An objective and sensitive method for quantitative measurement of stereotyped gnawing

Alterations in apomorphine concentration in spinal cord and brain follow the time course of catalepsies induced by different treatments

Because evidence for the neurotransmitter role of dopamine in the gray matter of the spinal cord is accumulating, a question arises of whether or not spinal dopamine receptors are also involved in the effects of dopaminomimetics which are believed to induce beneficial effects in Parkinson's disease through an action thought to be mediated mainly by striatal dopamine receptors. To test this hypothesis muscimol and picrotoxin were injected unilaterally into the posterior part of the substantia nigra of rabbits permanently implanted with stainless-steel cannulae. Muscimol (a GABA-mimetic) enhanced locomotor activity, evoked a stereotyped behavior and contralateral rotations, and increased apomorphine-induced gnawing. Picrotoxin, a substance which inhibits GABA transmission, induced ipsilateral rotations, evoked catalepsy and muscle rigidity, and inhibited locomotor activity. Picrotoxin abolished apomorphine-induced gnawing, and increased haloperidol-mediated catalepsy. The catalepsy induced by an intranigral injection of picrotoxin, and the picrotoxin-evoked blockade of the apomorphine-induced gnawing disappeared within 16 h after the intranigral injection. Alterations in the apomorphine concentration in brain structures (n. caudatus and cerebral cortex) and in spinal cord after picrotoxin injection followed the same time course as the behavioral changes, and returned to the control values 16 h after injection of picrotoxin. Apomorphine was always injected 30 min before the rabbits were killed. Moreover, the substantial increase (to 300%) in apomorphine concentration in the spinal cord probably reflects the antagonism between behavioral changes induced by picrotoxin and the haloperidol catalepsy, rather than the decreased apomorphine concentrations observed in the brain structures. We suggest, therefore, that there exists a correlation between the behavioral effects, which are generally accepted as laboratory models of Parkinson's disease, and the enhanced apomorphine concentration in the spinal cord.

The time and space machine: continuous measurement of drug-induced behavior patterns in the rat

Because of the increasing demand for refined techniques to record drug-induced motoric changes, we designed and evaluated a computer monitoring system with continuous measurement of different parameters of rat motor activity. This system is particularly useful for chronic drug studies because it can characterize patterns of behavior and combines the residential and experimental environments, thus enabling automated behavioral measurement without experimenter intervention. Behavioral responses are detected by a capacitance-sensing device that generates bipolar analog voltages representing the location of the rat in its home cage. These voltages are first transduced, then amplified, and finally converted to digital signals in a computer that processes the input using algorithms to define specific responses. The technique pinpoints the exact location of the rat and identifies many kinds of responses simultaneously (e.g., rearing, circling) by tracking the path of movement or setting threshold limits. Some threshold values (representing rearing, gross movements, fine movements) were validated against stereotypy rating scales for amphetamine, apomorphine, and beta-phenylethylamine. Among these drugs, quantitatively distinct response profiles were obtained. The system has wide applications for studies of biological rhythms, sleep, aging, and drug toxicology.

A quantitative analysis of stereotyped gnawing induced by apomorphine

An apparatus was designed and constructed to enable a quantitative analysis of the stereotyped gnawing produced by the dopamine agonist apomorphine. Using this apparatus it was discovered that increasing the subcutaneous dose of apomorphine increased (1) the number of animals that gnawed, and (2) the duration of gnawing in those animals that gnawed at all doses. Other aspects of apomorphine-induced gnawing, in particular the latency to respond and the frequency and duration of individual gnaws, were relatively unaffected. Likely properties of the system responsible for the organization of sterotyped gnawing are discussed.

A method for simultaneous recording of eight behavioral parameters related to monoamine neurotransmission

In response to the increasing demand for refined techniques to record drug induced changes in motor activity we have designed and evaluated against observations an automatic test box that quantifies eight defined components of behaviour in rats. Activity, corresponding to the recordings from the commonly used photocell activity boxes. Total, and forward locomotion, expressing the actual distance the rat walks. Corner count, and corner time, reflecting the position of the animal in the box. Hole count, and hole time, expressing the reaction of the rat to an environmental stimulus i.e. holes in the bottom of the test box. Gnawing, which is a direct counting of the number of gnaws made by the animal. The recording parameters relate to our interest in behaviour influenced by monoamine neurotransmission and the result shows that the selected parameters are recorded with high reliability.

Effects of intrastriatal injections of atropine and methacholine on the apomorphine-induced gnawing in the rabbit

To find out the anatomical location of the target point of cholinergic-dopaminergic equilibrium, atropine (40 microng) or methacholine (10 microng) were injected through previously implanted cannulas into various places of caudate nucleus and putamen of the rabbit, and the effect of the injections on stereotype gnawing induced by subcutaneously or intravenously administered apomorphine (1--2 mg/kg) was assessed. The intensity of gnawing was measured using a special apparatus, counting each bite. Atropine inhibited the stereotype, while metacholine potentiated it. The effects were evident with the method used, but difficult to reveal with the classical method of assessing the intensity of stereotyped behavior, based on visual observation. The results suggest that the striatum is not a target point for the cholinergic component of the cholinergic-dopaminergic equilibrium in the central nervous system.