Luigia Trabace

Intranigral GR-113808, a selective 5-HT4 receptor antagonist, attenuates morphine-stimulated dopamine release in the rat striatum

GR-113808, a potent and selective 5-HT4 receptor antagonist, was infused through a microdialysis probe into the striatum and nucleus accumbens of awake rats, and basal and morphine-stimulated extracellular concentrations of dopamine (DA) were measured in these regions. At 1 and 10 microM GR-113808 did not affect the extracellular concentrations of DA in either region and 100 microM significantly reduced dialysate DA only in the striatum. A subcutaneous dose of 5 mg/kg morphine significantly raised extracellular concentrations of DA in the striatum and nucleus accumbens from 60 to 120 min after injection and the effect was not modified by 10 microM GR-113808 infused through the probe 20 min before and for 60 min after morphine. Bilateral injections of GR-113808 (1, 2.5 and 10 micrograms/0.5 microliter) in the substantia nigra pars compacta did not affect dialysate DA in the striatum, except for a significant increase 120 min after the injection of 10 micrograms but the highest dose of GR-113808 prevented the increase of striatal DA caused by 5 mg/kg morphine s.c. The results suggest that 5-HT4 receptors in the substantia nigra modulate the activity of the dopaminergic nigrostriatal system only when the neurons are activated.

Genetic Factors Involved in the Effects of Developmental Low-Level Alcohol Induced Behavioral Alterations in Rats ☆

Behavioral and neurochemical effects of perinatal alcohol exposure (3% v/v solution from Day 15 of gestation to Day 7 after parturition) have been investigated in Sardinian alcohol-preferring (sP) and alcohol-nonpreferring (sNP) rat lines, selectively bred for opposite alcohol preference and consumption. In an elevated zero-maze model of anxiety, sucrose-exposed sP rats (sP-S): (i) spent significantly less time on the open arms (TO); (ii) exhibited a significantly lower number of head dips (HDIPS); and (iii) showed a higher number of stretched attend-postures (SAP) than sucrose-exposed sNP rats (sNP-S) at 90 and 180 days of age. The two rat lines displayed different emotional reactivity in response to alcohol exposure. Subtle differences in sexual behavior and ultrasonic emission (latency to the first intromission and to the first 50 kHz call) were observed between sP-S and sNP-S rats. sP-alcohol exposed (sP-A) offspring exhibited a higher latency to the first intromission than sNP-alcohol (sNP-A) treated rats. Moreover, a lower number of sP-A rats exhibited both intromission and ejaculation with respect to sNP-A animals. sP-S rats were significantly slower in recover of the righting reflex than sNP-S animals after a challenge dose of alcohol (3 g/kg, i.p.). Perinatal alcohol did not affect either onset or duration of sleep time in either line. Neurochemical experiments have shown that perinatal alcohol did not influence basal dopamine levels or amphetamine-induced dopamine increase in the prefrontal cortex of either sP or sNP offspring. These results, showing an endpoint-specific differential sensitivity of sP and sNP lines to perinatal low alcohol exposure, indicate that genetic factors could be responsible for selective susceptibility to behavioral alterations induced by developmental treatment with this drug of abuse.

Neurofunctional Effects of Developmental Alcohol Exposure in Alcohol-Preferring and Alcohol-Nonpreferring Rats

The neurofunctional effects of developmental alcohol exposure (3% v/v solution from day 15 of gestation to day 7 after parturition) have been investigated in Sardinian alcohol-preferring (sP) and alcohol-nonpreferring (sNP) rat lines, selectively bred for opposite alcohol preference and consumption. Alcohol exposure significantly decreased the rate of ultrasonic emission in sP male pups; whereas, it did not affect this indicator of emotional reactivity in sNP animals. Perinatal alcohol intake did not influence either learning of an active avoidance task or hippocampal long-term potentiation in both offspring lines. Significant differences in time spent exploring novel objects were observed between control sP and sNP rats subjected to the novel exploration object test. Alcohol exposed sP rats, but not alcohol exposed sNP rats, apparently lost the capacity to discriminate between the novel and the familiar object, even though this difference is difficult to interpret because of the large differences in the respective responses to the novel objects. Neurochemical experiments have shown that basal levels of dopamine (DA) and homovanillic acid (HVA) were significantly higher in the nucleus accumbens (NAC) of sP rats with respect to sNP animals. Perinatal alcohol did not affect basal DA and HVA concentrations or amphetamine-induced DA increase and HVA decrease in the NAC of either sP or sNP offspring. These results suggest that subtle behavioral alterations induced by developmental exposure to low doses of alcohol, which do not cause malformations and/or overt neurotoxicity, may be associated with genetic factors, although not necessarily those responsible for differences in alcohol preference.

Effects of prenatal exposure to low concentrations of carbon monoxide on sexual behaviour and mesolimbic dopaminergic function in rat offspring

1 Inhalation of low concentrations of carbon monoxide (CO) by pregnant rats (75 and 150u2003p.p.m. from day 0 to day 20 of gestation) leads to changes in mesolimbic dopaminergic transmission associated with an impairment of sexual behaviour in male offspring. 2 Eighty day old males exposed in utero to CO (150u2003p.p.m.) exhibited a significant increase in mount/intromission latency as well as a significant decrease in mount/intromission frequency. A significant decrease in ejaculation frequency was also found in CO (150u2003p.p.m.)‐exposed animals. 3 The acute administration of amphetamine, at a dose (0.5u2003mgu2003kg−1 s.c.) stimulating copulatory activity in control rats, failed to reduce mount/intromission latency and did not increase mount frequency in 80‐day offspring exposed to CO (150u2003p.p.m.) during gestation. 4 These behavioural alterations were paralleled by neurochemical changes (in vivo microdialysis) showing that prenatal CO exposure, at concentrations (150u2003p.p.m.) that did not affect basal extracellular levels of dopamine in the nucleus accumbens, blunted the amphetamine (0.5u2003mgu2003kg−1 s.c.)‐induced increase in dopamine release in 80‐day old male rats. 5 No significant changes in either behavioural or neurochemical parameters were observed in 10‐month old rats exposed prenatally to CO. 6 Since the alterations in sexual behaviour and dopaminergic transmission have been produced by prenatal exposure to CO levels resulting in maternal blood carboxyhaemoglobin concentrations equivalent to those maintained by human cigarette smokers, the present data further point out the large risk that the smoking mother poses for her offspring.

In vivo neurochemical effects of the acetylcholinesterase inhibitor ENA713 in rat hippocampus

Oral ENA713 (0.5, 1.5 and 4.5 mg/kg), an acetylcholinesterase inhibitor (AChEI), dose-dependently enhanced extracellular acetylcholine concentrations in the hippocampus of freely moving rats. This effect was paralleled by changes in both noradrenergic and dopaminergic transmission. In particular, ENA713 significantly decreased noradrenaline concentrations, whereas it significantly increased homovanillic acid levels, without affecting dopamine concentrations. Neither serotonin nor gamma-aminobutyric acid levels were modified by ENA713. These findings extend the neurochemical profile of ENA713 and suggest that it could be useful for the treatment of Alzheimer-type dementia which is associated with multiple neurotransmitter abnormalities in the brain.

Prenatal exposure to low levels of carbon monoxide alters sciatic nerve myelination in rat offspring.

Prenatal exposure to low concentrations of carbon monoxide (CO, 75 and 150 ppm from day 0 to day 20 of gestation), resulting in maternal blood HbCO concentrations equivalent to those maintained by human cigarette smokers, leads to subtle myelin alterations in the sciatic nerve of male rat offspring. The rapid growth spurt in pup body weight was related to the period of maximal increase in myelin sheath thickness in both control and CO-exposed animals. A significant reduction in myelin sheath thickness of sciatic nerve fibers, paralleled by changes in the frequency distribution, occurred in both 40- and 90-day-old rats exposed in utero to CO (75 and 150 ppm). Myelin deficit observed in 75 and 150 ppm CO-exposed animals showed up only after the major spurt in myelination but not early during development. The subtle myelin alterations observed in CO-exposed offspring were not accompanied by changes in developmental pattern of axon diameters and did not result in a gross impairment of motor activity. These results suggest that the myelination process is selectively targeted by a prenatal exposure model simulating the CO exposure observed in human cigarette smokers.

Prenatal low-level exposure to CO alters postnatal development of hippocampal nitric oxide synthase and haem-oxygenase activities in rats.

The effects of prenatal CO exposure (150 ppm from days 0 to 20 of pregnancy) on the postnatal development of hippocampal neuronal NO synthase (nNOS) and haem-oxygenase (HO-2) isoform activities in 15-, 30- and 90-d-old rats were investigated. Unlike HO-2, hippocampal nNOS activity increased from postnatal days 15-90 in controls. Prenatal CO produced a long-lasting decrease in either nNOS or HO-2. The results suggest that the altered developmental profile of hippocampal nNOS and HO-2 activities could be involved in cognitive deficits and long-term potentiation dysfunction exhibited by rats prenatally exposed to CO levels resulting in carboxyhaemoglobin (HbCO) levels equivalent to those observed in human cigarette smokers.

Effects of ENA713 and CHF2819, two anti-Alzheimer’s disease drugs, on rat amino acid levels

The effects of oral ENA713 and CHF2819 (0.5, 1.5 and 4.5 mg/kg), two novel acetylcholinesterase inhibitors, on extracellular concentrations of amino acids in rat hippocampus, were evaluated using in vivo microdialysis. ENA713, at 4.5 mg/kg, but not CHF2819, significantly decreased glutamate, taurine, arginine and citrulline levels, without affecting aspartate concentrations. These results suggest that the modulation of amino acidergic transmission could represent an additional mechanism of action in Alzheimers disease for some acetylcholinesterase inhibitors.

Prenatal exposure model simulating CO inhalation in human cigarette smokers: sphingomyelin alterations in the rat sciatic nerve.

Prenatal exposure to low concentrations of carbon monoxide (CO, 150 ppm) causes long-term alterations in sphingomyelin (SM) homeostasis in peripheral nervous system, but not brain of male rat offspring. In particular, unlike sphinganine (intermediate of complex sphingolipid biosynthesis de novo), the concentrations of sphingosine (intermediate of complex sphingolipid turnover) were increased by 2.35-fold in the sciatic nerve of CO-exposed offspring with respect to controls (P<0.05, overall one-way ANOVA). These subtle alterations were not accompanied by changes in motor activity (F=0.25, df=1/10, n.s., overall one-way-ANOVA). The results suggest that the SM homeostasis in the sciatic nerve is particularly susceptible to prenatal CO exposure resulting in maternal carboxyhaemoglobin (HbCO) levels equivalent to those found in human cigarette smokers.