Unilateral lesion in the tuberomammillary nucleus region: behavioral asymmetries and effects of histamine precursor

Chlorpheniramine impairs functional recovery in Carassius auratus after telencephalic ablation

We determined the effect of an H1 receptor antagonist on the functional recovery of Carassius auratus submitted to telencephalic ablation. Five days after surgery the fish underwent a spatial-choice learning paradigm test. The fish, weighing 6-12 g, were divided into four groups: telencephalic ablation (A) or sham lesion (S) and saline (SAL) or chlorpheniramine (CPA, ip, 16 mg/kg). For eight consecutive days each animal was trained individually in sessions separated by 24 h (alternate days). Training trials (T1-T8) consisted of finding the food in one of the feeders, which were randomly blocked for each subject. Animals received an intraperitoneal injection of SAL or CPA 10 min after the training trials. The time spent by the animals in each group to find the food (latency) was analyzed separately at T1 and T8 by the Kruskal-Wallis test, followed by the Student Newman-Keuls test. At T1 the latencies (mean +/- SEM) of the A-SAL (586.3 +/- 13.6) and A-CPA (600 +/- 0) groups were significantly longer than those of the S-SAL (226.14 +/- 61.15) and S-CPA (356.33 +/- 68.8) groups. At T8, the latencies of the A-CPA group (510.11 +/- 62.2) remained higher than those of the other groups, all of which showed significantly shorter latencies (A-SAL = 301.91 +/- 78.32; S-CPA = 191.58 +/- 73.03; S-SAL = 90.28 +/- 41) compared with T1. These results support evidence that training can lead to functional recovery of spatial-choice learning in telencephalonless fish and also that the antagonist of the H1 receptor impairs it.

Organization of histamine-immunoreactive, tuberomammillary neurons projecting to the dorsal tier of the substantia nigra compacta in the rat

Following the injection of a retrograde tracer, gold-conjugated and inactivated wheatgerm agglutinin-horseradish peroxidase (WGA-apo-HRP-gold), into the dorsal tier of substantia nigra compacta (SNCD), histamine immunostaining was performed for the tuberomammillary nucleus (TMN) in order to investigate the projection from the TMN to the SNCD. At the rostral pole of the TMN, the retrograde labeling in the dorsomedial subdivision following medial SNCD injections was predominantly ipsilateral (78%), whereas only a few cells were located bilaterally following lateral SNCD injections. Following tracer injections along the medio-lateral location along the SNCD, the labeling at the ventrolateral TMN was bilateral with slightly ipsilateral (58-61%) dominance. At rostral and caudal TMN levels, clusters of labeled neurons were localized within two discrete columns of the ventrolateral TMN. At rostral TMN level, a lateral column of cells was located at the lateral tip of the ventrolateral TMN just medial to the internal capsule, while the medial column was close to the protruded region along the ventral, pial border. At the caudal TMN level, two columns were located on either side of the lateral mammillary nucleus. Taken together, the present study suggests that ventrolateral as well as dorsomedial TMN might provide arousal-related information to medial, intermediate, and lateral regions of the SNCD, which in turn influence extrapyramidal, behavioral functions performed by the substantia nigra compacta.

Involvement of the histaminergic system on appetitive learning and its interaction with haloperidol in goldfish

This study investigated the actions of the histaminergic system on appetitive learning and memory, and its interaction with the dopaminergic system in goldfish. It consisted of nine sessions, in which fish were tested in a four-arm tank. On day 1, the animals were habituated for 10 min. On day 2, they were placed in one arm and had to find food at the left or the right arm. Time to begin feeding was recorded, and the procedure repeated for more 3 days (training phase). On training day 4, seven groups were injected with saline, seven with haloperidol (2.0 mg/kg) and one with DMSO solution before training and after feeding, three groups received saline, six chlorpheniramine (CPA) (1.0, 4.0 and 8.0 mg/kg), and six l-histidine (LH) (25, 50 and 100 mg/kg). Saline groups were considered as control of CPA and LH treated groups and DMSO as control of haloperidol. A non-injected group was also included. Testing occurred after 24 h. A reversal procedure was conducted 24h after testing and repeated for 3 days. The groups receiving CPA at 1.0 and 8.0 mg/kg and LH at 25, 50 and 100 mg/kg differed between Test and Reversal day 1. Pre-treatment with haloperidol plus 8.0 mg/kg of CPA and 25 and 50 mg/kg of LH reverted the treatment effect. However, in the groups treated with 1.0 mg/kg of CPA and 100 mg/kg of LH, the difference remained. This study confirmed the interaction between the histaminergic and the dopaminergic systems on memory process in goldfish.

Effects of Chlorpheniramine and L-histidine on vestibular compensation in goldfish, Carassius auratus

Histamine is thought to be involved in the recovery of vestibular function after damage to the vestibular receptors of the inner ear. This study evaluated the effects of post-operative treatment using Chlorpheniramine (H1 histamine antagonist) and L-histidine, (a histaminergic precursor), after hemilabyrinthectomy in goldfish. In this lesion model, the unilateral removal of the labyrinth induces a transient postural imbalance in response to light. After the lesion, the animals were injected intraperitoneally, during 12 consecutive days, with Chlorpheniramine, L-histidine and saline. All the substances were administered in a volume of 1 ml/kg body weight. Another group, which served as a non-lesion control, did not receive hemilabyrinthectomy or systemic injections. Chlorpheniramine accelerated the functional recovery when compared with that of the saline group. These data suggest that the inhibition of the histaminergic system facilitates the functional recovery in goldfish.

Haloperidol and chlorpheniramine interaction in inhibitory avoidance in goldfish

The purpose of this study was to investigate a possible interaction between histaminergic and dopaminergic systems in learning and memory processes, in an inhibitory avoidance test in goldfish. Haloperidol, a dopaminergic antagonist, was administrated pre-training and the chlorpheniramine (CPA), a histaminergic antagonist, post-training. The inhibitory avoidance procedure was performed in 3 days, using a rectangular aquarium divided into two compartments (black and white), with a central door. On the first day, the animals were habituated for 10 min. On the second day, they were injected with 2 mg/kg of haloperidol or dimethyl sulfoxide (DMSO) 20 min before training. Then, the animals were placed in the white compartment, the central door was opened and the time spent for crossing between compartments was recorded. After the fish crossed the line between compartments a 45 g weight was dropped. This procedure was done five times in a row. Immediately after the fifth trial, the fish were injected intraperitoneally (i.p.) with either saline or CPA (0.4, 1.0, 4.0, 8.0 or 16 mg/kg). On the next day (test) the time to cross was recorded again. On the training trials, the animals treated with DMSO or haloperidol presented a significant increase in the latencies indicating learning (Friedman P = 0.0062 and 0.0001). The latencies in the test day showed that groups pre-treated with haloperidol and treated with CPA presented a dose-dependent increase in latencies, and those treated with the 16 mg/kg CPA group showed a significant increase (ANOVA two-way followed by Student-Newman-Keuls (SNK) P < 0.01). Thus, it can be suggested that the facilitatory action occurs due to an additive interaction between both systems, in a dose-dependent way.

Neurochemical analysis of brain monoamines after L-histidine and chlorpheniramine administration in goldfish

This study investigated the effects of chlorpheniramine (CPA) and L-histidine (LH) administration on catecholaminergic levels in goldfish brain using neurochemical analysis. Fifty-eight animals were used. After 20 min of i.p. administration of the drugs or saline the animals were decapitated, and the telencephalon and the diencephalon were dissected. We also measured catecholamines in a non-injected (NI) group. Results showed lower homovanillic acid (HVA) levels after treatment with 100 mg/kg of LH when compared to saline and 5-hydroxyindoleacetic acid levels were lower in the saline group when compared to the NI group. In the diencephalon the NI group and animals treated with CPA at 4.0 and 8.0 mg/kg had lower HVA levels. Results suggest that LH had an inhibitory effect on dopaminergic activity and an anxiolytic-like effect for CPA results is suggested.

Analysis of the role of histamine in inhibitory avoidance in goldfish

1. Teleost fish have histaminergic cell bodies on the posterior part of the basal hypothalamus. It was suggested that they are homologous to the tuberomammillary E group in rats. However, unlike in rats, fish have fewer ascending fibers. The main projection runs through the ventral telencephalic area reaching the dorsal telencephalon. This projection is considered homologous to the prosencephalic forebrain bundle. 2. The aim of this study was to verify if the histaminergic system has an inhibitory action on learning and memory in goldfish, as suggested previously for higher vertebrates. 3. A two-compartment aquarium with a central sliding door was used. The animals were placed in one of them, the central door was opened after 30 sec and the time spend for crossing between compartments was recorded. After the fish dorsal fin crossed the line between the compartments a 45 g weight was dropped into the compartment the fish entered. 4. On the training day this procedure was done 3 times. Immediately after the 3rd trial the fish was injected i.p. with either vehicle (2 ml/kg), chlorpheniramine (CPA; 1.0, 4.0 and 8.0 mg/kg) or histidine (500 mg/kg). On the next day, fishes were placed in the start compartment and the latency to cross between compartments was again recorded. 5. The group treated with CPA at the dose of 8 mg/kg, presented a significant increase in the latency to leave the start compartment (Wilcoxon rank sum test, p<0.0232). On the other hand, the vehicle and 1-histidine (500 mg/kg) treated groups, presented a decrease in test latency. 6. Thus, we suggest that also in fish, the histaminergic system has an inhibitory role on learning and memory.

Differential modulation of hippocampal signal transfer by tuberomammillary nucleus stimulation in freely moving rats dependent on behavioral state

Tuberomammillary histamine neurons (TM) in the posterior hypothalamus project to extensive parts of the brain, including the hippocampal formation. The purpose of the present experiments was to investigate whether activation of the TM modulates signal transfer from the perforant pathway (PP) or ventral hippocampal commissure (VHC) to the dentate gyrus (DG) in freely moving rats. Paired pulses of electrical stimulation were delivered to PP or VHC, and evoked field potentials (fEPSPs and pop spikes) were recorded in the DG. Before activating PP or VHC, the TM was triggered by electrical stimulation. Experimentation was performed during four behavioral conditions: exploration, grooming, awake immobility, and slow-wave sleep. Electrical activation of the TM was found to modify dentate fEPSPs evoked by PP or VHC stimulation without generating a field potential by itself. Train stimulation of the TM (100 Hz, 500 ms) preceding paired pulses on the hippocampus by 50 ms decreased dentate fEPSPs in dependence of the ongoing behavior and the pathway stimulated. During exploration but not consummatory behavior, the PP signal was reduced when preceded by TM stimulation; during consummatory behavior but not exploration, the VHC signal was reduced. In contrast to other hippocampal afferents which increase pop spikes but leave fEPSPs unchanged, TM stimulation decreased dentate fEPSPs without affecting pop-spike activity. Thus, the TM-histaminergic system seems to modulate signal processing in the dentate gyrus in a specific way, exerting an inhibitory action on the entorhinal input only during learning-related exploratory behavior.

Conditioned place-preference analysis in the goldfish with the H1 histamine antagonist chlorpheniramine

The aim of this study was to investigate whether the histamine H1-receptor blocker, chlorpheniramine (CPA), has a reinforcing effect in goldfish. We used a place-preference procedure in an aquarium with two chambers colored black and white. On day 1, the animals were placed in the test chamber for 10 min for habituation. On day 2, they were placed in the start compartment for 30 s, the sliding doors were opened, and the time spent in each compartment was recorded over the 10 min to determine the natural compartment preference for each animal. On day 3, they were injected either with 0.1, 0.4, 1.0, or 4.0 mg/kg of CPA or only with vehicle and placed in the less preferred compartment for 25 min. On day 4, the animals were placed in the start compartment and the time spent in each compartment during the 10-min test period was recorded again. The groups treated with 1.0 and 4.0 mg/kg of CPA, spent significantly more time in the compartment in which they experienced the drug effect than the group treated with vehicle. On the other hand, the group treated with 0.4 mg/kg spent significantly less time in the drug-paired compartment. The results indicate a biphasic effect of CPA. Considering that there is evidence that low doses of CPA can also block H3-receptors, we suggest that in goldfish the histaminergic neural system has an inhibitory role in the reinforcing process.

The tuberomammillary nucleus projections in the control of learning, memory and reinforcement processes: evidence for an inhibitory role

The tuberomammillary nucleus (TM), a cluster of magnocellular cells in the posterior hypothalamus, is the main source of neuronal histamine in the brain. Although this nucleus is well described in terms of anatomy and neurochemistry, only little is known about its function. Our earlier work showed that the TM projection system may be involved in behavioral asymmetries and behavioral recovery after unilateral manipulations of the brain. Using horseradish peroxidase (HRP) labeling we found an increase in strength (structure and/or activity) in the crossed and uncrossed tuberomammillary-striatal projections in the course of recovery from behavioral asymmetries produced by unilateral removal of the rats' vibrissae, which were in the same direction as the asymmetries found in projections from the substantia nigra to the striatum. Experiments performed with unilateral lesions of the TM region provide evidence for an involvement of the TM system in reinforcement mechanisms. Unilateral destruction of the TM with direct current (DC) or ibotenic acid was found to increase the rate of lateral hypothalamic self-stimulation ipsilateral to the lesion site, suggesting that the TM (particularly the E2 subgroup in its rostral part) may function as a reinforcement inhibiting neural substrate. Experiments performed with bilateral DC or ibotenic acid lesions of the TM region suggest a role of the nucleus in learning and mnemonic processes. A bilateral electrolytic or neurotoxic lesion of the TM region was found to facilitate the performance of adult and behaviorally impaired aged rats in a variety of learning tasks, including a habituation paradigm, aversively motivated learning tasks and water mazes. Examination of the site of the neurotoxic lesion in the TM region with immunohistochemical techniques revealed a marked decline of histamine-staining neurons mainly in the rostral part of the TM nucleus, suggesting that the facilitatory effects on reinforcement and mnemonic processes might be related to the destruction of TM intrinsic histaminergic cells. In summary, the present results indicate that the TM nucleus is involved in neural plasticity and functional recovery following damage to the CNS and may function as an inhibitory neural substrate in the control of reinforcement and mnemonic processes.

Facilitation of learning in adult and aged rats following bilateral lesions of the tuberomammillary nucleus region

In the present experiment, adult (3-month-old) and aged (31-month-old) rats received bilateral DC or sham-lesions in the region of the tuberomammillary (TM) nucleus before they were trained and tested on a one-trial step-through inhibitory avoidance task. Bilateral lesions of the TM nucleus led to significantly longer latencies in the step-through response during retention test in both adult and aged rats, indicative of superior learning of the task. Thus, lesions of the TM nucleus may have a facilitatory effect on learning and mnemonic functioning which is possibly related to a lesion-induced disinhibition or facilitation of reinforcement processes ("stamping-in") as revealed in previous studies.

The tuberomammillary nucleus region as a reinforcement inhibiting substrate: facilitation of ipsihypothalamic self-stimulation by unilateral ibotenic acid lesions

The tuberomammillary nucleus (TM), located in the posterior hypothalamic region, consists of five subgroups and is the only known source of brain histamine. Knowledge about the function of this nucleus is still scarce. In a previous study we found an increase in the rate of ipsihemispheric hypothalamic self-stimulation following a dc lesion in the rostroventral part of this nucleus, suggesting that this region has an inhibitory action on a neuronal reward system or on the brain's reinforcement mechanism. In the present study we examined whether this facilitating effect on reinforcement was due to the destruction of fibers passing through the lesion area or of intrinsic cells, by lesioning subgroups of the TM with ibotenic acid, an excitatory amino acid, that selectively destroys neural cell bodies, leaving fibers largely intact. Following such lesions in the rostroventral part of the TM the operant response rates increased over the six days of testing when the animals stimulated themselves in the lateral hypothalamus in the hemisphere located ipsilateral but not contralateral to the lesion. No significant changes in response rate occurred following the lesion in the caudal part of the ventral TM. The results indicate that the region influenced by the lesion exerts inhibitory control over lateral hypothalamic self-stimulation, and that it is possible that histamine-containing neurons are involved in this effect.

Amplification of rewarding hypothalamic stimulation following a unilateral lesion in the region of the tuberomammillary nucleus

The tuberomammillary nucleus, a cluster of cells in the posterior hypothalamus, is the only known source of brain histamine. Although this nucleus is well described in terms of anatomy and neurochemistry, only little is known about its function. In the present study, the effect of a lesion in the region of this nucleus on intracranial self-stimulation was examined. Rats were implanted bilaterally with stimulating electrodes in the lateral hypothalamus and unilaterally with one lesion electrode in the region of this nucleus. After three days of baseline testing, half of the animals were given an electrolytic lesion. The animals were retested for six consecutive days, and thereafter weekly for another seven weeks. From the second day postlesion on, we unexpectedly found a gradual increase in response rate, which peaked on day 13 in the ipsilateral hemisphere only. Although there was no further increase over subsequent days, response rates remained elevated during the following seven weekly tests. The observed increase in lateral hypothalamic self-stimulation after an electrolytic lesion of the tuberomammillary nucleus is discussed in terms of an inhibitory system, possibly located in the region of this nucleus which, when removed by the lesion, increased reinforcing effects of the electrical brain stimulation. The fact that the effects on self-stimulation were lateralized to one hemisphere rules out an interpretation in terms of unspecific "performance" variables that could influence rate of lever pressing.