Habituation failure of skin conductance response after intraventricular administration of 6-hydroxydopamine in cats

Genetics, molecular control and clinical relevance of habituation learning

Habituation is the most fundamental form of learning. As a firewall that protects our brain from sensory overload, it is indispensable for cognitive processes. Studies in humans and animal models provide increasing evidence that habituation is affected in autism and related monogenic neurodevelopmental disorders (NDDs). An integrated application of habituation assessment in NDDs and their animal models has unexploited potential for neuroscience and medical care. With the aim to gain mechanistic insights, we systematically retrieved genes that have been demonstrated in the literature to underlie habituation. We identified 258 evolutionarily conserved genes across species, describe the biological processes they converge on, and highlight regulatory pathways and drugs that may alleviate habituation deficits. We also summarize current habituation paradigms and extract the most decisive arguments that support the crucial role of habituation for cognition in health and disease. We conclude that habituation is a conserved, quantitative, cognition- and disease-relevant process that can connect preclinical and clinical work, and hence is a powerful tool to advance research, diagnostics, and treatment of NDDs.

Psychiatric symptoms of noradrenergic dysfunction: a pathophysiological view

What psychiatric symptoms are caused by central noradrenergic dysfunction? The hypothesis considered in this review is that noradrenergic dysfunction causes the abnormalities in arousal level observed in functional psychoses. In this review, the psychiatric symptoms of noradrenergic dysfunction were inferred pathophysiologically from the neuroscience literature. This inference was examined based on the literature on the biology of psychiatric disorders and psychotropics. Additionally, hypotheses were generated as to the cause of the noradrenergic dysfunction. The central noradrenaline system, like the peripheral system, mediates the alarm reaction during stress. Overactivity of the system increases the arousal level and amplifies the emotional reaction to stress, which could manifest as a cluster of symptoms, such as insomnia, anxiety, irritability, emotional instability and exaggerated fear or aggressiveness (hyperarousal symptoms). Underactivity of the system lowers the arousal level and attenuates the alarm reaction, which could result in hypersomnia and insensitivity to stress (hypoarousal symptoms). Clinical data support the hypothesis that, in functional psychoses, the noradrenergic dysfunction is in fact associated with the arousal symptoms described above. The anti-noradrenergic action of anxiolytics and antipsychotics can explain their sedative effects on the hyperarousal symptoms of these disorders. The results of animal experiments suggest that excessive stress can be a cause of long-term noradrenergic dysfunction.

Dopamine and migraine: a review of pharmacological, biochemical, neurophysiological, and therapeutic data

The dopamine theory of migraine pathogenesis, first proposed by F. Sicuteri in 1977, has attracted renewed interest after an increased frequency of the dopamine D2 receptor (DRD2) gene allele NcoI C was found in patients with migraine with aura. Therefore we reviewed the relevant literature. The most compelling argument favoring an interictal hypersensitivity of dopamine receptors in migraineurs stems from pharmacologic studies of the gastric and autonomic effects of dopaminergic agents such as apomorphine, but none of these studies was blinded and placebo-controlled. Various DRD2 antagonists abort migraine attacks after parenteral administration, while there is circumstantial evidence that dopamine agonists may be useful for prophylaxis. Most drugs used in these trials, however, lack selectivity for dopamine receptors. Both in pharmacological and therapeutic studies most patients had migraine without aura. We conclude that data suggesting a primary role for the dopaminergic system in migraine pathogenesis are unconvincing. Based on well established interactions between central amines, a reduced release of serotonin between attacks could lower dopamine release which would lead to receptor hypersensitivity.

Functional influence of the central noradrenergic system on the skin conductance activity in rats

Pharmacological studies on neuroleptics and amphetamine strongly suggest that some dysfunction of the central catecholamine system may play a key role in the pathogenesis of schizophrenia. Our previous studies have demonstrated that intraventricular administration of 6-hydroxydopamine, a selective neurotoxin of the catecholamine neuron, can reproduce schizophrenia-like abnormalities in the skin conductance activity. In the present experiments, effects of pharmacological modulation of the central noradrenergic activity were studied in rats. Stimulation of the central noradrenergic activity by yohimbine (0.6 mg/kg, i.m.) slowed down the habituation of the skin conductance response (SCR) and increase the spontaneous fluctuation of the skin conductance (SF), while inhibition of the activity by clonidine (0.06 mg/kg, i.m.) accelerated or obliterated the SCR and decreased the SF frequency. If the functional significance of the central noradrenergic system lies in vigilance control, the present results are consistent with classical theory in psychophysiology: the habituation rate of SCR and the frequency of SF are correlated well with each other and both indices reflect arousal level. The disorder of the system should produce not only these psychophysiological abnormalities but also psychological disturbances; i.e., overarousal and underarousal syndromes. Therefore, the dysfunction of the noradrenergic system might constitute an essential aspect of schizophrenic disorder.

Possible noradrenergic dysfunction in schizophrenia

In spite of extensive studies over the last 2 decades to find direct evidence in support of the dopamine hypothesis of schizophrenia, no undisputed experimental data has been obtained. In contrast, estimation of noradrenalin (another major catecholamine) and its metabolites in postmortem brain and in the cerebrospinal fluid appears to be producing consistent results. To understand the meaning of this change for the pathogenesis of the illness, we have carried out animal experiments in which reproducibility of schizophrenic signs and symptoms by noradrenergic dysfunction, and treatability of the disorder by modulation of noradrenergic activity were studied. First, psychophysiological signs in skin conductance responsiveness (nonhabituating or nonresponding change) and smooth pursuit eye movement (spiky or stepwise pursuit) could be reproduced by enhancing or suppressing central noradrenergic activity. Behavioral abnormalities resembling schizophrenic symptoms are known to be reproducible by over- or underactivity of the system (overarousal or underarousal syndrome). Secondly, the action of various drugs capable of modulating schizophrenic symptoms was analyzed in relation to noradrenergic activity. Haloperidol, in particular, had a potent suppressing effect on skin conductance activity (spontaneous fluctuation rate and habituation rate) when administered chronically, suggesting its inhibitory action on noradrenergic activity.

Central α-adrenoceptor subtypes involved in the emetic pathway in cats

The intracerebroventricular (i.c.v.) injection of clonidine, xylazine, adrenaline and methoxamine elicited dose-dependent vomiting in cats in that order of potency. The vomiting induced by clonidine, xylazine and adrenaline was antagonized by i.c.v. yohimbine and phentolamine possessing alpha 2-adrenoceptor-blocking activity, but not by prazosin showing alpha 1-adrenoceptor-blocking activity. In contrast, methoxamine-induced vomiting was antagonized by prazosin, but not by yohimbine. The vomiting induced by xylazine and adrenaline was not prevented by i.c.v. 6-hydroxydopamine treatment, but was prevented by i.c.v. reserpine treatment. Ablation of the area postrema with some damage to extremely adjacent areas abolished the vomiting induced by each alpha-adrenoceptor agonist. These results indicate that both central alpha 1- and alpha 2-adrenoceptors are involved in the emetic pathway in cats, although alpha 2-adrenoceptors seem to have the main role. It is also suggested that monoamines, and in particular 5-hydroxytryptamine in the brain, are involved in the regulation of alpha-adrenoceptor-mediated vomiting.

The effects of immobilization stress on electrodermal activity and brain catecholamine levels in rats

The effects of immobilization stress on electrodermal activity (EDA); skin conductance response magnitude and rate, skin conductance level and habituation number, and brain catecholamine levels; norepinephrine (NE) and dopamine (DA) were investigated in rats. Electrodermal activity was recorded using constant current method. Brain catecholamine levels were determined by a spectrophotophlorometric method. Electrodermal activity parameters (except skin conductance level) increased during immobilization. It was observed that, during immobilization stress, the alteration of norepinephrine and dopamine levels in rat brain was related to cerebral region and the duration of immobilization stress. It was concluded that these electrodermal activity alterations can be attributed to the changes in central norepinephrine metabolism induced by immobilization.

Autonomic activity

A review such as this can do no more than provide an indication of the issues involved in using autonomic activity as a means of providing a "window on the brain." Several points arise. One of the most important is that of careful and appropriate use of techniques available. One well-known textbook of experimental psychology published some time ago advocated the use of two dimes applied to the palm of the hand for the measurement of electrodermal activity. It was this sort of recommendation that led to the use of psychophysiological measurement falling into disrepute. As indicated in the second section, it is important to understand fully the peripheral mechanisms involved before measurement of electrodermal activity can be usefully carried out. Appropriate use of silver/silver chloride electrodes and physiologically appropriate levels of saline in the electrolyte medium can lead to accurate and repeatable measurement where artefact is not carelessly introduced. Equally important is the context in which studies are carried out. The psychological invasiveness of the technique is important to recognize, and it is here that measurement of autonomic activity probably scores over other methods that are available insofar as very little restriction of the subject is required and the number of transducers that must be applied is minimal. The measurement of autonomic activity within the totality of the experimental context is all important. As an example Dawson and Schell investigated the SCR to words which had previously been associated with shock. When these words were presented to the ear to which attention was not directed in a dichotic listening paradigm, an SCR could be elicited although the subject was unaware of the presentation of the stimulus. The importance of the Dawson and Schell study was the care that they took to make sure that the subject really was unaware of the critical stimulus and had not momentarily switched attention from the attended ear. More important, their experiment, in contrast to some which had gone before, used a balanced design in which the critical stimuli were presented on different occasions to each ear. As a result of this it was found that critical stimuli, which were presented to the left ear, right hemisphere, gave rise to SCRs, even when the subject was not aware of their presentation, whereas stimuli presented to the right ear, left hemisphere elicited no response.(ABSTRACT TRUNCATED AT 400 WORDS)

Skin conductance activity after intraventricular administration of 6-hydroxydopa in rats

Absence of skin conductance response (SCR) and failure of its habituation are psychophysiological signs observed in most schizophrenics. In the present experiments, skin conductance activity was studied in rats before and after intraventricular administration of 6-hydroxydopa (6-OHdopa), a neurotoxin that selectively destroys noradrenaline nerve terminals and induces denervation supersensitivity at the synapse. All intact rats studied (n = 32) showed SCR and its habituation to repeated auditory stimuli (500 Hz, 90 dB, 1 sec, 20 times). They also showed some spontaneous fluctuation (SF) of the skin conductance. In the early stage following the 6-OHdopa (100 micrograms) administration (n = 16), it was noted that the SCR disappeared and the SF were markedly reduced in frequency (p less than 0.001). From the third day to the fourth week after this treatment, there was some recovery of the SF rate, and the SCR tended to reappear with a marked slowing down of its habituation. Eight weeks after the treatment, the majority (11/16) of the 6-OHdopa rats showed habituation failure of the SCR (p less than 0.005); vehicle-treated rats (n = 16) did not show these alterations. Estimation of catecholamine concentration after the experiment confirmed the selective depletion of brain noradrenaline. These results suggest that destruction of the noradrenergic fibers after the 6-OHdopa treatment and denervation supersensitivity which developed later are the cause of the nonresponding and nonhabituating changes of SCR, respectively.

Skin conductance response after 6-hydroxydopamine lesion of central noradrenaline system in cats

Absence of skin conductance response (SCR) is a psychophysiological sign frequently observed among schizophrenic patients. This alteration of electrodermal activity can be reproduced in cats and rats by intraventricular administration of 6-hydroxydopamine (6-OHDA), a neurotoxin selectively destroying catecholamine neurons. The finding appears to be quite consistent with the catecholamine hypothesis of schizophrenia. To determine which catecholamine system--the dopamine (DA) or the noradrenaline (NA)--is responsible for the induction of this abnormality, the same dose of 6-OHDA was microinjected to either the ventral tegmental area (VTA, n = 3), through which most DA fibers ascend, or to the ascending noradrenergic bundle (ANB, n = 3), through which most NA fibers ascend. Four cats remained intact as a control for later brain catecholamine estimation. The skin conductance of all pretreatment intact cats (n = 10) showed not only spontaneous fluctuations but also SCRs to auditory stimuli (5 kHz, 100 dB, 1 sec) which habituated with repetition. In contrast, ANB-lesioned cats showed a complete abolition of auditory SCRs, few spontaneous fluctuations, and a low basal skin conductance level. These abnormalities were statistically significant. On the other hand, no change was found in the skin conductance activity of the VTA-lesioned cats. Catecholamine estimation after the experiment confirmed selective destruction of the appropriate system corresponding to each type of lesion. These findings are discussed in the context of the DA or NA theory of schizophrenia, and involvement of the NA system in the pathogenesis of this illness is suggested.

Increased firing of locus coeruleus neurons associated with preparatory set in rats

The activity of locus coeruleus (LC) neurons was studied during the performance of a reaction-time task with warning. Seventeen cells were tentatively identified as LC neurons using two criteria: (1) Relative location from the mesencephalic trigeminal (Me5) neurons, which have large-amplitude bursting discharges synchronized with masticatory movements. (2) The presence of an antidromic response to the stimulation of the dorsal pathway. Of these 17 cells, 16 neurons showed intense and consistent firing during the period between the warning stimulus and the response. Neither the stimuli nor the lever pressing movements alone were accompanied by such a change, suggesting that increased firing occurs in association with preparatory set. The one remaining neuron of the 17 cells showed no change with the task performance. It is supposed that only the 16 homogeneous neurons belong to the LC.

Two types of changes in skin conductance activity after intraventricular administration of 6-hydroxydopamine in rats

Sixteen male Wistar strain rats were trained to have their skin conductance activity recorded through the soles of their hind limbs, and the effects of the intraventricular administration of 6-OHDA (200 micrograms) on this activity were studied. The intact rats showed skin conductance response and its habituation to repeated auditory stimuli (500 Hz, 90 dB, 1 sec). The 6-OHDA-treated rats exhibited either obliteration of the response or impairment of the habituation. The nonresponding state tended to be accompanied by a low rate of spontaneous skin conductance fluctuation, but the nonhabituating state was not accompanied by changes of the rate. The vehicle-treated rats showed no change in these activities. These electrodermal characteristics were discussed along with the CA hypothesis of schizophrenia.