Propylthiouracil tasting as a possible genetic association marker for two types of alcoholism.

The ability to taste 6-n-propylthiouracil (PROP) as bitter is determined genetically. The present study investigated whether this genetic ability was correlated with alcoholism and/or depression. Four groups of community college students (n = 25 each) were constituted based on the presence or absence of alcoholism and/or depression in themselves or their parents. Family history was assessed using the Family History-Research Diagnostic Criteria. Each subject was given a taste test using paper saturated with PROP. The results showed that subjects who had only alcoholism in their family were more likely to be nontasters of PROP than the control group, whereas subjects with both alcoholism and depression in their family were more likely to be so-called supertasters of PROP; that is, they found it extremely bitter. These findings suggest that PROP tasting might function as a genetic marker for two types of alcoholism.

Dorsal cortex lesions impair habituation in turtles (Chrysemys picta).

Two experiments investigated habituation in painted turtles (Chrysemys picta). In the first, turtles were given lesions of the dorsal cortex or sham lesions and then trained on a restraint. Although the sham-lesioned turtles learned to tolerate the restraint, the lesioned animals continued to struggle against it. Thus dorsal cortex lesions disrupted habituation to restraint. In order to test habituation to a looming stimulus in a second experiment, all animals were habituated to the restraint before surgery. Postoperatively they continued to be habituated to the restraint. The looming stimulus was a circular shadow that enlarged suddenly on a screen in front of the turtle. It was presented 5 times per day for 15 days. Between-day or long-term habituation was impaired by dorsal cortex lesions.

The perceived bitterness of beer and 6-n-propylthiouracil (PROP) taste sensitivity.

Pelchat and Danowski found a significantly higher proportion of nontasters of 6-n-propylthiouracil (PROP) among children of alcoholics than among children of nonalcohlics, suggesting a possible genetic association between alcoholism and PROP tasting ability. They suggested that nontasters may not find alcohol as bitter as tasters do and may be at greater risk for alcoholism because they like the taste of alcoholic beverages more. In the present study we tested this hypothesis by examining how nontasters, medium tasters, and supertasters of PROP judged the taste of two kinds of beer. Forty-seven males and 53 females between the ages of 21 and 49 rated the perceived bitterness of Budweiser and Pilsner Urquell on the oral Labeled Magnitude Scale (LMS). Subjects also rated their degree of liking or disliking for the two beers on a 9-point Likert scale. PROP papers and the LMS were used to classify subjects into tasting groups. The results lent some support to the hypothesis in that male nontasters liked the taste of Pilsner Urquell better than male supertasters, when they tasted Pilsner Urquell after Budweiser. (This finding was not replicated for females). Also, as subjects' ratings of bitterness for the two beers increased, their degree of liking for the taste decreased. Supertasters rated Pilsner Urquell significantly more bitter than medium tasters. Subjects were asked about their drinking habits, and supertasters reported consuming significantly less beer than nontasters when they first started drinking beer on a regular basis. There were no significant differences in current drinking behavior between tasting groups. These results suggest that supertasters are distinct from nontasters with regard to their taste for beer and may to some degree be protected against alcoholism by their dislike for bitter substances.

To blink or not to blink: inhibition and facilitation of reflex blinks.

A reflex blink typically inhibits subsequent blinks. In this study, we investigated whether the nature and time course of this inhibition vary when different combinations of blink-evoking stimuli are used. We used the paired stimulus paradigm, in which two blink-evoking stimuli-a conditioning stimulus followed by a test stimulus-are presented with a variety of interstimulus intervals, to examine the interactions between blinks evoked by trigeminal and acoustic stimuli in rats and humans. In addition, we studied the effect of a blink-evoking trigeminal stimulus on subsequent gaze-evoked blinks in humans. The results revealed that long-lasting inhibition occurred when the conditioning and test stimuli were within the same modality. A shorter period of inhibition followed by facilitation occurred when the stimuli were in different modalities. The data demonstrate that a blink-evoking stimulus initiates a lengthy period of inhibition in its own sensory pathway and a shorter period of inhibition in the reticular formation and/or in blink motoneurons. In addition, the results show that the blink-evoking stimulus also initiates a facilitatory process. Thus, the magnitude of a blink reflects a balance between inhibitory and facilitatory processes.

An explanation for reflex blink hyperexcitability in Parkinson's disease. I. Superior colliculus.

Hyperexcitable reflex blinks are a cardinal sign of Parkinson's disease. We investigated the neural circuit through which a loss of dopamine in the substantia nigra pars compacta (SNc) leads to increased reflex blink excitability. Through its inhibitory inputs to the thalamus, the basal ganglia could modulate the brainstem reflex blink circuits via descending cortical projections. Alternatively, with its inhibitory input to the superior colliculus, the basal ganglia could regulate brainstem reflex blink circuits via tecto-reticular projections. Our study demonstrated that the basal ganglia utilizes its GABAergic input to the superior colliculus to modulate reflex blinks. In rats with previous unilateral 6-hydroxydopamine (6-OHDA) lesions of the dopamine neurons of the SNc, we found that microinjections of bicuculline, a GABA antagonist, into the superior colliculus of both alert and anesthetized rats eliminated the reflex blink hyperexcitability associated with dopamine depletion. In normal, alert rats, decreasing the basal ganglia output to the superior colliculus by injecting muscimol, a GABA agonist, into the substantia nigra pars reticulata (SNr) markedly reduced blink amplitude. Finally, brief trains of microstimulation to the superior colliculus reduced blink amplitude. Histological analysis revealed that effective muscimol microinjection and microstimulation sites in the superior colliculus overlapped the nigrotectal projection from the basal ganglia. These data support models of Parkinsonian symtomatology that rely on changes in the inhibitory drive from basal ganglia output structures. Moreover, they support a model of Parkinsonian reflex blink hyper-excitability in which the SNr-SC target projection is critical.

A role for acetylcholine in spatial memory in turtles.

The present research was undertaken to determine whether acetylcholine plays a role in memory for a maze in turtles. Cholinergic cells have been observed in the basal forebrain of turtles, and the basal forebrain of turtles projects to the dorsal cortex, a region that has been implicated in associative function. In Experiment 1, turtles were trained on an X-maze for water reward and then given lesions of the dorsal cortex or basal forebrain or sham lesions and retested postoperatively on the maze. Both dorsal cortex and basal forebrain lesions impaired performance on the maze. In Experiment 2, turtles were trained on the maze and then given saline, scopolamine, or methylscopolamine on a 1-day retention test. Scopolamine in the higher doses impaired maze performance on the test day, but methylscopolamine did not. The highest dose of scopolamine had no effect on measures of general activity, showing that the effects of the drug were specific to the learned task.

Not looking while leaping: the linkage of blinking and saccadic gaze shifts.

Many vertebrates generate blinks as a component of saccadic gaze shifts. We investigated the nature of this linkage between saccades and blinking in normal humans. Activation of the orbicularis oculi, the lid closing muscle, EMG occurred with 97% of saccadic gaze shifts larger than 33 degrees. The blinks typically began simultaneously with the initiation of head and/or eye movement. To minimize the possibility that the blinks accompanying saccadic gaze shifts were reflex blinks evoked by the wind rushing across the cornea and eye-lashes as the head and eyes turned, the subjects made saccadic head turns with their eyes closed. In this condition, orbicularis oculi EMG activity occurred with all head turns greater than 17 degrees in amplitude and the EMG activity began an average of 39.3 ms before the start of the head movement. Thus, one component of the command for large saccadic gaze shifts appears to be a blink. We call these blinks gaze-evoked blinks. The linkage between saccadic gaze shifts and blinking is reciprocal. Evoking a reflex blink prior to initiating a voluntary saccadic gaze shift dramatically reduces the latency of the initiation of the head movement.

The distribution of cholinergic neurons in the central nervous system of turtles.

The distribution of cholinergic neurons was studied in painted and red-eared turtles using antisera against choline acetyltransferase (ChAT). The results showed that the organization of cholinergic systems in the central nervous system of turtles was remarkably similar to that previously described in diverse other species. For example, the present studies revealed the presence of cholinergic neurons in the striatum, the basal telencephalon, the isthmo-tectal system, and a region of cells near the cerebellar peduncle. The motoneurons of the III, IV, V, VI, VII, X and XII cranial nerves and the spinal ventral horn were also shown to be cholinergic. Additional cholinergic neurons were observed in the hypothalamus and rhombencephalic reticular formation. These results help to clarify the precise extent and location of the major cholinergic cell groups of the turtle brain, thereby adding to our understanding of the organization of the turtle nervous system. The results also reveal that the cholinergic systems of the striatum, basal forebrain, isthmic region, and cerebellar peduncular region are ancestral features of the amniote brain and are common to all living amniotes that have been studied. Thus, the organization and, presumably, the function of the cholinergic systems appear to be conservative.

Effects of dorsal and medial cortex lesions on reversals in turtles.

Two experiments were performed to investigate the effect of cortical lesions on the acquisition and reversal of simultaneous discriminations in turtles. The first experiment examined the effect of cortical lesions on the acquisition and reversal of a spatial discrimination. The results of the first experiment revealed that lesions of the dorsal cortex produced a deficit in spatial learning. The results of the first experiment also revealed that when damage to the dorsal cortex was accompanied by substantial damage to the medial cortex, no deficit was manifest. The second experiment examined the effects of cortical lesions on the acquisition and reversal of a brightness discrimination. The results of the second experiment revealed that damage to neither the dorsal cortex nor the medial cortex produced a deficit. It was suggested that brightness is not represented in the thalamofugal visual pathway but is instead represented in the tectofugal visual pathway in reptiles. It was also suggested that the medial cortex, which is the evolutionary precursor to the mammalian hippocampal formation, functions differently from the mammalian hippocampus.

Function of the dorsal and medial cortex of turtles in learning.

The effects of damage to the dorsal and medial cortex of turtles were investigated in two experiments. In the first, damage to the dorsal cortex disrupted acquisition and reversal of a go-no-go discrimination but had no effect on retention of the discrimination if it had been learned preoperatively. Medial cortex damage had no effect. In the second experiment, dorsal cortex damage impaired acquisition, but not extinction or reacquisition, of a discrete-trial keypress. Again, medial cortex damage had no effect. The results suggest that the dorsal cortex is involved in learning in turtles.

Wulst lesions in pigeons disrupt go/no-go reversal.

Pigeons with lesions of either the Wulst or ectostriatum were compared to controls on reversal of a go/no-go pattern discrimination. The Wulst-lesioned animals were slower to acquire the response to the new S+ but were not different from the other groups on extinction of response to the old S+. The ectostriatum-lesioned group was not different from controls. The results extend the range of situations in which Wulst-lesioned pigeons have been found to show a reversal deficit and are consistent with the notion that Wulst lesions may disrupt learning.

The effects of lesions of telencephalic visual structures on visual discriminative performance in turtles (Chrysemys picta picta).

Ascending thalamotelencephalic visual pathways that terminate in specific telencephalic regions have been described in all reptiles studied. Although the anatomical data suggests that such telencephalic regions may play a role in visual processing in reptiles, few behavioral data are available. In the present study, the effects of destruction of either the core nucleus (CN) of the dorsal ventricular ridge (telencephalic terminus of the tectothalamofugal pathway) or the dorsal cortex (telencephalic terminus of the retinothalamofugal pathway) on visual discriminative performance in the turtle were examined. Following extensive bilateral destruction of the CN, turtles were severely impaired in their performance of both a simultaneous pattern discrimination and a simultaneous visual intensity discrimination. The extent of the discriminative impairment was found to be specifically correlated with the amount of CN damage. In contrast to the effects of CN lesions, lesions of the dorsal cortex had no evident effect on the performance of either a simultaneous pattern discrimination or a simultaneous visual intensity discrimination. The present results suggest that, as in birds and mammals, telencephalic visual areas play an important role in visual functions in reptiles. As in at least some birds (such as pigeons), the telencephalic terminus of the tectothalamofugal visual pathway appears to play a larger, or at least more readily measurable, role in visual discrimination than does the telencephalic terminus of the retinothalamofugal pathway.

The effects of lesions of nucleus rotundus on visual intensity difference thresholds in turtles (Chrysemys picta).

Intensity difference thresholds were assessed behaviorally in 7 painted turtles (Chrysemys picta) before and after lesions of nucleus rotundus thalami or control lesions. Three subjects with control lesions and two subjects with slight bilateral damage to nucleus rotundus showed no permanent elevation of threshold postoperatively. In contrast, two subjects with severe damage to nucleus rotundus showed threshold elevations postoperatively and did not recover with further training. The impairment shown by these subjects with damage to nucleus rotundus appeared to be only on the more difficult problems; they performed as they had preoperatively on easy discriminations.

The effects of lesions in telencephalic visual areas of pigeons on dimensional shifting.

Two experiments on dimensional shifting in pigeons with lesions of telencephalic visual areas are reported. In the first, pigeons were initially trained on a pattern discrimination with color irrelevant and then the color discrimination was made relevant and pattern irrelevant. Pigeons with ectostriatal lesions made more errors than shams or Wulst-lesioned animals on the pattern problem, but there was no difference among the three groups on the shift to color. In the second experiment, the same discriminations were studied in the reverse order: the animals first learned the color problem and then shifted to pattern. In this case the ectostriatal-lesioned animals showed a deficit on both problems. The Wulst-lesioned animals, on the other hand, showed a deficit on the shift to pattern but not on the original color problem. The results are discussed in terms of the nature of the deficits caused by the two lesions and their meaning for questions of comparative neurobiology.

The effects of extensive forebrain lesions on visual discriminative performance in turtles (Chrysemys picta picta).

Though anatomical research has demonstrated major ascending telecephalically directed visual channels in reptiles, little behavioral research has examined reptilian forebrain visual functions. The present study reports the effects of extensive forebrain lesions, involving either severe destruction of dorsal thalamus or disruption of the fibers of the lateral forebrain bundle (by lesions of the basolateral telecephalon), upon visual discriminative performance in the turtle. Such lesions, which extensively damage the ascending visual pathways, rendered turtles incapable of relearning preoperatively acquired visual discriminative problems. The magnitude of the visual impairments observed following such forebrain lesions suggest a major role on the part of the forebrain in visual processing in reptiles.

A stereotaxic atlas of the forebrain and midbrain of the eastern painted turtle (Chrysemys picta picta).

A stereotaxic atlas of the telencephalon, diencephalon and mesencephalon of a turtle (Chrysemys picta picta) is presented. A description is given of the procedures employed in the construction of the atlas and a few suggestions are offered as to possible uses. The importance of the study of the turtle in the comparative approach is emphasized.

Interference and forgetting in bird and fish.

Retention in the pigeon and in the goldfish was measured 1 day or 2 weeks after the mastery of each of a series of color discrimination. The amount of forgetting in the pigeon increased with the number of prior problems and increased more rapidly at the longer than at the shorter interval. the amount of forgetting in the goldfish was independent, at both intervals, of the number of prior problems. These results point to the operation of different memory mechanisms in the two animals.