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

Neurotoxic effects of DSP-4 on the central noradrenergic system in male zebra finches

When administered systemically, the noradrenergic neurotoxin N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) appears to target the noradrenergic innervation originating in the locus coeruleus causing long-term decrements in noradrenergic function. In songbirds, DSP-4-treatment decreased female-directed singing by males and copulation solicitation responses of females to male songs. However, DSP-4 treatment in songbirds did not lower measures of NE function in the brain to the same extent as it does in mammals. The current study had two goals: determining if two DSP-4 treatments 10 days apart would cause significant decrements in noradrenergic function in male zebra finches and determining if, as in other species, the noradrenergic innervation of midbrain and cortical areas would be profoundly affected while hypothalamic areas were spared. Dopamine-beta-hydroxylase immunoreactivity (DBH-ir) was quantified in thirteen brain regions (five vocal control nuclei, one auditory nucleus, two hypothalamic nuclei, and five additional areas that demonstrated high DBH labeling in controls). Within 20 days, DSP-4 treatment profoundly reduced the number of DBH-ir cells in both the locus coeruleus and ventral subcoeruleus. Unlike a previous study, DBH labeling delineated four out of five vocal control nuclei and an auditory nucleus. As expected, DSP-4 treatment significantly decreased DBH labeling in all areas examined in the mesencephalon and telencephalon without significantly affecting DBH-ir in hypothalamic areas. This double treatment regime appears to be much more effective in decreasing noradrenergic function in songbirds than the single treatment typically used.

Catecholamine systems in the brain of vertebrates: new perspectives through a comparative approach

A comparative analysis of catecholaminergic systems in the brain and spinal cord of vertebrates forces to reconsider several aspects of the organization of catecholamine systems. Evidence has been provided for the existence of extensive, putatively catecholaminergic cell groups in the spinal cord, the pretectum, the habenular region, and cortical and subcortical telencephalic areas. Moreover, putatively dopamine- and noradrenaline-accumulating cells have been demonstrated in the hypothalamic periventricular organ of almost every non-mammalian vertebrate studied. In contrast with the classical idea that the evolution of catecholamine systems is marked by an increase in complexity going from anamniotes to amniotes, it is now evident that the brains of anamniotes contain catecholaminergic cell groups, of which the counterparts in amniotes have lost the capacity to produce catecholamines. Moreover, a segmental approach in studying the organization of catecholaminergic systems is advocated. Such an approach has recently led to the conclusion that the chemoarchitecture and connections of the basal ganglia of anamniote and amniote tetrapods are largely comparable. This review has also brought together data about the distribution of receptors and catecholaminergic fibers as well as data about developmental aspects. From these data it has become clear that there is a good match between catecholaminergic fibers and receptors, but, at many places, volume transmission seems to play an important role. Finally, although the available data are still limited, striking differences are observed in the spatiotemporal sequence of appearance of catecholaminergic cell groups, in particular those in the retina and olfactory bulb.

Castration differentially alters [3H]nisoxetine binding to norepinephrine uptake sites in olfactory bulb and frontal cortex of male rats

In the present study, [3H]nisoxetine binding to norepinephrine (NE) uptake sites and [3H]norepinephrine uptake were investigated within olfactory bulb (OB) and frontal cortex homogenates from intact and castrated male rats. Statistically significant reductions in the number of [3H]nisoxetine binding sites (Bmax) were found in OB from the castrates, while significantly increased Bmax values were obtained in the frontal cortex. Castration also significantly altered the affinity (Kd) of [3H]nisoxetine binding in the frontal cortex, but not in the OB. Assessment of [3H]norepinephrine uptake showed that in neither brain regions were there any statistically significant differences in Km nor Vmax between the castrated and intact male rats, indicating that the basal uptake process is not changed following castration in either of these brain areas. These results demonstrate the differential effects of castration upon [3H]nisoxetine binding sites between the OB and frontal cortex. Such findings provide new evidence for one of the mechanisms by which androgens may modulate central noradrenergic activity.

Castration reduces olfactory bulb norepinephrine transporter function as indicated by responses to noradrenergic uptake blockers

It has been demonstrated that castration alters the functioning of the olfactory bulb (OB)-norepinephrine (NE) system. In the present experiment, we examined one of the mechanisms by which castration modulates the OB-NE system by comparing NE uptake activity between intact and castrated male rats as studied using an in vitro superfusion technique. To accomplish this goal, NE output from the OB of intact and castrated male rats in response to infusion with two different drugs which alter NE uptake functions, tomoxetine and talsupram, were tested. Overall, NE outputs in response to tomoxetine were significantly higher in the castrated than in intact rats and both groups were significantly greater than non-infused controls. For the talsupram infusion group, NE outputs from the castrated, but not intact rats, were significantly greater than controls. No statistically significant differences were detected between the castrated and intact rats. These results demonstrate that castration alters the NE uptake activities in response to these noradrenergic uptake blockers and suggest that one mechanism by which castration alters OB-NE functioning is through reducing the uptake activity of NE within the OB. Such findings have important implications for olfactory-based learning and memory/recognition processes which are believed to involve the OB-NE system and are altered following castration.

DSP-4 treatment influences olfactory preferences of developing rats

Control cagemates of rats treated with the norepinephrine (NE) neurotoxin DSP-4, showed normal olfactory learning as infants, but abnormal aversion to home-cage odors as juveniles. Neither age nor social housing conditions influenced the odor preferences of DSP-4-treated rats: they showed tolerance or attraction to familiar odors at both developmental stages. Controls, but not DSP-4-treated juveniles, housed in mixed treatment groups, showed elevated concentrations of a serotonin metabolite and reduced NE concentrations in the hippocampus, suggesting that this social situation was particularly stressful for the controls. DSP-4-treated juveniles, but not infants, produced odors that were discriminable from controls'. Thus, conflicting olfactory signals in the home-cages of mixed juvenile groups may have led to the development of stress in controls. NE depletion appeared to lessen social stress effects in their DSP-4-treated cagemates. These findings support other data suggesting that NE modulates the biobehavioral effects of the social environment.

Involvement of the brain catecholaminergic system in the regulation of dominant behavior

The role of the brain catecholaminergic system in establishing dominant-subordinate relationships in mice of different genotypes was studied using inhibitors of tyrosine hydroxylase (alpha-methyl-p-tyrosine) or of dopamine-beta-hydroxylase (FLA-57) or FLA-57 plus the dopamine precursor, DOPA. Demotion in all dominant and subdominant animals was associated with decreased noradrenaline levels, but the aggressive behavior of dominant male mice depended on the noradrenaline/dopamine ratio. Alterations in this relationship seem to have specific effects on social dominance in animals in the micropopulation, as drug-treated mice do not exhibit changes in their general activity. It can be concluded that brain catecholamines are of prime importance in maintenance of dominance.

Social interactions in rats: behavioral and neurochemical alterations in DSP-4-treated rats

Noradrenergic neurotoxin DSP-4, preceded by zimelidine to prevent serotonin depletion, was administered IP to rats behaving in a defensive-submissive manner in a resident-intruder paradigm. Computer-based ethological analysis revealed the decrease of frequency and duration of defensive episodes and marked increase of offensive aggression. This might suggest an increase of aggressiveness and therefore support the notion of an inhibitory role of the noradrenergic system in aggressive behavior independently of the model used. Dramatically changed attitude toward the partner might also result from fear reduction or inadequate responsiveness to environmental factors because DSP-4-treated rats explored more than controls in stressogenic, highly illuminated area. HPLC analysis showed significant reduction of noradrenaline (NA) concentration in amygdala, hypothalamus, hippocampus, and frontal cortex. Simultaneously there occurred a considerable decrease in dopamine (DA) and serotonin (5-HT), and their metabolite levels. This suggests an attenuated activity of the DA and 5-HT systems that we consider as an effect secondary to NA depletion, which reflects the functional interactions between DA, 5-HT, and NA systems.

Depletion of olfactory bulb norepinephrine by 6-OHDA disrupts chemical cue but not social recognition responses in male rats

In the present experiment, 6-OHDA was infused directly into the olfactory bulb (OB) to produce a localized neurotoxic lesion. Habituation/dishabituation behavioral tests were then conducted to measure recognition responses to chemical cues (urine as a stimulus) and to social stimuli (ovariectomized rat as a stimulus). Infusion of 6-OHDA resulted in a near complete depletion of OB-norepinephrine (NE), whereas it had little effect (15% reduction) on OB dopamine (DA) contents. Nor were any significant effects on hypothalamic, hippocampal, olfactory tubercle, and corpus striatal NE and DA contents observed. Behaviorally, dishabituation responses to chemical cues were greatly impaired, however, there was relatively little effect on social behavior dishabituation responses. These results demonstrate that 6-OHDA can be used to produce a near complete but localized depletion of OB-NE. This treatment impairs dishabituation responses to chemical cues but not social stimuli indicating that OB-NE appears necessary for processing of chemical cue, but not social memory recognition process.

Role of olfactory bulb norepinephrine in the identification and recognition of chemical cues

In this report the role of olfactory bulb (OB) norepinephrine (NE) in the identification and recognition of urinary chemical cues was examined. In Experiment 1, sexually naive adult male Sprague-Dawley rats were treated with either the noradrenergic neurotoxin, DSP-4, or the water vehicle, and tested for their ability to identify and recognize urinary chemical cues using a habituation-dishabituation paradigm. Treatment with DSP-4 produced an overall decrease in the amount of investigation directed to urine stimuli, with greatest reductions to urine from Zucker females. Overall, DSP-4 treatment did not alter habituation-dishabituation responses. Animals treated with DSP-4 showed a significant reduction in OB-NE, but not dopamine, concentrations. In Experiment 2, hypothalamic catecholamine concentrations and serum samples assayed for testosterone were determined from identically treated animals. Although the NE and dopamine content in MBH was significantly lower in the DSP-4 group, no significant differences in testosterone concentrations were obtained between DSP-4 and controls. These results demonstrate that DSP-4 produces significant reductions in OB-NE and in the amount of investigation directed to urinary chemical cues from females without altering serum testosterone levels. Treatment with DSP-4 treatment does not impair the male rats' ability to demonstrate a habituation-dishabituation response.

Castration reduces potassium-stimulated norepinephrine release from superfused olfactory bulbs of male rats

In order to investigate the possible relationship among the olfactory bulb (OB), norepinephrine (NE) and gonadal steroids, we measured NE release from superfused anterior and posterior OB in intact and castrated male rats (Expt. I) as well as in castrated male rats implanted with either empty or testosterone filled silastic capsules (Expt. II). Both basal and potassium (K+ 30 mM)-stimulated release of NE was greater in posterior compared to anterior OB. All groups were responsive to the K+ stimuli showing increases in NE release. The degree of K(+)-stimulated release was significantly greater in intact compared to that of castrated rats. No differences in K(+)-stimulated release were observed between castrated and castrated plus testosterone-treated groups. These results demonstrate that castration of male rats significantly reduces OB noradrenergic responsiveness to K+ stimulation, an effect which was not restored following administration of silastic capsules containing testosterone.