processing the predator odor stimulus. Older rats had reduced Fos expression in several defense-related brain regions that are normally activated by predator odors such as the medial amygdala and dorsal premammillary nucleus. These results indicate that aged rats are less reactive than younger rats to predator odors due to decreased responsiveness in defense-related but not necessarily olfactory circuits.

Forebrain c-fos expression under conditions conducive to pair bonding in female prairie voles (Microtus ochrogaster)

Repeated mating over a period of 6 h facilitates pair-bond formation in monogamous prairie voles. Using this paradigm, we examined fos expression in brain areas implicated in social behavior in voles. We hypothesized that the presence of the fos protein after a period of time sufficient for pair bonding to occur may indicate brain areas that are especially important in pair bond formation. We found elevated levels of fos immunoreactivity in the medial and cortical amygdala, medial preoptic area (MPOA), and bed nucleus of the stria terminalis (BNST) in females that mated several times over a 6-h period as compared to a variety of unmated controls. No treatment effects were found in the central amygdala, nucleus accumbens (NAcc), or lateral septum (LS). We suggest that areas that show evidence of fos expression after sufficient time for pair bonding to occur may be important in the formation of associations between the partner and mating stimuli.

Kynurenic acid enhances electroacupuncture analgesia in normal and carrageenan-injected rats

The interaction between electroacupuncture (EA) and an intrathecally administered wide-spectrum excitatory amino acid (EAA) receptor(s) antagonist, kynurenic acid (KYNA) on carrageenan-induced thermal hyperalgesia and spinal Fos expression was investigated. Intrathecal (i.t.) injection of 0.1, 1, 10, and 100 nmol KYNA markedly and dose-dependently increased the latency of paw withdrawal (PWL) of the carrageenan-injected paw. While the PWLs of the non-injected and normal saline (NS)-injected paws were not obviously affected by application of KYNA at the doses tested. Intrathecal injection of 0.1 nmol KYNA significantly potentiated the anti-nociception induced by EA stimulation of contralateral 'Zu-San-Li' and 'Kun-Lun' acupoints either in the carrageenan- or NS-injected rats. Three hours after intraplantar (i.pl.) injection of carrageenan, the number of Fos-like immunoreactive (Fos-LI) neurons was significantly increased in all layers of ipsilateral spinal cord at L(4)-L(5) with the higher density in laminae I-II and V-VI. Intrathecally pre-administered KYNA (10 nmol) significantly reduced the total number of carrageenan-induced Fos-LI neurons with more apparent reduction in laminae I-II and IV-V. Pre-coapplication of 10 nmol KYNA and EA of bilateral 'Zu-San-Li' and 'Kun-Lun' acupoints, the numbers of carrageenan-induced Fos-LI neurons in laminae I-II and V-VI further reduced. The level of Fos expression in the spinal cord induced by carrageenan was significantly lower compared with that of i.t. injection of KYNA or EA alone. These results demonstrated that EAA receptor(s) antagonist could enhance EA-induced anti-nociception and anti-hyperalgesia.

Fos imaging reveals ageing-related changes in hippocampal response to radial maze discrimination testing in mice

A two-stage radial arm maze (RAM) task has been designed recently to demonstrate a specific age-related memory deficit in mice. It highlights the contrast between normal and deficient memory expression in a spatial discrimination problem depending on how to-be discriminated arms were presented to the animal. This specific deficit has been interpreted as a preferential loss in a relational/declarative form of memory, thereby implying an underlying hippocampal dysfunction. To test this hypothesis, neuronal activation measured by Fos immunostaining was compared in aged (21-23 months) and adult (4-6 months) mice trained in the aforementioned task and killed after a retention session consisting in age-insensitive probe trials, performed 6 days later (6-day RAM). Two comparison conditions were included: (i) repeated locomotor training on a treadmill (TM); (ii) the same RAM training, except for the use of a longer (30 days instead of six) retention interval (30-day RAM). Although all RAM groups displayed similar levels of performance at the end of the experiment, immediately before the mice were killed, significant between-group differences in brain activation were observed. In adult mice, 6-day RAM testing was associated with greater septal and hippocampal (CA1, CA3, DG) Fos expression than the TM condition. Lengthening the retention interval from 6 days to 30 days resulted in a significant decrease in RAM testing-induced Fos expression in most of the septo-hippocampal regions. With respect to adult mice, aged mice displayed reduced Fos expression (except for DG) and a lack of interrelationships between levels of Fos produced in each of the SH regions, in the 6-day RAM testing condition. Conversely, there was no effect of ageing on Fos expression associated with either TM training or 30-day RAM testing. These results are interpreted as reflecting age- (or time-) related alterations in recruiting of brain structures that underlie a relational/declarative form of memory expression.

Age-related alterations in responses of the nucleus basalis magnocellularis neurons to frontal cortex stimulation in rats

The present study investigated the age-related alterations in responses of the nucleus basalis magnocellularis (nbM) neurons to frontal cortex (FCX) stimulation. Single unit extracellular recording from the nbM neurons were obtained with glass micropipettes in urethane-anesthetized rats. A total of 137 units were located within the nbM in the three age groups (young, 3 months; adult, 12 months; old, 24 months). FCX stimulation elicited responses in 91% of the 137 neurons. Most of them were excited. The frequency of occurrence of excitatory responses in the nbM neurons was decreased with aging. The thresholds and latencies of excitatory responses evoked by FCX stimulation were increased in old rats. The mean peak-firing rate of exciting phase was gradually reduced with aging. These findings indicate that there might be some functional changes in the nbM neurons with aging.

Age-related alterations in responses of nucleus basalis magnocellularis neurons to peripheral nociceptive stimuli

The present study investigated the effects of peripheral noxious stimuli on the spontaneous activity of the nucleus basalis magnocellularis (nbM) neurons in young, adult and old rats. Single unit extracellular recordings from the nbM neurons were obtained with glass micropipettes in urethane-anesthetized rats. A total of 104 units were antidromically identified as nbM-cortical neurons. Noxious but not innocuous mechanical stimulation elicited responses in 72% of the 104 neurons. Most of them were excited. The receptive fields were usually very large and bilateral. Most of the neurons also responded to noxious thermal, chemical and electrical stimuli. No marked differences were observed in the incidence of neurons having different spontaneous firing rates, firing patterns and response type among the three age groups. However, the latency of responses evoked by noxious thermal or electrical stimulation and the threshold of excitatory responses evoked by electrical stimulation were increased with aging. The duration and peak-firing rate of excitatory responses evoked by noxious thermal, chemical or electrical stimulation were decreased in old rats. These findings indicate that there might be some functional changes in the nbM neurons and its projection pathway with aging, which impair their responsive ability to peripheral nociceptive stimuli.

Inhibitory effects of intrathecally administered interleukin-1beta on carrageenan-induced hyperalgesia and spinal c-Fos expression in rats

The present study investigated the effects of interleukin-1beta (IL-1beta) injected intrathecally (i.t.) on carrageenan-induced thermal hyperalgesia and spinal c-Fos expression. The paw withdrawal latency (PWL) by the thermal stimulus was taken as an index of the thermal hyperalgesia of rats. I.t. injection of 10 ng IL-1beta significantly increased the PWL of the carrageenan-injected paw. Expression of c-Fos induced by intraplantar (i.pl.) injection of carrageenan was examined in the spinal cord with immunohistochemical methods. Three hours after i.pl. injection of carrageenan, the number of c-Fos-like immunoreactive (c-Fos-LI) neurons was significantly increased in laminae I-II, III-IV and V-VI of the ipsilateral spinal cord at L4-5 with the higher density in laminae I-II and V-VI. I.t. pre-injected IL-1beta significantly decreased the number of carrageenan-induced c-Fos-LI neurons in laminae I-II in the ipsilateral spinal cord and also inhibited the hyperalgesia induced by i.pl. carrageenan. These results suggested that i.t. injection of IL-1beta suppressed the central nociceptive input into laminae I-II and produced an antinociceptive effect.

17beta-Estradiol increases, aging decreases, c-Fos expression in the rat accessory olfactory bulb

In the present paper we investigated the c-Fos immunoreactivity in the accessory olfactory bulb (AOB) of juvenile, adult and old rats of both sexes, as well as the effect of 17beta-estradiol on the expression of this immediate early gene. Basal c-Fos expression in the olfactory bulb decreased with age, and estrogen treatment caused an increase in the number of neurons expressing c-Fos in the AOB. The results indicate that both aging and estrogen have roles in the ability of neurons to co-ordinate genetic activity. Our observations may explain the decrease in age-related changes of brain plasticity, and provide data for the understanding of hormonally regulated neuronal plasticity.