Motivation in concurrent variable-interval schedules with food and water reinforcers

The lever pressing of four food- and water-deprived rats was reinforced on concurrent variable-interval schedules. Food reinforced one response, and water reinforced the other. Response rates in baseline were higher in the food component than in the water component. After response patterns and body weights had stabilized, the animals were given access to either food only, water only, both food and water, or neither food nor water (baseline) before daily sessions. Giving food before a session decreased per cent time in the food component, decreased overall response rates for food, and increased overall response rates for water. Giving water before a session increased per cent time in the food component, increased overall response rates for food, and decreased overall response rates for water. Giving both food and water before a session resulted in a combination of prefeeding and prewatering effects. More food and more water were consumed when both were available than when only one was available before a session.

Kinematic analyses of air-stepping in normal and decerebrate preweanling rats

We studied the ability of L-DOPA (100 mg/kg, subcutaneous) to elicit air-stepping in decerebrate and sham-operated Sprague-Dawley rats from postnatal Day 5 through postnatal Day 20. The most common gait consisted of fore- and hindlimb alternation, but between 10 and 20 days of age, patterns of coordination resembling swimming, in which the forelimbs remained adducted, and galloping became more frequent in both decerebrate and sham-operated rats. Because episodes of galloping were rarely more than two or three step cycles in length, our analyses focused on episodes of stepping in which limbs within the girdles stepped in alternation and diagonal pairs of limbs moved in synchrony ("trot"). The rate of stepping of both decerebrate and sham-operated rats increased from about 2.9 steps/s at Day 5 to about 4 steps/s at Day 20. In both groups, this increase was found to result from a decrease in the duration of the retraction phase of the step cycle. Amplitudes of movement at the wrist, knee, and ankle increased with age in both decerebrate and sham-operated neonates, whereas those of the shoulder, elbow, and hip did not change in either group. The timing of movements at joints within each limb also changed similarly with age in sham-operated and decerebrate pups. During development, forelimb movement was increasingly led by the wrist, which was followed by the elbow and then finally by the shoulder. Hindlimb movements were increasingly led by the knee, followed by the ankle, and finally by the hip. At all ages, diagonal limbs moved in synchrony, and heterolateral limbs within each girdle moved in antiphase. However, the phase relationship between hindlimb and forelimb movements changed both in sham-operated rats and in decerebrate rats during ontogeny. On Day 5, movement of each hindlimb was phase-delayed relative to that of the diagonal forelimb whereas on Days 15 and 20, the hindlimb was phase-advanced. The parallel emergence of different gaits and the similarity of coordination during diagonal progression in sham-operated and decerebrate pups show that age-related changes in gait are mediated no more rostrally than the midbrain.

The locomotor effects of quinpirole in rats depend on age and gender

Periadolescence in the rat [postnatal day (PND) 35-50] is an important but understudied period of neurobehavioral development. In this experiment, an ongoing survey of the effects of quinpirole in developing rats was completed by the addition of periadolescent rats to the range of ages tested. PND40 or 50 rats were injected subcutaneously with the dopamine D2/D3 receptor agonist, quinpirole (0.0, 0.02, 0.2, or 2.0 mg/kg), and their locomotor activity was recorded. Periadolescent rats showed adult-like locomotor responses to either the 0.2 or 2.0 mg/kg doses of quinpirole, i.e., the responses were biphasic with respect to time: early suppression of locomotion followed by later activation within a single test session. In younger female rats (PND40) but older male rats (PND50), the lowest dose of quinpirole suppressed activity early in the test session but did not increase it later. In male rats, the magnitude of locomotor activation declined with age. Taken together with previous data from this laboratory, these results suggest that periadolescent rats exhibit locomotor responses that fall along a continuum from a high level of activation just after weaning to a low level of activation in early adulthood.

The NMDA antagonist, MK-801, alters L-DOPA-induced air-stepping in neonatal rats

Administration of L-DOPA (sc) to neonatal rats suspended in harnesses induces coordinated stepping of all four limbs (diagonal progression; L-DOPA-induced air-stepping) by 5 days of age. Because NMDA also induces locomotion in several species, NMDA receptor activation may be required for L-DOPA to elicit coordinated air-stepping. The purpose of the present experiment was to determine if the NMDA receptor antagonist, MK-801, would block L-DOPA-induced air-stepping in developing rats. Neonatal rats administered MK-801 alone rarely air-stepped with the forelimbs or hindlimbs in a coordinated fashion, whereas those treated with L-DOPA alone primarily stepped with all four limbs using a diagonal progression pattern during the session. In contrast, the number of limbs that stepped during the session was gradually altered in 5- to 20-day-old rats treated with MK-801 + L-DOPA. Gaits of those rats progressed from diagonal progression to extension of the forelimbs beneath the chin with hindlimb alternation, to forelimb extension without hindlimb activity. Twenty-day-olds treated with MK-801 + L-DOPA subsequently became completely inactive when the forelimbs dropped from their elevated position beneath the chin. In addition to the sequence just described, 15-day-old rats treated with the lowest concentration of MK-801 + L-DOPA occasionally stepped with one pair of homolateral limbs or stepped with the hindlimbs in near synchrony while the forelimbs either stepped in alternation, were extended beneath the chin or groomed the face. Because limb participation during L-DOPA-induced air-stepping was altered in neonatal rats pretreated with MK-801, NMDA receptor activation may be important for locomotor coordination (gait).

Locomotion elicited by MK801 in developing and adult rats: temporal, environmental, and gender effects

The effects of environmental novelty on locomotion elicited by an N-methyl-D-aspartate (NMDA) receptor antagonist, (+)MK-801 hydrogen maleate [(5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5, 10-imine], were investigated. Male and female rats aged 10, 20, 30 or 54-68 days were injected s.c. with MK801 and placed in activity monitors either immediately (no-delay) or after a 60 min delay (delay). In the no-delay condition, MK801 induced an inverse U-shaped dose-response effect on locomotion; peak activation occurred with 0.1 mg/kg and ataxia occurred with higher doses. The introduction of a novel environment 60 min after drug injection shifted the dose-effect function of MK801 to the left; i.e., in rats 20 days of age and older, the activity induced by 0.1 mg/kg MK801 was potentiated in the delay condition. For the 0.5 mg/kg dose, 20-day-olds showed activation in the no-delay condition but ataxia in the delay condition. This dose induced ataxia followed by activation in 30-day-olds and adult males or ataxia in adult females, regardless of delay condition. Age-, gender-, and novelty-dependent variations in MK801-induced locomotion may reflect differences in limbic-motor circuitry.

The locomotor effects of MK801 in the nucleus accumbens of developing and adult rats

This developmental study was an investigation of locomotion induced by the NMDA receptor antagonist, (+)MK-801 hydrogen maleate [(5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5, 10-imine], at doses of 0, 3 or 10 microg injected bilaterally into the nucleus accumbens of rats at 11, 21, 31, or 61-66 days of age. During a 2-h test session, only a few 11-day-old pups responded to either dose of MK801; they displayed short bouts of obstinate progression. In contrast, 21- and 31-day-olds were not affected by 3 microg MK801 but exhibited robust activation after 10 microg MK801. The activation was greatest in 21-day-olds and also occurred after mid-striatal injections in 21- but not 31-day-old rats. Adult rats injected with MK801 were not robustly activated, but they maintained their initial level of activity throughout the test session, instead of habituating to the test monitor, as controls did. Ontological changes in MK801-induced activity are likely to reflect maturation of glutamate transmission in the nucleus accumbens.

Temporal and environmental effects on quinpirole-induced biphasic locomotion in rats

The dopamine D2/D3 agonist quinpirole induces suppression of locomotor activity at low doses, and suppression followed by activation at high doses when given to rats of 30 days of age and older that are immediately placed in activity monitors. The duration of suppression is longer and the level of activation is lower at 60 than at 30 days of age, suggesting that the mechanism responsible for the suppression may play a role in the lesser activation in the older rats. However, habituation limits the ability to measure the duration of locomotor suppression. Therefore, 0, 0.2, or 0.2 mg/kg quinpirole was injected S.C. either 30, 60, or 120 min before placing male or female rats of 30 or 60 days of age in activity monitors for 30 min. At both ages, both doses of quinpirole suppressed activity when the animal was placed in the monitor 30 or 60 min after injection; at 60 days the drug also suppressed activity at 120 min after injection. Previously, 0.2 mg/kg quinpirole elicited locomotor activity 60 min after injection in rats placed immediately in activity monitors at both ages. Thus, not only time after injection but novelty of the environment are critical factors in the expression of locomotor suppression or activation in response to quinpirole.

Effects of the putative dopamine D3 receptor antagonist PNU 99194A on motor behavior and emotional reactivity in C57BL/6J mice

Due to the regional expression of D3 dopamine receptors in limbic areas of the brain, there has been considerable interest in the potential role of this receptor subtype in mediating emotional behavior. Previous studies in habituated rats have shown that the putative dopamine D3 receptor antagonist 5,6-dimethoxy-2-(di-n-propylamino)indan (PNU 99194A) increased locomotor behavior. The present study examined the effects PNU 99194A on motor and emotional behaviors in C57BL/6J mice. Motor behavior was assessed in both habituated and nonhabituated mice. Emotional behavior was assessed using the elevated plus-maze and a social context involving an isolated C57BL/6J mouse and a nonaggressive conspecific. In mice habituated to the activity chamber prior to drug administration, PNU 99194A increased locomotion and rearing at lower doses (5, 10 mg/kg) whereas higher doses (20, 30 mg/kg) reduced these behaviors early in the test session. Thigmotaxis was increased independently of the effects on motor behavior. In mice exposed to the activity chamber for the first time, PNU 99194A produced a weak motor activation at lower doses and an initial decrease in motor behavior at higher doses that was followed by an increase in locomotion later in the test session. PNU 99194A had no systematic effects on activity in the elevated plus-maze, but dose-dependently increased flight reactivity in the social reactivity paradigm. These and previous findings raise questions about the role of dopamine D3 receptors in mediating motor behavior and emotional reactivity as well as the pharmacology of this putative dopamine D3 receptor antagonist.

L-DOPA and quipazine elicit air-stepping in neonatal rats with spinal cord transections

Acute mid-thoracic spinal cord transection eliminates hindlimb air-stepping in neonatal rats suspended in harnesses and administered L-DOPA. Because spinal cord transection eliminates all descending inputs to the hindlimb locomotor circuits, this experiment determined if coadministration of L-DOPA and quipazine (serotonin receptor agonist) would induce hindlimb air-stepping in rat pups 24 hr after transection. Hindlimb steps of spinally transected pups that received L-DOPA or quipazine alone were infrequent and slow; hindlimb steps induced by L-DOPA + quipazine occurred more frequently and were faster than those elicited by either drug alone. These findings suggest that catecholaminergic and serotonergic systems both contribute to hindlimb stepping.

L-DOPA and quipazine elicit air-stepping in neonatal rats with spinal cord transections

Acute mid-thoracic spinal cord transection eliminates hindlimb air-stepping in neonatal rats suspended in harnesses and administered L-DOPA. Because spinal cord transection eliminates all descending inputs to the hindlimb locomotor circuits, this experiment determined if coadministration of L-DOPA and quipazine (serotonin receptor agonist) would induce hindlimb air-stepping in rat pups 24 hr after transection. Hindlimb steps of spinally transected pups that received L-DOPA or quipazine alone were infrequent and slow; hindlimb steps induced by L-DOPA + quipazine occurred more frequently and were faster than those elicited by either drug alone. These findings suggest that catecholaminergic and serotonergic systems both contribute to hindlimb stepping.

Dopamine D1 and D2 antagonists block L-DOPA-induced air-stepping in decerebrate neonatal rats

L-DOPA administered to neonatal rats suspended in air elicits stereotypic locomotor activation termed air-stepping; it can be dose-dependently blocked by a dopamine (DA) D1 or D2 antagonist. In order to determine whether the forebrain is the site for this blockade, decerebrate 5-day-old rats were pretreated subcutaneously with either the DA D1 receptor antagonist SCH 23390 (16 mg/kg), the DA D2 receptor antagonist spiperone (6 mg/kg), or vehicle before receiving 100 mg/kg L-DOPA. Both antagonists blocked L-DOPA-induced air-stepping in both decerebrate and intact pups.

A kinematic comparison of L-DOPA-induced air-stepping and swimming in developing rats

In Experiment 1, rats of 5, 10, 15, and 20 days of age were injected with L-DOPA to elicit stepping and videotaped while suspended in air and in warm water. Inter- and intralimb coordination were similar for L-DOPA-induced air-stepping and swimming at all ages. Other parameters of locomotion, such as step length and step rate, varied by substrate. In Experiment 2, pups of 5 to 20 days of age received an injection of L-DOPA or the vehicle and were videotaped while freely swimming. L-DOPA-induced free swimming was more stereotyped and "automatonlike" than that of vehicle-injected animals. Through 15 days of age, all pups swam using all four limbs, but L-DOPA induced stricter synchrony of movement in diagonal limbs than was used by pups injected with the vehicle. At postnatal Day 20, vehicle-injected pups adopted the adult swimming pattern in which only the hindlimbs were used, whereas L-DOPA-injected pups continued to use the immature pattern, diagonal progression with all four limbs. These results suggest that L-DOPA-induced air-stepping and swimming are manifestations of the same central mechanisms and that parameters of L-DOPA-induced stepping are modified by the sensory and/or biomechanical effects of the substrate. Although the free swimming of L-DOPA-injected pups was kinematically similar to vehicle-treated pups, L-DOPA retarded transition to the adult swimming pattern.

The locomotor effects of a putative dopamine D3 receptor agonist in developing rats

Dopamine receptors have been categorized into subfamilies D1 and D2, each with separate roles in dopamine-mediated behaviors. Of the D2 subfamily, the dopamine D3 receptor has been cloned, but the behavioral effects of selectively stimulating the D3 receptor are largely unknown. The purpose of this study was to quantify the locomotor responses of developing rats to the putative dopamine D3 receptor agonist, 7-hydroxy-N,N-di-n-propyl-2-aminotetralin (7-OH-DPAT). One of three doses of 7-OH-DPAT (0.01, 0.10, 1.00 mg/kg) or saline was injected subcutaneously into rats at the age of 10,20,30, or 60 days. Five minutes after the injection, rats were placed in automated activity monitors which recorded locomotor behavior at 5 min intervals for 2 h. The high dose of 7-OH-DPAT increased locomotor activity in rats of all ages. The medium and low doses increased activity in 10- and 20-day-old rats but not in 30- or 60-day-old rats. The level of drug-induced activation peaked at 20 days of age. In 30- and 60-day-old rats, but not 10- and 20-day-old rats, a period of locomotor suppression preceded the activation in response to the high dose of 7-OH-DPAT. In rats aged 20 days and older, the middle and low doses decreased locomotion early in the test session, but activation did not ensue. This dose-response pattern across ontogeny closely resembles that induced by quinpirole, an agonist at the dopamine D2 receptor subfamily.

Sulpiride antagonizes the biphasic locomotor effects of quinpirole in weanling rats

Low doses of dopamine (DA) agonists such as the D2 receptor subfamily agonist quinpirole are thought to stimulate DA autoreceptors selectively, thereby inhibiting locomotor activity. High doses of quinpirole initially suppress and later activate locomotion during a single test-session; the activation is presumably due to stimulation of postsynaptic receptors. The aim of this study was to investigate whether pretreatment with a selective DA D2 receptor antagonist, sulpiride, could block the putative autoreceptor-mediated inhibition at a lower dose than was required to block the postsynaptically mediated activation. Male and female 30-day-old rats were injected SC with one of eight doses of sulpiride (0.313-40 mg/kg) or the vehicle. Sixty minutes later, rats were injected SC with 0.2 mg/kg quinpirole or the vehicle. Five minutes after the second injection, rats were placed in automated activity monitors which recorded locomotor behavior for 60 min at 5-min intervals. Quinpirole at this dose first suppressed and later increased locomotor activity. Sulpiride pretreatment dose-dependently reversed both the early inhibition and later activation of quinpirole-induced locomotion. However, sulpiride did not block the quinpirole-induced early suppression at a lower dose than was required to block the later activation. Thus, there was no evidence that the locomotor suppression elicited by quinpirole is mediated by a more sensitive subset of DA receptors.

L-dopa-induced air-stepping in preweanling rats. II. Kinematic analyses

Coordination of air-stepping elicited by subcutaneous injections of L-DOPA (25-100 mg/kg) was studied in rats from the day of birth through 20 days of age. Results revealed a nearly linear increase in the rate of stepping from about 1.5 steps/s at day 0 to about 4.5 steps/s at day 20, independent of the dose of L-DOPA. The ontogenetic increase in the rate of stepping was found to result from decreases in the duration of both retraction and protraction phases of the step cycle, but the decrease in the retraction phase was greater. There was an ontogenetic increase in the amplitude of movement at the wrist, knee and ankle joints, a slight decline in the amplitude of movement at the elbow and little change in amplitude at either the shoulder or hip. The relative timing of movements at joints within each limb also changed with age. Forelimb movements were led by the wrist throughout development, followed by the elbow and then the shoulder, which increasingly lagged behind the other two joints of the forelimb. Hindlimb movements were increasingly led by the knee, followed by the ankle and then the hip. Diagonal progression, in which the diagonal limbs moved in phase with each other and in antiphase with the contralateral limb of the same girdle, was seen at all ages. However, other gaits, which resembled galloping (air-galloping) and swimming (air-swimming), became more prevalent between 10 and 20 days of age.(ABSTRACT TRUNCATED AT 250 WORDS)

L-dopa-induced air-stepping in preweanling rats. I. Effects of dose and age

The effects of several doses of L-DOPA (25, 50, 75 and 100 mg/kg) on air-stepping were studied in rats on the day of birth and on 5, 10, 15 and 20 days of age. Occurrence of air-stepping increased and latency to air-stepping generally decreased with dose except at 10 days of age; duration of air-stepping increased with increasing dose of L-DOPA at every age. The occurrence of a variety of air-stepping gaits was age-dependent. On the day of birth, air-stepping consisted primarily of episodes of forelimb alternation; on days 5-20, diagonal progression was the predominant gait, but beginning at day 10, episodes of air-swimming, air-galloping and other locomotor patterns were interspersed. Not only could the durations of most of these gaits be increased with increasing dose of L-DOPA, but at some ages, increasing the dose of L-DOPA led to gait changes.

Ontogeny of biphasic locomotor effects of quinpirole

The effects of the dopamine D2/D3 receptor agonist quinpirole (LY171555) on locomotor activity were tested on rats of 10, 15, 20, 30, and 60 days of age. In two separate experiments, doses of 0 (vehicle), 0.02, 0.2, or 2.0 mg/kg quinpirole were injected SC into rats at each age, and their effects measured either for 2 h at 15-min intervals, or 30 min at 5-min intervals. At 10, 15, and 20 days of age, quinpirole significantly increased distance travelled in a dose-dependent manner. At 30 and 60 days of age, quinpirole significantly decreased distance travelled early in the session and increased it later. These results suggest that a dopamine autoreceptor begins to function between 20 and 30 days of age. Concomitant with the appearance of quinpirole-induced locomotor suppression early in the session, the amount of quinpirole-induced activation late in the session declined.

Noradrenergic alpha-1 and alpha-2 antagonists block L-dopa-induced air-stepping in neonatal rats

Five-day-old rat pups suspended in air and administered L-3,4-dihydroxyphenylalanine (L-DOPA) engage in a highly stereotyped and coordinated locomotor behavior termed air-stepping. L-DOPA is a precursor for dopamine and noradrenaline and one or both of these neurotransmitters could play a role in L-DOPA-induced air-stepping. The role of noradrenaline was investigated by assessing the abilities of the alpha-1 noradrenergic receptor antagonist prazosin and the alpha-2 noradrenergic receptor antagonist idazoxan to block L-DOPA-induced air-stepping in 5-day-old rats. Both antagonists decreased the duration of air-stepping. In addition, prazosin altered the topography of air-stepping by interfering with coordination of the hindlimbs. The results suggest that alpha-1 and alpha-2 noradrenergic receptor subtypes are involved in L-DOPA-induced air-stepping.

Differential effects of SCH 23390 on immobility behaviors in developing rats

The effects of a single injection of a dopamine D1 antagonist, SCH 23390, at doses of 0, 0.05, 0.1, and 0.2 mg/kg on three different kinds of immobility behavior were tested in rats of 10, 15, 20, and 30 days of age. Each animal was tested for the dorsal immobility response (DIR), vertical cling catalepsy, and bar catalepsy. A different pattern of results was found for each of the three immobility behaviors. SCH 23390 significantly increased the DIR at each age except 15 days; there was a progressive increase in effect from 10 to 20 to 30 days of age. At the lowest dose, drug-induced bar catalepsy peaked at 15 days of age and declined at 20 and 30 days of age. The effect of SCH 23390 on vertical cling catalepsy increased with age, plateauing at 20 days. Thus, the developmental pattern of immobility responses to this dopamine D1 antagonist differs with each behavior measured.

Locomotor activity following intra-accumbens microinjections of dopamine D1 agonist SK&F 38393 in rats

The present study examined the effects of the dopamine D1 receptor subtypes agonist SK&F 38393 on locomotor activities after bilateral microinjection (0.00, 0.01, 0.1, 1.0, 10.0 micrograms) into the nucleus accumbens (Acb). The dose of 0.1 microgram elicited the highest response rate across measures of locomotion, rearing and stereotypy behavior. On the other hand, the largest dose of 10.0 micrograms was associated with significant increase in center time behaviors. The data were supportive of the hypothesis that dose-related locomotor activities elicited by microinjections of SK&F 38393 into the Acb are independently mediated by D1 receptors.

Effects of dopamine D1 antagonists SCH23390 and SK&F83566 on locomotor activities in rats

The effects of the dopamine D1 antagonists R-(+)-7-chloro-8-hydroxy-3-methyl-1phenyl-2,3,4,5-tetrahydro-1-H-3 -benzazapine (SCH23390) and (+-)-7-bromo-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1- H-3-benzazapine (SK&F83566) were tested for 2 h on linear locomotor, rearing, stereotypy, and margin times in an open field. Each of the antagonists attenuated the duration of linear locomotion, rearing, and stereotypy times in a dose- and time-dependent manner. The effectiveness of the antagonists was relatively brief and SCH23390 was more effective than SK&F83566 on each behavior. The two antagonists had differential effects on margin time.

Intracerebral haloperidol potentiates the dorsal immobility response in the rat

The effects of intracerebral microinjections of 4-[4-(4-chlorophenyl)-4-hydroxy-1-piperidinyl]-1-(4- fluorophenyl)-1-butanone (haloperidol) (1.0 microgram, 0.5 microliter) in five regions of the brain were tested on the duration of the dorsal immobility response (DIR) and the cling and bar catalepsy in the rat. The duration of the DIR was significantly potentiated (but not the cling and bar catalepsy) following 2-h postinjection of haloperidol in the caudate putamen, nucleus accumbens, and globus pallidus but not in the substantia nigra pars compacta or cortex. These data further expand the previous evidence of regional variations in dopamine to the effects upon inhibitory behaviors.

Differential effects of intrastriatal estradiol on the dorsal immobility response in male rats

The effects of implants of 17 beta-estradiol and cholesterol in four regions of the dorsal striatum were tested on the duration of the dorsal immobility response in gonadectomized male rats. The dorsal immobility response was significantly potentiated by 4-h implants of 17 beta-estradiol in the dorsomedial and dorsolateral regions of the dorsal striatum but not in the ventromedial and ventrolateral regions. These data further support the growing evidence that estradiol acts directly but differentially on the striatum to affect behaviors in the rat.

Dopamine D1 and D2 antagonists block L-dopa-elicited air-stepping in neonatal rats

When administered to rat pups that have been suspended in air, L-3,4-dihydroxyphenylalanine (L-DOPA) induces a highly stereotypic locomotor response referred to as air-stepping. In order to determine the respective roles of dopamine D1 and D2 receptors in the expression of air-stepping, the abilities of the selective D1 antagonist SCH 23390 and the selective D2 antagonist spiperone to block L-DOPA-induced air-stepping in 5-day-old rat pups were assessed. Both antagonists increased latency to onset, and both decreased total duration of air-stepping by decreasing the number and length of air-stepping episodes. Neither SCH 23390 nor spiperone altered the topography of the air-stepping response; however, subjects receiving lower doses of spiperone spent significantly more time with the body dorsiflexed and limbs extended (extension/tremor activity) than did control subjects. The results suggest that both the D1 and D2 receptor subtypes are involved in the production of L-DOPA-induced locomotor activity.

Differential effects of dopamine D2 agonist quinpirole upon the dorsal immobility response in rats

The effects of various dose levels of systemically injected quinpirole upon the dorsal immobility response (DIR) over a time course was investigated in male rats. A low dose of quinpirole (0.01 mg/kg) significantly attenuated the duration of the DIR following the 10-min interval, whereas the highest dose (1.0 mg/kg) had a biphasic effect so that at the 10-min interval the duration of the DIR was significantly potentiated and at the 60-min interval the duration of the DIR was significantly attenuated. The intermediate dose (0.1 mg/kg) had intermediate behavioral effects. The data support the growing evidence that quinpirole has differential effects upon behavior over time as a function of the dose levels. The present data were discussed in reference to presynaptic and postsynaptic dopamine D2 receptor theory.

Effects of intracerebral quinpirole on locomotion in rats

The effects of the dopamine D2 receptor agonist quinpirole (LY 171555) on locomotor activity and margin time (thigmotaxis or wall-hugging) were measured for 2 h in rats injected either s.c. (vehicle, 0.02, 2.0 mg/kg) or directly into either the dorsal striatum or nucleus accumbens (vehicle, 0.1, 1.0, 10, 20 or 40 micrograms bilaterally in each site). In all groups, margin time decreased as drug dose increased. As in previous research, quinpirole given s.c. decreased locomotor activity at a low dose and had a biphasic effect on locomotor activity at the high dose. Both of these effects were also elicited by quinpirole injected directly into the dorsal striatum; 10 and 20 micrograms decreased locomotion immediately, while 40 micrograms led to both the immediate decrease and a later increase. In contrast, the lowest doses of quinpirole (0.1 and 1.0 microgram) injected into the nucleus accumbens led to an increase in locomotion from 20 to 60 min, while the higher doses led only to the early decrease. Thus, both the locomotor activating and inhibiting effects of quinpirole are found in both the nucleus accumbens and the dorsal striatum, but the differing dose-response relationships indicate that the mechanisms are not the same in these two brain regions.

Dopamine D1 antagonists potentiate the durations of bar and cling catalepsy and the dorsal immobility response in rats

The effects of dopamine D1 antagonists SCH 23390 or SK&F 83566 (at SC doses of 0.00, 0.01, 0.05, and 0.1 mg/kg) were tested for 2 h on bar and cling catalepsy and the dorsal immobility response. Each of the drugs potentiated the duration of each of the three measures of immobility in a dose- and time-dependent manner. Each of the drugs had rapid but brief effects on all three response measures; the peak effect of SK&F 83566 took place at 20 min and that for SCH 23390 at 40 min for each behavior. At each effective drug dose, SCH 23390 had a greater effect than SK&F 83566 on each behavior. Dopamine D1 antagonists potentiated three different immobility responses, as do dopamine D2 antagonists.

L-dopa-induced air-stepping in decerebrate developing rats

Developing rats were anesthetized and a precollicular brainstem transection performed. Administration of L-3,4-dihydroxyphenylalanine (L-DOPA, 100 mg/kg, s.c.) induced locomotion in groups of animals 0-3, 6-8, 14-16 and 20-22 days of age. At early stages in development (0-3 days), continuous, long-lasting air-stepping was induced consisting of 4-limb walking with stronger alternation in the forelimbs compared to the hindlimbs. At 6-8 days of age, continuous air-stepping was characterized by better agreement between forelimb and hindlimb step cycles. By 14-16 days of age, the hindlimbs showed stronger and faster stepping than the forelimbs. The first evidence of consistent galloping was observed in this age group. In some cases, the forelimbs were held extended and only the hindlimbs walked or galloped. At 20-22 days, walking and galloping became episodic and the hindlimbs typically galloped while the forelimbs alternated. Each age group was tested for overground locomotion. Only in the 20-22 day group was weight-bearing overground stepping observed. At earlier ages, limb alternation was evident but of insufficient strength to lift the body off the ground. In general, the duration of the effect of the same dose of L-DOPA decreased with age. Animals in each group which received a mid-thoracic spinal cord transection showed forelimb alternation but not hindlimb stepping. These results indicate that L-DOPA induces stepping by activating brainstem and/or spinal centers via an as yet unknown mechanism. The pattern of the development of gait (forelimb to hindlimb gradient) at various ages was similar to that observed in intact developing rats.

L-dopa-induced air-stepping in developing rats

Rat pups at postnatal day (PN) 0, 5, 10, 15, and 20 were injected with 100 mg/kg L-3,4-dihydroxyphenylalanine (L-DOPA; s.c.) or the control vehicle and suspended in a sling. L-DOPA induced highly stereotyped air-stepping that varied along several dimensions across development. The latency to air-stepping was constant across age, but the duration was significantly shorter in the older pups. At all ages, air-stepping was preceded or accompanied by raising of the head and dorsiflexion of the tail. The rate of stepping increased across age and gait varied with age. At PN 0, L-DOPA induced alternating forelimb movements with little involvement of the hindlimbs. At PN 5 and 10, both forelimb and hindlimb alternation were observed. At PN 10 and 15 swimming-like behavior emerged, and at PN 10, 15, and 20, episodes of galloping were interspersed with limb alternation. Thus, highly coordinated activity can be elicited by L-DOPA at all ages studied when the rat pup needs not support its own body weight and has no contact with a substrate. Drug-induced air-stepping promises to be an important new paradigm for pharmacological and behavioral studies of the development of locomotor controls in mammals.

Effects of cholinergic agonists on the dorsal immobility response

The effects of pilocarpine, arecoline, and physostigmine on the dorsal immobility response in ovariectomized female rats were tested. The effect of pretreatment with the cholinergic antagonist scopolamine was also tested. Pilocarpine, arecoline, and physostigmine all significantly decreased the duration of the dorsal immobility response in a dose-dependent way. Scopolamine significantly blocked the effect of pilocarpine. Thus, cholinergic agonists attenuate the dorsal immobility response via their effect on cholinergic systems in the central nervous system.

Effects of intrastriatal hormones on the dorsal immobility response in male rats

Previous research has shown that estradiol administered either peripherally or directly into the striatum potentiates the dorsal immobility response (DIR) in ovariectomized female rats. Male rats are even more responsive than females to intrastriatal estradiol, and furthermore respond to the effects of catecholestrogens while females do not. In order to determine whether the heightened effects of estrogens in males are due to conversion to catecholestrogens, castrated male rats were given bilateral intrastriatal implants of moxestrol, which cannot be readily converted to a catecholestrogen, and diethylstilbestrol, which can. To determine whether the effects of intrastriatal estradiol in male rats might be related to the effects of androgens on the striatum, castrated male rats were given bilateral intrastriatal implants of testosterone, which can be aromatized to estrogen, and 5 alpha-dihydrotestosterone, which cannot. The effects of each of the hormones tested were measured against those of cholesterol (an inactive control substance) and 17 beta-estradiol. In each case the DIR was measured four hours after the hormone implant. Both synthetic estrogens and 17 beta-estradiol significantly potentiated the DIR, while neither of the androgens had an effect. Thus, the effects of estradiol, synthetic estrogens and catecholestrogens on the male striatum appear to be due to the estrogenic properties of these hormones.

Effects of intrastriatal hormones on the dorsal immobility response in the rat

Previous research has shown that the dorsal immobility response (DIR) changes significantly in duration across the estrous cycle. In order to test whether gonadal steroid hormones act directly on the striatum to modulate this behavior, ovariectomized female Long-Evans hooded rats were given bilateral intrastriatal implants of 17 beta-estradiol, 2-hydroxyestradiol, progesterone, or cholesterol. These implants were made at one-week intervals, each animal receiving each treatment in a Latin square design. Four hours after each hormone implant, the animals were tested for the DIR. Only rats receiving the intrastriatal 17 beta-estradiol implant were significantly different from those receiving cholesterol, and showed greatly potentiated DIR's.

The effects of intrastriatal hormones on the dorsal immobility response in gonadectomized male and female rats

Previous research has shown that intrastriatal estradiol potentiates the dorsal immobility response in ovariectomized female rats. In order to test whether the gonadal steroid hormones act on the male striatum in the same way, gonadectomized male and female Long-Evans hooded rats were given bilateral intrastriatal implants of 17 beta-estradiol (17 beta-E2), 17-alpha-estradiol (17-alpha-E2), 2-hydroxyestradiol (2-OH-E2), 4-hydroxyestradiol (4-OH-E2), or cholesterol. Four hours after the hormone implant the dorsal immobility response (DIR) was measured. In the ovariectomized females, the DIR was significantly potentiated only by 17 beta-E2 and 17-alpha-E2. In the castrated males, the DIR was significantly potentiated by 17 beta-E2, 17-alpha-E2, 2-OH-E2, and 4-OH-E2. While the DIR durations did not differ between males and females after intrastriatal cholesterol, the males had significantly longer DIR durations after each of the other hormones. These results are discussed in terms of estradiol stereospecificity and the properties of catechol estrogens in male and female rats.

Effects of intracerebral estradiol on the dorsal immobility response in the rat

The effects of intracerebral implants of 17 beta estradiol and cholesterol in five brain regions were tested on the duration of the dorsal immobility response in ovariectomized female rats. The dorsal immobility response was significantly prolonged by 4-hr implants of 17 beta estradiol in the dorsal striatum and nucleus accumbens, but not in the cortex, the globus pallidus, or the substantia nigra pars compacta. These data further support previous evidence that estradiol acts directly on the striatum to affect behavior in the rat.

Transient midline raphe glial structure in the developing rat

A major glial structure is present during development within the midline raphe of the midbrain, hindbrain, and cervical spinal cord of the rat. It is composed of great numbers of glial cell bodies lying immediately ventral to the cerebral ventricular system and the large radial processes extending from these cells toward the ventral surface of the brain roughly within the midsagittal plane. There is also a smaller group of glial cells on the dorsal surface of the aqueduct and the central canal whose processes extend to the dorsal surface of the brain. The entire structure exhibits an intensely positive immunoreactivity with the antibody to the S-100 protein, a nervous-system-specific protein found primarily in the cytoplasm of astrocytes. This immunoreactivity makes possible a clear visualization of the extent, magnitude, and continuity of this structure from at least embryonic day 15, the first age examined, until postnatal days 7-8, when it is no longer visible by this technique. This glial structure has several prominent morphological characteristics. During prenatal and early postnatal development the fibers forming the ventral aspect of the structure in the midbrain and hindbrain are formed into two parallel plates on either side of the midline with S-100-negative tissue between the plates. As development progresses, S-100-positive fibers are continually added so that the plates become thicker at the expense of the nonstaining intervening area. By postnatal day 4 only a single midline plate of fibers is visible, occupying the entire midline raphe. In the region of the pontine flexure the entire structure takes on a distinctly pleated configuration. This fact produces a curious "sine wave" appearance when the plane of section crosses these vertical pleats. At postnatal day 5 the structure begins to disappear, and it is no longer visible by 7-8 days postnatal. This glial structure does not stain with antisera to glial fibrillary acidic protein, a protein associated with fibrous astrocytes, or routine cell stains such as cresyl violet. With these techniques the raphe area appears essentially devoid of identifiable cellular elements.

Effects of estrogen on the basal ganglia

Recent research suggests that estrogen regulates the activity of dopamine-containing fibers originating in the midbrain and terminating in the basal ganglia, and/or dopamine-sensitive cells in the basal ganglia. The mechanism by which estrogen acts is not clear, since cells in neither of these regions concentrate estrogens. Nevertheless, estrogens clearly affect behaviors mediated by the basal ganglia, as illustrated in human patients suffering from extrapyramidal disorders. Both biochemical and behavioral research in animals has confirmed that estrogen modulates basal ganglia function, but there has not been agreement concerning either the locus, the direction, or the mechanism of its action. These topics are the focus of this review. The effects of estrogen on behaviors mediated by DA in the basal ganglia depend on the dose of estrogen administered, the time interval between estrogen treatment and testing, the behavior measured, and the part of the basal ganglia from which the behavior is elicited. A high dose of estrogen results in an initial suppression and later enhancement of DA-related behaviors elicited from the striatum. However, no later enhancement of these behaviors occurs if a low dose of estrogen is given. Even after low doses of estrogen, the latency to behavioral suppression varies depending upon the behavior measured. These varying latencies suggest that more than one mechanism is involved in the effects of estrogen on basal ganglia output. In addition, estrogen may also act on some regions in the mesolimbic DA system. While estrogen may act indirectly via the catechol estrogens and prolactin, it has been demonstrated that estrogen can act directly on the striatum. These findings are related to the effects of estrogen on human extrapyramidal disorders.

Effects of estrus, estrogen-progesterone priming, and vaginal stimulation on tonic immobility, dorsal immobility, and lordosis in the female rat

Three complex inhibitory responses, tonic immobility, the dorsal immobility response, and lordosis, were studied in the intact female rat during estrus and diestrus and in ovariectomized rats with estrogen-progesterone treatment or controls. In each condition, the effects of vaginal-cervical stimulation were also studied. The results of two experiments indicate that estrus and estrogen-progesterone treatment significantly potentiate lordosis and the dorsal immobility response with or without vaginal-cervical stimulation. Tonic immobility was also potentiated by estrus and estrogen-progesterone treatment, but only if vaginal-cervical stimulation was applied. Vaginal-cervical stimulation potentiated both tonic immobility and the dorsal immobility response, but not lordosis, which was already at a high level.

Effects of ovariectomy and estrogen replacement on intrastriatal dopamine-elicited postural deviation

The effects of ovariectomy, sham ovariectomy, and estradiol benzoate replacement on unilateral intrastriatal dopamine-induced postural deviation were studied in rats. Animals were tested prior to surgery, and at both two and seven days after surgery. Relative to the pre-surgery test, ovariectomized rats greatly increased this behavioral response two days after surgery while sham ovariectomy resulted in no significant change. Estradiol benzoate treatment in ovariectomized animals not only prevented this increase but significantly suppressed it at both two and seven days after surgery relative to pre-surgery levels. Thus, removal of endogenous estrogen in female rats resulted in an acute increase in a striatal DA-mediated behavior which could be prevented by hormone replacement. These results are consistent with the hypothesis that estrogen suppresses some striatal DA-mediated behaviors.

Dopamine-mediated behaviors: characteristics of modulation by estrogen

Several behaviors produced by intrastriatal injection of dopamine (DA) and amphetamine (AMPHET) in ovariectomized (OVX) rats were each modulated by estradiol benzoate (EB) in different ways. Contralateral postural deviation and rotation, induced by unilateral injections of DA and AMPHET into the dorsal striatum, were differentially suppressed with EB treatment. Postural deviation was suppressed by 1/2 hour after a single treatment with EB (2 micrograms). In contrast, suppression of contralateral rotation required two treatments with EB separated by an interval of 48 or 96 hours, and the suppression was observed at 24 hours after the last treatment with EB. However, treatment with the antiestrogen CI-628 blocked the suppressive effects of EB on either behavior. The enhanced locomotion produced by bilateral injections of AMPHET into the ventral striatum was not suppressed with EB. In fact, AMPHET-enhanced locomotor activity decreased after a 3-week absence of estradiol as a consequence of OVX, and was returned to early OVX levels by EB. Therefore, postural deviation, rotation, and locomotor activity are mediated by different underlying mechanisms in the striatum and are affected differently by estradiol.

Haloperidol differentially potentiates tonic immobility, the dorsal immobility response, and catalepsy in the developing rat

The effects of a single subcutaneous injection of haloperidol (1 or 10 mg/kg) or the vehicle solution on three kinds of behavioral inhibition were investigated in rats of 10, 15, and 20 days of age. The behaviors measured were tonic immobility, a response induced by placing an animal on its back supported by a V-shaped trough; the dorsal immobility response, which can be elicited in young rodents by grasping the skin of the dorsal surface of the neck and lifting the animal into the air; and catalepsy, a form of immobility in which animals remain in unusual postures but are capable of righting themselves, and which can be elicited by drugs which block dopamine receptors. Haloperidol (10 mg/kg) significantly potentiated the duration of tonic immobility only at 10 days of age; potentiated catalepsy at all age levels, but significantly less in the 15-day-old rats than in the 10- or 20-day-old rats; and potentiated the duration of the dorsal immobility response in the 10- and 20-day-old animals but not in the 15-day-olds. These results are discussed with respect to the development of neurotransmitter systems in the brain.

Estradiol application to one striatum produces postural deviation to systemic apomorphine

In order to test whether estrogen acts directly in the dorsal striatum to affect dopamine-mediated behavior, ovariectomized female Long-Evans rats were given a unilateral striatal application of estradiol, injected systemically with apomorphine (APO), and tested for lateralization of stereotypic behaviors. In the first experiment, estradiol, cholesterol, or an empty cannula was inserted and the rat given 0.7 mg/kg APO 1-4 hours later. Rats directed their stereotypic behaviors to the side ipsilateral to the insert of estradiol with dorsal striatal inserts, but not with inserts in ventral striatum or neocortex. Neither cholesterol nor the empty cannula inserts were effective in producing lateralization of the stereotypic behaviors. In the second experiment, intrastriatal inserts of 17 alpha-estradiol were ineffective in producing a lateralization of APO-induced stereotyped behavior. In the third experiment, several doses of APO (0.07, 0.75 and 3.0 mg/kg) were tested. At the highest dose no lateralization of APO-induced stereotypic behavior was observed. These results strongly suggest that estradiol acts directly in the dorsal striatum to antagonize APO and thus produce a lateralization of stereotypic behaviors (postural deviation).

Behaviors induced by intrastriatal dopamine vary independently across the estrous cycle

Unilateral intrastriatal injections of dopamine (DA; 25 micrograms/0.25 microliters) or amphetamine ( AMPHET ; 25 micrograms/0.25 microliters) induced contralateral postural deviation and contralateral rotation that varied systematically across the estrous cycle of Long-Evans hooded rats. Both the deviation and rotation elicited by either drug were suppressed during the early part of the day of proestrus (2-6 hours after lights on) and were enhanced on the day of estrus, compared to the other days of the estrous cycle. However, when the behaviors elicited by the two drugs were examined across the day of proestrus, it was found that postural deviation and rotation changed independently. Postural deviation elicited by intrastriatal DA and AMPHET was suppressed on the day of proestrus at 4 and 7 hours after lights on, but was enhanced to the level seen during estrus at 11 hours after lights on. In contrast, contralateral rotation induced by either drug was suppressed 4, 7 and 11 hours after lights on and was enhanced only by the morning of estrus. These data suggest that there are separate DA-modulated mechanisms within the striatum for postural deviation and contralateral rotation, and that these mechanisms are differentially affected across the estrous cycle.

Systemic apomorphine reverses intrastriatal dopamine-induced contralateral deviation

Contralateral deviation induced by unilateral injection of 25 micrograms or 100 micrograms dopamine into the dorsal CPU was reversed to ipsilateral deviation by apomorphine administered systemically (1 mg/kg s.c.) before, at the same time, or after the dopamine. Contralateral deviation to a unilateral intrastriatal injection of 6.25 micrograms apomorphine was also reversed to ipsilateral deviation by systemically administered apomorphine. No significant effects on postural deviation were found when a control solution was injected unilaterally into the striatum, followed by systemic apomorphine. Contralateral deviation to the unilateral intrastriatal dopamine injection continued following a further bilateral intrastriatal injection of either dopamine or apomorphine. These results suggest that intrastriatal dopamine indirectly affects sites receptive to dopamine outside the striatum.

Behavioral effects of unilateral dopamine injection into dorsal or ventral striatum

Dopamine or its vehicle saline was injected unilaterally into dorsal striatum, ventral striatum, or sites outside the striatum in adult male rats. Direction, duration and frequencies of ongoing behaviors were measured. Dopamine injected into any site within the striatum immediately elicited more contralaterally directed behavior than the vehicle injected into the same site. The contralaterally directed behaviors were no longer duration when injected into the dorsal than into the ventral striatum, a result which might reflect regional differences in numbers of dopamine receptors or distribution of efferents. At the doses employed (25 and 100 microgram), dopamine injected unilaterally into the striatum did not induce rotation, stereotyped behavior, or even a significant change in the frequencies of ongoing behaviors; rather, all ongoing behaviors were expressed in a contralateral direction. Thus, the behavioral effects of dopamine in the striatum are best understood as a change in sensory-motor responsiveness.

Functional development of dopamine receptors in the rat forebrain

Dopamine (DA) was injected unilaterally into the dorsal caudate-putamen (D-CPU), ventral caudate-putamen (V-CPU), piriform cortex (PIR), olfactory tubercle (OTU) and frontal cortex (FC) of two day old rats and rotational behavior observed. Injection of DA into D-CPU, PIR, and OTU produced a contralateral postural deviation which differed significantly from the ipsilateral deviation produced by control injections. Only DA injections into PIR and OTU produced contralateral turning differing significantly from the effects of control injections. These results suggest that the DA receptors in C-CPU, PIR, and OTU involved in rotational behavior are functionally mature at two days of age and that the two components of rotation, postural deviation (direction) and turning (locomotion), involve different neural systems at this age. The developing rat is suggested as a valuable tool for understanding the neural circuitry and pharmacology of rotational behavior.

Behavioral effects of unilateral basal gangliar lesions in neonatal rats

Two-day-old rats were given unilateral lesions of the caudate-putamen, globus pallidus, or hippocampus and their postural orientation was observed for 30 min immediately after surgery. All groups with damage to the caudate-putamen and/or globus pallidus showed a significant postural deviation toward the side ipsilateral to the lesion. At this age, neurogenesis in the basal ganglia is complete but synapses, neurotransmitters, and enzymes for neurotransmitter synthesis are far below adult levels. These results indicate that the basal ganglia have a role in motor function prior to their full maturation as measured by neuroanatomical and biochemical techniques.

Epileptogenic effects of several penicillins and penicillin-related compounds in rat neocortex

Several penicillins and penicillin-related compounds were tested for their ability to produce epileptiform activity in rat neocortex. (1) Alterations in the side chain of penicillin G decreased epileptogenic capability in all the compounds tested in this study: Phenoxymethylpenicillin produced a primary focus but no mirror focus, suggesting a dissociation of the mechanisms underlying these two processes. Ampicillin, 6-aminopenicillanic acid, and potassium 6-aminopenicillanic acid, and potassium 6-aminopenicillanic acid produced little or no epileptiform activity. All these compounds have free amino grounds and are amphoteric. (2) Breaking the beta lactam ring of penicillin G (potassium penicillin G penicilloate) eliminated epileptogenic capability. (3) Potassium salts of penicillin or its derivatives (potassium penicillin G, propicillin, potassium 6-aminopenicillanic acid, potassium penicillin G penicilloate) consistently suppressed cortical activity, regardless of the ability of the compound to produce spike discharges. Thus, mechanisms underlying these two properties can be dissociated. (4) Antibiotic activity of penicillins bears no relationship to epileptogenic capability.

Effects of differential hippocampal damage upon rhythmic and stress-induced corticosterone secretion in the rat

The effects of dorsal, ventral, and near-total hippocampal lesions upon both rhythmic and stress-induced corticosterone secretion in adult male rats were examined. All hippocampally-damaged, cortically-damaged, and intact rats showed rhythmic corticosterone secretion as measured in 4 blood samples for each animal taken at 6-h intervals at least 1 week apart. There were no significant differences among the groups. In addition, there were no significant differences in the amount of stress-induced corticosterone across experimental groups.