Differences in medical students' empathy.

Medical students' Balanced Emotional Empathy Scale scores were compared by year, sex, and expressed specialty choice. Scores were lower for students choosing non-core specialties, and for M4 men students compared with M3 men students.

Intracellular recording of lamina X neurons in a horizontal slice preparation of rat lumbar spinal cord.

A horizontal slice preparation of postnatal rat lumbar spinal cord has been developed which allows correlative observations of the morphology, electrophysiology, and receptor pharmacology of lamina X neurons. These slices better maintain afferent input and somatodendritic morphology and are amenable to subsequent immunohistochemical processing. Stable intracellular recordings obtained from postnatal day 14-45 animals reveal that a number of different intrinsic membrane conductances contribute to the regulation of excitability in lamina X neurons. In addition, lamina X neurons possess inhibitory GABAergic as well as excitatory glutamate and cholecystokinin receptors. This preparation will be useful in future studies designed to characterize developmental changes in the intrinsic membrane properties, synaptic profiles and neuropeptide responsiveness of lamina X neurons in the rat. Such a characterization is important given that lamina X represents a unique sexually dimorphic region that is a convergence site for somatic and visceral afferent inputs, which includes nociceptive information.

Sex differences in the response of postnatal rat lumbar lamina X neurons to exogenously applied galanin recorded in vitro.

Intracellular recording techniques were used in a horizontal slice preparation of postnatal rat lumbar spinal cord to compare the responses of male and female lamina X neurons to exogenously applied galanin. Although there was no significant sex difference in the resting membrane potential or input resistance of neurons, superfusion of galanin 1-16 (1 microM) produced a membrane hyperpolarization that averaged -5.3 mV in males and only -2.0 mV in females. The galanin-induced membrane hyperpolarization of lamina X neurons was accompanied by an inconsistent and varied change in input resistance. No depolarizing effect of galanin was detected in either sex. Galanin did not significantly alter the spike shape, amplitude, after hyperpolarization or locally evoked synaptic responses. The more than 2.5 fold significant sex difference in response to galanin occurred at a developmental timepoint at which lamina X expressed a comparably higher amount of galanin-like immunoreactivity in males compared to females. These results provide the first indication of a sex difference in the response of lamina X neurons to any neuropeptide. Given the antinociceptive role of galanin in the spinal cord, these results raise the possibility for the presence of distinct physiological and anatomical substrates for sex-dependent differences in nociceptive processing in lamina X of the lumbosacral spinal cord.

Cholecystokinin-8-like immunoreactivity is sexually dimorphic in a midline population of rat lumbar neurons.

The gray matter surrounding the central canal of rat lumbar spinal cord contains a population of spinothalamic neurons which has been shown to co-contain cholecystokinin-8 (CCK-8) and galanin (GAL) (Ju, G., Melander, T., Hökfelt, T. and Frey, P., Immunohistochemical evidence for a spinothalamic pathway co-containing cholecystokinin- and galanin-like immunoreactivities in the rat. Neuroscience, 20 (1987) 439-456). A previous study from our laboratory has shown that female rats have only 62% the number of GAL-containing midline neurons present in males. Counts of CCK-8-containing midline neurons reveal that females have 59% the number observed in males. These results indicate that the degree of sexual dimorphism seen for CCK-8 is the same for GAL in these midline lumbar neurons, and suggests that androgens modulate the production of the co-contained GAL and CCK-8 in a similar fashion within male rat spinal cords.

Cholecystokinin-8-like-immunoreactive fibers in rat lumbosacral autonomic regions are sexually dimorphic and altered by a reduction of androgen receptors.

Cholecystokinin-8-like-immunoreactive (CCK-8-LI) fibers in laminae VII and X of the rat lumbosacral spinal cord demarcate the position of preganglionic autonomic neurons. This investigation reveals that adult male Sprague-Dawley, or King-Holtzman/Sprague-Dawley rats contain more CCK-8-LI fibers in lumbosacral laminae VII and X than adult females. Furthermore, testicular feminization mutation male rats (which lack 85-90% of their functional androgen receptors) contain fewer CCK-8-LI fibers than normal male or female rats, with the amount of CCK-8-LI being reduced to a greater extent in the sympathetic vs. the parasympathetic regions of the lumbosacral spinal cord. Thus, CCK-8-LI in testicular feminization mutation male rats has a distinctly female-like pattern. These results suggest that testosterone is a regulatory factor for CCK-8-LI fibers found in laminae VII and X of the lumbosacral spinal cord. Sexual dimorphism in lumbosacral CCK-8-LI fibers may contribute to modulating the final common pathway which differentially regulates the reproductive organs and stereotypic reproductive behavior, and may be involved with the sex differences described for pain.

Lack of feminization of the cremaster nucleus by prenatal flutamide administration in the rat and pig.

PURPOSE: The sexually dimorphic cremaster nucleus contains motoneurons that project via the genitofemoral nerve and theoretically direct androgen dependent testicular descent. The effects of flutamide on descent and masculinization of the cremaster nucleus were studied in the rat and pig. MATERIALS AND METHODS: Flutamide was given to pregnant rats and pigs on days 16 to 22 and 65 to 113 of gestation, respectively. Tissues were perfused and examined at birth (pigs) or at age 30 days (rats). Spinal cords were removed, sectioned and immunohistochemically stained for serotonin (rats) or substance P (pigs) to demarcate the position of the cremaster nucleus and allow the determination of cremaster motoneuron number. RESULTS: After exposure to flutamide testes were undescended in 6 of 9 rats and 7 of 10 pigs. Cremaster motoneuron number per nucleus were 288 +/- 22 in control versus 250 +/- 27 in flutamide treated rats, and 165 +/- 28 in control versus 148 +/- 24 in flutamide treated pigs. The decrease in motoneuron number by flutamide was significant in both species (p < 0.02) but it did not approach the levels in female rats (93 +/- 11) and pigs (57 +/- 12). Cremaster motoneuron number did not correlate with testicular position. Porcine undescended testes were associated with a significant increase in mean gubernacular volume. CONCLUSIONS: Unlike other sexually dimorphic spinal cord nuclei masculinization of the cremaster nucleus appears to be largely androgen independent and it does not correlate with ipsilateral testicular descent. These data suggest that androgens do not mediate descent of the testes via the efferent limb of the genitofemoral nerve.

Lack of feminization of the cremaster nucleus in cryptorchid androgen insensitive rats.

Androgens may control rat testicular descent via effects on the genitofemoral nerve or cranial gonadal ligaments. Androgen-mediated release of calcitonin gene-related peptide from the genito-femoral nerve (whose motoneuron cell bodies reside in the sexually dimorphic cremaster nucleus) may stimulate cremaster sac formation and testicular descent. Alternatively, androgens may cause regression of cranial gonadal ligaments and thereby allow the testes to descend. To evaluate these theories testicular position, and the cremaster sac and nucleus were studied in Tfm (androgen insensitive) rats. Testes were abdominal, inguinal and scrotal in 20%, 67% and 13% of Tfm male rats, respectively, and cranial ligaments were present in all cases. Mean cremaster nucleus motoneuron number was lower in female rats (70 +/- 14) but not significantly different between normal male (256 +/- 44) and Tfm male (231 +/- 42) rats, and it correlated poorly with testicular position. Calcitonin gene-related peptide immunoreactivity was rarely observed in cremaster motoneurons. These data suggest that the cremaster nucleus is not androgen-dependent, calcitonin gene-related peptide release from cremaster motoneurons is not the likely mechanism of testicular descent and persistent cranial ligaments may cause cryptorchidism in the Tfm rat.

An in situ hybridization and immunohistochemical study of vasotocin neurons in the hypothalamus of water-deprived chickens.

The distribution of immunoreactive vasotocin (IR-AVT) and AVT mRNA in the hypothalamus of White Leghorn cocks was determined by immunohistochemistry and in situ hybridization, respectively. In control birds that were provided with water ad lib, AVT mRNA was distributed in the periventricular and lateral regions of the hypothalamus in clusters of neurons that correspond structurally with the mammalian paraventricular (PVN) and supraoptic (SON) nuclei. Although the distribution of AVT, identified by immunohistochemistry of adjacent serial sections within the hypothalamus, was similar to the distribution of AVT mRNA, the possibility that some positive staining was due to mesotocin neurons was not excluded. Water deprivation for 2 and 4 days resulted in both an increase in levels of AVT mRNA per neuron and the number of AVT mRNA-containing cells. Additionally, water deprivation resulted in a decrease in the amount of IR-AVT per neuron. The results indicate that osmotic stimulation increases AVT gene expression not only in individual neurons but also by activating subpopulation of neurons that are not observed in normally hydrated birds.

Galanin immunoreactivity in rat spinal lamina IX: emphasis on sexually dimorphic regions.

Fibers and puncta that contained galanin-like immunoreactivity (GAL-LI) were distributed within lamina IX in a heterogeneous fashion. In cervical spinal segments, GAL-LI was almost absent except for the phrenic nucleus, which received the most robust GAL-LI innervation in lamina IX. In high and mid-thoracic segments, GAL-LI was found in moderate amounts, but the number of GAL-LI fibers gradually diminished in a caudal fashion, so that in low thoracic segments GAL-LI was sparse. Throughout all thoracic segments, GAL-LI fibers surrounded some clusters of motoneurons, while other groups of motoneurons were devoid of GAL-LI fibers. In lumbar segments, three sexually dimorphic nuclei received sparse to moderate amounts of GAL-LI, while GAL-LI in the remainder of lumbar lamina IX was very sparse. In sacral spinal segments, GAL-LI was very sparse. These data indicate that fibers and puncta that contain GAL-LI preferentially surround motoneurons that innervate muscles associated with the axial skeleton, while motoneurons that innervate appendicular or tail-associated skeletal muscles only have an occasional GAL-LI fiber associated with them.

Galanin-like immunoreactivity in autonomic regions of the rat lumbosacral spinal cord is sexually dimorphic and varies with the estrous cycle.

These investigations show that there is a heterogeneous distribution of galanin-like immunoreactivity (GAL-LI) within laminae VII and X of the rat thoraco-sacral spinal cord. In either sex, GAL-LI fibers sparsely outline the position of male and female preganglionic sympathetic neurons in thoracic spinal segments; whereas in lumbosacral segments, far greater numbers of GAL-LI fibers surround autonomic preganglionic neurons. An unusual feature of the GAL-LI fibers in lumbosacral autonomic regions is their sexually dimorphic distribution with males containing greater numbers of GAL-LI fibers than all females examined. In this regard, although the number of GAL-LI fibers observed in males was consistent from animal to animal, the amount of GAL-LI in females fell into two qualitative categories: an 'average' and a 'heavy' amount. These data indicate that the difference in the amount of GAL-LI in the female rat lumbosacral spinal cord is related to the estrous cycle, such that heavy amounts of GAL-LI are observed during proestrus and estrus, while average amounts of GAL-LI are associated with metestrus and diestrus.

A sexually dimorphic population of galanin-like neurons in the rat lumbar spinal cord: functional implications.

The rat lumbar spinal cord contains a population of galanin- and cholecystokinin-containing neurons which are located dorsolateral to the central canal and project to the thalamus. New data are presented herein which reveal that the number of these neurons, as shown by galanin-like immunostaining, is sexually dimorphic with males containing 62% more of these neurons than females. This is the first demonstration of a sexually dimorphic population of intraspinal neurons which projects to higher CNS centers rather than to peripheral targets.

Origin of galanin-immunoreactive nerve fibers in the rat paracervical autonomic ganglia and uterine cervix.

Retrograde axonal tracing with fluorogold in conjunction with immunohistochemistry was used to examine the source of galanin-immunoreactive nerve fibers in the paracervical ganglia and uterine cervix of the female rat. Immunohistochemistry revealed galanin-immunoreactive neuron somata in lumbosacral dorsal root ganglia and around the central canal of the lumbosacral spinal cord (lamina X). Injection of fluorogold into the paracervical ganglia resulted in labelled cells in dorsal root ganglia and the sacral parasympathetic nucleus of the spinal cord; but fluorogold-labelled, galanin-immunoreactive cells were found only in dorsal root ganglia. Injection of the tracer in the cervix resulted in labelled cells in the paracervical ganglia and dorsal root ganglia; however, fluorogold-labelled, galanin-immunoreactive cells were again evident only in dorsal root ganglia. It is suggested that the galanin-immunoreactive nerve fibers and varicosities in the paracervical ganglia and uterine cervix are sensory fibers from spinal dorsal root ganglia. The galanin-immunoreactive varicosities in the ganglia could play a role in the modulation of pelvic visceral activity, while those in the musculature of the cervix could influence contractility.

Peptidergic innervation of the cremaster nucleus. I. A sexually dimorphic population of substance P-containing intraspinal neurons exists in the substance P pathway to the rat cremaster nucleus.

The cremaster nucleus (CN) lies in the lumbar spinal cord and is sexually dimorphic: the male CN contains three times as many motoneurons as the female. The substance P (SP) innervation of the CN is also sexually dimorphic with males receiving a very prominent innervation which is greatly diminished in females. These investigations examined SP-containing neurons located in the ventral half of lamina IV and the lateral aspects of laminae V, VII, and IX, in lumbar spinal levels 1,2. SP-containing intraspinal neurons in these laminae are at least three times as numerous in males than females. This provides the first demonstration of a sexually dimorphic population of spinal neurons which is not motor or preganglionic in nature. These SP-containing interneurons are found within, or adjacent to, the SP-containing fibers which constitute the massive SP pathway to the male CN. Processes of these SP-containing neurons were observed to contribute to the formation of the SP pathway to the male CN. The immunohistochemically demonstrable presence of these lumbar 1,2, laminae IV-IX, SP-containing neurons validates former studies which suggested their existence (Gibson et al., Brain Research, 301 (1984) 243-251; Uda et al., Neurosci. Lett., 57 (1985) 185-190).

Monoamine synaptic structure and localization in the central nervous system.

The monoamines dopamine, noradrenaline, adrenaline, and serotonin as well as the diamine histamine have a widespread distribution in the central nervous system within synaptic terminals and nonsynaptic varicosities. In certain regions of the central nervous system the monoamines are contained in varicosities that have no synaptic specialization associated with them, suggesting a possible neuromodulatory role for some of the monoamines. The majority of monoamine labelled structures are synaptic terminals which are characterized by the presence of small, clear vesicles (40-60 nm) and large, granular vesicles (70-120 nm) within the terminal. A third population of vesicles--small, granular vesicles--which are visible only after histochemical staining, are probably the equivalent of the small, clear vesicles present after either autoradiographic or immunohistochemical labelling. Most monoamine containing terminals contact dendrites and dendritic spines and, less frequently, neuronal somata and other axons. Both asymmetrical and symmetrical membrane specializations are associated with monoaminergic terminals; however, asymmetrical contacts are the most frequent type found. These ultrastructural results indicate that monoamine containing terminals and varicosities in general share many common morphological features, but still have diverse functions.

Calcitonin gene-related peptide and somatostatin immunoreactivities in the rat lumbar spinal cord: sexually dimorphic aspects.

The immunohistochemical distribution of calcitonin gene-related peptide and somatostatin in rat lumbar spinal laminae VII-X was investigated using the peroxidase-antiperoxidase technique. Within L1,2 laminae VII and X, calcitonin gene-related peptide and somatostatin fibers demarcate the location of preganglionic sympathetic neurons in a similar fashion in either sex but somatostatin is distributed in a sexually dimorphic manner in the lumbosacral (L5-S2) spinal cord with the male rat containing more somatostatin fibers and neurons than females. Within the ventral horn (lamina IX), calcitonin gene-related peptide has a sexually dimorphic distribution. Calcitonin gene-related peptide varicose fibers are found within the sexually dimorphic male cremaster nucleus but are virtually absent in the female cremaster nucleus. Calcitonin gene-related peptide varicose fibers are nearly absent in the remainder of the male and female lamina IX: this area includes the other two known sexually dimorphic spinal motonuclei: the dorsomedial and dorsolateral nuclei. Virtually all motoneurons in the lumbosacral spinal cord which are not sexually dimorphic contain calcitonin gene-related peptide. However, calcitonin gene-related peptide containing motoneurons have a heterogeneous distribution within sexually dimorphic nuclei. Calcitonin gene-related peptide containing motoneurons within the male and female cremaster nucleus are extremely rare. Some motoneurons within the male and female dorsomedial and dorsolateral nuclei contain calcitonin gene-related peptide with the female dorsomedial and dorsolateral nuclei containing a greater percentage of calcitonin gene-related peptide-containing motoneurons (c. 50%) than males (c. 20%). Somatostatin fibers are preferentially located in sexually dimorphic nuclei of either sex and are distributed in a sexually dimorphic manner within these nuclei with males containing a greater amount of somatostatin fibers than females. The amount of somatostatin immunoreactivity is most dense in the medial aspect of the dorsolateral nucleus, dense in the dorsomedial nucleus, moderate in the cremaster nucleus, and sparse in the lateral portion of the dorsolateral nucleus. In addition, a small column of motoneurons, between the dorsomedial and dorsolateral nuclei at the L5 level, is outlined by somatostatin fibers in females but is absent in males. Somatostatin containing motoneurons were not observed within the lumbar sexually dimorphic nuclei of either sex.

The ontogeny of substance P- and serotonin-like immunoreactivities in the sexually dimorphic cremaster nucleus of the rat spinal cord.

This study investigates the ontogeny of two transmitter systems which innervate the sexually dimorphic cremaster nucleus (CN). Since these transmitter systems arise from separate extra- and intraspinal sources, their ontological sequences differ. In males, substance P (SP) innervates CN motoneurons on postnatal day (P) 0, while serotonin (5-HT) is first observed on P2. SP reaches a mature innervation pattern on P20, while 5-HT maturation is prolonged to P40-60. It is suggested that part of the reason for the differing rates of development of 5-HT and SP within CN is due to the source of the innervating fibers; 5-HT descends from the brainstem while SP is of intraspinal origin. On P6, the SP innervation of the dorsal processes of the male CN is so advanced that the spinal cord may be 'sexed' according to the male presence, or the female 'absence', of this SP pattern. In developing and adult females, the 5-HT innervation of the CN is greater than the SP innervation. In addition, the 5-HT and SP innervation of the female CN is greater than the surrounding motor columns. Compared to surrounding ventral gray horn motor nuclei, the CN receives a slightly delayed SP and 5-HT innervation and this may be a reflection of the postnatal formation of the cremaster muscle.

Target regulation of the serotonin and substance P innervation of the sexually dimorphic cremaster nucleus.

The effects of perinatal castrations on the serotonin (5-HT) and substance P (SP) innervation patterns of the adult male cremaster nucleus (CN) were examined in Sprague-Dawley rats. These investigations reveal that day-of-birth bilateral castration precludes cremaster muscle formation, significantly reduces CN motoneuron number, and dramatically reduces the 5-HT and SP innervation of the adult male CN. Day-of-birth castration reduces the adult CN SP innervation pattern to a greater degree than the 5-HT pattern and this may be attributed to a substantial loss of primary afferent information to the dorsal horn of the spinal cord. Furthermore, day-of-birth unilateral castration causes an ipsilateral reduction in the adult 5-HT and SP immunostaining patterns. This may be correlated with the failure of the ipsilateral cremaster muscle to form with a subsequent ipsilateral reduction of CN motoneuron number. On the contralateral side the intact testis is accompanied by normal cremaster muscle gross morphology, CN motoneuron number, and CN immunostaining. Together these observations suggest that the sexually dimorphic 5-HT and SP innervation of the male CN is predominantly under target control vs androgen control. Castration during adulthood does not alter the 5-HT and SP innervation patterns of CN; thus, a time-dependent period, probably initiated by cremaster muscle formation, underlies these target organ regulatory effects.

Postnatal ontogeny of enkephalin fibers in spinal sympathetic nuclei.

The postnatal distribution of enkephalin (Enk) fibers is described in preganglionic containing sympathetic nuclei in the rat thoracolumbar spinal cord. In high thoracic spinal cord, at birth, Enk fibers are present in moderate numbers in the intermediolateralis nucleus, pars principalis (ILp), and nucleus intercalatus spinalis (IC). Enkephalin fibers first appear in the dorsal commissural nucleus (dcn) on postnatal day 2. Postnatal day 6 represents a pivotal timepoint when the basic Enk innervation pattern is established. From postnatal day 11 through day 20 there is a gradual accumulation of Enk fibers within each of the sympathetic nuclei such that the density and distribution of immunoreactive fibers approaches the adult appearance by postnatal day 20. An adult pattern is achieved by postnatal day 30. There is a rostral-caudal gradient in the developmental appearance of Enk fibers in sympathetic nuclei such that the ILp nucleus contains Enk fibers on postnatal day 0 in the high thoracic spinal levels compared to postnatal day 6 in low thoracic-high lumbar spinal levels. Examination of the location of Enk fibers during ontogeny highlighted several additional features of the distribution of Enk fibers in the adult animal. Enkephalin fibers delineate two subdivisions of the IC nucleus; a thin dense core of Enk fibers contained within a broader band of moderate numbers of Enk fibers. We also report variations in the general overall pattern of the Enk fiber distribution in high thoracic, middle thoracic, and lwo thoracic-high lumbar spinal cord levels.

Cholecystokinin octapeptide immunoreactivity in the nucleus tractus solitarius of the cat.

The nucleus tractus solitarius possessed distinct patterns of cholecystokinin immunoreactive fibers and cell bodies within its various subdivisions. The commissural, medial, intermediate, parvocellular, dorsolateral and interstitial subdivisions contained relatively dense amounts of CCK immunolabelled fibers. In contrast, CCK immunoreactivity within the ventrolateral subdivision consisted of a few scattered fibers and small neurons. The commissural, intermediate, medial, dorsolateral and parvocellular subdivisions contained CCK immunoreactive neurons following colchicine treatment. The presence of CCK in the NTS suggest that it may be involved as a neuromodulator and/or neurotransmitter in circuitry that mediate cardiovascular, respiratory, gastrointestinal and taste functions.

Immunohistochemical distribution of serotonin in spinal autonomic nuclei: I. Fiber patterns in the adult rat.

The differential distribution of serotonin (5HT) fibers in spinal laminae VII and X is described for the adult rat. The results indicate that descending 5HT fibers preferentially innervate those regions of lamina VII that contain sympathetic and parasympathetic neurons. In lamina X, especially the dorsal commissural nucleus, large numbers of 5HT fibers are observed throughout the spinal cord. Moreover, sympathetic nuclei are more richly innervated with 5HT than the spinal parasympathetic nuclei. Spinal cord hemisections reveal that spinal autonomic nuclei are differentially innervated: ipsilateral serotoninergic projections to the intermediolateral cell column are preferentially interrupted. In addition, a large crossed 5HT projection exists throughout the length of the spinal cord that decussates five to six spinal segments rostral to its termination. Both crossed and uncrossed 5HT fibers span many spinal segments and have large numbers of collaterals. Spinal cord transections show that the vast majority of spinal 5HT descends from the brainstem but that some 5HT fibers are of intrinsic origin.