Mice that are incapable of expressing the small G protein Rhes have been generated and have shown to have abnormalities in behaviors mediated by the striatum, a region in which Rhes is highly expressed. Moreover, conditions that result in dopamine supersensitivity and a breakdown in D1/D2 synergism in rodents, consistently decrease rhes mRNA in striatum. Thus, Rhes may play have relevance in dopamine signal modulation. For evaluating the role of Rhes in anxiety, stereotypy and basal motor activity, adult male and female wild-type (WT) mice, Rhes knockout (KO) mice, and mice heterozygous for the KO and WT alleles (Het) were tested. There was no genotype differences in the distance traveled in the open field. However, female KO mice showed lower anxiety than either WTs or Hets, based on the quantity of time spent in the periphery vs. the central area of the open field (p<0.05). With respect to striatally-mediated motor stereotypy, the mixed D1/D2 agonist apomorphine elicited a significant greater response in male KO and Het compared to WTs (p<0.05). In previous studies of D1/D2 synergism, it has been consistently found in rats and mice that when D2 receptors alone are stimulated, there is an early and brief, D1 independent peak in stereotypy that disappears by 20 minutes. In the present study, this effect was more intense in male KO mice compared to the other two genotypes during the interval between 5 and 10 minutes (p<0.05). The current findings favor the hypothesis that the GTP-binding protein Rhes interacts with as yet unidentified cellular proteins to buffer the transduction of synaptic dopamine signals into intracellular responses. Decreased or loss of Rhes therefore results in increased DA signal transduction.

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / Visando estudar os efeitos da retirada abrupta apÃs o tratamento crÃnico com brometo de ipratrÃpio (BI) ratos machos pesando 200-250 g no inÃcio dos experimentos, foram introduzidos em uma caixa de acrÃlico e submetidos durante 7 minutos à inalaÃÃo de brometo de ipratrÃpio (600ÂM). Este procedimento se repetiu a cada quatro horas durante um perÃodo de 14 dias. Foram utilizadas duas cÃmaras de inalaÃÃo, uma para o grupo experimental (tratado com BI) e outra para o grupo controle (CONT, salina). Outro grupo de animais foi sensibilizado (SENS) e submetido ao mesmo protocolo de inalaÃÃo com BIque inalaram o brometo de ipratrÃpio e outra para os animais controle. Os animais SENS foram desafiados 24 horas antes do sacrifÃcio com inalaÃÃes do antÃgeno (OVA: 1mg/ml; 5mg/ml; 15/15 minutos; grupo DESF). Ao fim de uma Ãnica inalaÃÃo ou ao tÃrmino do perÃodo de tratamento crÃnico com BI os animais foram sacrificados 0, 4, 8, 12 horas apÃs a Ãltima inalaÃÃo e as traquÃias rapidamente removidas. ApÃs a dissecaÃÃo a traquÃia foi montada sob a forma de anÃis, em banho para ÃrgÃo isolado contendo 8 ml de soluÃÃo de Krebs-Henseleit (37ÂC, 95% O2, 5% CO2). Foram entÃo, confeccionadas curvas concentraÃÃo-efeito (CCE), ao carbacol (Cch), serotonina (5-HT), potÃssio (KCl), cÃlcio(CaCl2) e estÃmulo elÃtrico. As CCE ao Cch obtidas com traquÃias isoladas de ratos apÃs uma Ãnica inalaÃÃo de brometo de ipratrÃpio demonstrou desvio para a direita com significativo aumento da CE50[CE50x10-7M: CONT=1,78(1,32 â 2,32); BI 14,6(2,05 â 58,1), p<0,05). Imediatamente apÃs o fim do tratamento crÃnico as CCE ao Cch tambÃm apresentaram aumento significativo da CE50 [CE50x10-7M: CONT=2,33(1,25 â 4,32); BI=42,5(21,1 â 85,8), p<0,01). Nos experimentos realizados com traquÃias isoladas de ratos 4, 8 e 12 horas apÃs o fim do tratamento crÃnico ocorreu um progressivo aumento da contratilidade, com a resposta mÃxima(RM) atingindo um valor mÃximo 12 horas apÃs a supressÃo do tratamento crÃnico com BI (RM 12h: CONT= 1,69Â0,04, BI 2,64Â0,23 gF, p<0,01). Esta supersensibilidade caracterizada por aumento vertical, tambÃm se manifestou para outros agonistas e estÃmulos contrÃteis. Assim, ocorreu supersensibilidade para a serotonina (RM-12h: CONT=0,59Â0,04; BI=1,06Â0,10gF, p<0,01) potÃssio (RM: CONT= 0,70Â0,05; BI=1,27Â0,17 gF; p<0,01) e ao estÃmulo elÃtrico (RM: CONT=1,25Â0,07; BI=1,64Â0,06 gF; p<0,01). As CCE obtidas 12 horas apÃs o fim do tratamento crÃnico com BI, pela adiÃÃo de cÃlcio ao lÃquido de incubaÃÃo, apÃs ter sido obtida resposta contrÃtil ao KCl ou ao Cch, as quais avaliaram, respectiva e indiretamente, a entrada de cÃlcio via canais VOC e ROC demonstraram que a entrada de cÃlcio està facilitada em ambos os tipos de canal de cÃlcio estudados (RM-12h CaCl2/KCl: CONT=1,00Â0,09; BI=1,54Â0,19 gF; p<0,01) (RM-12h CaCl2/Cch: CONT=1,27Â0,10; BI=1,66Â0,05 gF; p<0,01). Nos experimentos realizados com animais desafiados, a supressÃo do tratamento crÃnico imediatamente apÃs Ãltima inalaÃÃo diminuiu a sensibilidade desviando para a direita a CCE ao Cch [CE50x10-7M: CONT=2,10(1,28 â 3,44); BI=17,12(4,37 â 67,05), p<0,01)]. Enquanto que, traquÃias isoladas de animais desafiados 12 horas apÃs o fim do tratamento ocorreu aumento significativo da contratilidade e da resposta mÃxima obtida para o carbacol (RM-12h: CONT=2,48Â0,19; BI=3,48Â0,13 gF; p<0,01). Estes resultados sugerem que a supressÃo do processo de inalaÃÃo crÃnica com BI induz um aumento de resposta contrÃtil ao Cch atingindo um valor mÃximo 12 horas apÃs a interrupÃÃo do tratamento crÃnico. Esta supersensibilidade 12 horas apÃs a supressÃo do tratamento crÃnico com BI, tambÃm foi manifestada para vÃrios outros agonistas, bem como para o estÃmulo elÃtrico. A supersensibilidade foi tambÃm detectada na resposta contrÃtil ao Cch, seguindo o mesmo protocolo experimental de interrupÃÃo do tratamento em traquÃias isoladas de ratos desafiados a OVA. Este aumento de resposta contrÃtil observado na musculatura traqueal de ratos, 12 horas tambÃm que a supersensibilidade està presente, apÃs o desafio antigÃnico, com incremento ainda maior na resposta contrÃtil quando comparada traquÃias isoladas de animais nÃo desafiados submetidos à retirada abrupta apÃs tratamento crÃnico com BI / In order to evaluate ipratropium bromide (IB) abrupt withdrawal effects after chronic treatment in isolated rat tracheas, male rats weighing 200-250g were placed in plastic chambers and submitted to inhalation of IB (600ÂM) during seven minutes. This protocol was repeated each four hours during 14 days. Two inhalation chambers were used, one with experimental group (IB inhalation) and the other with control group (CONT, saline). Another group was ovalbumin (OVA) actively sensitized (SZ) and submitted to the same protocol of inhalation. These animals were challenged 24hours before the beginning of the experiments by antigen inhalation (OVA: 1mg/ml; 5mg/ml; 15/15 minutes) (group DESF). At the end of IB treatment period the animals were killed and 0, 4, 8, 12 hours after the last inhalation the tracheas were quickly removed. After dissection the tracheal rings were transferred to a 8 ml organ bath containing Krebs-Henseleit solution mMol/l: NaCl 113.0; KCl 4.7; CaCl2.2H2O 1.2; KH2PO4 1.2; MgSO4.7H2O 1.2; NaHCO3 25.0; Glucose 11.0; 37 C; 95%O2/5%CO2). Concentration-effect curves (CEC) were constructed to carbachol (Cch), serotonin (5-HT), potassium (KCl), calcium (CaCl2) and electric stimulus. CEC to Cch obtained with tracheas isolated from rats submitted to only one IB inhalation showed shift to the right with an increase in the EC50 values [EC50x10-7M: CONT=1.78(1.32-2.32); IB=14.6(2.05-58.1) p<0.05]. Immediately after chronic treatment CEC to Cch also showed significant increase at EC50 level [EC50x10-7M: CONT=2.33(1.25-4.32); IB=42.5(21.1-85.8); p<0,01]. Experiments realized with isolated rats tracheas 4, 8, 12 hours after ended the IB chronic treatment showed a Cch maximum response (MR) progressive increase, reaching the greater value 12 hours after IB chronic treatment interruption [MR-12h: CONT=1.69Â0.04; IB=2.64Â0.23 gF, p<0.01). This kind of supersensitivity characterized by a vertical increase, was also obtained to other agonists and contractile stimulus. In this way the results showed supersensitivity to serotonin (MR-12h: CONT=0.59Â0.04; IB=1.06Â0.10; gF; p<0.01), potassium (MR-12h: CONT=0.70Â0.05; IB=1.27Â0.17; gF; p<0.01) and electric stimulus (MR-12h: CONT=1.25Â0.07; IB=1.64Â0.06; gF; p<0.01). Calcium CCE were obtained 12hours after the end of IB chronic treatment, after the addition of KCl or Cch in calcium free buffer. This kind of experiment measured, respsctively and indirectly the influx of calcium by voltage operated channelsVOC) and by receptor operated channels(ROC). The results demonstrated that influx of calcium was facilitated in both calcium channels studied in this work (MR-12h: CaCl2/KCl: CONT=1.00Â0.09; IB=1.54Â0.19; gF; p<0.01) (MR-12h: CaCl2/Cch; CONT= 1.27Â0.10; IB=1.66Â0.05; gF; p<0.01). The experiments with OVA challenged animals, realized immediately after the end of chronic treatment, showed a decreased in the sensibility. The CEC to Cch were shift to the right [EC50X10-7M: CONT=2.10(1.28-3.44); IB=17.13(4.37-67.05), P<0,01]. However, trachea isolated from rat challenged 12 hours after the end of the treatment, showed an increase in the contractility and in the MR obtained to carbachol (MR-12h: CONT=2.48Â0.19; IB=3.48Â0.13; gF; p<0,01). These data suggest that IB chronic inhalation process follow suppression induced an evident Cch contractile response increase in isolated rat trachea, reaching a maximum value 12 hours after interrupted IB chronic treatment abrupt suppression, was here demonstrated to several agonists and electric stimulus. Supersensitivity was also detected to carbachol contractile response through the same withdrawal experimental protocol in isolated tracheas from rats challenged with OVA. This increased contractile response obtained in rats tracheal smooth muscle, 12 hours after the end of ipratropium bromide chronic treatment, could be related with a component linked with the facilitation influx of calcium by voltage operated channels (VOC) and/or receptor operated channels (ROC)

Ontogenetic dopaminergic denervation of rat forebrain is associated with latent supersensitization of dopamine (DA) receptors that is unmasked only by a priming process entailing repeated DA agonist treatments. Similar denervation supersensitivity holds for serotonin (5-HT) and most other neurochemical systems. Because DA and 5-HT neurons compete for target sites in the brain and mimic or replicate actions of the others, we investigated the modulatory influence of DA neurons on 5-HT receptor sensitivity; and role of 5-HT neurons in modulating DA receptor sensitivity. In these studies rats were lesioned with the DA neurotoxin B-hydroxydopamine (6-OHDA, icv; desipramine pretreatment) or 5-HT neurotoxin 5,7-dihydroxytryptamine (5,7-DHT, icv; desipramine pretreatment) either at 3 days after birth or in adulthood. Responses to DA and 5-HT agonists were determined in several behavioral paradigms in adulthood. In assessing oral responses to agonists, we found that the D1 agonist (±)-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine-7,8-diol (SKF 38393) profoundly induced activity if rats were lesioned neonatally with 6-OHDA, but not if rats were co-lesioned as neonates or as adults with 5,7-DHT. The D2 agonist quinpirole induced profound oral activity, but only if rats were lesioned as neonates with 5,7-DHT; or if rats were lesioned with both 6-OHDA (neonatally administered) and 5,7-DHT (adult stage). In all rats lesioned as neonates with 6-OHDA, the 5-HT2 agonist m-chlorophenylpiperazine produced enhanced activity, regardless of 5,7-DHT treatment. These findings demonstrate that DA neurons modulate receptor sensitivity status of both DA and 5-HT receptors; and 5-HT neurons do so similarly. This phenomenon is pertinent to animal models of human disorders and in the syndrome spectrum and treatment approach of human neurodegenerative disorders (e.g. parkinsonism, tardive dyskinesia), developmental disorders (e.g. hyperkinetic activity) and psychiatric disorders.

Repeated ontogenetic treatment with quinpirole produces enhanced quinpirole-induced yawning and antinociceptive actions in adult rats. We now report the occurence of a bizarre behavior jumping inrats so treated. Rats were treated daily from birth with quinpirole HCl (3.0 mg/kg per day × 28 days i.p., salt form) or saline vehicle. After each daily injection, the rats were observed for at least 1 h. Starting on the 18th day after birth, quinpirole treatment was associated with the appearance of jumping behavior. On the 20th day after birth a dose-effect relationship was found for quinpirole HCl (0.10-3.0 mg/kg), with maximal jumping activity occurring between 30 and 150 min after the 3.0 mg/kg dose. On the 26th day after birth, both spiperone HCl (0.30 mg/kg i.p.) and SCH 23390 HCl (0.30 mg/kg i.p.) attenuated the quinpirole effect. At 34 days the jumping response was virtually absent. The age-related jumping behavior appears to be another manifestation of the abnormal responses meduated by supersensitized dopamine receptors in quinpirole-primed rats. Based on the ability of dopamine D1 and D2 receptor antagonists to attenuate this effect, quinpirole-induced jumping behavior may be a reflection of cooperativity of dopamine D1 and D2 receptor types.

Repeated daily treatments of perinatal rats with the dopamine D2-receptor (D2-R) agonist quinpirole for a week or more produces the phenomenon of ‘priming’—gradual but long-term sensitization of D2-R. In fact a daily dose of quinpirole as low as 50 µg/kg/day is adequate for sensitizing D2-R. Primed rats as neonates and in adolescence, when acutely treated with quinpirole display enhanced eating/gnawing/nursing on dams, also horizontal locomotor activity. Between 3 and 5 weeks of age, acute quinpirole treatment of primed rats produces profound vertical jumping with paw treading—a behavior that is not observed in control rats. At later ages acute quinpirole treatment is associated with enhanced yawning, a D2-R-associated behavior. This long-term D2-R supersensitivity is believed to be life-long, despite the relatively brief period of D2-R priming near the time of birth. D2-R supersensitivity is not associated with an increase in the number or affinity of D2-R, as assessed in the striatum of rats; nor is it induced with the D3-R agonist 7-OH-DPAT. However, quinpirole-induced D2-R supersensitivity is associated with cognitive deficits, also a deficit in pre-pulse inhibition and in neurotrophic factors, and low levels of the transcript regulator of G-protein signaling (RGS) RGS9 in brain; and acute reversal of these alterations by the antipsychotic agent olanzapine. In sum, rats ontogenetically D2-R supersensitized have face validity, construct validity and predictive ability for schizophrenia.

Adult female cats (2.4-2.8 kg) underwent surgical removal of the left ciliary ganglion under pentobarbital anesthesia. Twenty-one, 560 and 616 days later, pupil size of both left and right (control) eyes was measured in response to progressively increasing doses of carbachol applied topically. By 21 days after denervation, ganglionectomized eyes showed marked supersensitivity to the miotic effects of pilocarpine and carbachol. By 560 days, however, responsiveness of the denervated eyes to lower and intermediate doses of carbachol was the same as that of contralateral control eyes, while responsiveness to higher doses was significantly reduced. Responsiveness to both lower and higher doses of carbachol was significantly less than that of the controls on the 616th day. Ganglionectomized eyes showed no pupillary response to light 14, 562, or 620 days after surgery. Histochemical analysis of iris tissue collected from eyes of these cats 720 days after ganglion removal revealed an almost complete absence of acetylcholinesterase-containing nerve fibers on the denervated side. These findings indicate that the return to normal or lower sensitivity to carbachol of denervated eyes at prolonged periods after ciliary ganglion removal is not due to significant cholinergic reinnervation of the iris sphincter muscle.

The characteristics feature of neurotoxicity is a definable lesion which can account for observed deficits, corresponding to loss of nuclei or axonal fibers normally comprising a specific pathway or tract. However, with ontogenetic lesions, the operative definition fails. In rats lesioned as neonates with 6-hydroxydopamine (6-OHDA), near-total destruction of dopamine-(DA-) containing nerves is produced, and this itself is definable. However, the most prominent feature of rats so-lesioned is the DA receptor supersensitivity (DARSS) that develops and then persists throughtout the lifespan. DA D1 receptors show overt supersensitivity to agonists producing vacuous chewing movements (VCMs), while D1 receptors associated with locomotor activity have a latent supersensitivity that must be unmasked by repeated D1 or D2 agonist treatments - a 'priming' phenomenon. This D1 DARSS is not usually associated in either a change in D1 receptor number (Bmax) or affinity (Kd). In contrast to D1 DARSS, D2 receptors are not so predictably supersensitized by a lession of DA neurons. In reality, the permanently exaggerated response to an agonist by supersensitized receptors is per se a manifestation of neurotoxicity. Despite dramatic behavioral responses mediated by supersensitized receptors, DARSS has not been easy to correlate with enhanced production of second messengers or early response genes. Altered signaling (i.e., neuronal cross-talk) in defined pathways may represent the mechanism that produces so-called receptor supersensitization. Longlived agonist-induced behavioral abnormality, with or without anatomic evidence of a neuronal lesion, is one of the products of DA D1 receptor supersensitization - it self an index of neurotoxicity.

Tardive dyskinesia (TD), a movement disorder produced by long-term treatment with a classical antipsychotic drug, is generally considered to be a disorder of dopamine (DA) systems, since classical antipsychotics are potent DA D2 receptor blockers. Also, acute DA D1 agonist treatment of rats is known to produce vacuous chewing movements (VCMs), a behavioral feature resembling the oral dyskinesia that is so prominent in most instances of TD. In this paper we outline a series of studies in a new animal model of TD in which DA D1 receptor supersensitivity was produced by neonatal 6-hydroxydopamine (6-OHDA)-induced destruction of nigrostriatal DA fibers. In rats so-lesioned 5-HT receptor supersensitivity is additionally produced, and in fact 5-HT receptor antagonists attenuate enhanced DA D16-lesioned rats treated with haloperidol for one year, there is a 2-fold increase in numbers of VCMs (versus intact rats treated with haloperidol); and this high frequency of VCMs persists for more than 6 months after discontinuing haloperidol treatment. During this stage, 5-HT2 receptor antagonists, but not DA D1 receptor antagonists, attenuate the incidence of VCMs. This series of findings implicates the 5-HT neuronal phenotype in TD, and promotes 5-HT2 receptor antagonists, more specifically 5-HT2C receptor antagonists, as a rational treatment approach for TD in humans.

This mini review focuses on the importance of the dopamine D2-like receptor family and its importance in psychosis. Past findings from this laboratory along with collaborators have been that neonatal quinpirole (a dopamine D2-like receptor agonist) results in increases in dopamine D2 receptor sensitivity that persists throughout the animal’s lifetime. Findings from this model have been shown to have particular application and validity to schizophrenia, but may have broader implications toward other psychoses, which is reviewed in the present manuscript. In the present review, we also highlight other models of psychoses that have been centered on the subchronic administration of quinpirole to rats in order to model certain psychoses, which has uncovered some interesting and valid behavioral findings. This review highlights the importance of the combination of behavioral findings and neurobiological mechanisms focusing on neural plasticity in discovering underlying pathologies in these disorders that may lead to treatment discoveries, as well as the value of animal models across all psychoses.

The neurochemical changes occurring between the preweanling period and adolescence could be crucial for understanding the role development plays in the manifestation of psychotic behaviors. N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) fully attenuates the DA agonist-induced behaviors of adult rats, while potentiating the DA agonist-induced locomotor activity of preweanling rats. My specific hypotheses were as follows: (1) Systemically administered EEDQ would block the cocaine-induced locomotor activity of adult rats. (2) Systemically administered EEDQ would potentiate the cocaine-induced locomotion of preweanling rats. (3) EEDQ would increase the Emax values (a measure of D2 receptor sensitivity) of preweanling rats, but not adolescent or adult rats. And, (4) EEDQ would reduce dorsal striatal β-arrestin-2 (ARRB2) and GRK6 levels (measures of D2 receptor sensitivity) of preweanling rats. Behavioral results were as expected, because EEDQ attenuated the locomotion of adult and adolescent rats, while EEDQ potentiated locomotor activity of preweanling rats. EEDQ enhanced the GTPγS binding of preweanling rats, while depressing ARRB2 levels. These results are consistent with the overarching hypothesis that EEDQ causes DA supersensitivity in preweanling rats. Thus, it is here proposed that EEDQ inactivates a significant number of D2 receptors in preweanling rats, but that the remaining D2 receptors are supersensitive and capable of mediating a potentiated locomotor response.