Biomedical subjects

D A Hopkins

Publications and source records attributed to D A Hopkins.

80 records · Page 5Linked to original sources

PubMed1977

Amygdala afferents from the mediobasal hypothalamus: an electrophysiological and neuroanatomical study in the rat.

Electrophysiological techniques and the retrograde transport of horseradish peroxidase (HRP) were used to determine the efferent projections from the caudal mediobasal hypothalamus to the amygdala. In pentobarbital anesthetized rats, the activity of 1780 mediobasal hypothalamic neurons was examined for response to stimulation sites in the amygdala and stria terminalis. Evidence of orthodromic activation from both stimulation sties was commonly observed. Sixty-five cells mostly located in the ventromedial nucleus displayed antidromic invasion from the basolateral, basomedial or cortical amygdala over a latency range of 5-34 msec (mean 15.3 +/- 6.7 msec S.D.). Three of 440 tested cells displayed antidromic activation from stimulation on the stria terminalis. Amygdala evoked antidromic responses were still present after lesions of the stria terminalis. May ipsilateral ventromedial hypothalamic neurons and a few cells in the ipsilateral arcuate nucelus and periventricular region and contralateral ventromedial nucleus displayed retrograde transport of HRP after an infection into the amygdala. Lesions of the stria terminalis had little effect on the numbers of HRP labeled neurons. Relatively more neurons were labeled retrogradely after medial injections than after lateral injections in the amygdala. Data from both electrophysiological and anatomical techniques therefore indicate that certain mediobasal hypothalamic neurons, particularly those located in the ipsilateral ventromedial nucleus, project to the amygdala probably via a route other than the stria terminalis. Thus there is substantial evidence in the rat for reciprocal connections between the amygdala and the hypothalamic ventromedial nucleus.

Afferent Pathways↗

PubMed1976

The development of motor control in the rhesus monkey: evidence concerning the role of corticomotoneuronal connections.

Corticospinal fibres terminate in three areas in the spinal grey matter of the rhesus monkey: the nucleus proprius of the dorsal horn, the intermediate zone and directly upon motoneurons, particularly those inervating limb muscles. It was suggested at their earliest discovery that direct corticomotoneuronal (CM) connections might constitute a critical anatomical substrate for the type of fractionated movement exemplified by relatively independent finger movements (RIFM). The present study was undertaken in an attempt to provide further evidence in support of this idea. The evidence is based upon the anatomical finding that few CM connections are present at birth in the monkey, the bulk being formed postnatally to reach an adult density at approximately 8 months of age. There were two experimental approaches: in the first it was argued that if RIFM are dependent upon the presence of CM connections it would be expected that such movements would appear only gradually postnatally, developing in parallel with the development of the connections. In 2 normal monkeys studied from this point of view discrete distal movements did develop only gradually with RIFM reaching an adult level at 7 to 8 months of age. The second experimental appraoch was based upon the fact that pyramidal lesions in newborn animals interrupt corticospinal fibres before CM connections are formed. It was argued that such a situation might provide a better opportunity for other descending pathways to establish the connections necessary for RIFM. Five infant monkeys had bilateral pyramidal tract lesions made from 5 days to 4 weeks after birth and were observed for a period of three years. In the 4 animals in which the lesions were complete, RIFM failed to develop. In the fifth animal, in which the lesions were incomplete, there was development of some degree of RIFM. It was concluded that the development of RIFM is dependent upon fibres passing in the pyramidal tracts and that in infant monkeys, as well as in adults, other descending pathways are unable to form the connections necessary for these movements. The possible contribution to RIFM of the corticospinal fibres arise in the somatosensory cortex and terminate in the dorsal horn was studied by bilateral removal of the arm and leg area of the somatosensory cortex in one animal. Since RIFM were only minimally and transiently altered, it was concluded that such movements are not dependent upon these fibres. The different lines of evidence presented in the study are interpreted as giving further support to the idea that corticomotoneuronal connections constitute an essential anatomical substrate for fractionated movements such as RIFM. Observations were also made of the development of general locomotor activity in normal and pyramidotomized infant monkeys.

Age Factors↗

PubMed1975

On the absence of a rubrothalamic projection in the monkey with observations on some ascending mesencephalic projections.

In order to determine whether there is a rubrothalamic projection in the rhesus monkey, the ascending degeneration resulting from electrolytic lesions made in the red nucleus and adjacent mesencephalon in animals surviving at least one year after bilateral interruption of the superior cerebellar peduncles (PCS) was studied by means of the Fink-Heimer technique. In a necessary preliminary step it was shown that virtually all of the degeneration disappeared from the thalamus within twelve months after PCS interruption so that degeneration resulting from the subsequent electrolytic mesencephalic lesions could be attributed to interruption of non-cerebellar ascending fibres. The results show that degeneration was present in the thalamus following the electrolyte mesencephalic-diencephalic lesions but it could be accounted for on the basis of damage either to residual PCS fibres, to somatosensory pathways, to intrathalamic connections or to cell groups or projection fibres of the reticular formation, substantia nigra or globus pallidus. It is concluded that there is no direct rubrothalamic projection in the monkey and, in particular, no evidence of a projection from the red nucleus to the ventral lateral or ventral anterior thalamic nuclei. The results also indicate that the mesencephalic reticular formation is the main source of ascending afferents to the nucelus reticularis thalami. Some observations were made concerning nigrostriatal and nigrothalamic projections. Retrograde cell changes resulting from unilateral lesions made caudal to the red nucleus were studied in three animals. The observed cell changes are interpreted as being consistent with the conclusion that there is no rubrothalamic projection.

Age Factors↗

PubMed1973