Differences in Behavioral Responding in Adult and Aged Rats Following Chronic Ethanol Exposure

BACKGROUND

Research suggests symptoms of chronic alcoholism, and withdrawal may be more severe in elderly compared with younger adults. However, examination of the effects of long-term ethanol (EtOH) consumption and withdrawal is limited in aged rodents. We thus investigated EtOH withdrawal and potential deficits in cognitive and motor behavior in young adult and aged rats. We also examined the effects of acute allopregnanolone as a potential mechanism contributing to age-related differences in EtOH's cognitive-impairing effects.

METHODS

Male young adult (postnatal days 70 to 72) and aged (approximately 18 months) Sprague-Dawley rats were treated with liquid EtOH diet in a modified chronic intermittent EtOH (modified-CIE) paradigm. The severity of EtOH withdrawal was determined using a 4-item rating scale, and withdrawal-induced anxiety-like behavior was assessed in the elevated plus maze (EPM) and open field. After a 14-day EtOH-free period, spatial performance was assessed in the Morris water maze (MWM) during sober acquisition and in response to a subsequent EtOH and allopregnanolone challenge.

RESULTS

Modified-CIE adults consumed more EtOH during treatment and exhibited robust EtOH withdrawal using a behavioral rating scale compared to aged rats. In the EPM, adult and aged modified-CIE groups spent increased time in the closed arms, while aged animals also made significantly more closed arm entries, fewer open arm entries, and spent less time in the open arms during withdrawal compared to controls. Modified-CIE decreased MWM performance of adult and aged rats, but did not result in motor impairments in either age group. Finally, acute allopregnanolone increased time to the MWM platform in adults but not aged animals.

CONCLUSIONS

The elderly may be vulnerable to EtOH withdrawal as modified-CIE aged rats displayed anxiety-like behavior compared to controls during withdrawal despite achieving lower blood EtOH concentrations during treatment than younger adults. Our data also indicate that modified-CIE and EtOH withdrawal cause persistent cognitive impairments in both age groups. The results from this study provide further evidence indicating the elderly may be sensitive to the effects of alcohol.

Alcohol use across the lifespan: An analysis of adolescent and aged rodents and humans

Adolescence and old age are unique periods of the lifespan characterized by differential sensitivity to the effects of alcohol. Adolescents and the elderly appear to be more vulnerable to many of alcohol's physiological and behavioral effects compared to adults. The current review explores the differential effects of acute alcohol, predominantly in terms of motor function and cognition, in adolescent and aged humans and rodents. Adolescents are less sensitive to the sedative-hypnotic, anxiolytic, and motor-impairing effects of acute alcohol, but research results are less consistent as it relates to alcohol's effects on cognition. Specifically, previous research has shown adolescents to be more, less, and similarly sensitive to alcohol-induced cognitive deficits compared to adults. These equivocal findings suggest that learning acquisition may be differentially affected by ethanol compared to memory, or that ethanol-induced cognitive deficits are task-dependent. Older rodents appear to be particularly vulnerable to the motor- and cognitive-impairing effects of acute alcohol relative to younger adults. Given that alcohol consumption and abuse is prevalent throughout the lifespan, it is important to recognize age-related differences in response to acute and long-term alcohol. Unfortunately, diagnostic measures and treatment options for alcohol dependence are rarely dedicated to adolescent and aging populations. As discussed, although much scientific advancement has been made regarding the differential effects of alcohol between adolescents and adults, research with the aged is underrepresented. Future researchers should be aware that adolescents and the aged are uniquely affected by alcohol and should continue to investigate alcohol's effects at different stages of maturation.

The effects of acute alcohol on motor impairments in adolescent, adult, and aged rats

Acute alcohol exposure has been shown to produce differential motor impairments between aged and adult rats and between adolescent and adult rats. However, the effects of acute alcohol exposure among adolescent, adult, and aged rats have yet to be systematically investigated within the same project using a dose-dependent analysis. We sought to determine the age- and dose-dependent effects of acute alcohol exposure on gross and coordinated motor performance across the rodent lifespan. Adolescent (PD 30), adult (PD 70), and aged (approximately 18 months) male Sprague-Dawley rats were tested on 3 separate motor tasks: aerial righting reflex (ARR), accelerating rotarod (RR), and loss of righting reflex (LORR). In a separate group of animals, blood ethanol concentrations (BEC) were determined at multiple time points following a 3.0 g/kg ethanol injection. Behavioral tests were conducted with a Latin square repeated-measures design in which all animals received the following doses: 1.0 g/kg or 2.0 g/kg alcohol or saline over 3 separate sessions via intraperitoneal (i.p.) injection. During testing, motor impairments were assessed on the RR 10 min post-injection and on ARR 20 min post-injection. Aged animals spent significantly less time on the RR when administered 1.0 g/kg alcohol compared to adult rats. In addition, motor performance impairments significantly increased with age after 2.0 g/kg alcohol administration. On the ARR test, aged rats were more sensitive to the effects of 1.0 g/kg and 2.0 g/kg alcohol compared to adolescents and adults. Seven days after the last testing session, animals were given 3.0 g/kg alcohol and LORR was examined. During LORR, aged animals slept longer compared to adult and adolescent rats. This effect cannot be explained solely by BEC levels in aged rats. The present study suggests that acute alcohol exposure produces greater motor impairments in older rats when compared to adolescent and adult rats and begins to establish a procedure to determine motor effects by alcohol across the lifespan.

Acute alcohol produces ataxia and cognitive impairments in aged animals: a comparison between young adult and aged rats

BACKGROUND

Aging in both humans and rodents appears to be accompanied by physiological changes that increase biologic sensitivity to ethanol (EtOH) intoxication. However, animal models designed to investigate this increased alcohol sensitivity have yet to be established. For this reason, we sought to determine whether acute EtOH administration produces differential effects on motor coordination and spatial cognition in young adult and aged rats.

METHODS

Male young adult (postnatal day 70 to 72) and aged (~18 months) Sprague-Dawley rats were assessed on 2 motor tasks (the accelerating rotarod [RR] and the aerial righting reflex [ARR]) and a single cognitive performance task (the Morris water maze [MWM]). Following acute EtOH exposure via intraperitoneal injection, animals' performance was reassessed.

RESULTS

Aged rats showed a dramatic increase in EtOH-induced ataxia on the RR and the ARR relative to young adult animals. Similarly, results from the MWM revealed that aged animals had slightly greater EtOH-induced impairments compared with young adult animals. Importantly, the increased impairments produced by EtOH were not due to differential blood EtOH levels.

CONCLUSIONS

We demonstrate for the first time that aged rats show greater EtOH-induced deficits compared with young adults in tasks of motor and cognitive performance. The possible role of protein kinase C as a mechanism for increased sensitivity to the motor-impairing effects of EtOH is discussed. Given the high prevalence of alcohol use among the elderly, increased vulnerability to alcohol-induced deficits may have a profound effect on injury in this population.

The effect of chronic intermittent ethanol exposure on spatial memory in adolescent rats: the dissociation of metabolic and cognitive tolerances

Using a rapid chronic intermittent ethanol (CIE) vapor exposure paradigm, we demonstrate the dissociability of metabolic tolerance from cognitive tolerance in adolescent rats. Adolescent rats were trained to spatially navigate in the Morris Water Maze and then exposed to CIE vapor or air 16 h a day for 4 days. After a final 28 h withdrawal, all rats received a saline or ethanol challenge, followed by a test of spatial memory 30 min after administration. Results indicate that CIE vapor exposure did not significantly impair adolescent spatial memory. Although CIE-exposed rats developed metabolic tolerance to a subsequent ethanol administration, CIE exposure did not alter dose-dependent ethanol-induced spatial memory impairments. These data indicate that metabolic ethanol tolerance can be distinguished from cognitive ethanol tolerance during adolescence and suggest that blood alcohol levels alone do not fully explain ethanol-induced spatial memory impairments.

Low and moderate doses of acute ethanol do not impair spatial cognition but facilitate accelerating rotarod performance in adolescent and adult rats

Adolescents and adult rodents have differing sensitivities to the acute effects of ethanol on a variety of behavioral and electrophysiological measures. Often, these differences are revealed using high ethanol doses and consequently little is known about these age-related effects using lower ethanol doses. We sought to determine if low-dose ethanol produces differential effects on cognition and motor behavior in adolescent and adult rats. Adolescent (postnatal day PD 30-32) and adult (PD 70-72) male Sprague Dawley rats were trained on the standard version of the Morris Water Maze (MWM) for 5 days or received 5 training trials on an accelerating rotarod (ARR). Adolescents learned the location of the submerged platform in the MWM significantly slower than adults during training and, acute ethanol administration (0.5 g/kg, 0.75 g/kg, or 1.0 g/kg) 30 min before testing did not impair spatial memory in either age group. On the ARR test, adolescent rats spent significantly more time on the rotarod compared to adults and, alcohol exposure (1.0 g/kg) significantly increased ARR performance 30 min following administration. Our findings address the utility of investigating low and moderate doses of ethanol during different developmental stages in rats.

Colocalization of calretinin and glucagon in rat pancreatic A cells

Calretinin is a calcium-binding protein whose major functions are assumed to be buffering, transport of Ca2+, regulation of various enzyme systems and cellular protection. Moreover, calretinin does not seem to be a specific marker for any particular cell since it has been discovered in various mammalian and avian organs. In order to give clue to its function(s), we investigate its distribution in the rat pancreas using immunocytochemistry and transmission electron microscopy. We have found calretinin immunoreactive cells in rat pancreas only in the islets of Langerhans. These cells correspond to A cells producing glucagon. The colocalization of calretinin and glucagon was confirmed with double-labelling immunofluorescence. Nevertheless, the role of calretinin and its relationship with the production and/or the exocytosis of glucagon granules remains to be elucidated.

Calretinin immunoreactivity in pineal gland of different mammals including man

Calretinin (CR) is a calcium-binding protein, found in a variety of organs and systems such as the central nervous system and the pineal gland. It was first thought to be a specific neuronal marker but this selectivity is now in question since CR has been demonstrated in avian thymus, rat ovary, rat and guinea pig inner ear, rat testis, and chicken and rat pineal gland. To contribute to the knowledge of the presence of CR-positive cells in the pineal parenchyma of rat and other mammalian including man, we performed immunocytochemistry on pineal glands of gerbils, rats, goats, cows, and humans, using a CR anti-serum. To confirm it was actually CR that was demonstrated, we performed Western Blot analyses. Finally, to precisely identify the nature of CR-positive cells we accomplished double-labelling immunofluorescence, using antisera against some nerve cell specific cytosquelettal proteins such as MAP-5, MAP-2, NF-L, NF-M, and NF-H. CR-positive cells were found in all pineal glands studied. These cells all possess a round, oval, or polygonal-shaped perikaryon sending one or more processes of different lengths into the glandular parenchyma. There is a lack of CR immunoreactivity in the nucleus and cell organelles while the cytosol contains a high concentration of this protein. Nevertheless, there are some slight differences between species, especially concerning the number of reactive cells and their relationships with different parenchymal structures such as blood vessels or acervuli. Among the CR-positive cells, only a few were actually nerve cells, contributing probably to an intrinsic innervation of the gland. The remaining CR-reactive cells seem to correspond mostly to pinealocytes in a specific histophysiological state and possibly to neuron-like cells. The significance of the CR-positive cells in the pineal glands remains to be elucidated.

Nitric oxide synthase in the subfornical organ of Mongolian gerbil (Meriones unguiculatus), mouse and rat

The present paper aims to contribute to the knowledge of the histophysiologic role of the subfornical organ. Using nicotinamide adenine dinucleotide phosphate diaphorase histochemistry (NADPH-diaporase) and nitric oxide synthase immunocytochemistry, we detected a high concentration of the neuronal isoform of nitric oxide synthase in neurons of the subfornical organ of the adult Mongolian gerbil (Meriones unguiculatus), mouse and rat. Our results suggest that neurons of the subfornical organ produce a considerable amount of nitric oxide which acts, not only as a neurotransmitter, but could also diffuse into cerebral blood vessels and cerebrospinal fluid.