Unilateral mesolimbicocortical dopamine denervation decreases locomotion in the open field and after amphetamine

Loss of cocaine locomotor response in Pitx3-deficient mice lacking a nigrostriatal pathway

Both the dorsal and ventral striatum have been demonstrated to have a critical role in reinforcement learning and addiction. Dissecting the specific function of these striatal compartments and their associated nigrostriatal and mesoaccumbens dopamine pathways, however, has proved difficult. Previous studies using lesions to isolate the contribution of nigrostriatal and mesoaccumbens dopamine in mediating the locomotor and reinforcing effects of psychostimulant drugs have yielded inconsistent and inconclusive results. Using a naturally occurring mutant mouse line, aphakia, that lacks a nigrostriatal dopamine pathway but retains an intact mesoaccumbens pathway, we show that the locomotor activating effects of cocaine, including locomotor sensitization, are dependent on an intact nigrostriatal dopamine projection. In contrast, cocaine reinforcement, as measured by conditioned place preference and cocaine sensitization of sucrose preference, is intact in these mice. In light of the well-established role of the nucleus accumbens in mediating the effects of psychostimulants, these data suggest that the nigrostriatal pathway can act as a critical effector mechanism for the nucleus accumbens highlighting the importance of intrastriatal connectivity and providing insight into the functional architecture of the striatum.

Effects of chronic neuroticization on the monoaminergic systems of different structures in the brains of rats with different typological characteristics

The levels of monoamines and their metabolites were studied by HPLC with electrochemical detection in homogenates of hypothalamus, hippocampus, prefrontal cortex, and amygdala in intact and neuroticized Wistar rats with different types of behavior in the open field and forced swimming tests. Intact rats with intermediate levels of activity and depressivity had higher serotonin concentrations in the hypothalamus and lower noradrenaline and hydroxyindoleacetic acid levels in the hippocampus than rats characterized by low activity and high depressivity. In neuroticization, the levels of study monoamines and their metabolites decreased in all the brain structures investigated with the exceptions of an increase in the dopamine concentration in the hippocampus and the dihydroxyphenylacetic acid concentration in the prefrontal cortex. The effect of neuroticization on the neurotransmitter systems in all study structures except the hypothalamus depended on the typological characteristics of the rats. This was most marked in rats with the extreme types of behavior--active and passive--in which changes in monoamine and metabolite contents were seen in all brain structures studied. Rats of the intermediate type showed no changes in any of the substances studied in the hippocampus.

Lifetime influence of one year with Gerry Smith

I spent just one year working with Gerry Smith; it was during the research elective portion of my last year of psychiatry residency. That single year's experience has had a lasting influence on my career choices, not just in terms of content of work, but also in the approach to the professional life as a whole. Whereas the work I do today may bear little direct resemblance to what I did in the Bourne Laboratory more than 25 years ago, Gerry had a major influence on the what and the how of my professional career. Gerry was more than a mentor; he was a friend, philosopher, and guide. He promoted a value system that included a passion for learning and collegiality. He always stressed that empirical data trumped expert opinions, and that it was necessary to challenge long-held scientific dogmas from time to time. Through personal example, he showed the importance of giving back to one's trainees what one had received from the mentors. He also showed how even animal research could be an enjoyable social activity. Last but not least, Gerry's way of treating the laboratory staff, including faculty and trainees, as a family, was one of a kind. Most mentors are useful for teaching content of research; Gerry is one of those few who serve as role models-not only as scientists but also as professionals.

Biochemical correlates of individual behavior

This article is a review of data (results of the authors' investigations and data from the literature) concerning neurochemical correlates of individual behavior in rats. The "emotional resonance" test was used for behavioral selection of rats. Individual behavior in this test is related to the differences in free radical-mediated processes, membrane lipid content, nitric oxide synthase activity, and cAMP pattern in cerebral macrostructures. Behavior-related differences may be revealed in intact animals; however, most of them are reactive (induced by significant external factors). These differences depend on age; they may be global, specific for selected brain regions, and/or related to interhemisphere lateralization of biochemical parameters.

Lack of an inhibitory effect of hyperprolactinemia on androgen-dependent marking

An experiment was performed to determine if hyperprolactinemia (chronically elevated serum prolactin levels), which inhibits testosterone-activated male sexual activity, also affects other androgen-dependent behaviors. Thus defecation and urine marking in response to a novel environment were examined in sham-operated and pituitary-grafted (hyperprolactinemic) male rats that had been castrated or castrated and given subcutaneous testosterone implants. Both castration and pituitary grafting significantly inhibited defecation, with the inhibitory effects of hyperprolactinemia being most pronounced in the castrated non-testosterone-treated animals. In contrast, castration significantly reduced the amount of urine marking observed, but pituitary grafting was without effect on this behavior. Thus, although hyperprolactinemia may inhibit sexual activity through an antagonism of the activational effects of testosterone, these results suggest that this effect is specific to sexual behavior and does not involve a more generalized inhibition of the effects of testosterone on androgen-dependent behaviors.

Daily changes in pentylenetetrazol-induced convulsions and open-field behavior in rats

Susceptibility to pentylenetetrazol (PTZ)-induced clonic convulsions was measured in rats over the 24-hr light-dark cycle at four-hour intervals. The results showed a higher sensitivity to PTZ around 2200 hr. Other groups of rats were exposed to a four-min open-field session. In the first two min of the session the animals were submitted to open-field environmental stimuli. The next two-min observation occurred with sound and light presented to the animals. Differences through the 24-hr period of the day for both sessions were seen. A reduction in rearing at 2200 hr and increase in defecation at 2200 hr and 0200 hr was observed.

Extra-hypothalamic dopamine is not involved in the effects of hyperprolactinemia on male copulatory behavior

Experiments were performed to determine if the inhibition of copulatory behavior observed in male rats with chronically elevated serum prolactin levels (hyperprolactinemia) is associated with changes in central dopaminergic function in the nigrostriatal and mesolimbic systems. Chronic hyperprolactinemia, induced by ectopic pituitary grafts, inhibited sexual activity but was not associated with changes in locomotor activity, serotyped behavior in response to various doses of apomorphine, or 3H-spiroperidol binding to striatal homogenates. However, open-field defecation was reduced in the pituitary grafted animals. The results of the present study show that changes in nigrostriatal dopamine receptor sensitivity do not contribute to the inhibition of sexual behavior in hyperprolactinemic male rats. In addition, these results also demonstrate that the effects of hyperprolactinemia are relatively specific to copulatory behavior and appear not to involve general behavioral suppression.

Role of dopaminergic system(s) in mediation of the behavioural effects of bombesin

To test the effects of dopamine receptor blockade on bombesin (BN)-induced behavioural changes, adult male Sprague-Dawley rats were administered fluphenazine (0.01, 0.025, 0.1, 0.25 mg/kg, IP) followed 30 min later by BN (1 micrograms in 5 microliter) or saline (5 microliter) intracerebroventricularly (ICV). Subsequent behavioural effects were monitored in chambers equipped with strategically located infrared beam grids, controlled by a microprocessor. The following behaviours were monitored: locomotor activity (distance traversed), floor activity (horizontal or lateral displacement) and rearing activity (frequency of vertical displacement extending 17.8 cm above the floor). At all but the highest dose (0.25 mg/kg, which suppressed floor activity), fluphenazine failed to significantly alter any of the behavioural parameters monitored. Whereas at doses of 0.025 or lower, fluphenazine failed to alter BN-induced behavioural output, at doses of 0.1 mg/kg or greater, it significantly blocked the behavioural effects BN. In the next experiment, dopamine neurons of adult male Sprague-Dawley rats were lesioned using 6-hydroxydopamine (6-OHDA) (250 micrograms/10 microliter, ICV). The 6-OHDA and sham-lesioned (control) rats were administered BN (0.001, 0.01, 0.1 or 1.0 microgram, ICV) and their behaviour monitored. In the control animals, BN stimulated locomotor, floor and rearing activity in a dose-dependent manner. However, these behavioural effects of BN were markedly attenuated or absent in the 6-OHDA-lesioned animals. These data further support our contention that centrally administered BN may mediate its behavioural effects, through the dopaminergic system(s).

Role of nigral dopamine in amphetamine-induced locomotor activity

Dopamine (100 micrograms) injected into the substantia nigra pars reticulata of rats pretreated with the monoamine oxidase inhibitor, pargyline, resulted in a stimulation of locomotor activity. Bilateral injection of the dopamine antagonist haloperidol (5 micrograms) into the substantia nigra pars reticulata resulted in a reduction of the locomotor activity evoked by a low dose of amphetamine (1.25 mg/kg s.c.). These results suggest that the release of dopamine from nigral dendrites is involved in amphetamine-induced locomotor activity.

Early recovery of function after olfactory tract section correlated with reinnervation of olfactory tubercle

Behavioral recovery and cortical reinnervation after early olfactory tract section were assessed in the infant golden hamster (Mesocricetus auratus). Hamster pups show strong thermotaxis at birth which declines abruptly after postnatal day (P) 8 in normal pups. Unilateral olfactory bulbectomy on P5 causes persistent thermotaxis through the second postnatal week. In this study, the bulb's output pathway, the lateral olfactory tract, was unilaterally severed on P5 and pup thermotaxis was tested through P15. Complete tract section, like bulbectomy, prolonged thermal responding beyond P8. In contrast to bulbectomy, however, some tract-sectioned pups showed recovery before P15 while others continued to show persistent thermotaxis throughout testing. The olfactory bulb projection was examined 10 days after tract section in order to determine whether recovery and persistent thermotaxis were associated with different patterns of cortical innervation. Eleven pups with complete transections showed recovery during the second week. In 10 of these pups, olfactory bulb fibers had penetrated the damaged region after surgery to reinnervate the olfactory tubercle. Three of these pups also exhibited some reinnervation of piriform cortex. The lesions of pups showing persistent thermotaxis were more severe, extending bilaterally or into deep cortical layers, and olfactory fibers had failed to reinnervate caudal terminal fields. All pups with olfactory tract sections showed extensive sprouting rostral to the cut, regardless of their behavioral profile. In no case had postlesion growth innervated the entorhinal or amygdaloid areas. Inhibition of thermotaxis was associated with reinnervation of the olfactory tubercle rather than more rostral, lateral or caudal olfactory cortex. We conclude that regrowth of olfactory tract fibers caudal to early transection is rapid and has functional consequences for early behavioral development.

Intracerebral 6-hydroxydopamine produces extensive damage to the blood-brain barrier in rats

Extensive extravasation of intravenously administered horseradish peroxidase (HRP) was observed in rat brains infused intranigrally with 8 microgram/4 microliter or 4 microgram/2 microliter 6-hydroxydopamine (6-OHDA), suggesting that the cytotoxin produced widespread alterations in the integrity of the blood-brain barrier. Such damage was dose-dependent and occurred in the mesencephalon around the cannula tip, along the cannula tract, and in the cerebral cortex. The extent of HRP extravasation diminished as a function of increasing time after 6-OHDA administration. These findings indicate that alterations in blood-brain barrier permeability may contribute to the constellation of dysfunctions and possible recovery of function following intranigral infusions of the cytotoxin.