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Single cell activity in the auditory cortex of the unanesthetized, behaving monkey: correlation with stimulus controlled behavior.

The neural activity of 60 cells in the auditory cortices of two rhesus monkeys was examined in relation to systematic variations in cued reinforcement conditions. Subjects were trained on a variant of the auditory reaction time (RT) task. In the final behavioral paradigm monkeys were rewarded for rapid key releases to all tonal stimuli in one reinforcement condition (frequency irrelevant = FI), while in the other stimulus-cued condition (frequency discrimination = FD) releases to certain tonal test frequencies were unrewarded. Upon completion of behavioral training, RTs to identical tonal test stimuli were longer and more variable when presented in the unrewarded (FD) condition. Following neurosurgery it was possible to observe the effects of reinforcement condition on auditory RT performance and the activity of single auditory cortical cells simultaneously. Of the auditory cortical cells sampled, 25% showed definite and repeatable alterations in evoked activity to the same tonal stimulus which were correlated with reinforcement condition. For nearly all cells examined the influence of reinforcement condition was much the same: on excitatory responses were increased in the FD condition. A few of the cells also showed alterations in latency and/or pattern of evoked discharge. Importantly, none of the units examined showed changes in their spontaneous discharge rates as a function of reinforcement condition. both peripheral mechanical and central neural theories were considered as a basis for the observed neural alterations. The specificity and latency of the alterations as well as the absence of tonic effects seemed to indicate that the neural changes observed were mediated by central mechanisms. Our results strongly suggest that the activity of a sample of auditory cortical neurons depends on the behavioral state of the preparation. We propose that 'behavioral state", appropriately defined, can be a useful concept for neurophysiologists.

Action Potentials

Effects of azaprophen, scopolamine and trihexyphenidyl on schedule-controlled behavior, before and after chronic physostigmine.

The effects of the muscarinic acetylcholine receptor antagonists, azaprophen (0.3-10.0 mg/kg), scopolamine (0.01-3.0 mg/kg) and trihexyphenidyl (0.3-10.0 mg/kg) were examined in rats using a VI 18 s schedule of food reinforcement, before and after chronic physostigmine administration. All three compounds produced dose-dependent decreases [corrected] in the rate of responding. Scopolamine was more potent than trihexyphenidyl which was equipotent to azaprophen. All three compounds antagonized the response rate-decreasing effects of physostigmine in a dose-dependent fashion. Following 43 consecutive daily administrations of physostigmine (0.4 mg/kg), partial tolerance developed to its response rate-decreasing effects. When the three antagonists were again examined (alone and in combination with physostigmine), their effects were generally unchanged. These results further characterize the behavioral effects of azaprophen, scopolamine and trihexyphenidyl. These results also suggest that tolerance to physostigmine's effects can be mediated through behavioral rather than pharmacological mechanisms.

Acetylcholine

Effect of soman on schedule-controlled behavior and brain acetylcholinesterase in rats.

Rats were trained to press a lever under a multiple fixed-ratio 25 fixed-interval 50-second (FR25 FI50-sec) schedule of food reinforcement. Soman, 70-90 micrograms/kg, s.c., suppressed response rates in both components, with a slightly greater effect in the FI schedule. The pattern of responding under the FI schedule, however, was maintained until lever-pressing was nearly completely suppressed. At the highest doses, soman occasionally caused tremors or mild tonic seizures with hindlimb abduction. The suppression of response rate was correlated with inhibition of acetylcholinesterase (AChE) in all brain regions examined: cortex, striatum, hippocampus, hypothalamus and brainstem. Cortical AChE was inhibited to the highest degree, while striatal AChE was most resistant to inhibition by soman.

Acetylcholinesterase

Inhibition of acetylcholinesterase in the gut inhibits schedule-controlled behavior in the rat.

Rats were trained to press a lever under a multiple Fixed-Ratio 25 Fixed-Interval 50-second schedule of food reinforcement. Subcutaneous injection of soman, 80 micrograms/kg, suppressed responding under both schedules and inhibited acetylcholinesterase (AChE) in the brain. AChE activity in the gastrointestinal tract was not significantly inhibited. In contrast, i.p. injection of either soman (10-40 micrograms/kg), neostigmine (75 micrograms/kg) or DFP (350 micrograms/kg) caused marked suppression of behavior and AChE activity of the gut, without affecting brain AChE. These doses caused marked increases in peristaltic activity and likely caused gastrointestinal spasm. Injection of DFP, 500 micrograms/kg, s.c., inhibited AChE in both the brain and gut. The results indicate that inhibition of AChE in the gastrointestinal tract by certain anticholinesterase agents may be involved in the behavioral effects attributed to these drugs.

Animals

Tolerance to oxotremorine's effects on schedule-controlled behavior in physostigmine-tolerant rats.

Tolerance to the effects of physostigmine and oxotremorine in rats was evaluated using a multiple fixed-ratio 10, extinction schedule of food presentation. Physostigmine was administered either once daily or three times daily for 18 consecutive days. Tolerance to physostigmine's response decreasing effects was observed under both administration regimens. Cumulative dose-effect functions for oxotremorine (0.0056-0.562 mg/kg) were determined before and after chronic physostigmine administration. Oxotremorine's potency to produce response rate suppression decreased in rats receiving physostigmine three times daily but did not substantially change in rats receiving single daily injections. These results demonstrate that the dose or duration of action of physostigmine can determine whether tolerance to physostigmine's effects is accompanied by cross-tolerance to oxotremorine's effects.

Animals

Effects of MK-212 (6-chloro-2[1-piperazinyl]pyrazine) on schedule-controlled behavior and their reversal by 5-HT antagonists in the pigeon.

The effects of MK-212 (6-chloro-2[1-piperazinyl]pyrazine), a centrally-active 5-hydroxytryptamine (5-HT; serotonin) agonist, were studied alone and in combination with the 5-HT antagonists, methysergide (0.01-0.1 mg/kg), metergoline (0.01-1.0 mg/kg) and ketanserin (0.01-3.0 mg/kg). Pigeons were maintained under a procedure where key pecks were reinforced under a multiple fixed-interval (FI) fixed-ratio (FR) schedule of food presentation. In the fixed-interval component, the first response after 3 min had elapsed, produced food, while in the fixed-ratio component, the thirtieth response was reinforced. The drug MK-212 (0.1-3.0 mg/kg) produced dose-related decreases in response rates under both components of the schedule. In smaller doses of MK-212 (0.3 and 1.0 mg/kg), the decrease in the response rate was greater in the fixed-interval component than in the fixed-ratio component. Small doses of methysergide (0.03 mg/kg) and metergoline (0.1 mg/kg), which had little effect when given alone, partially blocked the effects of MK-212 (1.7 and 3.0 mg/kg) in decreasing rate. Larger doses of these compounds, which sometimes increased the response rate when given alone, resulted in a more complete restoration of response rates when administered with MK-212. Ketanserin, a selective 5-HT2 antagonist, reversed the effects of MK-212 in some cases, but the patterning of responses remained disturbed.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals

Effects of selected analogs of adenosine on schedule-controlled behavior in rats.

Acute administration of N6(L-phenylisopropyl)adenosine (L-PIA; 0.01-0.178 mg/kg, s.c.), N6-cyclohexyladenosine (CHA; 0.01-0.178 mg/kg, s.c.), 2-chloroadenosine (2-CA; 0.32-0.56 mg/kg, s.c.), N6-cycloheptyladenosine (CHPA; 0.032-1.0 mg/kg, s.c.), N6-phenyladenosine (PA; 0.1-1.0 mg/kg, s.c.), N6(D-phenylisopropyl)adenosine (D-PIA; 0.32-1.0 mg/kg, s.c.) and N6-benzyladenosine (BA; 1.0-17.8 mg/kg, s.c.) produced dose-related decreases in responding under a fixed-ratio (FR) schedule of food reinforcement. Dose-effect curves were determined by administering cumulative doses (s.c.) during periods that preceded the sequential components of the schedule. Neither 2-chloroadenine arabinoside (2-CAB) nor 2',5'-dideoxyadenosine (2',5'-DDA) altered fixed-ratio responding at the doses studied (0.1-3.2 and 1.0 and 3.2, respectively). Caffeine (0.32 and 3.2 mg/kg) antagonized the behavioral effects of L-PIA in a dose-related, surmountable manner. Daily administration of L-PIA (0.1 mg/kg) resulted in the development of tolerance to the effects of L-PIA decreasing rate and cross-tolerance to other analogs of adenosine (CHA, BA, D-PIA). No cross-tolerance was produced to caffeine, levorphanol or chlordiazepoxide. The activity and order of potency of the analogs of adenosine tested were consistent with the effects of agonists at A1 adenosine receptors. Furthermore, the results demonstrate that the behavioral effects of N6- and 2-chlorine-substituted analogs of adenosine probably act through similar CNS mechanism(s).

Adenosine

Lateralization of visually controlled behavior in pigeons.

Pigeons were trained binocularly on two different successive pattern discrimination tasks. After reaching criterion they performed the tasks with either the left or the right eye occluded or with both eyes unobstructed. The number of responses emitted was greater when the right rather than the left eye was uncovered. Also the percent correct discrimination scores were better when seeing with the right eye than with the left one. Some pigeons originally acquired the discrimination monocularly, generally using the right eye, although both eyes were uncovered. The results are discussed in relation to brain structures that may mediate this performance.

Animals

Exercise-induced changes in schedule controlled behavior.

This experiment was designed to measure the direct effect of acute exercise on performance of an operant task in rats. Treadmill exercise was manipulated along two dimensions: speed and duration. Separate groups of rats (n = 12) were tested under a multi-component time-out fixed-ratio (MULT TO FR) schedule following four exercise treatments. The first group of animals (Group A) ran at a constant speed for four different periods of time. A second group (Group B) ran for a constant period of time at four different treadmill speeds. For both groups, running took place just before operant test sessions. Operant responding on test days was compared with operant responding on the immediately preceding day. Both exercise duration and exercise speed had significant effects on operant performance.

Animals

Effects of delta-9-THC and a water soluble ester of delta-9-THC on schedule-controlled behavior.

delta-9-Tetrahydrocannabinol (delta-9-THC) and one of its water soluble esters (SP-111) decreased the rates of responding by pigeons working under a variable interval 3-min schedule of food presentation, or a multiple fixed-ratio 30, fixed-interavl 5-min schedule of food presentation. delta-9-THC was 3-6 times more potent than SP-111 and had a faster onset of effects on behavior.

Animals