Reduction of motor behavioral deficits in senescent animals via chronic prolactin administration. II. Non-stereotypic behaviors

Neuroprotective effect of hesperidin against emamectin benzoate-induced neurobehavioral toxicity in rats

Emamectin Benzoate (EMB) is an avermectin insecticide widely used in agriculture and veterinary medicine. Hesperidin (HSP) is a flavanone glycoside predominantly found in citrus fruits and has various beneficial health effects. The current research was conducted to study the neurobehavioral toxic effects of EMB in rats and also to evaluate the protective effect of HSP against these toxic effects. Sixty Sprague-Dawley rats were randomly divided into 4 equal groups: control group, EMB group, HSP group, and EMB + HSP group. EMB (8.8. mg/kg) and/or HSP (100 mg/kg) were administered daily by gavage for 8 weeks. The behavioral assessment demonstrated the adverse effects of EMB on the behavioral, motor, and cognitive brain functions. Exposure to EMB also decreased the activity of antioxidants (catalase and reduced glutathione) and increased the malondialdehyde level in nervous tissue. Moreover, EMB increased the level of inflammatory cytokines (tumor necrosis factor-α and interleukin-1β) and decreased brain-derived neurotrophic factor (BDNF) levels in rats' brains. On the other hand, concurrent administration of HSP ameliorated the toxic effects of EMB as indicated by improvements in neural functions and reduction of oxidative stress and inflammation. The study concluded that exposure to EMB induces toxic effects in the brain of rats and that HSP has a protective effect against these toxic effects.

Behavioral tests in rodent models of stroke

Rodents are the most widely used experimental animals in stroke research due to their similar vascular anatomy, high reproductive rates, and availability of transgenic models. However, the difficulties in assessing higher brain functions, such as cognition and memory, in rodents decrease the translational potential of these studies. In this review, we summarize commonly used motor/sensorimotor and cognition tests in rodent models of stroke. Specifically, we first briefly introduce the objective and procedure of each behavioral test. Next, we summarize the application of each test in both ischemic stroke and hemorrhagic stroke. Last, the advantages and disadvantages of these tests in assessing stroke outcome are discussed. This review summarizes commonly used behavioral tests in stroke studies and compares their applications in different stroke types.

Detection of prolactin receptor mRNA in the corpus striatum and substantia nigra of the rat

The observation of prolactin modulation of the nigrostriatal dopaminergic system suggests the expression of prolactin receptor in the corpus striatum or substantia nigra. The present study investigated expression of prolactin receptor mRNA in tissues microdissected from the corpus striatum and substantia nigra of the rat. By using reverse transcription PCR combined with Southern hybridization, the long form of prolactin receptor mRNA was detected in the substantia nigra, caudate putamen, globus pallidus, and ventral pallidum in ovariectomized rats, whereas the short form was not detectable in any of these areas. Estrogen had no effect on expression of the long-form mRNA in the substantia nigra and corpus striatum. By using the RNase protection assay, the expression of both short and long forms of prolactin receptor mRNA was observed in the corpus striatum in ovariectomized rats. Again, levels of expression were not significantly altered by estrogen treatment. Both forms of prolactin receptor mRNA were clearly expressed in the choroid plexus and were up-regulated by estrogen treatment. The expression of both forms of prolactin receptor mRNA in nigrostriatal areas may help to support the hypothesis that prolactin has direct actions on these brain regions.

The effects of dietary antioxidants on psychomotor performance in aged mice

Male C57BL/6NIA mice were provided one of six different antioxidant diets: vitamin E, glutathione, vitamin E plus glutathione, melatonin, strawberry extract, or control, beginning at 18 months of age. A battery of motor tests--rod walk, wire hang, plank walk, and inclined screen-was administered either: 1) before dietary treatment and then 6 months later at 24 months of age: or 2) only after 6 months of dietary treatment at age 24 months. An untreated group of 4-month-old mice served as young controls. Psychomotor performance was lower in 18-month-old mice compared with 4-month-old mice in the rod walk, wire hang, and inclined screen tests; however, no further decline was seen from 18 to 24 months on any measure. Chronic dietary antioxidant treatments were not effective in reversing age-related deficits in psychomotor behavior, except for the glutathione diet on inclined screen performance. It seems that motor performance deteriorates profoundly with age, because deficits at 18 months of age were as severe as they were at 24 months, and these age-associated motor deficits may be difficult to reverse, even with antioxidant treatment.

The effects of aging and oxidative stress on psychomotor and cognitive behavior

Decrements in motor and cognitive function occur in aging, possibly due to oxidative stress-induced damage to the brain. Declines in antioxidant defense mechanisms have been postulated as a causative factor in these age-related decrements, however a clear link between oxidative stress (OS) and behavioral changes in aging has yet to be established. This review shows that age-validated psychomotor and cognitive tests are sensitive to behavioral deficits under different models of OS, including: 1) decreasing OS protection by depleting glutathione and then increasing the OS with dopamine; 2) 100% oxygen exposure; and 3) radiation. Furthermore, interventions that reduce OS result in concurrent improvements in age-associated behavioral deficits. Therefore, age-related changes in behavior may result from an inability to cope with OS that occurs throughout the life-span.

Psychomotor and spatial memory performance in aging male Fischer 344 rats

Psychomotor and spatial memory performance were examined in male Fischer 344 rats that were 6, 12, 15, 18, and 22 months of age, to assess these parameters as a function of age and to determine at what age these behaviors begin to deteriorate. Complex motor behaviors, as measured by rod walk, wire suspension, plank walk, inclined screen, and accelerating rotarod performance, declined steadily with age, with most measures being adversely affected as early as 12 to 15 months of age. Spatial learning and memory performance, as measured by the working memory version of the Morris water maze (MWM), showed decrements at 18 and 22 months of age (higher latencies on the working memory trial), with some change noticeable as early as 12-15 months of age (no improvement on the second trial following a 10-min retention interval); these differences were not due to swim speed. Therefore, complex motor and spatial memory behaviors show noticeable declines early in the lifespan of the male Fisher 344 rat. This cross-sectional age analysis study using the latest behavioral techniques determines the minimal age at which psychomotor and spatial learning and memory behaviors deteriorate; this information is important when planning for longitudinal studies where interventions are tested for their efficacy in preventing or restoring age-related behavioral deficits.

Cellular and molecular mechanisms of impaired dopaminergic function during aging

One important cause of impaired motor function during aging is deterioration of the dopamine system. Such motor deficits in experimental animals can be closely related to loss of striatal dopamine receptors, and similar observations have now been made in humans. Two mechanisms account for the age-related decrease in striatal dopamine receptor levels: loss of receptor-containing neurons and reduced rates of receptor synthesis. The striatal neurons affected by aging appear to reside in a kainic-acid-sensitive population. Attempts to mimic those death mechanisms which occur in vivo using cultured neurons suggest that large D2-dopamine-receptor-containing cells may be the most vulnerable. Whether dopamine itself, the endogenous neurotransmitter for the cells, may ultimately be toxic to these neurons remains to be determined. The levels of D2-receptor mRNA in the surviving neurons is reduced during aging. This decrement is apparently due to a decreased rate of mRNA biosynthesis. Future experiments must therefore focus on the regulatory elements of this gene in order to determine why its transcription is selectively affected by aging. Finally, various interventions have been shown to delay or reverse the age changes characteristic of the dopaminergic system. Both dopamine receptors and motor function have been manipulated by diet and exercise as well as 6-OH-dopamine lesions and estrogen and prolactin administration. The possibility that such treatments might eventually be utilized therapeutically has become increasingly real as our knowledge of the affected cellular and molecular processes continues to expand.

Reduction of motor behavioural deficits in senescence via chronic prolactin or estrogen administration: time course and putative mechanisms of action

The effects of chronic estrogen (E2), rat prolactin (rPRL), modified ovine prolactin (mPRL) administration on motor behavior (inclined screen performance) and striatal dopamine (DA) (D2subtype) receptor concentrations were examined in senescent (greater than 24 months of age) female rats, mPRL possesses no lactotrophic activity. Administration of either E2 or rPRL was effective in improving both inclined screen performance (increased time that the animal could remain on the screen by 95 and 413 s, respectively, compared to highest pre-injection performance) and striatal D2 receptor concentrations (14 and 20% respectively). These were indications, however, from separate analyses that improvements in inclined screen performance were seen prior to any increases in striatal D2 receptor concentrations. These early performance increases seemed instead to be the result of improved muscarinic receptor control over striatal DA autoreceptor function. Later improvements in inclined screen performance (at 6-7 days after the E2 injections were begun) were more dependent on increased striatal DA receptor concentrations. A second set of experiments which involved the injection of E2 into senescent male as well as female rats indicated that there were no sex differences in improvements in inclined screen performance, and that once the E2 injections were discontinued, performance returned to preadministration levels. The results are discussed in terms of two important processes that may be involved in mediating enhanced inclined screen performance following E2 administration: (1) enhancement of muscarinic receptor regulation of DA autoreceptor function; and (2) increases in striatal DA receptor density.

Antagonism of behavioral effects of bromocriptine by prolactin in female cats

The effects of the dopaminergic agonist bromocriptine (BC) and exogenously administered prolactin (PRL) on the spontaneous behavior of female cats were investigated. The objective was to test whether BC-induced behavioral effects may be antagonized by PRL. BC (6 mg/kg ip) administration induced abnormal behaviors such as limb flicks, abortive grooms, head/body shakes, and hallucinatory-like behavior/escape as well as excessive grooming. PRL (5 mg/kg ip) administration induced biphasic changes in grooming. The first change was an increase in grooming frequency averaging 256% of baseline control values and lasting for 1 h. This change was followed by reductions in grooming of 75 and 82.5% below baseline during Hours 2 and 3 postinjection, respectively. Combined BC and PRL treatment antagonized the frequency of BC-induced motor effects such as limb flicks, abortive grooms, and head/body shakes. Limb flicks occurred nine times more often 2 h after BC alone than after BC and PRL. The combined treatment also antagonized the excessive grooming observed after separate administrations of BC and PRL. The observed interactions between PRL and BC behavioral effects support the notion that PRL may be an important modulator of dopamine-dependent motor behavior in female cats.

Effect of aging on striatal dopamine receptor subtype recovery following N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline blockade and relation to motor function in Wistar rats

Recovery of D1- and D2-dopamine receptors in Wistar rat corpora striata were assessed following N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ blockade). Absolute recovery declines during senescence approximately 25 and 40% for the D1- and D2-subtypes, respectively. Net biosynthetic reductions are comparable to the overall age-related decreases in receptor concentrations for this rat strain. EEDQ administration also induces catalepsy behavior and impairs ability of animals to remain on an inclined screen. Recovery of inclined screen performance is also reduced with age, but is not strictly proportional to recovery of receptor concentrations.