Net effect of acute administration of desipramine on the locus coeruleus - hippocampal system

Sensation seeking: A comparative approach to a human trait

A comparative method of studying the biological bases of personality compares human trait dimensions with likely animal models in terms of genetic determination and common biological correlates. The approach is applied to the trait of sensation seeking, which is defined on the human level by a questionnaire, reports of experience, and observations of behavior, and on the animal level by general activity, behavior in novel situations, and certain types of naturalistic behavior in animal colonies. Moderately high genetic determination has been found for human sensation seeking, and marked strain differences in rodents have been found in open-field behavior that may be related to basic differences in brain neurochemistry. Agonistic and sociable behaviors in both animals and humans and the trait measure of sensation seeking in humans have been related to certain common biological correlates such as gonadal hormones, monoamine oxidase (MAO), and augmenting of the cortical evoked potential.

The monoamine systems in the rodent brain are involved in general activity, exploratory behavior, emotionality, socialization, dominance, sexual and consummately behaviors, and intracranial self-stimulation. Preliminary studies have related norepinephrine and enzymes involved in its production and degradation to human sensation seeking. A model is suggested that relates mood, behavioral activity, sociability, and clinical states to activity of the central catecholamine neurotransmitters and to neuroregulators and other transmitters that act in opposite ways on behavior or stabilize activity in the arousal systems. Stimulation and behavioral activity act on the catecholamine systems in a brain–behavior feedback loop. At optimal levels of catecholamine systems activity (CSA) mood is positive and activity and sociability are adaptive. At very low or very high levels of CSA mood is dysphoric, activity is restricted or stereotyped, and the organism is unsocial or aggressively antisocial. Novelty, in the absence of threat, may be rewarding through activation of noradrenergic neurons.

Allopregnanolone reduces immobility in the forced swimming test and increases the firing rate of lateral septal neurons through actions on the GABAA receptor in the rat

Since allopregnanolone reduces the total time of immobility in rats submitted to the forced swimming test, we decided to explore whether this neuroactive steroid shares other antidepressant-like actions, such as increasing the neuronal firing rate in the lateral septal nucleus (LSN). In order to discard the influence of the oestrous cycle on immobility and on the firing rate of LSN neurons, all Wistar rats used in the study underwent ovariectomy before treatments. A group of rats received different doses of allopregnanolone (0.5, 1.0, 2.0 and 3.0 mg/kg, i.p.) 1 hour before being forced to swim in order to identify the minimum effective dose diminishing immobility. None of the tested doses of allopregnanolone produced significant changes in motor activity in the open-field test. The minimum dose of allopregnanolone producing a significant reduction in the total time of immobility (p<0.05) against the vehicle was 1.0 mg/kg, while 2.0 mg/kg and above also increased the latency to the first period of immobility (p<0.05). The minimum effective dose of allopregnanolone reducing immobility in the forced swimming test (1.0 mg/kg) significantly (p <0.05) produced a higher (twofold) neuronal firing rate in LSN neurons, but did not produce any change in septofimbrial nucleus neurons, which fired at a rate similar to that of vehicle-treated rats. The pretreatment with the non-competitive GABAA receptor antagonist, picrotoxin (1.0 mg/kg), blocked the aforementioned actions of allopregnanolone on both immobility and LSN firing rate. In conclusion, allopregnanolone produces an antidepressant-like effect in the forced swimming test, associated with an increase in the LSN neuronal firing rate, seemingly mediated by the GABAA receptor.

Intraaccumbens dopaminergic lesion suppresses desipramine effects in the forced swim test but not in the neuronal activity of lateral septal nucleus

The nucleus accumbens (NAcc) function is related to locomotor activity, while the lateral septal nucleus (LSN) is related to the motivational aspects of behavior. Thus, a dopaminergic lesion of the NAcc blocks the antiimmobility effect of desipramine (DMI) and this tricyclic increases the firing rate of the LSN; however, it is unknown whether a relation exists between a dopaminergic lesion of the NAcc and the response of LSN neurons to DMI treatment. Therefore, we conducted a longitudinal study to further explore the participation of NAcc dopaminergic terminals in the immobility reduction exerted by DMI in the forced swim test and its relation to the firing rate of the LSN, at the same time exploring motor and motivational aspects of DMI-dopaminergic relationships in the animals. A dopaminergic lesion was bilaterally produced by 6-hydroxydopamine (6-OHDA) injection into the NAcc of adult ovariectomized Wistar rats pretreated with DMI (25 mg/kg ip, 30 min before lesion to protect NA terminals but to destroy DA endings). Treatments with DMI or saline began 24 h after stereotaxic surgery. The results showed that DMI once a day during 9 days (10 mg/kg) reduced immobility in the forced swim test in the sham-lesion group (P<.02); however, in the dopaminergic lesion group submitted to DMI treatment, immobility remained at control level in agreement with other reports. DMI increased the firing rate of the LSN (P<.001) independently of the 6-OHDA lesion. In conclusion, the dopaminergic terminals of the NAcc seem to be essential for the motor manifestation associated with motivation induced by DMI in the forced swim test, given that the antiimmobility actions of DMI are blocked after a dopaminergic NAcc lesion; however, the effect on the firing rate of LSN neurons is still present.

Stress versus depression

1. Exhaustive evidence is quoted showing that uncontrollable (uncoping) stress provoked in experimental mammals leads to depletion of central noradrenergic activity+ adrenomedullary-cortical gland hyperactivity. These physiological disorders cause the typical neuroendocrine peripheral profile: a) raised catecholamines (CA) in plasma [noradrenaline (NA)+adrenaline (Ad)+dopamine (DA), b) reduced NA/Ad ratio in plasma and c) raised plasma cortisol. 2. Exhaustive evidence is quoted which indicates that severely ill humans show peripheral neuroendocrine profile similar to that found in mammals submitted to uncontrollable stress situation. Further, the NA/Ad ratio does not increase but decreases during orthostasis and exercise stress challenges, as well as oral glucose stress (tolerance) test. 3. Exhaustive evidence is quoted which indicates that endogenous depressed subjects show a neuroendocrine profile opposite to that observed in stressed mammals and severely ill humans. This profile consists of central NA (neural sympathetic) hyperactivity+ adrenomedullary glands hyporresponsivity. These disorders are reflected in a three to ten fold increase of the NA/Ad ratio in plasma. 4. Exhaustive evidence is also quoted showing that dysthymic depressed patients show low plasma catecholamines+low NA/Ad plasma ratio (< 2) during supine-resting condition, it is normalized at orthostasis and exercise periods. 5. It is quoted evidence showing that whereas platelet serotonin is increased in dysthymics, the same is reduced in both endogenous depressed and stressed mammals as well as severely ill humans. 6. It is quoted evidence showing that free serotonin in plasma is greatly raised in uncoping stressed mammals and severely ill humans. The same parameter is normal or slightly increased in dysthymic and endogenous depressed humans. These findings are consistent with the increased platelet aggregability observed in "uncontrollable" stressed mammals and in severely ill, but not depressed patients. 7. It is also quoted evidence showing that whereas parasympathetic activity is absent in uncontrollable stressed mammals and severely ill humans, the same is increased in both types of depressed humans. 8. According to the above, the authors postulate the existence of 3 distinct central+ peripheral neuroendocrine profiles for endogenous depression, dysthymic depression and maladaptation to stress syndrome. These different profiles should lead researchers to attempt different therapeutical approach. 9. In view of the fact that the authors found much clinical overlap among the three syndromes (endogenous depression, dysthymic depression and severely ill patients), they believe that a differential diagnosis should be based on neurochemical, neuroendocrine, physiologic, metabolic and neuropharmacological grounds. 10. The experimentally induced uncontrollable stress (behavioral despair) syndrome in mammals should not be used as a valid model of human depressive syndrome.

REM sleep inhibition by desipramine: evidence for an alpha-1 adrenergic mechanism

The acute administration of drugs that block norepinephrine (NE) reuptake suppresses rapid eye movement (REM) sleep in cats and other mammals. The mechanism is presumed to involve NE acting on cells in a pontine REM sleep-generator region. Postsynaptic noradrenergic receptor mechanisms have not been identified. In the present experiments, we tested the ability of the alpha-1 antagonist prazosin and the beta antagonist propranolol to reverse the REM sleep suppression produced by the NE reuptake blocker desipramine (DMI) in the cat. DMI reduced the number of REM sleep episodes, the REM percentage (REM sleep time/total sleep time), and the average REM sleep episode duration. The co-administration of prazosin, but not propranolol, increased the REM percentage and the average REM sleep episode duration toward the placebo level. The co-administration of the peripherally-acting, anti-hypertensive agent hydralazine did not reverse the DMI-induced REM sleep suppression. While the identity of the brain region(s) involved in mediating the alpha-1 noradrenergic suppression of REM sleep by DMI remains unclear, there is reason to consider forebrain structures including the amygdala as well as the pontine areas that generally have been implicated in REM sleep control.

Increase in number of LHRH neurones in septal-preoptic area of rats following chronic amitriptyline treatment: implication in antidepressant effect

Recent studies have implicated the peptide LHRH in a variety of actions including a role in modulation of affective behavior. The present study has been undertaken to determine its involvement in the action of antidepressants, if any, using amitriptyline (AMT) as the model antidepressant drug. The repeated administration of AMT (10 mg/kg/day) in rats increased the number of LHRH neurones in the septal-preoptic area. While 1 week of AMT treatment slightly augmented the number of LHRH neurones, the rise was not statistically significant, however, following 2 weeks of AMT treatment, a significant (P < 0.05) increase (41.05%) was observed. Three and four weeks of AMT treatment further increased the number of neurones by 60.84% and 72.96% respectively; a remarkable rise in the LHRH immunoreactivity around organum vasculosum of lamina terminalis (OVLT) was also noticed. Acute AMT treatment had no effect on the number of neurons; however, the intensity of immunoreaction in the OVLT was slightly decreased. In the behavior despair test, a single dose of AMT displayed an immobility reducing effect which was also shown by a single dose of LHRH (1 mg/kg). The combination of LHRH (1 mg/kg) and AMT also reduced the immobility; the effect was the same as one produced by each drug given separately. The results suggest that chronic AMT treatment may induce transcription and translation in LHRH cells and that the peptide LHRH may be involved in the mediation of the antidepressant effect, characteristic of AMT.

Effect of desipramine and amphetamine on noradrenergic neurotransmission: electrophysiological studies in the rat brain

The present electrophysiological experiments were undertaken to investigate the effect of desipramine and d-amphetamine on noradrenergic neurotransmission in the rat central nervous system. The effectiveness of electrical stimulation of the locus coeruleus and of microiontophoretic application of norepinephrine (NE) in suppressing the firing activity of CA3 pyramidal neurons was studied in the dorsal hippocampus. Desipramine (0.5 and 5 mg/kg i.v.) and d-amphetamine (0.25 and 5 mg/kg i.v.) decreased the effectiveness of locus coeruleus stimulation and prolonged the effect of microiontophoretically applied NE on the same pyramidal neurons. Subsequent i.v. administration of idazoxan, an alpha 2-adrenoceptor antagonist, reversed the effects of desipramine and d-amphetamine on the effectiveness of locus coeruleus stimulation and decreased that of microiontophoretically applied NE. In addition, idazoxan prevented the effect of subsequent administration of desipramine (5 mg/kg i.v.) on the effectiveness of locus coeruleus stimulation. High doses of d-amphetamine (5 and 10 mg/kg i.v.) decreased the firing activity of hippocampus pyramidal neurons by 70 and 98%, respectively, whereas low doses of desipramine (0.5 mg/kg i.v.) or of d-amphetamine (0.25 mg/kg i.v.) were without effect. After lesioning of NE projections with 6-hydroxydopamine, the effect of the 5 mg/kg dose of d-amphetamine on the firing activity of hippocampus pyramidal neurons was markedly reduced, whereas the cumulative 10 mg/kg dose of d-amphetamine completely suppressed, as in control rats, the firing activity of these neurons. This effect of d-amphetamine in 6-hydroxydopamine-pretreated rats was reversed by the administration of the 5-HT1A receptor antagonist BMY 7378. These data provide evidence that acute administration of desipramine and d-amphetamine decreases the effectiveness of locus coeruleus stimulation by increasing the activation of terminal alpha 2-adrenoceptor autoreceptors. In addition, acute administration of high doses of d-amphetamine decreases the firing rate of hippocampus pyramidal neurons by increasing NE and serotonin release.

Clinical and biochemical aspects of depressive disorders: II. Transmitter/receptor theories

The present document is the second of three parts in a review that focuses on recent data from clinical and animal research concerning the biochemical bases of depressive disorders, diagnosis, and treatment. Various receptor/transmitter theories of depressive disorders are discussed in this section. Specifically, data supporting noradrenergic, serotonergic, cholinergic, dopaminergic, GABAergic, and peptidergic theories, as well as interactions between noradrenergic and serotonergic, or cholinergic and catecholaminergic systems are presented. Problems with the data and future directions for research are also discussed. A previous publication, Part I of this review, dealt with the classification of depressive disorders and research techniques for studying the biochemical mechanisms of these disorders. A future publication, Part III of this review, discusses treatments for depression and some of the controversies in this field.

Chronic clomipramine increases firing rate in lateral septal nuclei of the rat

A single dosage of several antidepressants produces an increased rate of firing in lateral septal nuclei of the rat. The objective of the present study was to clarify the long-term treatment action of clomipramine on the septal nuclei of the rat. A progressive increase of firing rate appeared after long-term treatment with clomipramine (1.25 mg/kg, IP; twice a day, for 25 days). The most noticeable firing increase occurred in the lateral septal nuclei, which primarily receive serotonergic innervation. Irregular changes occurred in the corpus callosum and cingulum. Finally, in other poorly innervated serotonergic septal regions, the treatment lacked effects. This suggested that the action of clomipramine was primarily due to interaction with the serotonergic system.

Action of antidepressants on the septal nuclei of the rat

Studies on neuronal firing have shown a decrease in frequency of firing in structures not directly related to emotional processes. However, studies of the hippocampus have shown increases in firing rate. Other limbic structures not yet explored in regard to the action of antidepressants include the septal nuclei. The present work describes a common effect of various therapeutic antidepressant models. Extracellular unit recordings were obtained from the septal nuclei of rats exposed to different acute treatments: clomipramine, isocarboxazid, trazodone, sleep deprivation, and electroshock. Frequencies and firing intervals were analyzed. After treatment, an increase in firing frequency in cells of the dorsolateral septal nucleus was found. This supports the hypothesis that brain structures related to the phenomenon of self-stimulation participate in the mechanism of antidepressant treatments.

DMI, Wy-45,030, Wy-45,881 and ciramadol inhibit locus coeruleus neuronal activity

Wy-45,030 and Wy-45,881 block the uptake of norepinephrine and serotonin in rat brain synaptosomal preparations and share several in vivo and in vitro effects with known tricyclic antidepressants. To further characterize their activity, these compounds were compared to desipramine and ciramadol in electrophysiological studies of their acute effects on noradrenergic neuronal activity. All four compounds inhibited locus coeruleus neuronal activity with a rank order of potency of desipramine greater than Wy-45,881 greater than Wy-45,030 greater than ciramadol. Administration of the alpha-adrenergic blocking drug, piperoxane, increased locus coeruleus firing rate after desipramine, Wy-45,030 and Wy-45-881. Pretreatment with naloxone prevented the reduction in locus coeruleus impulse flow observed after ciramadol administration but had no effect on the inhibition produced by Wy-45,030. Wy-45,030 and Wy-45,881, like classical antidepressants, appear to inhibit locus coeruleus neuronal firing by potentiating neuroinhibitory transmission of locus coeruleus neurons by blocking the uptake of norepinephrine into presynaptic terminals.