Effect of chronic antipsychotic drug treatment on preprosomatostatin and preprotachykinin A mRNA levels in the medial prefrontal cortex, the nucleus accumbens and the caudate putamen of the rat

Contextual and behavioral control of antipsychotic sensitization induced by haloperidol and olanzapine

Repeated administration of haloperidol (HAL) and olanzapine (OLZ) causes a progressively enhanced disruption of the conditioned avoidance response (CAR) and a progressively enhanced inhibition of phencyclidine (PCP)-induced hyperlocomotion in rats (termed antipsychotic sensitization). Both actions are thought to reflect intrinsic antipsychotic activity. The present study examined the extent to which antipsychotic-induced sensitization in one model (e.g. CAR) can be transferred or maintained in another (e.g. PCP hyperlocomotion) as a means of investigating the contextual and behavioral controls of antipsychotic sensitization. Well-trained male Sprague-Dawley rats were first repeatedly tested in the CAR or the PCP (3.2 mg/kg, subcutaneously) hyperlocomotion model under HAL or OLZ for 5 consecutive days. Then they were switched to the other model and tested for the expression of sensitization. Finally, all rats were switched back to the original model and retested for the expression of sensitization. Repeated HAL or OLZ treatment progressively disrupted avoidance responding and decreased PCP-induced hyperlocomotion, indicating a robust sensitization. When tested in a different model, rats previously treated with HAL or OLZ did not show a stronger inhibition of CAR-induced or PCP-induced hyperlocomotion than those treated with these drugs for the first time; however, they did show such an effect when tested in the original model in which they received repeated antipsychotic treatment. These findings suggest that the expression of antipsychotic sensitization is strongly influenced by the testing environment and/or selected behavioral response under certain experimental conditions. Distinct contextual cues and behavioral responses may develop an association with unconditional drug effects through a Pavlovian conditioning process. They may also serve as occasion setters to modulate the expression of sensitized responses. As antipsychotic sensitization mimics the clinical effects of antipsychotic treatment, understanding the neurobiological mechanisms of antipsychotic sensitization and its contextual control would greatly enhance our understanding of the psychological and neurochemical nature of antipsychotic treatment in the clinic.

Use of antipsychotic medication in chemotherapy-induced nausea and vomiting

Nausea and vomiting continue to present significant problems for cancer patients undergoing chemotherapy. Initial work suggested an important role for central dopamine transmission in the underlying pathophysiology. However, recent evidence has implicated central and peripheral serotonin release. Although the implementation of 5-HT(3) receptor antagonists has resulted in significant improvement in acute symptoms of nausea and vomiting, they have not demonstrated optimal efficacy in anticipatory and delayed emetic syndromes and are significantly more expensive than other antiemetic therapies. The use of typical antipsychotic medication to reduce nausea and vomiting in cancer patients is discussed, as is the potential efficacy of newer atypical antipsychotics, which have activity at receptors implicated in the control of chemotherapy-induced nausea and vomiting and demonstrate an improved side-effect profile.

Alterations in somatostatin mRNA expression in the dorsolateral prefrontal cortex of subjects with schizophrenia or schizoaffective disorder

Alterations in the inhibitory circuitry of the dorsolateral prefrontal cortex (DLPFC) in schizophrenia include reduced expression of the messenger RNA (mRNA) for somatostatin (SST), a neuropeptide present in a subpopulation of gamma-aminobutyric acid (GABA) neurons. However, neither the cellular substrate nor the causal mechanisms for decreased SST mRNA levels in schizophrenia are known. We used in situ hybridization to quantify the compartmental, laminar, and cellular levels of SST mRNA expression in the DLPFC of 23 pairs of schizophrenia or schizoaffective disorder and control subjects. We also explored potential causal mechanisms by utilizing similar methods to analyze SST mRNA expression in 2 animal models. The expression of SST mRNA was significantly decreased in layers 2-superficial 6 of subjects with schizophrenia, but not in layer 1, deep 6 or the white matter. At the cellular level, both the density of cortical SST mRNA-positive neurons and the expression of SST mRNA per neuron were reduced in the subjects with schizophrenia. These alterations were not due to potential confounds and appeared to be a downstream consequence of impaired neurotrophin signaling through the trkB receptor. These findings support the hypothesis that a marked reduction in SST mRNA expression in a subset of GABA neurons contributes to DLPFC dysfunction in schizophrenia.

Immunohistochemical localisation of the NK1 receptor in the human amygdala: preliminary investigation in schizophrenia

The amygdala has a role in the modulation of moods and emotion, processes that are known to be affected in people with psychiatric disorders such as schizophrenia and depression. The tachykinin NK(1) receptor is known to be expressed in the amygdala. However to date, there is limited knowledge of the distribution of the NK(1) receptor in this region. This study used immunohistochemistry to analyse the distribution of the NK(1) receptor in fixed human amygdala tissue in control subjects with no history of psychiatric illness and matched subjects with a diagnosis of schizophrenia (n=4 pairs). The NK(1) receptor was observed sparsely distributed in cell bodies in all amygdaloid nuclei with the basolateral and lateral having a greater relative density of NK(1) receptor-immunoreactive cell bodies than the other nuclei. Double labelling with antibodies to microtubule associated protein and the NK(1) receptor revealed that the NK(1) receptor is expressed by large pyramidal, small stellate and large bipolar neurons. Interestingly, the basal nucleus of Meynert, which is just dorsal to the amygdala, was observed to have a significantly higher relative density of NK(1) receptor-immunoreactive cell bodies compared to any of the amygdaloid nuclei. Preliminary analysis of the density of NK(1) receptor-immunoreactive cell bodies in the major amygdaloid nuclei and the basal nucleus of Meynert revealed no significant differences between schizophrenia and control subjects. Real-time PCR showed that the mRNA for both the short and long isoforms of the NK(1) receptor was expressed at low levels in fresh frozen human amygdala tissue from control subjects and that this was not different in matched subjects with schizophrenia (n=11 pairs). In conclusion, this study has demonstrated that the NK(1) receptor is widely distributed in the amygdala, and has shown for the first time a high relative density of NK(1) receptor-immunoreactive cell bodies in the basal nucleus of Meynert.

The effects of haloperidol treatment on the distribution of NK1 receptor immunoreactive neurons in guinea-pig brain

Previous studies have observed increased tachykinin NK(1) receptor immunoreactivity (NK(1)-IR) in the prefrontal cortex in subjects with schizophrenia. Since the subjects were medicated the possibility of a treatment effect could not be excluded. Thus, the present study was undertaken to determine the effect of chronic treatment with the antipsychotic drug, haloperidol, on the distribution of NK(1)-IR neurons in the guinea-pig brain. Guinea pigs were treated each day for 21 days with either haloperidol (1mg/kg) or vehicle and the brains were then processed for immunohistochemistry using an NK(1) receptor-specific polyclonal antibody. NK(1)-IR neurons and fibres were abundant in the forebrain cortex and caudate putamen and more sparsely distributed in a number of other brain regions. The relative density of NK(1)-IR neurons was significantly increased in the forebrain cortex, but not in the caudate putamen in guinea pigs treated with haloperidol. This study has shown that haloperidol causes region-specific changes to the density of NK(1)-IR neurons. Whether these changes are related to the therapeutic effects or to the side effects of haloperidol in individuals with schizophrenia, remains to be determined.

Antipsychotic drug treatment alters expression of mRNAs encoding lipid metabolism-related proteins

Using an automated PCR-based genomics approach, TOtal Gene expression Analysis (TOGA), we have examined gene expression profiles of mouse striatum and frontal cortex in response to clozapine and haloperidol drug treatment. Of 17 315 mRNAs observed, TOGA identified several groups of related molecules that were regulated by drug treatment. The expression of some genes encoding proteins involved in neurotransmission, signal transduction, oxidative stress, cell adhesion, apoptosis and proteolysis were altered in the brains of both clozapine- and haloperidol-treated mice as recognized by TOGA. Most notable was the differential expression of those genes whose products are associated with lipid metabolism. These include apolipoprotein D (apoD), the mouse homolog of oxysterol-binding protein-like protein 8 (OSBPL8), a diacylglycerol receptor (n-chimerin), and lysophosphatidic acid (LPA) acyltransferase. Real-time PCR analysis confirmed increases in the RNA expression of apoD (1.6-2.2-fold) and OSBPL8 (1.7-2.6-fold), and decreases in the RNA expression of n-chimerin (1.5-2.2-fold) and LPA acyltransferase (1.5-fold) in response to haloperidol and/or clozapine treatment. Additional molecules related to calcium homeostasis and signal transduction, as well as four sequences of previously unidentified mRNAs, were also confirmed by real-time PCR to be regulated by drug treatment. While antipsychotic drugs may affect several metabolic pathways, lipid metabolism/signaling pathways may be of particular importance in the mechanisms of antipsychotic drug action and in the pathophysiology of psychiatric disorders.

Autoradiographic distribution of tachykinin NK2 binding sites in the rat brain: comparison with NK1 and NK3 binding sites

The autoradiographic distribution of tachykinin NK(2) binding sites was determined in the adult rat brain using [(125)I]neurokinin A in the presence of either senktide (NK(3) agonist) and [Pro(9)]substance P (NK(1) agonist) or senktide and SR 140333 (NK(1) antagonist). Indeed, this radioligand labels two subtypes of NK(1) binding sites (which present a high affinity not only for SP but also for neurokinin A, neuropeptide K and neuropeptide gamma) as well as NK(3) binding sites. The distribution of NK(2) binding sites was also compared with those of NK(1) and NK(3) binding sites, these sites being labeled with [(125)I]Bolton and Hunter substance P and [(125)I]Bolton and Hunter eledoisin, respectively. In agreement with our results obtained with membranes from various brain structures, NK(2)-sensitive [(125)I]neurokinin A labeling was mainly observed in few structures including the dorsal and ventral hippocampus, the septum, the thalamus and the prefrontal cortex. The density of NK(2) binding sites was weak when compared with those of NK(1) and NK(3) binding sites. Marked differences were observed in the distributions of NK(1), NK(2) and NK(3) binding sites. These results are discussed taking into consideration differences or similarities between the distributions of NK(2)-sensitive [(125)I]neurokinin A binding sites and of their endogenous ligands (neurokinin A, neuropeptide K and neuropeptide gamma) but also local NK(2) agonist responses blocked by NK(2) antagonists. Insights on the roles of endogenous tachykinins in several brain functions are also discussed on the basis of the respective distributions of different neurokinin binding sites.

Delayed mesolimbic system alteration in a developmental animal model of schizophrenia

Pharmacological and imaging studies indicate that the prefrontal cortex and nucleus accumbens and their dopamine innervation are central elements of the pathophysiology of schizophrenia. Although symptoms typically appear in young adults, a developmental component has been suggested, primarily in the hippocampus. A neonatal hippocampal lesion in rats and monkeys produces changes resembling schizophrenia symptoms only after the animals reach adulthood, indicating that this procedure could be used as a developmental animal model of this disorder. Here, we explored whether the dopamine projection to the nucleus accumbens becomes functionally altered in these animals. In vivo intracellular recordings revealed abnormal responses in accumbens neurons to activation of their dopamine afferents in adult but not prepubertal animals with a neonatal lesion. This alteration was absent after antipsychotic drug treatment. These results indicate that neonatal hippocampal damage can result in delayed functional deficits in the mesolimbic system, providing a link between the developmental hippocampal deficit and altered dopamine systems postulated to occur in schizophrenia.

Neurokinin(1) receptor antagonists as potential antidepressants

Selective, nonpeptide antagonists for tachykinin receptors first became available ten years ago. Of the three known tachykinin receptors, drug development has focused most intensively on the substance P-preferring receptor, neurokinin(1) (NK(1)). Although originally studied as potential analgesic compounds, recent evidence suggests that NK(1) receptor antagonists may possess antidepressant and anxiolytic properties. If confirmed by further controlled clinical studies, this will represent a mechanism of action distinct from all existing antidepressant agents. As reviewed in this chapter, the existing preclinical and clinical literature is suggestive of, but not conclusive, concerning a role of substance P and NK(1) receptors in the pathophysiology of depression and/or anxiety disorders. The ongoing clinical trials with NK(1) receptor antagonists have served as an impetus for much needed, basic research in this field.

Effects of antipsychotic drugs on cholecystokinin and preprotachykinin (substance P) mRNA expression in the rat hippocampal formation

To assess the involvement of substance P (SP) and cholecystokinin (CCK) in the effects of antipsychotic drugs, preprotachykinin-A (PPT-A) and CCK mRNA expression was studied in the hippocampal formation using in situ hybridisation following 21 daily i.p. injections with the typical antipsychotic drug haloperidol (1 mg/kg) and the atypical drug clozapine (15 mg/kg). PPT-A mRNA levels were increased in the hippocampal CA3 subregion and in the entorhinal cortex after haloperidol, whereas a decrease was observed in the CA1 after clozapine. CCK mRNA levels increased in the CA1, the entorhinal cortex and in hilus, following both haloperidol and clozapine. It is suggested that earlier findings of increased SP levels in the hippocampal formation of schizophrenics may be a consequence of haloperidol treatment and that reduced hippocampal CCK and CCK mRNA levels found earlier in schizophrenics do not result from antipsychotic drug treatment. These results are consonant to the hypothesis that increased cortical CCK transmission may be beneficial in the treatment of psychosis.