Long-term haloperidol treatment decreases somatostatin binding in rat brain

Effects of the antipsychotic drug haloperidol on the somastostatinergic system in SH-SY5Y neuroblastoma cells

Antipsychotics are established drugs in schizophrenia treatment which, however, are not free of side effects. Lipid rafts are critical for normal brain function. Several G protein-coupled receptors, such as somatostatin (SRIF) receptors, have been shown to localize to lipid rafts. The aim of this study was to investigate whether haloperidol treatment affects the composition and functionality of lipid rafts in SH-SY5Y neuroblastoma cells. Haloperidol inhibited cholesterol biosynthesis, leading to a marked reduction in cell cholesterol content and to an accumulation of sterol intermediates, particularly cholesta-8,14-dien-3beta-ol. These changes were accompanied by a loss of flotillin-1 and Fyn from the lipid rafts. We next studied the functionality of the SRIF receptor. Treatment with haloperidol reduced the inhibitory effect of SRIF on adenylyl cyclase (AC) activity. On the other side, haloperidol decreased basal AC activity but increased forskolin-stimulated AC activity. Addition of free cholesterol to the culture medium abrogated the effects of haloperidol on lipid raft composition and SRIF signaling whereas the AC response to forskolin remained elevated. The results show that haloperidol, by affecting cholesterol homeostasis, ultimately alters SRIF signaling and AC activity, which might have physiological consequences.

Activation of D1 and D2 dopamine receptors increases the activity of the somatostatin receptor-effector system in the rat frontoparietal cortex

The role of dopamine D1 and D2 receptor subtypes in the regulation, in vivo, of the somatostatin (SRIF) receptor-effector system in rat frontoparietal cortex was investigated. The D1-receptor agonist SKF 38393 (4 mg/kg) or the D2-receptor agonist bromocriptine (2 mg/kg), administered intraperitoneally to rats, increased the number of SRIF receptors without altering the affinity constant, an effect antagonized by both SCH 23390 (0.25 mg/kg) and raclopride (5 mg/kg), D1 and D2 receptor antagonists, respectively. These antagonists alone had no effect on [(125)I]Tyr(3) octreotide binding to its receptors. No change in binding was detected when the dopamine agonists were added in vitro. Basal adenylyl cyclase (AC) activity was increased by SKF 38393 treatment and decreased by bromocriptine. Octreotide (SMS 201-995)-mediated inhibition of basal and forskolin-stimulated AC was increased by SKF 38393 or bromocriptine treatment. In frontoparietal cortical slices, basal inositol-1,4, 5-triphosphate (IP(3)) levels were decreased by bromocriptine treatment but were unaffected by SKF 38393. SMS 201-995 increased the IP(3) accumulation in control, SKF 38393-, and bromocriptine-treated rats. Insofar as SRIF and dopamine appear to be involved in motor regulation and could well modulate somatosensory functions in frontal and parietal cortex, respectively, heterologous receptor regulation may have important repercussions regarding the control exerted by these neurotransmitters on frontal and parietal cortical function in the intact animal.

Acute effects of D1- and D2-receptor agonist and antagonist drugs on somatostatin binding, inhibition of adenylyl cyclase activity and accumulation of inositol 1,4,5-trisphosphate in the rat striatum

A recent study carried out by our group demonstrated that exogenous dopamine increases the somatostatin (SS) receptor-effector system in the rat striatum. The present study examined the participation of the D1- and D2-dopaminergic systems in the modulation of the rat striatal SS receptor-effector system by use of the D1-receptor agonist and antagonist SKF 38393 and SCH 23390, respectively, and the D2-receptor agonist and antagonist bromocriptine and raclopride, respectively. In view of the rapid onset of dopamine action, the effect of dopaminergic agents on the SS mechanism of action were studied 3 h after their administration. SKF 38393 (4 mg/kg i.p.) or bromocriptine (2 mg/kg i.p.) administered to male Wistar rats increased the number of 125I-Tyr3-SMS receptors in the striatum (52 and 30%, respectively) without changing the affinity constant. The effect of SKF 38393 on 125I-Tyr3-SMS binding was antagonized by the D1-specific antagonist SCH 23390 (0.25 mg/kg i.p.) whereas the effect of bromocriptine was abolished by the D2-specific antagonist raclopride (5 mg/kg i.p.). No change in binding was produced when SKF 38393 or bromocriptine were added directly to the incubation medium. The acute systemic administration of SCH 23390 or raclopride alone had no effect on the binding of 125I-Tyr3-SMS to its receptors. The increase of the number of 125I-Tyr3-SMS receptor induced by SKF 38393 or bromocriptine was accompanied by an increase in the capacity of SMS 201-995 to inhibit basal and forskolin (FK)-stimulated adenylyl cyclase (AC) activity when compared to the control groups. In addition, the effect of SMS 201-995 on the mass accumulation of inositol 1,4,5-trisphosphate (IP3) was investigated. SKF 38393 as well as bromocriptine increased the capacity of SMS 201-995 to accumulate IP3 in the rat striatum although this effect was only statistically significant in the case of SKF 38393. These results suggest that the activation of D1 and D2 receptors increases the activity of the SS receptor-effector system, the effect being greater in the case of D1 receptors. These findings are consistent with a functional interaction between dopamine and SS in the rat striatum.

Effect of prenatal dopamine receptor blocking on somatostatin receptor binding in the developing rat brain

To date, the possible functional interaction between the dopaminergic and the somatostatinergic system during the development of the brain is unknown. This study examines whether blockage of brain dopamine receptors during fetal life might influence postnatal somatostatin (SS) receptor development. Pregnant Sprague-Dawley rats were injected intraperitoneally with either haloperidol (2.5 mg/kg/day), which blocks dopaminergic receptors, or saline. The injections were given for 16 days, commencing on the 4th or 5th day after conception (as counted from the appearance of spermatozoa in daily vaginal smear). The administration of haloperidol during gestation did not affect the levels of somatostatin-like immunoreactivity (SLI) in the two brain areas at any of the times studied. However, this treatment resulted in a decrease in the total number of receptors for 125I-Tyr11-SS in frontoparietal cortex and hippocampal plasma membranes in the 14-day-old offspring but not at 21, 35, or 60 days after birth. No significant differences in the apparent SS binding affinity values were seen after fetal exposure to haloperidol. These results suggest that the development of SS receptors in rat frontoparietal cortex and hippocampus can be transitorily delayed by fetal blockage of dopamine receptors.

Somatostatin receptors increase in the olfactory bulb of developing pups after perinatal exposure to cocaine

The effects of chronic prenatal and/or postnatal exposure to cocaine on somatostatin concentration and receptors were studied in the olfactory bulbs of rat pups at birth and at 15 days old. Wistar rats were injected subcutaneously with single daily doses of 40 mg cocaine hydrochloride/kg from days 7 to 19 of gestation, from day 7 of gestation to day 15 postpartum or from parturation to day 15 postpartum. Fetal exposure to cocaine decreased SS concentrations in the olfactory bulb of the newborn pups while prenatal-plus-postnatal exposure increased this parameter. Administration of cocaine only during lactation did not induce any change. Exposure during gestation or during nursing induced an increase in the total number of somatostatin receptors and a decrease in the affinity constant in the olfactory bulb of newborn and 15-day-old pups. These results suggest that the development of somatostatin receptors in the olfactory bulb can be altered by prenatal and/or nursing period exposure to cocaine.

Changes in striatal somatostatin receptors in pups after cocaine administration to pregnant and nursing dams

Primiparous female Wistar rats were injected subcutaneously with single daily doses of 40 mg of cocaine hydrochloride/kg from day 7 to 19 of gestation, from day 7 of gestation to day 15 postpartum or from parturation to day 15 postpartum. At birth, some of the offspring were fostered to control mothers to limit the effect of cocaine to the prenatal period and some were left with their mothers with the aim of studying prenatal plus postnatal exposure to cocaine. Prenatal and/or postnatal cocaine exposure did not affect the content of somatostatin (SS)-like immunoreactivity (SLI) in the striatum of the offspring as compared with the control groups on day 15 in all experimental groups. Prenatal and prenatal-plus-postnatal exposure to cocaine increased the total number of binding sites for 125I-Tyr11-SS in the rat striatum at 15 days of age. Prenatal exposure to cocaine also decreased the apparent affinity of the receptors. Postnatal exposure to cocaine alone had no such post-treatment effect on 125I-Tyr11-SS binding. These results suggest that the development of SS receptors in the rat striatum can be altered by prenatal exposure to cocaine.

Effect of prenatal and postnatal cocaine exposure on somatostatin content and binding in frontoparietal cortex and hippocampus of developing rat pups

The effects of cocaine administration to pregnant and/or nursing rats on somatostatin (SS) concentration and receptors in offspring brains at birth and 15 days of age were studied. SS was measured by radioimmunoassay and SS receptors by radio receptor assay in frontoparietal cortex and hippocampus. In newborn and 15-day-old animals the exposure to cocaine produced an increase in SS concentration in the frontoparietal cortex and a decrease of this parameter in the hippocampus. Administration of cocaine only during lactation did not induce such changes. Exposure during pregnancy or nursing induced in 0- or 15-day-old offspring an increase in the total number of SS receptors and a decrease in the affinity constant only in the cortex.

Effect of haloperidol withdrawal on somatostatin level and binding in rat brain

The effects of withdrawal on the level and specific binding of somatostatin in the frontoparietal cortex and hippocampus of the rat after chronic haloperidol treatment were examined using 125I-Tyr11 somatostatin as tracer. One week after haloperiodol withdrawal the number of specific somatostatin receptors in both brain areas returned to control values, after having decreased as the result of chronic administration. Neither administration of haloperidol nor withdrawal of it affected the levels of somatostatin-like immunoreactivity (SLI) in the two brain areas studied. The return of the somatostatin receptor number to control values after haloperidol withdrawal may be related to the motor side-effects that are clinically observed when the haloperidol treatment is terminated.

Preclinical and clinical studies with somatostatin related to the central nervous system

1. The tetradecapeptide somatostatin (SS) has a widespread, uneven distribution within several organs including the central nervous system (CNS), with particularly high concentration in the hypothalamus. 2. The SS-related peptides (SS28, SS28(1-12), SS28(15-28)) are originated from the precursor pre-prosomatostatin. 3. SS is suggested to be involved in a large number of CNS functions, locomotion, sedation, excitation, catatonia, body temperature, feeding, nociception, paradoxical sleep, self-stimulation, seizure, learning and memory. 4. SS influences central neurochemical processes. 5. It is possible that SS is related to various neurological and psychiatric illnesses, like Huntington's disease, multiple sclerosis, Parkinson's disease, epilepsy, eating disorders, Alzheimer's disease, schizophrenia and major depressive illness.