Activation of pallidal H2 receptors induces catalepsy in Wistar rats: a regulatory role of CRF1 receptors

An increased concentration of histamine was found in the globus pallidus of parkinsonian patients. The role of this abnormality in the development of parkinsonism is unclear. We examined cataleptogenic activity of histamine injected into the globus pallidus (GP); also, the role of H₂ receptors in histamine effect was evaluated. Given a possible role of the GP in integration and processing of stress signals, we tested the involvement of CRF₁ receptors in the regulation of histamine effect. The experiments were conducted with male Wistar rats, catalepsy was assessed using bar test. The entopeduncular nucleus (EPN) was used as a neuroanatomical control. Intrapallidal injections of histamine (1.0 and 10.0µg) produced clear cataleptic response whereas intra-EPN injections were ineffective. Histamine-induced catalepsy was dose-dependently attenuated by H₂ receptor antagonist ranitidine and CRF₁ receptor antagonist NBI 35965. The results suggest the involvement of pallidal H₂ and CRF₁ receptors in the development of catalepsy in rats. These findings may provide novel insight into the mechanism of parkinsonian-like disorders. In light of the presented data, H₂ and CRF₁ receptors might be potential targets for therapy of parkinsonism.

Anticataleptic activity of nicotine in rats: involvement of the lateral entorhinal cortex

RATIONALE

Recently, it was found that cyclosomatostatin-induced catalepsy in middle-aged rats is accompanied by neuronal hypoactivation in the lateral entorhinal cortex (LEntCx); this hypoactivation was reversed by systemic administration of nicotine combined with diphenhydramine. These findings suggest the ability of nicotine to regulate catalepsy and the involvement of the LEntCx in this nicotine effect.

OBJECTIVES

The study was aimed to assess whether nicotine alone influences catalepsy when injected into the LEntCx and some other neuroanatomical structures.

METHODS

Experiments were conducted with male Wistar rats of 540-560 days of age. Catalepsy was induced by intracerebroventricular injection of cyclosomatostatin and assessed by the standard bar test. Nicotine was injected into the LEntCx, prelimbic cortex (PrCx), or basolateral amygdala (BLA). The tissue levels of tyrosine hydroxylase, dopamine, and DOPAC in the substantia nigra pars compacta and dorsal striatum were measured with use of HPLC and ELISA.

RESULTS

Injections of nicotine into the LEntCx but not into the PrCx and BLA produced anticataleptic effect; the nicotine effect was significantly reversed by intra-LEntCx administration of NMDA and non-NMDA glutamate receptor antagonists. Nicotine also attenuated cataleptogen-induced changes in nigrostriatal dopamine metabolism.

CONCLUSIONS

This may be the first demonstration of anticataleptic activity of nicotine. The results show that the effect is mediated by nicotine receptors in the LEntCx, via a glutamatergic mechanism. These findings may help advance the development of novel treatments for extrapyramidal disorders, including parkinsonism.

Histamine H1 receptors regulate anhedonic-like behavior in rats: Involvement of the anterior cingulate and lateral entorhinal cortices

A decreased H₁ receptor activity is observed in the anterior cingulate cortex (aCgCx) of depressed patients. The role of this abnormality in the development of depression-related processes is unstudied. We examined the influence of a decreased brain H₁ receptor activity on rat behavior in the sucrose preference test. The H₁ receptor deficit was simulated by injection of an H₁ antagonist into the aCgCx; also, two aCgCx projection areas, lateral and medial entorhinal cortices were examined. A blockade of H₁-receptors in the aCgCx and lateral entorhinal cortex (LEntCx) significantly reduced sucrose preference. These findings suggest the existence of H₁ receptor-mediated aCgCx-LEntCx circuitry mechanism regulating anhedonic-like behavior in rats. The presented data suggest that H₁ receptor-mediated processes might be a therapeutic target in depressive disorders.

Cyclosomatostatin-induced catalepsy in aged rats: Specific change of brain c-Fos protein expression in the lateral entorhinal cortex

Aging represents the largest risk factor for developing Parkinson's disease (PD); another salient feature of this disorder is a decreased brain levels of somatostatin. Recently, in aged Wistar rats, we simulated the central somatostatinergic deficiency by intracerebroventricular injections of a somatostatin antagonist, cyclosomatostatin (cSST). The treated animals displayed catalepsy, a state that resembles the extrapyramidal signs of Parkinson's disease; young animals were insensitive to cSST. The neuroanatomical substrates responsible for the increased cataleptogenic activity of cSST in aged animals, are currently unknown. To study this issue, we assessed the cSST effect on brain c-Fos-protein expression in aged and young rats; thirty three brain regions were examined. cSST was employed at the dose cataleptogenic for aged animals and non-cataleptogenic for young ones. c-Fos expression patterns in the 'cataleptic' and 'non-cataleptic' animals were very similar, with the only distinction being a decrease in the c-Fos expression in the aged lateral entorhinal cortex (LEntCx). This decrease was not observed when the cSST-induced cataleptic response was inhibited by administration of diphenhydramine and nicotine. Thus, the development of catalepsy in the aged Wistar rats appeared to be associated with a hypoactivation of the LEntCx; possibly, there exists a mechanistic link between the LEntCx hypoactivation and increased susceptibility of aged rats to catalepsy. Apparently, these findings may provide novel insight into the link between mechanisms of parkinsonian motor disorders and aging.

Neuroanatomical correlates of the inhibition of tremulous jaw movements in rats by a combination of memantine and Δ9 -tetrahydrocannabinol

BACKGROUND AND PURPOSE

Memantine and marijuana smoking have been found to inhibit tremor in parkinsonian patients, although the observed effects were relatively weak. The tremorolytic effects of combinations of memantine and cannabinoids have not been studied. Here, we have evaluated the anti-tremor activity of memantine, Δ⁹ -tetrahydrocannabinol (THC) given alone and of their combination. The involvement of some neuroanatomical structures in the effects of the combination was evaluated.

EXPERIMENTAL APPROACH

Haloperidol-induced tremulous jaw movements (TJMs) in rats were used as a model of parkinsonian-like tremor. To evaluate the role of central receptor systems in the drug effects, receptor ligands were administered locally into certain brain areas.

KEY RESULTS

Memantine and THC alone were without effect, although co-administration of these drugs decreased the number of haloperidol-induced jaw movements. The anti-tremor activity of the combination was antagonized (a) by injections of l-glutamate into the dorsal striatum, entopeduncular nucleus, substantia nigra pars reticulata, globus pallidus, and supratrigeminal and trigeminal motor nuclei but not into the subthalamic and cuneiform nuclei; (b) by injections of CGS 21680 into the ventrolateral striatum; and (c) by injections of bicuculline into the rostral part of the parvicellular reticular nucleus.

CONCLUSIONS AND IMPLICATIONS

Memantine and THC supra-additively inhibit haloperidol-induced TJMs, suggesting that co-administration of these drugs might be a new approach to the treatment of tremor. Our results identified brain areas influencing parkinsonian-like tremor in rats and can help advance the development of novel treatments for repetitive involuntary movements.

Synergistic anticataleptic effect of imipramine and nicotine in a rotenone-induced rat model

RATIONALE

Some antidepressants have been previously found to produce anti-parkinsonian effect; nicotine was known to mitigate experimental neurotoxic lesions. The anticataleptic efficacy of antidepressant-nicotine co-administration is unstudied.

OBJECTIVES

This work aimed to evaluate anticataleptic action of imipramine-nicotine combination in rotenone model.

METHODS

Catalepsy was measured by the bar test. Concentrations of tyrosine hydroxylase, dopamine, and DOPAC were determined in the substantia nigra and dorsal striatum using ELISA and HPLC techniques; additionally, dopamine/DOPAC ratio was calculated for both areas.

RESULTS

Imipramine and nicotine alone were ineffective; however, co-administration of the drugs significantly (p < 0.01) inhibited rotenone-induced catalepsy and mitigated neurochemical changes in the nigrostriatal system. Anticataleptic effect of the combination exceeded that of levodopa, a standard drug for anti-parkinsonian treatment.

CONCLUSION

The combined use of imipramine and nicotine at relatively low doses inhibits neurotoxin-induced catalepsy and nigrostriatal neurochemical changes. The co-administration of these drugs might be a new approach to the treatment of extrapyramidal dysfunctions.

Cyclosomatostatin- and haloperidol-induced catalepsy in Wistar rats: Differential responsiveness to sleep deprivation

Total sleep deprivation (SD) has been found to mitigate motor dysfunctions in Parkinson's disease. Apparently, the similar sensitivity of an animal model for parkinsonism would support the model's validity. Recently, we described catalepsy induced in Wistar rats by somatostatin antagonist, cyclosomatostatin (cSST); this model simulates such a disease-associated abnormality as a fall in brain somatostatin levels. To evaluate the similarity between the cSST model and Parkinson's disease, we assessed here the responsiveness of cSST-induced catalepsy to 1-h and 3-h SD. In parallel, the influence of SD on catalepsy induced by a dopamine receptor antagonist, haloperidol, was examined. It was found that the short-term SD failed to influence cataleptic responses of both types (sleep deprived rats and undisturbed ones displayed a similar duration of immobility, p > 0.05). By contrast, 3-h SD suppressed (p < 0.01) cSST-induced catalepsy, however, enhanced (p < 0.01) cataleptic response to haloperidol. Thus, the anti-cataleptic effect of SD appears to be cSST-specific. These findings support the validity of the cSST-induced catalepsy in Wistar rats as a model for parkinsonian motor dysfunctions.

Brain sites mediating cyclosomatostatin-induced catalepsy in Wistar rats: A specific role for the nigrostriatal system and locus coeruleus

A decrease in somatostatin activity is observed in the Parkinsonian brain. In recent experiments on rats, we simulated this abnormality by intracerebroventricular injections of a somatostatin antagonist, cyclosomatostatin. The treated animals displayed catalepsy, a state that resembles the extrapyramidal signs of Parkinson's disease. The neuroanatomical substrates mediating the catalepsy-inducing effect of cyclosomatostatin are unknown. To clarify this issue, we assessed here the action of cyclosomatostatin injected into the substantia nigra pars compacta (SNc), dorsal striatum (DS), locus coeruleus (LC), pedunculopontine tegmental nucleus (PPTg), and inferior colliculus (IC). The experiments were conducted with male Wistar rats of 270-290 g bw, catalepsy was evaluated by using the bar test. The injections into the PPTg and IC were without effect whereas the intra-SNc, intra-DS, and intra-LC administrations produced distinct cataleptic response. Thus, it was shown for the first time that the LC is a brain center capable of causing catalepsy. These data provide new insights into the neuroanatomical organization of the catalepsy-initiating mechanism and suggest the LC representing a potential target for therapeutic manipulations of extrapyramidal dysfunctions.

Somatostatin antagonist induces catalepsy in the aged rat

RATIONALE

Extrapyramidal motor signs are the major features of Parkinson's disease (PD). It is unclear whether there is a link between these signs and such PD-associated factors as brain somatostatin deficiency and aging.

OBJECTIVES

This study aimed to examine whether an inhibition of the brain somatostatin system can initiate catalepsy, a model of extrapyramidal disorders, in young and aged rats.

METHODS

The animals of 100-110 and 540-560 days of age were used. Catalepsy was measured using the bar test. The inhibition of the brain somatostatin activity was simulated by intracerebroventricular administration of a somatostatin antagonist, cyclosomatostatin.

RESULTS

Cyclosomatostatin dose-dependently induced catalepsy in aged, but not in young rats. The cataleptic response was reversed by a somatostatin analog, octreotide.

CONCLUSIONS

The combination of aging and brain somatostatin deficiency can lead to catalepsy in rats. Since both factors are frequently observed in PD patients, the present results might be of relevance for pathogenesis of extrapyramidal signs in this disease.

Amyloid-beta production in aged guinea pigs: atropine-induced enhancement is reversed by naloxone

Advanced age, cholinergic deficit, and elevated brain levels of enkephalin are associated with sporadic Alzheimer's disease. The influence of these factors on production of amyloidogenic peptides (Abeta) is uncertain. In the present experiments, the levels of 40/42 amino acid-residue Abeta were measured in the brain cortex of guinea pigs aged 15-16 weeks (young) and 25-26 months (aged). As was found, injections of atropine (21 days, 5mg/kg/day) increase Abeta levels in aged but not young animals. This atropine-induced effect was antagonized by simultaneous injections of naloxone (3mg/kg/day) whereas naloxone alone failed to affect Abeta accumulation. These results are discussed in the light of a possible "acetylcholine - Abeta" feedback loop and an influence of enkephalin on the loop function.