Denigration and sensorimotor disability induced by ventral tegmental injection of 6-hydroxy-dopamine in the cat

Toward a general psychobiological theory of emotions

Emotions seem to arise ultimately from hard-wired neural circuits in the visceral-limbic brain that facilitate diverse and adaptive behavioral and physiological responses to major classes of environmental challenges. Presumably these circuits developed early in mammalian brain evolution, and the underlying control mechanisms remain similar in humans and “lower” mammals. This would suggest that theoretically guided studies of the animal brain can reveal how primitive emotions are organized in the human brain. Conversely, granted this cross-species heritage, it is arguable that human introspective access to emotional states may provide direct information concerning operations of emotive circuits and thus be a primary source of hypotheses for animal brain research. In this article the possibility that emotions are elaborated by transhypothalamic executive (command) circuits that concurrently activate related behavior patterns is assessed. Current neurobehavioral evidence indicates that there are at least four executive circuits of this type – those which elaborate central states of expectancy, rage, fear, and panic. The manner in which learning and psychiatric disorders may arise from activities of such circuits is also discussed.

Opposite effects of intranigral ibotenic acid and 6-hydroxydopamine on motor behavior and on striatal neuropeptide Y neurons

Unilateral lesions of the basal ganglia circuit induce a disequilibrium of motor processing, most obviously expressed by the resulting circling behavior. Compensatory events, which reduce the motor asymmetry, could be accompanied by changes in neurotransmitter/modulator parameters in the involved brain regions. In the present investigation, the effects of an interruption of the striato-nigro-thalamic loop by ibotenic acid (IBO)-induced lesions of total substantia nigra (SN) on circling behavior and on striatal neuropeptide Y (NPY) neurons were compared with those after the selective destruction of the dopaminergic nigrostriatal projection with 6-hydroxydopamine (6-OHDA). Directly after the operation, IBO-lesioned rats showed a high circling rate to the side contralateral to the lesion, whereas 6-OHDA-lesioned rats showed ipsiversive circling. With the lesion-induced development of dopamine receptor supersensitivity, 6-OHDA-treated rats, when stimulated with the dopaminergic agonist apomorphine, change their circling direction to the contralateral side. Complete IBO lesions of the SN abolished this effect: rats continued to circle to the contralateral side. These observations suggest that not only the dopaminergic denervation of the striatum but also the imbalance in the activity of the thalamo-cortical projection (reduced after 6-OHDA, augmented after IBO) are instrumental in determining the degree and direction of circling. Quantification of NPY-immunoreactive neurons in striatum revealed a decrease in 6-OHDA lesioned rats after 3 days on the side contralateral to the lesion, an effect even more pronounced after 4 month's survival time. IBO-induced lesions of the SN had an opposite effect on NPY-immunoreactivity in the striatum: neuron counts were lower on the ipsi- than on the contralateral side. In addition, a time-dependent variation in total number of NPY-neurons was noted: during the early postoperative periods an increase, followed by a prolonged decrease to values below 50% of the controls after 4 months. Taken together, these results provide evidence that a dopaminergic deafferentation and its consequences on the nigro-thalamo-cortical loop will determine NPY expression in the striatal interneurons. In particular, it is suggested that the number of striatal NPY-neurons and the imbalance in cortical activity are tightly coupled in terms of a negative correlation.

Influence of catecholamines on reward-related neuronal activity in monkey orbitofrontal cortex

Reward-related neuronal activity and its regulation by catecholaminergic input were investigated in the orbitofrontal cortex of the behaving monkey by means of extracellular unit recording and microiontophoretic application of drugs. Neuronal activity was modulated by reward situations and catecholamines. The activity of a majority of the noradrenaline-sensitive cells decreased and of the dopamine sensitive cells increased during food acquisition behavior. The results suggest that catecholamines could be involved in reward-related neuronal activity in the monkey orbitofrontal cortex.

Ventral mesencephalic tegmentum (VMT) controls electrocortical beta rhythms and associated attentive behaviour in the cat

When a cat is immobile, very alert and displaying behaviour suggesting focused attention toward a target in its environment, beta rhythms (ca. 40 Hz) develop in the fronto-parietal cortical areas. After bilateral electrolytic lesions of the ventral mesencephalic tegmentum (VMT), these beta rhythms are suppressed (while other cortical activities, with other behavioural correlates, persist), and at the same time, attentive immobility is no longer observed: the same experimental situation as in the control now elicits locomotor hyperactivity. Arguments are produced, favouring the hypothesis that both behavioural immobility and the accompanying thalamocortical beta rhythms are controlled through one of the dopaminergic system that originate from the VMT and are distinct from the nigrostriatal one.

Behavioral alterations and loss of caudate modulation in the centrum medianum--parafascicular complex of the cat following electrolytic lesions of the substantia nigra

Extracellular activity in the centrum medianum--parafascicular complex was examined following electrolytic lesions of the substantia nigra in the cat. Three major changes were observed in the activity of these polysensory medial thalamic neurons: (1) normally quiescent in the intact animal, about 70% of the neurons now displayed spontaneous activity; (2) many of these spontaneously active neurons no longer responded to caudate stimulation and the responses to sensory stimulation were not changed; and (3) while caudate stimulation alone did inhibit some neurons, such stimulation in a conditioning test procedure often failed to inhibit the test response to limb stimulation which 'broke through' the inhibitory period. All of these changes were correlated with the extent of damage to the ipsilateral substantia nigra. Additionally, a noticeable change was observed in the behavior of the lesioned animals; intense circling, contralateral to the side of the lesion, persisted for several days following surgery. Other symptoms were arrest reactions, abnormal rhythmic pawing and sluggishness of movement. The results indicate that the substantia nigra is an important element in funneling caudatofugal activity to the centromedian--parafascicular complex where it interacts with, and modulates incoming sensory activity. The loss of this modulation and the removal of a tonic background inhibition, indicated by the increased proportion of spontaneously active neurons, may be important factors in producing the observed behavioral abnormalities.

Activation and lateralization of sensorimotor field for perioral biting reflex by intranigral GABA agonist and by systemic apomorphine in the rat

In Experiment 1 unilateral injection of the GABA agonist, muscimol (20 ng in 0.1 microliter saline) into the substantia nigra (SN) of rats elicited contraversive turning and a correlated transient asymmetry in responsiveness to tactile stimulation of the mouth area. On the side of the face contralateral to the injected SN they responded stronger than on the ipsilateral side, and, furthermore, they responded to tactile stimulation with a withdrawal of the lip, followed by a vigorous biting of the probe. In Experiment 2, systemic injection of apomorphine also sensitized the perioral biting response to tactile stimulation. Unilateral injection into the SN of 8 micrograms 6-OHDA blocked this response to stimulation of the side of the face ipsilateral to the lesion. The experiments demonstrate: (1) pharmacological control of sensory-motor neglect, the asymmetry being determined by the direction of turning; and (2) a possible neuropharmacological basis of the perioral biting reflex, which may be related to certain types of aggressive behaviors.

Specificity of dopaminergic neuronal degeneration induced by intracerebral injection of 6-hydroxydopamine in the nigrostriatal dopamine system

The neurotoxic specificity of injections of 6-hydroxydopamine (6-OHDA) into areas containing either dopamine (DA) cell bodies (substantia nigra) or DA axon terminals (striatum) was studied. This selective effect was compared to the unspecific effects of copper sulfate (CuSO4) injection and electrocoagulation. One to two days after unilateral nigral injection of 2 mug of either 6-OHDA or CuSO4 into the nigra the volume of the unspecific lesions around the tip of the cannula was very similar. Only the 6-OHDA-induced lesions were associated with elective degeneration of the nigral DA neurons. Ten days after the administration of the same compounds the gliosis in the substantia nigra was much more extensive in CuSO4-than in 6-OHDA-treated rats; however, the reduction of DA concentrations in the ipsilateral striatum was only noticeable after 6-OHDA (-62%). A somewhat similar decrease of striatal DA levels (-52%) was observed after large electrocoagulation of the substantia nigra. Ten days after 6-OHDA (8mug) or electrolytic lesion of the striatum the Km for DA, serotonin and choline uptakes were similar in the striata of both sides, suggesting that the uptake process in the non-damaged neurons of the lesioned side was functionally normal. Following electrolytic lesion of the striatum, serotonin and choline Vmax values were decreased to about the same extent as the striatal reduction in weight and DA levels. When directly administered into the striatum 6-OHDA also produced a decline in DA concentration and Vmax but in contrast did not affect serotonin and choline uptake (Vmax), suggesting that the drug specifically destroyed dopaminergic neurons. The present data confirm that selective DA denervation can be achieved when appropriate amounts of the drug are injected into brain tissue in order to limit the unspecific lesion.

Ventral midbrain stimulation, blood pressure responses and their relation to the dopaminergic nigro-striatal pathways

In 40 cats systematic, electrical stimulation of ventral midbrain structures was performed. In the lightly anaesthetised animals, fixed in a stereotaxic frame, ECoG and arterial blood pressure were registrated. As a result stimulation-induced phasic blood pressure increases have been found within a distinct area including substantia nigra and ventral tegmentum. From the same region nonspecific responses in the ECoG (spindling, recruiting and desynchronisation by low and middle frequent stimulation) could be obtained. The blood pressure responses were enhanced after hemisection at the level of the posterior hypothalamus ipsilateral to the stimulation side. Drugs (Haloperidol, alpha-methyltyrosin and 6-hydroxydopamine), affecting the dopamine metabolism in different ways, abolished the stimulation-induced blood pressure responses. In agreement with previous findings it is concluded that motor and autonomic activation, elicited in ventral midbrain structures are mediated by catecholaminergic transmission.