Joseph P. Huston

The thalamic rat: General behavior, operant learning with rewarding hypothalamic stimulation, and effects of amphetamine ☆

Abstract In 52 rats the major forebrain areas, including the cortex, hippocampus, striatum, amygdala and septum were bilaterally ablated, resulting in a chronic thalamic preparation. Experiment 1 measured body temperature and motor activity, showing continuous cyclic 10–60 minute rest- activity cycles. Intragastric feeding was followed by periods of quiescence accompanied by hypothermia lasting from 1–5 hrs. Experiment 2 demonstrated sucessful operant conditioning of limb movements in 12 animals by use of rewarding hypothalamic stimulation. Once a response was strengthened by conditioning no extinction could be observed, although the response was modifiable by further conditioning. In Experiment 3 the effects of d-amphetamine were investigated. Amphetamine induced hyperthermia, hyperactivity and stereotyped behaviors, and was found to facilitate primarily the performance of the previously conditioned behavior.

Memory facilitation by posttrial hypothalamic stimulation and other reinforcers: A central theory of reinforcement☆

Abstract A central theory of reinforcement is presented, which is based on the assumption that reinforcers act directly on dynamic memory processes. One prediction from the model is that learning of various tasks should be improved as a result of reinforcement presented during the period of short-term memory. To test this hypothesis the reinforcers food, water or electrical stimulation of the lateral hypothalamus were presented posttrial in diverse learning situations. Posttrial food reinforcement facilitated passive avoidance learning in mice. In rats 30 sec of posttrial reinforcing brain stimulation facilitated learning of a shuttle-box avoidance, step-down avoidance, and small box avoidance. Appetitive T-maze learning was improved with posttrial reinforcing brain stimulation contingent on errors. Learning of a conditioned taste aversion was not influenced by reinforcing brain stimulation presented during the CS - UCS interval.

Control of sleep states in the rat by short light-dark cycles

The effects of 60-60 min light-dark (LD) cycles on sleep, feeding, drinking and motor activity were investigated in the rat. Waking, consummatory behaviour and motor activity were inhibited by light, while sleep was enhanced. The effects were dependent on the intensity of light. The percentage of slow wave sleep (SS) increased within the first 15 min of the light period and reached a plateau within 30 min. The reduction of SS during darkness showed a similar time-course. The percentage of paradoxical sleep (PS) started to increase only 15 min after the onset of light and continued to rise during the first 15 min of darkness. All parameters exhibited a free-running circadian rhythm. The LD-induced changes of SS were largest during the circadian phase in which the animal was active. The changes of PS which succeeded the onset or offset of light, were largest in the inactive circadian phase. The most immediate influence of changes in illumination is exerted on the slow wave component of sleep. Hypotheses to account for the temporary dissociation between the two sleep states are discussed.

Physiological and behavioral effects of parachlorophenylalanine in the rat.

The effect of parachlorophenylalanine (PCPA 300 mg/kg i.p.) on several physiological and behavioral parameters was investigated with telemetric methods in the unrestrained rat. Body temperature did not change with the exception of an immediate and short-lasting decrease after drug injection. Food and water intake were maximally depressed on the day following drug administration, and recovered gradually during the subsequent days, drinking more rapidly than feeding. Click-evoked potentials recorded from the auditory cortex and inferior colliculus maintained their typical waveforms during synchronized and desynchronized sleep indicating that PCPA does not produce a qualitative change of the sleep stages. A short-lasting increase of the potentials was observed after drug injection. PCPA exerted profound changes on motor activity. The activity during the light periods was significantly increased. However, motor behavior was altered more in its temporal pattern than in intensity, especially during the dark periods. The circadian rhythms of feeding, drinking and motor activity were attenuated. Since the time-course of these changes corresponds to that known for serotonin depletion in the brain, serotoninergic neuronal mechanisms may play a major role in the organization of behavioral rhythms.

Facilitation of learning by reward of post-trial memory processes

Unter Verwendung einer passiven Vermeidungsreaktion mit Futterbelohnung nach verschiedenen Zeitintervallen zwischen 0 und 120 sec konnte gezeigt werden, dass belohnung 20, 30 und 50 sec nach dem Fusschock signifikant verbessertes Lernen bewirkt. Diese Daten unterstützen die Hypothese, dass Gedächtnisprozesse-konzeptionell als operante Reaktion aufgefasst-durch Belohnung modiiizierbar sind.

Effects of two-hour light-dark cycles on feeding, drinking and motor activity of the rat ☆

Abstract The effect of two-hour light-dark cycles on feeding, drinking and motor activity in the rat was compared with behavior under the usual 12 12 hour cycle. The two-hour cycles consisted of 60 60 min, 80 40 min and 40 80 min light-dark schedules which were maintained each for 7 days. Water intake, frequency of feeding, and motor activity were still significantly higher during dark than during light, although their occurrence during dark was reduced as compared to the 12 12 hour control schedule. A free-running circadian rhythm of consummatory behavior with a period length exceeding 24 hours was present throughout the experimental period. The amplitude of the circadian feeding rhythm gradually decreased over time, whereas the percentage of feeding during dark increased. During the circadian phase of minimal food intake, illumination changes affected feeding behavior more strongly than during the phase of maximal food intake. After restoration of the orginal 12 12 hour cycle, the amplitude of the nocturnal feeding rhythm increased gradually over several days, whereas the amplitude of the drinking rhythm showed a more rapid recovery. The experiments show that even short cycles of illumination may exert control over the rats consummatory and motor activity. Short light-dark schedules provide a way for studying separately effects of illumination and of circadian rhythms.

Influence of 6-hydroxydopamine injections in the substantia nigra on lateral hypothalamic reinforcement

Repeated unilateral injections of 6-hydroxydopamine (6-OHDA) into the substantia nigra of rats caused massive non-specific lesions and disrupted self-stimulation by lever-pressing equally from electrodes in the ipsilateral and contralateral hypothalamus. Repeated bilateral injections of 6-OHDA abolished self-stimulation when lever-pressing was the criteria, but not when simpler motor responses were used as operants. Hence, nigrostriatal dopamine is unlikely to be critically involved in operant learning and reward processes.

Differential effects on learning by ventromedial vs lateral hypothalamic posttrial injection of substance P

The effects of post-trial injection of substance P (SP) into the lateral hypothalamus (LH) and the ventromedial hypothalamus (VMH) on passive avoidance learning was studied in rats. In the VMH, 50 ng and 500 ng SP influenced neither learning of a step-down avoidance nor of an alcove avoidance response. In contrast to these findings, 500 ng SP injected into the LH significantly enhanced retention of the alcove avoidance task. Similarly, in the step-down avoidance experiment, learning was strongly facilitated by posttrial injection of 50 ng as well as 500 ng SP into the LH. These results, together with our previous data showing amnesia with posttrial injection of SP into amygdala and substantia nigra, suggest that exogenously applied SP influences the activity of those brain regions shown to contain high densities of SP-positive nerve terminals. Interestingly, the effects of posttrial SP injection parallel the effects of post-trial electrical brain stimulation on passive avoidance learning. Hence, posttrial SP retroactively facilitates or impairs learning depending on where in the brain it is injected.

Post-trial reinforcing hypothalamic stimulation can facilitate avoidance learning

Thirty seconds (0.2 sec on, 0.8 sec off) reinforcing electrical stimulation of the lateral hypothalamus of rats (presented 30 sec after the trial) facilitated learning of an avoidance task. This result was interpreted in terms of a direct influence of reinforcement on short-term memory processes.

Up-hill avoidance: a new passive-avoidance task.

Abstract Rodents and many other animal species orient and locomote up-hill when placed on a tilted surface. When placed with head facing downwards on an incline, rats turn around and climb up reliably within a few seconds. This behavior can be suppressed by a contingent tail-shock, and therefore is a suitable response for studying passive avoidance learning. The present report summarizes the effectiveness of various combinations of angle of incline and levels of tail-shock intensity on up-hill avoidance learning in rats.