Behavioral and biochemical effects of neonatal treatment of rats with 6-hydroxydopa

Perinatal Lesioning and Lifelong Effects of the Noradrenergic Neurotoxin 6-Hydroxydopa

6-hydroxydopa (6-OHDOPA) was synthesized with the expectation that it would be able to cross the blood-brain barrier to be enzymatically decarboxylated to 6-hydroxydopamine (6-OHDA), the newly discovered neurotoxin for noradrenergic and dopaminergic neurons. In part, 6-OHDOPA fulfilled these criteria. When administered experimentally to rodents, 6-OHDOPA destroyed peripheral sympathetic noradrenergic nerves and did exert neurotoxicity to noradrenergic nerves in brain-in large part, from its conversion to 6-OHDA. However, the efficacy of 6-OHDOPA was less than that of 6-OHDA; also, 6-OHDOPA was relatively selective for noradrenergic neurons; near-lethal doses of 6-OHDOPA were required to damage dopaminergic nerves; and ultimately, 6-OHDOPA was found to be an agonist at AMPA receptors, thus accounting for more non-specificity. Nevertheless, 6-OHDOPA was found to be a particularly valuable tool in uncovering processes and mechanisms associated with noradrenergic nerve regeneration and sprouting, particularly when administered to perinatal rodents. Also, 6-OHDOPA was a good tool for selective mapping of noradrenergic nerve tracts in brain, since dopaminergic tracts were unaffected and did not interfere with the histofluorescent methodology used for this purpose in the early 1970s. As an experimental research tool, 6-OHDOPA was valuable in a short time-window, but its utility is largely limited because of newer research technologies that provide better means today for nerve tract mapping, and for experimental approaches engaged toward study of processes and mechanisms attending nerve regeneration. AMPA actions of 6-OHDOPA have not been extensively studied, so this avenue may enliven use of 6-OHDOPA in the future.

Selective lesion of central dopamine or noradrenaline neuron systems in the neonatal rat: motor behavior and monoamine alterations at adult stage

Different parameters of motor behavior (locomotion, rearing and total activity counts) were studied in the adult rat following neonatal intracisternal 6-hydroxydopamine (6-OHDA, 50 micrograms) treatment combined with noradrenaline (NA) uptake blocker (desipramine) or dopamine (DA) uptake blockers (amfolenic acid or GBR 12909) to obtain selective DA or NA lesions respectively. At 61-65 days of age, selective DA-lesioned animals showed an initial decrease in spontaneous motor behavior at test days 1 and/or 2, while at test days 4 and 5 hyperactivity was observed. However, following amfolenic acid or GBR 12909 pretreatment leading to a selective NA lesion, no difference in spontaneous motor behavior was seen on any of the 5 test days. Determination of regional brain levels of NA and DA confirmed the type of lesion predicted from the various pretreatments with selective uptake blockers. These data suggest that changes in motor behavior in the adult rats, following neonatal 6-OHDA treatment, are specifically related to a DA-denervation, whereas an NA lesion does not seem to influence the spontaneous motor behavior. However, following the selective DA lesion, significant increases of serotonin levels in striatum and cerebellum were observed, while following selective NA lesions an increase of cerebellar NA levels was found concomitant with drastic reductions of NA levels in frontal cortex and spinal cord.

DSP4, a noradrenergic neurotoxin, impairs male rats' attraction to conspecific odors

Olfactory investigation was examined in male Sprague-Dawley rats injected with 50 mg/kg of the noradrenergic neurotoxin, DSP4, 10 days before testing. In a two-choice preference test, the odor of pine shavings from the nest of a female and her litter attracted sexually experienced control males, but not drug-treated males. Further, odors from anesthetized females increased the mean number of entries made by control males, but not drug-treated males, into a cage containing pups' nest shavings. Combining a novel odor with nest shavings significantly reduced the number of entries made by both groups of males. Drug treatment decreased norepinephrine (NE) levels by 66, 62, and 68% in the olfactory cortex, olfactory bulb, and frontal cortex, respectively. Dopamine concentrations were not significantly affected. NE concentrations in the heart, and serotonin levels in the olfactory bulb, were moderately depleted (by 37 and 40%, respectively). The results support the view that central NE modulates systems regulating attraction to conspecific odors in male rats.

Catecholamines and aggression in animals

This paper assesses the evidence for the role of catecholamines in the aggressive behaviour of animals. The effects of manipulating dopamine and noradrenaline function, either alone or in combination, are considered with respect to two categories of aggression, predatory and affective. Affective aggression is further subdivided into shock-induced defensive fighting, isolation-induced aggression and irritable aggression. The results indicate that catecholamines may not have a specific role in aggressive behaviour. Rather, they may act more to excite or inhibit general behavioural systems, although certain treatments do have a specific influence on aggressive behaviour. The review also highlights certain problems concerning the psychopharmacology of aggression; different species may make varying responses to the same treatment, whilst treatments exerting a similar pharmacological action may result in diverse behavioural effects.

Amine accumulation in behavioural pathology

When nigro-striatal and meso-cortical neurons degenerate there is a loss of dopamine in the terminal fields and an accumulation of amines in the axons of these systems as they traverse the hypothalamus through the medial forebrain bundle. Traditional lines of thought have attributed the occurrence of motor and consummatory deficits which occur after dopamine neuron degeneration to the loss of functional dopamine neurotransmitter in the terminal fields. However, we have hypothesized that hypothalamic amine accumulation represents an area of brain tissue where processes such as neurotransmitter release, ephaptic transmission or local axon swelling may be affecting adjacent neurons and may thereby participate in the production of behavioural deficits. There is a considerable amount of evidence from studies on both peripheral and central catecholamine-containing neurons indicating that when their axons degenerate a release of functional neurotransmitter can occur. Information from neuropharmacological studies indicates that several drugs which facilitate behavioural recovery from dopamine-depleting lesions may do so by affecting amine release or receptor sensitivity near areas of accumulation rather than depleted terminal fields. We conclude that amine accumulation is a component of dopamine neuron degeneration which should be considered when assessing the role of the central catecholamine systems in the control of various behavioural and physiological processes.

Comparison of hyperactivity in adult rats induced by neonatal intraventricular 6-hydroxydopamine following pargyline or desmethylimipramine treatment

The relative roles of norepinephrine (NE) and dopamine (DA) in sustaining neonatal hyperactivity were assessed in rats given 6-hydroxydopamine (6-OHDA) neonatally into the lateral ventricles after pargyline (P) or desmethylimipramine (DMI) pretreatment. On day 5 after birth, male and female rat pups were pretreated with P (50 mg/kg IP) or DMI (25 mg/kg IP) 30 min before receiving bilateral injections of 6-OHDA (200 micrograms/5 microliters saline containing ascorbic acid 1.0 mg/ml) into the lateral ventricles. Controls were pretreated with P or DMI and then received injections of saline containing the ascorbate. Spontaneous activity was measured in a stabilimeter at ages 30-31, 42-45, 60-63, 75-77, and 120-122 days. Activity in controls and P + 6-OHDA animals was also measured at 254 days of age. The sessions lasted 45 min, except those testing activity in the 254-day-old rats which lasted 12 h. Regional assays of catecholamines carried out when the animals were 150 days old revealed that in the P + 6-OHDA group the levels of NE were reduced in frontal cortex (7% of control levels), caudate (21%), and hippocampus (14%). The NE levels were unchanged or slightly elevated in hypothalamus, ventral midbrain, and pons. The DA levels in the P + 6-OHDA group were depleted in caudate (8%) and ventral midbrain (32%), and unchanged in hypothalamus and pons. In the DMI + 6-OHDA group the NE levels were reduced in caudate (25%) and elevated in hippocampus (188%). The DA levels were depleted in caudate (3%) and ventral midbrain (22%).(ABSTRACT TRUNCATED AT 250 WORDS)

A role for amine accumulation in the syndrome of ingestive deficits following lateral hypothalamic lesions

Lesions of the lateral hypothalamus produce ascending catecholamine neuron degeneration which results in terminal depletion and proximal accumulation above the lesions. The occurrence of deficits in ingestive behaviour has been attributed traditionally to the loss of functional dopamine neurotransmitter in the terminal fields. However, release of functional amines may occur in the lateral hypothalamus at areas of accumulation, to produce at least some of the behavioural symptoms characterizing the lateral hypothalamic syndrome. Recovery from behavioural deficits as a result of various pharmacological treatments, after dopamine-depleting lesions, may be mediated by changes in amine release or modified sensitivity of receptors affected by released amines. We conclude that amine accumulation should be considered when interpreting experiments implicating central catecholamine systems in the control of consumatory behaviour and the regulation of body weight.

Differential effects of selective dopamine, norepinephrine or catecholamine depletion on activity and learning in the developing rat

The present experiment investigated the behavioral changes which occurred following neonatal depletion of central catecholamine systems in the rat. The behavioral effects which resulted from selective dopamine (DA) depletion were compared with those resulting from selective norepinephrine (NE) depletion as well as depletion of both catecholamines (CA). Neonatal 6-hydroxydopamine (6-OHDA) was administered intracisternally at 5 days of age following pretreatment with desmethylimipramine in order to selectively deplete DA. NE levels were reduced by intraperitoneal injections of 6-OHDA at 1 and 2 days of age. Depletion of both catecholamines was effected by combining the procedures used for selective depletion of both DA and NE. Activity was time sampled during an hour at 3 preweanling ages. Avoidance and escape learning were measured in a T maze when pups were 20 days of age and in a Shuttlebox apparatus on day 28. Results revealed that DA and CA depleted animals were hyperactive in comparison to controls and displayed severe learning impairments in both T maze and Shuttlebox performance. In contrast, NE depleted animals showed activity levels which were similar to controls but were significantly impaired on both learning paradigms. These results suggest that selective lesions of DA and NE in infancy lead to a constellation of behaviors which are distinctly unique. The implications of these findings is discussed in terms of clinical research into the Attentional Deficit Disorder of childhood.

Neonatal 6-hydroxydopa alters conspecific odor investigation by male rats

Odor-guided behavior was examined in male rats injected at birth and 48 h later with either the catecholaminergic neurotoxin 6-hydroxydopamine (60 micrograms/g, i.p.) or vehicle. In odor preference tests administered 8 or 74 days postnatally, drug-treated animals avoided novel odors which were neutral for controls and showed reduced preference for conspecific nest odors. In emergence tests administered 73-75 days postnatally, odors from an anesthetized female reduced approach latency and increased investigation of familiar conspecific odors for control but not drug-treated males. Neonatal drug treatment decreased adult olfactory cortex norepinephrine (NE) levels by 50%, but did not significantly influence either cardiac NE or olfactory cortex dopamine. The results imply that brain NE facilitates attraction to familiar conspecific odors.

Effects of neonatal treatment with 5,7-dihydroxytryptamine or 6-hydroxydopamine on the ontogenetic development of the audiogenic immobility reaction in the rat

The ontogenetic development of the audiogenic immobility reaction (freezing) was studied in rats given intracisternal injections of the neurotoxins 5,7-dihydroxytryptamine (5,7-DHT), 25 micrograms, or 6-hydroxydopamine (6-OHDA), 100 micrograms, neonatally (Day 1). The duration of the freezing response was strongly reduced in the 5,7-DHT-treated rats between 20-30 days of age, when normal animals show very prolonged responses. During the same period increased motor activity was observed in the 6-OHDA-treated rats while only a slight reduction of the freezing response was noted. Biochemical analyses performed on brains from animals 35 days of age showed a selective reduction (about 50%) of whole brain levels of serotonin in the 5,7-DHT-treated rats, while the noradrenaline levels were selectively reduced by about 60% in the 6-OHDA rats. A longitudinal investigation on the effects of neonatal treatment with 5,7-DHT showed a persistent selective reduction of the whole brain level of serotonin up to at least 90 days of age. Since 5,7-DHT mainly affects the serotonergic pathways, the results suggest that the disturbances noted in the ontogeny of the freezing response may be due to interference with the developing serotonergic system.

Effects of neonatal 6-hydroxydopamine treatment on catecholamine levels and behavior during development and adulthood

The effects of neonatal intraventricular 6-hydroxydopamine (6-OHDA) (50-400 microgram) treatment on catecholamine levels in various brain regions, and on motor activity, were investigated in rats during development and adulthood. At 30 days catecholamine levels were lower in the frontal cortex and ventral diencephalon; minor reductions were observed in midbrain and pontine regions. At 90 days the effects of 6-OHDA treatment were similar in frontal and rostral midbrain regions but in the pontine area norepinephrine levels were substantially elevated. Behavioral tests in a stabilimeter indicated 6-OHDA-treated rats were hyperactive during development, at 25 and 35 days of age, as well as in adulthood. However, 6-OHDA-treated rats did not differ from controls in habituation. These effects are interpreted as supporting the notion that low catecholamine levels in the forebrain alter activity during development and in adulthood.

Effects of neonatal 6-hydroxydopa on behavior in female rats

Litters of female rats were treated at birth and 48 hr later with either saline or 6-hydroxydopa (60 microgram/g, IP), were ovariectomized in adulthood and tested on a number of behavioral tasks including age of vaginal opening, sexual receptivity, open-field activity, equilibrium, and habituation to acoustic startle. Results of the open-field test indicated that the treated animals were more active overall, were more likely to enter inner segments, reared more often, and defecated less than the control animals. On a rod-balancing task, the treated animals exhibited impaired equilibrium. Treated animals were more reactive than controls in response to acoustic startle, but there were no differences between the groups in rate of habituation or sensitization to the startle stimulus. Norepinephrine content of treated animals was significantly lower than controls in the cortex, amygdala, hippocampus, and spinal cord, but higher in the cerebellum and brainstem. There was no difference between the groups in cardiac norepinephrine nor in striatal dopamine.

Effects of 6-hydroxydopamine and 6-hydroxydopa on development of behavior

Rats treated at birth with 6-hydroxydopamine (6-OHDA) (60 microgram/g, IP) or 6-hydroxydopa (6-OHDOPA X2) (60 microgram/g, IP at birth and 48 hr later) exhibited increases in general activity throughout the initial 5 weeks after birth, with peak activity occurring around 20 days postnatally. Activity changes in the 6-OHDOPAx2 group appeared to be due to increased exploratory behavior (ambulation, climbing, rearing, sniffing), while the 6-OHDA changes appeared to be due to the increased self-directed behavior (eating, grooming, scratching). Despite these behavioral differences there was no obvious difference between treated groups in norepinephrine (NE) levels in the various brain regions, i.e., all treatments resulted in a reduction in neocortical and hippocampal NE and an elevation in cerebellar NE. These findings suggest that noradrenergic neurons may be altered to different degrees by each agent in more discrete brain regions than were tested, or that other neurotransmitter systems may be more selectively altered by either of the drug treatments. Because striatal dopamine was unaltered in any of the groups, however, there is reason to question a previously suggested link between minimal brain dysfunction (MBD) and dopamine depletion in the neonatal brain.

An holistic developmental view of neural and psychological processes: a neurobiologic-psychoanalytic integration

The authors attempt to integrate several psychoanalytical and more recent neurobiological concepts regarding the development of the organism and emergence of psychopathology. They highlight the rough temporal correspondence of neurodevelopmental myelination cycles with stages of psychosocial development. They discuss concepts of critical periods and unique times of vulnerability to psychosocial insult and recurrence of critical stresses, gleaned from a multidisciplinary point of view, in relation to the occurrence of psychic aberrations. They suggest that it may be fruitful to explore further psychological constructs such as fixation and regression, as well as unconscious mental processes, in relation to their biochemical, physiological, and anatomical representations in the brain.

Age pigments, cell loss and hippocampal function

The specific aims of this study were to perform direct correlational analyses of age differences in learning, short-term memory and arousal in relation to cell loss and lipofuscin increase in the hippocampus CA1 zone and in visual area 17 of the Fisher 344 rat. The following tentative conclusions can be made from the results presented in this study: (1) significant age differences in 2 and 6 hour passive-avoidance retention or memory between mature and old rats were related to non-significant age differences in days to criterion learning, starting latencies, running distance and time in original approach learning, and (2) significant age differences in 2 and 6 hours retention of old, compared to mature rats were correlated significantly with loss of neurons, and very significantly with increases in intraneuronal lipofuscin in the hippocampus CA1 zone and in visual area 17.

Studies on the mechanism of sprouting of noradrenergic terminals in rat and mouse cerebellum after neonatal 6-hydroxydopa

The effect of various pharmacologic agents on the noradrenergic innervation of rat cerebellum was observed. It was found that the neurotoxin 6-hydroxydopa (6-OHDOPA), when given to rats at birth, caused a 46% reduction at 5 weeks of age in tyrosine hydroxylase activity in the locus coeruleus, the nucleus of origin for noradrenergic fibers innervating the cerebellum. At the same time, however, both tyrosine hydroxylase activity and NE content were elevated by 50% in the cerebellum. By treating gravid mice with the 6-OHDOPA, which crosses the placental barrier to affect the brains of developing pups, a dissociation has been shown between the elevated cerebellar NE levels and reduced telencephalic NE content. None of the other assorted pharmacological agents--namely amphetamine, metaraminol, apomorphine, alpha-methyl-p-tyrosine. L-dihydroxyphenylalanine and tyramine--when given at birth, caused a permanent elevation in cerebellar NE content. This series of studies suggests that a reduced number of noradrenergic perikarya are providing a greater innervation of the cerebellum than in control rats. Also, alteration of the telencephalic noradrenergic fibers, which are also derived from the locus coeruleus, does not appear to be a necessary event for the initiation of sprouting of noradrenergic fibers in the cerebellum. Because none of the acute-acting pharmacological agents caused a permanent elevation of NE in the cerebellum, it appears that damage, and not mere stimulation or blockade, is a necessary event for initiation of sprouting.

A biochemical and morphological study of the altered growth pattern of central catecholamine neurons following 6-hydroxydopamine

In this study the effect of administering 6-hydroxydopamine (6-OHDA) intracisternally on brain catecholamine content and fluorescence patterns of cerebellar processes was examined. It was found that intracisternal injection of 6-OHDA resulted in widely diverging effects depending upon the dose of 6-OHDA, age of the animal upon injection and the length of the post injection interval. Small doses of 6-OHDA (3 and 10 microgram) selectively depleted telencephalic and upper brain stem NE while larger doses of 6-OHDA (30 and 100 microgram) infringed on dopaminergic as well as noradrenergic neurons. In addition, the lower doses of 6-OHDA, but not the higher ones, led to an approximately two-fold accumulation of NE in the lower brain stem and cerebellum. Morphological observations suggested that the cerebellar norepinephrine accumulation after 10 microgram 6-OHDA was attributable primarily to an invasion of noradrenergic processes into the cerebellum.

Infant rats: sensorimotor ontogeny and effects of substantia nigra destruction

The ontogeny of sensorimotor behaviors of albino rats were evaluated from birth through adulthood (Experiment 1). Sensorimotor behaviors (e.g., visual and tactile orientation, forelimb and hindlimb hopping, righting reflexes) achieved mature (adultlike) characteristics at various ages during ontogeny and a rostral-caudal developmental pattern was revealed. In Experiment 2, the substantia nigra was bilaterally or unilaterally destroyed in rats at 10 or 25 days of age and the ontogeny of sensorimotor and regulatory (feeding, drinking, body weight regulation) behaviors were evaluated. Bilateral destruction of the substantia nigra, zona compacta, at 10 and 25 days of age resulted in transient cessation of suckling and/or feeding and drinking followed by recovery. Male brain-damaged rats had reduced body weight through 150-170 days of age. Specific feeding and drinking tests revealed the presence of residual regulatory deficits which seemed permanent. Sensorimotor testing revealed transient dysfunction for a variety of sensorimotor behaviors, with eventual recovery of normal sensorimotor capacity. The results are related to sensorimotor ontogeny and recovery from infant brain damage.

Differential effect of various 6-hydroxydopa treatments on the development of central and peripheral noradrenergic neurons

6-Hydroxydopamine or 6-hydroxydopa injected systemically into newborn rats produced marked changes in the development of central and peripheral noradrenergic neurons. Noradrenaline concentration was elevated in the brain stem, particularly in the pons, and decreased in the cerebral cortex and the spinal cord while in the cerebellum, the effects were dependent on the mode of administration. The changes produced by 6-hydroxydopa in brain regional noradrenaline were related to the dose injected at birth. Similar modifications in the development of central noradrenergic neurons were found in the offspring of rats which had received 6-hydroxydopa at 16 days of gestation. The involvement of peripheral sympathetic neurons varied with the compound used and the form of its administration. Thus, 6-hydroxydopamine produced a permanent although partial peripheral sympathectomy, an effect which was less evident following multiple injections of 6-hydroxydopa after birth and almost minimal after a single injection. The prenatal administration of 6-hydroxydopa did not alter peripheral sympathetic neurons. It is concluded that with the appropriate treatment schedule, it is possible to lesion selectively the noradrenergic neurons in the central nervous system.