Tolerance to amphetamine hypophagia: a microstructural analysis of licking behavior in the rat

A Dual-Mode Magnetic-Acoustic System for Monitoring Fluid Intake Behavior in Animals

We have developed an unobtrusive magnetic-acoustic fluid intake monitoring (MAFIM) system using a conventional stainless-steel roller-ball nipple to measure licking and drinking behavior in animals. Movements of a small permanent magnetic tracer attached to stainless-steel roller balls that operate as a tongue-actuated valve are sensed by a pair of three-axial magnetometers, and transformed into a time-series indicating the status of the ball (up or down), using a Gaussian mixture model based data-driven classifier. The sounds produced by the rise and fall of the roller balls are also recorded and classified to substantiate the magnetic data by an independent modality for a more robust solution. The operation of the magnetic and acoustic sensors is controlled by an embedded system, communicating via Universal Serial Bus (USB) with a custom-designed user interface, running on a PC. The MAFIM system has been tested in vivo with minipigs, accurately measuring various drinking parameters and licking patterns without constraints imposed by current lick monitoring systems, such as nipple access, animal-nipple contact, animal training, and complex parameter settings.

Role of instrumental learning in tolerance to cathinone hypophagia

The effects of dl-cathinone on milk intake and motor activity were investigated in bottle- and cannula-fed rats. Acute injections of cathinone produced dose-dependent increases in activity in both groups but only produced decreased intake in bottle-fed rats. With chronic injections, tolerance to the suppression of intake developed in the bottle-fed group, accompanied by decreased activity. After the tolerance phase, switching from bottle to cannula feeding produced further increases in intake, whereas switching from cannula to bottle feeding produced decreased intakes. These results suggest that (a) cathinone suppresses intake by inducing locomotion and stereotypy, which interfere with the appetitive phase of feeding, and (b) tolerance to drug-induced hypophagia involves learning to suppress such movements, as proposed by the instrumental learning model.

Orbitofrontal ensemble activity monitors licking and distinguishes among natural rewards

The classification of rhythmic licking into clusters has proved to be useful for characterizing brain mechanisms that modulate the ingestion of natural rewards (sucrose and water). One cortical area that is responsive to rewarding stimuli is the orbitofrontal cortex (OFC). However, it is not presently known how OFC neurons respond while rodents freely lick for natural rewards and whether these responses are related to the structure of licking clusters. We addressed these issues by showing that temporary inactivation of the OFC decreases the duration and increases the number of clusters and that the activity of OFC neurons changed at precise times before, during, and after the cluster terminates. Furthermore, analysis of the activity of OFC neuronal ensembles showed that they could discriminate cluster onset from termination, predict when a behaving animal will begin a cluster, and distinguish and anticipate between natural rewards. These results provide a new role for the OFC in influencing licking clusters and anticipating specific rewards.

Tolerance to amphetamine hypophagia: a real-time depiction of learning to suppress stereotyped movements in the rat

To analyze how tolerance develops to amphetamine-induced hypophagia, the authors recorded real-time licking responses in rats given chronic injections of the drug and access to milk for 30 min. Initially, licking was greatly reduced and occurred only late in the session. The acquisition of tolerance was characterized by a decrease in the latency to initiate licking, a gradual increase in the number of licks, and a reorganization of the temporal licking pattern such that licks were distributed throughout the session, interspersed with pauses. On post-tolerance dose-response tests, licking was directly proportional to drug dose in some rats. The results support the view that tolerance to amphetamine hypophagia involves a behavioral adaptation to the motor effects of the drug.